Experimental Study On The Thixotropic Properties Of Soft Soils In The Pearl River Estuary

With the development of economic construction,many large buildings have been built in the Pearl River estuary,and the stability of the buildings depends on the stability and safety of the foundation.The complex changes in the water of the Pearl River have caused a large number of fine-grained soils to be deposited in the area to form a deep layer of soft soil,which is characterised by high water content,high compressibility,low shear strength,low permeability and easy thixotropy.Therefore,it is of great engineering value and scientific significance to study the thixotropic properties of soft soils.In this paper,the thixotropic properties of soft soils in the Pearl River Estuary are studied by various indoor testing methods,and the microstructure evolution of the soil is analysed by microstructure testing tests and digital image processing techniques,revealing the microscopic evolution mechanism of the thixotropic properties of soft soils:1.By conducting a large number of basic physical and mechanical property tests on soft soils in the Pearl River estuary,it is concluded that soft soils in the Pearl River estuary are characterised by high water content,high porosity ratio,high compressibility,low permeability and low strength,and the permeability coefficient of soft soils in the estuary is generally in the order of 10-6-10-8cm/s,while the permeability coefficients of silt and silty soils in most parts of the country are in the order of 10-7-10-8cm/s magnitude,which is the most typical characteristic of soft soils in the inlet compared to other regions.2.The thixotropic properties of soft soils in the estuary were investigated by cross-plate shear test and lateral limitless compression test,and the effects of different resting times and water contents on thixotropic strength were analysed.The shear strength obtained from the cross-plate shear test was higher than that obtained from the unconfined compression test;based on the results of the cross-plate shear test,a thixotropic model for the strength of soft soils in the Pearl River Estuary was established to reflect the effects of moisture content and resting time.3.The effects of resting time and water content on the compression index and rebound index were analysed.The thixotropic stiffness ratio of the low moisture content specimens increased slowly with increasing resting time,while the thixotropic stiffness ratio of the high moisture content specimens increased rapidly and eventually stabilised with increasing resting time.In combination with the microstructure test results,i.e.the microstructure porosity increases linearly with increasing water content,the corresponding compression index also increases with increasing water content,revealing the mechanism of thixotropic stiffness evolution in soft soils.4.A cyclic triaxial test was carried out on the soft soils of the inlet using a GDS dynamic triaxial instrument to analyse the effects of cyclic circumferential pressure and loading frequency on the deformation and pore pressure of the soft soils.The results show that: the accumulated axial strain generated by the specimen decreases with increasing cyclic envelope pressure and loading frequency;based on the test results,expressions for the normalised axial accumulated axial strain versus stress path slope and loading frequency were established;the maximum and minimum pore pressure increases with increasing stress path slope,and the trend is not consistent with the loading frequency.5.The evolution of the shear strength and elastic modulus of soft soil under the influence of different post-vibration reconsolidation degrees was investigated by means of GDS dynamic triaxial apparatus for soft soil at the inlet.The results show that the post-vibration stress-strain curves have similar trends under different conditions.The undrained shear strength and modulus of elasticity increased with the increase of reconsolidation degree.A critical consolidation degree exists,such that the post-vibration shear strength and modulus of elasticity of the soft soil are equal to the shear strength and modulus of elasticity of the specimens not subjected to cyclic loading.The effect of reconsolidation on the post-cyclic shear strength and modulus of elasticity of soft soils in the Pearl River Estuary was significant,with the post-cyclic shear strength of the incompletely consolidated soil samples decreasing by 27% and the stiffness attenuating by 57%.