DX嵌岩桩承载特性现场试验研究

Field Tests on Bearing Characteristics of Rock-socketed DX Piles

DX桩作为一种新型变截面桩,可有效提高单桩承载力、控制桩顶沉降,近年来得到广泛应用。本文介绍DX嵌岩桩首次代替直孔嵌岩桩的现场静载试验及工程应用研究。根据桩身钢筋应力计及桩底压力盒实测数据,对其荷载沉降特性及承载机理进行了分析。结果表明:(1)DX嵌岩桩Q-s曲线变化平稳,未呈现明显加速变形趋势;(2)承力盘位于强风化泥质粉砂岩表层或中层,盘阻力发挥较早,占总承载力比例达23.3%~31.6%,承载作用明显;此外,当侧阻力及盘阻力达到其承载极限时,端阻力能进一步发挥,占总承载力比例达26.2%~37.4%,桩身各部分能协调工作;(3)将该成果应用在广州太平洋广场及广西防城港钢铁项目中,采用Ф600 mm DX嵌岩桩代替Ф800 mm直孔桩,可提高单桩抗压承载力63%,减小嵌岩深度3~5 m,节约混凝土方量40%~50%,缩短施工时间40%以上,降低单桩造价31%~37%,经济效益十分显著。

It has been confirmed that DX pile as a new variable cross section pile has huge advantage in bearing capacity and settlement control,which has been widely used in recent years. Static load tests are conducted and engineering application are introduced to evaluate the performance of DX piles socketed into weak rock as alternatives to the conventional rock-socketed piles. Load settlement behavior and bearing mechanism are investigated through the data obtained by the stress gauges along the length and load cells embedded in pile tip. The results show that: 1) the Q-s curves of rock-socketed DX piles change slowly and the test piles do not show any sign of what could be considered failure in the process of loading. 2) the bearing resistance of the bulb is mobilized once the pile loaded,the loading sharing ratio maintains at 23. 3% ~ 31. 6% when it rests on or socketed into the highly weathered argillaceous siltstone. In addition,the base resistance becomes significant when side resistance and bulb resistance are fully mobilized,the load sharing ratio increases to 26. 2% ~ 37. 4%,different parts are working together. 3) the research results are applied to the engineering of Taipingyang square projects in Guangzhou and the steel project in Fangchenggang in Guangxi,in which the conventional rock-socketed pile with a diameter of 800 mm is replaced by DX pile with a diameter of 600 mm. As a result,the compression bearing capacity of single pile is increased by 63%,rock socketing length is reduced by 3 ~ 5m,concrete conservation is amount to 40% ~ 50%,construction period is shorten by 40%,the cost of single pile is decreased by 31% ~ 37% compared with the former and achieve significant economic profit.