静力触探锥头阻力与软土强度相关性分析

发布时间：2019-01-24 13:30

【摘要】：静力触探试验(CPT)具有快速、准确及重复性高等优点,经常用于现场勘测地层信息。在软土地区,应用静力触探试验推定土体不排水抗剪强度是可能的。国内外众多研究学者和相关科研单位进行了这方面的探索,并在大量试验基础上建立了不同地区软土不排水抗剪强度的经验公式。这些经验公式普适性不强,并且不知道公式的准确程度。为了深入理解CPT贯入机理,并建立更加准确的锥头阻力和软土强度之间的关系,本文围绕静力触探贯入阻力与土体强度相关关系展开研究,具体内容如下：首先,对静力触探的基本设备、基本原理和机理进行了介绍,并详细综述了静力触探锥头阻力的理论研究、室内模拟试验研究和数值模拟分析。然而各理论解均对土壤行为做各种假设,不同的假设所估算的结果有较大差别,利用经验法配合统计分析的角度推算软土不排水抗剪强度是更为实际的方法。然后,对实测资料进行统计分析。根据上海地区和武汉地区部分静力触探数据和室内实验数据(上海地区19个工程和武汉地区33个工程,共632组数据),回归分析其比贯入阻力Ps与抗剪强度Su的经验关系式。统计分析按照粘土和粉质粘土两种土类分别进行。经过统计分析得到两地区粘土土体中锥尖承载力系数Nc的概率特征,包括均值,方差和分布概型。数据分析表明,武汉地区锥尖承载力系数Nc要高于上海地区。在此基础上,本文总结了该地区浅地基的抗剪强度指标Su确定方法。随后,使用ABAQUS建立有限元模型,模拟分析静力触探的贯入过程。通过土体参数敏感性分析,考察土体参数对锥尖阻力qc和锥尖承载力系数Nc的影响,并与经验公式对比分析。计算结果表明：锥尖阻力和锥尖承载力系数均随着内摩擦角、弹性模量和粘聚力的增加而不同程度的增加,该结论合理解释了武汉地区锥尖承载力系数Nc高于上海地区的原因。对锥头阻力qc与抗剪强度Su进行线性回归分析得到两者相关关系表达式。最后,通过武汉市实际工程案例分析,将实测回归分析与有限元计算结果进行对比分析,结果表明：采用回归分析方法确定的经验函数表达式估算不排水强度的方法结果比较稳定,与强度公式推求结果吻合度较高。有限元模拟计算结果与实测结果相差较大,但整体上仍反映出了土层不同深度处的强度特征。
[Abstract]:Static penetration test (CPT) has the advantages of high speed, accuracy and repeatability, and is often used in the field survey of stratum information. In soft soil area, it is possible to apply static penetration test to predict undrained shear strength of soil. Many domestic and foreign research scholars and related research institutions have explored this aspect and established the empirical formula of undrained shear strength of soft soil in different areas on the basis of a large number of tests. These empirical formulas are not universally applicable and do not know the accuracy of the formulas. In order to deeply understand the mechanism of CPT penetration and establish a more accurate relationship between cone resistance and soft soil strength, this paper focuses on the relationship between static penetration resistance and soil strength. The specific contents are as follows: first, The basic equipment, basic principle and mechanism of static penetration are introduced, and the theoretical research, laboratory simulation test and numerical simulation analysis of the resistance of static penetration cone head are summarized in detail. However, all the theoretical solutions make various assumptions about soil behavior, and the results of different assumptions are quite different. It is more practical to calculate the undrained shear strength of soft soil from the angle of empirical method and statistical analysis. Then, the measured data are statistically analyzed. Based on some static penetration data and laboratory experimental data in Shanghai and Wuhan (19 projects in Shanghai and 33 projects in Wuhan, 632 sets of data), the empirical relationship between specific penetration resistance (Ps) and shear strength (Su) was analyzed by regression analysis. The statistical analysis was carried out according to clay and silty clay respectively. Through statistical analysis, the probability characteristics of the cone tip bearing capacity coefficient (Nc) in the clay soil in the two regions are obtained, including the mean value, variance and distribution probability type. The data analysis shows that the Nc of the cone tip in Wuhan is higher than that in Shanghai. On this basis, this paper summarizes the method of determining shear strength index (Su) of shallow foundation in this area. Then, the finite element model is established by ABAQUS, and the penetration process of static penetration is simulated and analyzed. Based on the sensitivity analysis of soil parameters, the influence of soil parameters on cone tip resistance (qc) and cone tip bearing capacity coefficient (Nc) was investigated and compared with empirical formula. The results show that the resistance of cone tip and the coefficient of cone tip bearing capacity increase in varying degrees with the increase of internal friction angle, elastic modulus and cohesive force. This conclusion reasonably explains the reason why the coefficient of bearing capacity of cone tip in Wuhan area is higher than that in Shanghai area. The linear regression analysis between cone resistance qc and shear strength Su was carried out to obtain the expression of correlation between them. Finally, through the actual engineering case analysis of Wuhan City, the results of the measured regression analysis and the finite element analysis are compared and analyzed. The results show that the method of estimating undrained strength by the empirical function expression determined by regression analysis method is stable and has a good agreement with the result derived from the strength formula. The result of finite element simulation is quite different from the measured result, but it still reflects the strength characteristics of soil layer at different depth on the whole.
【学位授予单位】：北京交通大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TU447

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