【摘要】：靜力觸探試驗(CPT)具有快速、準(zhǔn)確及重復(fù)性高等優(yōu)點,經(jīng)常用于現(xiàn)場勘測地層信息。在軟土地區(qū),應(yīng)用靜力觸探試驗推定土體不排水抗剪強度是可能的。國內(nèi)外眾多研究學(xué)者和相關(guān)科研單位進行了這方面的探索,并在大量試驗基礎(chǔ)上建立了不同地區(qū)軟土不排水抗剪強度的經(jīng)驗公式。 這些經(jīng)驗公式普適性不強,并且不知道公式的準(zhǔn)確程度。為了深入理解CPT貫入機理,并建立更加準(zhǔn)確的錐頭阻力和軟土強度之間的關(guān)系,本文圍繞靜力觸探貫入阻力與土體強度相關(guān)關(guān)系展開研究,具體內(nèi)容如下： 首先,對靜力觸探的基本設(shè)備、基本原理和機理進行了介紹,并詳細綜述了靜力觸探錐頭阻力的理論研究、室內(nèi)模擬試驗研究和數(shù)值模擬分析。然而各理論解均對土壤行為做各種假設(shè),不同的假設(shè)所估算的結(jié)果有較大差別,利用經(jīng)驗法配合統(tǒng)計分析的角度推算軟土不排水抗剪強度是更為實際的方法。 然后,對實測資料進行統(tǒng)計分析。根據(jù)上海地區(qū)和武漢地區(qū)部分靜力觸探數(shù)據(jù)和室內(nèi)實驗數(shù)據(jù)(上海地區(qū)19個工程和武漢地區(qū)33個工程,共632組數(shù)據(jù)),回歸分析其比貫入阻力Ps與抗剪強度Su的經(jīng)驗關(guān)系式。統(tǒng)計分析按照粘土和粉質(zhì)粘土兩種土類分別進行。經(jīng)過統(tǒng)計分析得到兩地區(qū)粘土土體中錐尖承載力系數(shù)Nc的概率特征,包括均值,方差和分布概型。數(shù)據(jù)分析表明,武漢地區(qū)錐尖承載力系數(shù)Nc要高于上海地區(qū)。在此基礎(chǔ)上,本文總結(jié)了該地區(qū)淺地基的抗剪強度指標(biāo)Su確定方法。 隨后,使用ABAQUS建立有限元模型,模擬分析靜力觸探的貫入過程。通過土體參數(shù)敏感性分析,考察土體參數(shù)對錐尖阻力qc和錐尖承載力系數(shù)Nc的影響,并與經(jīng)驗公式對比分析。計算結(jié)果表明：錐尖阻力和錐尖承載力系數(shù)均隨著內(nèi)摩擦角、彈性模量和粘聚力的增加而不同程度的增加,該結(jié)論合理解釋了武漢地區(qū)錐尖承載力系數(shù)Nc高于上海地區(qū)的原因。對錐頭阻力qc與抗剪強度Su進行線性回歸分析得到兩者相關(guān)關(guān)系表達式。 最后,通過武漢市實際工程案例分析,將實測回歸分析與有限元計算結(jié)果進行對比分析,結(jié)果表明：采用回歸分析方法確定的經(jīng)驗函數(shù)表達式估算不排水強度的方法結(jié)果比較穩(wěn)定,與強度公式推求結(jié)果吻合度較高。有限元模擬計算結(jié)果與實測結(jié)果相差較大,但整體上仍反映出了土層不同深度處的強度特征。
[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.
【學(xué)位授予單位】：北京交通大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2014
【分類號】：TU447

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