Fang Xinqiu, Zhang Fan, Shi Zongshen, Liang Minfu, Song Yang
School of Mines, China University of Mining and Technology, Xuzhou 221116, China.
Research Center of Intelligent Mining, China University of Mining and Technology, Xuzhou 221116, China.
Sensors (Basel). 2022 Aug 30;22(17):6551. doi: 10.3390/s22176551.
The mine shaft is an important channel linking the underground with the surface, undertaking important functions such as personnel and material transportation and ventilation. Thus the shaft, known as the throat of the mine, is the production hub of the whole mine. Since 1980, damage to coal mine shafts has occurred in many areas of China, which has seriously impacted the safety of mine production. Therefore, real-time monitoring of the shaft wall condition is necessary. However, the traditional monitoring method cannot achieve long-term, continuous and stable monitoring of the shaft wall due to the harsh production environment downhole. Hence, a multi-mode joint sensing system for shaft wall deformation and damage is proposed, which is mainly based on FBG sensing and supplemented by vibrating-string sensing. The principle of FBG sensing is that when the external environment such as temperature, pressure and strain changes, the characteristics of light transmission in the FBG such as wavelength, phase and amplitude will also change accordingly. Using the linear relationship between the strain and the wavelength shift of the FBG, the strain of the measured structure is obtained by calculation. Firstly, this paper introduces the basic situations of the mine and analyzes the causes shaft damage. Then the vertical and circumferential theoretical values at different shaft depths are derived in combination with the corresponding force characteristics. Moreover, a four-layer strain transfer structure model of the shaft consisting of the fiber, the protective layer, the bonding layer and the borehole wall is established, which leads to the derivation of the strain transfer relational expression for the surface-mounted FBG sensing on the shaft wall. The strain-sensing transfer law and the factors influencing the strain-sensing transfer of the surface-mounted FBG on the shaft wall are analyzed. The order of key factors influencing the strain-sensing transfer is obtained by numerical simulation: the radius of the protective layer, the length of the FBG paste, and the elastic modulus of the adhesive layer. The packaging parameters with the best strain-sensing transfer of the surface-mounted FBG on the shaft wall are determined. A total of six horizontal level monitoring stations are arranged in a coal mine auxiliary shaft. Through the comprehensive analysis of the sensing data of the two sensors, the results show that the average shaft wall strain-transfer efficiency measured by the FBG sensor reaches 94.02%. The relative average error with the theoretical derivation of shaft wall transfer efficiency (98.6%) is 4.65%, which verifies the strain transfer effect of the surface-mounted FBG applied to the shaft wall. The shaft wall's deformation monitoring system with FBG sensing as the main and vibrating-string sensing as the supplement is important to realize the early warning of well-wall deformation and further research of the shaft wall rupture mechanism.
井筒是连接井下与地面的重要通道，承担着人员和物料运输、通风等重要功能。因此，井筒作为矿井的咽喉，是整个矿井的生产枢纽。自1980年以来，我国许多地区的煤矿井筒都出现了损坏，严重影响了矿井生产安全。因此，有必要对井筒壁状况进行实时监测。然而，由于井下生产环境恶劣，传统的监测方法无法实现对井筒壁的长期、连续和稳定监测。为此，提出了一种基于光纤光栅（FBG）传感为主、弦式传感为辅的井筒壁变形与损伤多模式联合传感系统。FBG传感原理是，当温度、压力和应变等外部环境发生变化时，FBG中的光传输特性如波长、相位和幅度也会相应改变。利用FBG应变与波长漂移的线性关系，通过计算得到被测结构的应变。本文首先介绍了矿井的基本情况，分析了井筒损坏的原因。然后结合相应的受力特性，推导了不同井筒深度处的竖向和周向理论值。此外，建立了由光纤、保护层、粘结层和井壁组成的井筒四层应变传递结构模型，进而推导了井筒壁表面粘贴FBG传感的应变传递关系式。分析了井筒壁表面粘贴FBG的应变传感传递规律及影响应变传感传递的因素。通过数值模拟得出影响应变传感传递的关键因素顺序为：保护层半径、FBG粘贴长度、粘结层弹性模量。确定了井筒壁表面粘贴FBG应变传感传递效果最佳的封装参数。在某煤矿副井布置了6个水平监测站。通过对两种传感器传感数据的综合分析，结果表明，FBG传感器测得的井筒壁平均应变传递效率达到94.02%。与井筒壁传递效率理论推导值（98.6%）的相对平均误差为4.65%，验证了井筒壁表面粘贴FBG的应变传递效果。以FBG传感为主、弦式传感为辅的井筒壁变形监测系统对于实现井壁变形预警及进一步研究井筒壁破裂机理具有重要意义。
