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  5. 青藏工程走廊冻土路基水-热-力耦合损伤演化机理与全寿命周期可靠性评估研究

青藏工程走廊冻土路基水-热-力耦合损伤演化机理与全寿命周期可靠性评估研究

深度研究匿名用户发表于 2026年03月09日 18:203阅读
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1. 青藏高原冻土路基工程特性与水热环境缓变特征

1.1 冻土路基的特殊工程属性与关键参数

青藏高原拥有大面积的多年冻土区，其路基工程面临独特且复杂的挑战。冻土路基的特殊工程属性主要体现在其显著的相变敏感性、独特的冰-土结构特性以及在冻融循环下力学参数的显著衰减。这些特性共同决定了冻土路基的脆弱性，使其极易发生工程病害。

首先，冻土路基的相变敏感性是其最核心的特征之一。土体中的水分在温度低于冰点时会发生相变，由液态水转变为冰。这一相变过程伴随着体积膨胀（冻胀）和相变潜热的释放/吸收，对土体的结构和力学性质产生剧烈影响。特别是在青藏高原这种多年冻土区，路基内部的未冻水含量会随温度动态变化，甚至在零度以下仍存在一定量的未冻水，其孔隙水压力是表征孔隙水状态和相变的关键参数1。

其次，冰-土结构特性是冻土路基区别于非冻土路基的重要方面。在多年冻土区，地温通常在-1.5°C到0°C之间，且活动层厚度在1.4米到3.4米不等，地表冰含量高，但活动层土壤相对干燥2。这种独特的温冰条件导致了土体中冰晶与土颗粒胶结形成的复杂结构。冰的存在显著改变了土体的强度、变形和渗透性。当温度升高导致冰融化时，冰胶结作用消失，土体强度急剧下降，孔隙率增加，形成融沉。

再者，冻融循环是导致冻土路基力学参数持续衰减的关键因素。在季节性冻土和多年冻土区的活动层中，路基土体常年经历周期性的冻结和融化过程。研究表明，冻融循环会导致土体的无侧限抗压强度（UCS）、波速以及剪切强度显著降低，而内摩擦角可能略有增加但变化不明显34。例如，经过15次冻融循环后，普通水泥土的波速损失率可达95%，无侧限抗压强度损失率高达95.4%5。即使是经过改良的土体，如水泥改良黄土，在干湿和冻融循环作用下，强度也会持续劣化6。冻融循环作用下，土体内部的孔隙和裂隙不断发展和演化，水和低温的共同影响导致土体强度持续恶化，并在经历约12次冻融循环后趋于稳定6。此外，土体的初始含水量和细颗粒含量也对冻胀变形产生显著影响，过高或过低的含水量均不利于抑制冻胀7。

青藏高原多年冻土的分布特征进一步凸显了其工程脆弱性。该区域的年平均地温通常较低，且地表冰含量丰富，使得路基一旦受到扰动，极易引发冻土退化。例如，在青藏高原中部地区的多年冻土区，地表水的稳定同位素值（δH和δO）普遍高于北极苔原生态系统和东西伯利亚多年冻土区，这反映了冻融过程中地下水循环的复杂性，也暗示了水分在冻土路基劣化中的重要作用8。这种脆弱性使得青藏工程走廊的道路工程长期面临融沉、冻胀等病害的威胁。

1.2 区域水热环境长期缓变规律与驱动机制

近几十年来，青藏高原作为全球气候变化的敏感区域，其水热环境表现出显著的长期缓变特征，这不仅体现在气温和降水的趋势性变化上，也深入影响着区域地温和冻土的稳定性。全球变暖是驱动青藏高原水热环境变化的主导因素，而局部工程活动，特别是青藏工程走廊的道路建设，则对路基水热状况产生了特定的扰动和协同影响。

气温变化趋势

青藏高原的气温呈现出明显的升高趋势。例如，有研究表明，气温以每年0.03-0.04°C的速度上升，加速了热喀斯特湖的扩张，导致湖泊数量和面积在1995年至2020年间显著增加9。在日尺度上，白天的气温升高速率可能低于夜间，这种不对称增温现象也会对高寒植物的生殖物候产生影响10。

降水变化趋势

青藏高原的降水也表现出复杂的时空分布变化。总体而言，该地区呈现出“暖湿化”的气候趋势，即气温升高伴随着降水的增加11。从2000年到2020年，青藏高原的年降水量呈现增加趋势，特别是在部分区域，降水量的增加速率达到每年1.76-3.07毫米9。降水结构也发生了变化，中等强度的夜间降水频率普遍增加12。在水汽来源方面，青藏高原西部高山地区的水汽来源复杂，受西南季风和西风共同影响，而降水同位素分析显示，高海拔地区的降水δO值海拔效应为-1.3‰/100米13。这种降水量的增加，尤其是极端降水事件的增多，在高原西南麓地区尤为明显，增加了洪水等自然灾害的潜在风险12。

地温变化趋势

地温是冻土路基状态的直接指标，其变化与气温和降水密切相关。在1981年至2020年间，青藏高原浅层土壤（0-50厘米深度）的温度普遍升高。其中，0-20厘米深度的土壤年平均温度约为9.15-9.57°C，每十年升温0.49-0.53 K；而40厘米深度的土壤年平均温度为8.69°C，每十年升温速度高达0.98 K14。这表明深层土壤的升温速度可能快于浅层，对冻土的稳定性构成更大威胁。特别是年平均地温高于-1.5°C的暖冻土区域，热喀斯特湖的发展尤为显著，这进一步证实了地温升高对冻土退化的驱动作用9。

全球变暖与局地工程活动的协同影响

全球变暖是青藏高原水热环境缓变的主导因素，但局地工程活动，特别是青藏工程走廊（如青藏铁路和公路）的建设和运营，对路基及其周边区域的水热状况产生了额外的扰动。交通基础设施的修建可能导致地表植被破坏，改变地表能量平衡，从而影响地温和活动层厚度。有研究指出，在连续多年冻土区，公路距离的增加对碳固存有负面影响，这暗示了气温升高可能加剧连续多年冻土区碳固存的下降，而这与路基工程活动可能存在的关联15。此外，工程活动还可能影响地表水径流和地下水路径，进而改变区域水分平衡。例如，路基修筑可能阻断地表径流，导致局部积水或排水不畅，改变土壤含水量，进而影响冻土的热稳定性和路基的力学性能。这种全球气候变化与局地工程扰动的协同作用，使得青藏高原道路工程面临的水热缓变问题更为复杂，对路基的长期服役性能构成持续威胁。

2. 冻土路基水-热-力多物理场耦合作用机制

2.1 单场作用下的路基响应特征

冻土路基在水、热、力单一物理场作用下，均会产生不同程度的响应和损伤效应，这些效应是理解多场耦合机制的基础。

温度场（冻融循环）对路基的损伤效应

温度场的作用主要表现为冻融循环对路基土体和结构层的劣化影响。在青藏高原地区，地表温度的季节性波动导致路基活动层周期性地经历冻结和融化过程。

  1. 冰透镜体发育与冻胀：当路基土体处于负温且有充足水分补给时，水分会向上迁移并在冻结锋面附近聚集形成冰透镜体。冰透镜体的生长会引起土体体积膨胀，导致路基表面发生不均匀隆起，即冻胀现象。冻胀会使路面结构产生裂缝和变形，降低路面的平整度和承载能力。
  2. 强度衰减：冻融循环对路基材料的力学性能造成显著损害。混凝土、沥青路面以及路基填料在冻融作用下，其强度、刚度会大幅降低。例如，研究表明，经过多次冻融循环后，混凝土的动弹性模量和质量损失明显增加，抗压强度随冻融次数增加而降低16。在青藏高原低温负温条件下养护的混凝土，其抗压强度会随着养护温度的降低而减小，且抗冻性能显著低于标准养护条件下的混凝土17。即使是纤维增强混凝土，在冻融循环下，其与BFRP（玄武岩纤维增强聚合物）筋材之间的粘结性能也会下降，导致峰值滑移增大，粘结刚度和粘结强度降低18。这些都表明温度场的周期性变化是导致路基材料性能退化的关键因素。
  3. 微观结构破坏：冻融循环还会导致材料内部微观结构的破坏。冰晶生长产生的膨胀应力以及相变过程中水分子重新分布，会在土体或混凝土内部产生微裂纹，并使其扩展。对于混凝土，冻融损伤会导致其内部有害孔隙和多有害孔隙的比例增加，T2谱曲线右移，表明孔径增大，连通性增强，从而加速材料的宏观损伤17。

湿度场（水分迁移）对路基的损伤效应

湿度场的作用主要体现在水分在路基土体中的迁移、分布变化及其对土体力学性质的影响。

  1. 水分重分布与土体软化：在温度梯度作用下，路基土体中的水分会从高温区向低温区迁移，尤其是在冻结过程中，水分会从非冻结区向冻结锋面移动，导致冻结区含水量增加，非冻结区含水量减少。这种水分的重新分布会导致土体局部含水量过高，进而降低土体的承载能力和抗剪强度，发生土体软化。对于高含冰量土体，融化后大量融水难以排出，使得土体处于饱和甚至过饱和状态，形成泥浆状，导致路基失稳。
  2. 毛细水上升与冻胀加剧：地下水或地表水通过毛细作用上升到路基内部，为冰透镜体的形成提供了充足的水源，从而加剧冻胀现象。有研究指出，砂砾石置换层可以通过阻断毛细水迁移路径，有效抑制土体的水分迁移和冻胀发展19。
  3. 不均匀沉降：融化期，高含水量的土体在自重和交通荷载作用下发生固结，导致路基出现不均匀沉降。水分迁移导致的不同部位含水量差异会加剧这种不均匀性，进而引发路面开裂、错台等病害。

应力场（交通荷载）对路基的损伤效应

应力场主要指交通荷载作用下路基所承受的循环应力，其对路基的损伤效应主要表现为累积变形和疲劳损伤。

  1. 累积变形：车辆荷载是典型的循环荷载，在冻土路基上长期反复作用会导致路基土体产生不可恢复的累积塑性变形。尤其是在融化期，土体强度显著降低，累积变形效应更为明显，表现为路面车辙、凹陷等病害。这种累积变形会逐渐发展，最终可能导致路基结构的整体破坏。
  2. 疲劳损伤：循环荷载作用不仅引起宏观变形，还会导致路基材料内部结构的疲劳损伤。土体颗粒间的联结在反复应力作用下逐渐松弛甚至断裂，导致土体模量和强度进一步降低。对于路面结构层，如沥青混凝土和水泥混凝土，循环荷载会加速其疲劳裂纹的萌生和扩展，缩短路面使用寿命。
  3. 强度弱化：在冻土地区，交通荷载对路基的损伤效应还与土体状态密切相关。冻结状态下土体强度较高，但融化状态下，特别是融化初期，土体强度急剧下降，此时交通荷载更容易引起土体的剪切破坏和失稳，如边坡滑塌等。蠕变效应也是应力场作用下的重要表现，尤其是在负温条件下，冻土和结构界面在剪应力作用下会发生蠕变，导致桩基等结构物产生持续变形20。

综上所述，温度、湿度和应力单一物理场的作用都能独立地对冻土路基产生显著的损伤效应。然而，在实际工程中，这些物理场并非独立作用，而是相互关联、相互影响，共同构成复杂的水-热-力耦合作用过程。

2.2 多场耦合的非线性交互过程

冻土路基的损伤和劣化并非单一物理场作用的简单叠加，而是水-热-力多物理场相互作用、相互影响的非线性复杂过程。理解这些耦合机制对于准确评估冻土路基的长期性能至关重要。

温度-水分耦合：未冻水含量与水分迁移

温度与水分之间存在密切的耦合关系，主要体现在未冻水含量随温度的变化以及由此驱动的水分迁移。

  1. 未冻水含量与温度的动态平衡：在负温条件下，冻土中并非所有水分都冻结成冰，总会存在一部分未冻水。未冻水含量是温度的函数，随着温度降低，未冻水含量逐渐减少，但不会完全消失。这种未冻水的存在对于冻土的导热、导水性质以及力学行为具有决定性影响。未冻水的动态变化可以理解为一种“非均匀水状态动力学”，其密度和孔隙水压力随距离基质界面的距离而变化 1。在冻结阶段，冷却过程中的未冻水含量总是高于升温过程中的未冻水含量，这表明存在滞后效应，且最大滞后发生在对应的土壤冰点附近 21。这种滞后效应也反映了温度-水分耦合的复杂性。
  2. 水分在温度梯度下的迁移：当冻土路基存在温度梯度时，未冻水会在温度差和吸力差的作用下从高温区向低温区迁移。例如，在路基冻结过程中，地表下方的冻结锋面向下推进，而深层土体温度相对较高。此时，深层土体中的未冻水会向冻结锋面迁移，并在锋面处结冰，形成冰透镜体。这种水分迁移过程直接影响到冰透镜体的大小和数量，从而加剧冻胀的程度。水分的重新分布改变了土体的含水量，进而影响其热物理性质（如导热系数、比热容），反过来又影响温度场的分布。

温度-应力耦合：相变引起的体积膨胀与应力重分布

温度与应力之间的耦合关系主要体现在相变引起的土体体积变化和由此产生的应力重分布。

  1. 冻结膨胀与收缩：当土体中的水冻结成冰时，体积会膨胀约9%，这种体积膨胀会对周围土体施加应力，导致冻胀变形。反之，当冰融化时，体积收缩，可能导致融沉。这些相变引起的体积变化直接导致路基内部应力场的重新分布，影响土体的有效应力状态。
  2. 力学参数的温度依赖性：冻土的力学参数（如强度、模量、蠕变特性）强烈依赖于温度。例如，冻土的无侧限抗压强度和蠕变特性随温度降低而增加 22。在冻结锋面附近，由于温度梯度大，土体的力学性质呈现出显著的非均匀性。这种温度依赖性意味着在分析冻土路基的应力-应变行为时，必须考虑温度场的动态变化。
  3. 热力学本构模型：为了定量描述温度-应力耦合作用，需要建立合适的热力学本构模型。这些模型通常考虑了温度变化对土体强度、刚度以及蠕变特性的影响，并能反映冻融循环引起的损伤累积。通过引入损伤变量或使用弹塑性理论，可以模拟相变引起的应力-应变响应。

