桩端后注浆钻孔灌注桩承载特性及影响因素分析

Analysis of Bearing Characteristics and Influencing Factors of Post Grouting Bored Pile at Pile End

钻孔灌注桩为研究桩端后注浆承载特性及影响因素,依托某钻孔灌注桩桥梁基础工程,通过现场单桩静载荷试验分析了桩的沉降特性以及轴力和侧摩阻力分布规律,并基于有限元方法分析了不同注浆量和注浆体强度对桩端后注浆灌注桩承载力的影响,结果表明:桩轴力随深度的增大而逐渐减小,随着施加荷载的逐渐增大,桩端荷载承担比例不断增大;桩侧摩阻力大致呈现“R”型分布,试桩下半部分的侧摩阻力明显增大,桩端后注浆工艺在桩端附近产生了侧阻强化效应;随着桩端扩大头半径和弹性模量的增大,桩的承载力和承载力提高比均不断增大,当桩端扩大头半径小于1 m或桩端扩大头弹性模量小于2000 MPa时,承载力提高比增幅较大;随着桩长的增大,普通灌注桩和桩端后注浆灌注桩的承载力和沉降值均呈现不断增大的趋势,且桩长越短,后压浆工艺对灌注桩承载力的提高比例越大。

In order to study the bearing characteristics and influencing factors of post grouting bored pile at the pile end,this article relies on a bridge foundation project using a composite post grouting technology at the pile end.Through on-site single pile static load tests,the settlement characteristics of the pile,as well as the distribution of axial force and lateral friction resistance,were analyzed.Based on the finite element method,the influence of different grouting amounts and grouting body strength on the bearing capacity of post grouting bored pile at the pile end was analyzed,The following conclusion is drawn:The axial force of the pile gradually decreases with the increase of depth,and the proportion of pile end load bearing continuously increases with the gradual increase of applied load.The lateral friction resistance of the pile roughly presents an“R”distribution,and the lateral friction resistance in the lower part of the test pile significantly increases.The post grouting process at the pile end has produced a strengthening effect on the lateral resistance near the pile end.As the radius and elastic modulus of the pile end expand,the bearing capacity and bearing capacity improvement ratio of the pile continue to increase.When the radius of the pile end expand is less than 1m or the elastic modulus of the pile end expand is less than 2000 MPa,the bearing capacity improvement ratio increases significantly.As the pile length increases,the bearing capacity and settlement values of ordinary cast-in-place piles and post grouting cast-in-place piles at the pile end show a continuous increasing trend,and the shorter the pile length,the greater the proportion of improvement in the bearing capacity of cast-in-place piles by post grouting technology.