Investigation On The Lateral Response Of Single Pile Under Combined Load

In actual engineering,pile foundations are often not subjected to axial load,but to combined load.This phenomenon is particularly evident in bridges,towering buildings,docks,drilling platforms and so on.In addition to the axial load,the horizontal force and bending moment generated by the braking force of the vehicle,vertical force and bending moment generated by the eccentricity of the structure,and the horizontal force and the bending moment generated by the earthquake,wave and wind all act on the pile foundation at the same time.Under the combined action of horizontal force,axial force and bending moment,the pile foundation is complicated and the bearing characteristics are not clear.In the actual design,the combined effects are often ignored.The research direction mainly includes the calculation method of pile foundation,the study of interaction of combined loads and the envelope surface of bearing capacity of pile.The main methods used include theoretical derivation,numerical simulation,model test,and field test.The research on combined loaded piles usually simplifies the pile into a linear elastic model,and does not consider the influence of the nonlinearity of the pile material.Therefore,the conclusions about the bearing behavior of the pile under combined load are different.At the same time,the current research focus on piles which is not set in slope.With the development of infrastructure,more and more pile foundations are built on the slopes.The bearing mechanism of the slope pile is significantly different from that of the flat pile.The current design is still designed according to the flat pile.It is necessary to study the slope pile under combined load.Based on the previous work,starts with model test,and studies the bearing behavior of pile foundation under the combination of horizontal force and bending moment.It is verified and extended by 3D finite difference software FLAC3 D.The prototype pile was analyzed to study the influence of cracking and slope on pile under combined load.The main results of the thesis are:(1)It is proved by model test that with the increase of bending moment,the displacement increase of the pile top becomes larger,the ultimate bending moment increases,and the ultimate horizontal bearing capacity decreases.(2)For horizontally loaded reinforced concrete piles with large displacements,ignoring the influence of cracks will overestimate the ultimate bearing capacity of the pile foundation.Using FLAC3 D,the influence of pile foundation cracking can be simulated by a suitable constitutive model and modeling method.If there is a vertical load,the results will be different without considering the crack effect.If there is no vertical load,the ultimate bearing capacity is different without considering the crack effect.But the crack has little effect on the relative reduction value of ultimate bearing capacity.(3)It is proved by numerical simulation method that the slope,the bending moment and the soil properties significantly affect the ultimate horizontal bearing capacity of the pile foundation.The axial force has little effect on the ultimate horizontal bearing capacity of the pile foundation.The influence of slope and bending moment on the horizontal bearing capacity of pile foundation is similar under different soils,so the formula of bending moment influence and slope influence can be obtained by fitting.In actual design,any ultimate bearing capacity of slope pile under the action of the bending moment can be calculated by ultimate horizontal bearing capacity of flat pile foundation.