Research On Failure Mechanisms And Stability Analysis Method Of Embankment Supported On Composite Ground Reinforced With Rigid Piles

Overall stability of an embankment is the key problem of embankment rapidconstruction on soft ground. To meet the requirements of the stability andpost-construction settlement of the embankment on soft subgrade, the compositeground reinforced with rigid piles is used extensively to support the embankment.However, due to the irrationality of the existing stability analysis methods, some casehistories have been reported that stability failure occurred to the embankmentssupported on composite ground reinforced with rigid piles.In order to evaluate the stability of the embankment supported on compositeground reinforced with rigid piles reasonably, centrifuge modeling tests are performedto study failure mechanisms of the embankments supported on soft ground andcomposite ground reinforced with rigid piles. The results show that the piles atdifferent locations under the embankment did not fail simultaneously but fail one byone by bending failure mode. For piles with a high bending stiffness and strength, alarge spacing, and a sufficient embedded depth into stiff stratum, the soil may flowaround the pile body and then it can further lead to overall failure of the embankment.But for piles with a low bending stiffness and strength, the piles would fail firstly bybending failure mode at the interface of the soft and stiff strata, and then thesecondary bending failure or collapse failure may occur to the upper part of the pilebefore the embankment failure.Based on the centrifuge modeling tests,3D finite difference numerical analysesare carried out to study the embankment supported on composite ground reinforcedwith rigid piles. The deformation behavior, load transfer and failure mechanisms ofthe piles and embankment are investigated with different pile bending stiffness andstrength, pile slenderness ratio, pile tip embedment，pile spacing and different soildistribution. The results show that the numerical simulation results confirm thecentrifuge test results, and bending failure of a pile is more critical than shear failure.The results also show that progressive failure occurs among the piles subjected toembankment loading and the embankment approaches failure progressively too. Withdifferent bending stiffness and strength, pile slenderness ratio, pile tip embedment,pile spacing and soil distribution, the piles would fail by different failure modes:(1) bending failure+collapse failure;(2) bending failure+bending failure;(3) collapsefailure;(4) sliding failure+tilting toward the embankment center;(5) soil flowaround the pile.Then based on the research of the failure mechanisms of the embankments onsoft subgrade reinforced with rigid piles, a few of simplified stability analysismethods are suggested and compared with each other by analyzing the stability of thetypical examples of the embankments on composite ground reinforced withunreinforced concrete piles (concrete piles) or reinforced concrete piles. It issuggested that a comprehensive analysis of the stability of the embankments oncomposite ground reinforced with rigid piles can be carried out by the equivalentshear strength method, the equivalent load method, the equivalent sand pile methodand the BS8006method. In order to ensure the redundancy of the design，differentsafety factor values are advised for different simplified stability analysis methods.