Excavation Stability Analysis And Support Optimization Design Of High And Steep Rock Slope

With the rapid development of China's economy,highways and high-rise buildings stand in cities,resulting in more and more artificial slopes.If this kind of artificial slope is not handled properly,it will threaten people's lives and cause serious economic losses,especially the high and steep rock slopes in mountainous cities.The stability of high and steep rock slope is directly related to the decision-making of project site selection,design and construction scheme.It is also an important basis for the safety evaluation of surrounding roads and buildings.When analyzing the stability of high and steep rock slopes in mountainous cities,restricted by the scope of land acquisition and complex engineering geological conditions,engineers tend to be very conservative in the excavation and support design of such slopes.Although the safety is greatly guaranteed,the project cost is very high,Therefore,it is of great practical and economic significance to analyze the excavation stability and support optimization design of medium high and steep rock slope in mountainous cities.Therefore,this paper selects the high and steep rock slope project to be excavated for the reconstruction project of Zhenhua South Road in Duyun City as the engineering background.On the basis of on-site geological investigation and data collection,the stability of the slope in the study area is evaluated qualitatively and quantitatively by using polar stereographic projection method,limit equilibrium method and numerical simulation method,combined with the original excavation and support design scheme of the slope,The slope excavation scheme and support scheme are optimized by orthogonal test.Finally,on the premise of ensuring the safety and reliability of the project,the original design scheme and the optimization scheme are compared from the aspects of quantities and cost to verify the feasibility,rationality and economy of the scheme.After the research,the following important results are obtained:(1)By collecting the data before and during the excavation of the slope,combined with the field observation,it is found that the rock mass of the slope is broken and the joint fissures are developed,and two groups of joints are mainly developed.The stereographic projection method is used to qualitatively evaluate the slope.It is found that the inclination of the rock layer is opposite to the slope direction,the inclination of joint 1 is the same as the slope direction,and the inclination is less than the slope angle,and the inclination of joint 2 is almost perpendicular to the slope direction.The results show that the rock layer and joint 2 have little impact on the slope,belonging to a stable structural plane,while joint 1 is an unstable structural plane,It is the dominant structural plane of the slope.On this basis,the limit equilibrium method is used to quantitatively evaluate the slope after excavation.The results show that the stability coefficient of the slope is 1.107,and the slope is basically stable in the natural state.(2)Through the discrete element numerical simulation software 3DEC,the three-dimensional excavation numerical model of the slope is established by using the face command code to analyze the stress and strain of the slope in the natural state.According to the slope displacement vector diagram,the influencing factor causing the instability of the original slope is the artificial excavation of the slope toe.Through the excavation stability analysis and potential instability mechanism research of the slope,the results show that the rock mass of the slope is disturbed by excavation,and the primary joint fissures in the rock mass expand for secondary development.When the slope encounters rainstorm,due to the very low permeability of the rock mass,the rainwater infiltrates along the secondary developed joint fissures,increasing the sliding force and floating drag force of the slope,reducing the stability of the slope.By applying prestressed anchor to the slope,the maximum horizontal displacement of the slope is reduced from 124mm to 71mm,which shows that the use of prestressed anchor has obvious effect on slope support.(3)The slope excavation stability is not only restricted by its own geological conditions,but also greatly affected by human factors.The excavation slope angle,bench width and excavation height greatly affected by human factors are selected for orthogonal experimental design.The limit equilibrium method and discrete element numerical simulation method are used to calculate the slope stability coefficient,slope displacement increment,slope shear strain increment and slope earthwork excavation under different combination conditions,which are used as evaluation indexes.On this basis,the range analysis method is used to determine the main control factors and the optimal scheme of the excavation scheme.The results show that the excavation slope angle is the main controlling factor,which should be considered when determining the optimal scheme.Then,the comprehensive balance method is used to calculate the slope stability coefficient and slope earthwork excavation volume under various working conditions according to the variation trend diagram of each evaluation index with factor level,and the limit balance method.The comprehensive research shows that the optimization scheme of slope excavation is:excavation slope angle 45°,bench width 2m and excavation height 10m.After comparison and verification,on the basis of ensuring safety,The excavation volume of the optimized scheme per unit width is reduced by 80m~3compared with the original design excavation scheme.(4)Design parameters of prestressed anchor:incident angle??The length L,spacing D and prestress T are orthogonal tested.Taking the slope horizontal displacement as the evaluation index,the slope horizontal displacement under different working conditions is calculated by numerical simulation method.Combined with the range analysis method,the optimal support design parameters of slope anchorage are selected,and the optimal design scheme of prestressed anchor anchorage is obtained:the horizontal spacing D is 2m,the length L is 18m,and the incident angle?is 10°,and the prestress is 410KN.The slope stability coefficient of the optimized scheme and the original design scheme under rainstorm conditions is greater than 1.35,meeting the design requirements.The quantities and cost of the original design excavation and support scheme and the optimized excavation and support scheme are calculated.After comparison,the optimized scheme saves about2.619 million yuan in cost and shortens the construction period by about 6 days,which meets the economic rationality and the design principle of less excavation and more support for slope,The slope optimization scheme can provide a reference for the excavation and support design of similar high and steep rock slope engineering to a certain extent.