Experimental Study On The Static And Dynamic Behavior Of Saturated Calys Considering The Influence Of Stress Paths

The safety and comfort of high-speed traffic, such as highway, railway and urban subway and so on is the most pressing problem of vehicle running. The safety and comfort of vehicle running in addition to related to driving speed and the dynamic properties of the vehicle itself, also closely related to the settlement and differential settlement of subgrade soil, Therefore, based on the characteristics of high speed traffic load, study the deformation characteristics of saturated soft clay under cyclic load is the key to solve the soft soil subgrade cumulative settlement and stability.In this paper, based on the soft soil foundation settlement problem caused by high-speed traffic load as the research object, through the indoor unit cell test combined with cyclic stress strain relations theory analysis of soft soil under traffic load, reveal the complex mechanism and general law of long-term settlement of soft soil under traffic load.The main research work is as follows:1. Firstly, high quality samples of natural soft clay are obtained by thin-walled tube cutting method, and determined its basic physical and mechanical properties index. Conventional triaxial undrained static shear test with different overconsolidation ratios are conducted on them through GDS triaxial apparatus, the relationship between the undrained shear strength of Wenzhou saturated soft clay and overconsolidation ratio is established and provide reference for dynamic stress selecting of subsequent cyclic loading test.2. According to the actual consolidation state of natural soft clay, undrained shear tests on Ko consolidated specimens under different triaxial stress path have been conducted. The influence of stress path on the undrained shear strength, pore pressure and secant modulus of Ko consolidated saturated soft clay isinvestigated. Based on the test results, the formulas for undrained shear strength、pore pressure coefficient and secant modulus of Ko consolidated saturated soft clay under different stress paths in p-q plane are established respectively.3. Triaxial static shear tests of saturated soft clay samples with different overconsolidation ratios have been conducted in undrained and drained conditons respectively. The coupling effect of stress path and overconsolidation ratio on the shear strength, pore pressure and secant modulus of saturated soft clay is investigated. Based on the test results, the formulas for the undrained shear strength and drained strength considering the coupling effect of stress path and overconsolidation ratio are established respectively.4. According to the complex dynamic stress field of subgrade soil under traffic load, a series of undrained cyclic loading test are conducted on saturated soft clay with different overconsolidation ratios under different cyclic triaxial stress paths through GDS triaxial apparatus. The empirical formulas for the permanent axial strain and resilient modulus considering the coupling effect of cyclic deviator stress and cyclic confining pressure are established based on the experiment results.5. According to the actual drainage state of subgrade soil under long term traffic loading, a series of Partially-drained cyclic triaxial tests with the coupling of cyclic confining pressure and cyclic deviator stress have been conducted on saturated soft clay samples with different overconsolidation ratios through GDS dynamic triaxial apparatus. The results showed that the coupling effect of cyclic deviator stress and cyclic confining pressure on the permanent axial strain of soft clay have nothing to do with overconsolidation ratios, but the impact on the permanent volumetric strain are greatly influenced by the over consolidation ratio; Based on the partially-drained dynamic triaxial test results,the empirical formulas for the permanent volumetric strain and permanent volumetric strain of normally consolidated soft clay considering the coupling effect of cyclic deviator stress and cyclic confining pressure are established; Further by the relationship between increments of permanent volumetric strain of normally consolidated soft clay or permanent axial strain of soft clay with different overconsolidation ratios and the increments of amplitudes of cyclic volumetric stress,the effect of cyclic volumetric stress on the permanent volumetric strain of normally consolidated soft clay or permanent axial strain of soft clay with different overconsolidation ratios are abtained.6. According to the actual consolidation state of natural soft clay, a series of cyclic loading test are conducted on Ko consolidated saturated soft clay under different stress paths in p-q plane in undrained and partially-drained conditions respectively.In undrained condition, based on the maximum excess pore pressure ratio under the stress path of η=0 and skempton theory can obtained the instantaneous excess pore pressure ratio under different stress paths; per 1 increment of η will cause 23% decrement of permanent axial strain and 13% decrement of resilient modulus; Based on the partially-drained dynamic triaxial test results,the empirical formulas for the permanent volumetric strain and permanent volumetric strain of normally consolidated soft clay considering the coupling effect of cyclic deviator stress and cyclic confining pressure or considering the effect of cyclic volumetric stress are established.