砾性土液化阈值模型与机理研究

Gravelly soils are widely used in civil engineering practice because of its high permeability and bearing capacity. Gravelly soils liquefaction widespread occurred during 2008 Wenchuan earthquake, about 70% of 118 liquefied cases were gravelly soils sites. The large amount occurrence of gravelly soils liquefaction brought some new issues, which are worthwhile to investigate and essential to figure out in engineering practice. This proposal intends to investigate hydraulic and geological background, permeability and drainage conditions of liquefied sites of gravelly soils, select typical cases to trench and collect gravelly samples at liquefied layer, and conduct large diameter triaxial test to examine liquefaction features, liquefaction resistance strength, pore water pressure changes, and threshold site conditions during liquefaction of gravelly soils. The method and computer program for computing the pore water pressure development and dissipation of gravelly soils liquefaction will be proposed, and their feasibilities will be verified through field investigation. The liquefaction mechanism of gravelly soils will be revealed in aspects of liquefaction field effects, pore water pressure changes and threshold site conditions during liquefaction, according to results of the laboratory test, numerical computation, and field investigation.

砾性土的分布范围与工程应用十分广泛，2008年汶川地震118个液化点中约70%液化点为砾性土液化，引发了很多科学上需要研究、工程上需要解决的新问题。以汶川地震大量砾性土液化及其液化震害为背景，研究饱和砾性土的液化机理以及埋藏条件、排水条件等复杂地质环境对砾性土液化特性的影响规律，基于现场调查、室内试验及数值模拟等手段，阐明砾性土场地孔压增长/消散机制及关键影响因素，并确定砾性土液化的阈值条件，为规范修订提供必要的技术支持。

本项目以汶川地震砾性土液化及其液化震害为背景，补充了10余个钻孔、进一步丰富了砾性土液化场地常规物理特性指标，调查了液化土的水位、埋深、覆盖层厚度、排水通道等埋藏条件，研究了饱和砾性土的液化机理以及埋藏条件、排水条件等地质环境对砾性土液化特性的影响规律。讨论了土性条件、试验条件、应力条件对砾性土变形与强度特性、动孔压的影响规律，针对汶川地震砾性土液化场地的“二元地质结构”计算模型，分析不同土性条件、埋藏条件、排水条件、门槛条件等多种工况下的孔压增长与消散演变规律，建立了砾性土液化阈值模型与判别条件，为砾性土场地采取有效的抗液化处理措施以及规范修订提供技术支持。