基于汶川地震的砂砾层液化生成条件及发生规律研究

At this time being, many academic scholars and engineers doubt liquefaction potential of gravel. The conditions and relevant rules for gravel liquefaction are "black boxes". In 2008 Wenchuan Ms8.0, China, earthquake, liquefaction and its damage were observed and systematically investigated. One of the eminent liquefaction characteristics is widespread gravel liquefaction phenomenon. Based on Wenchuan earthquake, the generating conditions and inner rules of gravel liquefaction are investigated according to earthquake intensity and engineering geotechnical and geological site conditions. Employing in-situ and laboratory testing techniques, the fundamental indices concerning on gravel liquefaction sites and gravely soil properties can be obtained. The threshold conditions for gravel liquefaction occurrence, which are related to geological ages and depth of liquefiable gravel, up bounds of underground water tables and gravel content, will be pursued. Selecting core characteristic parameters, a theoretical threshold model of gravel liquefaction potential is constituted and critical curves for gravel liquefaction will be plotted. Meanwhile, the influence of many fundamental characteristic values on gravel liquefaction potential is analyzed to propose gravel liquefaction generating rules. Through research of this project, complete and systematic acquaintance of gravel liquefaction generating conditions and rules will be displayed, which paves the ways for understanding gravel liquefaction mechanism, and provides theories for developing gravel liquefaction evaluation methods and prediction techniques.

目前学术界大多数学者以及工程界绝大部分人员对砂砾层出现液化可能性均持怀疑态度，关于砂砾层液化生成条件和发生规律的认识几近空白。2008年我国发生的8.0级汶川大地震，液化及其震害现象明显，最显著的特征是大量的砂砾层液化。本项目以汶川地震为背景，研究包括地震强度与工程地质条件这两种主客观基本要素在内的砂砾土液化生成条件和发生规律。采用现场勘察和室内试验，获取砂砾土液化场地及土性参数基本信息。研究砂砾土液化生成的门槛条件，提出可液化砂砾层生成地质年代、深度和地下水位上限关联曲线以及含砾量上限门槛值。选取核心特征量，构建砂砾层液化势阈值理论模型，推导出临界特征线。分析各基本特征量对砂砾土液化势的影响，提出砂砾层液化发生规律。通过本研究，可获取砂砾土液化生成条件和发生规律较为全面、系统的认识，为掌握砂砾土液化机理、发展砂砾土液化预测方法和评价技术提供理论基础。

以汶川地震为背景，提出了砾性土地震液化的新概念，阐明了其内涵和外延，打破了天然沉积砾性土层为非液化安全场地的传统认识，极大丰富了人类关于可液化土类的知识；指出地震中地表（井中）喷出物与地下实际液化土类大相径庭，以往以地表喷出物反推地下液化层土性类型的做法不再成立；获取了全球最丰富的砾性土液化场地实测数据，取得了砾性土场地基本特征的新认识；指出虽然液化砾性土层剪切波速很高，但实际上大多松散状态，认为砾性土层波速大、透水性好而不会液化的传统认识不再成立，但砂土液化判别方法不适于砾性土场地；以一个理论模型和计算公式完成土层液化判别的方法仅适用于砂土层，埋藏条件方面的特殊要求应是砾性土区别于砂土液化判别方式的标志，触发砾性土层液化的具体条件和指标应是今后重点研究的课题。