Experimental Research On The Effect Of Stress History To Strength Characteristics Of Saturated Expansive Soil

In the engineering construction, such as high slope, river channel excavation or pit, the original stress state of soil was changed because of the excavation, which could lead to soil strength characteristics’ changing. Especially, after running a period of time mostly, expansive soil slopes exist unstable situation. This was actually related to the ignorance to the effect of stress history on soil’s strength characteristics. Therefore, it was necessary to research the effect from stress history on soil’s soil’s strength characteristics. In the paper, the typical expansive soil from Hefei was selected for the study, experimental research on the effect of stress history to strength Characteristics of saturated expansive soil were conducted.Firstly, the theoretical analysis about the stress history of excavation soil was conducted, and come to the conclusion that a big difference between actual excavation slope soil stress history and the samples’stress history in conventional soil test, and the corresponding test program was developed. Secondly, for soil stress history factor, the direct shear tests and triaxial tests under different OCR were conducted. As a comparison of stress paths, the lateral unloading triaxial tests under the same OCR values were conducted. Finally, the comparison and analysis were conducted on soil’s strength properties from the experimental research, such as shear properties, shear strength, shear strength index. The main results are as follows:1) Remolded clay shear curve, showed strain hardening properties under less consolidated state, strain softening properties under state of state of normal consolidation and over consolidation. And with the OCR value’s increasing, shear displacement decreases at the peak value point of shear stress. Under the state of less consolidation, normal consolidation and over consolidation, undisturbed clay mostly showed strain hardening properties.2) With the OCR value’s increasing, the shear strength of sample increases. Under the same conditions, the shear strength from lateral unloading triaxial compression tests was about 50% of that from conventional triaxial compression tests. It can be said, the shear strength from conventional triaxial compression tests have great difference with the actual value.3) With the OCR value’s increasing, the value of c would decrease and the value of φ increase, and the trend line showed significant bending at the transition from the less-consolidated state to state over-consolidated state. Under the same conditions, compared to conventional triaxial compression tests, the clay shear strength index from lateral unloading triaxial compression tests:the value of c was smaller, was about the 67% of that from conventional tests, but the value of φ was bigger, was 1.5 times of that from the conventional tests. It can be said, the bigger the clay depth, the smaller the value of c, the greater the value of φ, and the variation width was larger at the transition from the less-consolidated state to state over-consolidated state. The clay shear strength index of the pit slope clay from conventional triaxial compression tests have great difference with the actual value.