摘 要

土体的干燥开裂产生的问题涉及到多个领域，对此进行研究有一定必要。本文通过室内试验，针对武汉某基坑项目取得的黏性土进行研究，主要研究了饱和软土的表面形状对干缩裂缝的发生和发展的影响，所得结果对于研究土体的开裂机制具有一定价值。

当土体厚薄不均匀时，在水分蒸发速率相同的情况下，表层土体会首先收缩，相同厚度中的土体收缩量相同而土体表面形状不同，土体开裂的形态定然会发生变化。

因此本文通过将试样表面处理为倾斜、圆环状、球面凹陷、球面凸起四种形状，具体研究这四种表面形状对土体干燥收缩的影响。

实验通过统计获得的裂缝图案中表面裂缝节点个数、块区个数、裂缝长度、裂缝长度、裂缝宽度等数据对干缩裂缝表面的结构特征进行描述和定量分析，得出：当外界条件不变时，黏土内同一厚度的水分蒸发速率相同，而土体各部位厚度不均，这就让土体中的收缩应力会在某些薄弱的部位集中，使裂纹的产生具有一定的规律性。因此土体表面形状变化越剧烈，土体开裂程度越高。然而土体表面过于破碎时，土体中的缺陷和土体径向和环向裂纹的开裂顺序会对开裂的程度有一定的影响。在理想的条件下，土体的最终开裂图案倾向于最省能量的六边形。

本文的特色：在国内外的很多研究中，主要研究的是外界条件对土体干缩龟裂的影响,或针对集中不同的土体，研究其在相同外界条件下的干缩裂缝的区别，对于土体表面形状对干缩裂纹的影响的研究几乎没有。因此，本文的研究可以对土壤干裂的研究有一定的填补，相关结果对于更好的了解土体的开裂机制具有一定意义。同时，本文针对武汉地区的黏土进行研究，研究成果具有针对性。

关键词：黏性土；裂缝；表面形状；蒸发速率

Abstract

The problem of soil desiccation cracking involves many fields, so it is necessary to study it. In this paper, the clay obtained from a foundation pit project in Wuhan has been studied by laboratory tests. The effects of the surface shape of saturated soft soil on the occurrence and development of dry shrinkage cracks were studied. The results are valuable for studying the cracking mechanism of soil.

When the soil thickness is not uniform, in the case of the same evaporation rate of water, the surface soil will first shrink the same thickness of the soil in the same amount of shrinkage and soil surface shape is different, the soil will certainly change the shape of the crack.

Therefore, the effect of the four surface shapes on the drying and contraction of the soil is studied by using the four surfaces of the specimen to be inclined, circular, spherical concave surface, and convex spherical surface.

The structural characteristics of the surface of the dry shrinkage cracks are described and quantitatively analyzed by the data such as the number of surface crack nodes, the number of blocks, the length of cracks, the length of cracks and the width of cracks in the fractured patterns. The results show that when the external conditions are not at the same time, the evaporation rate of the same thickness in the clay is the same, and the thickness of each part of the soil is not uniform, which makes the shrinkage stress in the soil concentrated in some weak parts, so that the crack has certain regularity. So the soil surface shape changes more intense, the higher the degree of soil cracking. However, when the surface of the soil is too broken, the defects in the soil and the radial and circumferential crack initiation of the soil will have a certain influence on the degree of cracking. Under ideal conditions, the final crack pattern of the soil tends to be the most energy-efficient hexagon.

The characteristics of this paper: in many studies at home and abroad, the main study is the external conditions on the soil shrinkage of the impact of shrinkage or for different concentrations of soil, to study the same external conditions in the dry shrinkage of the difference between the study of the effect of soil surface shape on dry shrinkage cracks is almost none. Therefore, the study of this paper can fill the research of soil dryness, and the relevant results have certain significance for a better understanding of soil cracking mechanism. At the same time, this article for the Wuhan area of clay research, research results are targeted.

Key words: clay; crack; surface shape; evaporation rate

目录

第1章绪论 1

第2章 材料和试验方法 4

2.1试验材料 4

2.2 实验方案 5

2.3 试验步骤 7

2.3.1预实验及在实验过程中出现的问题 7

2.3.2 正式试验 11

第3章 结果处理和分析 15

3.1 人工测量 15

3.2 数字图像处理 15

3.3 裂缝随时间的发展 18

3.4 裂缝发展规律 19

3.5 数据分析 21

第4章 结论 24

参考文献 25

致 谢 26

第1章绪论

自然界中，土在干燥环境下失水收缩会在表面产生裂纹，即龟裂。土体的龟裂在一定程度上会对土体的工程性质产生影响，如降低土的承载力。土体龟裂时也会产生一定的收缩，这些变化都可能导致各种工程问题。在农业方面，土体的裂缝会增加土体的渗透性，增加土壤中的水分增发，使土壤表层的水分加速流失，裂缝的走向和大小还会影响地表水的运移，从而影响农作物对养分的吸收。在环境岩土工程中，垃圾填埋场覆盖层中的土壤产生龟裂会导致覆盖层丧失屏蔽功能，对地下水和地质环境产生威胁。此外，土体的龟裂还是影响边坡稳定的关键因素。土体中的裂缝能给雨水的入渗提供便捷通道，加快入渗的速度，使边坡的安全系数下降，增加滑坡灾害发生的可能性。由此可见，土体的干燥收缩产生的问题涉及的领域多，范围广，对此进行研究有一定必要。

武汉市软土分布较广，土层厚度大，是软土分布最多的内陆城市^[23]。而近年来，武汉市加快了城市建设的速度，大量建筑、道路工程和地铁隧道等项目先后开始建设，基础施工中软土就成为威胁建筑基础安全的主要因素之一，因软土沉降等原因引发的地面沉降等问题常常见诸报端。而软土的开裂会对工程的安全产生很大的威胁，因此针对性地研究武汉软土的开裂机制有一定必要。