Experimental Study On The Effect Coefficient Of Pile Group Horizontal Bearing Capacity

With the continuous increase of investment in infrastructure in China and the vigorous development of the construction field,pile foundations have been widely used because of their excellent characteristics in terms of effective control of building(structure)building settlement,wide application site and wide engineering scope,etc.application.In actual engineering,in addition to the vertical load brought by the superstructure,the pile foundation sometimes needs to withstand horizontal loads such as seismic loads,wind loads,wave loads,and earth pressure from the side.Compared with the vertical load-bearing characteristics,the horizontal load-bearing characteristics of the pile foundation are more complicated.At present,most of the experimental research on the horizontal bearing behavior of pile foundations focuses on the bearing characteristics and pile foundation stability calculation of single piles and small group piles.For the experimental research of large pile groups,there are few in-situ measured data available for reference;model tests and centrifuge tests are affected by cost constraints and size effects,and the application of test results is also relatively limited;some existing small pile group tests The research results are different due to the different research factors and experimental conditions,the data difference is large,and the conclusions are different,which has little reference effect on the analysis of the horizontal bearing behavior of large pile groups.Therefore,it is necessary to further carry out in-depth research on the targeted horizontal bearing characteristics of the group pile foundation.In this paper,the following research work is mainly carried out on the horizontal bearing performance of reinforced concrete group piles and single steel tube concrete piles:(1)Consult a large number of relevant Chinese and English literatures on the horizontal bearing characteristics of pile foundations,and summarize,organize and summarize them from theoretical analysis,experimental research and numerical calculations;(2)Carry out large-scale indoor model experiments of reinforced concrete single pile,reinforced concrete pile group and steel tube concrete single pile horizontal static load.Through the above work,this article has the following main conclusions:(1)Under the action of horizontal load,the bearing characteristics of the concretefilled steel tube single pile and the single reinforced concrete pile are similar,which can be divided into three stages: elastic deformation stage,elastoplastic deformation stage and failure stage.The boundary point of the three stages is the pile foundation The horizontal critical load and ultimate load.The critical load Hcr of reinforced concrete piles is the horizontal load corresponding to the cracking of the pile body,and the sudden change in the bending stiffness of the pile body is clearly reflected in the horizontal force-displacement gradient curve.However,the degraded point of the pile stiffness of the concrete-filled steel tube single pile before being loaded to the ultimate load is not obvious.The critical load is the load corresponding to the change of the working state of the soil around the pile and the change from elasticity to plasticity.(2)Compared with the reinforced concrete single pile,the horizontal bearing capacity of the concrete filled steel tube pile has been significantly improved.Under the same displacement conditions,the horizontal bearing capacity of the latter can reach 1.57-1.74 times of the former;under the same load conditions,the horizontal displacement of the concrete-filled steel tube pile is significantly smaller than that of the reinforced concrete pile.(3)Under the action of horizontal load,the maximum bending moment point depth of the reinforced concrete single pile is 2d-4d,and the range of bending moment of the pile body is 8d-10d;the maximum bending moment point depth of the pile body of the concrete-filled steel tube single pile is 4d-6d,The range of bending moment of the pile body is 10d-22 d.With the continuous increase of horizontal force,the depth of the maximum bending moment point of the reinforced concrete single pile and the single steel tube concrete pile and the range of the pile body subjected to the bending moment continue to move downward and increase.(4)The depth of the reverse bending point of the front row of piles in the reinforced concrete pile group is obviously shallower than that of the back row of piles.The maximum bending moment point depth of the piles of the front and rear rows of piles has a small difference,which is concentrated in 6d-10 d.The range of the bending moments of the piles of the front and rear rows is 14d-22 d,which is almost the entire pile length range.(5)Under the same horizontal load,the horizontal deformation rebound rate of the single-pipe concrete piles is 70%-80%,while the rebound rate of the reinforced concrete single piles is 40%-70%.When the displacement of the reinforced concrete single pile is close to 10 mm,as the load increases,the rebound rate decreases greatly;while the rebound rate of the concrete-filled steel tube pile changes little.(6)Under the same load and displacement,the m value of the single concrete-filled steel tube pile is significantly greater than the m value of the single reinforced concrete pile.(7)Under this test condition,the ratio of the horizontal ultimate load to the critical load of the reinforced concrete single pile is between 1.1 and 1.4;the ratio of the horizontal ultimate load to the critical load of the concrete filled steel tube pile is between 1.33 and 1.50;the horizontal limit of the single pile with cap The ratio of the load to the critical load is 1.3;the ratio of the horizontal limit load of the group pile to the critical load is greater than 1.3.(8)The limited pile top constraints allow the bending moment to be redistributed along the pile body.The maximum bending moment value of the pile body(top)is only 0.2-0.5 times of the free pile at the pile top.As the pile top displacement and load increase,the ratio gradually decreases.(9)The mutual effect of piles leads to different load distribution and deflection curves of the piles in the group.Overall,the front row piles bear the largest load,the rear row piles the smallest,and the middle piles second;the deflection of the front row piles changes with depth faster than the rear row piles,and the displacement zero is shallower.(10)Under the combined action of the pile top restraint effect and the pile’s mutual influence effect,the front row of corner piles in the pile group share the largest load,but the maximum value of the pile body(top)bending moment is about the same as the pile top free single pile under the same displacement condition About 0.4 times the maximum body bending moment.The loads shared by the remaining piles are relatively close,and the maximum value of the bending moment of the pile body(top)is about 0.2 times of the maximum value of the free single pile body under the same displacement conditions.(11)When the pile spacing is fixed,the increase in the number of piles will improve the horizontal bearing capacity of the pile foundation to a lesser degree,but it can make the load distribution of each pile in the group pile more uniform.(12)When the pile spacing is fixed,the increase in the number of piles improves the horizontal bearing capacity of the pile foundation to a lesser degree,but it can make the load distribution of each pile in the group pile more uniform.