基于中美规范对地基土液化等级判定的探讨

Exploration on the Determination of Foundation Soil Liquefaction Grade Based on Chinese and American Codes

研究目的:地震会导致饱和砂土出现液化现象,从而使得地基失去承载力,造成建筑物产生不均匀沉降。我国现行《建筑抗震设计规范》(2016版)(GB 50011—2010)(以下简称《建筑抗规》)以标准贯入试验作为判别方法,采用液化指数将地基液化程度划分为三级。美国国家地震研究中心也提出了基于贯入度试验数据评估土体液化的方法,但没有液化等级这一综合性判定地基液化程度的指标,缺乏一定的实用性。本文结合孟加拉铁路工程项目实例,分别对砂土液化区域进行取样,并就同一批样品分别按中、美规范进行各土层液化判别试验,通过对比大量试验数据后,采用美标的评估数据建立适用于本工程的LPI(液化指数)表达式。研究结论:(1)从Idriss和Golesorkhi的地基土液化判定公式中,判定各土层液化综合考虑液化土层FS(抗液化安全系数)、液化土层厚度及液化土层深度、上覆有效应力等因素,为液化指数判定提供了一种思路;(2)目前中国《建筑抗规》对液化指数的计算结果偏于保守,考虑液化影响因素并不全面,需引入测试桩及上覆有效应力修正参数,对标准贯入锤击数基准值进行修正,才能得到与实际情况相结合的标准贯入锤击数临界值;(3)本文研究可应用于美规液化土壤判别试验数据,得到LPI(液化指数)与液化等级对应的表格,使得美抗规中提出的抗液化安全系数(FS)有了工程的实用性。

Research purposes:As the earthquake causes the liquefaction of saturated sand,the foundation will lose its bearing capacity to result in uneven settlement of buildings.China’s current Code for Seismic Design of Buildings(2016 Edition)GB 50011-2010(hereinafter referred to as Building Code)uses the standard penetration test as a determination method,and it adopts the liquefaction index to divide the foundation liquefaction into three grades.The US National Earthquake Research Center also proposes a method for evaluating soil liquefaction based on penetration test data;however,it lacks certain application since there is no comprehensive index for determining the degree of foundation liquefaction.Taking the railway project of certain country as an example,this paper takes samples from different sand liquefaction areas respectively,and conducts the liquefaction determination test of each soil layer on the same sample according to Chinese and US codes.The evaluation data of US code is adopted by comparing large amount of data and the expression of LPI(liquefaction index)suitable for this project is established.Research conclusions:(1)The liquefaction of each soil layer is determined based on the formula of foundation soil liquefaction of Idriss and Golesorkhi.Liquefied soil layer FS(safety factor against liquefaction),its thickness,depth and overlying effective stress shall be considered to provide a kind of method for determining the liquefaction index.(2)At present,the calculation result of the liquefaction index of China’s Building Code is conservative.Since liquefaction does not have a complete influencing factors,it is necessary to introduce test piles and overlying effective stress correction parameters to modify the benchmark value of standard penetration blow counts,so that the critical value of the standard penetration blow counts can be acquired in line with the actual situation.(3)This research can be use for liquefaction determination test by US code,the comparison table for LPI(liquefaction index)and liquefaction level can be got,which made FS(Anti-liquefaction safety factor)for US code has comparatively strong practicality in engineering.