【作者】 侯晋芳；

【导师】 闫澍旺；

【作者基本信息】 天津大学 ， 岩土工程， 2007， 博士

【摘要】 我国东部沿海地区的港口、码头大都修建在软粘土地基上,因此软粘土土坡稳定性是重要的工程课题。在港口、码头建设阶段,软粘土土坡的安全储备较低,抗剪强度指标的正确选取对安全性的评估非常重要,只有得到接近真实抗剪强度的强度指标才能准确地评估土坡稳定性。在软粘土土坡稳定性中如果采用室内固结快剪强度会过高估计欠固结土坡的稳定性;若采用快剪强度又过于保守;原位测试的十字板强度最可靠,但实际工程分析表明采用十字板强度计算的安全系数偏小,与实际工程度安全度不符。因此需对软粘土的强度指标的确定方法进行深入研究。本文密切结合《港口工程地基规范》修订工作,针对这一问题及与之相关的其它问题,进行了以下几个方面的研究探索工作:1.通过计算分析和比较证明,对于软粘土土坡安全系数的估算,抗剪强度指标的影响要大于计算模式的影响。2.通过分析十字板剪力仪的工作机理和软粘土土坡破坏时滑动面的特点,阐述了用十字板强度计算的安全系数偏小的原因:一是十字板强度主要反映的是土体竖直面上的强度,是强度的较小值;二是土坡破坏的滑动面是一斜面,十字板强度小于该滑动面上的抗剪强度。3.通过对十字板试验测试土体工作机理的研究,结合地基土的十字板强度随深度线性变化的特点,提出了由十字板强度推算土体强度指标的方法,在计算方法中考虑土体的各向异性,并引入侧压力系数以及平均固结度,认为该方法回归出的抗剪强度指标更接近软粘土土坡的真实强度。4.采用由十字板强度回归得到的抗剪强度指标对多个实际的软粘土土坡进行了分析计算,计算结果与实际工程非常吻合。同时,将该法用于新型箱筒型基础稳定性的分析计算,取得了较好的计算结果,说明了该法的广泛适用性。5.依据极限分析的上、下限定理提出了软粘土土坡破坏的渐进发展过程,并可以用于分析计算软粘土土坡破坏引起的对码头后方填土的影响范围。更多还原

【Abstract】 In the east coastal areas of our country, most of the ports, docks and dikes are built on the soft clay foundation. Therefore, it is an important problem for the slope stability consisting of soft clay, which has lower shear strength. The proper shear strength parameters are needed to estimate the slope stability of the soft clay. However, because of the complex physical and mechanical properties, it is difficult to know exactly the shear strength of the soft clay. Among the common shear strength indexes, the shear strength parameters by CU test and those by UU test cannot be used to calculate the stability of the soft clay correctly. The former is usually over eatimated the safety of the slope, and the latter is consistently under estimated the safety of the same slope. The in-situ vane shear test is frequently performed to determine shear strength for slope stability analysis. But without considering the increase of the shear strength, the safety factors of stable slopes are always calculated less than 1.0. In this thesis, for the sake of revising the Code for Soil Foundations of Port Engineering, the shear strength for soft clay slope stability analysis is studied. The main research work consists of the following parts.1. Calculating results show that between the shear strength parameters and calculation methods, the safety factor of soft soil slopes are more sensitity to the shear strength parameters than to the calculation methods.2. According to the analysis of the work mechanism of the vane shear test and the characters of the sliding surfaces, it is shown the in-situ vane shear strength may not represent the shear strength mobilized along the analyzed sliding surfaces, which is the shear strength of the vertical plane. It is known to all that the shear strength on vertical plane is the smallest shear strength in all plane of the soil element. Therefore, the in-situ vane shear strength is less than the real shear strength on the slipping surface of the slope. Using the vane shear strength, the safety factor would be under estimated.3. Based on the analysis of the work mechanism of the vane shear test, and using the linear relation between the vane shear strength and the depth, this thesis presented a method of converting in-situ vane shear strength into undrained shear strength parameters. The Mohr-Coulomb theory is used on the vane shear strength calculation equation. The shear strength parameters determined for in-situ vane shear strength are subjected to statistical regression analysis, which is taken into consideration the anisotropy, the lateral compression coefficient and the average consolidation degree in the soft clay.4. Using the regressed shear strength parameters, the slope stability analysis method is performed for some existing slopes. Based on the results, it can be concluded that the presented method is effective to convert in-situ vane shear strength into undrained shear strength parameters for slope stability analysis. Simultaneously, the regressed analysis method is used to calculate the stability of cylindrical foundation. The results are closed to the practical engineering. Therefore, the method has a wide application.5. The upper bound and lower bound theorem is used to analyze the process of the progressive failure for the slope of the soft clay, and the calculation method is feasible to calculate the effective broken range of the slope of the soft clay.更多还原