Study On Mechanism And Time-effect Of Drainage On Soft Soil Under Vibration Load

In 2021,the State Council issued the outline of national comprehensive three-dimensional transportation network planning,which pointed out that by the middle of this century.As the "leader" of China’s economic construction,the coastal cities along the Yangtze River urgently need to meet the needs of high-speed railways,large airport,underground railway and other infrastructure projects.However,the urban belt contains most of the southeast coastal areas in China,which is a typical soft soil foundation.The soft soil foundation has special physical and mechanical properties such as low bearing capacity,high compressibility,low permeability and high water content,which is easy to cause serious engineering problems.Therefore,effective reinforcement of soft soil foundation is not only a requirement of engineering construction,but also the basic guarantee of the deepening of China’s reform and opening up and the steady progress of economic development.At present,there are many reinforcement methods for soft soil foundation,such as replacement cushion method,vacuum preloading method,surcharge preloading method,cement reinforced soil,dynamic drainage consolidation method and so on,but most of them only meet the effectiveness under static loading conditions.In order to ensure the stability of the soft soil foundation after reinforcement,it is necessary to study the mechanical properties of the soft soil foundation after dynamic load reinforcement.At the same time,the form of load in traffic system is periodic cyclic load,while the dynamic load in dynamic drainage consolidation method is impact load.Therefore,the project team proposed to use cyclic load instead of impact load in dynamic drainage consolidation method to reinforce the foundation,namely "vibration drainage consolidation method".In this paper,through the indoor vibration drainage consolidation test of soft soil samples,the drainage consolidation characteristics and plastic strain development characteristics were analyzed,and the vibration drainage consolidation mechanism of soft soil was discussed from the micro perspective,which provides a valuable research basis for the application of vibration drainage consolidation method in practice.The main research results are as follows:(1)It was found that the time effect has a significant effect on the displacement and vertical strain of soft soil.The results showed that the vibration load considering the time interval could significantly improve the drainage consolidation effect of the sample;it could increase the proportion of the displacement of the vertical strain after stabilization;the influence decreased with the increase of the confining pressure;and there was the best time interval for the best drainage effect.(2)According to the porous media theory and the stress state changes of two-phase matrix in the process of vibration oil recovery,the unit stress state of saturated soft soil under vibration load was established from the microscopic point of view,and the vibration drainage conditions of soft soil were determined according to the microscopic stress state.Finally,the load size and load type,amplitude and time interval were analyzed and verified combined with the indoor test results The mechanism of vibration drainage was discussed.(3)Based on the classic Monismith model,considering the factors of confining pressure,frequency and time interval of the vibration loading process factors,the model was modified to predict the cumulative plastic strain on the confining pressure and the time interval;the effect of frequency and time interval under cyclic loading Soft soil,and verified the accuracy of the model.