| Rock high slope problem has always been one of the hot spots of geotechnical engineering in China. It involved in water conservancy and hydropower engineering, mining engineering, railway and road engineering, and many other engineering field, and also mountain slope, bank slope and other natural areas. In recent years, with the continuous development of national economic development, and the growing emergence of large scale engineering construction projects, the stability of high rock slope has received more and more attention. Jiaozuo city is located in the northwest of Henan province, north Tai-hang Mountains, south the Yellow River. It is an emerging industrial city and tourist city developed on the mineral resources. After decades of strongly development, the geological environment of Jiaozuo city is worsening and combined with the particular natural geological environment and unreasonable human economic activity, many environmental geological problems in mining area have raised. Because of open-pit mining, many high and steep rock slopes have formed in the abandoned mines. The (potential) collapse geological hazard has development in these abandoned mines, has seriously restricted the geological environment restoration work of the mines. Therefore, to research the stability of high rock slope and collapse disaster has become an urgent topic. It can effectively promote the the solution of the geological environment problem in Jiaozuo city.This paper is focus on the characteristics analysis of slope structure and stability study of high rock slope and take the high rock slopes in Longsi mine, Jiaozuo city as a case study. Combined with the geological data and field investigation, the geological environmental conditions and the characteristics of high rock slope are analyzed. The types of slope structure and the failure modes of high rock slope are summarized, and on this basis, the analysis method of slope structure is established. Through field investigation, rock tests and 3D laser scanning, the slope structure feature of typical high rock slope in Longsi mining is analyzed. The flat-joint contact model is chose for the rock bonded particle model. The relationship between the macroparameters and microparameters is analyzed, and on this basis, microparameters calibration method of rock was established. Particle flow code (PFC) model of direct shear test of rock discontinuity is established, and the microparameters calibration method is put forward, on the basis, the PFC modeling method of high rock slope is established based on the synthetic technology of rock mass. The rock falling type of high rock slope is summarized, and the rock falling type and formation mechanism of high rock slope in Longsi mining is analyzed. A new grey model for deformation prediction of dangerous rock is established and its application is illustrated through a cased study. The contact bond model is used to establish the PFC model of dangerous rock based on the fracture mechanics theory, and so that the stability evaluation of dangerous rock based on particles flow simulation can be realized. The relationship between mesoscopic strength reduction and macro strength reduction of PFC model is analyzed, on this basis, mesoscopic strength reduction method for rock slope stability evaluation is put forward, and it is used to evaluate the stability of the typical high rock slope in Longsi mining. The main research content and results of this paper are as follows:1. Through data collection and field investigation, the regional geological environment characteristics including natural geographical conditions, landform, stratum lithology, geological structure and the characteristics of high rock slope are analyzed. The rock mass joints and fissures of the slope are developed. Because of the disorder of strip mining mode for a long time, the slope is generally high and steep, and is subject to the influence of external force such as blasting and excavation, often results in fractured rock mass. According to the on-site investigation, rock falling is the main failure model of the high rock slope in the mining area. High and steep rock slope, development joint fissure, and strong dissolution are the main internal factors of rock falling in Longsi mining. Mining is the main inducing factors of rock falling. With the influence of excavation unloading, the rock mass along the joints and fissures deforming toward free face direction formed dangerous rock. Under the inducing of the rain or earthquake, the dangerous rock prone to fall.2. In reference to the related researches of slope structure, the slope structure types and failure modes of the high rock slope are summarized and concluded. The slope structure of the rock slope can be divided into five categories:weak zone controlled slope structure, layered slope structure, soft hard alternate slope structure, joint controlled slope structure and approximate homogeneous slope structure. On this basis, the basic process of slope structure