基于改进接触模型的灰岩微观裂纹扩展与溶蚀机理的研究

The development of karst is a complicated chemical and physical process. Natural rock fissures provided favorable conditions for water transportation and dissolution activities, and thus promoted the development of karst in rock. This project will study the problem of karst in limestone (the most common type of karst rock) based on the interaction mechanism of micro crack propagation and limestone dissolution process. With the great advantages of using Discrete Element Method to deal with fracture seepage coupling problem, through the analysis of the micro crack mechanism of limestone failure process from indoor experiments, it is easy to build improved three-dimensional discrete element contact model that can fit both the macro-mechanical properties of limestone and its micro fracturing behavior based on the researcher’s past study. Then this study will establish the correct numerical model of limestone with prefabricated cracks using the newly developed contact model. Through the analysis these numerical models behavior under uniaxial loading, summarize the basic rules of crack initiation, propagation, coalescence and failure process in limestone; finally, study these numerical models behavior under different water pressure and water dissolution condition, analyze the micro crack initiation, propagation, coalescence and failure process of limestone, and summarize the typical rules of limestone failure process under different water pressure condition. This research seeks the micro field crack development mechanism of limestone using DEM method as a breakthrough, and can provide a new way to understand the long-term development karst problems and contribute to the remediation of karst disasters for future underground engineering practice.

岩溶的发育是一个复杂的化学、物理过程。岩层中天然存在的裂隙为岩溶水活动和溶岩作用提供了有利条件，进而促进了岩溶的发育。本课题将岩溶问题的研究以灰岩（最常见的可溶岩类型）中微观裂纹扩展与溶蚀的相互作用机理作为切入点，结合离散元断裂与渗流耦合分析的优势，通过分析室内实验中灰岩微观破坏的机理，建立适用于灰岩物理力学属性的改进三维离散元接触模型；基于新的接触模型建立灰岩预制裂隙的数值模型试样，进而分析灰岩在单轴荷载状态下，预制裂隙尖端裂纹起始、扩展和破坏的规律；最后结合不同水头压力以及水力溶蚀作用下，分析预制裂隙试样的破坏过程，总结水力耦合作用对灰岩裂纹扩展与破坏的规律。本课题以微观领域灰岩裂纹发育机理研究作为突破口，为理解岩溶问题长期发育规律，解决地下工程中岩溶地质灾害提供新的思路。

岩体中裂纹扩展与贯通一直是岩石力学研究的热点问题，不少岩体工程的失稳破坏就是由于其内部裂隙的扩展贯通引起的。岩石材料具有不均匀性和不连续性，且岩体裂隙扩展理论尚不完善，目前对岩石或类岩石材料进行裂纹扩展试验时，受制于观测仪器及设备的精度，很难获得岩体内部裂纹扩展的准确信息。本研究以含双裂隙石膏和灰岩试样的裂纹扩展规律为切入点，结合离散元分析断裂和大变形的优势，基于室内试验的裂纹扩展结果，设立了含中心预置单裂隙灰岩棱柱颗粒流模型，进行单轴压缩模拟试验，探究其微裂纹扩展特征。探究在不同预置裂隙倾角的影响下，裂隙尖端处微裂纹的萌发、扩展和连通的相关特点。并通过控制接触强度比和刚度比的细观参数，获取它们对微裂纹扩展和裂缝发育所产生的影响规律进而分析在单轴和双轴加载条件下。采用改进PBM接触模型建立预制双裂隙的类岩石数值试样，预制双裂隙尖端裂纹起始、扩展和贯通破坏的规律；并根据裂纹扩展数值试验，对比了改进PBM模型与平直节理接触模型（FJM）的适用性。