薄层状软硬复合岩体弯曲断裂机理及强度特征试验研究

The thinly layered composite soft-hard rock strata are widely distributed in China, in which many geologic hazards often occur such as the toppling and sliding-bending failure of slopes and roof collapse as well as floor heave of underground cavities. The structure of strata and bending-load pattern intensively influence on the bending-fracture properties of layered composite rock masses. Up to date, for the studies on bending-fracture of this kind of rock masses, there are lack of the recognized test method and in-depth intrinsic mechanical mechanism. The geological structure of thinly layered soft-hard rock strata is first mapped to obtain its qualitative representation model. Based on the stress analysis of bending-fracture in different engineering rock masses, the physical and numerical bend tests on the multi-scale composite soft-hard test samples are conducted under four bending stresses conditions, i.e., three-point, simply-supported, cantilever and translational push bend tests. After revealing the strata-combined and sample-scale effects on the fracture properties of thinly layered composite rock masses, the theoretical solution on its fracture toughness and the corresponding test method to obtain the fracture parameters are put forward. The influences of load pattern, strata structure, shear parameters of bedding plane, joints in hard rock, rocks strengths and rock fracture toughness on the bending-fracture mechanism and strength of thinly layered soft-hard composite rock masses are captured. Combined with the theoretical studies, for the different bend load, the corresponding coupling elastic-plastic-brittle mechanical models of composite beams are established. The hybrid stability theory combined fracture strength with deformation will be presented in order to assess the bending-facture of engineering rock masses. These future research results will enrich innovatively the basic mechanical theory of rock masses bending-facture and provide the theoretical supporting for the evaluation of stability of engineering rock masses.

我国薄层状软硬复合岩层分布广泛，此类岩体边坡倾倒及滑移-弯曲和洞室顶板坍塌及底鼓等地质灾害非常普遍。层状复合岩体弯曲断裂性质具有强烈的岩层结构及荷载作用模式效应，至今仍缺乏成熟的试验技术及深入的内在力学机理研究。在薄层状复合岩体地质结构调查及量化表征研究基础上，针对不同工程岩体弯曲断裂的应力状态，开展多尺度三点弯曲、简支弯曲、悬臂弯曲及平推弯曲的物理及数值模拟试验。揭示薄层状复合岩体断裂韧度等力学参数的岩层组合及试件尺寸效应，建立其计算及试验测试方法。揭示荷载模式、岩层结构、层面剪切性质、层间裂隙、岩石强度及断裂韧度等参数对薄层状复合岩体弯曲断裂机制及强度的量化影响规律。结合理论研究，建立三类典型弯曲荷载下薄层状复合岩体弹-塑-脆性组合梁力学模型，形成断裂强度-变形耦合的工程岩体弯曲断裂稳定性评价理论。研究成果将创新性丰富岩体弯曲断裂力学基础理论，为工程岩体弯曲断裂破坏的稳定性评价提供理论依据。

我国薄层状软硬复合岩层分布广泛，此地层易发生边坡倾倒、滑移-弯曲及洞室顶板坍塌、底鼓岩层等岩层弯曲断裂灾害。层状复合岩体弯曲断裂行为具有强烈的岩层结构及荷载作用模式效应，本项目针对薄层状软硬复合层状岩体弯曲断裂机理、强度及边坡岩层弯曲断裂灾变机制等问题，开展了三点弯曲、平推弯曲等断裂力学和反倾倒边坡离心模型试验与理论研究，并拓展应用于反倾边坡弯曲倾倒、顺层陡倾边坡滑移弯曲的机制及稳定性研究，主要取得四个方面的重要成果：1）提出了层理面倾角、强度及间距对层状岩体弯曲断裂的影响机制，建立了断裂模式的岩层结构关联准则；2）揭示了层厚、层间粘结强度、层间裂隙及荷载模式对滑移-弯曲断裂的影响规律，建立了层状岩体滑移弯曲稳定性计算理论；3）揭示了岩脉夹层及软硬岩层厚比对复合层状岩体断裂强度、裂缝扩展等断裂行为的影响规律；4）建立了薄层状软硬岩复合反倾边坡和陡倾顺层边坡的弯曲倾倒与滑移弯曲灾变演化机制。依托本项目，课题组在IJRMMS、RMRE、EG等知名期刊上发表高水平学术论文43篇，授权发明专利13项，参加国内外学术会议17次，项目负责人做特邀报告7次，负责人以第一完成人获得2020年河北省科技进步一等奖等省部级奖励。这些研究进展，丰富了层状岩体工程地质与岩体力学基本理论，为薄层状洞室围岩、边坡岩层的弯曲折断灾害防控提供了重要的理论基础与技术参考。