An analysis of the influence of clay structure on piezocone penetration test results
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摘要:
针对目前黏土结构性对孔压静力触探结果的影响及其机理尚不是很清楚的问题，首先在ABAQUS软件中对结构性剑桥模型进行了程序实现，然后建立了孔压静力触探贯入结构性黏土的数值模型，通过数值计算分析了黏土结构性对孔压静力触探结果的影响。数值计算结果表明：（1）黏土的结构性会导致锥尖周围土体的偏应力增大，由于锥尖附近土体的结构性损伤，最大偏应力出现在距锥尖一定距离的右下方；（2）表征结构性强度的参数——初始结构屈服应力$ p{\text{'}}_{ {\rm{yi}}} $越大，锥尖阻力qc越大，而表征结构性损伤速度的参数——结构性对流动法则影响参数ω越大，qc值越小；（3）$p\text{'}_{ {\rm{yi}}} $值越大，贯入停止时的超静孔隙水压力u越大，而ω值越大，贯入停止时的u值越小；（4）经验圆锥系数Nkt随$p\text{'}_{ {\rm{yi}}} $增大明显减小，随ω的增大略有减小。因此，黏土的结构性强度及其损伤会明显影响孔压静力触探的测量结果，基于锥尖阻力qc估算结构性黏土的不排水抗剪强度su时应采用考虑结构性影响的经验圆锥系数Nkt，否则将会低估结构性黏土的su。研究结果可为孔压静力触探结果的分析和应用提供参考。
Abstract:The effect of clay structure on the piezocone penetration test results and its mechanism are not very clear, the structured Cam-clay model is firstly program-implemented in the ABAQUS software. Then, the numerical model of piezocone penetration into structured clay is established, and the effect of clay structure on piezocone penetration test results is analyzed through numerical simulation. The numerical calculation results show that (1) the clay structure causes the increase of deviatoric stress of the soils surrounding the cone tip, and the maximum deviatoric stress appears at the lower right at some distance from the cone tip due to the structural damage of the soils near the cone tip. (2) The larger the parameter $p\text{'}_{ {\rm{yi}}} $ representing structural strength is, the larger the cone tip resistance qc, and the larger the parameter w representing structural damage speed, the smaller the qc value. (3) The larger the $p\text{'}_{ {\rm{yi}}} $ value is, the larger the excess pore water pressure u when the penetration stops, and the larger the w value is, the smaller the u value when the penetration stops. (4) The value of the empirical cone factor Nkt decreases obviously with the increasing $p\text{'}_{ {\rm{yi}}} $, and decreases slightly with the increasing w . Therefore, the structural strength of clay and its damage will obviously affect the measurement results of the piezocone penetration test, and the empirical cone factor Nkt considering the structural effect should be used to estimate the undrained shear strength su of the structural clay based on the cone resistance qc, otherwise, the su of the structural clay will be underestimated. The research results can provide reference for the analysis and application of piezocone penetration test results.
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表 1 结构性剑桥模型参数
Table 1. Structured cam-clay model parameters
参数 M λ κ E/kPa eIC υ b ω γ $\sigma\text{'}_ {{\rm{vyi}}} $ /kPa$p\text{'}_ {{\rm{yi}}} $ /kPa侧限压缩试验 1.50 0.505 0.020 0 — 5.383 — 0.7 — 0.5 430 — 三轴固结排水试验 1.50 0.208 — 76 923 2.383 0.13 30.0 4 2.1 — 2 400.0 三轴固结不排水试验 1.28 0.355 0.047 7 — 2.910 0.25 1.0 1 0.5 — 57.5 CPTU贯入模拟 1.50 0.300 0.050 0 — 3.770 0.30 5.0 1 1.0 — 250.0 注：E为弹性模量； eIC为重塑土正常固结曲线上p' = 1 kPa时的孔隙比； $\sigma \text{'}_ { {\rm{vyi} } }$ 为一维固结试验中的竖向屈服有效应力；“—”表示参数不需要设置。
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