Triaxial shear tests on soil-rock mixture and 3D multi-shear bounding surface model
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摘要: 土石混合体是介于离散和连续介质之间的特殊地质材料，其颗粒分布特征和力学特性是控制土石混合体高填方工程稳定性的重要因素。以白鹤滩水电站库区象鼻岭移民安置点防护堤工程为依托，利用大型三轴试验仪，对两种土石混合体填筑料在3种不同围压条件下进行固结排水剪切试验，分析了土石混合体的偏差应力和体积应变随轴向应变的变化规律以及剪缩和剪胀特性。在此基础上，根据粒状土的临界状态和边界面弹塑性理论，引入了适合于土石混合体的临界黏聚力和状态参数，并基于空间随机分布微观剪切结构，建立了土石混合体状态相关三维多重剪切边界面模型。通过模型模拟结果与三轴剪切试验结果的比较，验证了该模型能够合理地描述土石混合体在低围压下的应变软化和剪胀特性，以及在高围压下的应变硬化和剪缩特性。Abstract: The soil-rock mixture is a special geological material between discrete and continuous media. Due to the influences of genesis, component type and content, its mechanical behavior is complex and changeable, which may lead to the excessive deformation and shear failure of high fill projects of soil-rock mixture. Therefore, it is of great theoretical significance and engineering application value to study the deformation and strength characteristics of soil-rock mixture and its constitutive models. Based on the protection embankment project of Xiangbiling resettlement site in the reservoir area of Baihetan Hydropower Station, the consolidation and drainage shear tests on two kinds of fill materials of soil-rock mixture under three different confining pressures are carried out by using the large-scale triaxial test device, and the variation laws of deviatoric stress and volumetric strain with axial strain and the characteristics of shear contraction and dilation of soil-rock mixture are analyzed. On this basis, according to the critical state and bounding surface elastoplastic theories of granular soil, the critical cohesion and state parameter suitable for the soil-rock mixture are introduced, and based on the spatially randomly distributed micro-shear structures, a state-dependent three-dimensional multi-shear bounding surface model for the soil-rock mixture is established to decompose the complex macro-deformation of the soil-rock mixture into a macro-volume deformation and a series of spatially distributed and mutually independent one-dimensional micro shear deformation. The simulated results of the model are compared with the triaxial shear test ones, which verifies that the proposed model can reasonably describe the strain softening and shear dilation characteristics of the soil-rock mixture under low confining pressure and the strain hardening and shear contraction characteristics under high confining pressure.
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Keywords:
- soil-rock mixture /
- triaxial shear test /
- stress-strain relationship /
- dilatancy /
- multi-shear /
- bounding surface
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图 1 象鼻岭移民安置点防护堤工程鸟瞰图
Figure 1. Aerial view of protection embankment project of Xiangbiling resettlement site
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图 5 土石混合体剪胀角-轴向应变关系
Figure 5. Relationship between dilatancy angle and axial strain of soil-rock mixture
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图 9 #1土石混合体的模型模拟和试验结果比较
Figure 9. Comparison between model simulations and test results of soil-rock mixture No. 1
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图 10 #2土石混合体的模型模拟和试验结果比较
Figure 10. Comparison between model simulations and test results of soil-rock mixture No. 2
表 1 模型参数
Table 1 Model parameters
参数 取值 #1土石混合体 #2土石混合体 弹性模量 G0 70 100 κ 0.0013 0.0009 n 0.1 0.1 塑性模量 λ 0.0026 0.0018 h1 2.5 2.5 h2 0.5 0.5 临界状态 Mc 1.673 1.663 cc 0.144 MPa 0.198 MPa ec0 0.322 0.326 λc 0.044 0.041 剪胀 d1 1.5 1.5 nd 2.5 3.5 边界应力 nb 0.5 0.5 
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