天津滨海淤泥质黏土次固结特性试验研究

发布时间：2018-04-01 14:09

本文选题：淤泥质黏土　切入点：单向固结　出处：《中国地质大学（北京）》2014年硕士论文

【摘要】：浅海相沉积软土广泛分布于我国沿海地区，不同程度地影响工程建设。淤泥质黏土是最为常见的海积软土，其主要特点是天然含水率和孔隙比大、重度小、塑性指数较大，宏观性质方面表现出强度低、承载力小、渗透性小、压缩性高等特征，同时还具有明显的次固结特性。软土的次固结特性和微观结构对其宏观力学性质有重要影响，因此导致工程建设出现沉降量过大、变形不满足要求以及长期变形不稳定等问题。基于上述情况，本文以天津滨海南港地区埋深约7米的原状海积淤泥质黏土作为试验和研究对象，进行分级加荷和预固结分别加荷两种单向固结试验以及微观试验，探讨其在不同加荷方式下的次固结变形特征，并通过微观试验分析次固结过程中微观变化与宏观力学特性的关系。结合地基预压工程测试实例对试验结果进行分析，得出了一些对软土地区工程建设尤其是地基预压有指导作用的结论和建议。本文主要研究成果如下：（1）本次研究的淤泥质黏土先期固结压力pc为63kPa，超固结比OCR约为1，属于传统观念的正常固结土。单向固结试验结果表明其主次固结分界点的时间约在150～200min。相对于加荷比η，固结压力p对次固结特性影响更大。当固结压力p从较小值逐渐增加，，次固结系数逐渐增大，当p接近2pc时次固结系数达到最大，其后随着固结压力p进一步增大，次固结系数逐渐减小，当p400kPa后，次固结系数减小趋缓。（2）微观结构试验揭示了淤泥质黏土初始状态的微观结构以及在次固结过程中微观结构的变化，并获得了主要微观形态参数的时效规律。（3）研究了次固结过程中次固结系数和压缩模量的变化规律。结果表明，在相同的应力水平下，随着荷载作用时间延续，次固结系数都有减小的趋势且衰减逐渐变缓，压缩模量都有增大的趋势但没有明显数值规律。基于次固结系数的衰减性，在前人研究基础上，对常规次固结沉降计算公式进行了分析和改进。（4）将上述试验结果与软土地基预压工程实践综合分析研究，认为在地基极限承载力范围内，适当的超载预压可以使软土提前发生一部分次固结变形，工后次固结沉降会减少；采取有效的降、排水措施以快速消除土中的超静孔隙水压力，减少土体中的孔隙以降低连通率，可使次固结系数一定程度减小，也有利于控制工后次固结沉降。
[Abstract]:Shallow marine sedimentary soft soil is widely distributed in coastal areas of China, which affects engineering construction to varying degrees. Silt clay is the most common marine soft soil. Its main characteristics are high natural moisture content and porosity ratio, small degree of gravity and large plastic index. The macroscopical properties show the characteristics of low strength, small bearing capacity, low permeability, high compressibility, and obvious secondary consolidation properties. The secondary consolidation characteristics and microstructure of soft soil have important influence on its macroscopic mechanical properties. As a result, the settlement of engineering construction is too large, deformation does not meet the requirements and long-term deformation instability and so on. Based on the above situation, this paper takes the silt clay of the undisturbed sea with a depth of about 7 meters in Tianjin Binhai South Port as the test and research object, and carries out two kinds of unidirectional consolidation tests and microscopic tests, respectively, of graded loading and preconsolidation. The characteristics of secondary consolidation deformation under different loading modes are discussed, and the relationship between microscopic changes and macroscopic mechanical properties in the process of secondary consolidation is analyzed through microscopic tests. The test results are analyzed by combining with the test examples of foundation preloading engineering. Some conclusions and suggestions for soft soil engineering construction, especially foundation preloading, are obtained. The main research results of this paper are as follows:. 1) the preconsolidation pressure (PC) and the overconsolidation ratio (OCR) of the silt clay studied in this study are about 63 KPA and 1, respectively, which belong to the traditional normal consolidation soil. The results of unidirectional consolidation test show that the time of the primary and secondary consolidation boundary is about 150 ~ 200 min. The consolidation pressure p has a greater effect on the secondary consolidation characteristics than 畏. When the consolidation pressure p increases gradually from the smaller value, The secondary consolidation coefficient increases gradually, the secondary consolidation coefficient reaches the maximum when p is close to 2pc, and then decreases with the consolidation pressure p increasing, and the secondary consolidation coefficient decreases slowly after p400kPa. (2) the microstructure of the silt clay is revealed by the microstructure test, and the change of the microstructure during the secondary consolidation process is revealed, and the aging law of the main microscopic morphology parameters is obtained. The variation of secondary consolidation coefficient and compression modulus during secondary consolidation is studied. The results show that the secondary consolidation coefficient decreases and the attenuation gradually decreases with the extension of loading time at the same stress level. Based on the attenuation of secondary consolidation coefficient, the conventional formula of secondary consolidation settlement is analyzed and improved on the basis of previous studies. 4) based on the comprehensive analysis of the above test results and the practice of soft soil foundation preloading engineering, it is concluded that in the range of ultimate bearing capacity of foundation, appropriate overload preloading can make soft soil occur part of secondary consolidation deformation ahead of time, and the secondary consolidation settlement will be reduced after construction. Effective reduction and drainage measures are taken to quickly eliminate the excess pore water pressure in the soil and reduce the porosity in the soil to reduce the connectivity. The secondary consolidation coefficient can be reduced to a certain extent and the secondary consolidation settlement can be controlled.
【学位授予单位】：中国地质大学（北京）
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TU447

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