Abstract:The silt under a retaining wall foundation in the Hangu area of Tianjin was studied in this paper.Specifically,a consolidated undrained dynamic triaxial shear test on the silt of different particles is described,and the conclusion is that the dynamic strength of silt was impacted by the particles.The test used isotropic consolidation,and the ambient pressure is equal to 100 kPa.After consolidation,we applied an axial dynamic load in the undrained condition.The test waveform is a sine wave,and the vibration frequency is equal to 1.0 Hz.The sample used a periodic shear axial strain of 5% as the failure criterion.The test instrument is a DDS-70-type dynamic three-axle instrument.Silt samples were compacted in three layers in the cylindrical specimen.The sample water content is equal to 20%,and the dry density is 1.60 g/cm3.The diameter of the sample is 39.1 mm,and the height is 80 mm.We prepared soil samples with different clay contents.The soil's dynamic strength refers to,under the static stress conditions,the cycle load necessary to make the soil sample achieve certain failure criteria.We have drawn the following conclusions.Under the same test conditions,silt particles had a great influence on the dynamic strength.When the dynamic load is equal to 100 N,and the No.1 silt clay content is 20.3%,the vibration frequency reached 42,far less than that for the No.2 and No.3 silty soils.The clay contents of silts Nos.2 and 3 are 13.2% and 7.2%,respectively.With the increase in dynamic load,the No.3 silt vibration frequency is 2.2 times that of No. 1.A higher clay content means that the proportion of fine particles is greater,the coarse particle content is lower,and the plasticity is greater.That is,it is closer to clay.Friction of fine particles was significantly less than that of coarse particles.Therefore,the coarse silt's dynamic strength is relatively large.Pore water pressure generated under a vibrating load is an important factor affecting the soil strength and deformation.Pore water pressure is the key to the analysis of dynamic strength by effective stress.From the test results,for the three kinds of silt in the shearing process, the pore water pressures grow but do not reach the value of 100 kPa of the applied confining pressure.The pore water pressure is stable between 75 and 85 kPa.The more fine the particles,the lower the dynamic strength contained by the silt.The cyclic shear stress ratio (CSR) of silt with 7.2% of viscosity particles was about two times that of silt with 20.3% of viscosity particles.The dynamic strength of silt could be fitted by the CSR and power function relation created by the failure time of the vibration.In the shearing process,the pore water pressure of silt did not reach the numerical result of the ambient pressure,and eventually stabilized at 75~85% of the ambient pressure.Additionally,from this trial it could also be concluded that the growth pattern of pore water pressure could not be fitted by the unified Seed model,and the growth of pore pressure was influenced by many factors.
