砾性土层液化的触发条件  

Necessary trigger conditions of liquefaction for gravelly soil layers

作　　者：袁晓铭[1] 秦志光 刘荟达 曹振中[3] 徐鸿轩 YUAN Xiao-ming;QIN Zhi-guang;LIU Hui-da;CAO Zhen-zhong;XU Hong-xuan(Institute of Engineering Mechanics, China Earthquake Administration, Key Laboratory of Earthquake Engineering and Engineering Vibration of China Earthquake Administration, Harbin 150080, China;Key Laboratory of Environment Protection ＆ Safety in Foundation Engineering of Transportation;Guangxi Key Laboratory of Geomechanics and Geoteehnieal Engineering, Guilin University of Technology, Guilin 541004, China)

机构地区：[1]中国地震局工程力学研究所中国地震局地震工程与工程振动重点实验室,黑龙江哈尔滨150080 [2]中交交通基础工程环保与安全重点实验室,广东广州510230 [3]广西岩土力学与工程重点实验室桂林理工大学,广西桂林541004

出　　处：《岩土工程学报》2018年第5期777-785,共9页Chinese Journal of Geotechnical Engineering

基　　金：中央级公益性研究所基本科研业务费专项(2016B01);国家重点研发计划政府间国际科技创新合作重点专项(2016YFE0105500);国家自然科学基金项目(41272357);广西自然科学基金项目(2014GXNSFBA118257,2016GXNSFAA380117)

摘　　要：天然沉积砾性土场地液化是一个超出现有认识与现有规范的新问题,其触发条件至关重要,从震害现场调查提炼出相关认识最为可靠,是后续研究的基础和导引。鉴于2008年汶川地震砾性土液化规模远超以往,以其调查结果为主,综合历史砾性土液化全部资料,提出砾性土层液化的触发条件。现有资料分析表明：0.15g应为触发天然沉积砾性土层液化的地表最低地震强度,大规模砾性土层液化发生则需要0.2g-0.4g（Ⅷ度区）的地震强度;松散和接近松散状态是天然砾性土层液化的基本条件,液化砾性土密实度可随地震强度增大而增高但仍以稍密状态为上限;液化砾性土含砾量可达85%及更大,并且不随地震强度减弱而降低;高剪切波速天然砾性土层会发生液化,砾性土与砂土密实程度的剪切波速分界线相差悬殊,砂土液化判别公式不适于砾性土层;上覆渗透性差非液化土层（帽子）的存在是地下砾性土层可发生液化的必要条件,可称为帽子效应,此厚度至少应为0.5 m;地下水位与帽子间不能有过厚的可排水层间隙也是下卧砾性土层可发生液化的必要条件,可称为间隙效应,此间隙上限可取为2.0 m;区别于砂土液化判别方法,砾性土液化判别需要埋藏条件方面的特殊要求,否则容易出现误判。The liquefaction of the natural gravelly soils is a new problem beyond the existing awareness and codes, and the trigger conditions of liquefaction are critical. It is the most reliable to extract the relevant knowledge from field investigation of earthquake damages. In view of the world＇s largest scale of gravelly soil liquefaction in the 2008 Wenchuan earthquake, using the post-earthquake field investigation data from the meizoseismal area in the Wenchuan earthquake and the historical documents on liquefaction of gravelly soils in the world, the necessary trigger conditions for liquefaction of gravelly soils and the relevant characteristic parameters are studied. The analytical results indicate：（1） The minimum ground shaking of 0.15 g is essential to trigger liquefaction of natural gravelly soils, yet the liquefaction of massive gravelly soils requires 0.20 g to 0.40 g of ground shaking intensity;（2） The most natural gravelly soil layers are very loose. Even though the gravelly soils can be compacted with the increasing ground shaking, the compacted gravelly soils are still slightly dense.（3） The gravel contents of the liquefied soils can reach 85% and even larger in reality, and they do not decrease with the decreasing seismic intensity;（4） The layers of gravelly soils with high shear wave velocity can be liquefied. The shear wave velocities dividing different compactions for sands and gravels are different, and the liquefaction evaluation methods for sand cannot be applied in gravelly soils.（5） The existence of a cap of overburden low-permeability and a non-liquefiable layer with minimum 0.5 m in thickness is a necessary condition for possibility of liquefaction of gravelly soils, which can be defined as the cap effect.（6） The gap for drainage between theunderground water table and the overburden cohesive layer cannot be large, which is another necessary condition for possible occurrence of liquefaction of gravelly soils, and the thickness should be less than 2.0 m, which can be de

关 键 词：砾性土液化 上覆渗透性差非液化土层 帽子效应 可排水层间隙 间隙效应 

分 类 号：TU43[建筑科学—岩土工程] O319.56[建筑科学—土工工程]