| In the disasters aspect of water conservancy,open-pit mining and railway projects at home and abroad,the toppling deformation and landslide failures of anti-dip layered rock slope often occur in recent years,which causes serious threat to human engineering activities.Therefore,it is necessary to explore the instabilty failure mechanism and control measures of anti-dip rock slope.In this paper,the large-scale toppling and landslide failures of the anti-dip slope in Changshanhao mine of Inner Mongolia province were taken as an example,according to the field slope engineering geological investigation,the regional geological characteristics of changshanhao mine area were systematically analyzed from the aspects of topography,geological structure characteristics,hydrogeological characteristics,and rock mass quality integrity and quality evaluation.At the same time,the instability characteristics and failure modes of the existing landslide mass in southwest pit were summarized,and combined with the previous research,based on the superposition cantilever beam theory and the maximum tensile stress strength theory,the bending-toppling failure mode was used to analyze the stress condition of the anti-dip rock blocks,the toppling failure mechanical mechanism of the anti-dip rock slope was established,and a method for determining the instability of rock slope was proposed.Finally,the physical and mechanical characteristics of typical rocks in the mining area were studied and analyzed,which provides the accurate geological information for the following laboratory physical model test and numerical simulation.Taking a representative slope in the landslide area in southwest pit of Changshanhao mine as the research background,the"engineering disaster physical model experiment system"was adopted to construct the geological generalization model for carring out the physical model experiment.According to the physical similarity theory,combined with the field rock mechanics parameters,the geometric parameters,strain parameters and other parameters of the model rock mass are determined.Through the triaxial compression test of the standard specimens with different material proportion schemes,the optimum material proportion scheme that conforms to the mechanical properties of the model rock mass was found out,and the unit plate was made according to the determined material proportion scheme.The physical model experiment was carried out by stacking the unit plates according to the design.The main contents are as follows:No.1 Experiment:According to the distribution of the rock strata in Changshanhao mine and the principle of the physical finite element plate,the slope model of 75~o strata inclination was constructed,and the angle of model was 36~o.To better simulate the stratification state of the real rock slope,the gypsum unit plates of 40 cm×40 cm×2 cm and 40 cm×20 cm×2 cm were alternately stacked in the model building process.The size of constructed physical model is:160 cm length*40 cm width*145 cm height,and the excavation area is located at the slope toe.During the experiment,the horizontal stress of P=0.2 MPa was first applied on both sides of the model.After loading for 10 min,the horizontal confining stress was kept constant at 0.2 MPa,and the slope was excavated layer by layer.The excavation area was divided into nine layers,and the total length of the excavation area was37 cm,the depth was 40.5 cm,and the slope excavation depth of each layer was 4.5 cm.In the experiment,various monitoring equipments including static strain data acquisition equipment,infrared thermal camera,and digital speckle displacement field measurement equipment were used to capture the deformation and failure information of slope model.Through the evolution characteristics analysis of the displacement field,strain field and temperature field of the slope physical model,the internal mechanical mechanism of the deformation and failure of the layered anti-dip slope under the excavation action was revealed,and the slope deformation failure process and mechanism with the development of slope excavation were analyzed,which is compared and verified with the deformation and failure characteristics of the field slope.Finally,taking the anti-dip slope physical model as the simulation object,according to the mechanical parameters of the physical model and the excavation path in the model experiment,the corresponding slope numerical model was established using 3DEC software,and the slope failure process during the excavation was simulated,which is compared with the failure and instability characteristics of the slope physical model,and the accuracy of the toppling failure mechanism of the anti-dip slope obtained from the physical model experiment was verified.No.2 Experiment:Based on the supernormal mechanical property research results of engineering-scale negative possion's ratio(NPR)anchor cable,the model-scale NPR anchor cable was developed according to the similarity theory.On the basis of the toppling failure model experirment of anti-dip slope,combined with the deformation and failure situation of field slope,model-scale NPR anchor cable and ordinary(PR)anchor cable were embedded respectively on both sides of the slope model to reinforce the model in this experiment.The model size,material proportion,loading design and excavation path were the same as those of No.1 Experiment.The physical model was monitored by static strain data acquisition equipment,infrared thermal imager,tension sensor and digital speckle displacement field measurement equipment,and the evolution characteristics of displacement field,strain field,temperature field and anchor force of the physical model reinforced by anchor cable under the effects of excavation were obtained.Through the deformation failure characteristics comparison of both sides of slope reinforced by two kinds of anchor cables,in addition to comparing with the instability and failure images of the previous anti-dip slope physical model experiment,the control mechanism of NPR anchor cable on toppling deformation and failure of layered anti-dip slope was revealed,which provides a reliable reference for the application of NPR anchor cable in the treatment and control of layered anti-dip rock slope.Finally,the numerical model of the slope strengthened by anchor cable was established by 3DEC software.By comparing with the experimental results of the physical model,the control effect of NPR anchor cable on the toppling deformation of anti-dip slope was further explored.Based on the field engineering geological investigation,13 sections were firstly selected along the east-west axis of the southwest pit in Changshanhao mine,and the stability of the southwest pit was analyzed by FLAC3D software.Each section was calculated with two working conditions of the current mining boundary and the final mining boundary.The numerical calculation results showed that the main dangerous areas of the southwest pit are located near the W8 section in the middle of the north part,the joint cutting zone of the north side of the U-shaped mouth in the west part,and the north side of the U-shaped mouth in the east part(landslide area).Among them,the north side of W8section has an overall sliding trend,and large-scale landslide may occur along the jointed zone at the bottom of the north side after the excavation of the final boundary,and the potential sliding surface depth of most sections under the final boundary is about 10-18 m,and the length of the sliding body is30-110 m.Based on the toppling deformation and failure characteristics of anti-dip slope in Changshanhao mine,the instability mechanism and reinforcement failure mechanism of slope were summarized from four aspects of mining design,material design,energy design and dynamic load design.Finally,the typical damaged section W13 of the southwest pit was selected as the numerical calculation section,and the FLAC3D software was used to explore the deformation evolution regulation of the slope under the reinforcement of NPR anchor cable and PR anchor cable respectively.By comparing the displacement of two slopes reinforced by different anchor cables,it can be seen that the slope defomation and failure phenomenon has not been significantly improved after the reinforcement of the ordinary anchor cable with a design value of 70kN,and the whole sliding body has a large range of displacement failure;on the other hand,after the reinforcement of the NPR anchor cable with a constant resistance value of 70kN,the slope deformation and failure phenomenon has been effectively restrained,only the lower slope toe is partially damaged,and the energy inside the slope is effectively released after a small displacement of upper sliding body,thus the overall slope maintains a good stability.Therefore,based on the reinforcement concept of NPR anchor cable,according to the field investigation results and numerical calculation conclusions of the southwest pit,the reinforcement treatment schemes of each section in the southwest pit were proposed to ensure the safe mining of Changhaoshan mine.As the gradual increase of mining depth and scale in Changshanhao mine,under the influence of rainfall,weathering and mining disturbance,in addition to causing the landslides,a series of secondary rolling stone disasters will also occur.Therefore,combined with the slope stability analysis results of each section,the rolling stone prone areas in each section were identified,and the corresponding prevention and control measures were put forward according to the distribution characteristics of rolling stone in different slopes.Finally,taking W6 and W8 slopes as examples,Rocfall software was adopted to explore the control effect of rolling stone by using the coupling measures of gravel cushion and protective net.Through the numerical calculation,the rationality and effectiveness of proposed control measures for rolling stone in this open-pit mine were proved. |
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