Hu Yintao, Ru Nan, Zhou Qiujing, Cheng Heng, Zhang Guoxin
China Institute of Water Resources and Hydropower Research, Beijing 100038, China.
State Key Laboratory of Simulation and Regulation of Water Cycle in River Basin, Beijing 100038, China.
Materials (Basel). 2024 Nov 29;17(23):5868. doi: 10.3390/ma17235868.
Concrete stress is a key factor influencing the operational safety of concrete dams, and understanding the true distribution and variation of stress is a major research focus in the field of dam engineering. In the heel region of the dam, internal voids in the concrete may allow external water infiltration under high hydraulic head, leading to changes in the concrete's elastic modulus and Biot coefficient. These changes, in turn, affect the effective stress experienced by the concrete. Consequently, the measured stress in the heel and toe regions may differ from conventional understanding and standard calculation methods for dam stresses. This is particularly evident in the following aspects: after water impoundment, compressive stress in the dam heel is higher than in the dam toe, with the heel stress exceeding the calculated value by a significant margin, and the variation in stress during the impoundment process being smaller than the calculated value. To address these issues, this paper proposes a theoretical method for measuring the Biot coefficient of concrete through experimental testing and innovatively develops the corresponding experimental equipment. This equipment can accurately simulate the conditions of the dam under different water depths (confining pressures) and measure the deformation of concrete caused by changes in water depth. Based on this equipment, tests were conducted on the elastic modulus and Biot coefficient of dry and saturated concrete specimens under different confining pressures. The Voigt-Reuss-Hill mixed average modulus formula was applied to calculate the elastic modulus of the concrete matrix, exploring the influence of pore water on the mechanical properties of the concrete. The results indicate that the pore water inside the concrete increases its equivalent elastic modulus during the testing process. In numerical simulations of the dam, this increased modulus due to pore water is often overlooked, leading to an underestimation of the results. This partially explains why the measured compressive stress in the dam heel consistently exceeds the calculated values. According to the Biot coefficient calculation theory proposed in this paper, the Biot coefficient of concrete varies with its water content. The Biot coefficient is lower in specimens with high water content compared to those with low water content. Using the Voigt-Reuss-Hill mixed average modulus formula, the elastic modulus of the concrete matrix obtained from the tests was found to be 28 GPa, which is in good agreement with the results from regression analysis. These findings are of significant importance for the safe operation of concrete dam engineering.
混凝土应力是影响混凝土坝运行安全的关键因素，了解应力的真实分布和变化是大坝工程领域的主要研究重点。在坝踵区域，混凝土内部的孔隙可能会在高水头作用下使外部水渗入，导致混凝土的弹性模量和比奥系数发生变化。这些变化进而影响混凝土所承受的有效应力。因此，坝踵和坝趾区域的实测应力可能与传统的坝应力理解和标准计算方法不同。这在以下方面尤为明显：蓄水后，坝踵的压应力高于坝趾，坝踵应力大幅超过计算值，且蓄水过程中的应力变化小于计算值。为解决这些问题，本文提出了一种通过试验测试来测量混凝土比奥系数的理论方法，并创新性地开发了相应的试验设备。该设备能精确模拟大坝在不同水深（围压）下的工况，并测量水深变化引起的混凝土变形。基于此设备，对不同围压下干燥和饱和混凝土试件的弹性模量和比奥系数进行了试验。应用Voigt-Reuss-Hill混合平均模量公式计算混凝土基体的弹性模量，探讨孔隙水对混凝土力学性能的影响。结果表明，试验过程中混凝土内部的孔隙水使其等效弹性模量增大。在大坝的数值模拟中，这种因孔隙水导致的模量增加常常被忽视，从而导致结果被低估。这部分解释了为什么坝踵实测压应力一直超过计算值。根据本文提出的比奥系数计算理论，混凝土的比奥系数随其含水量而变化。含水量高的试件的比奥系数低于含水量低的试件。使用Voigt-Reuss-Hill混合平均模量公式，试验得到的混凝土基体弹性模量为28GPa，与回归分析结果吻合良好。这些发现对混凝土坝工程的安全运行具有重要意义。
