Study On Slope Stability And Supporting Measures Of The Material Yard Of Yangfanggou Hydropower Station

Yangfanggou Hydropower Station is located in Muli County,Liangshan Yi Autonomous Prefecture,Sichuan Province.It is the fifth stage of the development of one reservoir and six reservoirs in the middle reaches of Yalong River(Lianghekou-Jiangkou section).The hydropower station has entered the construction stage and is scheduled to be completed by 2022.Stone yard is located in the upper reaches of the left bank of Yalong River,about 1.5 km away from the upper dam site.At present,the slope of the material yard has entered the construction stage.The slope has the characteristics of large excavation volume,steep slope,high height,many free faces and the development of weak structural planes.Rapid excavation of the slope will inevitably lead to stress redistribution in the slope and unloading deformation.Once the material yard produces large-scale landslides,it will be dangerous.And the safety of downstream dams.At present,the slope of material yard is in the early stage of excavation,and the geological data are relatively few.The stability of slope excavation is a major geological engineering problem in the process of slope excavation.Therefore,before excavation,it is of great significance for Yangfanggou Hydropower Station to study the deformation and failure mechanism and stability of the slope to ensure the safety of the slope excavation and the rationality,economy and effectiveness of the supporting measures.In this paper,the stability of the slope of the material yard is analyzed by means of the investigation of the engineering geological conditions of the slope,the analysis of the structural characteristics of the rock mass,the analysis of the development characteristics of the structural plane and the classification of the rock mass quality.On the basis of the stability analysis,the corresponding supporting measures are studied.Through long-term stationed in Yangfanggou hydropower station site,geological sketch of excavated slope of material yard is made in time,and then the obtained data are sorted out indoors.The whole process is aimed at the study of slope stability and supporting measures.The specific contents and research methods are as follows:(1)Combining the field investigation data of the hydropower station and the data of the present experiment in East China Hospital,the geological background of the material site is analyzed.(2)According to the relevant specifications and the data collected in the field,the rock masses in the study area are classified,the structural planes are classified,and their development characteristics are studied respectively.(3)The factors causing the deformation and failure of the material yard slope are analyzed.On this basis,the deformation and failure mode of the slope in the study area is studied.(4)The stability of side slope is analyzed by UDEC/3DEC numerical simulation software.On the basis of stability analysis,the supporting scheme is put forward,and the supporting effect is analyzed by UDEC.Finally,the field monitoring data and numerical simulation results are compared and analyzed.Through the above research,the main results are as follows:(1)According to the field geological survey of the slope of the material yard,it is found that the main structural planes of the slope are small faults and joints with medium and steep dip angles,the main structural planes of the rock mass are massive to sub-massive,the second is mosaic structure,and the main types of rock mass are II and III.(2)The main failure modes of slope rock mass in material yard are plane failure and tine failure.In the unloading weathered zone outside the slope opening line,cutting with the dominant joint fissures can form potential unstable blocks with different scales.The main potential failure modes are plane failure,multiple dominant structural planes are developed in engineering slope and engineering slope.During excavation,wedge-shaped blocks with different scales can be formed locally on the excavated slope due to combined cutting of dominant structural planes.Under the influence of excavation and blasting disturbance,unloading of shallow rock mass is relaxed and the strength of structural planes is reduced,and there is a widespread phenomenon of wedge failure.(3)Through UDEC two-dimensional numerical simulation analysis of three sections of material yard slope,it can be concluded that:(1)The stress field of the whole slope shows typical characteristics of Valley stress distribution.The maximum principal stress of the excavation surface of the engineering slope is generally within 8 MPa,and the minimum principal stress is generally within 3 MPa.The overall stress level of the slope is good,and there is basically no rock burst risk.(2)The overall deformation of the slope can reach 5-7 cm,and the unloading rebound deformation of some excavation faces is more prominent.Effective blasting control technology is needed to minimize the impact of excavation disturbance on the rock mass of the slope.(3)The overall stability of the slope in the natural state of the material yard project is good,but after the excavation of the slope(without support),some sections are in the ultimate equilibrium and basic stable state under the rainstorm and earthquake conditions,and the safety margin of the slope is insufficient,which can not meet the requirements of the code.On the steep cliffs outside the opening line,the working conditions of natural slope are basically stable-stable,the coefficient of slope excavation under rainstorm condition is 1,which is in the limit equilibrium state,and the safety factor of seismic condition is 0.97,which is in the unstable state.Comprehensive analysis shows that the overall stability of the engineering slope is good,but the safety margin is insufficient,and the stability of the cliff outside the opening line is poor.(4)Considering that the slope of material yard has three-dimensional effect from the slope topography,geological structure,excavation shape and other angles,the 3DEC three-dimensional numerical analysis of the slope is further carried out.As a comparison,continuation and deepening of UDEC's two-dimensional analysis work,it is found that the three-dimensional numerical results are basically consistent with the two-dimensional analysis results.The potential failure mode of the cliff is still block sliding failure,and the stability is poor.The engineering slope has a certain overall stability.(5)In view of the different stability characteristics of the slope and the cliff area outside the opening line of the material yard project,the supporting measures of the slope and the cliff area of the material yard project are studied in this paper.(1)three rows of 2000 KN system pre-stressed anchor cables are adopted to reinforce the cliff.It is found that the stability of the cliff is not greatly improved and the safety factor can not meet the requirements of the code.After the reinforcement measures of excavating part of unstable block + 3 rows of 2000 KN system prestressing anchor cable are adopted,the safety factor of rainstorm condition and earthquake condition is 1.22 and 1.17 respectively.It is found that the slope cutting has obvious effect on the stability of steep cliffs.(2)According to the characteristics of the overall stability of the slope of the material yard project,the stability of each section of the slope has been greatly improved and the overall deformation of the slope has been effectively controlled by adopting zonal support measures according to different lithological conditions.The support effect is better from the original 6-7 cm to 1-2 cm.(6)The comparison of monitoring data analysis results and numerical simulation results shows that it is more appropriate to analyze the excavation response characteristics and overall stability of rock slope in Jinbo Stone Material Field by combining the two-dimensional/three-dimensional discrete element method and strength reduction method,which can reflect the potential deformation and failure mechanism and stability characteristics of the slope,and the supporting effect of the slope in the material field is better.