嵌岩灌注桩单桩竖向极限承载力标准值新旧规范对比

Comparison of standard value vertical ultimate bearing capacity of single rock-socketed cast-in-place pile with old and new codes

1980年以来,嵌岩灌注桩大量应用于建筑工程。此后三十余年,规范经多次制定及修订,嵌岩灌注桩的设计方法逐步深化。本文以某实际工程为例,对比研究《建筑桩基技术规范》(JGJ94-94)、《建筑桩基技术规范》(JGJ94-2008)、《建筑地基基础设计规范》(GBJ7-89)、《建筑地基基础设计规范》(GB50007-2011)四本规范中嵌岩灌注桩单桩竖向极限承载力标准值Q_(uk)的计算方法及计算结果,证明现行规范《建筑桩基技术规范》(JGJ94-2008)和《建筑地基基础设计规范》(GB50007-2011)计算结果远大于《建筑地基基础设计规范》(GBJ7-89)、《建筑桩基技术规范》(JGJ94-94)。因此,在涉及改造项目时,如原设计实际采用原建造时的设计规范(旧规范)计算给出的嵌岩灌注桩单桩竖向极限承载力标准值较小而无法满足改造后荷载的情况,可根据现行设计规范(新规范)重新进行计算,并结合单桩静载试验或其他方法进行确定,以利用原有桩基的安全储备,达到少加固、甚至是不加固基础的目的。

Since 1980,rock-socketed pile has been widely used in construction projects.After more than 30 years,the specification has been formulated and revised for many times,and the design method of rock-socketed pile has been deepened gradually.Taking a practical project as an example,this paper compares and studies the calculation methods and results of the standard value of ultimate vertical bearing capacity of a single rock-socked piles(Q_(uk))in four codes:Technical Code for Building Pile Foundations(JGJ94-94)and Technical Code for Building Pile Foundations(JGJ94-2008),Code for Design of Building Foundations(GBJ7-89),Code for Design of Building Foundations(GB20007-2011).It is proved that the calculation result of the standard value of ultimate vertical bearing capacity of a single rock-socked piles in the current standard is greater than that in the old codes.Therefore,in the reconstruction project,if the standard value of ultimate vertical bearing capacity of a single rock-socketed pile calculated in the original standard is too small to meet the post-reconstruction load,it can be re-calculated according to the new current standard and determined in combination with the static load test or other methods of single pile,to make use of the safety reserve of the original pile foundation and achieve the goal of less reinforcement or even no reinforcement of the foundation.