考虑部分排水和土体流变性影响的应变保持试验数值分析

旁压应变保持试验(SHT)是测定土体水平固结系数的有效原位测试方法之一。通常采用Clarke建议的步骤,由于包含了一些简化的假设而导致对固结系数的不准确地评估。以Drucker-Prager理想弹塑性模型为基础,利用有限元法模拟饱和黏土中SHT,分析了Clarke等固结时间因数曲线(根据Randolph和Wroth解)的适用条件,并考虑渗透性及应变加载率引起的部分排水的影响,对Clarke曲线进行修正,建议了误差曲线。进一步地采用Drucker-Prager理想弹塑性与土体流变的耦合模型模拟SHT,分析土体流变性对超孔隙水压力消散的影响。研究表明:土体流变对超孔隙水压力消散的影响,除了通过应力松弛改变边界应力水平而使超孔隙水压力下降,还通过改变超孔隙水压力的分布而减缓其渗透固结速度;渗透系数越小,土体流变性对超孔隙水压力的消散速度影响越明显。忽略土体流变性会高估水平固结系数,可高估几倍到数十倍。

Numerical analysis of strain holding test considering partial drainage and soil rheology

Strain holding test(SHT),part of self-boring pressuremeter test,is one of the most effective in-situ tests in determining horizontal coefficient of consolidation(ch).However,the commonly used interpretation method proposed by Clarke et al for deriving ch from SHT results can lead to an inaccurate estimation of ch due to simplified assumptions.Numerical analysis of SHT in saturated clay is carried out to illuminate the applied conditions of Clarke consolidation curve(after Randolph and Wroth) based on elastic-perfectly plastic Drucker-Prager model.And the values of time factor T50 provided by Clarke el al to estimate ch are modified in view of the effects of soil permeability and strain rate on partial drainage during cavity expansion.Moreover,analysis is performed considering the soil rheology during SHT based on the coupling Drucker-Prager and creep model to investigate the influence of soil rheology during SHT on the decay of excess pore pressure.It is concluded that for the lower permeability,the soil rheology has significant impact on the dissipation of excess pore pressure,and that ignoring the soil rheology during SHT will overestimate ch by several times,and even tens of times for some conditions.