基于弹黏塑性模型的部分排水柱孔扩张分析

Partially drained cylindrical cavity expansion using elastic-viscoplastic model

孔穴扩张的速率效应不仅与孔穴周围土体的排水条件有关,还与土体的率相关力学特性密切相关。现有孔穴扩张理论多聚焦于土体部分排水条件引起的率相关性,较少关注土体排水条件和率相关力学特性的联合影响效应。采用数值分析方法,基于过应力弹黏塑性本构模型,分析了考虑部分排水条件的柱孔扩张过程,围绕孔壁处土体的径向总应力、剪切应力和超孔隙水压力随扩孔的发展规律,探讨了土体率相关力学特性对孔穴膨胀响应的影响。分析表明:当仅考虑土体部分排水条件时,径向总应力和剪应力随加载速度增加而单调减小,其中,扩孔初期,当扩孔速度在10^(-4)~10^(-1)mm/s范围内时,其对径向总应力的影响较小。当同时考虑部分排水条件和土体率相关力学特性的影响时,扩孔初期,径向总应力和剪应力随扩孔速度增加而显著增加,这一规律与Burswood黏土和湛江黏土的原位自钻旁压试验结果一致;随着扩孔的进行,径向总应力和剪应力随加载速度的增加,呈现先减小后增加的规律。土体黏塑性参数(γ^(vp)和n)的敏感性分析显示,相同扩孔速度下,径向总应力、剪切强度和初始剪切模量随γ^(vp)或n的增加而逐渐减小,且减小的幅度越来越小。扩孔速度、土体渗透系数、超固结比对孔壁处土体的排水条件影响较大,对参数γ^(vp)和n的影响相对较小。土体排水条件可通过无量纲速度V进行评价,部分排水条件对应的V值范围为0.04~250.00。建议在应用柱孔扩张理论分析黏性土相关问题时考虑土体力学性能的时间相关性。

The rate effect of cavity expansion is not only related to the drainage conditions of the soil surrounding the cavity,but also closely associated with the rate-dependent mechanical properties of the soil.Most existing cavity expansion theories primarily focus on the rate effect caused by partial drainage conditions,with little attention given to the combined influence of drainage conditions and the rate-dependent mechanical behavior of soil.By employing numerical analysis and utilizing the overstress elasto-viscoplastic(EVP)model,the study focuses on the partial drainage conditions during cylindrical cavity expansion.The analysis indicates that when only the effect of partial drainage conditions is considered,the total radial stress and shear stress decrease monotonically as the expansion velocity increases,and the expansion velocity ranging from 10^(−4) to 10^(−1) mm/s has a small impact on the total radial stress during the initial expansion stage.When the effect of partial drainage conditions and rate-dependent behavior is considered simultaneously,the total radial stress and shear stress gradually increase with the increase of expansion velocity during initial expansion stage,which is consistent with the results of in-situ self-boring pressuremeter tests conducted on the Burswood clay and Zhanjiang clay.With the cavity expansion,the radial total stress and shear stress show a pattern of first decreasing and then increasing with the increase of expansion velocity.Sensitivity analysis of the soil's viscoplastic parameters(γ^(vp) and n)reveals that,for a given expansion velocity,the total radial stress,shear strength,and initial shear modulus gradually decrease asγ^(vp) or n increase,with the rate of decrease diminishing over time.The expansion velocity,permeability coefficient,and overconsolidation ratio of the soil significantly impact the drainage conditions at the cavity wall,while the influence ofγ^(vp) and n is relatively minor.The drainage conditions of the soil can be assessed using a dimensionless velocity V,with values of V corresponding to partial drainage conditions ranging from 0.04 to 250.It is suggested that the time-dependent mechanical behavior should be considered when applying cylindrical cavity expansion theory to analyze geotechnical problems related to cohesive soils.