水分-应力耦合：孔隙水压力对土体强度的弱化

水分与应力之间的耦合关系主要体现在孔隙水压力的变化对土体有效应力及其强度的影响。

  1. 孔隙水压力积累与有效应力降低：在降雨入渗或融雪作用下，水分会渗透到路基土体中，导致孔隙水压力升高。根据Terzaghi的有效应力原理，土体的有效应力等于总应力减去孔隙水压力。孔隙水压力的升高会降低土体的有效应力，从而削弱土体的抗剪强度，使其更容易发生变形甚至失稳破坏 23。特别是在路基处于融化状态时，土体强度本来就较低，此时孔隙水压力的升高将进一步加剧土体软化，提高其剪切破坏的风险。
  2. 固结与沉降：当路基土体含水量过高且受到交通荷载作用时，孔隙水会逐渐排出，导致土体固结并发生沉降。这个过程是水分迁移与应力作用共同驱动的。在冻土路基融化期，高含水量的土体在车辆荷载作用下更容易发生固结沉降，形成车辙等病害。
  3. 排水条件的影响：路基的排水条件直接影响水分-应力耦合作用的程度。良好的排水系统可以及时排出路基中的积水，降低孔隙水压力，从而减缓土体强度的劣化。反之，排水不畅则会加剧水分的积累，使路基长期处于高孔隙水压力状态，加速其损伤进程。

综上所述，冻土路基中的水-热-力多物理场耦合作用是一个高度非线性的过程。温度变化影响水分相变和迁移，进而影响土体力学参数和孔隙水压力；水分分布和孔隙水压力又反作用于土体有效应力，影响其变形和强度；而应力场的动态变化（如交通荷载）则加速了土体的损伤累积，并进一步改变了土体的孔隙结构和导水导热能力，从而影响温度和水分场的演化。这些复杂的交互过程共同决定了冻土路基的长期服役性能和病害发展趋势。在进行路基设计和病害防治时，必须充分考虑这些耦合效应。

3. 冻土路基典型工程病害演化机理

3.1 主要病害类型与表征特征

青藏高原地区的冻土路基因其独特的水热环境及复杂的地质条件，长期以来面临多种典型工程病害的威胁。这些病害不仅影响道路的正常运营，更可能引发严重的安全事故。主要的病害类型包括融沉、冻胀、纵向裂缝和边坡滑塌等，它们在青藏工程走廊（如青藏公路和青藏铁路沿线）具有特定的空间分布规律和形态特征。

  1. 融沉：
    融沉是冻土路基中最常见且危害最大的病害之一。它主要发生在多年冻土区的活动层或冰融化后形成的水饱和土层。当气温升高导致冻土融化时，特别是高含冰量冻土（如冰碛物、冰楔、地下冰等）融化后，土体结构被破坏，水分流失或形成饱和软土层，在自重和交通荷载作用下发生固结变形，导致路基下沉。

    • 形态特征：路面出现波浪形变形、车辙、不均匀下沉、错台，甚至路基断裂。在路基两侧，常伴随湿地化、泥石流或滑坡。
    • 空间分布规律：融沉病害在高含冰量冻土区、年平均地温接近0℃的“暖冻土”区以及路堤填筑高度不足或保温措施不当的路段尤为普遍。青藏工程走廊沿线，尤其是在多年冻土南界附近、高温冻土区（如昆仑山垭口至五道梁段、沱沱河至安多段）以及有地下冰赋存的区域，融沉现象尤为突出。这些区域的冻土对热扰动更为敏感，一旦融化，产生的融水量大，易导致路基失稳。

  2. 冻胀：
    冻胀是由于土体中水分在负温作用下冻结成冰，体积膨胀，引起路基隆起的现象。它主要发生在富含水分且具备毛细水上升条件的细粒土路基中。

    • 形态特征：路面出现季节性隆起，裂缝（特别是纵向和横向裂缝），路基两侧排水沟被挤压变形。
    • 空间分布规律：冻胀病害主要分布在季节性冻土区、多年冻土区的活动层底部以及地下水位较高或地表水丰富的路段。在青藏工程走廊，这类病害在季节性冻土向多年冻土过渡区、融区或不连续多年冻土区较为常见。例如，在路基两侧有积水或地下水位较高的地段，由于水分补给充足，冻胀现象会更加严重。

  3. 纵向裂缝：
    纵向裂缝是路面结构破坏的一种常见形式，其形成机制与冻胀、融沉及不均匀温度场密切相关。

    • 形态特征：沿行车方向或路基边缘出现的连续或不连续裂缝。裂缝初期可能较细，但随着冻融循环和交通荷载的反复作用，裂缝会逐渐加宽、加深，并可能发展成网裂或坑槽。
    • 空间分布规律：纵向裂缝常伴随冻胀和融沉病害而生。当路基发生不均匀冻胀或融沉时，路面结构会受到拉伸应力，从而产生纵向裂缝。此外，路基横向温差（如路堤阴阳坡效应）导致的不均匀变形，也可能引发纵向裂缝。在青藏工程走廊，路堤两侧的纵向裂缝可能与边坡变形有关，而路面中间的纵向裂缝则更多地与路基内部不均匀变形或材料老化有关。

  4. 边坡滑塌：
    边坡滑塌是指路基边坡土体在重力作用下沿一定滑动面发生整体或局部向下、向外移动的现象。在冻土地区，热融滑塌是其特有的一种类型。

    • 形态特征：边坡土体出现裂缝、鼓包、下错台阶、整体滑动、坡脚隆起等。当发生热融滑塌时，滑塌体常呈现泥流状或舌形堆积。
    • 空间分布规律：边坡滑塌主要发生在高陡边坡、富含冰土体或地下冰的边坡、地下水位高或地表径流冲刷严重的路段。在青藏工程走廊，沿线有大量穿越山区的路段，这些路段的边坡在气候变暖导致多年冻土退化、活动层增厚的情况下，特别容易发生热融滑塌。例如，有研究指出，在青藏工程走廊沿线，仅在2016年至2022年间就识别出1298处热喀斯特滑坡（Thermokarst Landslide, TLs），其中有97.8%的活动层滑脱（Active-Layer Detachment, ALD）演变为逆行性融陷（Retrogressive Thaw Slumps, RTS）24。这些滑坡主要发生在海拔适中、坡度较缓的北向草甸坡地，厚冰层接近多年冻土上限是ALD发生的重要物质基础24。异常高温显著增加了活动层厚度，导致冰层融化并形成融化夹层，这是ALD的直接原因24。这表明，在青藏工程走廊的斜坡路段，随着全球变暖的加剧，边坡滑塌，尤其是热融滑塌的风险正显著增加。

这些病害的发生与发展并非孤立的，它们之间常常相互关联，共同构成冻土路基的复杂损伤体系。例如，严重的冻胀可能导致路面开裂，进而加速水分入渗，加剧融沉；而融沉又可能改变路基的排水条件，进一步影响冻胀和边坡稳定性。因此，对这些病害的综合防治需要深入理解其演化机理。

3.2 水热缓变驱动下的病害演化路径

青藏高原特有的水热环境长期缓变是冻土路基病害，尤其是融沉病害，发生和演化的根本驱动力。以融沉病害为例，其演化是一个从水热条件波动到宏观结构破坏的全链条过程，其中关键阈值的触发作用至关重要。

水热条件波动：活动层增厚与年最大融深增加

融沉病害的最初触发机制源于区域水热环境的长期缓变，最直接的体现就是活动层厚度（夏季融化深度）的增加和年最大融深的逐年增大。全球气候变暖导致青藏高原气温升高和降水模式改变，使得地表热量输入增加，促进了冻土融化。例如，有研究指出，气候变暖会加速有机碳的微生物分解和温室气体释放，对气候变化产生反馈作用 25。这种地表热量的增加和水分的渗透，使得活动层融化深度逐年加深，融化持续时间延长。活动层的增厚意味着更多的冰胶结土体在夏季进入融化状态，为融沉的发生提供了物质基础。同时，工程活动对地表覆被的改变，如道路建设导致的地表扰动和植被破坏，会改变地表能量平衡，进一步影响地温和活动层厚度 26。路基结构本身也可能成为热岛效应的载体，导致其下方冻土加速融化。

冰胶结土体退化：冰融成水与土骨架软化

随着活动层厚度的增加和融化深度的深入，原来处于冻结状态、具有较高强度和承载力的冰胶结土体开始融化。

  1. 冰融成水：冰胶结土体中的冰晶融化成液态水，这个过程伴随着体积收缩，并产生大量的融水。特别是高含冰量冻土，其融化会释放出巨量的水。这些融水在路基内部迁移，并可能在局部形成饱和或超饱和区域。
  2. 土骨架软化与强度急剧下降：冰的融化导致土颗粒间的冰胶结作用消失。对于细粒土而言，融水会显著增加土体的含水量，降低土颗粒间的有效应力，导致土体剪切强度和承载能力急剧下降。这种现象在工程上表现为土体的“软化”甚至“液化”，从坚硬的冻土变为泥浆状的流塑状态。例如，在冻土融化过程中，孔隙水压力的变化会显著影响地下水微生物群落的结构和功能，暗示了水文地球化学过程的活跃变化，进而影响土体特性 27。有研究也对热喀斯特湖和地下水的水文地球化学特征进行了分析，指出其受冻土融化的影响 28。

土体压缩变形：承载力下降与不均匀沉降

冰胶结土体退化导致的土体软化直接削弱了路基的承载能力。在自重和交通荷载的反复作用下，软化的土体更容易发生压缩变形和剪切破坏。

  1. 固结沉降：融化后的饱和土体在上方填土自重和车辆循环荷载作用下，孔隙水被逐渐排出，土体发生固结。这个过程表现为路基的持续性下沉。
  2. 不均匀沉降：由于冻土路基下方土体的含冰量分布不均、融化深度差异以及路基横向温度场不均匀等因素，不同位置的土体融化量和压缩量不同，导致路基发生不均匀沉降。这种不均匀沉降是导致路面结构破坏的关键因素。

路面结构破坏：裂缝、车辙与结构失稳

不均匀沉降和土体压缩变形最终反映在路面结构上，导致一系列病害。

  1. 裂缝：路面在不均匀沉降引起的拉应力作用下产生纵向、横向或网状裂缝。这些裂缝不仅影响路面的美观和行车舒适性，更重要的是为地表水渗入路基内部提供了通道，加速了路基的劣化。
  2. 车辙：在车辆循环荷载作用下，路面材料和路基土体发生塑性变形，形成车辙。尤其是在融化期，路基承载力降低，车辙更容易发生和发展。
  3. 结构失稳：严重的融沉可能导致路基整体失稳，如边坡滑塌，甚至危及行车安全。例如，青藏高原热喀斯特景观中冻土退化导致的微生物群落变化和碳代谢潜力，可能进一步影响碳动态和生态稳定性 2930。

关键阈值对病害加速发展的触发作用

在融沉病害的演化过程中，存在一系列关键阈值，一旦这些阈值被突破，病害发展将加速甚至失控。

  1. 临界融深：当活动层融化深度超过一定临界值，触及高含冰量土层或地下冰时，融化土体体积将显著增加，导致融沉量骤增。这一临界融深是评估路基稳定性风险的重要指标。
  2. 临界含水量：当融化土体的含水量达到或超过液限时，土体将失去工程承载能力，表现出流塑性，极易在荷载作用下发生大规模塑性变形。
  3. 临界地温：年平均地温升高并长期保持在-1.5°C至0°C之间，使得冻土处于“暖冻土”状态，此时冻土对热扰动最为敏感，最易发生融化和退化。例如，施工扰动会增加隧道垂直位移 31，而土体的剪切模量对土层有明显影响 32。
  4. 地表覆盖改变的临界影响：路基及其周边地表覆盖类型的改变，如植被破坏导致的反照率降低、吸热增加，或者沙土堆积形成的保温层效应 26，都可能成为加速冻土融化的临界因素，从而间接触发或加速融沉病害的发展。

综上所述，青藏高原冻土路基的融沉病害是一个由水热环境缓变驱动，通过冰胶结土体退化、土骨架软化、土体压缩变形，最终导致路面结构破坏的链式反应过程。理解这些水热条件波动、冰胶结土体退化、土体压缩变形、路面结构破坏以及关键阈值间的内在联系，对于制定有效的融沉防治策略具有指导意义。

4. 道路全寿命周期水热环境缓变致病模态与权重量化

4.1 全寿命周期致病模态分类

青藏工程走廊道路工程在全寿命周期内，受水热环境长期缓变的影响，其路基病害呈现出不同的致病模态。这些模态根据其发生阶段、驱动机制和表现形式，可以划分为初始损伤模态、累积损伤模态和突发灾变模态。对这些致病模态的分类和主导因素的识别，是开展道路全寿命周期可靠性评估的基础。

4.1.1 初始损伤模态

初始损伤模态主要指道路在设计和施工阶段，由于水热环境扰动或未充分考虑水热环境缓变影响而形成的潜在损伤或病害隐患。这些隐患可能在道路投入运营后加速演化。

  1. 施工扰动致热场失衡：

    • 描述：青藏高原冻土区道路施工过程中，对地表植被的破坏、土体的开挖与回填、工程机械的碾压以及填筑材料的选择，都会显著改变原有的地表热平衡状态。例如，清除植被层会增加地表吸热，路基填筑则可能形成隔热层或热桥，从而扰动地下热场，导致局部冻土融化或冻结条件改变。在“暖冻土”区域，这种扰动尤其敏感，可能导致多年冻土下界抬升或冻融循环加剧。
    • 主导因子：
      • 填料含冰量与类型：施工期使用的填料若含有较高的冰量或易冻胀土，在后期融化或冻结过程中极易引起路基不均匀变形。
      • 施工工艺与保护措施：不合理的开挖和回填方式、缺乏有效的保温（如碎石路基、热棒等）或降温措施，会导致冻土热扰动加剧。
      • 地表植被破坏程度：植被去除程度越大，对地表热平衡的影响越显著，地温升高越明显。

  2. 设计不合理导致的水热不匹配：

    • 描述：若设计阶段未充分考虑区域水热环境的长期缓变趋势（如未来升温、降水增加），或未根据冻土类型（如高温冻土、高含冰量冻土）采取针对性措施，可能导致路基结构（如路基高度、边坡坡度、排水系统）与实际水热条件不匹配。例如，融沉敏感路段的路基高度不足或边坡设计过于陡峭，易在后期出现稳定问题。
    • 主导因子：
      • 设计地温参数预测不准：对未来几十年年平均地温、活动层厚度等关键参数预测不足，导致设计裕度不够。
      • 排水系统设计缺陷：未充分考虑降水增加和冻融作用对排水能力的影响，导致路基长期处于高含水状态。

