河谷下切过程中岸坡不对称卸荷机理

岸坡异常卸荷是西南深切河谷地区大规模水电工程建设过程中常遇到的典型问题之一,经现场平硐调查发现,拟建澜沧江上游河段的第四级水电站上、中坝址左右两岸均存在不对称卸荷现象,即右岸卸荷深度明显大于左岸,根据坝址工程地质条件建立了河谷下切二维离散元模型,并模拟了河谷下切过程中岸坡的卸荷过程。结果表明,左右岸坡不同的坡体结构和岩性组合是导致不对称卸荷的控制性因素,上、中坝址右岸均发生压缩—倾倒变形,韧性剪切带在坡体分布位置的不同,产生不同程度的软弱基座效应,也会导致卸荷深度不同。

Asymmetric Unloading Mechanism of Bank Slope during Valley Trenching

The abnormal slope unloading is one of the typical engineering problems that were encountered in the large-scale hydropower project construction process in southwest deep valley area. By adit investigation at site, it is found that the asymmetric unloading occurs at both the left and right banks of the middle dam site and the fourth hydropower station in the upper reaches of Langcanjiang River. The unloading depth of the right bank is obviously larger than that of the left bank. Two-dimensional discrete element model of valley undercut was established according to the engineering geological conditions of the dam site. The unloading process of the bank slope was simulated during the valley trenching. The results show that different slope structure and lithologic combination of the left and right bank slopes are the controlling factors that lead to asymmetric unloading. Compression toppling deformation occurred on the right bank of the upper and middle dam sites. The different distribution positions of ductile shear zones in the slope can cause different degrees of weak base effect that leads to different unloading depth.