Evaluation Method of Maximum Shear Modulus of Cohesionless Soil Based on State Parameters from Piezocone Penteration Test
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摘要: 土体最大剪切模量是动力基础设计和地震场地响应分析的重要参数，目前该参数的确定主要来源于室内试验，但室内试验值难以反应现场土层的真实情况，因而采用原位测试技术确定土体最大剪切模量的方法备受关注. 以宿迁-新沂高速公路为工程背景，利用地震波孔压静力触探（SCPTU）对现场场地进行测试，在总结已有的最大剪切模量确定方法研究成果的基础上，以实测剪切波速计算得到的最大剪切模量作为参考值，研究了孔压静力触探（CPTU）测试参数与最大剪切模量之间的关系；基于临界状态土力学理论，研究了联合CPTU测试参数和状态参数与最大剪切模量的关系. 结果表明：最大剪切模量与CPTU测试参数存在良好的相关关系，可通过锥尖阻力和孔压参数来近似估计最大剪切模量值；将状态参数作为孔隙比或孔压参数比的有效代替参数，能够同时考虑围压应力与孔隙比双重因素，所估算的最大剪切模量与参考值基本一致. 因此，CPTU原位状态参数可作为一种新方法来初步评价无黏性土的最大剪切模量.Abstract: The maximum shear modulus of soil is an important parameter for dynamic design of foundations and response analysis of seismic sites. At present, this parameter is mainly determined through laboratory tests, but such tests cannot represent the real situation in the field. Thus, in situ testing technologies have attracted much attention. The Suqian-Xinji Expressway was regarded as the engineering background and seismic piezocone test (SCPTU) was conducted at the site. Based on the summary of research results for existing methods used to determine the maximum shear modulus, the relationship between the piezocone penetration test (CPTU) parameters and the maximum shear modulus was studied in terms of the reference value of the maximum shear modulus calculated using the measured shear wave velocity. The relationship between the joint CPTU parameters, state parameters, and maximum shear modulus was also analysed. The results show a good correlation between the maximum shear modulus and CPTU parameters. The maximum shear modulus value can be approximated by cone tip resistance and pore pressure parameters. The state parameter can serve as an effective alternative parameter for void ratio or pore pressure parameter ratio, and the dual factors of confining pressure and void ratio can be considered simultaneously. The estimated maximum shear modulus is the same as the reference value. Therefore, the in situ state parameters of CPTU can be used as a new method to evaluate the maximum shear modulus of cohesionless soil.
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Key words:
- seismic piezocone test /
- sand /
- maximum shear modulus /
- shear wave velocity /
- state parameter
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图 2 宿迁高速场地各参数随深度的变化曲线
Figure 2. Curves of each parameter with depth at the Suqian expressway site
图 3 基于SCPTU测试资料Gmax/（1+Bq）4.59与qt的关系
Figure 3. Gmax/（1+Bq）4.59 versus qt for SCPTU test data
图 4 SCPTU测试资料Gmax/（1+
$\psi $ ）4.59与qt的关系Figure 4. Gmax/（1+
$\psi $ ）4.59 versus qt for SCPTU test data
图 5 SCPTU测试的Gmax与预测值的比较
Figure 5. Comparison between measured SCPTU data and inferred Gmax profiles
表 1 试验场地土层的主要物理力学性质指标
Table 1. Main physico-mechanical indexes of test site soils
层号 名称 深度/m 含水量/% 液限/% 标贯击数N ① 填土 1.0 11.27 31.47 9 ② 粉土 4.8 26.12 29.25 4 ③ 粉质砂土 6.0 29.48 28.43 10 ④ 砂土 未揭穿 27.72 27.64 24 
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