大型炼厂地基钻孔灌注桩处理现场试验与分析

In-situ test and analysis of bored pile treatment of large-scale refinery foundation

针对大型炼厂工程软弱地基处理的复杂性,完成了不同桩径、是否嵌岩条件下水平、抗压及抗拔钻孔灌注桩的现场试验,试验内容包括钻孔灌注桩施工后的低应变动力检测、钻芯试验、桩身内力测试及单桩静载荷试验。基于低应变动力检测和钻芯试验结果,分析了桩身质量及完整性;通过大量桩身内力测试结果,详细分析了抗拔和抗压试桩在各级竖向荷载作用下轴力和侧摩阻力变化及传递特征,详细分析了抗水平桩在各级水平荷载作用下内力和弯矩变化规律;基于载荷试验结果,分析了单桩水平、抗拔及抗压承载能力;此外,利用试桩水平和抗拔静载荷试验结果,通过散点拟合,建立抗拔承载力特征值的平均值与桩径和单桩水平极限承载力的平均值与桩径的估算公式。研究结果表明:弯矩最大位置随推力增大而逐渐下移,在最大水平推力下,Φ600,Φ800和Φ1 000mm桩弯矩最大点位于推力点以下3.6,4和5m左右;单桩抗拔承载力极限值的平均值与桩径和水平承载力特征值的平均值与桩径均成线性关系。

Treatment of soft foundation in large-scale refinery project is very complex. In view of this condition, in-situ tests of horizontal, compressive and uplift bored piles with different pile diameters and rock-socketed conditions were carried out. The contents of in-situ tests included low strain dynamic test, core drilling method test, pile-body interual force test and static load test of single pile after construction of bored pile. Based on results of low strain dynamic test and core drilling method test, pile quality and integrity were analyzed. With large amounts of pile stress monitoring results, axial force and frictional resistance change and transferring characteristics of compressive or uplift piles under the vertical loads were analyzed in details. A detailed analysis of the internal force and bending moment variation laws were conducted on the pile under all levels of horizontal loads. Based on the load test results, the horizontal bearing capacity, uplift and compression capacities of the single pile were analyzed. In addition, through scatter fitting, the static load uplift test results and the horizontal test results of the pile were used to establish estimation formulas for the average value of uplift bearing capacity characteristic value and the pile diameter and estimation formulas for the average value of horizontal ultimate bearing capacity of single pile and pile diameter. The research results show that the position with maximum bending moment moves gradually down with thrust increase, and under the maximum horizontal thrust force, maximum bending moment position is located in the position 3.6m, 4m and 5m below thrust force position respectively for piles with diameters of 600mm, 800mm and 1 000mm. The average value of pullout capacity limit value of single pile is in linear relationship with pile diameter, and the average value of horizontal bearing capacity characteristic value is also in linear relationship with pile diameter.