摘 要

土体表面和内部形成大量龟裂裂缝的现象屡见不鲜，尤其在黏性膨胀土中，龟裂的产生更为频繁。土体的龟裂会很大程度的改变土体的各种性质，诱导产生工程问题。本文针对武汉地区黏土开裂情况做了深入研究，主要探究颗粒孔隙尺寸对其裂缝发展规律，裂缝分布规律，以及黏土开裂的开裂率、缝隙形态、速率等的影响。对多种孔隙尺寸组合所制成的土样开裂情况种情况进行了比较研究，得到了一些有意义的结果和结论。

针对孔隙尺寸，本文具体研究了0.075mm以下粒径、0.075mm~0.25mm粒径、0.25~0.5mm粒径的单一粒径和混合粒径土样，将土体混合搅拌均匀，并排除土体中气泡，利用改变土体材料的粒径来改变其孔隙尺寸。粒径大的孔隙尺寸大，粒径小的孔隙尺寸小。

研究发现：土体首先从试样有缺陷处（如气泡，孔洞，沟壑）开裂，首先边缘收缩；黏性膨胀土开裂裂缝夹角以90°为主，其余多数为60°和120°；裂缝平均长度均为20mm左右；收缩率最大的土样为0.075mm 0.25~0.5mm粒径的土样，收缩率达到了12.88%，开裂形态最好的为 0.075mm以下 0.075~0.25mm粒径的土样。

结论：黏土开裂主要受外部因素和内部因素共同作用，产生及发展过程极其复杂，当由于干缩产生的拉力大于其内部的抗拉强度时即会产生开裂；开裂形态与孔隙尺寸无明显相关性；裂缝的总长度、裂缝条数、节点个数之间有明显的相关性，而表面干缩率与上述参数无关联性；0~0.5mm粒径土样中存在最优开裂孔隙尺寸和最优干缩孔隙尺寸；平均长度与颗粒粒径无明显的相关性。

本文的特色：国内外相关研究主要研究的是材料、外界因素的影响如：干燥速率、干湿循环次数、温度与湿度等，另外还有开裂过程的分析和数值模拟与计算，而并未涉及孔隙尺寸对于干燥开裂的影响。此外，不同地区的土样性质并不相同，考虑武汉地区土质条件，针对本地土样开展深入研究十分必要。

关键词：黏土；开裂；粒径；孔隙尺寸

Abstract

The phenomenon of cracks in the soil surface and inside is very common, especially in viscous expansive soils, the occurrence of cracks is more frequent. Soil cracks will greatly change the properties of the soil, induced engineering problems. In this paper, the cracking of clay in Wuhan area is studied deeply，including development law, distribution, and the influence of pore size on cracking rate, gap shape and rate of clay cracking is mainly discussed. The samples of different pore size are compared, and the results are important for further studies of clay cracking.

In this paper, the particle size of 0.075mm or less, 0.075mm ~ 0.25mm and 0.25 ~ 0.5mm are studied, which include the single particle size and mixed particle size. The method that change the particle size of soil material is used to change its pore size, at the same time to exclude the impact of the original bubble in the soil. The method means the simple of large particle size has large pore size, and the same as small size. Mix the soil evenly in the experiment, to ensure that the pore size uniform.

The discoveries: toil crack from the defective of samples (such as bubbles, holes, gully) firstly, and shrink from the edge of samples; the angle of the clay cracks are dominantly 90 °, and the remaining majority are 60 ° and 120 °; the average length of fractures are all about 20mm; the soil samples with the largest shrinkage rate are 0.075mm 0.25 ~ 0.5mm particle size, and the shrinkage rate reached 12.88%,; the sample of 0.075mm or less 0.075 ~ 0.25mm particle size has the best cracking pattern.

The conclusions: clay cracking is mainly restricted by external factors and internal factors, and the process of production and development is extremely complicated. When the tensile strength is greater than the tensile strength of the internal shrinkage, the clay will crack; there are significant relevance between the total length of cracks, the number of cracks, and the number of nodes, but the surface shrinkage is not related; there is a best shrinkage pore size exists in 0~0.5mm soil particle size, as well a best cracking pore size is exist; the average length of fractures has no obvious correlation with the particle size.

Article features: the main research at home and abroad is the study of materials or external factors, such as drying rate, wet and dry cycles, temperature and humidity, etc. Analysis and numerical simulation and calculation of cracking process as well. But they do not involve the effect of particle gradation on dry cracking. In addition, the characteristic of soil samples in different regions is not the same, considering the soil conditions in Wuhan, local soil samples for in-depth study is necessary

Key Words：clay；cracking；particle size；pore size

目 录

第1章 绪论 3

1.1 研究背景 3

1.2 研究意义及目的 3

1.3 国内外研究现状 4

1.4 预期目标 5

第2章 土样试验 6

2.1 实验材料 6

2.2 实验仪器 6

2.3 实验过程 6

2.3.1 碎土与筛土 6

2.3.2 土的液限测量 7

2.3.3 模具制作 8

2.3.4 预实验 8

2.3.5 正式实验 10

第3章 实验结果 12

3.1 手工测量 13

3.2 图像处理 13

3.3 量度指标 15

3.4 实验异常 17

第4章 实验结果分析 18

4.1 裂缝发展规律 18

4.2 裂缝分布规律 19

4.3 孔隙尺寸影响规律 20

4.4 龟裂成因分析 26

第5章 结论 27

参考文献 28

致谢 29

第1章 绪论

·1.1 研究背景

自然条件下，土体表面和内部常常会形成大量的干缩裂隙，尤其在黏性膨胀土中，这种现象产生的更为频繁。土体的龟裂会很大程度的改变土体的各种性质，诱导产生工程问题。

如 1978 年和 1988 年—1992 年，中国南阳地区和欧洲地区分别出现大规模房屋建筑开裂破坏，根本原因在于持续干旱导致地基土发生严重收缩^[6]。变形龟裂的出现会成倍增加土体的渗透性，对一些水利结构物产生负面影响。如我国2007年重庆地区遭遇的重大旱情使1200多座水库大坝严重开裂，直接面临大幅降水的威胁和蓄水的考验；美国Stockton和Wister大坝因龟裂诱发管涌而最终垮塌；1989一1993年匈牙利境内数百公里防洪大堤因龟裂其整体稳定性显著降低，并出现险情^[10]。此外，龟裂是影响土质边坡稳定性的关键因素^[9]。龟裂会破坏土体的完整性，弱化土体结构，同时为雨水入渗提供便利条件，并使土体抗剪强度和边坡的安全系数大幅下降，诱导滑坡和泥石流灾害的发生。龟裂还会增加土体的风化程度，加重坡面水土流失，破坏生态环境^[13]。在农业方面，龟裂亦有显著影响，会破坏作物的根系，增加土壤水分的蒸发速率，龟裂网络的形状和尺寸会改变水的径流以及土壤中溶质的迁移规律，从而影响农作物对养分的吸收和最终产量 ^[2]。由此可见，土体干缩裂隙的影响范围极其广泛，涉及土木、地质、农业、环境工程等众多学科领域，关系国计民生。在全球气候变化的大背景下，近年来极端干旱性气候频发，土体干缩开裂问题引起了越来越多学者的关注。

·1.2 研究意义及目的