Pile foundation,as an important form of foundation,is widely used in various foundation constructions.With the advancement of foundation construction technology,pile foundations not only have to withstand vertical loads,but also horizontal loads in fields such as high-rise buildings and bridges.Pile foundation engineering belongs to hidden engineering,which is easy to produce necking defects in construction and use due to the limitation of construction technology and geological conditions,which seriously affects the safety performance of pile foundation.For a single pile with cap,its horizontal bearing capacity is the foundation of the safe use of pile foundation,which is mainly provided by the soil resistance around the pile,so it is important to study the influence of diameter reduction on the horizontal bearing performance of the pile monopile through the angle of pile-soil interaction.This study relies on the National Natural Science Foundation of China(51978247)to conduct horizontal loading tests on one intact pile and 7 piles with necking on pile caps using transparent soil technology combined with Mat PIV,and simulate the horizontal loading state of a single pile on a pile cap through Abaqus finite element software to study the influence of necking on the mechanical properties,horizontal bearing capacity and deformation law of the soil around the pile.The specific research work and main conclusions are:(1)Transparent soil indoor model tests were conducted on one intact pile and 7 piles with shrinkage on the pile caps,and horizontal incremental loading tests were performed.The slow maintenance load method was used and the horizontal displacement of the pile top was recorded under each level of load.The H-Y0 curve was plotted based on the collected data,and the influence of different shrinkage parameters on the horizontal bearing capacity of a single pile on a pile cap was analyzed.The research shows that when the geometric dimensions of necking are the same,the shallower the position of the necking,the greater the loss of horizontal bearing capacity of the pile.When the position of the necking is the same,the longer the axial dimension and the smaller the radial dimension of the necking,the greater the loss of horizontal bearing capacity of the pile.When the axial dimension of necking is greater than20%of the pile length and the radial dimension is less than 20%of the pile diameter,the bending failure of the pile body occurs and the loss of bearing capacity is the most severe.(2)Based on experimental data,a three-dimensional finite element numerical simulation of a pile foundation with cap was conducted using Abaqus software with the model dimensions taken into account.The simulation results were used to obtain the distribution curves of the bending moment of the pile shaft and the soil resistance on the pile side.The influence of necking on the mechanical properties of the pile shaft under horizontal loading was comprehensively analyzed,and the effect of necking on the mechanical performance of the pile shaft under the horizontal ultimate load of intact pile foundation was studied accordingly.The research shows that when the geometric dimensions of the necking are the same,the shallower the position of the necking,the higher the peak values of the bending moment of the pile shaft and the soil resistance on the pile side.When the position of the necking is the same,the longer the axial dimension and the smaller the radial dimension of the necking,the higher the peak values of the bending moment of the pile body and the soil resistance on the pile side.Necking mainly changes the mechanical characteristics of the upper part of the pile shaft,while the distribution of bending moment and soil resistance on the lower part of the pile shaft is basically consistent with that of the intact pile.(3)Based on model experiments,the displacement images of the soil-pile system were recorded under each level of load using an image acquisition system.The displacement vector map of the soil around the pile was obtained through Mat PIV program.Based on the deformation angle of the soil around the pile,the influence of shrinkage on the internal load transfer law of the foundation pile was analyzed.The research shows that when the geometric dimensions of necking are the same,the shallower the position of the necking,the greater the bending deformation of the pile shaft and the deformation of the soil around the pile at the necking,which weakens the horizontal load transfer capacity of the pile shaft.Under the same level of load,the displacement of the pile top of the pile is greater and the loss of horizontal bearing capacity is more severe.When the position of the necking is the same,the longer the axial dimension and the smaller the radial dimension of the necking,the greater the deformation and plastic yielding range of the soil around the pile.When the axial dimension of necking is greater than 20%of the pile length and the radial dimension is less than 20%of the pile diameter,the pile behaves like a flexible pile,and the horizontal load transfer capacity of the lower part of the pile body is completely lost,which greatly reduces the horizontal bearing capacity of the pile. |