Seepage-deformation Analysis And Water Disaster Treatment Method Of Unsaturated Soil Foundation

Recently,a large number of industrial plants have been built in various places as China’s urbanization is accelerating.In the process of plant construction,excavation and backfilling are usually adopted to carry out site leveling treatment,forming a large number of non-uniform filling foundation.Due to the demand of industrial site selection for transportation,land flatness,floor area and water source,many foundations are located in low-lying areas.These foundations are easy to collect water,and are prone to water damage such as high water level of foundation and uneven ground settlement.The foundation water damage are closely related to the engineering and hydrogeological conditions,the prevention consideration in the design and construction process,the construction and operation of the drainage system in the factory,etc.Therefore,it is of theoretical significance and practical value to analyze the disaster causing factors of foundation water damage and design a reasonable drainage system for the prevention and treatment of water damage in such foundations.Therefore,a variety of analysis methods such as site investigation and survey,theoretical analysis,numerical simulation and so on was used on the water damage of a typical low-lying foundation project with high excavation and low filling in adjacent waters.The field investigation and cause analysis of water damage are carried out,The numerical analysis of seepage and deformation of unsaturated high filling foundation under the condition of rainfall is done.Lastly,a interception-dredginge-drainage composite drainage system is proposed,and the parameters of the drainage system are optimized.There are some main research achievements summarized as follows:Firstly,in view of the basic fact that a certain foundation project with high excavation and low filling is located near the bottom of a gentle slope and adjacent to a river ditch,and the foundation water damage happens frequently,the site investigation is conducted,and the engineering geology and hydrogeology data are consulted.The main causes of foundation water damage are systematically analyzed based on the consideration of multiple factors such as the original and current hydrologic and engineering geological conditions,topography and geomorphology,types and distribution of water damage.The foundation water damage mainly includes four types: shallow stagnant water,uneven ground settlement,frost-thaw subsidence deformation and buried pipeline fracture.The frequent occurrence of the foundation water damage is caused by the poor permeability of the filling soil,the poor drainage path of groundwater and the shallow groundwater.It is obviously pointed out that improving the groundwater flow field and lowering the groundwater level of foundation are the key to water pollution control.Then,based on the fluid-solid coupling theory of soil,a finite element model for seepage and deformation analysis of unsaturated foundation soil considering rainfall process is established.The influence law of slope excavation,rainfall intensity,retaining wall layout and soil permeability coefficient on the water distribution and surface displacement of the land filling base is analyzed in the model.It was found that before the slope excavation,the groundwater flow was good,and the ground water level at the site of the factory was deep,revealing that the ground water level significantly increased after the slope excavation.The retaining wall arranged on the drainage side of the canal in the factory area intensifies this effect.In addition,rainfall significantly raised the groundwater level,resulting in uneven surface deformation and water damage.Finally,a interception-dredging-drainage composite drainage system combined with the drainage ditch arranged in the way of balanced water collection and interception-drainage ditch set in the direction of groundwater inflow is designed.The design parameters of the drainage system,such as the number of drainage ditchs,the permeability of fillings and the way of collecting water,are optimized by repeated calculation of the finite element for the seepage and deformation of foundation.The results show that the groundwater level of the foundation and the vertical settlement of the ground can be effectively reduced by the the composite drainage system.And the effect should be better if the drainage ditch are arranged by the balanced water collecting way and the permeability of the fillings are high.The uniformity of ground water level can be effectively improved by increasing the number of drainage ditches.And the effect of the drainage system should be further improved by setting up interception-drainage system in the direction of water flow to the plant at the west and south sides.The research results provide necessary theoretical support and technical guidance for the design and construction of drainage system in the same kind of high excavation and low filling foundation,and also provide necessary technical reference for the treatment and prevention of water damage in similar filling projects.