Strength and deformation behaviour of coarse-grained soil by true triaxial tests

In order to investigate the influence of intermediate principal stress on the stress-strain and strength behaviour of a coarse-grained soil,a series of true triaxial tests were performed.The tests were conducted in a recently developed true triaxial apparatus with constant minor principal stressσ3 and constant value of intermediate principal stress ratio b=(σ2-σ3) /(σ1-σ3) (σ1 is the vertical stress,andσ2 is the horizontal stress) .It is found that the intermediate principal strain,ε2,increases from negative to positive value with the increase of parameter b from zero to unity under a constant minor principal stress.The minor principal strain,ε3,is always negative.This implies that the specimen exhibits an evident anisotropy.The relationship between b and friction angle obtained from the tests is different from that predicted by LADE-DUNCAN and MATSUOKA-NAKAI criteria.Based on the test results,an empirical equation of g(b) that is the shape function of the failure surface onπ-plane was presented.The proposed equation is verified to be reasonable by comparing the predicted results using the equation with true triaxial test results of soils,such as coarse-grained soils in this study,sands and gravels in other studies.

In order to investigate the influence of intermediate principal stress on the stress-strain and strength behaviour of a coarse-grained soil, a series of true triaxial tests were performed. The tests were conducted in a recently developed true triaxial apparatus with constant minor principal stress σ3 and constant value of intermediate principal stress ratio b=（σ2-σ3）/（σ1-σ3） （al is the vertical stress, and % is the horizontal stress）. It is found that the intermediate principal strain, ε2, increases from negative to positive value with the increase of parameter b from zero to unity under a constant minor principal stress. The minor principal strain, ε3, is always negative. This implies that the specimen exhibits an evident anisotropy. The relationship between b and friction angle obtained from the tests is different from that predicted by LADE-DUNCAN and MATSUOKA-NAKAI criteria. Based on the test results, an empirical equation of g（b） that is the shape function of the failure surface on re-plane was presented. The proposed equation is verified to be reasonable by comparing the predicted results using the equation with true triaxial test results of soils, such as coarse-grained soils in this study, sands and gravels in other studies.