4.1.2 累积损伤模态

累积损伤模态是指道路在长期运营过程中，由于持续性的冻融循环、交通荷载、水分迁移等因素的反复作用，导致路基材料性能逐渐退化、结构损伤不断累积而形成的病害。这是青藏高原道路工程中最普遍且影响深远的致病模态。

  1. 长期冻融循环致材料劣化：

    • 描述：路基土体和路面结构层常年遭受季节性或日循环的冻结-融化作用。这种循环导致土体内部冰-水相变，产生反复的冻胀-融沉，破坏土体骨架结构，降低土体强度和刚度；同时，对于路面材料（如沥青、混凝土），冻融循环会引起微裂纹的萌生与扩展，加速材料疲劳损伤。
    • 主导因子：
      • 冻融循环次数与强度：年冻融循环次数越多、温度变化幅度越大，材料劣化越快。
      • 土体含水量与性质：高含水量且富含细颗粒的土体对冻融循环更敏感。
      • 路面材料抗冻性：路面材料自身的抗冻性能是决定其劣化速度的关键。

  2. 水热迁移与平衡失调引发的持续损伤：

    • 描述：在温度梯度作用下，路基内部水分从高温区向低温区迁移，导致局部含水量过高或过低。融化期，大量融水在重力作用下向下渗透或在毛细作用下向上蒸发；冻结期，水分向冻结锋面迁移，形成冰透镜体。这种持续的水分迁移过程会引起土体内部孔隙结构变化，改变土体力学性质，进而导致路基不均匀变形和强度降低。
    • 主导因子：
      • 地下水位与地表径流：高地下水位和充足的地表径流为水分迁移提供了充足的水源，加剧了损伤。
      • 路基横向温差（阴阳坡效应）：路基两侧太阳辐射差异导致地温不均，驱动横向水分迁移，引发不均匀冻胀和融沉。
      • 年最大融深与活动层厚度变化率：这些指标反映了冻土退化程度，直接影响水分迁移的深度和范围。

  3. 交通荷载与冻融损伤协同作用：

    • 描述：交通荷载是道路损伤的直接原因，但在冻土路基中，其作用并非独立，而是与冻融损伤协同进行。在冻融循环导致路基材料强度和刚度降低后，即便常规交通荷载也会引起更大的变形和更快的累积损伤。特别是在融化初期，路基承载力急剧下降，交通荷载极易诱发车辙、不均匀沉降甚至剪切破坏。
    • 主导因子：
      • 交通荷载频率与轴重：高交通量和重载车辆会加速疲劳损伤和累积变形。
      • 路基承载力随冻融状态的变化：路基在不同冻融状态下的承载力差异是协同作用的关键。

4.1.3 突发灾变模态

突发灾变模态是指由于极端气候事件或剧烈环境变化，导致水热条件在短时间内发生急剧变化，从而引发的道路工程快速破坏或失稳。

  1. 极端气候事件致水热突变：

    • 描述：青藏高原地区极端降水（暴雨、持续降雪）、极端高温（持续性热浪）等事件的发生频率和强度可能增加。暴雨可能导致路基冲刷、边坡失稳和路面积水，甚至引发泥石流和滑坡。极端高温则会加速多年冻土的融化，引发大规模融沉和热喀斯特地貌发育。这些突变性的水热条件变化会使路基承受远超设计负荷的应力或变形，导致快速破坏。
    • 主导因子：
      • 年最大日降雨量：反映暴雨强度，直接影响冲刷和地表径流。
      • 极端高温持续时间与强度：影响冻土融化速度和融化深度。
      • 融雪性洪水：春季快速融雪可能引发洪水，对路基造成冲刷和浸泡。

  2. 气候变化引发的生态环境突变：

    • 描述：全球气候变化不仅影响气温和降水，还可能引发区域生态环境的连锁反应，如植被退化、地下水位变化、水文径流模式改变等。例如，冻土退化可能改变地下水位，进而影响路基稳定性。极端天气导致的洪水也可能冲毁水基础设施 33。
    • 主导因子：
      • 地下水位波动：反映区域水文环境的改变。
      • 植被覆盖变化：影响地表热平衡和水土保持能力。
      • 区域地质灾害频率：如泥石流、滑坡等自然灾害频率的增加。

通过对这些致病模态的分类，可以更系统地理解青藏高原道路工程面临的风险，并在道路全寿命周期的不同阶段采取针对性的评估和防治策略。

4.2 环境因子权重的量化方法

在青藏高原道路全寿命周期致病模态分析的基础上，量化不同水热环境因子对病害发展的影响权重，对于建立精准的病害预测模型和可靠性评估体系至关重要。这需要整合多源数据，并运用先进的统计分析或机器学习方法来识别关键环境因子并量化其贡献度。

4.2.1 多源数据的采集与预处理

有效量化环境因子权重的基础是全面、准确的多源数据支撑。

  1. 地温监测数据：
    • 采集：通过在路基、边坡及周边地段布设地温传感器，长期连续监测不同深度（如0.1m, 0.5m, 1.0m, 2.0m, 5.0m甚至更深）的土体温度。这些数据能够直接反映路基内部的热状态和冻土退化程度。
    • 特征：年平均地温、年最低/最高地温、年平均地温变化率、活动层厚度及变化率、0℃等温线深度及持续时间等。
  2. 气象站数据：
    • 采集：获取道路沿线及周边气象站的历史气象数据，包括气温（日平均、日最高、日最低）、降水（日降水量、降水强度）、日照时数、风速、相对湿度等。
    • 特征：年平均气温、极端气温事件（如持续高温天数）、年降水量、极端降水事件（如日最大降水量）、冻融循环日数等。
  3. 遥感反演数据：
    • 采集：利用卫星遥感技术（如Landsat、MODIS、Sentinel等）获取地表温度、植被指数（NDVI）、地表含水量、地表反照率、活动层厚度（Active Layer Thickness, ALT）等大尺度、长时序的区域数据 34。遥感数据能够弥补点位监测的不足，提供宏观的区域水热环境变化信息。
    • 特征：长时间序列地表温度趋势、植被覆盖变化、地表湿润度变化、活动层厚度年际变化率等。例如，有研究利用遥感数据结合机器学习方法评估阿拉斯加活动层厚度（ALT）的动态变化，并识别出年平均温度和坡度是ALT的最强预测因子，分别贡献了19%和18%的方差 34。
  4. 工程病害数据：
    • 采集：记录道路病害类型、发生时间、位置、严重程度（如沉降量、裂缝宽度、滑塌规模）以及修复情况等。
    • 特征：病害发生频率、发展速率、修复成本等，作为量化环境因子对病害影响的响应变量。

这些数据在输入分析模型之前，需要进行清洗、缺失值处理、异常值检测、标准化以及时间/空间匹配等预处理步骤，以确保数据质量和一致性。

4.2.2 权重赋值与关键因子识别方法

在多源数据的基础上，可以采用多种方法来识别关键环境因子并量化其对道路病害发展的贡献度，从而进行权重赋值。

  1. 统计分析方法：

    • 主成分分析 (Principal Component Analysis, PCA)：PCA可以用于降低数据维度，识别出解释数据变异性最大的几个主成分。通过分析主成分中各个原始环境因子的载荷，可以初步判断哪些因子对水热环境的整体变化贡献最大，进而推断其对病害发展的影响潜力。PCA有助于揭示潜在的环境变化模式。
    • 相关性分析 (Correlation Analysis)：计算各个环境因子与不同类型病害（如融沉量、裂缝发展速率、边坡变形量）之间的相关系数。高相关性的因子通常被认为是重要的影响因子。例如，融深、活动层厚度变化率与融沉病害呈显著正相关。
    • 逐步回归分析 (Stepwise Regression)：在建立病害预测模型时，逐步回归可以自动选择对病害影响最显著的预测变量，并给出这些变量的回归系数，从而间接反映其权重。
    • 结构方程模型 (Structural Equation Modeling, SEM)：SEM允许同时处理多个因变量和自变量，并能检验复杂的因果关系。通过构建水热环境因子（如气温、降水、地温）—冻土退化（如活动层增厚）—路基病害（如融沉）的理论模型，并利用实际数据进行拟合，可以量化各个路径上的系数，从而得到环境因子对病害影响的直接和间接权重。

  2. 机器学习方法：
    机器学习方法在处理非线性关系和高维数据方面具有显著优势，能够更准确地识别复杂的水热环境因子对病害发展的贡献。

    • 随机森林 (Random Forest, RF)：随机森林是一种集成学习方法，通过构建大量的决策树并取其平均结果来提高预测准确性。其内置的特征重要性评估机制可以直接量化每个环境因子对模型预测的贡献度。例如，有研究使用随机森林模型预测活动层厚度，发现年平均温度和坡度是最重要的预测因子，分别贡献了19%和18%的方差 34。这种方法能够有效地识别出导致病害的关键环境因子，即使这些因子之间存在复杂的非线性关系或交互作用。
    • 支持向量机 (Support Vector Machine, SVM)：SVM在冻土分布预测方面表现出较好的空间泛化能力 3536。虽然SVM本身不直接提供特征权重，但可以通过敏感性分析或结合其他方法（如递归特征消除）来评估不同环境因子对病害预测模型性能的影响。
    • 梯度提升决策树 (Gradient Boosting Decision Tree, GBDT) / XGBoost：这些方法与随机森林类似，也是基于决策树的集成学习算法，具有强大的预测能力和特征重要性评估功能。通过这些模型，可以直接输出每个环境因子在预测路基病害时的相对重要性分数，从而实现权重赋值。
    • 神经网络 (Neural Networks)：深度学习模型，尤其是人工神经网络，能够学习并捕捉环境因子与病害之间高度非线性的复杂关系。通过分析训练好的神经网络模型中各输入层连接权重，或者利用SHAP (SHapley Additive exPlanations) 等可解释性AI技术，可以量化每个环境因子对病害预测的贡献。

量化环境因子权重的具体步骤：

  1. 确定响应变量：选择能够代表病害发展程度的指标，如年平均沉降速率、裂缝扩展速度、融沉量增幅等。
  2. 构建特征数据集：将预处理后的地温监测数据、气象站数据、遥感反演数据中提取的各项环境因子作为模型的输入特征。
  3. 模型训练与验证：使用历史数据对选定的统计或机器学习模型进行训练，并通过交叉验证等方法评估模型的性能和泛化能力。
  4. 特征重要性评估/权重提取：
    • 对于随机森林、XGBoost等模型，直接获取其内置的特征重要性分数。这些分数反映了特征在模型决策中的平均贡献，可以直接作为该环境因子对病害发展影响的权重。
    • 对于回归模型，回归系数的绝对值可以作为权重的参考，经过归一化处理后作为相对权重。
    • 对于SEM，路径系数可以直接作为权重。
  5. 权重归一化与解释：将得到的权重进行归一化处理，使其总和为100%或1，便于直观比较各个环境因子的相对重要性，并结合专业知识对结果进行解释。

通过上述方法，可以识别出青藏工程走廊路基病害发展中的关键环境因子，如活动层厚度变化率、年最大融深、极端高温持续时间、降水强度、年平均地温升幅等，并对其贡献度进行量化。这些量化结果将为路基设计优化、病害早期预警和风险管理提供科学依据。

5. 融合多源信息的路基服役可靠性动态评估体系构建

5.1 多源信息的采集与特征提取

构建青藏工程走廊路基服役可靠性动态评估体系，其核心在于对路基状态及其影响因素的全面感知。这需要整合来自不同渠道、不同尺度的多源信息，并通过精细化的特征工程方法，将其转化为能够表征路基健康状态的关键指标。

1. 多源信息的采集

多源信息的采集覆盖了路基从设计、施工到运营维护的全寿命周期，主要包括以下几个方面：

  • 现场监测数据：

    • 地温数据：通过深层地温测孔、路基截面温度传感器阵列等设备，实时获取路基不同深度、不同位置的温度场分布和变化规律。这包括年平均地温、冻结深度、融化深度（活动层厚度）、冻融循环次数、地温梯度等关键指标。这些数据是判断冻土稳定性、预测融沉和冻胀的基础。
    • 沉降数据：利用沉降观测标、GNSS监测系统、或非接触式测量技术（如雷达干涉测量InSAR）定期或连续监测路基和路面垂直变形。关键参数包括累积沉降量、沉降速率、不均匀沉降差等。
    • 含水量数据：通过时域反射仪（TDR）、频域反射仪（FDR）等传感器，监测路基土体的含水量变化。含水量的变化直接影响土体的热物理和力学性质，是水分迁移和冻融作用的重要表征。
    • 孔隙水压力：埋设孔压计监测路基土体中的孔隙水压力，特别是在融化期，孔隙水压力的升高是导致土体强度降低和失稳的关键因素。
    • 应力-应变数据：在关键部位（如路基与路面交界面、高填方路堤底部）布设土压力盒和应变片，监测交通荷载和温度应力引起的应力-应变响应。
    • 气象环境数据：沿线气象站获取的气温、降水、风速、湿度、辐射等宏观气象参数，为路基水热平衡提供外部输入。

  • 数值模拟结果：

    • 水热-应力场预测：基于冻土水热力学耦合模型，结合未来气候情景预测，对路基内部的温度场、湿度场和应力场进行数值模拟。这包括预测活动层厚度、融化深度、孔隙水压力以及路基变形等。数值模拟结果可以弥补现场监测点有限的不足，提供路基内部的精细化状态信息。

  • 历史病害记录：

    • 巡检数据：道路养护部门的日常巡检记录，包括病害类型（融沉、冻胀、裂缝、坑槽、边坡失稳等）、位置、发生时间、严重程度描述、发展趋势以及维修历史。
    • 病害图像/视频数据：利用无人机、车载图像采集设备等获取的路面及边坡病害图像和视频资料，通过图像识别技术进行病害的自动化识别和量化。

  • 设计与施工资料：

    • 地质勘察报告：包括沿线冻土类型、含冰量、地下冰分布、水文地质条件、土体物理力学性质等。
    • 设计图纸：路基结构、路面结构、排水系统、保温隔热措施等设计参数。
    • 施工记录：填料来源、压实度、施工温度、施工过程中的异常情况等。

