Field Test And Numerical Simulation Study Of Double-row Pile-anchor Support Structure In Deep Foundation Pit

The double-row pile support structure is a space gantry structure system composed of two rows of reinforced concrete piles,a connecting beam between the two piles,and a crown beam at the top of the pile.This kind of structure has high stiffness against lateral displacement and can effectively limit the lateral displacement of the support structure.Compared with single-row cantilever piles,the double-row pile support structure has greater stiffness against lateral movement,which can more effectively limit the deformation of the support structure;Compared with the inner supporting structure,it has the advantages of convenient subsequent earthwork excavation construction and saving construction period.The double-row pile-anchor support structure combines the advantages of double-row piles and pile-anchor support,and has been popularized and applied in recent years.Some achievements have been made in experiments,numerical simulation,etc.,but there is a lack of relatively complete field tests,so the research on this support method still needs to be further deepened.The main research contents are as follows:1.Based on an example of a deep foundation pit project,a systematic on-site test was carried out around the mechanical characteristics of the double-row pile-anchor support system,and the internal force of the pile body and the piles of the double-row pile under different excavation conditions were studied.The changing laws of top displacement,earth pressure,and deep soil displacement.2.With the help of ABAQUS finite element software,a three-dimensional finite element model is constructed,and the numerical simulation results and the field measured data are simulated and compared and analyzed.3.Change different parameters through finite element numerical simulation,such as pile diameter,pile row spacing,pile length,etc.,and analyze the deformation and stress characteristics of the double row pile supporting structure under different working conditions.Through the above research,the following conclusions are drawn:1.For the deep foundation pit project under the alluvial stratum of the Yellow River,the double-row pile-anchor support structure can play a better supporting effect.2.When the distance between the front and rear rows of piles is 4D(D is the pile diameter),the bending moment of the front row of piles is "S" shaped,and the bending moment of the rear row of piles is parabolic.The coupling beam is a compression-bending member and plays an important role in the entire supporting system,ensuring the coordinated deformation between the front and rear rows of piles,and controlling the development of the pile top displacement.In the actual project,the front and rear rows of piles and the The joint treatment of coupling beam and crown beam can better exert the supporting performance of double row piles.3.During the excavation of the foundation pit,the earth pressure on the supporting structure is decreasing as a whole.Under the combined influence of the excavation depth and time effect,the change of the earth pressure has a certain hysteresis;The bending moment of the beam is greatly affected by time.After the foundation pit is excavated to a given depth,the bending moment of the support system gradually increases with the change of time,indicating that the force change of the double-row piles and the coupling beam is relatively Excavation of foundation pit has obvious lag effect.4.Through the numerical simulation analysis of different parameters,it is concluded that changing the elastic modulus of the pile body has little effect on the bending moment and displacement of the double-row pile;Especially the restriction on the displacement of the pile top,and the characteristic of "bulging belly" is becoming more and more obvious;by increasing the pile diameter,the bending moment of the pile body of the front and rear row piles is obviously increased,and the displacement of the pile body can be effectively controlled;The length of the pile can reduce the displacement of the pile body,especially when the insertion ratio is greater than 1,the change is particularly obvious;by increasing the prestress of the anchor,the displacement of the supporting structure can be effectively controlled.