荷载与干湿循环协同下红黏土的强度特性与裂隙演化规律

Strength characteristics and fissure evolution law of red clay under the synergistic action of load and dry-wet cycle

为获取符合工程实际的设计参数,研发一种荷载与干湿循环协同作用下土的直剪试验装置与方法,采用图像处理系统,提出了考虑表面裂隙和侧面裂隙下土的裂隙率计算方法,分析了荷载与干湿循环协同作用下红黏土抗剪强度指标及裂隙演化规律,建立了抗剪强度指标与裂隙率、压实度的关系。结果表明:红黏土在荷载与干湿循环协同作用下,黏聚力随干湿循环次数增加在前3次降低显著,后趋于稳定;随上覆荷载增加先显著增加,后缓慢增加;内摩擦角随干湿循环次数和上覆荷载变化总体在10°范围内波动;表面和侧面裂隙都随着干湿循环次数的增加而不断发育,其中表面裂隙在10 kPa时裂隙宽度达到最大,且大、中裂隙发育最明显,同时侧面裂隙由环向裂隙向纵向裂隙发展;裂隙率随压实度的增大而降低,随干湿循环次数增加而增加,随上覆荷载增加先增加后降低,在上覆荷载为10 kPa时达到最大,黏聚力、内摩擦角与裂隙率、压实度的关系可以用二元非线性函数关系来拟合。此研究可为获取符合工程实际的红黏土设计参数提供参考。

In order to obtain the design parameters in line with the engineering reality,a direct shear test device and method of soil under the synergistic action of load and dry-wet cycle are developed,the fracture ratio is analyzed by using an image processing system,and a method for calculating the fracture ratio of soil under the consideration of surface fissures and lateral fissures is proposed.The shear strength index and fissure evolution law of red clay under the synergistic action of load and dry-wet cycle are examined,and the relationship between the shear strength index and the fracture ratio and compaction degree is established.The research results of red clay under the synergistic effect of load and dry-wet cycle show that:the cohesion decreases significantly with the number of wet-dry cycles in the first three times,and then stabilized,and increases significantly with the overlying load,and then increases slowly;the angle of internal friction varies with the number of wet-dry cycles and the overlying load,generally fluctuating within a range of 10°;both surface and side cracks developes with the increase of the number of wet-dry cycles,in which the surface cracks reaches the maximum width at 10 kPa,and the development of large and medium cracks is the most obvious,while the side cracks developes from annular to longitudinal cracks;the fracture ratio decreases with the increase of compaction,increases with the increase of the number of wet-dry cycles,increases and then decreases with the increase of the overlying load,and reaches the maximum at the overlying load of 10 kPa.The relationship between cohesion,internal friction angle and fracture ratio and compaction can be fitted by the relationship of binary nonlinear function.The research in this paper can provide a reference for red clay for practical engineering design and construction.