武汉天然老黏性土的压缩和剪切特性试验研究与数值模拟

武汉天然老黏性土是一种超固结硬黏土 ,在开挖卸载条件下容易产生应变软化 ,经常给深基坑、边坡工程带来不利影响.目前对其超固结性、结构性以及剪切特性等还缺少深入认识.利用高压固结仪和三轴剪切仪对其饱和原状样和饱和重塑样分别进行了压缩试验和三轴不排水剪切试验 ,并且应用上下负荷面剑桥模型对原状样的三轴不排水剪切试验进行了模拟.研究结果表明 :天然老黏性土为一种强超固结的结构性土 ,采用两种方法得到的原状土前期固结压力和结构强度基本一致 ;在低围压下 ,原状样明显表现出应变软化和剪胀性 ,其破裂面易受微裂纹影响;与文献中的天然软土不同 ,天然老黏性土在结构破坏后剪缩并不明显 ;原状样的黏聚力明显高于重塑样 ,两者内摩擦角非常接近 ;采用上下负荷面剑桥模型模拟的原状样应力-应变曲线和孔压曲线与室内试验结果基本一致.

Experimental Investigation and Numerical Simulation of Compression and Shear Characteristics of Natural Stiff Clay in Wuhan

The natural old clay in Wuhan is an overconsolidated stiff clay .It often shows strain-softening under the exca-vating and unloading condition ,which might cause some adverse impacts on deep pits and slopes .However ,its over-con-solidation ,structure and shear properties are not well recognized .In this paper ,first ,a set of high-pressure oedometer tests and undrained triaxial tests were carried out on its saturated undisturbed and remoulded samples ,respectively .Sec-ond ,the undrained triaxial tests of undisturbed samples were numerically simulated with super-loading Cam-clay model . It was founded that the natural old clay could be classified as a strong overconsolidated clay ,and the preconsolidation pressure and the structural strength obtained by two methods were consistent .Under low confining pressure ,the undis-turbed samples obviously present strain softening and shear dilatancy ,and the failure patterns are often influenced by the micro fissures .After the structure collapses ,the natural old clay presents little contraction ,which is different from natu-ral soft soils in the literature .The cohesion values of undisturbed samples are much higher than those of remoulded ones , and their internal frictional angles are very close .The stress-strain curves and pore pressure variation simulated by the su-per-loading Cam-clay model are generally in agreement with the experimental results .