2. 特征提取方法

将采集到的海量异构数据转化为具有物理意义和工程价值的特征指标，是构建动态评估体系的关键步骤。

  • 时间序列分解与分析：

    • 趋势项提取：对地温、沉降等长期监测数据进行时间序列分析，分离出长期趋势项，反映路基状态的缓慢变化。例如，年平均地温的长期升高趋势、累积沉降量的增长速率。
    • 周期项提取：分离出年周期、季节周期等周期性变化，反映冻融循环、季节性融沉和冻胀等特征。例如，活动层厚度的季节性波动。
    • 异常检测：通过时间序列模型（如ARIMA、Holt-Winters）预测，结合统计控制图，识别监测数据中的异常点或异常变化趋势，可能预示着病害的发生或发展加速。例如，沉降速率的突然增大可能表明路基失稳。
    • 波动性分析：分析数据在周期性变化中的幅度、频率等，如地温波动的振幅和衰减深度，反映路基热稳定性的变化。

  • 空间插值与可视化：

    • 三维空间场构建：利用空间插值方法（如克里金插值、反距离加权法）将离散的监测点数据（如地温、含水量、沉降量）插值到整个路基结构和周边区域，构建路基内部及沿线的三维连续空间场。
    • 病害空间分布模式识别：结合GIS技术，对历史病害数据进行空间分析，识别病害高发区段、病害类型聚类区域，以及病害与特定地质地貌、水热环境条件的关联性。例如，融沉病害多发生在高温冻土区和高含冰量区域，而冻胀病害则可能与地下水位较高区域相关联。
    • 高程数据处理：利用高精度传感器（如旋转编码器、加速度计、姿态传感器）采集的路面高程数据，通过数字地面模型（DTM）或数字高程模型（DEM）构建路面三维形貌，计算路面平整度（IRI）、车辙深度、横坡等指标37。

  • 损伤指数与安全裕度计算：

    • 损伤指数（Damage Index, DI）：基于路基材料的力学性能退化、变形累积以及结构完整性降低等多个维度，建立综合损伤指数。例如，可以基于土体强度折减率、弹性模量降低率、累积塑性应变等参数，构建反映路基土体损伤程度的DI。DI的量化方法可采用加权平均、模糊综合评价或专家系统等。
    • 安全裕度（Safety Margin, SM）：SM衡量路基在当前状态下抵抗破坏或失效的能力。它可以定义为路基的承载能力与所受荷载之差，或路基实际性能指标与失效阈值之比。例如，路基土体的抗剪强度与实际剪应力之比，或活动层厚度与临界融深之差。安全裕度应考虑材料性能的劣化、荷载的变异性以及环境因素的不确定性。例如，管道在冻胀作用下可能发生变形，从而影响其结构安全38。

通过上述多源信息采集与特征提取，可以将原始数据转化为一系列可量化、可比较、具有物理意义的特征向量，为后续的动态评估模型的输入提供高质量的数据基础。这些特征应能全面反映路基在水-热-力多场耦合作用下的健康状态、损伤累积程度和失效风险。

5.2 动态评估模型与验证

构建融合多源信息的路基服役可靠性动态评估体系，核心在于开发高效、准确的动态评估模型，实现路基健康状态的实时诊断与剩余寿命预测。本研究拟采用基于贝叶斯网络或机器学习的方法来构建评估模型，并通过与青藏工程走廊的长期观测数据对比进行验证。

5.2.1 动态评估模型构建

  1. 基于贝叶斯网络的动态评估模型：
    贝叶斯网络（Bayesian Network, BN）是一种有向无环图，能够清晰地表示变量间的条件依赖关系及其概率分布，特别适用于处理不确定性信息和多因素耦合问题。在路基可靠性评估中，BN可以有效整合不同来源的数据和专家知识，进行前向推理（预测病害状态）和后向推理（诊断病害原因）。

    • 模型结构构建：

      • 节点定义：BN的节点可以分为三类：
        • 根节点（Root Nodes）：表示影响路基性能的初始环境因素，如年平均气温、年降水量、冻融循环次数、地质条件（冻土类型、含冰量）、交通荷载（轴重、频率）等。
        • 中间节点（Intermediate Nodes）：表示路基内部状态和损伤累积过程，如活动层厚度、融深、路基土体强度、含水量、孔隙水压力、损伤指数、安全裕度等。
        • 叶节点（Leaf Nodes）：表示路基病害状态或可靠性指标，如融沉等级、裂缝长度/宽度、边坡稳定性系数、剩余寿命等。
      • 有向边连接：根据冻土路基水-热-力耦合损伤演化机理，建立节点间的因果关系和依赖关系。例如，“年平均气温升高”可能导致“活动层厚度增加”，进而导致“融沉损伤指数升高”。“交通荷载”和“土体强度降低”共同影响“路基承载力”。
      • 条件概率表（Conditional Probability Tables, CPTs）：每个非根节点都需要定义一个CPT，表示在给定其父节点状态下，该节点取不同状态的概率。CPTs可以通过历史数据统计、专家经验、或结合数值模拟结果来确定。

    • 模型推理与应用：

      • 健康状态诊断：通过输入实时监测数据（如地温、沉降、含水量），BN可以计算出路基当前处于不同病害状态（如轻微融沉、中度冻胀、严重开裂）的后验概率，从而实现路基健康状态的实时诊断。
      • 风险预测：基于未来气候情景（如IPCC报告预测的未来气温和降水变化），BN可以预测未来一段时间内路基发生特定病害的概率，为预警提供依据。
      • 剩余寿命预测：通过模拟不同环境条件和养护措施下的病害演化路径，结合预设的失效阈值，可以估算路基达到失效状态的预期时间。

  2. 基于机器学习的动态评估模型：
    机器学习模型在处理非线性关系、高维数据和模式识别方面具有强大能力，可以用于直接从多源数据中学习路基病害的演化规律。常用的模型包括深度学习（如长短期记忆网络LSTM）、随机森林（Random Forest）和梯度提升树（Gradient Boosting Trees, GBTs）等。

    • 模型选择与输入/输出：

      • 输入特征：将特征提取阶段得到的关键指标作为模型的输入，包括气象因子（年平均气温、降水、极端事件）、地温因子（活动层厚度、融深、地温变化率）、水文因子（含水量、孔隙水压力）、荷载因子（交通量、轴重）以及路基结构参数等。这些输入可以是瞬时值、时间序列或统计特征（如均值、方差）。
      • 输出目标：模型的输出可以是：
        • 健康状态分类：将路基划分为“健康”、“预警”、“轻度损伤”、“重度损伤”等类别。
        • 病害严重程度回归：预测具体的病害指标，如未来一年累积沉降量、裂缝扩展速率、边坡变形量等。
        • 失效概率预测：预测路基在特定时间内达到失效阈值的概率。
        • 剩余寿命预测：直接输出路基的预期剩余使用寿命。

    • 模型训练与优化：

      • 数据准备：将采集到的历史数据进行时间/空间匹配、归一化等预处理，构建训练集、验证集和测试集。
      • 模型训练：利用训练集对选定的机器学习模型进行训练，通过优化模型参数（如神经网络的层数、节点数、学习率，随机森林的树的数量等）来最小化预测误差。例如，LSTM网络特别适用于处理时间序列数据，可以捕捉路基状态随时间变化的动态特征。
      • 模型验证：使用验证集评估模型在未见过数据上的性能，防止过拟合。

    • 实时诊断与预测：
      将实时监测数据输入训练好的机器学习模型，模型即可输出当前的健康状态诊断结果或未来的病害发展预测，从而实现动态评估。

5.2.2 模型验证

模型的验证是确保其适用性和准确性的关键环节。本研究将通过与青藏工程走廊的长期观测数据进行对比，全面评估所建模型的性能。

  1. 数据对比验证：

    • 历史数据回溯验证：利用模型对过去某一时间段（例如，最近10-20年）的路基状态进行回溯性预测，并与该时间段内的实际监测数据（地温、沉降、病害记录）进行对比。通过计算预测值与实际值之间的误差（如均方根误差RMSE、平均绝对误差MAE）来评估模型的准确性。
    • 案例分析验证：选择青藏工程走廊内典型病害路段（如严重融沉段、冻胀段、边坡滑塌段），收集其详细的监测数据和病害发展记录。将这些数据输入模型，观察模型能否准确识别出病害的发生、发展趋势，并预测其严重程度。

  2. 模型性能指标评估：

    • 准确率 (Accuracy)、精确率 (Precision)、召回率 (Recall)、F1-score：对于分类模型（如健康状态分类），这些指标可以评估模型识别不同健康状态的性能。
    • R-squared、RMSE、MAE：对于回归模型（如沉降量预测、剩余寿命预测），这些指标用于评估模型预测结果与真实值之间的拟合程度和误差大小。
    • ROC曲线与AUC值：评估模型在不同分类阈值下的性能，特别适用于评估模型对二分类问题（如“是否会发生病害”）的判别能力。
    • 可靠性指标对比：将模型预测的失效概率或剩余寿命与实际观测到的失效事件进行对比，验证模型在可靠性评估方面的准确性。例如，对比模型预测的结构安全裕度与实际结构失效时的裕度。

  3. 不同水热条件和病害阶段的适用性评估：

    • 区域泛化性：评估模型在青藏工程走廊不同地理区域（如多年冻土区、季节性冻土区、高温冻土区）的适用性。例如，在针对不同冻土类型训练模型时，可以采用迁移学习或领域适应技术来提高模型的泛化能力。
    • 病害阶段识别能力：验证模型能否准确识别病害从萌芽、发展到加速破坏的不同阶段，并提供相应的预警信息。
    • 外部气候扰动敏感性：评估模型对极端气候事件（如异常高温、暴雨）的响应能力，即模型能否在这些事件发生时及时预测路基的潜在风险。

通过上述严格的验证过程，可以确保所构建的动态评估模型在青藏工程走廊复杂的冻土环境下具有良好的适用性和可靠性，为道路工程的全寿命周期管理提供科学依据。

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参考文献

1Spatial state distribution and phase transition of non-uniform water in soils: Implications for engineering and environmental sciences.PubMed

Lianhai Zhang, Qianlai Zhuang, Zhi Wen, et al.
Adv Colloid Interface Sci. 2021 Aug;294:102465. doi: 10.1016/j.cis.2021.102465. Epub 2021 Jun 9.
The physical behaviors of water in the interface are the fundamental to discovering the engineering properties and environmental effects of aqueous porous media (e.g., soils). The pore water pressure (PWP) is a key parameter to characterize the pore water state (PWS) and its phase transition in the micro interface. Traditionally, the water in the interface is frequently believed to be uniform, negative in pressure and tensile based on macroscopic tests and Gibbs interface model. However, the water in the interface is a non-uniform and compressible fluid (part of tensile and part of compressed), forming a spatial profile of density and PWP depending on its distance from the substrate interface. Herein, we introduced the static and dynamic theory methods of non-uniform water based on diffuse interface model to analyze non-uniform water state dynamics and water density and PWP. Based on the theory of non-uniform water, we gave a clear stress analysis on soil water and developed the concepts of PWS, PWP and matric potential in classical soil mechanics. In addition, the phase transition theory of non-uniform water is also examined. In nature, the generalized Clausius-Clapeyron equation (GCCE) is consistent with Clapeyron equation. Therefore, a unified interpretation is proposed to justify the use of GCCE to represent frozen soil water dynamics. Furthermore, the PWP description of non-uniform water can be well verified by some experiments focusing on property variations in the interface area, including the spatial water density profile and unfrozen water content variations with decreasing temperature and other factors. In turn, PWP spatial distribution of non-uniform water and its states can well explain some key phenomena on phase transition during ice or hydrate formation, including the discrepancies of phase transition under a wide range of conditions.

2Effects of local factors and climate on permafrost conditions and distribution in Beiluhe basin, Qinghai-Tibet Plateau, China.PubMed

Guoan Yin, Fujun Niu, Zhanju Lin, et al.
Sci Total Environ. 2017 Mar 1;581-582:472-485. doi: 10.1016/j.scitotenv.2016.12.155. Epub 2017 Jan 2.
Beiluhe basin is underlain by warm and ice-rich permafrost, and covered by vegetation and soils characteristic of the Qinghai-Tibet Plateau. A field monitoring network was established to investigate permafrost conditions and to assess potential impacts of local factors and climate change. This paper describes the spatial variations in permafrost conditions from instrumented boreholes, controlling environmental factors, and recent thermal evolution of permafrost in the basin. The study area was divided into 10 ecotypes using satellite imagery based classification. The field investigations and cluster analysis of ground temperatures indicated that permafrost underlies most of the ground in swamp meadow, undisturbed alpine meadow, degrading alpine meadow, and desert alpine grassland, but is absent in other cover types. Permafrost-ecotope relations examined over a 2-year (2014-2016) period indicated that: (i) ground surface temperatures varied largely among ecotopes; (ii) annual mean ground temperatures ranged from -1.5 to 0°C in permafrost, indicating sensitive permafrost conditions; (iii) active-layer thicknesses ranged from 1.4m to 3.4m; (iv) ground ice content at the top of permafrost is high, but the active-layer soil is relatively dry. Long-term climate warming has driven thermal changes to permafrost, but ground surface characteristics and soil moisture content strongly influence the ground thermal state. These factors control local-scale spatial variations in permafrost conditions. The warm permafrost in the basin is commonly in thermal disequilibrium, and is sensitive to future climate change. Active-layer thicknesses have increased by at least 42cm and the mean annual ground temperatures have increased by up to 0.2°C in the past 10years over the basin. A permafrost distribution map was produced based on ecotypes, suggesting that permafrost underlies 64% of the study region.

3Effects of Freeze-Thaw Cycles on Strength and Wave Velocity of Lime-Stabilized Basalt Fiber-Reinforced Loess.PubMed

Wensong Wang, Guansen Cao, Ye Li, et al.
Polymers (Basel). 2022 Apr 4;14(7):1465. doi: 10.3390/polym14071465.
Basalt fiber is a new environmentally-friendly material with excellent potential for soil reinforcement in geotechnical engineering construction. This study explores the effects of freeze-thaw cycles on the unconfined compressive strength (UCS) and P-wave velocity () of lime-stabilized basalt fiber-reinforced loess. Reinforced loess samples with different proportions of basalt fiber and lime were subjected to 0, 1, 5, and 10 freeze-thaw cycles, and their UCS and were subsequently measured. The test results showed that the addition of basalt fiber and lime to loess could enhance strength and improve resistance against freeze-thaw damage, and the freeze-thaw damage of reinforced loess decreases with the increase of basalt fiber content and length. A relationship between UCS and of the reinforced samples was obtained for the same number of freeze-thaw cycles, and this relationship exhibited linear characteristics. The fitting results indicate that the can be used to estimate the UCS after freeze-thaw damage. The research results not only have important practical significance in the application of basalt fiber in geotechnical engineering but also provide a reference for the non-destructive testing of the strength of loess after freeze-thaw cycles.

