Research On The Characteristic Of The Negative Skin Friction And Design Method Of Single Pile In Deep Filling Soil Foundation Under Surcharge Load

In the hilly area of south China,the terrain is more complicated,so the deep filling soil foundation is widely used in engineering practice.With the use of the piles in deep filling soil foundation,the problem of negative skin friction of pile arise.Compared with the general foundation,the large filling compaction degree is the main characteristic of the deep filling soil foundation,and the pile foundation area can not avoid the surcharge load by the large equipment and filling soil.Therefore,the study on this area is to be further studied and discussed.This article on the basis of previous studies,Starting from the indoor model test and numerical simulation of piles of the deep filling soil foundation,it makes an exploratory study on the time effect of negative skin friction,the characteristic of negative skin friction,the calculation of the negative skin friction resistance and the design of bored pile.The main research and results are as follows:(1)According to the stress characteristics of the pile,the plexiglass pipe pile model and the indoor model test device are designed and made.(2)The indoor model tests of different load were carried out.The time effect of the negative skin friction of piles is discussed by considering the compaction degree of the Background engineering.The results show that the soil settlement,the lateral negative skin friction and the position of the neutral point have obvious time effect.The settlement of the soil around the pile and the development of the axial force of the pile completely takes a long time and all exceeds the 180 h.When the load is 2.5kPa,the neutral point is at the bottom of the pile and does not drift with time.When the load are 5.0kPa and 7.5kPa,the neutral points move at 144 h and 96 h respectively.Under the loading conditions of three different sizes,the final neutral positions are at the pile depths-75 cm,-70 cm and-65 cm respectively.(3)In order to verify the results of laboratory model test,the numerical simulation of the indoor model test was carried out by using FLAC 3D.The results show that there are some differences in the numerical value of the calculated results,but the axial force distribution of the pile is consistent.Considering the limitation of the indoor model test condition,the original numerical model is improved.The influence of the load of pile top,the order of surcharge load and the load of pile top,and the boundary conditions on the characteristics of the pile's negative skin friction are studied,and some regular conclusions are obtained.(4)The calculation method of the negative skin friction resistance of single pile in multiple layer foundation is used to calculate the indoor model test,the results are in good agreement with each other.According to the quality of pile,the construction scheme of bored pile is improved from two aspects of pore forming method and slurry wall protection,and the scheme effect is tested.