Research On The Bearing Characteristics Of Single Pile Influenced By Pile-side Cave In The Beaded Karst Area

The geological conditions in the beaded karst area are complex,and the size and distribution of caves are irregular,which makes the existence of caves on the pile side a common phenomenon in the beaded karst area.However,the current research on karst pile foundations is more in terms of the bearing ability of single pile when there are caves at the bottom of pile,but the research on caves on pile side is not only less and concentrated on single cave,but also lack of research on multiple caves on pile side.And the current relevant pile design code does not propose the calculation method of pile bearing capacity when there is cave on the pile side.In order to improve the theory of karst pile foundation design and ensure engineering safety,this paper relies on the Qujiang Avenue Jiangwan Bridge project and studies the influence of pile-side caves on the bearing characteristics of single pile.The staple tasks of this paper are shown below:(1)The pile load transfer process,load transfer function and determination of vertical bearing capacity of rock-inlaid piles are introduced.Some modifications are made to the load transfer model considering interface debonding.Based on the modified model,the load transfer function is theoretically analyzed and solved for the existence of caves on the pile side.To provide some theoretical basis for the analysis of the pile foundation bearing characteristics in the later paper.(2)MIDAS GTS finite element software is used to model and analyze the pile-side caves at different horizontal spacing between piles and caves,different vertical spacing between pile tops and caves,different cave heights,different cave widths and multiple caves to obtain the influence of each cave parameter on the bearing characteristics of the monopile.It is found that as the horizontal distance between pile and hole(or vertical distance between pile top and hole)increases,the ultimate bearing capacity of monopile increases;as the height(or width)of cave increases,the ultimate bearing capacity of monopile decreases;multiple caves on the pile side will increase the influence of the above parameters many times,and may lead to tensile damage before the ultimate bearing capacity of pile foundation is reached.(3)Based on the numerical simulation results,the correlation degree of pile-side cave parameters is calculated by using gray correlation analysis.According to the calculation results,the sensitivity strength of each parameter change to the monopile bearing capacity and the maximum horizontal displacement of the pile is analyzed.It is found that when the ultimate bearing capacity of the single pile and the maximum horizontal displacement of the pile are used as the reference sequence,the sensitivity rules of the parameters affecting the bearing capacity and horizontal displacement of the single pile are the same,which are: number of caves > height of caves > width of caves > vertical distance between the top of the pile and the cave > horizontal distance between the pile and the cave.(4)The BP neural network structure was constructed by MATLAB,and the calculation results in Chapter 3 were used as data samples to predict the monopile bearing capacity of double and triple caves on the pile side.The conclusions of the finite element analysis are verified,and it is proved that the BP neural network can cope with the complexity and irregularity of the distribution of pile-side caves in the beaded karst area.