桩-土界面残余强度影响因素分析

Analysis of Influencing Factors of the Residual Strength of the Pile-Soil Interface

桩周土体因卸载或上部堆载使桩-土界面应力发生变化,并导致桩-土界面峰值剪切强度受损而下降为残余强度。为研究法向应力、压实度、含水率及预压力等多因素对桩-土界面的残余强度影响,利用自制的剪切试验装置对桩-土界面试件进行了剪切试验。试验结果表明:剪切应力达峰值强度后出现软化,法向应力越大软化越明显。残余强度随压实度和法向应力提高而增大,随含水率的提高先增后减,且在最优含水率附近达到最大值;在不同的法向应力情况下,受含水率和压实度的影响下,残余强度表现为山峰型,在最优含水率附近和压实度最大处达峰值,且预压对法向应力较小情况下残余强度提高比例更高。对不同压实度下的法向应力-残余强度、法向应力-残余应力比进行了讨论,得知有无预压界面残余强度与法向应力存在显著的线性关系,符合莫尔-库伦剪切破坏准则,不同压实度下残余应力比均随着法向应力的增长而衰减,而有预压影响时,这种现象会更明显。

In view of the fact that the stress of the pile-soil interface changes due to unloading or upper stacking load of soil around the pile,which leads to the damage of the peak shear strength of the pile-soil interface and decreases to the residual strength,a shear test has been carried out by the self-made shear device of the research group so as to study the effects of normal stress,compactness,moisture content and preloading on the residual strength of pile-soil interface.The results show that a softening effect can be observed with the shear stress reaching the peak strength.The greater the normal pressure is,the more pronounced this softening effect will be.The residual strength will be improved with the increase of normal stress and degree of compaction of soil,showing an initial increasing and a subsequent decreasing trend with the increase of water content,until finally reaching the maximum near the optimal water content.Under different normal pressures,due to the influence of moisture content and degree of compaction,the residual strength is characterized with a peak distribution,reaching the maximum near the optimal moisture content and the maximum at the maximum degree of compaction.When the normal pressure of preloading is relatively small,the proportion of residual strength will be higher.Based on a study on the normal stress residual strength and normal stress residual stress ratio under different degrees of compaction,it is concluded that there is a significant linear relationship between the residual strength,the residual strength after considering preloading and the normal stress.The shear failure of the interface conforms to the Mohr Coulomb shear failure criterion.Under is different degrees of compaction,the residual stress ratio decreases with the increase of normal stress,meanwhile the decrease more is obvious under the influence of preloading.