桩端后注浆上返高度及桩顶冒浆处理

在幂律型浆液平板窄缝流动模型的基础上,推导出了桩端后注浆浆液上返高度的计算公式。并对上返高度随注浆压力、桩埋深、桩径、泥皮厚度的变化情况进行计算分析,结果表明:桩底浆液压力越大、桩侧泥皮越厚、桩长越短,浆液上返高度越大,即越容易发生桩顶冒浆。工程实例研究表明,桩顶冒浆的主要原因包括桩侧泥皮厚、试桩龄期短、持力层可注性差和桩底沉渣厚。通过降低注浆压力,减小桩侧泥皮及桩底沉渣厚度,提高泥皮强度可以防止桩顶冒浆的发生。对于发生桩顶冒浆的试桩,可采用间歇注浆进行处理。与未发生桩顶冒浆的桩相比,发生桩顶冒浆并通过复注达到设计注浆量的桩,其极限承载力较高。这是由于沿桩侧泥皮上返的浆液,通过劈裂、置换桩侧泥皮,使桩侧摩阻力略微提高。

Climb Height and Overflow of Grout in Shaft Base Grouting

Based on the assumptions of exponential fluid and narrow plate model, formulas for calculating the climb height of grout in shaft base post grouting was deduced. It is shown that the climb height of grout is mainly related to the grouting pressure, the shaft length, the shaft diameter and the mudcake thickness. With the theoretic analysis and case study, it is indicated that thicker mudcake, higher grouting pressure and shorter shaft length would lead to larger climb height and larger risk of overflow. The overflow of grout would be prevented by reducing the grouting pressure, the mudcake thickness and debris thickness. The overflow of grout can also be prevented by increasing the strength of mudcake. For the overflow shafts, intermission grouting would be employed. Compared with the ordinary shafts, the former has higher bearing capacity than the latter, resulting from the grout upwards along the shaft soil interface.