膨胀土边坡长期强度变形特性和稳定性研究

调查表明,许多经计算分析认为稳定的新开挖膨胀土边坡随着时间的推移发生了失稳破坏,笔者利用离心模型试验针对这一问题开展了较为深入的试验研究。结果发现,干湿循环是导致这一问题产生的根本原因。干湿循环使得膨胀土边坡产生裂缝,随着干湿循环次数的增加,裂缝逐渐变宽变深。裂缝的存在不仅削弱了膨胀土边坡土体的结构,而且为水的入渗提供了通道,从而使土体软化,强度降低。每次干湿循环,膨胀土边坡均累积了向坡下的沉降和水平位移,随着干湿循环的次数的增加,不论边坡土体密度高低,最终都将导致膨胀土边坡的渐进破坏。室内三轴试验由于不能模拟干湿循环作用下膨胀土边坡裂缝的产生和发展过程以及水的入渗对其强度和变形特性的影响,因此,其得出的强度和变形指标直接应用于膨胀土边坡的变形和稳定分析是不合适的。防止膨胀土边坡发生破坏的最关键的措施是尽可能隔断其与外界的水分交换,如不能隔断其与外界的水分交换,也应采取合适的排水措施,以尽可能防膨胀土边坡充分湿化。

Researches on long-term strength deformation characteristics and stability of expansive soil slopes

Investigation shows that many newly excavated expansive soil slopes considered to be stable in computational analysis become unstable and damaged. A detailed research on this problem was carried out by use of a geo-centrifuge model. Test results indicated that the dry-wet cycling was the main factor of the problem. The dry-wet cycling led to cracks in the slopes. With the increase of the times of the dry-wet cycling, the width and the depth of the crack got larger and deeper. The crack not only weakened the soil structure of the slope, but also provided passage for water penetration, which further led to soil softening and strength decrease. Each dry-wet cycling resulted in the accumulation of the downward settlement and horizontal displacement of the slopes. With the increase of times of the dry-wet cycling, the expansive soil slopes became gradually damaged no matter what soil density was. Since the triaxial tests in the lab can not simulate the formation and process of the cracking and the water penetration process in the expansive soil, it is not proper to directly use the strength and deformation data obtained from the triaxial tests for the analysis of the deformation and stability of the expansive soil slopes. The key measure to prevent the damage of the expansive soil slopes is to stop the water exchange with the outside. If water exchange could not be stopped, some drainage measures should be taken to prevent the wetting of the slopes.