三峡库区塌岸防护方法适宜性分析

根据组成库岸的岩土类型和组合型式,将三峡库区库岸地质结构概括为岩质、土质、岩土混合三大类及若干亚类,并对各类库岸的破坏方式进行了分析与总结,认为三峡水库蓄水后,库岸的破坏形式主要表现为崩塌与滑坡。根据库岸地质结构类型、破坏方式与规模,对三峡库区库岸防护设计的适宜性进行了详细的研究,认为三峡库区库岸宜采用如下5种方案进行防护:(1)对于易风化岩质岸坡或软硬互层岩质岸坡,宜以喷锚工程为主,结合局部支撑与挖方等进行防护;(2)对于土层比较厚(≥10m),地表有明显的变形破坏迹象的岸坡;或夹软弱层的易滑顺向岩质岸坡,宜以抗滑桩工程为主,结合护坡与地表排水等进行防护;(3)对于下伏完整基岩,且土层较薄(<6m)的土质岸坡或混合型岸坡,宜以挡土墙工程为主,结合地表排水等进行防护;(4)对于土层较厚(≥6m)且坡度较缓(< 20°)的土质岸坡或混合型岸坡,宜以干砌条石护坡工程为主,结合石笼、水下抛石压脚等进行防护;(5)对于坡度较陡(>20°)、厚度较大(≥6m)的土质岸坡、或强风化的花岗岩岸坡,宜以格构锚工程为主,结合地表排水等进行防护。针对这5种防护方案,选择典型库岸段进行库岸防护设计。结果表明,采用这5种方案防护库岸1 km直接工程费用分别为:857.2万元、2246.0万元、931.5万元、625.5万元、2288.8万元。

SUITABILITY OF PREVENTION METHODS OF BANK SLOPES IN THREE-GORGE RESERVOIR

In the first part of this paper, the bank slope structures are divided into rock bank slope, soil bank slope and combination bank slope of soil and rock, and many subdivisions are based on the types and combinations of rocks and soils in the Three-Gorge Reservoir. Next, the failure models of each kind of bank slopes were analyzed and summarized, and the results showed that the major failure models are rockfalls and landslides when water level goes up and down. Then, the suitability of prevention methods of bank slopes in the Three-Gorge Reservoir was studied in detail based on the geological structure, failure model and scale of bank slopes. The results showed that 5 suitable stabilization methods of bank slopes in the Three-Gorge Reservoir are presented as follows: (1) to stabilize those rock bank slopes which are easily weathered, and to stabilize those in which competent layers alternate with incompetent layers, tieback and shotcrete + part buttressing or unloading should be taken; (2) to stabilize those soil bank slopes which are thicker than 10 m, and in which failures have already taken place; and to stabilize those rock bank slopes which exit incompetent beds and incline in the same direction as those of strata, driven piles + surface slope protection and surface drainage should be taken; (3) to stabilize those soil and combination bank slopes which are thinner than 6 m, and their base grounds are stable, retaining walls + surface drainage should be taken; (4) to stabilize those soil and combination bank slopes which are thicker than 6 m, and their gradients are less than 20°, rip-rap with cuboid stone + gabions or block stones should be taken; and (5) to stabilize those soil and strong weathered granite bank slopes which are thicker than 6 m, and their gradients are greater than 20°, grid anchorage technique + surface drainage should be taken. Finally, typical bank slopes are designed to be stabilized with the methods mentioned above. The results showed that the total costs of 1-km bank slope stabilization work are about 857. 2×104, 2246×104 , 931. 5×104 ,625. 5×104 and 2288. 8×104 yuan, respectively.