含水泥岩卸荷蠕变数值模拟及劣化机制研究

Numerical simulation of unloading creep and deterioration mechanism of waterbearing mudstone

为揭示含水泥岩卸荷蠕变破坏机制,开展不同含水率泥岩升轴压卸围压蠕变试验、细观结构测试及数值模拟分析。试验结果表明,含水率对泥岩蠕变变形影响显著,且同一蠕变应力水平下,轴向应变受含水率影响显著大于侧向。SEM图像分析表明,含水率增大导致泥岩内部孔隙度增大,矿物颗粒被溶解弱化,由致密程度好、强度高向强度低、疏松多孔不规则的堆积结构转化;并基于真实的泥岩细观结构特征,生成了统计学上等价的细观结构网络,建立了相应的GBM-PSC数值模型,并进行了验证。数值模拟计算结果发现,各类微裂纹数量均随含水率增大而增加,晶内张拉裂纹数量呈先增大后稳定再增大趋势,而晶间剪切裂纹数量则随含水率增大而持续增加;接触切向力角度偏转值及平均孔隙度均随卸荷蠕变时间增大呈先减小后稳定再增大趋势,且含水率越大,变化趋势越显著。最后,建立干燥及含水泥岩三阶段卸荷蠕变劣化演化模型。研究结果可为水作用下软岩工程开挖卸荷蠕变变形破坏机制研究提供一定的理论参考。

In order to reveal the unloading creep failure mechanism of water-bearing mudstone,the rising axial pressure-reducing confining pressure creep tests,meso-structure tests and numerical simulation analysis were carried out for mudstone with different water contents.The test results show that the water content has a significant effect on the creep deformation of mudstone,and the axial strain is significantly more affected by the water content than laterally at the same creep stress level.SEM image analysis shows that the increase of moisture content leads to the increase of internal porosity of mudstone,and the mineral particles are dissolved and weakened,which is transformed from a dense and high strength to a loose porous and irregular accumulation structure with low strength.Based on the real meso-structure characteristics of mudstone,a statistically equivalent meso-structure network is generated,and the corresponding GBM-PSC numerical model is established and verified.The numerical simulation results show that the number of microcracks increases with the increase of moisture content,and the number of intragranular tensile cracks increases first and then stabilizes and then increases,while the number of intergranular shear cracks continues to increase with the increase of moisture content.The contact tangential force,angular deflection value and average porosity decrease first and then stabilize and then increase with the increase of unloading creep time,and the more the moisture content increases,the more significant the trend.Final,a threestage unloading creep deterioration evolution model of dry and water-bearing mudstone is established.The research results can provide a theoretical reference for the study of the creep deformation failure mechanism of excavation and unloading of soft rock engineering under the action of water.