Modeling of monotonic and cyclic behaviors of sand under small and normal confining stresses

Abstract

Soil is commonly confined under very small stress at shallow depth of ground and in small scale 1 g model test. Considering Toyoura sand as example, it shows relatively less compressibility under small confining stress (<50 kPa) than normal confining stress (50∼1000 kPa) in both static and dynamic conditions. To investigate the mechanical behavior of Toyoura sand under different confining stresses (CS), a series of element tests were conducted. These tests were performed on loose and medium dense sand by applying isotropic consolidation and unloading conditions, under the confining stress ranged from very small to normal values (5 kPa∼700 kPa). It is found that the gradient of e -ln p curves of both loose and medium dense Toyoura sands consolidated under 700 kPa is about 2.5 times of the specimens consolidated under 50 kPa. While during unloading, the gradient of e -ln p curves of specimen consolidated under 700 kPa is about 3 times of the specimen consolidated under 50 kPa. Based on these test results, a new model is proposed based on Cyclic Mobility model, and this model has competency to describe the compressibility of sandy soils accurately even under small CS. In proposed model, a new power function relationship between void ratio and confining stress is established, and a new evolution equation for overconsolidation is also adopted. The proposed model is verified by isotropic consolidation tests, drained monotonic triaxial tests, and undrained cyclic triaxial tests. Moreover, it is also established that the predictive accuracy of compressibility of proposed model is significantly improved than the original model especially under small CS. • A new constitutive model was proposed to describe the low compressibility of sand under small confining stress (CS). • The isotropic loading and unloading tests with the stress range from small CS to normal CS (5 kPa∼700 kPa) were conducted. • The power function relation between void ratio and confining stress in the isotropic consolidation tests is almost linear. • The proposed model can describe the mechanical behavior of sands with various conditions in a unified way.