Test Analysis of Post-Grouting Improvement Coefficient for Cast-in-situ Pile in Thick Sand Layers
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摘要: 关于深厚砂层区域钻孔灌注桩后注浆效果，目前可循经验有限。通过北京通州新城某工程项目试验桩静载试验，对比研究了钻孔灌注桩后注浆与未后注浆的单桩承载性能，以及后注浆工艺在本场地（深厚砂层）的效能。现场足尺试验研究表明，在该区域后注浆可有效减小桩顶沉降；与未后注浆试验结果相比，后注浆综合提高系数可达2.22；与根据勘察报告所得未后注浆桩承载力计算值相比，钻孔灌注桩的后注浆综合提高系数约为2.53～3.57。该研究可为后续类似地质条件的桩基设计提供参考和借鉴。Abstract: The experience of the post-grouting effect for cast-in-situ pile in thick sand layer is limited presently. Based on the static pile load test in a project of Tongzhou New Town, Beijing, the bearing capacity of single pile after post-grouting and without post-grouting was analyzed and compared, and the efficiency of post-grouting technology in this thick sand layer site was studied. It shows that post-grouting can effectively reduce settlement. Compared with the test results of pile without post-grouting, the comprehensive improvement coefficient of post-grouting can reach 2.22. Compared with the calculated value based on geotechnical report for bearing capacity of non-post-grouting pile, the comprehensive improvement coefficient of post-grouting for cast-in-situ pile is about 2.53～3.57. This study can provide reference for the subsequent design of pile foundation with similar geological conditions.
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图 1 试验场地土层信息及试验桩应力计布置示意图
注：N为标准贯入试验锤击数；qsik为桩的极限侧阻力标准值；βsi为后注浆侧阻增强系数；qpk为桩的极限端阻力标准值；βp为后注浆端阻增强系数。
表 1 后注浆提高系数汇总表
试验桩 Quk/kN 各土层侧摩阻力qsi/kPa 端阻力qpk/kPa ③上 ③下 ④上 ④下 ⑤ ⑥ TP4 18600 35.6 199.6 224.5 238.0 204.6 221.6 2077.4 TP9 8361 30.6 90.8 155.9 187.1 94.4 60.9 1930.5 提高系数 2.22 1.16 2.20 1.44 1.27 2.17 3.64 1.08 
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