某水电站洼里滑坡的成因机制及其稳定性研究
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摘要
滑坡发生于拟建的水文站坝址I勘探线下游约300m的左岸陡倾顺向坡(倾角85～87°)中。据平硐揭露,坡体主要由薄层(单层厚2～3cm)泥质板岩组成。岩层倾倒变形极为强烈,由硐口至硐底(220m)岩层均呈反倾坡内,且倾角随硐深增加呈明显增大趋势,即16～55°。沿硐不时可见因岩层弯曲而形成的楔形张裂缝(隙),倾倒变形的范围(平硐水平深度)达220m以上。洼里滑坡正是在上述的弯曲一拉裂变形基础上发展而成的大规模滑坡。即谷坡岩体在重力作用下,向临空方向作悬臂梁弯曲,并逐渐向坡内发展。弯曲的板梁之间互相错动并伴有拉裂,弯曲后缘出现拉裂缝。由于岩层薄而相对较软,其弯曲角度很大,在岩层最大弯曲部位出现与层面垂直的楔形拉裂缝(隙)。随着河谷强烈下切及江水对凹岸的冲刷,上述倾倒一拉裂变形则进一步加剧,一旦各层最大弯曲部位的缓倾坡外楔形拉裂隙(缝)相互贯通,形成统一的滑动面(带),就容易发生大规模的滑坡;通过用简化毕肖普法对该滑坡进行了稳定性计算,结果表明:只有在蓄水位达到1800m高程时或在此种情况下遇到Ⅶ度地震,滑坡体有可能局部发生失稳。而在其它工程情况下,滑坡体处于稳定状态。
The landslide lies at steep consequent sloping ground whose slope angle is 85～87° in the left bank about 300?m near lower reach in Dahewan hydrologic station Ⅰ exploratory line.The exploration tunnel shows that the slope is mostly made of thin-layer argillites whose thickness of each layer is 2～3?cm.Rock stratum tipping deformations which are counter-inclined in the whole tunnel are very strong.The more going into the inner of the tunnel,the steeper the angle is becoming,that is,the angle is from 16° to 55°.There are a lot of wedge-shape separation fractures in the tunnel and their deformation length is more than 220?m.On the basis of the bent-fracture,the Wali landslide developed into a large scale slope,that is,under the gravity action,each strata becomes bent like a cantilever beam,in the back of which there were fractures when the bent cantilever beams slid outside the slope.There were wedge-shape separation fractures which are perpendicular to the rock stratum in the maximum bending angle because the rock stratum are thin and relatively soft and bending angles are large.With the strongly down-cutting river valley and river water washing concave bank,the bent-fracture deformations are stronger,then they became a fracture(or a belt) when they were combined at the maximum bent part,finally the slope was formed.The calculating data of stability by using Bishop method indicates that only when the water level reaches 1800?m or there is a Ⅶ intensity degree earthquake,the slope may partly slide down, and it is safe under the natural conditions.
The landslide lies at steep consequent sloping ground whose slope angle is 85～87° in the left bank about 300?m near lower reach in Dahewan hydrologic station Ⅰ exploratory line.The exploration tunnel shows that the slope is mostly made of thin-layer argillites whose thickness of each layer is 2～3?cm.Rock stratum tipping deformations which are counter-inclined in the whole tunnel are very strong.The more going into the inner of the tunnel,the steeper the angle is becoming,that is,the angle is from 16° to 55°.There are a lot of wedge-shape separation fractures in the tunnel and their deformation length is more than 220?m.On the basis of the bent-fracture,the Wali landslide developed into a large scale slope,that is,under the gravity action,each strata becomes bent like a cantilever beam,in the back of which there were fractures when the bent cantilever beams slid outside the slope.There were wedge-shape separation fractures which are perpendicular to the rock stratum in the maximum bending angle because the rock stratum are thin and relatively soft and bending angles are large.With the strongly down-cutting river valley and river water washing concave bank,the bent-fracture deformations are stronger,then they became a fracture(or a belt) when they were combined at the maximum bent part,finally the slope was formed.The calculating data of stability by using Bishop method indicates that only when the water level reaches 1800?m or there is a Ⅶ intensity degree earthquake,the slope may partly slide down, and it is safe under the natural conditions.
引文
[1] 张倬元,王士天,王兰生,等.工程地质分析原理(第2版)[M].北京:地质出版社,1994.134-137,321-338.
[2] 王士天,黄润秋,李渝生,等.雅砻江锦屏水电站重大工程地质问题研究[M].成都:成都科技大学出版社,1998.168-180.
[2] 王士天,黄润秋,李渝生,等.雅砻江锦屏水电站重大工程地质问题研究[M].成都:成都科技大学出版社,1998.168-180.
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