Reascher Of Bearing Capacity Of Large Diameter Root Bored Pile Foundation

The root foundation is a new type of foundation with many advantages such as good bearing capacity,small settlement deformation and low construction cost.As one type of root foundation,the root bored pile foundation has many advantages such as mature construction technology and short construction period,and is particularly suitable as a group pile foundation for large bridges.At the Chizhou Qiupu River Bridge,266 root foundations were designed,which is the first large-scale application of the root bored pile foundation.The outer diameter of the root pile foundation of the main pier reaches 2.5m.For large diameter root foundations,under the vertical load,the bearing capacity of the root foundation will directly affect the safety of the superstructure.Therefore,it is necessary to study the bearing capacity of the root foundation under the vertical downward loads and the vertical upward loads.This thesis relies on the Qiupu River Bridge of Chizhou Yangtze River Bridge Project.Based on the numerical analysis method,the parameters were assigned according to the geological survey data and the numerical model was verified by the field test pile data.On this basis,the bearing capacity of the root foundation and the traditional pile foundation were compared and the differences of the bearing mechanism between these two under vertical load(downward pressure and upward pull)were discussed.In addition,as key factor to the root foundation,root key's influence factors such as position and spacing were analyzed,and the bearing capacity of the root foundation under different forms were discussed.Specific research contents and conclusions include:1.Based on the root foundation of the main bridge pier of the Qiupu River Bridge project in Chizhou,the geometric model was built using ANSYS finite element software and imported into FLAC3 D finite difference software.According to the geological survey data,the soil parameters were determined,and the numerical model and soil parameters were verified according to the field test pile data,so that the rationality and reliability of the numerical analysis were guaranteed.2.Based on the verification of the numerical model,the vertical compression and vertical upward bearing capacity of the root foundation and the traditional pile foundation were compared.The similarities and differences of displacement,stress,axial force and basic side frictional resistance of the two under the same load were analyzed,and the principles were summarized.The results showed that compared with the traditional pile foundation,the root key can effectively utilize the surrounding soil and improve the side friction of the foundation,thereby improving the bearing capacity of the root foundation.The bearing capacity of the root foundation under the vertical downward load was increased by 11.38%,the bearing capacity of the key area has increased by 82.88%.On the other hand,the bearing capacity of the root foundation under vertical upward load was increased by 8.3%,the bearing capacity of the key area has increased by 102.9%.3.After comparing the vertical bearing capacity of the root foundation and the traditional pile foundation,the influence effects of the root key position and the root key spacing in the root foundation were analyzed.The numerical analysis results showed that under the same parameters,the position and spacing of the root keys had a certain influence on the vertical bearing capacity of the root foundation.The root key located in the middle part was most beneficial to the bearing capacity of the root foundation.When the root key layer spacing is small,the vertical bearing capacity of the root foundation will increase with the increase of the spacing,but the increasing rate will gradually decrease,and when When the root key spacing increases to a certain extent,the vertical bearing capacity of the root foundation will not increase any more.