Study On The Deformation And Stability Of Deep Foundation In Tunnel Open Excavation Section Of Export During Construction

Geotechnical workers have done a lot of research about Internal force and deformation law of foundation pit engineering in the excavation process.Long and narrow type of foundation pit during excavation of foundation pit stress and deformation mechanism are also measured and analyzed,but the achievements are very few.Along with our country large-scale urban rail construction,this type of foundation pit will encounter a lot.To this kind of foundation pit in the process of excavation,stress and deformation mechanism are studied for the design and construction experience of similar projects in the future.On the basis of reading a large number of related literature and summarizes the relevant research results at home and abroad,this paper is based on the field monitoring for passenger dedicated line between Harbin and Mudanjiang deep foundation pit in the excavation process.Combining theoretical analysis and the three-dimensional numerical simulation analysis,the achievements could guide the on-site construction 、 feedback design and explore the mechanism of deformation of foundation pit engineering in this area.Doing some composite optimization for retaining structure parameters through three-dimensional numerical simulation analysis method.The achievements could guide foundation pit engineering design and construction of this area.In this paper,the main content and the related conclusion are as follows:(1)Through the field monitoring,the amount of each monitoring project failed to meet the alarm value during the whole process of foundation pit construction and retaining structure to work normally.The maximum horizontal displacement of pile located in the pile top down about 8.0 m was 13.72 mm,the location moved down constantly with the increase of the maximum from 7.0m when the excavation had just finished.The maximum bending moment took place on the pile between the supporting pile.The maximum was 464.0 kN.m which was far less than flexural bearing capacity of normal section pile body1410 kN.M.Because the pile top and pile bottom were measured a certain amount of horizontal displacement occurred from field,so it produced certain release effect for the internal force of retaining pile.The cross arm and crown beam displacement and stress obtained from field measured were in a smaller state all the while.(2)Comparing the horizontal displacement of pile which include the results by the specification method、 three-dimensional numerical simulation method and field monitoring,the maximum value is 16.78 mm located down the pile top about 7.5m.Field measurement of maximum located down the pile top 8.0m.pile body is 464 kN.m.Both differ with alarm value very large.The retaining structure design meets the requirements of the excavation fully.The maximum pile bending moment by three-dimensional numerical simulation method is 883.1 kN.M.The specification method got a result which is 966.5kN.m.The measured maximum was only 464.0 kN.M.Internal force and deformation of beam changed a little under the three methods.(3)By empirical formula and 3-d finite element analysis,this paper estimated the surface subsidence and uplifts to evaluate the stability of foundation pit Comprehensively.Empirical formula suggested the maximum ground surface settlement was 10.7 mm,which located behind the pile top 6.9m.Three-dimensional finite element suggested the maximum ground settlement is 11.2 mm and it was behind the pile top about 6.5m.Empirical formula thought the uplifts of the maximum was 10.2 mm and the three-dimensional numerical simulation method thought it was 12.1mm.(4)In the process of the deep foundation pit design,the influence of changing the anchorage length to the stress and deformation of retaining structure is least.Changing the diameter of retaining pile had a lot of influence to retaining piles and lateral brace.When the pile diameter decreases from 1.0 m to 0.7 m,the maximum horizontal displacement is 28.0 mm which is very close to 30 mm.Pile bending moment has reached 85.4% of the normal section bending bearing capacity of pile and crossbar bending moment increased 139% compared with the original model which had already surpassed the cross arm,flexural bearing capacity of normal section 815 k N.m.Crown beam bending moment is more sensitive to pile spacing of change.During the whole process of foundation pit construction,crown beam bending moment was in a smaller state constantly.Finally put forward a kind of retaining structure design apply to the scene,and the solution was economic and reasonable.