液化判别的双曲线模型
Hyperbolic model for estimating liquefaction potential of sand
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摘要: 基于国内外液化判别方法存在的问题,提出了一个双曲线形式的液化判别新模型。采用中国大陆以往156例液化数据完成了基于标准贯入试验的新公式构造,利用近来集集和阪神地震312例液化新数据进行了检验,并与现有规范方法和Seed方法进行了对比,结果表明:提出的双曲线模型和液化判别公式对不同地震烈度、地下水位和砂层埋深均有较好的适用性;新模型弥补了现有规范Ⅶ度下浅层液化(砂层埋深小于10 m)判别偏于危险的缺欠,对Ⅷ度和Ⅸ度下浅层土液化和非液化场地的成功率比现有规范表现得更为均衡;新模型可满足临界曲线浅层内快速变化、深层时明显变缓的客观实际要求,克服了规范Ⅷ度、Ⅸ度下深层土(砂层埋深10~20 m)判别严重保守的弊端;新模型具有渐近线形式,更符合实际情况,消除了Seed方法中标准贯入临界值随土层埋深增加先递增后递减的不正常现象。Abstract: A new hyperbolic model for estimating liquefaction potential of sand is proposed to solve the exiting problems in the available liquefaction discrimination methods. By collecting 156 in-situ SPT data from previously liquefied and non-liquefied sites in China, a new SPT-based formula is proposed. The reliability of the new formula is verified by 312 data collected from 1995 Kobe Earthquake and 1999 Chi-Chi Earthquake. The estimated results by the new formula are compared with those by the code method and Seed method, indicating that the hyperbolic model is quite adaptable for a wide range of seismic intensities, ground water level and buried depth of sand. The new model compensates the limitation that the discriminated results of shallow sand (less than 10 m deep) tend to be risky by the code method under intensity Ⅶ. Using the new model, the success discrimination ratios of liquefied and non-liquefied sites for shallow sand under intensities Ⅷ and Ⅸ are more uniform than those by the code method. The critical discriminating curve of the new model meets the fact that its slope is large in shallow while small in deep one. The disadvantage that the discrimination of soils 10 m to 20 m in depth under intensities Ⅷ and Ⅸ is significantly conservative by the code method is corrected. The proposed model adopts asymptotic form which is closely consistent with the real condition and avoids the abnormal phenomena using the Seed method in which Ncr increases and afterward decreases with depth.