| 干湿交替下膨胀土裂隙演化与强度衰减规律试验研究 |
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| 引用本文： | 汪时机,杨振北,李贤,骆赵刚,许冲,李达.干湿交替下膨胀土裂隙演化与强度衰减规律试验研究[J].农业工程学报,2021,37(5):113-122. |
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| 作者姓名： | 汪时机 杨振北 李贤 骆赵刚 许冲 李达 |
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| 作者单位： | 1. 西南大学工程技术学院，重庆 400715; 2. 长江师范学院重庆市建筑物全生命周期健康检测与灾害防治工程研究中心，重庆 408100; |
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| 基金项目： | 国家自然科学基金项目（11972311，11572262）；中央高校基本业务费专项资金（XDJK2018AB003） |
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| 摘 要： | 为揭示干湿循环效应下膨胀土胀缩裂隙的演化特征及土体结构强度的劣化规律,对合肥弱膨胀土试样开展不同循环幅度下的干湿循环试验,利用图像处理技术从试样表面裂隙图像中提取出裂隙参数,并进行低应力下的抗剪强度试验。试验结果表明:1)裂隙开展分为裂隙酝酿期、裂隙快速传播期和裂隙平稳发展期3个阶段,裂隙指标的增长主要集中在裂隙快速传播期,且循环幅度的增大会使土体的开裂程度加剧;2)在干湿循环作用下,膨胀土的内摩擦角变化幅度小于2.2°,其受干湿循环次数的影响很小,土体的强度衰减主要源于粘聚力的大幅降低。膨胀土的粘聚力呈现出先快后缓的衰减趋势,其中前4次干湿循环期间粘聚力的衰减率达到50.97%～66.92%,且衰减率也与干湿循环幅度的大小密切相关;3)通过灰色关联度分析发现,粘聚力的衰减与裂隙面积率、裂隙总长度、裂隙平均宽度的变化趋势具有明显的关联性,其中裂隙面积率的关联度最大,其与粘聚力衰减率间的关联度为0.785～0.832,相应的权重达到0.461～0.472,且裂隙面积率与粘聚力衰减率间具有较好的线性关系,而裂隙平均宽度的关联度最小,其与粘聚力衰减率间的关联度为0.392～0.414,对应的权重仅为0.228～0.240。研究成果可为进一步揭示剧烈温湿变化诱发的膨胀土边坡灾变机理提供重要依据。
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| 关 键 词： | 裂隙 抗剪强度 干湿循环 膨胀土 灰色关联分析 |
| 收稿时间： | 2021/11/17 0:00:00 |
| 修稿时间： | 2021/2/20 0:00:00 |
Experimental study on crack evolution and strength attenuation of expansive soil under wetting-drying cycles |
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| Wang Shiji,Yang Zhenbei,Li Xian,Luo Zhaogang,Xu Chong,Li Da.Experimental study on crack evolution and strength attenuation of expansive soil under wetting-drying cycles[J].Transactions of the Chinese Society of Agricultural Engineering,2021,37(5):113-122. |
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| Authors: | Wang Shiji Yang Zhenbei Li Xian Luo Zhaogang Xu Chong Li Da |
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| Institution: | 1. College of Engineering and Technology, Southwest University, Chongqing 400715, China; 2. Chongqing Engineering Research Center for Structure Full-Life-Cycle Health Detection and Disaster Prevention, Yangtze Normal University, Chongqing 408100, China; |
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| Abstract: | Expansive soil is characterized by high dilatability and low permeability, particularly sensitive to the change of external environment, due mainly to the fact that this kind of high plastic clay is rich in hydrophilic clay minerals. Crack initiation and expansion often occur, as a result of repeatedly uneven dilatancy and shrinkage of soil after rainfall and evaporation under the exposure of rain and sunshine. The crisscrossing network of cracks has harmed the integrity of soil structure. Infiltration of surface water via crack channels has caused a great threat to the anti-seepage barrier facilities, such as earth or rock dams, river reservoirs, and channels. Especially in the frequent occurrence of the rainy season, the rainwater can easily infiltrate through cracks, resulting in the softening of internal soil and the sharp decline in shear strength. As such, it is very easy to induce instability and collapse of a shallow layer of expansive soil slope, leading to the destruction of irrigation and water conservancy facilities, even aggravation of floods and droughts to the whole ecological environment. Therefore, the soil strength degradation in the cycling load of dry and wet has become an important factor endangering the long-term stability of expansive soil engineering in an extremely seasonal climate. This study aims to reveal the evolution characteristics of expansion and shrinkage cracks in the expansive soil under the dry and wet circulation, and thereby determine the perturbation of soil structure strength. The dry and wet circulation tests were carried out on the weak expansive soil sampled from Hefei, Anhui Province, China. The crack parameters were extracted from the crack images of soil samples by image processing technology. The shear strength test was carried out under low stress. The experiment results show that: 1) There were three stages: the gestation, the rapid development, and the stable development of cracks. The growth of the crack index focused mainly on the rapid development of cracks. 2) Under the action of wetting and drying cycles, the variation in the internal friction angle of the expansive soil was less than 2.2°, indicating little influence from the number of wetting and drying cycles. The decrease of soil strength was due mainly to the decrease of cohesive force. The cohesion of expansive soil decreased rapidly at first and then slowly, where the attenuation rate of cohesion during the first four dry-wet cycles was 50.97%-66.92%. The attenuation rate was also related to the amplitude of dry-wet cycles. 3) In grey correlation analysis, there were obvious correlations between the attenuation of cohesive force and the crack area ratio, the total length, and the average width of the crack trend. Specifically, the maximum correlation between the crack area ratio and the attenuation of cohesive force was 0.785-0.832 with the weights of 0.461-0.472, indicating a good linear relationship. The minimum correlation between the attenuation of cohesive force and the average width of crack was 0.392-0.414, where the weight was only 0.228-0.240. The findings can provide an insightful theoretical basis to further reveal the catastrophic mechanism of expansive soil slope induced by a drastic change in temperature and humidity. |
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| Keywords: | cracks shear strength wetting-drying cycles expansive soil grey correlation analysis |
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