砂砾土液化判别的基本方法及计算公式

2008年汶川8.0级大地震中液化现象显著且砂砾土液化占很大比重，而我国一些地区砂砾土分布广泛，发展相应液化预测和判别方法十分必要。我国规范液化判别方法来源于砂层（细粒土）液化资料，且按规范规定标准贯入试验不适于砂砾场地，故现有规范中基于标贯的液化判别方法对砂砾土不可行。以汶川大地震液化震害调查和现场测试为基础，提出了基于超重型动力触探试验（动探试验）的砂砾土液化判别方法并建立了计算模型和公式。结果表明：砂砾土液化判别由初判和复判两部分组成，初判以排除不可能液化及可不考虑液化影响情况为目标，复判则可采用动探击数N₁₂₀为基本指标的计算模型。初判包括地质年代、埋藏条件和含砾量3个条件，复判模型则由动探击数基准值、含砾量、砂砾土埋深、地下水深度和地震烈度等5个参数组成。根据此次地震液化砂砾土埋深及地下水位变化范围较大的特点，采用归一化方法导出动探击数基准值，利用优化方法推导出砂砾土深度及地下水位的影响系数。提出的砂砾土液化判别方法，较全面地考虑了砂砾土液化的影响因素，复判模型和公式表达简单明了，回判成功率较高，且与现有规范具有连续性，便于工程应用。

Fundamental method and formula for evaluation of liquefaction of gravel soil

The liquefaction behaviors in the great Wenchuan 8.0 Earthquake in 2008 are quite notable, and the liquefaction of gravel soil is significant. Considering the wide distribution of gravel soil in some places in China, the liquefaction prediction methods should be developed. The existing methods for evaluating the liquefaction of sand soil result from the sand liquefaction cases, however, SPT technique can not be conducted in the gravel soil layers, and as a result, the existing code is not suitable for the liquefaction assessment of gravel soil. After the investigation for the liquefaction-induced damages in the great Wenchuan Earthquake and in-situ tests for the liquefied and non-liquefied sites, the liquefaction prediction method of gravel soil based on DPT, i.e., the dynamic penetration tests, is presented, and the corresponding model and formula are obtained. The analytical results indicate the liquefaction discrimination of the gravel soil can be divided into two steps, the initial discrimination and the second discrimination. In the initial step, the impossible liquefaction cases are selected, and in the second, the calculation model is adopted by using N120 as the basic index from DPT. The geological ages, buried condition of the gravel soil layer and gravel contents of gravel soils are considered in the initial discrimination. In the second discrimination, five parameters including the reference value of N120, gravel content of gravel soils, depth of gravel soils, water table and seismic intensity are concerned. Considering the wide range of liquefied soil depths and its water levels, the reference value of N120 is deduced by the normalization method and the influence coefficients of the gravel soil depths and the water levels are obtained by the optimal method. The effect of various factors on liquefaction possibility of gravel soil is considered in the present method and the advantages of the model and formula for the second discrimination are noticed by clear expression, high success ratio of regression discrimination, good connection with the past work and convenience in engineering application.