Evaluation of strength-deformation behavior of clay ground based on the unconfined compression test with suction measurement and triaxial compression test with shear modulus measurement by bender element.

1.基于吸力测量的无侧限压缩试验估算现场不排水强度。基于一系列模拟饱和粘土从取样到无侧限和三轴压缩试验的试验，研究人员发现，用残余有效应力Siguma‘与准超固结比Qcr(=Siguma^1*Siguma^1_5)关系归一化的未排水强度Cu用对数曲线直线表示，其中a’由无侧限压缩试验前的吸力值计算得出，Siguma*为现场有效覆岩压力。利用该关系式，可以根据常规无侧限压缩吸力试验结果来预测粘土的原位不排水强度。在本研究中，通过将该方法得到的不排水强度沿深度的分布与现场测深结果进行比较，验证了该方法的有效性。粘性土地应力-变形特性的估算根据固结仪和三轴仪的试验结果，发现用弯管单元由剪切波速得到的刚性模数G与用单调和循环加载不排水三轴试验测得的弹性模数E计算的结果吻合较好。试验还发现，弹性模数G随试件扰动而减小，其大小取决于残余有效应力的大小。上述两组试验结果证实，如果能够适当地评价试件的残余有效应力，则可以现场估计粘性土的强度-变形特性。

1. Estimation of in-situ undrained strength based on the unconfined compression tests with suction measurement. Based on a series of test simulating the process from sampling to unconfined and triaxial compression test for saturated clay, the head investigator formerly found that the undrained strength Cu normalized by residual effective stress siguma' versus quasi-overconsolidation ratio QCR( = siguma^1 * siguma^1_5) relationship is represented by a straight line in logarithmic plot, where a', is calculated from measured suction value before unconfined compression test and siguma * is in-situ effective overburden pressure. By using the relationship, in situ undrained strength of clays can be predicted from the results of conventional unconfined compression test with suction measurement. In this study, the examination and confirmation of the validity of the proposed method was performed by comparing the distributions of undrained strength obtained by the method along the depth with those obtained by in situ sounding test results.2. Estimation of in-situ stress-deformation characteristics of clayey soilsBased on the test results by consolidometer and triaxial apparatus, both are equipped with bender element, it was found that modulus of rigidity (G)obtained by shear wave velocity with bender element well coincides with the ones calculated by using the modulus of elasticity (E ) obtained by monotonic and cyclic loaded undrained triaxial tests. It was also found that the modulus G decreases with sample disturbance and its value depends on the magnitude of residual effective stress.It was confirmed by two series of test results mentioned above that the strength-deformation characteristics of clayey soils in-situ can be estimated if the residual effective stress of the specimen can be suitably evaluated.