Study On Influence Of Shear Strength Parameters Determined By Different Test Methods On Design Of Piles In Row

The selection of test methods for rock and soil shear strength indexes in foundation pit design has always been controversial.The rationality of choosing shear strength indexes directly affects the safety and economy of the foundation pit engineering.Based on different testing methods of shear strength,the influence of shear strength parameters obtained from different testing methods,which were employed to conduct foundation pit design,on the supporting design of piles in row was discussed,and the main contents of this paper were outlined below.First,the research status quo of the shear strength testing methods and the factors influencing shear strength was elaborated in detail.Second,the theories of shear strength of saturated and unsaturated soil were detailly discussed,and the mechanism of how shear strength generated was analyzed.Third,the comparative analysis on experimental results of direct shear test and triaxial test showed that strength parameters of direct quick shear test were larger than that of triaxial unconsolidated-undrained test;the cohesion of direct consolidated quick direct shear test was smaller than that of consolidation-undrained triaxial test,while the internal friction angle was slightly larger.Indexes of direct slow shear test were less than that of triaxial consolidated-drained triaxial test.The relationship was not obvious between indexes of direct shear test under three testing methods.There was no obvious relationship between the cohesive obtained from triaxial tests under three different testing conditions,while the relationship of internal friction angle between these tests was apparent.The relationship of cohesive strength between these tests under six testing methods was not that regular,however,consolidated-undrained triaxial test had the largest internal friction angle and unconsolidated-undrained triaxial test had the smallest internal friction angle.Forth,the testing results of triaxially-compressed unsaturated soil with different matrix suction indicated that the cohesive of unsaturated soil went up with increasing matrix suction,and the internal friction angle changed little.Fifth,the results of row pile support design using different shear strength test indexes indicated that under the same drainage conditions,the result of support design using direct quick shear test parameters,compared with that of using unconsolidated-undrained triaxial test,was comparatively more dangerous,while the result of support design using direct quick consolidated test parameters was more conservative in comparison with the result from consolidated-undrained triaxial test.The same tendency was observed between result obtained from using direct slow shear test parameters and that from consolidated-drained triaxial test.By using the parameters obtained from unsaturated soil with different matrix suction to conduct design,it was found that the overall stability coefficient exhibited a positive trend with increasing matrix suction.It was better to choose testing parameters of triaxial tests according to testing conditions.Once parameters from unsaturated soil testing was adopted to carry out design work,a higher stability coefficient was achieved when compared with the efficient from conventional triaxial tests.It would be more appropriate to conduct design using shear strength parameters obtained from unsaturated soil in engineering practice including unsaturated foundation pit.