吹填软土一维固结蠕变研究

发布时间：2018-11-14 11:53

【摘要】：吹填土是一种特殊的人工土，其固结时间较长，具有十分明显的流变特性。吹填土作为地基会出现后期沉降过大，承载力不足等问题，严重的会导致地基不均匀沉降，地面开裂，建（构）筑物倾斜甚至倒塌等。学术界及工程界一直广泛关注吹填软土的长期变形问题，其中软土的固结特性和蠕变特性是导致其变形具有时效性的根本原因。故研究吹填软土的长期变形机理，探讨其固结蠕变特性，并进一步完善沉降计算模型，对建造在吹填土地基上的工程具有重要意义。目前在室内关于土体固结蠕变变形的研究大多假定其不产生侧向变形，但是对于吹填土来说，满足这一假设的区域是有限的，更多区域如大面积堆载的非中心地带，路堤等工程的非中心区域等其侧向变形常常不等于零。即使是中心区域，也不能忽视瞬时变形及其对后期变形的影响。本文针对汕头东部新溪地区吹填软土，基于室内侧限（刚性，柔性）试验，理论分析和相应的数值计算，研究了软土固结蠕变变形机理，分析了侧向变形条件对软土一维固结蠕变特性的影响。研究的主要内容以及得到的结论如下： 1.吹填软土的基本特性研究，，研究表明土层含有大量砂石贝壳等杂质，物理性质指标均为高含水率，高孔隙比，低渗透性，和低抗剪强度。土层目前仍处于欠固结土阶段，压缩性较大。 2.刚性侧限压缩试验（侧向变形等于0）结果表明，加荷比大于或等于1时土样的主次固结分界最明显，最适合用Casagrande方法确定主固结完成时间。次固结系数Ca均呈现先增大，在先期固结压力附近达到峰值后逐渐减小最后趋于稳定。土体物理参数如而含水率、孔隙比、及试验方法如加荷比等因素都会对次固结系数产生影响。另外，软土的次固结呈非线性特征，应力应变等时曲线比较符合对数函数关系。 3．柔性侧限压缩（竖向应力与水平应力之比等于常数）试验结果表明，吹填土的固结性状与上述刚性侧限相似，表明其固结机理时相同的。但试样产生了较大的瞬时变形，主固结完成的时间减少，次固结系数也相对减小。 4.基于三元件模型，建立了考虑瞬时变形的饱和土体的一维粘弹性固结方程，并推导出其相应的解析解。针对具体算例对大面积堆载的一维粘弹性固结性状进行了分析。
[Abstract]:The backfill is a special artificial soil with long consolidation time and obvious rheological properties. As a foundation, the filling soil will have some problems such as excessive settlement, insufficient bearing capacity and so on, which will lead to uneven settlement of the foundation, cracking of the ground, tilt of the building (construction) and even collapse of the building, etc. The academic and engineering circles have been paying close attention to the long-term deformation of filled soft soil, among which the consolidation and creep characteristics of soft soil are the fundamental reasons leading to the timeliness of deformation. Therefore, it is of great significance to study the long-term deformation mechanism of drilled soft soil, to discuss its consolidation and creep characteristics, and to further improve the settlement calculation model. At present, most of the researches on consolidation creep deformation of soil are based on the assumption that it does not produce lateral deformation, but the area satisfying this assumption is limited, and more areas, such as the non-central zone with large area of heaped load, are satisfied with this assumption. The lateral deformation of the non-central area of embankment is often not equal to zero. Even in the central region, the instantaneous deformation and its influence on the later deformation can not be ignored. In this paper, the mechanism of consolidation creep deformation of soft soil in Xinxi area of eastern Shantou is studied on the basis of indoor lateral limit (rigidity, flexibility) test, theoretical analysis and corresponding numerical calculation. The effects of lateral deformation conditions on one dimensional consolidation creep properties of soft soil are analyzed. The main contents and conclusions are as follows: 1. The basic characteristics of soft soil are studied. The results show that the soil layer contains a lot of impurities such as sand and stone shells, and the physical properties are high water content, high porosity, low permeability and low shear strength. The soil layer is still in the stage of underconsolidation, and its compressibility is great. 2. The results of the rigid lateral compression test (lateral deformation = 0) show that the primary and secondary consolidation boundaries of soil samples with loading ratio greater than or equal to 1 are the most obvious, and the Casagrande method is most suitable to determine the completion time of the main consolidation. The secondary consolidation coefficient (Ca) increased at first, and then decreased gradually and finally stabilized after reaching the peak near the pre-consolidation pressure. Physical parameters such as moisture content porosity ratio and test method such as loading ratio will affect the secondary consolidation coefficient. In addition, the secondary consolidation of soft soil is nonlinear, and the stress-strain isochronous curve accords with the logarithmic function. 3. The experimental results of flexible lateral compression (the ratio of vertical stress to horizontal stress is constant) show that the consolidation behavior of the filled soil is similar to that of the rigid lateral limit mentioned above, which indicates that the consolidation mechanism is the same. However, the sample has a large instantaneous deformation, the time of completion of the main consolidation is reduced, and the secondary consolidation coefficient is also relatively reduced. 4. Based on the three-element model, the one-dimensional viscoelastic consolidation equation of saturated soil considering instantaneous deformation is established, and the corresponding analytical solution is derived. The one-dimensional viscoelastic consolidation behavior of large area surcharge is analyzed for a concrete example.
【学位授予单位】：暨南大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TU449;TU43

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