Bearing characteristics of composite foundation with tapered pile in loess area
[Objective]The bearing capacity and stability of the whole structure can be improved by the composite foundation,which can exhibit the bearing capacity of the reinforced and natural soil.To tackle the problem of foundation bearing capacity in collapsible loess area and integrate the excellent bearing capacity of tapered pile into composite foundation,herein we conduct the experimental study.[Methods]Soil model tests with geometric similarity constant as the first basic quantity and heavy similarity constant as the second basic quantity are carried out to analyze the bearing capacity of foundation piles in different load areas,and bearing characteristics are further analyzed by the finite element method.A series of load parameters such as load settlement,pile axial force,side friction resistance,pile-soil stress ratio and load sharing ratio of tapered pile composite foundation under loess are studied by comparing these test results with these simulation results.[Results]The settlement of tapered pile-mesh composite foundation changes uniformly with the increase of load,no sudden change of settlement exists,and the load-settlement curve changes slowly.It is found that bearing characteristics of piles in the direct load area differ greatly from those in the non-direct load area through changes of axial force and side friction resistance.These changes in the direct load area are aligned with the typical axial force distribution law of friction piles,and the proportion of side friction resistance in the direct load area exceeds 80％,demonstrating the bearing capacity of tapered piles.However,the pile in the non-directly loaded area endures negative friction resistance under most loads from 20 kPa to 200 kPa,indicating that the pile in the non-directly loaded area does not fully exert its due bearing capacity,and only uses part of the bearing capacity.According to the weakening of the range of positive friction resistance along pile length in the area directly under load,and the flattening of axial force range and gradient of # 1 pile,it can be seen that,although the tapered pile-soil interaction is positively related with load and depth,a certain upper limit remains.Under large loads,changes of the pile-soil stress ratio curve and the proportion curve of pile side friction resistance tend to flatten or even decline.Furthermore,the tapered pile-soil interaction secures an upper limit.These tapered piles in the composite foundation can effectively disperse the pile body stress with the increase of load,and transfer the load from the pile body to the soil around the pile and also from the center of the foundation to the periphery,so that the bearing capacity of the soil around the pile can be effectively exerted.This tendency facilitates the pile-soil collaborative load of the composite foundation.[Conclusions]Through the analysis of load settlement,pile axial force,side friction resistance,pile-soil stress ratio and load sharing ratio of tapered pile-mesh composite foundation under loess,it is found that tapered pile structure performs excellently and also does differently in different regions.These aforementioned test results show that tapered pile-mesh composite foundation secures good bearing capacity and good load transfer performance.Piles in the direct loading area can better and more effectively play the bearing characteristics of tapered piles in the wedge-mesh composite foundation.Piles in the direct loading area need to be improved,such as changing wedge Angle,changing pile length and changing pile spacing.To give full play to the bearing characteristics of tapered pile,tapered pile can attain the joint action of pile and soil in the composite foundation,thus fitting the design concept of composite foundation satisfactorily.In this study,bearing characteristics of tapered pile-mesh composite foundation in collapsible loess area are studied.Hopefully,the proposed study provides theoretical design references for relevant practical projects and research ideas for bearing tests of tapered pile-mesh composite foundation in other poor geological environments.
foundation engineeringtapered pilepile-mesh composite foundationmodel testsFEMload-bearing characteristics
万方数据
维普