4Effect of repeated freeze-thaw cycles on mechanical properties of clay.PubMed

Haiqiang Jiang, Hongwei Han, Xingchao Liu, et al.
Heliyon. 2024 Feb 28;10(5):e27261. doi: 10.1016/j.heliyon.2024.e27261. eCollection 2024 Mar 15.
To investigate the variation in the mechanical properties of clay under freeze-thaw cycles (FTCs), a series of experiments were conducted in the laboratory. Samples with different water contents and dry densities were subjected to FTCs ranging from 0 to 11 times. Then, cohesion, shear strength, internal friction angle and elastic modulus were obtained using triaxial test. The results show that with the increase in the number of FTCs, the shear strength, cohesion and elastic modulus decreased, while the internal friction angle increased slightly. However, the variation in the internal friction angle is not obvious, and the maximum increment is within 4°. The cohesion exhibited the most decrease after the first freeze-thaw action. Besides, under a same number of FTCs, four mechanical properties are significantly affected by water content and dry density. The shear strength, cohesion, elastic modulus and internal friction angle decrease with water content while increasing with dry density. Additionally, the elastic modulus is associated with confining pressure, which increases with confining pressure. This study provides evidence for the variation in mechanical properties of the soils subjected to FTCs and guides the design and construction of the cold regional engineering.

5Freeze-thaw resistance mechanisms of rubber-cement soil: insights from a macro- and micro-level perspective.PubMed

Jie He, Rui Liu, Fangcheng Liu, et al.
Environ Technol. 2025 Sep;46(21):4394-4406. doi: 10.1080/09593330.2025.2505802. Epub 2025 May 18.
The waste tire rubber may be incorporated with the cement soil to improve its frost resistance. However, it remains a significant challenge to optimise the rubber content between its mechanical strength and durability under freeze-thaw conditions. In this study, the macroscopic mechanical properties of ordinary cement soil and rubber-cement soil (with particle sizes of 30 and 60 mesh) were explored under different freeze-thaw cycles (0, 3, 6, 9, 15) by taking the wave propagation and unconfined compressive strength (UCS) tests. Subsequently, a series of scanning electron microscope (SEM) and X-ray diffraction (XRD) tests were conducted to analyse the microstructure of the specimens, further clarifying the freeze-thaw damage mechanisms in rubber-cement soil. The results show that freeze-thaw cycles cause irreversible internal damage to the cement soil, leading to continuous reductions in both wave velocity and UCS. After 15 freeze-thaw cycles, the wave velocity loss rates are 95%, 72.2%, and 89.7% fo ordinary cement soil, cement soil mixed with 30-mesh and 60-mesh rubber particles, respectively. The corresponding UCS loss rates are 95.4%, 82.7%, and 89.2%, respectively. The above results suggest that 30-mesh rubber-cement soil exhibits superior frost resistance. From a microstructural perspective, the rubber particles delay and inhibit the propagation of frost heaving cracks, forming a denser spatial structure for calcium silicate hydrates (C-S-H) gel, thereby improving the freeze-thaw resistance. By integrating macroscopic mechanical testing and microstructural analysis, this study reveals the mechanical properties and damage mechanism of rubber-cement soil under freeze-thaw conditions, providing valuable insights for its engineering applications.

6Deterioration characteristics of cement-improved loess under dry-wet and freeze-thaw cycles.PubMed

Ying-Jun Jiang, Chen-Yang Ni, Hong-Wei Sha, et al.
PLoS One. 2021 Jul 1;16(7):e0253199. doi: 10.1371/journal.pone.0253199. eCollection 2021.
The effects of cement dosage, compaction coefficient, molding method (vertical vibration method and static pressure method), and dry-wet and freeze-thaw cycles on the mechanical strength of cement-improved loess (CIL) were studied to reveal its strength degradation law under dry-wet and freeze-thaw cycles. Results show that when using the vertical vibration molding method, the strength degradation effect of CIL can be improved by increasing the cement dosage and compaction coefficient; however, it is not obvious. Under the action of dry-wet cycle, damages, such as voids and cracks of CIL, develop continuously. Further, the strength deteriorates continuously and does not decrease after more than 15 dry-wet cycles. Therefore, the dry-wet cycle degradation system is selected by considering the most unfavorable conditions. In the process of freeze-thaw alternation, the pores and fissures of CIL develop and evolve continuously and the strength deteriorates continuously under the joint influence of water and low temperature. The strength tends to become stable after more than 12 freeze-thaw cycles. According to the safety principle, the deterioration coefficient of the freeze-thaw cycles is 0.3.

7Experimental and numerical study on the Frost-Heaving characteristics of subgrade soil in the Qinghai-Tibet plateau.PubMed

Ying Xiong, Haoming Li, Ning Nan, et al.
Sci Rep. 2025 Nov 21;15(1):44974. doi: 10.1038/s41598-025-28778-w.
To address the severe issue of subgrade frost heave in season-frozen soil highway engineering in the Qinghai-Tibet Plateau (QTP) region, this studied investigated the frost-heaving characteristics (FHC) of subgrade soil with different initial water content (IWC) and fine particle content (FPC) under unidirectional freezing (UDF) and surrounding freezing (SDF) conditions through laboratory experiments. Furthermore, based on the thermo-hydro-mechanical (THM) coupling theory, variations in the temperature, moisture, and stress fields were analyzed numerically. The findings aim to provide a reference for the development of preventive and control measures against subgrade frost heave. The results show that the frost-heaving deformation (FHD) of subgrade soil can be divided into four stages: frost-shrinkage deformation stage, FHD rapid increase stage, FHD slow increase stage, and FHD stabilization stage; A sensitivity analysis suggests that controlling the IWC and FPC at approximately 8% and 9%, respectively, in the subgrade gradation design can effectively inhibit frost heave. Compared to the SDF condition, the UDF condition resulted in a more significant temperature gradient and a distinct freezing front. However, stress concentration points were observed under both freezing conditions.

8Spatial variations and controlling factors of ground ice isotopes in permafrost areas of the central Qinghai-Tibet Plateau.PubMed

Weihua Wang, Tonghua Wu, Yaning Chen, et al.
Sci Total Environ. 2019 Oct 20;688:542-554. doi: 10.1016/j.scitotenv.2019.06.196. Epub 2019 Jun 14.
Ground ice is a distinctive feature of permafrost, and its thawing under climate change can alter the regional hydrological and biogeochemical cycles. Spatial variations and determinants of ground ice isotopes are critical to understand subsurface water cycling during freeze-thaw process in the context of climate change, while they are not well known in permafrost region due to lack of field investigation. We examined spatial distributions and controlling factors of ground ice isotopes using data of 8 soil profiles surveyed in permafrost areas of the Qinghai-Tibet Plateau (QTP). The stable isotope values (δH and δO) of subsurface water on the QTP were higher than those in Arctic tundra ecosystem and East Siberian permafrost region. Isotopic values of water components differed each other, and varied significantly among the sampling sites. The spatial distribution of isotopes was complex. Isotopes generally decreased with depth within the soil profile, implying a general isotope depth gradient across different permafrost-affected areas. Water source, evaporative and freeze-out fractionation, and cryoturbation affect soil water isotopes. Correlation analyses showed that δH and δO in soil water positively related to air temperature and soil temperature, while negatively related to soil moisture, depth, active layer thickness, vegetation coverage, elevation, and precipitation. Elevation and soil depth mainly controlled spatial distributions of ground ice isotopes. The results could provide a new insight into soil moisture movement and cycling during freeze-thaw process in the permafrost region of the QTP, which is helpful to understand subsurface water cycle mechanism in the context of permafrost degradation.

9Accelerating thermokarst lake changes on the Qinghai-Tibetan Plateau.PubMed

Guanghao Zhou, Wenhui Liu, Changwei Xie, et al.
Sci Rep. 2024 Feb 5;14(1):2985. doi: 10.1038/s41598-024-52558-7.
As significant evidence of ice-rich permafrost degradation due to climate warming, thermokarst lake was developing and undergoing substantial changes. Thermokarst lake was an essential ecosystem component, which significantly impacted the global carbon cycle, hydrology process and the stability of the Qinghai-Tibet Engineering Corridor. In this paper, based on Sentinel-2 (2021) and Landsat (1988-2020) images, thermokarst lakes within a 5000 m range along both sides of Qinghai-Tibet Highway were extracted to analyse the spatio-temporal variations. The results showed that the number and area of thermokarst lake in 2021 were 3965 and 4038.6 ha (1 ha = 10,000 m[Formula: see text]), with an average size of 1.0186 ha. Small thermokarst lakes ([Formula: see text]1 ha) accounted for 85.65% of the entire lake count, and large thermokarst lakes ([Formula: see text]10 ha) occupied for 44.92% of the whole lake area. In all sub-regions, the number of small lake far exceeds 75% of the total lake number in each sub-region. R1 sub-region (around Wudaoliang region) had the maximum number density of thermokarst lakes with 0.0071, and R6 sub-region (around Anduo region) had the minimum number density with 0.0032. Thermokarst lakes were mainly distributed within elevation range of 4300 m-5000 m a.s.l. (94.27% and 97.13% of the total number and size), on flat terrain with slopes less than 3[Formula: see text] (99.17% and 98.47% of the total number and surface) and in the north, south, and southeast aspects (51.98% and 50.00% of the total number and area). Thermokarst lakes were significantly developed in warm permafrost region with mean annual ground temperature (MAGT) > - 1.5 [Formula: see text]C, accounting for 47.39% and 54.38% of the total count and coverage, respectively. From 1988 to 2020, in spite of shrinkage or even drain of small portion of thermokarst lake, there was a general expansion trend of thermokarst lake with increase in number of 195 (8.58%) and area of 1160.19 ha (41.36%), which decreased during 1988-1995 (- 702 each year and - 706.27 ha/yr) and then increased during 1995-2020 (184.96-702 each year and 360.82 ha/yr). This significant expansion was attributed to ground ice melting as rising air temperature at a rate of 0.03-0.04 [Formula: see text]C/yr. Followed by the increasing precipitation (1.76-3.07 mm/yr) that accelerated the injection of water into lake.

10Asymmetric warming reduces the strength of selection pressure of moderate grazing on reproductive phenology in alpine plants.PubMed

Jianping Sun, Wangwang Lv, Bowen Li, et al.
Sci Total Environ. 2023 Oct 10;894:164980. doi: 10.1016/j.scitotenv.2023.164980. Epub 2023 Jun 20.
Both warming and grazing already affect the reproductive phenology of alpine plants. However, their effects have mostly been studied in isolation, and their interaction is still unclear. In this study, an asymmetric warming (average + 1.2 °C during daytime and + 1.7 °C during nighttime and + 1.5 °C during summer and + 2.0 °C during winter) with moderate grazing experiment was conducted for four years to determine their individual and interactive effects on the onsets and durations of reproductive phenophases for fifteen alpine plant species on the Qinghai-Tibetan Plateau. Individual warming and grazing simultaneously advanced the average start dates and ending dates of budding, flowering and fruiting by 5.3-6.2 days, and further resulted in smaller effects on their durations for most plant species. The interactions between warming and grazing on them varied with plant species and year, which advanced by average 12.1 days for all plant species. The effects of grazing on the temperature sensitivity of the start dates of reproductive phenophases (average by -8.5 days °C) were greater than that of warming alone (average by -3.4 days °C) and warming with grazing (average by -5.5 days °C) for most of the alpine plant species. There were significant effects of the previous phenological events on subsequent reproductive phenophases. Therefore, our results suggested that both warming and grazing advanced reproductive phenophases through altered soil temperature and soil moisture and carry-over effects of previous phenological events on subsequent phenological events. Warming reduced the temperature sensitivity of the start dates of reproductive phenophases to grazing, suggesting that it depressed strength of selection pressure of grazing on the onsets of reproductive phenology in alpine plants.

11[Temporal and spatial variations of net primary productivity (NPP) and its climate driving effect in the Qinghai-Tibet Plateau, China from 2000 to 2020].PubMed

Jie Liu, Yu-He Ji, Guang-Sheng Zhou, et al.
Ying Yong Sheng Tai Xue Bao. 2022 Jun;33(6):1533-1538. doi: 10.13287/j.1001-9332.202206.025.
Qinghai-Tibet Plateau is a "climate change laboratory" for China and the world. Driven by climate change, net primary productivity (NPP) in the Qinghai-Tibet Plateau has significant variations. Using the data of normalized difference vegetation index, digital elevation, annual precipitation, and annual temperature, we explored the temporal and spatial variation characteristics of NPP and its correlation with climate factors on the Qinghai Tibet Plateau from 2000 to 2020. The results showed that NPP of the Qinghai-Tibet Plateau increased significantly from 2000 to 2020, with an increase rate of 1.67 g C·m·a. The NPP was significantly positively correlated with temperature and precipitation. The climate trend of warming and wetting was an important driving force to promote the significant increase of NPP. The increases of NPP would continue if the climate become warmer and wetter.

12Temporal and spatial variations in the sub-daily precipitation structure over the Qinghai-Tibet Plateau (QTP).PubMed

Hou-Liang Lu, Jun Qiu, Meng-Jia Li, et al.
Sci Total Environ. 2024 Mar 10;915:170153. doi: 10.1016/j.scitotenv.2024.170153. Epub 2024 Jan 15.
Precipitation is a vital component of the global atmospheric and hydrological cycles and influencing the distribution of water resources. Even subtle changes in precipitation can significantly impact ecosystems, energy cycles, agricultural production, and food security. Therefore, understanding the changes in the precipitation structure under climate change is essential. The Qinghai-Tibet Plateau (QTP) is a region sensitive to global climate change and profoundly impacts the atmospheric water cycle in Asia and even globally, rendering it a hot topic in climate change research in recent years. Few studies have examined on the sub-daily scale precipitation structure over the QTP. In this paper, the characteristics of sub-daily precipitation on the QTP were systematically investigated from multiple perspectives, including the concentration index, skewness (the third standardized moment of a distribution), and kurtosis (the fourth standardized moment of a distribution). The results indicated that the frequency of moderate-intensity nighttime precipitation on the QTP generally increased, and the analysis of both the concentration index and kurtosis (skewness) suggested that extreme precipitation was more frequent in the southwestern foothills of the QTP. Furthermore, potential high-risk areas for natural disasters were identified on the QTP, and found that the southeastern part of the plateau constituted a potential hotspot area for flood disasters. Given the complexity of climate change, a comprehensive analysis of the spatiotemporal characteristics of diurnal and nighttime precipitation changes on the QTP could help reveal the regularity of precipitation changes. This has significant implications for forecasting, warning, disaster preparedness, and mitigation efforts on the QTP.

