清江隔河岩水利枢纽两岸坝肩施工期位移监测

Dam abutments displacement monitoring at Geheyan project during construction

清江隔河岩水利枢纽大坝采用下拱上重的型式,与岸坡相接的重力拱坝,重力坝段基础采用台阶式边坡,拱坝基础采用连续边坡,边坡最大高度达180余米。大坝基础主要为石龙洞灰岩,虽强度高,但岩层为软硬相间,且有断层、裂隙、夹层将岩体分割,破坏了它的整体性。边坡岩体失稳的主要形式是沿断层、裂隙及软弱结构面发生剪切位移,施工期间使用钻孔倾斜仪对两岸坝肩开挖边坡稳定性开展了监测工作,监测重点放在爆破振动、卸荷以及各种因素的综合作用下,断层、裂隙、软弱结构面及由它们切割组成的楔形体的稳定性。通过对监测成果的整理分析,说明施工过程中引起边坡岩体位移的主要原因是爆破振动与应力松驰。位移的主要部位是岩体软弱结构面。只要严格控制开挖过程中的爆破振动,且没有不利于稳定的软弱结构面,施工中采用1∶0.3的边坡基本上是稳定的。

Geheyan dam is made up of lower part of arch type and upper part of gravity type.Stepped rock slopes were excavated for foundation of gravity dam sections adjoining both banks,and single line rock slopes for the foundation of arch dam,the maximum height of slope is of more than 180 m.The foundation rock mainly consists of limestone.Although the strength of intact material is high,there are many faults,fissures and weak intercalation layers in rock mass.Potential shear failure of rock slope may take place on discontinuity planes.Displacement monitoring has been carried out during construe- tion on cut slopes by inclinometers installed in drill holes;and the emphasis of observation was put at displacements,caused by blasting,unloading and other effects.of faults,fissures,weak planes and wedges enclosed by them.Observed results during construction indicates that displacements of cut slope were chiefly caused by blastings and stress relief,and these displacements mainly occurred on weak planes.From our experience,if no unfavourable discontinuity plane exists in the rock slope,and blast- ing is strictly controlled during excavation,cut slope of 1:0.3 may be stable.