等效拉压荷载下饱和粉质黏土的弹塑性变形特性研究

动三轴试验中,若在一定轴向静偏应力基础上施加对称正弦波荷载,土体会在荷载正半部分出现轴向压缩状态,而在荷载负半部分有可能因为侧向应力大于轴向应力而出现轴向等效拉伸状态,将此类荷载暂称为等效拉压荷载。为研究等效拉压荷载下饱和粉质黏土的弹塑性变形,设计了多级正弦波荷载室内不排水动三轴试验。依据试验数据揭示了围压、静偏应力、动偏应力和压实系数对土体弹塑性变形发展的影响,并提出用拉压效应系数来确定轴向塑性累积应变的发展趋势。研究表明:若取轴向压缩方向为正方向,拉压效应系数存在一临界值,当实际值大于临界值时,塑性累积应变向负方向发展,反之则向正方向发展或基本保持不变;同时Hardin模型可以较好地描述饱和粉质黏土的动弹模-动应变关系,且塑性累积应变向负方向发展时动弹模量普遍偏小。

Elastoplastic Deformation Characteristics of Saturated Silty Clay under Equivalent Tension and Compression Load

In dynamic triaxial tests,if a soil sample undergoes symmetric sine loading in addition to static deviator stress and if the lateral stress is greater than the axial stress,the sample will assume an axial compressive state when the loading is positive and will change to an equivalent tensile state when the loading is negative.This kind of loading is defined as equivalent tension and compression loading in this study To study the elastoplastic deformation (EPD) of saturated silty clay under equivalent-tension-and-compression loading,we design and perform some undrained dynamic triaxial tests.To consider axial static deviator stress,we apply several levels of sine loading.We determine relations among EPD and confining pressure,static deviator stress,dynamic deviator stress,and compaction coefficients.Furthermore,we propose the tension-and-compression-effect coefficient (TCEC) to forecast the plastic accumulative strain development trend.Test results show that the TCEC is a critical value when considering positive axial compression.When the actual TCEC value is larger than a critical value,the plastic accumulative strain will negatively increase; otherwise,it will positively increase or remain unchanged.Meanwhile,we prove the Hardin model to be an ideal model for reflecting the relation between the dynamic elastic modulus and dynamic strain.The dynamic elastic modulus is typically small when the plastic accumulative strain negatively increases.