13A review of isotope ecohydrology in the cold regions of Western China.PubMed

Zhang Baijuan, Li Zongxing, Feng Qi, et al.
Sci Total Environ. 2023 Jan 20;857(Pt 2):159438. doi: 10.1016/j.scitotenv.2022.159438. Epub 2022 Oct 13.
The mountainous alpine area in western China is an Asian water tower and is an important ecological barrier area. Based on the previous research results, this study sorted out and summarized the isotopic ecohydrology of the alpine mountains in the western China and found that the local meteoric water line (LMWL) in the west of the alpine mountains is δD = 7.44δO + 5.23 (R = 0.86). The temperature effect showed an increasing trend from the south to north, while the precipitation effect showed an opposite direction. The water vapor sources in the western alpine mountains are complex. When the temperature coefficient is <0, the water vapor source is dominated by the southwest monsoon; when the temperature coefficient is 0-0.3, the water vapor source is jointly dominated by the southwest monsoon and the westerly wind; when the temperature coefficient is more significant than 0.3, the water vapor source is dominated by the westerly wind. Different water bodies are affected by water supply and evaporation differences. The altitude effect of δO value in precipitation in the western alpine mountains is -1.3 ‰/100 m, and the altitude effect of δO value in river water is -0.17 ‰/100 m. The primary source of plant water in the study area is soil water, and the utilization rate of water is closely related to plant types and the regional environment. Water vapor recycling has become an essential part of regional precipitation water vapor sources. However, with the deepening of the major national strategy of ecological civilization construction, the western alpine mountainous area are undergoing profound and drastic changes in the ecological and hydrological processes under the changing environment, which brings great challenges to regional water resources security, ecological security and sustainable development. In the future, the comprehensive innovations in observation, sampling, modeling and theory are urgently needed.

14Analysis on the temporal and spatial characteristics of the shallow soil temperature of the Qinghai-Tibet Plateau.PubMed

Yujie Li, Cunjie Zhang, Zhenchao Li, et al.
Sci Rep. 2022 Nov 17;12(1):19746. doi: 10.1038/s41598-022-23548-4.
Shallow soil refers to the soil layer within the 50 cm depth. Shallow soil temperature (ST) directly or indirectly affects many processes in the soil, such as seed germination, plant growth, and water evaporation. Therefore, the study of shallow ST is of great significance in understanding the surface energy, water cycle, ecology and climate change. This work collected observational data from 141 meteorological stations on the Qinghai-Tibet Plateau from 1981 to 2020 and ERA5 reanalysis data, used the "Moving Surface Spline Interpolation Algorithm Based on Green's Function" and "Fuzzy C-means algorithm", and analyzed the temporal and spatial change characteristics of ST at different levels. The results showed that 1) the temperature increase of 0-20 cm (the surface layer of the shallow soil) was roughly the same. The average annual ST was 9.15-9.57°, and the interdecadal variabilities were 0.49-0.53 K/10a. The average annual ST of 40 cm (the bottom layer) was 8.69°, and the interdecadal variability reached 0.98 K/10a. 2) Considering the 7 regions, the warming trend was obvious, and there were certain regional differences. The average annual ST in different regions ranged from 5.2 (northeastern Plateau) to 17.1 °C (western Sichuan Plateau), with a difference of nearly 12 K. The standard deviation ranged from 0.40 (western Sichuan Plateau) to 0.61 K (Qiangtang Plateau), with a difference of 0.21 K. 3) The errors of the obtained grid data were basically less than 3%, which were much smaller than the errors obtained from the ERA5 reanalysis data. This work is significant for understanding the characteristics of ST evolution and land‒atmosphere interactions on the Qinghai-Tibet Plateau and provides important data support for improving the underlying surface boundary conditions of models.

15Effects of transport infrastructures and climate change on ecosystem services in the integrated transport corridor region of the Qinghai-Tibet Plateau.PubMed

Siqi Yang, Lixiao Zhang, Gaoru Zhu
Sci Total Environ. 2023 Aug 10;885:163961. doi: 10.1016/j.scitotenv.2023.163961. Epub 2023 May 3.
The ecosystem services of the Qinghai-Tibet Plateau have been hot topics in recent decades due to their unique value, and the region's sensitivity to climate change and human activities is considered to be of major importance. However, few studies have focused on the variations of ecosystem services in response to traffic activities and climate change. This study applied different ecosystem service models, along with the buffer analysis, local correlation and regression analysis to quantitatively analyze the spatiotemporal variations of carbon sequestration, habitat quality, and soil retention, further detected the climatic and traffic influences in the transport corridor region of the Qinghai-Tibet Plateau from 2000 to 2020. The obtained results showed the following: (1) The carbon sequestration and soil retention increased over time, while the habitat quality decreased during the railway construction period; in addition, the variations of ecosystem services between the two periods exhibited substantial spatial differences. (2) The distance trends of ecosystem service variations were similar for the railway and the highway corridors, and the positive ecosystem service trends were mainly observed within 2.5 km and 2 km of railway and highway corridors, respectively. (3) The impacts of climatic factors on ecosystem services were predominantly positive; however, temperature and precipitation displayed contrasting distance trends in their impacts on carbon sequestration. (4) The types of frozen ground and locations away from the railway or highway were the combined factors affecting the ecosystem services, among which carbon sequestration was negatively influenced by the distance from the highway in the continuous permafrost areas. It can be speculated that rising temperatures caused by climate change may intensify the decline of carbon sequestration in the continuous permafrost areas. This study provides guidance on ecological protection strategies for future expressway construction projects.

16Freeze-thaw durability of air-entrained concrete.PubMed

Huai-Shuai Shang, Ting-Hua Yi
ScientificWorldJournal. 2013;2013:650791. doi: 10.1155/2013/650791. Epub 2013 Mar 21.
One of the most damaging actions affecting concrete is the abrupt temperature change (freeze-thaw cycles). The types of deterioration of concrete structures by cyclic freeze-thaw can be largely classified into surface scaling (characterized by the weight loss) and internal crack growth (characterized by the loss of dynamic modulus of elasticity). The present study explored the durability of concrete made with air-entraining agent subjected to 0, 100, 200, 300, and 400 cycles of freeze-thaw. The experimental study of C20, C25, C30, C40, and C50 air-entrained concrete specimens was completed according to "the test method of long-term and durability on ordinary concrete" GB/T 50082-2009. The dynamic modulus of elasticity and weight loss of specimens were measured after different cycles of freeze-thaw. The influence of freeze-thaw cycles on the relative dynamic modulus of elasticity and weight loss was analyzed. The findings showed that the dynamic modulus of elasticity and weight decreased as the freeze-thaw cycles were repeated. They revealed that the C30, C40, and C50 air-entrained concrete was still durable after 300 cycles of freeze-thaw according to the experimental results.

17Effect of curing temperature freeze-thaw failure mechanism and damage model of equal-strength air-entrained concrete.PubMed

YongHe Liu, Bo Yang, Aojun Guo
PLoS One. 2024 Dec 26;19(12):e0312890. doi: 10.1371/journal.pone.0312890. eCollection 2024.
The Belt and Road strategy has significantly advanced the scale of infrastructure construction in the Qinghai-Tibet Plateau permafrost area. Consequently, this demands higher requirements on the strength and frost resistance of concrete (FRC) cured under low-temperature and negative-temperature conditions. Accordingly, in this study, tests on the mechanical properties and FRC were conducted under standard curing, 5 °C curing, and -3 °C curing conditions. The pore structure characteristics of concrete subjected to freeze-thaw (F-T) damage (FTD) under different curing methods were analyzed using nuclear magnetic resonance. The study results show that when the air content is constant, the compressive strength of concrete (CSC) tends to decrease with the curing temperature. Moreover, the occurrence of an age lag phenomenon is evident. The compressive strength of concrete cured under standard curing for 28-d was comparable to that achieved by concrete cured at 5 °C curing for 56-d and at -3 °C curing for 84-d. Under the same curing conditions, the CSC decreases with increasing air content. Observations revealed that with the air content in the concrete set at 0.08%, the material's compressive strength was at its minimum. As the number of F-T cycles increases, the concrete transverse relaxation time (T2) curve shifts to the right, and the proportion of both harmful and multi-harmful pores increases. Based on the same CSC under different curing methods, the FRC under 5 °C curing and -3 °C curing conditions is considerably lower than that under standard curing conditions. Moreover, the FRC exhibits an increasing and then a decreasing trend with increasing air content. Concrete exhibits the best frost resistance when the air content is 3.6%. It was established that an optimal range exists for air content in concrete. If the air content is too low, there is only a slight improvement in the FRC. Conversely, if the air content was excessively high, it leads to a significant decrease in frost resistance. Further, this study establishes an FTD model for concrete under 5 °C curing and -3 °C curing conditions considering the compressive strength factors of concrete under standard curing conditions for 28-d. This study is anticipated to be used as reference for determining the FRC cured under different temperatures.

18Bond performance between hybrid fiber-reinforced concrete and BFRP bars under freeze-thaw cycle.PubMed

Yanming Su
PLoS One. 2024 May 13;19(5):e0303327. doi: 10.1371/journal.pone.0303327. eCollection 2024.
This study applied the pull-out test to examine the influence of freeze-thaw cycles and hybrid fiber incorporation on the bond performance between BFRP bars and hybrid fiber-reinforced concrete. The bond-slip curves were fitted by the existing bond-slip constitutive model, and then the bond strength was predicted by a BP neural network. The results indicated that the failure mode changed from pull-out to splitting for the BFRP bar ordinary concrete specimens when the freeze-thaw cycles exceeded 50, while only pull-out failure occurred for all BFRP bar hybrid fiber-reinforced concrete specimens. An increasing trend was shown on the peak slip, but a decreasing trend was shown on the bond stiffness and bond strength when freeze-thaw cycles increased. The bond strength could be increased significantly by the incorporation of basalt fiber (BF) and cellulose fiber (CF) under the same freezing and thawing conditions as compared to concrete specimens without fibers. The Malvar model and the Continuous Curve model performed best in fitting the ascending and descending sections of the bond-slip curves, respectively. The BP neural network also accurately predicted the bond strength, with relative errors of predicted bond strengths ranging from 3.75% to 13.7%, and 86% of them being less than 10%.

19Study on hydrothermal coupling and frost heave characteristics of trapezoidal concrete-lined canals with gradient sand-gravel replacement in cold regions.PubMed

Xinjian Fan, Fei Ye, Cuichao Pang, et al.
Sci Rep. 2025 Dec 17;15(1):43974. doi: 10.1038/s41598-025-27749-5.
This research focuses on the problem of frost heave damage in trapezoidal concrete-lined canals in cold regions. Using the main canal of the Jingdian Irrigation District, China, as the engineering prototype, the control effect of the thickness of the sand-gravel replacement layer on the temperature field, moisture field, and frost heave deformation of the canal foundation was systematically analyzed through a combination of prototype monitoring experiments and numerical simulation. The optimal sand-gravel replacement thickness suitable for trapezoidal concrete-lined canals in cold regions is proposed. The results indicate that the sand-gravel cushion layer significantly inhibits water migration and frost heave development during the freezing process of the foundation soil by blocking the capillary water migration path and regulating the heat conduction characteristics. Increasing the replacement thickness can effectively delay the advancement rate of the freezing front, significantly reducing the frost heave deformation, normal frost heave force, and tangential freezing force of the canal, resulting in a more uniform distribution. With a gradient replacement scheme ranging from 30 cm at the top to 70 cm at the bottom of the canal, the peak normal frost heave force and tangential freezing force were reduced by 40.3% and 38.7%, respectively, and the maximum normal displacement decreased from 4.26 cm of the original foundation soil to 0.95 cm, meeting the specification requirements of 0.5 to 1.0 cm, thereby achieving the frost-heave mitigation goal in a cost-effective manner. The results provide a theoretical basis for the design and application of sand-gravel replacement canal foundations in cold regions.

20Creep constitutive modeling of the shear strength of the permafrost-concrete interface considering the stress level at -1°C.PubMed

Fei He, Wanyu Lei, Erqing Mao, et al.
PLoS One. 2024 Apr 30;19(4):e0297824. doi: 10.1371/journal.pone.0297824. eCollection 2024.
The shear creep characteristics of the contact surface between the permafrost and the structure play an important role in the study of the law of deformation and the measures for the prevention and control of pile foundations. In order to study the creep law and the development tendency of the contact surface between permafrost and concrete, it is necessary to establish an accurate creep model. In this study, based on the Nishihara model, a nonlinear element and damage factor D were introduced to establish an intrinsic model of permafrost-concrete contact surfaces considering the effect of shear stress. Creep tests with graded loading of concrete and frozen silt with different roughness at -1°C were conducted using a large stress-controlled shear apparatus. The adequacy of the model was checked using the test data and the regularity of the parameters of the model was investigated. The results show that the creep curves of the contact surface obtained with the improved Nishihara model agree well with the test results and can better describe the whole process of creep of the contact surface of frozen concrete. The analysis of the experimental data shows that: the roughness of the concrete has an inhibiting effect on the creep deformation of the contact surface, When the roughness R varies from 0 mm to 1.225 mm, the specimen corresponds to a long-term strength of 32.84 kPa to 34.57 kPa. For the same roughness and creep time, the creep deformation of the contact surface is more significant with the increasing shear stress τ. The results of the study can provide a theoretical basis for the design and numerical simulation of pile foundations in permafrost regions.

