Research On The Distribution Characteristic Of The Negative Skin Friction Of Pile Groups In Weak Foundation Under Surcharge Load

With the rapid development of high-speed railways and expressways and high-rise buildings,the use of pile foundation is becoming more and more extensive,and the research of pile foundation is more and more.In the actual project,the application of the group pile is reached an unprecedented height.However,so far,the study of the working mechanism and pile group effect of pile foundation under pile loading condition in special soil is not a lot.Therefore,this paper refers to a practical project,through the model test of silty clay in the group pile foundation for bearing capacity,axial force,lateral friction and neutral point of the study.The settlement of the pile foundation,the settlement of the pile soil,the axial force of each pile in the pile group,the lateral friction resistance of the pile foundation and the change of the neutral point position are compared and analyzed by different loading forms.Finally,the numerical simulation of pile group foundation under the condition of loading is carried out by using Midas / GTS NX software in combination with the pile foundation of a bridge engineering,and the variation of the above points is studied.The main contents of this paper are:(1)To review the literature,to understand the negative resistance of the pile of the status quo,from the theoretical aspects of the field test study,the study of indoor model and numerical simulation of the study given in recent years,some domestic and foreign scholars research results.Based on the research of domestic and foreign researchers,the research on the group pile under the side load is relatively small,the relevant scheme of the indoor model test is worked out,and the main contents of this paper are put forward.(2)Indoor model test pile foundation for the diameter of 0.03 m acrylic bar,each length 1m,a total of 9,3 × 3 form of symmetrical layout,pile spacing of 3D,acrylic rod surface using epoxy adhesive coated with a layer of particle size of 0.2mm-0.5mm clean sand,and brushing the slurry;model box size 1.2m × 1.2m × 1.3m(length × width × height);filling the surrounding loess of Lanzhou,through the relevant geotechnical tests determine the basic parameters of the filling.The variation law of soil settlement,pile axial force,lateral friction resistance of pile foundation and neutral point position are analyzed and compared by two kinds of working conditions,and the bearing capacity of each pile under different working conditions is also explained Play the changing characteristics of the coefficient for the future construction of the relevant data to provide reference.(3)Under the surrounding conditions,the axial force and lateral friction of each pile are gradually increased with the increase of the enclosure level,and the position of the neutral point moves continuously with the increase of the enclosure,the axial force and side friction resistance of the corner pile are the largest,the side pile is the second,and the center pile is the smallest,and the position of the neutral point of the corner pile is the lowest,the side pile is centered and the center pile is closest to the filling surface.Under this working condition,the carrying capacity of the pile shall be kept below 0.7,and it is recommended that no more than 60 kPa is applied.(4)Under the side load condition,only the corner pile and side load near the load side of the side load and the center pile and the middle pile are negative friction and center point.The variation of axial force,lateral friction and neutral point of pile foundation and soil subsidence are similar to those of enclosure.Through the analysis of the test data,the position of the neutral point of each pile is gradually subsided with the increase of the load,and it tends to be horizontal,Under this working condition,the carrying capacity of the pile shall be kept below 0.7,and it is recommended that no more than 80 kPa is applied.(5)Based on Midas/GTS NX finite element software,relying on the existing railway bridge pile foundation in the use of the process by the surface of the load and the role of the side,the establishment of the relevant model to calculate the pile of the force characteristics.Numerical parameters such as soil layers are selected according to the actual parameters of the field.Based on the calculation results,the variation law of axial force,lateral friction resistance and neutral point position of each pile is mainly analyzed,and the variation characteristics of the bearing capacity of each pile are also analyzed.