Stability Analysis Of The Surrounding Rock Of Underground Powerhouse Of Cihaxia Hydropower Station In The Upstream Of The Yellow River

The Cihaxia hydroelectric power station,which is the planning and construction of the largest cascade hydroelectric power station,locates in the upstream of the Yellow River Longyangxia above and elevation below 3000m in the channel segment.The traffic position is located in Qinghai province Hainan Xinghai and Tongde County at the junction of the the Cihaxia exit section,far from the Cihaxia exit upstream about 6.5km.The underground buildings are located in the left bank of Cihaxia and distributed between 2721m and 2794m elevation.In addition,the elevation of water surface in valley bottom is 2750m,valley slope top elevation 3150m,slope height of 400m and terrain relative more neat,slope 40-55 degree.The underground chambers are composed of the main powerhouse,auxiliary room,installation room,main transformer room and tailrace surge chamber,moreover,the main powerhouse size is 216m*30m*60m?length*width*height?,main transformer room dimensions:163m*20m*25m,tailrace surge chamber size for 53m*17m*73m.The lithology of surrounding rock is mainly metamorphic sandstone,and the fracture fissure is relatively developed.Under such sophisticate geological conditions,the stability of the surrounding rock of the underground cavern with large span and high side wall can be a major engineering geological problem.In this paper,based on the research of geological conditions of surrounding rock,rock mass structure characteristics and rock mass quality of the underground powerhouse area,numerical simulation?FLAC-3D?,rock analysis software and other means are adapted to analyze and elevate the overall stability of underground caverns and rocks.Eventually,the following understanding are acquired:?1?By the study of surrounding rock engineering geological conditions and rock mass structure characteristics of the underground powerhouse.The results show that the stratum in the powerhouse area is Triassic middle?T2?,lithology is primarily metamorphic sandstone splint rock,cracks are fully developed,rock mass structure is mainly thin to inter bedded.?2?According to a variety of methods to be comprehensive evaluation of classification of the powerhouse area of surrounding rock,the results showed that the powerhouse area of surrounding rock is mainly III₁ types,class II has a certain distribution,class IV and III₂ kind of rock mass distribution is less,which accounted for 60.87%of the class III₁.?3?By the results of field investigation,firstly,the possible failure mode of the exploration adit and the future cavern group have a total of four kinds,respectively is?1?destruction of wedge blocks formed by cross cutting of hard structural plane;?2?destruction of FC dense zone broken rock mass in the interlayer shear zone;?3?Crumpled broken slate or peeling off block occurred;?4?Block instability in the formation of specific boundary between fault and bedding or interlayer shear zone.Then,the stability analysis using block calculation program of cavern in different tectonic positions potential block body,it can be seen that the unstable block number are the main powerhouse in 23 blocks,main transformer chamber is 13,tail gate adjustable pressure chamber into 12 blocks and block losing stability model is divided into slide,along the single plane sliding and along double sliding and stability of the four.?4?Based on geological generalization of engineering rock mass structure model,using FLAC-3D simulated after the excavation of underground cavern rock should force,surrounding rock stress,displacement,failure zone changes the whole characteristics and profile characteristics.Obtained the following understanding:?1?the original rock should force the maximum principal stress range should-17.05MPa⁰.019MPa,no tensile force;the minor principal should stress range to 0.211MPa¹3.534MPa.Some prominent ridge front appeared in the small range of tensile stress,these places in the size of the main force could local tensile failure,but the slope is stable as a whole.?2?the surrounding rock should be of maximum principal stress value between-34.77MPa 1.883MPa and local tensile force and larger stress concentration;intermediate principal stress strength values in between to1.176MPa-25.659MPa stress concentration mainly appears in the chamber end wall,the vault,camber angle,floor of;the Lord should be of strength between the-14.596MPa 1.775MPa,installed between the end wall and lower stress to the high degree of concentration;?3?displacement field overall performance for vault,floor heave,side wall restrained trend value should be the amount of force.The total displacement of the maximum value appears in the main factory room of the bottom plate,the amount of value reached about 8cm.?5?According to the Flac-3D numerical simulation analysis the influence of the distance,the position and the strike to the surrounding rock stability of the underground cavern.Obtained the following understanding:?1?not reduce main transformer chamber and tailrace surge chamber spacing,so the original design,the net distance of 50m is reasonable;?2?from the surrounding rock stress,deformation and plastic zone comprehensive evaluation,chambers not mountain in vitro to move large distances;?3?the chamber axis and layer parallel to the strike of stability of surrounding rock of adverse,therefore,it is suggested that chamber axis and strata to intersect with large angle,to 60 degrees and is suitable for more than.