钙质砂土原位试验对比与液化风险分析

Comparative in-situ tests of SPT and CPT at calcareous sand sites and liquefaction risk analysis

钙质砂是在特定环境下形成的一种特殊土,其物理特性与石英砂具有较大区别。目前尚无依据现场测试指标进行钙质砂土液化评价的方法,工程实践中一般采用基于陆源土类的液化判别方法,具有很大的不确定性。本文针对科威特Al-zour地区含钙量2%~10%和10%~36%两种钙质砂土进行SPT、CPT原位对比试验,并根据原位试验结果进行液化风险分析。结果表明:钙质砂土中SPT标贯值N 60与CPT锥尖阻力q c值具有较好的线性关系,其拟合优度达0.85,比值q c/N 60约为0.58;不同深度钙质砂依据土的特性指数I c计算得到的细粒含量F c与实测值具有较好的一致性;钙质砂土的CPT-SPT关系曲线较陆源土偏高,表明钙质砂的破碎特征对SPT影响更大;采用SPT、CPT液化评价方法的结果具有较好的一致性,但采用SPT液化评价方法得到的结果偏于保守,与CPT-SPT关系曲线偏高的结论相符;根据CPT方法判别为液化点属于土类分类图中的粉土或砂质粉土,非液点属于分类图中纯净砂或粉质砂,与实际钙质土类相符。

Calcareous sand is a kind of special soil formed in a special environment,and its physical properties are quite different from those of quartz sand.There is no method to evaluate the liquefaction of coral soil according to the field test index.The liquefaction discrimination method based on terrestrial soil is generally used in engineering practice,which has great uncertainty.In this paper,standard penetration tests(SPT)and cone penetration test(CPT)tests were carried out and liquefaction risk was analyzed according to the in-situ tests results at Al-zour area,Kuwait where deposited two kinds of calcareous sandy soils with calcium contest of 2%~10%and 10%~36%,respectively.The results show that:there is a good linear relationship between the standard penetration value N 60 and the cone tip resistance q c value in the calcareous sand.The goodness of fit is 0.85,and the ratio q c/N 60 is about 0.58;According to the characteristic index I c of calcareous sand in different depth,the calculated F c of fine content is in good agreement with the measured value.The CPT-SPT curve of calcareous sand is higher than that of terrestrial soil,which indicates that the fragmentation characteristics of calcareous sand have a greater impact on SPT.By using SPT and CPT liquefaction evaluation method,the liquefaction evaluation results are in good agreement,but the results obtained by SPT liquefaction evaluation method are conservative,which is consistent with the conclusion that the CPT-SPT relation curve is on the high side.The liquefaction sites are classified as silt or sandy silt,while non-liquefaction sites are classified as clean sand and silty sand in the CPT soil classification diagram,which is consistent with the actual calcareous soils.