21Spatiotemporal characteristics of hydrothermal processes of the active layer on the central and northern Qinghai-Tibet plateau.PubMed

Liming Yuan, Lin Zhao, Ren Li, et al.
Sci Total Environ. 2020 Apr 10;712:136392. doi: 10.1016/j.scitotenv.2019.136392. Epub 2020 Jan 2.
The spatial and temporal variations of the seasonal freeze-thaw cycles are important in understanding the ecological and hydrological processes and biogeochemical cycle associated with permafrost degradation caused by climate change, although observational data on the soil hydrothermal dynamics within the active layer of the permafrost region at the central and northern Qinghai-Tibet Plateau (QTP) are extremely scarce. In this study, soil temperature and moisture date from 11 observational sites along the Qinghai-Tibet Highway from 2010 to 2014 were used to analyze the freeze-thaw cycles of the active layer. The results revealed that mean annual ground surface temperature (MAGST) and mean annual temperature at the top of permafrost (TTOP) were the most closely related to the onset dates of soil freezing and thawing. The onset dates of soil freezing from bottom to top did not occur earlier than those from top to bottom. The differences between the onset dates of the two freezing directions and the proportion of bottom-up freezing depth increased with decreasing TTOP. The unfrozen water content of the cooling process was always higher than that of the warming process during the freezing stage. The hysteresis effect of the unfrozen water content could also be observed in the field experiment, and the maximum hysteresis levels occurred at their corresponding soil freezing points. Soil organic matter and soil moisture associated with vegetation cover are essential for water-heat exchanges between atmosphere and permafrost beneath active layer. We suggest that a better protected plant ecosystem, helps preserving the underlying permafrost on the Qinghai-Tibet Plateau.

22Fuzzy random evaluation of creep model of frozen soft soil in metro tunnel construction using artificial ground freezing technique.PubMed

Yafeng Yao, Yan Zhu, Dejian Shen, et al.
Sci Rep. 2023 Jun 10;13(1):9468. doi: 10.1038/s41598-023-36322-x.
Mastering the creep characteristics of artificial frozen soil and scientifically evaluating the creep model is an important guarantee for the safety of subway tunnel freezing construction. Base on the construction of Nantong metro tunnel, the uniaxial compressive strength tests of the artificially frozen soft soil were carried out to obtain the influence law of temperature on the uniaxial compressive strength, and the uniaxial creep tests were carried out to obtain the influence law of temperature and stress grade on creep, at - 5, - 10 and - 15 °C. The experimental results show that the creep characteristics of frozen soft soil specimens have obvious fuzzy randomness. The traditional ant colony algorithm is improved by optimizing the pheromone fuzzification coefficient, which improves the search efficiency and avoids the local optimum effectively. Subsequently, the improved fuzzy ant colony algorithm is used to invert the flexibility parameters of commonly used permafrost creep models. The fuzzy weight of evaluation index and the fuzzy random evaluation matrix were determined to evaluate the optimal creep model under three different stress levels of frozen soft soil. Finally, the reliability of the fuzzy random evaluation method was verified by engineering measured data.

23Mechanisms of pile-soil stress and deformation in excavations under the coupled effects of excavation disturbance and extreme rainfall infiltration.PubMed

Xiaorui Wang, Yu Zhang, Wenwei Li, et al.
Sci Rep. 2025 Dec 18;16(1):911. doi: 10.1038/s41598-025-30447-x.
Under the increasingly frequent extreme rainfall events, deep excavations are subjected to complex coupled effects of excavation-induced disturbance and rainfall infiltration, making it essential to clarify the deformation mechanisms of surrounding soils and retaining structures. In this study, a typical metro foundation pit in Zhengzhou was selected as the research object. By integrating field monitoring data with ABAQUS finite-element simulations, the deformation response and mechanical evolution of the pile-soil system under the combined influence of staged excavation and extreme rainfall infiltration were systematically investigated. The results indicate that rainfall infiltration leads to significant pore-water pressure accumulation, while the downward migration of the wetting front continuously reduces the effective stress and shear strength of the mid-to-deep soils. This process weakens the passive resistance at the pile toe and induces the downward movement of the primary deformation zone. The bending moment distribution of the retaining piles evolves from a "coexisting positive-negative moment" pattern to a "positive-moment dominant" mode, and the horizontal displacement at the pile toe changes from negative to positive, revealing a coupled mechanism involving deep-soil softening and arching loss. A mechanical chain of rainfall infiltration, pore-pressure evolution, stress redistribution, and pile-soil deformation is established to explain how extreme rainfall amplifies excavation-induced effects through dual pathways of mid-to-deep soil softening and accelerated seepage. Based on these findings, a prevention framework of source reduction, structural enhancement, and process control is proposed to improve the safety and resilience of deep excavations under extreme climatic conditions.

24Formation and evolution of thermokarst landslides in the Qinghai-Tibet Plateau, China.PubMed

Tao Wei, Hao Wang, Peng Cui, et al.
Sci Total Environ. 2024 Dec 1;954:176557. doi: 10.1016/j.scitotenv.2024.176557. Epub 2024 Sep 30.
Thermokarst landslide (TL) activity in the Qinghai-Tibet Plateau (QTP) is intensifying due to climate warming-induced permafrost degradation. However, the mechanisms driving landslide formation and evolution remain poorly understood. This study investigates the spatial distribution, annual frequency, and monthly dynamics of TLs along the Qinghai-Tibet engineering corridor (QTEC), in conjunction with in-situ temperature and rainfall observations, to elucidate the interplay between warming, permafrost degradation, and landslide activity. Through the analysis of high-resolution satellite imagery and field surveys, we identified 1298 landslides along the QTEC between 2016 and 2022, with an additional 386 landslides recorded in a typical landslide-prone sub-area. In 2016, 621 new active-layer detachments (ALDs) were identified, 1.3 times the total historical record. This surge aligned with unprecedented mean annual and August temperatures. The ALDs emerged primarily between late August and early September, coinciding with maximum thaw depth. From 2016 to 2022, 97.8 % of these ALDs evolved into retrogressive thaw slumps (RTSs), identified as active landslides. Landslides typically occur in alpine meadows at moderate altitudes and on gentle northward slopes. The thick ice layer near the permafrost table serves as the material basis for ALD occurrence. Abnormally high temperature significantly increased the active layer thickness (ALT), resulting in melting of the ice layer and formation of a thawed interlayer, which was the direct causing factor for ALD. By altering the local material, micro-topography, and thermal conditions, ALD activity significantly increases RTS susceptibility. Understanding the mechanisms of ALD formation and evolution into RTS provides a theoretical foundation for infrastructure development and disaster mitigation in extreme environments.

25Climate change and the permafrost carbon feedback.PubMed

E A G Schuur, A D McGuire, C Schädel, et al.
Nature. 2015 Apr 9;520(7546):171-9. doi: 10.1038/nature14338.
Large quantities of organic carbon are stored in frozen soils (permafrost) within Arctic and sub-Arctic regions. A warming climate can induce environmental changes that accelerate the microbial breakdown of organic carbon and the release of the greenhouse gases carbon dioxide and methane. This feedback can accelerate climate change, but the magnitude and timing of greenhouse gas emission from these regions and their impact on climate change remain uncertain. Here we find that current evidence suggests a gradual and prolonged release of greenhouse gas emissions in a warming climate and present a research strategy with which to target poorly understood aspects of permafrost carbon dynamics.

26Effects of desertification on permafrost environment in Qinghai-Tibetan Plateau.PubMed

Lin Chen, Wenbing Yu, Fenglei Han, et al.
J Environ Manage. 2020 May 15;262:110302. doi: 10.1016/j.jenvman.2020.110302. Epub 2020 Feb 27.
Soil thermal state exerts an important role in soil physicochemical properties, nutrient content, soil carbon losses, and hydrological processes in cold regions. In the Qinghai-Tibet Plateau, desertification and aeolian sand accumulation greatly change the surface cover types and simultaneously alter the surface energy budget. However, the quantification of their impacts on the soil thermal state hasn't been studied methodically. Here, a laboratory experiment was conducted to investigate the impact of surface cover types, including bare surface, grass-coved surface, dry and wet (3%) aeolian sand-covered surface, on underlying soil thermal state. Our results demonstrate that there is a reciprocal relationship between environment change and permafrost degradation. The amount of heat entering the active layer was determined by the surface cover types and soil water content. Using the bare surface case as a reference, vegetation layer acted as a buffer to reduce the amount of heat propagation downwards the ground by 20% and to lower the near surface temperature by 0.7 °C. In contrast, dry aeolian sand acted as an insulation layer and warmed the ground by about 2 °C. Also, wet aeolian sand with high thermal conductivity facilitated the heat exchange with the atmosphere and warmed the ground about 1.5 °C. Our results have implications for thermal and hydrological processes in the atmosphere-ground-permafrost system and thermal stability of infrastructure under the effect of the desertification and aeolian sand accumulation. The hydrothermal interaction of desertification and permafrost needs to be quantified in the further study through long-term field observations and a fully-coupled water flow and heat transport model under a changing climate.

27Structure, stability, and potential function of groundwater microbial community responses to permafrost degradation on varying permafrost of the Qinghai-Tibet Plateau.PubMed

Sining Zhong, Bin Li, Bowen Hou, et al.
Sci Total Environ. 2023 Jun 1;875:162693. doi: 10.1016/j.scitotenv.2023.162693. Epub 2023 Mar 8.
The ongoing permafrost degradation under climate warming has modified aboveground biogeochemical processes mediated by microbes, yet groundwater microbial structure and function as well as their response to permafrost degradation remain poorly understood. We separately collect 20 and 22 sub-permafrost groundwater samples from Qilian Mountain (alpine and seasonal permafrost) and Southern Tibet Valley (plateau isolated permafrost) on the Qinghai-Tibet Plateau (QTP) to investigate the effects of permafrost groundwater characteristics on the diversity, structure, stability, and potential function of bacterial and fungal communities. Regional discrepancy of groundwater microbes between two permafrost regions reveals that permafrost degradation might reshape microbial community structure, increase community stability and potential functions relevant to carbon metabolism. Bacterial community assembly in permafrost groundwater is governed by deterministic processes, whereas fungal communities are mainly controlled by stochastic processes, suggesting that bacterial biomarkers might provide the better 'early warning signals' to permafrost degradation in deeper layers. Our study highlights the importance of groundwater microbes in ecological stability and carbon emission on the QTP.

28Hydrogeochemical characteristics and processes of thermokarst lake and groundwater during the melting of the active layer in a permafrost region of the Qinghai-Tibet Plateau, China.PubMed

Xianmin Ke, Yujiao Li, Wei Wang, et al.
Sci Total Environ. 2022 Dec 10;851(Pt 2):158183. doi: 10.1016/j.scitotenv.2022.158183. Epub 2022 Aug 20.
Permafrost degradation and the development of thermokarst lakes are important factors driving the variability of regional hydrologic processes. Hydrogeochemical and isotopic analyses are important methods for investigating the hydrologic processes of thermokarst lakes. This study focused on comparing the chemical and hydrogeochemical characteristics between lake water and groundwater during the melting of the active layer in a typical thermokarst lake region on the Qinghai-Tibet Plateau (QTP). Ninety-five samples were collected during different periods of active layer melting and analyzed using statistical, isotope, hydrogeochemical, and modeling methods. Statistical results showed that the average concentrations of almost all ions were lower in lake water than in groundwater, with wider spatial variability in groundwater. The lake water is of the ClNa and HCO-Ca type with low TDS (total dissolved solids), whereas groundwater is of the HCO-Ca and mixed type (or transition type) with high TDS. The chemical types of the lake water and groundwater are mainly driven by rock weathering. In terms of the saturation index (SI), halite and gypsum are unsaturated dissolved, whereas dolomite and calcite are generally saturated. Evaporation significantly affects the chemical composition of groundwater, while the hydrochemical compositions of lake water are relatively stable under the joint control of evaporation, precipitation, surface runoff, and groundwater. The isotopic analysis results showed that the contribution of permafrost meltwater and precipitation to groundwater and lake water varied during different stages of active layer melting. According to hydrogeochemical modeling, the main chemical reactions in groundwater are the precipitation of calcite and the dissolution of halite, dolomite, and gypsum. The intensity of groundwater flow determines the degree of chemical reactions along the flow path at different stages of active layer melting. The findings can provide deeper insight into hydrogeochemical processes in thermokarst lake regions under the background of permafrost degradation.

29Bacterial functional redundancy and carbon metabolism potentials in soil, sediment, and water of thermokarst landscapes across the Qinghai-Tibet Plateau: Implications for the fate of permafrost carbon.PubMed

Ze Ren, Shengkui Cao, Tao Chen, et al.
Sci Total Environ. 2022 Dec 15;852:158340. doi: 10.1016/j.scitotenv.2022.158340. Epub 2022 Aug 27.
Permafrost thaw create widespread thermokarst landscapes. As a result, distinct habitats are provided to harbor different bacterial communities in degraded permafrost soil (PBCs), thermokarst lake sediment (SBCs), and lake water (WBCs), driving carbon metabolism differentially. In this study, we investigated functional diversity and redundancy, and carbon metabolism potentials of PBCs, SBCs, and WBCs in thermokarst landscapes across the Qinghai-Tibet Plateau. The results showed that PBCs and SBCs had higher taxonomic and functional alpha diversity than WBCs, while WBCs had lower functional redundancy. WBCs had the highest beta diversity followed by SBCs and PBCs, suggesting strong determination of taxonomic variations on functional differences. Community assembly processes also had significant influences on beta diversity, especially for SBCs. Metabolism pathways of carbohydrate metabolism, methane metabolism, and carbon fixation were enriched differentially in PBCs, SBCs, and WBCs, suggesting different C fate in distinct habitats. Carbohydrate metabolism data suggested that PBCs might have stronger potentials to mineralize a greater diversity of organic carbon substrate than SBCs and WBCs, promoting degradation of organic carbon stocks in degraded permafrost soils. Methane metabolism data showed that SBCs had a stronger methanogenesis potential followed by PBCs and WBCs, while PBCs had a stronger methane oxidation potential. High abundance of genes involving in formaldehyde assimilation might suggested that a large proportion of produced methane might be assimilated by methanotrophs in the thermokarst landscapes. Both aerobic and anaerobic carbon fixation pathways were enriched in PBCs. The results added our understanding of functional properties and biogeochemical carbon cycles in thermokarst landscapes, improving our abilities in accurate modeling of carbon dynamics and the ultimate fate of permafrost carbon in a warming world.

