Research On Vertical Load Transfer Mechanism And Determination Method Of Bearing Capacity Of Foundation Piles By The Self-anchored Test Pile Method Of Rock-socketed Piles

Rock-socketed pile is a type of pile foundation.Because of its stable bearing capacity,strong stratigraphic structure and small settlement,it is widely used in engineering.How to obtain the vertical bearing capacity of the rock-socketed pile accurately and evaluate whether it meets the design requirements has become an important engineering problem.The selfanchor static load test method of rock-socketed piles is a new type of vertical bearing capacity testing technology currently being studied,and its development has just begun.Due to its special reaction force device,the bearing mechanism and settlement characteristics of the foundation pile are different from the conventional static load test method during the test.In this paper,based on the existing research results,through the analysis of the load transfer mechanism of the rock-socketed pile and the load transfer and deformation mechanism of the anchorage section below the pile bottom,based on the actual rock-socketed pile test results and numerical simulation with the finite element software ABAQUS As a means,the following research work was carried out:1.Relying on the conventional static load test of rock-socketed piles,a theoretical analysis model was constructed,and a rock-socketed anchor solid at the bottom of the pressure-type pile was proposed at a certain depth to establish a finite element model of the rock-socketed pile self-anchor test method.Comparing and analyzing the self-anchor test method of rock-socketed pile and the conventional test method,the calculation results reveal:(1)The settlement value of the pile top obtained by the self-anchor test pile method is equal to or less than that obtained by the conventional pile test method;(2)Under the same level of load,the load ratio of the resistance at the pile end of the self-anchored test pile method has a certain increase compared with the conventional pile test method.And the effect of this increase will be significant with the increase of the load level.When it reaches the peak,it will gradually decrease with the increase of the load.Finally,it will tend to the resistance of the pile end of the conventional pile test method.Proportion of load undertaken;(3)In the process of providing reaction force at the bottom of the pile,the lateral resistance value of the pile end will increase in the rock-embedded section of the pile end compared with the conventional pile test method.The lateral resistance value is reduced compared with the conventional pile test method.2.Through the construction of the finite element model of the self-anchored test pile method of rock-socketed piles,based on the conventional static load test pile method,a comparative analysis is made from the three aspects of anchor parameter at the bottom of the pile,pile parameters and rock and soil parameters The influence of various factors on the settlement of the pile top and the load transfer in the self-anchored test method of rock-socketed piles is studied.The research shows that:(1)In the case of ensuring that the anchor at the bottom of the pile can provide sufficient reaction force for the self-anchor test pile test,the anchor with a smaller length and radius should be designed as much as possible.The influence of the anchorage at the bottom of the pile on the bearing characteristics of the foundation pile can be controlled by adjusting the relative anchorage depth;(2)In the self-anchored test method of rock-socketed piles,the impact of the anchor at the bottom of the pile on the resistance of the pile end is more direct,and it has a weaker effect on the bearing characteristics of the rocksocketed pile foundation pile that shows the friction pile or friction end bearing pile.3.By introducing the Mindlin solution under the concentrated force in the semi-infinite space and the stress distribution solution of the bolt anchorage section,the vertical displacement of the overburden rock layer under the anchor load is analyzed,and the corresponding calculation formula is obtained By superimposing the displacement field,the test pile method in the self-anchored system is obtained.When the pile-soil-anchor are in the elastic working state,the equivalent method of the self-anchored test pile test curve is converted into the conventional test pile test curve.