Study On Dynamic Drainage Of Saturated Soft Soil

After the reform and opening-up,a large number of construction projects have to be built on soft soil foundation since China's economic construction has developed rapidly with the acceleration of urbanization and the increasing shortage of land resources.Soft soils exhibit the characteristics of high water content,low strength and poor permeability.The problems in the treatment of soft soil foundation have plagued the constructors for a long time.Usual y,free water in soft soil flows through its micropore.Once the micro-pore is destroyed,free water and weak bonded water will be hold in the soil.The poor thixotropy of soft soil is not conducive to engineering construction,while the traditional dynamic compaction method is easy to destroy the "microstructure" of soft soil because of its large energy,and even the "rubber soil" may occur affecting the quality of engineering.Considering the engineering properties of soft soil,vibration loads are used in this study to replace the impact loads in dynamic compaction method developed from the principle of vibration oil recovery,in which the impact process is transferred to repeated periodical vibration to reduce the impact on the "micro-structure" of soil.A series of laboratory dynamic consolidation drainage tests were carried out on soft soil and the main conclusions are listed below:(1)Vibration drainage tests and static drainage tests are compared to verify the feasibility of vibration drainage.The effects of vibration frequencies and confining pressures on vibration consolidation drainage behavior were analyzed.Based on the test results,a calculation method of cumulative drainage under different confining pressures and vibration frequencies is proposed.(2)Through dynamic triaxial tests of undisturbed specimens of soft soil with different vibration waveforms,cyclic stress ratios and vibration frequencies,the dynamic characteristics of the soil in the test are analyzed.Considering the critical cyclic stress ratio,the development trend of cumulative strain is divided into two modes,i.e.,progressive mode and failure mode.The variation laws of deformation,hysteresis curve,resilient strain,softening index and dynamic elastic modulus of the specimens under the two modes are discussed.The variation laws of deformation,hysteresis curve,resilient strain,softening index and dynamic elastic modulus of the specimens under the two types are discussed.In the progressive mode,the hysteretic curve of the specimen is compact with the increase of vibration times,the resilience strain is smaller,the dynamic elastic modulus is larger,and the "micro-structure" is not destroyed.In the failure mode,the specimen shows opposite rule,and the specimen has the trend of continuous softening.(3)Monismith classical model is modified by introducing the exponential function,which can accurately predict the cumulative strain development trend of the sample of the failure mode.Based on the test data,an expression of the cumulative plastic strain considering the vibration frequency and the vibration load is proposed.