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中文核心期刊

考虑剪胀效应的各向异性本构模型及其在圆柱扩孔中的应用

AN ANISOTROPIC CONSTITUTIVE MODEL CONSIDERING DILATANCY EFFECT AND ITS APPLICATION IN CAVITY EXPANSION

  • 摘要: 自然沉积场地中的超固结黏土兼具各向异性与剪胀性质, 但能同时准确描述上述特性的本构模型较少, 而能将模型应用于土体的柱孔扩张分析就更为少见. 为此, 做了3点工作: (1)在超固结黏土UH模型基础上, 引入随超固结度变化的变相应力比, 并利用非相关联流动法则反映受超固结度影响的剪胀特性; (2)采用修正的旋转硬化规则, 利用塑性应变增量来驱动屈服面及塑性势面的转轴, 使之反映初始各向异性以及循环加载下应力诱导各向异性特性. 并采用基于SMP准则的变换应力方法来得到三维修正UH模型; (3)提出了一种自相似性模拟土体柱孔扩张方法. 实测数据表明, 在剪切加载下正常固结或者轻微超固结黏土处于体积收缩变形模式, 而中度超固结则处于先剪缩后剪胀的变形模式, 重度超固结黏土则是完全剪胀变形模式. K0固结黏土则表现为更高的剪切刚度以及稍高的残余强度, 所提模型能够描述上述的剪胀规律以及各向异性特性. 采用所提修正UH模型的三维本构方程及自相似性方法, 分析了考虑超固结度以及K0固结条件下柱孔扩张过程中的土体应力场分布状态, 并通过一系列各类型黏土的室内试验以及现场原位测试试验与所提模型及解析解方法的预测进行对比, 验证了所提模型及解析方法的合理性及适用性.

     

    Abstract: The overconsolidated clay in natural sedimentary site has both anisotropy and dilatancy properties, but there are few constitutive models that can accurately describe the above properties at the same time, and it is even more rare to apply the model to the analysis of soil cavity expansion stress field. Three points of work have been done in this paper. (1) Based on the UH model of overconsolidated clay, the phase transformation stress ratio with the overconsolidation degree is introduced, and the dilatancy behavior affected by the overconsolidation degree is reflected by the non-correlated flow rule. (2) The modified rotation-hardening rule is adopted to drive the rotation axis of the yield surface and the plastic potential surface by the increment of plastic strain to reflect the initial anisotropy and the stress-induced anisotropy under cyclic loading. The three-dimensional modified UH model is obtained by using the transform stress method based on SMP criterion. (3) A self-similarity method is proposed to simulate the cavity expansion of soil. The measured data show that the normal or slightly overconsolidated clay is in the volume shrinkage deformation mode under shear loading, the moderately overconsolidated clay is in the shear contraction and then dilatancy deformation mode, and the severely overconsolidated clay is in the complete dilatancy deformation mode. K0 consolidated clays exhibit higher shear stiffness and slightly higher residual strength. The proposed model can describe the dilatancy law and anisotropy properties. The three-dimensional constitutive equation and self-similarity method of the revised UH model are used to analyze the distribution of soil stress field for cavity expansion under the conditions of over-consolidation and K0 consolidation. A series of laboratory tests and in-situ tests of various types of clay are compared with the prediction of the proposed model and analytical solution method. The rationality and applicability of the proposed model and analytical method are verified.

     

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