Vertical Bearing Characteristics Of Super-long And Large-diameter Piles In Complex Interactive Strata

Super long diameter pile foundations are widely used in practical engineering.At present,there is no universally applicable calculation method for super long diameter piles.of waste.In this paper,based on the static load test of the Yellow River Bridge on the Puyang section of Yangxin Expressway and the existing related literature,combined with the numerical simulation software ABAQUS,the bearing characteristics of the super long diameter piles are studied.The bearing characteristics of super long diameter piles in complex interactive silty-fine sandy soil layers and complex interactive karst strata are mainly studied.The main research contents of this paper are as follows:(1)Summarize and analyze the common working conditions in the current super-long pile construction process,analyze the factors affecting the bearing characteristics of the pile foundation,and classify them into the pile side rock-soil medium interaction change,the pile end rock-soil medium interaction change,and the pile end.There are three types of interactive changes in body diameter.The bearing characteristics of super-long piles and the bearing characteristics of pile foundations in karst strata at home and abroad are analyzed,and the main problems existing in the current research on super-long diameter piles are summarized.(2)Combined with the construction process of on-site test piles of the Yellow River Extra Large Bridge in the Puyang Section of Yangxin Expressway,corresponding process improvements were made to address the problems existing in the construction,such as the stability of the construction platform,the stability of the well plate,concrete pouring and mud circulation;The large-tonnage tensile-compression anchor static load test system for root anchor piles,pile top columns,anchors and bearing bodies loads the field test piles,and measures the pile top settlement and pile body axial force by installing electronic displacement sensors and steel bar gauges.The development law of the pile top settlement,the axial force of the pile body and the side friction resistance of the super long diameter pile in the complex interactive silty-fine sandy soil layer is analyzed.(3)Based on the on-site static load test,the Mohr-Coulomb soil constitutive model was selected,the corresponding boundary conditions were set,and the in-situ stress balance was carried out by the life-death element method,and the three-dimensional finite element numerical model of the 73-1# test pile was established.On the basis of the field static load test,the pile top load is further applied,and the ultimate bearing capacity of the test pile is obtained when the pile top settles at 5%.The bearing characteristics of super long and large diameter piles under the ultimate load of the pile top in the complex interactive silty fine sand soil layer are analyzed.(4)Combined with the current research literature on overlength piles in karst strata,the finite element model of complex interactive karst strata is established.The corresponding working conditions of three influencing factors,namely,the number of pile body interactive Beaded karst caves,the change of pile body diameter and whether the pile body karst caves are backfilled,are studied,and the bearing characteristics of super-long large-diameter piles in complex interactive karst strata are analyzed.(5)Summarize the current calculation theory of pile foundation bearing capacity,compare the bearing capacity calculation method of super-long pile in the current code,calculate the bearing capacity of 73-1# test pile in complex interactive silty sand layer,and calculate the calculation method of all current codes.The values are smaller than those obtained by field and numerical simulations.The calculation method of the ultimate bearing capacity of large-diameter single piles in the " Technical code for building pile foundations " is revised,and the hardening phenomenon of the lateral friction resistance of the silty-fine sandy soil layer under the ultimate load is considered,and the silty-fine sandy soil layer is proposed.Side friction resistance hardening coefficient.Figure 46 Table 10 Reference 92...