True triaxial experiment of foundation pit considering initial stress

For the stress path of soil around pit in the excavation process,by using true triaxial apparatus the lateral unloading tests are carried out considering initial stress,and comparing routine triaxial test results with those of true triaxial test in lateral loading.Then some conclusions from analyzing contrastive results are made.The q-e s curve,which is hyperbolic relation,is similar to the()σ1-σ 3-e1 curve of routine triaxial shear test.The incipient strength of soil with true triaxial apparatus has increase because of intermediate principal stress.True triaxial incipient tangent slope is always higher than that of routine triaxial test during loading.Soil sample unloaded in minor direction collapses at smaller strain.The stress strength of soil in loading path is bigger than that in unloading path.