| The construction of foundation ditch on sandy soil coastal engineering is often affected by seepage,a project in Saudi Arabia is building by CCCC Fourth Harbor Engineering Co.,Ltd..This project had encountered the problem that drainage pipe installation was restricted by the construction schedule of upper structure on the foundation ditch,but the construction schedule was seriously lagging behind,the coastline needed to be further dredged inland.It is not only to ensure the slope stability of foundation ditch during the construction and catch up the progress but also save construction costs.In this paper,based on this background,research on the influence of seepage on foundation ditch construction and put forward an appropriate change scheme for this offshore foundation ditch engineering in Saudi Arabia.Through the laboratory test and in-situ investigation,a comprehensive analysis about the geological conditions has been done to get the basic properties of foundation soil in this project area.We elaborately laid out pumping and observation wells for the pumping test,obtained the true permeability coefficient of the foundation soil in the most unfavorable circumstances,which provided reliable parameters for subsequent numerical simulation analysis.Referred to a large number of related literatures at home and abroad,this paper discussed synthetically about the basic principle of seepage calculation,finite element analysis of slope and the mechanism of seepage influence on the slope stability.The two-dimensional models were established by using ABAQUS software and calculated the slope stability with or without the influence of seepage by using strength reduction method,verified the rationality and reliability of the model.Carried out the simulation analysis on the influence of seawater tide and different dredging coastline location on the excavated ditch slope stability,the high water level had a heavy interference on the stability of foundation ditch,and the subsequent models were carried out by this water level.Calculated the stability of the foundation ditch slope under the action of the seepage field according to the distance as 180,150,130,110,100,90m between shoreline and foundation ditch wall,and the distance should be reserved for 100m to ensure the stability of-the foundation ditch.In order to explore the dredging range which can be further increased,established models with steel sheet piles or dewatering wells added to analyze the slope stability.The result is that the distance between the shoreline and the foundation ditch can be reduced to 60m and 70m respectively under the two change schemes.At last,according to the actual site conditions,the engineering cost and construction schedule of the change schemes were comprehensive analyzed.And the change scheme of adding dewatering wells had good technical and economic advantages.The effect of the spacing of dewatering well on the this foundation ditch dewatering after the drainage wells increased was analyzed by using ABAQUS software again.At the same time,established the 3D model for the further analysis,the appropriate spacing is 15m.According to this,this paper summarized and proposed the change scheme,the construction technology and the precautions of dewatering walls to guide the follow-up site construction. |
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