Research On Skin Friction Of I-shaped Section Pile

With the rapid development of modern urbanization,pile foundation has become one of the most widely applied foundation types,and the role of pile foundation is to bear the loads from the superstructure and transfer the loads to the soil layer around piles and under piles.In engineering practice,piles are in the composite stress state in the vast majority of cases,namely composite piles,which need to bear vertical loads from the superstructure,besides,often need to withstand horizontal loads,such as the instantaneous horizontal force generated by earthquake action,the horizontal force and the bending moment to the pile foundations generated by transportation braking force in bridge engineering,the long-term erosion force generated by wave and so on,loads like those can not be ignored in bridge engineering,high-rise buildings,heavy industrial buildings,offshore oil platform and so on during the design of pile foundation.In order to meet the requirements of bearing capacity of composite piles,in recent years,the pile foundation engineering field has quietly emerged the special-shaped piles.Compared to the conventional piles,the special-shaped piles have larger specific surface area,which is very favorable to improve the vertical bearing capacity,besides,it also can save raw materials and reduce project cost,adapting to the needs of the development of pile foundations.The special-shaped piles are divided into longitudinal section and cross section of special-shaped piles,I-shaped section pile is a new cross section special-shaped pile,owing to mature construction technologies and significant economic benefits,which has a very broad application prospect,but researches on I-shaped section pile are lack at present,based on this,this paper utilizes indoor scale model test and ABAQUS finite element analysis to probe into I-shaped section pile's skin friction distribution law under different conditions,the main research conclusions are as follows:(1)Firstly,this paper utilizes the vertical static load test of I-shaped section single pile indoor scale model to collect a series of pile body strain data,after this,according to the relevant formula to obtain the axial force of the test sections of the pile and basing on this can draw the whole pile's axial force curve,and besides,this paper will research the pile skin friction distribution law deeply based on the pile axial force distribution curve and the relevant formula,finally this paper will confirm the I-shaped model pile's effective length.(2)This paper will also simulate and analyze the aforementioned test by using the large universal finite element analysis software ABAQUS on the basis of laboratory scale model test,this paper will also research the pile skin friction distribution curve deeply based on the pile axial force distribution curve.According to the comparative analysis,it is found that the calculation results of pile skin friction have the same change rules as the test results,and the numerical values are also similar.It is reasonable and suitable to use the finite element analysis method and the mechanical parameters of the selected model.(3)On the basis of the above researches,this paper will also analyze the vertical bearing capacity of I-shaped section single pile under the action of overloaded soil,with different loading sequences,here are some conclusions:1)Applying the over-load before the vertical load on the pile cap,in this paper,the vertical compressive ultimate bearing capacity of the I-shaped section model pile under the over-load 20 k Pa is about 2.0k N,compared with the non-overloaded condition,the value reduces about 33.3%.2)Applying the over-load before the vertical load on the pile cap,the curve of pile axial force is quite different from the non-overloaded condition in the first loading stage while the trends of two axial force curves are roughly same in the other loading stages;so is the pile skin friction curve.3)Applying the vertical load on the pile cap before the over-load,which is also divided into two conditions:1.The overloaded range is same while value is different,there are the following conclusions:under the same overloaded range,for same depth Z,the pile axial force increases with the increasing of overloaded value applied to soil model surface,and with the increasing of overloaded value the pile axial force curves are "convex" gradually,which just showing a single peak;For the pile skin friction,the maximum value of positive friction and negative friction increase with the increasing of overloaded value.In addition,the intersections(i.e.the position of neutral point)of the pile skin friction curve with the vertical axis,namely Z1/L value,are about 0.27,0.35,0.42,0.45,in which the neutral point gradually moves down,and the reduced rate decreases gradually.2.The overloaded value is same while range is different,there are the following conclusions:under the same overloaded value,with the increasing of overloaded range around the single pile,the distribution range of negative friction extends more widely along the pile.The intersections of the pile skinfriction curve with the vertical axis,namely Z1/L value,are about 0.28,0.28,0.32,0.44,the neutral point gradually moves down,and the reduced rate increases gradually.