| YangFangGou hydropower station is located in Muli County of Sichuan Xichang City.The total storage capacity of the hydropower station is 512 million 480 thousand cubic meters,and the installed capacity is about 1500 MW.The hydropower station has now entered the construction phase,is expected to be completed in 2022.The dam site of the hydropower station is a typical mountain canyon,the main body of the project is located in the Yanshan granodiorite,and there is no large-scale fracture in the dam site,the degree of weathering unloading of rock mass is also not very strong.It is found that the small faults and intermittent extension joints in the dam site area are very complicated,they are very easy to form the control boundary conditions of local and even global stability.The cableway platform excavation slope as the upper level of the abutment excavation slope,its stability is directly related to the safety of the construction process and operation period of the arch abutment slope and the dam,so it is very important to study the excavation slope of the cableway platform excavation slope.In this paper,the cableway platform excavation slope at left bank of YangFangGou hydropower station is the main research object,and the slope stability is taken as the main research direction,based on the study of the rock mass structure and the development and genetic characteristics of the structural plane of the slope,the analysis of the deformation and failure mode of the slope is also included,the overall and local stability of excavation slope is evaluated.Based on the research results of this paper,it is pointed out that the stability of the excavation slope,it can be provided for the construction of the project,and it also provides the reference value for the study of the excavation slope.In this paper,the geological data of each stage of slope excavation are collected through the long-term participation in the construction site.Based on the study of the rock mass structure and deformation and failure characteristics of the excavation slope,the study on the stability of the slope is taken as the objective:(1)Based on the field investigation,combined with the previous research results,the geological environment of the study area was analyzed.(2)According to the standard,the rock mass structure of excavation slope is classified.The geological sketch map of the excavation slope in each level is as the foundation data,and through the 3D digital photography technique of 3D model of the slope,it can be used to check the basic characteristics such as the shape and length of the structure,and to classify the structural planes according to the specifications and to study their development characteristics.(3)Different methods were used to classify the dominant groups of the joints,and their distribution characteristics were studied.Among them,the primary joints are mainly distinguished by the lithological contact surface and the primary structural features of the granodiorite in the left bank underground cavern;The structural joints are mainly distinguished by the structural joints of metamorphic siltstone in the underground caverns;The secondary joints are mainly classified by the joints in the natural slope,and are classified according to the degree of weathering unloading.(4)Investigating the deformation and failure of the slope in each stage,and classifying the deformation and failure mode of the slope,at the same time,the scale,quantity and control structure of each failure mode are investigated.and the main controlling factors of deformation and failure are also analyzed.(5)On the basis of the research above,the overall and local stability of the excavation slope on the left bank is analyzed,combining with the relevant rock mass and structural surface data obtained from the experiment,the appropriate control parameters are selected,the boundary conditions and the model are established.The stability of slope under different conditions is calculated by the limit equilibrium method.The numerical simulation software FLAC3D was used to analyze the stress and strain and displacement of natural slope and excavation slope.At the same time,the deformation and displacement of different positions were analyzed by using the existing monitoring data.This paper can draw the following main research results:(1)The excavation slope outcropped lithology are granodiorite of YanShan period and most of them belong to sub block structure,within the range of small faults(level III,IV structural planes)and the joints(level V structural planes)are well developed,upstream slope development more inclined slope faults,which parallel faults F14,F16 has great influence on the slope stability,also in the local area in the slope we can see 5 to 6 small complex fault intersection,it is no good for the local stability.The most developed dominant joints in the area is in the NWW direction,and there are many groups of NNE and NEE direction steep dip joints.(2)Based on the analysis of the structural plane features of the metamorphic siltstone and granodiorite in the underground caverns of the left bank,It can be seen that most of the dominant joints of the slope are revealed by the structural transformation,the primary structural planes are less and affected by the invation of granite,and some of them are mainly located in the vertical direction of the transverse direction.The surface structural plane is mostly formed on the basis of the structural transformation plane,which is formed by the secondary action,and a few of them are formed on the basis of the original joint or by the regional landform.(3)Under the influence of the development of the structural plane,semi deterministic and random wedge blocks is formed by the combination of the steep dip joint and the fault,which is inclined to the slope.Therefore,the main deformation and failure mode of the excavation slope is the wedge sliding mode,the second is the collapse mode and the toppling deformation instability mode.Affected by the slope direction and structure,the deformation and failure of rock mass in the upper reaches of the slope are obviously higher than those in the lower reaches.(4)According to the calculation results of excavation slope stability,which meet the safety standards in the natural and seismic conditions,but in heavy rain conditions,the slip surface combination of fault F14 and F16 as potential slip surface is in the limit equilibrium state and have security risks,At the same time,the fault F14 and F16 are also easy to appear at the bottom of the slope as the bottom slip boundary of the local deterministic block,so it is necessary to strengthen the support.The excavation slope range also developed a number of semi deterministic blocks and random block,Semi deterministic blocks’ overall stability is good,only the front part blocks may collapse,the size of most of the random blocks are small and usually use the method of direct scavenging.(5)Through the FLAC3 D software modeling and analysis,the maximum and minimum principal stress in the excavation slope was compressive stress,the maximum value is located inside of the slope,and has a range of of 0 ~ 6MPa,the minimum value is at the trailing edge and the front of cable machine platform,in the range of 0 ~ 1MPa,at the same time,the local tension stress is generated in the road and cable machine platform,the range value is 0 ~ 0.3MPa.The maximum displacement of the slope is in the range of 14 ~ 26 mm,displacement changes are mainly concentrated in the front edge of the cable machine platform,it is easy to form local deformation and failure.According to the existing monitoring data,we can see that the permanent monitoring point displacement is less than 0.3mm,and the temporary monitoring point displacement is less than 5mm.According to the main research results are analyzed and summarized,the whole slope is stable under natural and seismic conditions,but in heavy rain conditions,by the effect of F16 fault F14,the slope is in limit state,there are security risks,at the same time affected by F14,F16,F107,the local block also has security risks,they will directly affect the progress of the follow-up project,this conclusion is consistent with other geological engineers’ opinions.After these faults were be founded,the subsequent construction excavation work was suspended,and the corresponding reinforcement measures are taken for the above faults.Affected by the progress of construction,only a small number of monitoring devices are installed in the excavation slope,so the research on the development trend of slope deformation and failure after excavation is still lack of relevant data.At present,the cableway platform excavation slope at left bank is the only excavation slope in YangFangGou hydropower station that has been completed,in the future,the study on the stability of the slope will be more important because of the influence of the excavation depth,the scale and the complexity of the excavation.The research team led by the instructor will continue to carry out a systematic study on the excavation slope of the dam abutment. |
PDF Full Text Request