30Changing microbiome community structure and functional potential during permafrost thawing on the Tibetan Plateau.PubMed

Xiaotong Tang, Miao Zhang, Zhengkun Fang, et al.
FEMS Microbiol Ecol. 2023 Oct 17;99(11). doi: 10.1093/femsec/fiad117.
Large amounts of carbon sequestered in permafrost on the Tibetan Plateau (TP) are becoming vulnerable to microbial decomposition in a warming world. However, knowledge about how the responsible microbial community responds to warming-induced permafrost thaw on the TP is still limited. This study aimed to conduct a comprehensive comparison of the microbial communities and their functional potential in the active layer of thawing permafrost on the TP. We found that the microbial communities were diverse and varied across soil profiles. The microbial diversity declined and the relative abundance of Chloroflexi, Bacteroidetes, Euryarchaeota, and Bathyarchaeota significantly increased with permafrost thawing. Moreover, warming reduced the similarity and stability of active layer microbial communities. The high-throughput qPCR results showed that the abundance of functional genes involved in liable carbon degradation and methanogenesis increased with permafrost thawing. Notably, the significantly increased mcrA gene abundance and the higher methanogens to methanotrophs ratio implied enhanced methanogenic activities during permafrost thawing. Overall, the composition and functional potentials of the active layer microbial community in the Tibetan permafrost region are susceptible to warming. These changes in the responsible microbial community may accelerate carbon degradation, particularly in the methane releases from alpine permafrost ecosystems on the TP.

31Effects of construction disturbances on tunnel displacement and the protective role of soil reinforcement in metro tunnels.PubMed

Haomin Wang, Mushuang Lin, Jianbo Li, et al.
Sci Rep. 2025 Jun 5;15(1):19780. doi: 10.1038/s41598-025-04692-z.
This paper analyzes the effects of construction disturbances on tunnel displacement and the protective role of soil reinforcement in metro tunnels through laboratory tests and numerical simulation. Initially, disturbance zones were delineated for a specific project in Zhejiang Province based on the unloading ratio and field disturbance tests conducted at the Gaotangqiao metro station excavation site in Ningbo. The primary soil layer at the project site, silty clay, was artificially disturbed by incorporating salt grains and different amounts of cement into remolded soil. Uniaxial and triaxial tests were conducted to examine the engineering properties of disturbed and natural soils. The relationship between the cement content and the disturbance degree was established and verified through compressibility, shear strength, and structural yield stress indices, from which the parameters for the Hardening Soil Model with Small Strain Stiffness (HSS) were obtained. The impact of pit excavation construction on tunnel displacement was analyzed using Plaxis3D, taking into account the degradation of soil properties due to construction-induced disturbance. Additionally, the impact of disturbances from soil reinforcement construction on the protective efficacy for metro tunnels was systematically evaluated. The results show that with a cement content of 2%, the compression index, shear strength index, and structural yield stress were essentially equivalent to those of the undisturbed soil. The vertical displacement of the tunnel increased by 18.3% due to construction disturbances. During the construction of the foundation reinforcement, concrete mixing piles and tunnel grouting caused disturbances in the foundation soil, leading to additional displacements of the tunnel, with tunnel grouting showing the most significant disturbance-induced displacement. The portal reinforcement method was identified as the most effective at minimizing tunnel deformation, offering substantial protection with minimal intervention and ease of implementation.

32Site Investigations of the Lacustrine Clay in Taihu Lake, China, Using Self-Boring Pressuremeter Test.PubMed

Bin Wang, Kang Liu, Yong Wang, et al.
Sensors (Basel). 2021 Sep 9;21(18):6026. doi: 10.3390/s21186026.
Site investigations of the soils are considered very important for evaluation of the site conditions, as well as the design and construction for the project built in it. Taihu tunnel is thus far the longest tunnel constructed in the lake in China, with an entire length of over 10 km. However, due to the very insufficient site data obtained for the lacustrine clay in the Taihu lake area, a series of self-boring pressuremeter (SBPM) field tests was therefore carried out. Undrained shear strengths were deduced from the SBPM test, with the results showing generally higher than those obtained from the laboratory tests, which may be attributed to the disturbance to the soil mass during the sampling process. Degradation characteristics of the soil shear modulus () were mainly investigated, via a thorough comparison between different soil layers, and generally, the shear modulus would cease its decreasing trends and become stable when the shear strain reaches over 1%. Meanwhile, it was found that a linear relationship between the plasticity index and the shear modulus, and between the decay rate of the shear modulus and the plasticity index as well, could be developed. Further statistical analysis over the undrained shear strength and shear modulus distribution of the soils shows that the undrained shear strength of the soils follows a normal distribution, while the shear modulus follows a log-normal distribution. More importantly, the spatial correlation length of the shear modulus is found much smaller than that of the undrained strength.

33Climate change and health effects in Northwest Alaska.PubMed

Michael Brubaker, James Berner, Raj Chavan, et al.
Glob Health Action. 2011;4. doi: 10.3402/gha.v4i0.8445. Epub 2011 Oct 18.
UNLABELLED: This article provides examples of adverse health effects, including weather-related injury, food insecurity, mental health issues, and water infrastructure damage, and the responses to these effects that are currently being applied in two Northwest Alaska communities. BACKGROUND: In Northwest Alaska, warming is resulting in a broad range of unusual weather and environmental conditions, including delayed freeze-up, earlier breakup, storm surge, coastal erosion, and thawing permafrost. These are just some of the climate impacts that are driving concerns about weather-related injury, the spread of disease, mental health issues, infrastructure damage, and food and water security. Local leaders are challenged to identify appropriate adaptation strategies to address climate impacts and related health effects. IMPLEMENTATION PROCESS: The tribal health system is combining local observations, traditional knowledge, and western science to perform community-specific climate change health impact assessments. Local leaders are applying this information to develop adaptation responses. OBJECTIVE: The Alaska Native Tribal Health Consortium will describe relationships between climate impacts and health effects and provide examples of community-scaled adaptation actions currently being applied in Northwest Alaska. FINDINGS: Climate change is increasing vulnerability to injury, disease, mental stress, food insecurity, and water insecurity. Northwest communities are applying adaptation approaches that are both specific and appropriate. CONCLUSION: The health impact assessment process is effective in raising awareness, encouraging discussion, engaging partners, and implementing adaptation planning. With community-specific information, local leaders are applying health protective adaptation measures.

34Machine learning and process-based modeling of spatiotemporal changes in active layer thickness across Alaska.PubMed

Sagar Gautam, Umakant Mishra, Sarah N Scott, et al.
Sci Rep. 2025 Nov 27;15(1):42420. doi: 10.1038/s41598-025-26586-w.
Permafrost degradation poses a growing threat to infrastructure stability and ecosystem resilience in the rapidly warming Arctic. We investigated the spatiotemporal dynamics of active layer thickness (ALT) across Alaska by integrating field observations, environmental datasets, a physically based Stefan model, and machine learning (ML) techniques. Using weather projections from the Coupled Model Intercomparison Project Phase 6 under two Shared Socioeconomic Pathways (SSP 2-4.5 and SSP 5-8.5), we assessed ALT sensitivity to projected future weather conditions. The random forest (RF) model outperformed the Stefan approach in predicting ALT on the training dataset (R² = 0.84 vs. 0.53) but demonstrated lower generalizability on the test dataset (R² = 0.24 vs. 0.54). The root mean square error (RMSE) for the RF model for training and testing ranged from 14 to 22 cm, compared to 17 and 18 cm for the Stefan model. Variable importance analysis revealed that mean annual temperature and slope angle were the strongest predictors of ALT, accounting for 19% and 18% of the variance, respectively, followed by sediment transport index (14%) and stream power index (11%). Comparative analysis of baseline ALT predictions showed the Stefan model tended to project a thicker active layer (mean ± SD: 65 ± 16 cm), compared to the RF model (mean ± SD: 59 ± 8.8) cm). Both models indicated a latitudinal gradient in ALT, with shallower depths at higher latitudes. Projected ALT increases by 2100 were estimated at 3.3 ± 2.2 cm under SSP 2-4.5 and 5.9 ± 4.0 cm under SSP 5-8.5 for the ML model, whereas the Stefan model projected substantially larger increases of 13 ± 2.6 cm (SSP 2-4.5) and 28 ± 4.4 cm (SSP5-8.5). Spatial analysis showed the greatest ALT increases in northern Alaska, with relatively smaller changes in southern regions. These findings highlight the complex, multifactorial nature of ALT dynamics and the value of hybrid modeling approaches. As rising temperatures accelerate permafrost thaw, changes in ALT can disrupt ecosystems, damage infrastructures, and enhance the release of stored soil carbon, highlighting the urgent need for improved predictive capabilities to inform adaptation strategies in the Arctic.

35Data-driven mapping of the spatial distribution and potential changes of frozen ground over the Tibetan Plateau.PubMed

Taihua Wang, Dawen Yang, Beijing Fang, et al.
Sci Total Environ. 2019 Feb 1;649:515-525. doi: 10.1016/j.scitotenv.2018.08.369. Epub 2018 Aug 28.
Frozen ground degradation profoundly impacts the hydrology, ecology and human society on the Tibetan Plateau (TP) and the downstream regions. The spatial distribution and potential changes of permafrost and maximum thickness of seasonally frozen ground (MTSFG) on the TP is of great importance and needs more in-depth studies. This study maps the permafrost and MTSFG distribution in the baseline period (2003-2010) and in the future (2040s and 2090s) with 1-km resolution. Logistic regression (LR), support vector machine (SVM) and random forest (RF) are validated using 106 borehole observations and proved to be applicable in estimating permafrost distribution. According to the majority voting results of the three algorithms, 45.9% area of the TP is underlain by permafrost in the baseline period, and respectively 25.9% and 43.9% of the current permafrost will disappear by the 2040s and the 2090s projected by mean of the projections from the five General Circulation Models under the Representative Concentration Pathway 4.5 scenario. SVM performs better in spatial generalization than RF based on the results of nested cross validation. According to the MTSFG results derived from SVM, the most dramatic decrease in MTSFG will occur in the southwestern TP, which is projected to exceed 50 cm in the 2090s compared with the baseline period. This study introduces the statistics and machine learning algorithms to frozen ground estimation on the TP, and the high resolution permafrost and MTSFG maps produced by this study can provide useful information for future studies on the third pole region.

36Spatially-explicit estimate of soil nitrogen stock and its implication for land model across Tibetan alpine permafrost region.PubMed

Dan Kou, Jinzhi Ding, Fei Li, et al.
Sci Total Environ. 2019 Feb 10;650(Pt 2):1795-1804. doi: 10.1016/j.scitotenv.2018.09.252. Epub 2018 Sep 20.
Permafrost soils store a large amount of nitrogen (N) which could be activated under the continuous climate warming. However, compared with carbon (C) stock, little is known about the size and spatial distribution of permafrost N stock. By combining measurements from 519 pedons with two machine learning models (supporting vector machine (SVM) and random forest (RF)), we estimated the size and spatial distribution of N stock across the Tibetan alpine permafrost region. We then compared these spatially-explicit N estimates with simulated N stocks from the Community Land Model (CLM). We found that N density (N amount per area) in the top three meters was 1.58 kg N m (interquartile range: 1.40-1.76) across the study area, constituting a total of 1802 Tg N (interquartile range: 1605-2008), decreasing from the southeast to the northwest of the plateau. N stored below 1 m accounted for 48% of the total N stock in the top three meters. CLM4.5 significantly underestimated the N stock on the Tibetan Plateau, primarily in areas with arid/semi-arid climate. The process of biological N fixation played a key role in the underestimation of N stock prediction. Overall, our study highlights that it is imperative to improve the simulation of N processes and permafrost N stocks in land models to better predict ecological consequences induced by rapid and widespread permafrost degradation.

37The Key Technologies of Road Elevation Detection Based on Sensor Fusion.PubMed

Jin Han, Jia Liu, Hongmei Chang
Sensors (Basel). 2022 Aug 1;22(15):5756. doi: 10.3390/s22155756.
The detection of long-distance pavement elevation undulation is the main data basis for pavement slope detection and flatness detection, and is also the data source for 3D modeling and quality evaluation of pavement surfaces. The traditional detection method is to use a level and manual coordination to measure; however, the detection accuracy is low and the detection speed is slow. In this paper, the high-speed non-contact vehicle-mounted road undulationelevation detection method is adopted, combined with the advantages of each sensor measurement; three methods are proposed to detect the road undulation elevation: rotary encoders, accelerometers, attitude sensor data fusion detection; GPS RTK detection; and Kalman filtering detection. Through modeling and experimental comparison, Kalman filter detection is not disturbed by the environment, and the detection accuracy is higher than the current international standard.

38Frost Heaving Damage Mechanism of a Buried Natural Gas Pipeline in a River and Creek Region.PubMed

Wenxian Su, Shijia Huang
Materials (Basel). 2022 Aug 22;15(16):5795. doi: 10.3390/ma15165795.
When the buried pipeline passes through the permafrost zone, the phenomenon of frost swelling occurs in the permafrost zone, which causes a certain degree of bending and deformation of the pipeline. As a result, the pipeline's structural safety is compromised, and the pipeline finally fails during operation, posing a serious hazard to the natural gas pipeline's operation. Whereas the theoretical research on soil frost heave is relatively comprehensive, the applied research on engineering problems is not yet complete. Therefore, it is necessary to predict frost heaving through experiments and numerical simulation, and put forward reasonable control measures for existing or potential problems. For the problem of pipeline damage caused by frost swelling of soil in the natural gas high-pressure regulator station in a river and creek region, the Drucker-Prager elastic-ideal plastic model of soil was selected for finite element analysis, and a reasonable finite element model of pipe-soil was established in this paper. Through the temperature field analysis, it was found that the soil around the buried pipe is affected by the pipeline and is lower than its freezing temperature, which makes the soil freeze and swell. Furthermore, through the thermal-structural coupling analysis, it was found that the buried pipe is affected by the freezing and swelling of the soil and the structure is greatly likely to be damaged. In addition, by analyzing the temperature distribution and frost heave deformation of the soil around the pipeline, as well as the deformation and force of the pipeline at different pipe temperatures, this paper also determined the ideal temperature for preventing frost heave damage to natural gas at high-pressure regulator stations as -1 °C. Finally, based on the results of the abovementioned analysis, the heating method was determined to improve the frost damage phenomenon at the high-pressure regulator. The results of the anti-frost and swell study were used to conduct field trials at natural gas high-pressure regulator stations where frost and swell had occurred. By adding heating furnace to increase inlet temperature, frost heaving of gas transmission pipeline can be effectively prevented. The results of the research provide a reference for both existing and new natural gas pipelines, and also accumulate experience for winter maintenance design and construction of pipeline engineering in seasonally frozen soil areas.