characteristics analysis of high rock slope is established. For joint rock slope, the application of 3D laser scanning technology in the survey of structural plane is discussed. Through field investigation,3D laser scanning, rock tests and plane projection analysis, the slope structure characteristics of typical high rock slope in Longsi mining is studied. The results showed that the overall stability of slope is better, but local block of sliding and dumping failure may occur. In addition, in the upper slope, loose dangerous rock can be falling under the influence of r rainfall, earthquake and other external environment.3. The basic principle of particle flow simulation method is summarized, on this basis, the flat-joint contact model is chose as the rock bonded particle model, so as to obtain realistic rock tensile-compressive strength ratio. To design different combination of rock mesoparameters by orthogonal experiment and corresponding rock numerical experiments, many data of macrparameters and corresponding combination of mesoparameters are obtained. With these data, multi-factor analysis is adopted to analyze the relationship between the mesparameters and macroparameters, so as to determine the significant factors and its sorting of macro parameters. The deformation modulus E:Ec> kn/ks>σb; Poisson’s ratio v:kn/ks>cb/σb>μb>Ec> tanφb; the uniaxial compressive strengthσf:cb> σb> tanφb; tensile strengthσt:σb; internal friction coefficient tanφ:μb> tanφb; cohesion C:cb>μb> kn/ks>σb; tensile-compressive strength ratio σf/σt:cb/σb> tanφb; the biaxial compressive strength σf-2: cb>μb> tanφb> kn/ks; the biaxial compressive strength σf-8:μb> cb> tanφb> kn/ks. When the confining pressure is small (σ3= 2MPa), cb has relatively large influence on the peak intensity; when the influence of the confining pressure is bigger (σ3= 8MPa), μb has relatively large influence on the peak intensity. Relative to the uniaxial compressive strength, the biaxial compressive strength is effected to kn/ks. The equations of linear regression between macroparameters and its main factors are established. According to these equations, it is found that the deformation modulus E has a positively correlation relationship with Ec, and has a negative correlation relationship with kn/ks. Poisson’s ratio v has a negative correlation relationship with Ec and μb, and has a positively correlation relationship with kn/ks, cb/σb and tamφb. The uniaxial compressive strength of has a positively correlation relationship with σb, cb and tanφb. The tensile strength σt has a positively correlation relationship with σb. Cohesion C has a positively correlation relationship with kn/ks, σb and cb, and has a negative correlation relationship with μb. Tensile-compressive strength ratio σf/σt has a positively correlation relationship with cb/σb and tancpb. The biaxial compressive strength σf-2 and σf-8 both have a positively correlation relationship with kn/ks, cb, tanφb and μb. The simulation scale of particle flow model is put forward, namely, the ratio of minimum particle size to the shortest edge size of the simulating objects, Rmin/Lmin. Two cases of simulation scale are chose to study the change rule of macrparameters along with particle diameter. It was found that within a certain range, the macro properties of PFC model are little affected by simulating scale. If simulating scale invariant, the macroscopic properties of particle flow model are basically identical. According to the result of orthogonal experiment, the linear regression expressions with mesoparameters as the dependent variable, macroparameters as the independent variable can be established. On this basis, the mesoparameters calibration method of rock is proposed: firstly, calculate preliminary mesoparameters according to equation of linear regression, take 0.5 as the initial values for tanφb, secondly, conduct numerical test to obtain the macroparameters and compare these with the actual macroparameters, then according to the the relationship between mesoparameters and macroparameters, adjust the mesoparameters to reach a reasonable precision. PFC model of direct shear test is established, and the macroparameters and mesoparameters of structural plane are compared. It is found that differences between the macroparameters and mesoparameters are smaller. By comparing the numerical results and the actual results, the mesoparameters can be adjusted to reach a reasonable accuracy. In the case of low requirement of accuracy, the mesoparameters can be directly used the parameters of structure plane. For the weak structure surface, the mesoparameters can be calibrated through direct shear numerical experiments of weak structural plane. The synthesis rock mass technology is adopted to PFC modeling of high rock slope, and the modeling method is put forward. Analysis of high rock slope characteristics, selecting the appropriate model of rock and mesoparameters, and selecting the appropriate structural plane model and mesoparameters are three key problems of