Study On Stability Of Large Unstable Rock Mass On Left Dam Abutment Of Tibet Jiexu Hydropower Station

In the vast southwest mountainous region of China,mountains and mountains,sparsely populated,but also rich in resources,often the construction of major national people's livelihood projects,Tibet Jiexu Hydropower Station station is such a project.The construction of hydropower stations is often accompanied by the occurrence of dangerous geological disasters,which greatly hinders the progress of project construction and brings many losses to the country and the people.There is a very large-scale unstable rock mass?hereinafter referred to as The W5 Unstable Rock?on the left abutment of the planned site of the Tibet Jiexu Hydropower Station.The amount of rock is 3.75×10⁵m³.The stability of the unstable rock is relatively good.The construction safety of the dam and the operation safety of the hydropower station in the later period.Therefore,it is particularly important to study the The W5 Unstable Rock in-depth and meticulous.Using on-site investigations and surveys,reading a large number of documents related to unstable rock,indoor physical and mechanical tests,limit equilibrium methods,and numerical simulation methods,the engineering geological background,the characteristics of the development of unstable rocks,the deformation and failure mechanisms of The W5 Unstable Rocks,and the fracture mechanics The relevant mechanical parameters and the stability of the unstable rock mass were further studied,and the main results were as follows:First,through field investigations in the study area,the boundary conditions of the front,rear,left,and right of The W5 Unstable Rock were ascertained.The W5 Unstable Rock was controlled by five joint surfaces,of which three joint surfaces had the most obvious influence,and the leading edge joint surface was significantly affected by weathering.Stronger than other parts.The 3DEC method was used to simulate the deformation and failure mechanism of The W5 Unstable Rock.The failure mode was that the local small piece of the leading edge had slip-type instability and failure due to the internal and external actions,and the rock in the rear of the unstable rock lost support and was directly exposed.In the outside world,we continue to weather the unloading again due to internal and external effects until the block of the new leading edge continues to be destroyed.This way,it forms a“chain-like”destruction and development process.Secondly,the granodiorite samples at the site of the study area were collected,processed into pre-fabricated double-fracture square specimens,and type?fracture toughness test tests were carried out on the rock samples through shear box loading.The fracture surface of the granodiorite sample with prefabricated double-sided cracks on the failure morphology is generally straight and has a rough surface;the loading angle condition can be obtained that the loading angle is too small at 45°,and the actual failure is compression failure at 60°.The 75°test result is more reasonable.Through numerical simulation,it is found that under consideration of increasing the width of the prefabricated double cracks,the stress concentration of the cracks occurs on the left side of the cracks on the right side and on the bottom side of the bottom cracks,that is,the two corners of the prefabricated double crack have two stress concentration points.The test results also verified that the penetration of the prefabricated double sided cracks was the model,corrected the real expansion angle of the crack under the condition of increasing width and the length of the real rock bridge,and improved the formula of the fracture toughness test of Type?.The shear fracture toughness of the granodiorite samples with pre-fabricated cracks was between 3.38 and 3.77 MPa·m^0.5.Finally,the stability of W5 rock was quantitatively calculated by the limit equilibrium method.The results show that the overall stability of The W5 Unstable Rock is good,but it may only occur under accidental conditions;the stability of the leading edge in long-term conditions is good,and it is short-lived.Under the working conditions,it is in a basically stable state,but its safety is very low.Under accidental conditions,there is the possibility of instability and destruction.Through numerical simulation based on fracture mechanics,the stress intensity factor in the middle of The W5 Unstable Rock is the smallest,and the fracture stress at the leading edge and the leading edge undulation location has the largest stress intensity factor of the fracture.That is,the relatively stable fracture controlled by joint 2 is unstable.Cracks controlled by joint 1 The crack propagation of W5 rock was simulated by the XFEM module of numerical simulation software.There was no crack propagation under natural conditions.Under storm conditions,different degrees of crack propagation occurred in pre-crack 1,fracture 2,fracture 3,and fracture 6.However,the length of the crack extension is short and the crack does not penetrate the entire crack.Under accidental conditions,the cracks 1 to 6 all undergo crack propagation.The joints controlled by the joint 1 and the joint 2 control are interpenetrated and form a block together,and the occurrence of small blocks of instability damage.Through the use of multiple evaluation methods,the method for the evaluation of dangerous rock masses is broadened.It is no longer limited to the qualitative assessment in the standard,supplemented by quantitative assessment,and the overall stability of W5 rock is accurately analyzed and judged.Follow-up prevention measures for dangerous rock provide good theoretical support.