颗粒组成对粉土动强度的影响分析

以天津汉沽地区某挡土墙地基粉土为研究对象,首先对不同颗粒组成的粉土做固结不排水动三轴剪切试验,采用各向等压固结,周围压力等于100kPa。固结完成后在不排水条件下施加轴向激振力,试验波形为正弦波,振动频率1.0Hz,试验中以试样在周期剪切时轴向周期应变达到5%作为破坏标准,得出粉土的动强度受颗粒组成的影响。细颗粒含量越大,其动强度越小,黏粒含量为7.2%的粉土循环剪应力比CSR约为20.3%黏粒含量粉土的2倍。粉土的动强度可以用循环剪应力比和破坏振次建立的幂函数关系式较好地拟合。在剪切过程中,粉土的孔隙水压力一直没有达到所施加的围压数值,最终稳定在75%~85%围压之间。同时,试验还得出孔隙水压力的增长模式不能用统一的Seed模型拟合,孔压增长规律的影响因素较多。

Influence of Particle Composition on the Dynamic Strength of Silt

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.