high rock slope modeling.4. From the two aspects of failure mode and formation mechanism, the types and characteristics of rock fall in high rock slope are summarized. On this basis, the (potential) rock fall is divided into unloading-cracking-sliding type, unloading-cracking-dumping/ dislocation type and unloading-cracking-falling type according to the formation mechanism. For the dangerous rock deformation prediction problem, this paper proposes a new model NGM-NGM (1,1, k, c) model and its optimized mode. Through the analysis of Wangxia dangerous rock deformation, the results show that the fitting effect of NGM (1,1, k, c) model is better than GM (1,1) model. This indicates that dangerous rock deformation trend closer to inhomogeneous exponential sequence. Using the NGM (1,1, k) model combined with improved tangent angle to analyze and forecast dangerous rock deformation trend, can proved evaluation basis of stability and the development trend of a dangerous rock. The contact bond model is chose to establish PFC numerical experiment method of fracture toughness, and the fracture toughness of numerical sample is calculated through the stress intensity factor calculation formula. Analysis results show that it won’t appear type Ⅱ shear failure under type Ⅱ loading condition, but the pure shear failure type Ⅱ can be realized by reducing bond shear strength. On the situation of tangential strength equal to normal strength of bond, KIICL/KICL= 4·Fs(c)/Fn(c) is satisfied. For the energy method to calculate the rock fracture toughness, it does not reflect the interaction in the particle system, also cannot reflect the effect of external force on the particle system from point of view of a single mesoscopic bond energy balance. Considering fracture toughness as a macoparameters, it is more significant to calculate rock fracture toughness according to the particle system energy balance. However, the expressions of mode I fracture toughness based on particle system energy balance has some problems, which is ignoring the loss of the external force from kinetic energy and dissipated energy. This paper has established a new calculation formula to solve this problem. Through examples comparison results, it is showed that the results of calculation formula based energy method proposed in this paper are very close to these of linear elastic mechanics. The fracture toughness has a positive relationship with contact bond strength in the case of other parameters constant, thus mesoparameters calibration method of the fracture toughness is established. Through a case study, the stability evaluation by using PFC model is verified. The gravity increase method is used to calculate the stability coefficient combined with PFC model. It is points out that the gravity increase method is equivalent to the stability calculation method of fracture mechanics. Analysis results show that using the particle flow model to evaluate stability of dangerous rock is feasible, and can simulate the extension of master structure fracture.5. The stability evaluation methods for PFC model are summarized. Based on the tension-shear failure criterion of geotechnical material, the mesoscopic strength reduction method of PFC model is put forward, and the relationship between the macroscopic strength reduction and mesoscopic strength reduction is analyzed. It was found that the tensile strength, uniaxial and biaxial compressive strength has linear relationship with mesoscopic strength parameters under strength reduction, but the intensity parameters of tanφ and C has nonlinear relationship with mesoscopic strength parameters under strength reduction. According to the M-C failure criterion, the intensity parameters of tanφ and C, shear strength and biaxial compressive strength have nonlinear relationship between each other under strength reduction. But for structural plane, the intensity parameters of tanφj and Cj have nonlinear relationship with shear strength. The PFC model of the high rock slope in CIV-1 stope of Longsi mining is established, and its stability is analyzed by using the mesoscopic strength reduction method. It is found that the overall stability of the slope is well. The destruction region of the slope developed from the local to the whole along with the mesoscopic strength reduction. Local failure first appeared in the upper, and manifest as the ladder-like shear sliding failure. The PFC model of the dangerous rock mass is established, its stability is analyzed by using the mesoscopic strength reduction method. Analysis results show that the current stability of the dangerous rock mass is well. The failure type of the dangerous rock mass is shearing-slip mode and pull-topple mode. The stability of dangerous rock of shearing-slip type is effected by the combination relationship of the rock layer and steep joint. The stability of dangerous rock of pull-topple type is effected by cut-through degree of the steep joint in the trailing edge. |
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