Determining method of cohesionless soil state parameter based on resistivity CPTU and liquefaction evaluation
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摘要: 为研究基于现场原位测试技术的状态参数评估新方法, 以宿迁—新沂高速公路工程为背景, 利用电阻率孔压静力触探对饱和无黏性土进行了现场原位测试; 参考已有原位测试状态参数计算法的均值, 联合电阻率与土类指数建立了状态参数计算方法; 利用该方法评估的状态参数进行液化评价。分析结果表明: 状态参数与土类指数呈正比关系, 而土类指数与电阻率呈反比关系, 土类指数可作为连接无黏性土状态性能和电学性能的有效指标之一; 建立的电阻率CPTU状态参数计算方法所评估的状态参数沿深度变化趋势与已有方法一致, 提出的电阻率CPTU状态参数评估法主要适用土类指数为1.8~2.6的粉土和粉砂; 根据电阻率CPTU法计算的无黏性土原位状态参数与相对密实度呈现良好的线性关系, 变化趋势相反, 可作为一种相对密实度常用指标的有效替代参数来进行土体密实状态的评估; 基于电阻率CPTU法计算的无黏性土原位状态参数评估的液化阻力比与国际通用法基本一致, 判别粉质砂土层8 m以下为液化层, 与标准贯入试验结果相符, 状态参数可有效地用于液化势的可靠判别。Abstract: In order to study a new method for evaluating the state parameter based on in-situ testing technology, the Suqian-Xinyi Expressway project was taken as the background, the in-situ test of saturated cohesionless soil was conducted by using the resistivity piezocone penetration test (CPTU). By referring to the mean values of the existing in-situ state parameter calculation methods in the literatures, the state parameter calculation method was established by combining the resistivity and soil behavior type index. The state parameter evaluated by the method was applied to the liquefaction evaluation. Analysis result shows that the state parameter is proportional to the soil behavior type index, while the soil behavior type index is inversely proportional to the resistivity and can be used as one of the effective indexes to connect the state and electrical properties of cohesionless soil. The trend of state parameter evaluated by the proposed calculation method of resistivity CPTU state parameters is in agreement with the values of the existing methods. The proposed resistivity CPTU method is mainly applicable to the silt and silty sand whose behavior type indexes are between 1.8 and 2.6. The in-situ state parameter of cohesionless soil calculated by the proposed method has good linear relationships with the relative density, the trend is opposite, and it can be used as an effective alternative parameter for the commonly used index of relative density to evaluate the compactness of soil. The liquefaction resistance ratio of cohesionless soil calculated based on the state parameter from the proposed method is basically consistent with the values of international general methods. It is concluded that the silty sand layer below 8 m is liquefaction layer, which is consistent with the standard penetration test results. The state parameter can be effectively used for the reliable discrimination of liquefaction potential.
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图 11 相对密实度与状态参数关系
Figure 11. Relationship between relative density and state parameter
图 12 基于状态参数表示的现场历史液化数据
Figure 12. Field case history data on liquefaction based on state parameter
表 1 影响土体电阻率相关因素汇总
Table 1. Summary of related factors affecting soil resistivity
相关变量 电阻率 影响程度 孔隙率 增加 ★★★ 饱和度 增加 ★★★ 盐浓度 增加 ★★★ 粒径 减小 ★★ 级配 增加 ★★ 温度 增加 ★★ 活性 增加 ★★ 
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表 2 原位测试CPTU状态参数确定方法汇总
Table 2. Summary of CPTU in-situ testing methods to evaluate state parameter
方法 公式 参数及其他说明 1 λ=1/ (34-10I1) 2 λ=F/10 3 ψ=0.56-0.33lg (Q1) 基于Been等提出的方法 4 电阻率CPTU状态参数计算方法
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表 3 主要物理力学指标
Table 3. Main physico-mechanical indexes
名称 层厚/m 相对体积质量 细粒含量/% 含水量/% 液限/% 素填土 1.1 2.72 15.2 21.4 27.6 粉土 4.1 2.70 3.6 24.7 29.1 粉质砂土 9.8 2.69 5.2 29.8 28.4 粉土夹砂 未揭穿 2.68 5.7 27.2 29.8
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