Study On Static And Dynamic Characteristics Of Soil Arching Effect Of Cantilever Piles

Cantilever pileis used in the slope and foundation pit engineering as a kind ofcommon supporting method, however,the research of supporting principle is relativelyslowdespite the wide application of cantilever pile, especially based on the load transferprinciple of the arch and arch in the dynamic response, few studies of this kind ofproblem. Thisresearch work is being supported by grants from the the hundreds ofengineering technique talents project "cantilever anti-slide pile of three-dimensional soilarching effect and the dynamic disaster", based on the cantilever pile and pile after archeffect between theoretical analysis and finite element simulation analysis, the mainwork and research conclusions are as follows:1) The cantilever anti-slide pile is decomposed into horizontal and vertical archarch two cases, horizontal arch is due to the thrust in the plane of the horizon and thearch foot is formed on the back of piles, it mainly exist in the soil of the back piles;Vertical arch is due to the vertical surface of gravity and friction resistance on thesurface as the arch foot, which formed in the soil between piles, because of thecantilever anti-slide pile is mainly horizontal thrust, so the horizontal arch in soil is themain arch, The vertical arch effect the earth pressure on baffle of the distributionbetween piles formed in the soil between piles in the vertical plane of the existence.2) Research on the horizontal arch in the soil between piles. on the level of the archis reasonable for the parabolic arch axis and on the basis of combining the strengthcriterion of soil, the ultimate load ofthe horizontal archand the change of arch rise alongthe depth of pile is solved, the result of analysis as folllow: the arch rise isincreasedwiththe increase of internal friction Angle of soil, the arch effect increased along the depthdirection.Through the finite element simulation of different working conditions, themigration regularity of horizontal arch with the external load and the pile of soilcompaction area, the results show that with the increase of the loading, the horizontalarch to move away from the direction of the pile, soil compaction thickness changessmaller; Consideration of plate of a two-dimensional analysis between the pile andworking condition can be divided into: after pile set before the board and board, throughstudying the change of outside load that: after adding baffle the ultimate load of pile soilincreased by2.5times, soil stress distribution is more complex.3) Through the mechanical model of vertical soil arch between piles, it is concluded that the reasonable arch axis vertical arch for catenary, combined with thefeature of soil mass stress state change with depth, and platts arch theory, calculated thevertical arch arch feet buried depth and influencing factors. Through the finite elementsimulation of the stress variation in the pile soil contact surface, verify the vertical archarch foot position, through the analysis of external load increasing known: when theload increases to a certain extent, along the direction of pile length will be formed in thedifferent buried deep in the multiple vertical arch.4) In the analysis of the cantilever pile three-dimensional soil arching effect, thepile for the silty clay soil, pile for2m wide, clear distance between piles is2.5m, thecantilever length of8m, under the model of pile soil after the first principal stressarching effect significantly, along the depth direction of the arch effect increases afterthe first decreases, and the upper soil pile after the biggest vaults point distance frompile to pile wide3/4,3/5of the clear distance between pile; From the surface of theburied depth of3m in the first principal stress peak disappear, visible form the effectivedepth of the soil arch is about3m, the2/5cantilever pile length. By changing the heightof the cantilever section analysis of pile been arch effect, the influence of soil archingwithin the space curved surface soil piles cantilever section is located in the upperposition, combined with different cantilever section height of model analysis,comparison vault with depth change with the increase of cantilever anti-slide pilecantilever section height, enhance the soil arch effect, influence area increased.5) Considering the finite element dynamic analysis on the computer and timerequirements for two-dimensional horizontal and vertical arch arch of the research ofdynamic analysis, and compared with the corresponding arch effect analysis onstaticstate, the results show that under the effect of power, the horizontal arch exists or not isclosely related to the seismic wave input direction, when the earthquake force along theapproximation is perpendicular to the axis of the arch effect, horizontal arch area stressvalue increases, the soil arch effect, when the earthquake force along the approximateparallel role in arch axis, horizontal arch effect; The vertical arch under earthquakeforce to enhance performance.6) Through the establishment of three-dimensional model of cantilever pile andslope, the analysis of pile been the space effect of arch, and compared with indoor testand outdoor large-scale in-situ test verification, the results show that thethree-dimensional soil arch effect between pile along the direction of the pile lengthdecreases after first increases, resulting in soil between piles are mainly concentrated in the upper collapsed; Complex three dimensional cantilever pile dynamic analysis modelis set up, according to the building seismic design code, often encounter earthquakeacceleration time history analysis of the corresponding basic value of0.2g, EL Centrowave, seismic wave selected engineering location site type genus Ⅱ class site, seismicfortification intensity of8degrees, operating mode can be divided into: do not set platebetween pile and pile board two kinds of circumstances, after analysis of cantileversliding body arch effect between anti-slide piles under static and dynamic displacementresponse and stress response of the soil mass, the analytical results show that: the soilarch effect of cantilever piles under earthquake force to dissipate or strengthen related toseismic wave input direction, when the earthquake force along the perpendicular to thepile when the positive role, the soil arch effect enhancement, dynamic response beenarch in the donor compacting pile relative to other areas, minimum displacement, stress,and the formation of the soil arch area as the change of cantilever section increases withincreasing of the height characteristics.