水岩耦合作用下泥化弱胶结软岩巷道流变破坏演化机理研究

Mudding weakly-cemented soft rock widely exists in the mining area of western China, and its unique characteristics such as low strength, poor cementation and mudding easily in water make the long-term stability of the drift (chamber) an urgent science and technology problem to be solved. The crack propagation, aging feature and soaking degradation characteristics of the soft rock are researched through laboratory test, and the damage factors under loads are acquired. Considering the comprehensive damage mechanism under unloading, seepage, softening and rheological effects, the water-rock coupling rheological damage constitutive model describing the soft rock aging damage and mudding properties is established. On the basis of FLAC3D platform, the numerical simulation method for rock deformation and failure evolution process of mudding weakly-cemented soft rock drift is established. Numerical simulation and model test of typical engineering project are performed, based on test results, the whole gradual evolving process (initial unloading damage, rheological crack propagation, soaking degradation, failure zone’s escalation and support failure) is studied, the source of force conditions and its supply path of continuous large-scale deformation are explored and the evolution mechanism of cataclysm in weakly-cemented soft rock drift is revealed. Based on the boundary of surrounding rock division and its movement, the evaluation method of supporting effect is established, the laws of the deformation and failure mechanical mechanism of drift influenced by supporting parameters and timing are studied, and the key factors are discriminated to propose the targeted control measures.

泥化弱胶结软岩广泛存在于我国西部矿区，该类软岩强度低、胶结差、遇水泥化，巷道（硐室）的长久稳定成为亟待解决的科学技术问题之一。本项目拟通过室内试验研究泥化弱胶结软岩的裂隙扩展规律、时效演化特征和浸水劣化特性，获得多因素耦合作用下软岩损伤因子及其时变演化规律。考虑卸荷、渗流、软化、流变多种损伤机制，构建以裂隙扩展及损伤演化为内核且反映软岩损伤时效和泥化特性的水岩耦合流变损伤本构模型；基于FLAC3D平台，建立巷道围岩变形破坏演化过程的数值分析方法。开展典型工程的数值模拟和模型试验，分析巷道围岩由初始卸荷损伤经裂隙流变扩展、围岩浸水劣化诱发支护失效、破坏区扩大的演变过程，探究巷道围岩持续大变形破坏的力源和补给路径，揭示弱胶结软岩巷道的灾变演化机理。建立以围岩分区界面及其移动为核心的支护效果评价方法，研究支护参数、时机等对巷道变形破坏力学机制的影响规律，辨析关键因素，提出针对性控制对策。

项目采用室内试验、数值模拟和模型试验相结合的方法，系统研究了水岩耦合作用下泥化弱胶结软岩巷道流变破坏演化机理。通过对泥化弱胶结软岩进行常规加载、蠕变试验和软化试验，研究了多因素耦合作用下裂隙软岩的物理力学性质、裂隙扩展规律及二者的时效演化特征。结果显示，预制裂隙对软岩力学性质劣化作用明显，相较于完整岩样，起裂强度最大降低53%，峰值强度降低24%，与硬岩相比软岩受倾角的影响更大。水对泥岩的损伤机理是使其泥化软化，而对砂质泥岩是渗透作用让其层理中产生裂隙。在蠕变加载中，软岩强度随时间存在明显的劣化，且稳态蠕变速率远高于硬岩，达到了0.04%/h，且随着偏应力增长较快。以室内试验得到的软岩强度、变形及裂纹演化规律为基础，结合流变力学理论，在广义Kelvin模型的基础上引入非线性粘塑性元件，利用应变等价原理将初始损伤加入其中，构建出考虑流变损伤的粘塑性本构模型。依据Darcy定律和Biot固结理论，得到以裂隙扩展及损伤演化为内核的泥化弱胶结软岩水岩耦合流变损伤本构模型。以新上海一号煤矿114156工作面为例，对巷道变形破坏进行数值模拟，基于模拟结果和相似理论开展模型试验，揭示软岩巷道灾变演化机理为：煤层推采致使围岩不断应力重分布，巷道变形严重，左右帮移近量最大达到525mm，顶底板移近量是左右帮移近量的2-3倍；工作面前方10m范围内，超前支护应力集中严重，显现在巷道与开采区邻接一侧，使得巷道左右帮出现了明显的不对称变形。另一方面，软岩巷道发生的变形为流动性变形，实体煤侧应力集中系数大于2，变形逐渐由巷道两帮扩散传递到顶底板，导致巷道四周均发生不同程度的变形破坏，底板塑性区达到了3m，支护构件几乎完全失效。为控制软岩巷道持续变形，在支护优化的基础上，进一步开展切缝卸压护巷的数值模拟和模型试验，通过切缝阻隔巷道顶板与采空区顶板的联系，使得采空区顶板自然垮落而不再对巷道顶板产生挤压，从而改善巷道围岩受力状态，提高巷道稳定性。通过现场检验，技术效果明显。