中文摘要：

为了评价原位应力状态膨胀土在小应变作用下的刚度衰减特性,综合原位地震扁铲侧胀和室内共振柱试验,分析应力历史、应力状态和试样扰动对膨胀土剪切模量衰减规律的影响。结果表明,应力状态和应力历史对膨胀土剪切模量影响较大,相同应力历史下,剪切模量随围压增加而增大,随着应变的发展,衰减较快;相同应力状态下,经历加载–卸载过程的剪切模量–剪应变（G-γ）衰减曲线位于仅经历加载过程的曲线上方,但经历加载–卸载和加载–卸载–再加载过程后土的G-γ衰减曲线基本重合;另外,相同应力历史条件下,土的原位剪切模量较室内共振柱试验所得剪切模量值大,且衰减更快,说明取样卸荷、运输及制样等扰动因素对土体结构造成了不可逆的损伤,通过室内加卸载过程无法还原其原位力学性状;参考剪应变不同时,推求得到的原位G-γ衰减曲线的中间部分差异较大,参考剪应变越小,剪切模量衰减越快,说明合理选取参考曲线和小应变剪切模量是推求原位G-γ衰减曲线的关键。该研究可为类似场地地震分析和沉降分析提供理论基础和技术支持。

英文摘要：

In order to evaluate the characteristics of stiffness decay of expansive soil at the in-situ stress state under the small strain condition, the in-situ seismic dilatometer test and the resonant column test are carried out to analyze the influence of stress history, stress state and disturbance on the modulus decay of expansive soil. Results show that both the stress state and stress history significantly affect the shear modulus of expansive soil. The shear modulus increases with the increasing of the confining pressure under the same stress path and the modulus decays faster with the development of shear strain. The shear modulus of soils following the loading-unloading path is greater than that of soils only following the loading path, while the G-γ decay curve of former is nearly the same as that of soils following the loading-unloading-reloading path. Besides, the in-situ shear modulus is greater than that from the resonant column tests of the same stress history, which indicates that disturbance caused by sampling, unloading, transportation and sample preparation contributes to the irreversible damage, so that the in-situ characteristics were not be presented in the indoor test results following the loading and unloading path. The in-situ G-γ decay curves derived with different reference strains exhibit an evident difference in the middle strain range, which shows the shear modulus decays faster with smaller reference strain. Selecting a reasonable reference curve and the shear modulus of small strain are the key to get the right in-situ G-γ decay curves.