大直径深长钻孔灌注桩竖向承载力特性试验研究

Experimental study of vertical bearing capacity behavior of large-diameter bored cast-in-situ long pile

在唐山LNG罐区对9根大直径钢筋混凝土灌注桩进行了竖向荷载现场试验,其中桩端后注浆工艺试桩3根,三岔双向挤扩工艺试桩3根,挤扩支盘工艺试桩3根。基于现场静荷载和桩身应力测试结果,分析了3种不同施工工艺钻孔灌注桩竖向荷载传递规律。试验结果表明:3种不同施工工艺的大直径深长钻孔灌注桩试桩荷载-沉降曲线没有明显拐点,后注浆工艺试桩荷载传递过程表现为摩擦桩的特性,桩侧阻力几乎承担全部荷载,而三岔双向挤扩支盘工艺和挤扩支盘工艺试桩荷载传递过程表现为端承摩擦桩的特性,桩端阻力占总荷载的20%～30%;3种不同施工工艺试桩的轴力及桩-土相对位移变化规律基本相似,桩侧桩端阻力非同步发挥且相互影响,桩侧摩阻力均表现出强化现象。对整个罐区要求单桩承载力特征值不小于8 100 kN。3种施工工艺的钻孔灌注桩承载力均能满足要求。

The vertical load field test of nine large-diameter cast-in-situ bored piles is made in Tangshan LNG tank area,in which three piles are of tip post-grouting;three piles are of expanded branches and bells by 3-way extruding arms;three piles are of squeezed branch.Based on the static load and pile stress test results,the vertical load transfer laws of these three kinds of different construction techniques of cast-in-situ bored piles are analyzed.The results show that： the loading-settlement curves of three different construction technology piles have no obvious inflection point;the post-grouting pile load transfer process performs the characteristics of friction piles;pile lateral friction bears all load;the piles of expanded branches and bells by 3-way extruding arms and the squeezed branch piles load transfer performs the end bearing the characteristics of friction piles,pile tip resistance is 20% to 30% of the total load;the axial force and the pile-soil relative displacement variation of these three different construction technology test piles are similar;the tip resistance and lateral friction play asynchronous and influence each other;the pile lateral frictions have shown intensification.The entire tank area requirements of the single pile bearing capacity is not less than 8 100 kN,the bearing capacities of three construction technology piles can meet the requirements.