| Under the action of internal and external forces for a long time,rock mass,as the product of geological action,often develops discontinuities with different sizes and properties,such as joints and fissures.The existence of these discontinuities makes the rock mass structure extremely complicated,resulting in different mechanical properties of rock mass with different structures.Thus affecting the stability of rock mass related projects such as rocky slopes.Therefore,it is of great theoretical significance and practical value to study the characteristics of discontinuities and their controlling effect on rock mass stability.Yongji rocky slope is located on the left bank of Wende River bayonet section in Yongji County,Jilin Province.In recent years,this section of Wende River has caused many great flood disasters and caused great loss of life and property because of its insufficient over-flow capacity.In order to solve the problem of insufficient flow capacity in the bayonet section of the river and eliminate the hidden danger of repeated flood disaster,it is planned to excavate the tuff mountain on the left bank of the river to improve its flood discharge capacity.The fractured rock slope formed after excavation is large in scale,with the maximum relative height difference of 250m and the length of 1000m.The rocky slope has large undulation and steep slope shape,and the slope is mostly about 50°.According to the geological survey,it is found that the non-penetrating structural planes of small scale are generally developed in the slope and the rock mass structure is relatively complex.These non-penetrating structural planes have obvious control effect on the slope stability.Aiming at the special condition that the non-penetrating structural planes measurable area of slope rock mass is in the high position of steep slope body and it is difficult to carry out large-scale measurement.To study the stability of the rocky slope and the controlling effect of non-penetrating structural planes.Based on the idea of"Rock mass Structure Control"and considering the occurrence characteristics and block morphology of non-penetrating structural planes,this paper introduces UAV proximity photography technology to measure and obtain the non-penetrating structural planes of slope rock mass in large windows.At the same time,for the first time,multi-angle photography was used to obtain the high definition image of the measurement area of non-penetrating structural planes,and on this basis,a detailed3D model was established.Finally,a large number of parameters of discontinuities are obtained by measurement and interpretation.Then,the geometric characteristics of non-penetrating structural planes are studied in depth,and a 3D fracture network model with large Windows is constructed.At the same time,the 2D fissure network model of the main slip surface at the key part of the slope is intercepted from the 3D fracture network model,and the Dijkstra shortest path search algorithm is introduced to perform the geometric search of the most dangerous slip surface on the main slip surface.Considering that the non-penetrating structural planes may be subjected to stress concentration during the formation of the slip surface,the numerical model of the main slip surface is constructed by combining the 2D fracture network of the main slip surface with the particle discrete element synthetic equivalent rock mass technology.The improved gravity increase method is introduced to calculate the stability of the main sliding surface of the slope,and the analysis of the extended evolution mechanism of the non-penetrating structural planes during the formation of the dangerous sliding surface is realized.From the point of view of mechanics,the most dangerous sliding surface in the slope is determined,and the safety factor of the main sliding surface is calculated,which realizes the quantitative analysis of rock slope stability controlled by the non-penetrating structural planes.The main research contents and results of this paper are as follows:1.The engineering geological properties,rock mass structure and quality characteristics of the Yongji fissure rock slope were identified through on-site geological investigation and non-contact measurement on the structural plane of the large window.The slope is located in a low mountain and hilly landform area,and the rock mass structural plane types are mainly bedding and commonly developed joints and fissures.Among them,most of the joints and fissures are non-penetrating,forming a complex structural plane system,which has obvious control effects on the stability of rock mass structure and slope.The occurrence of non-penetrating structural planes can be divided into 4 groups,of which the first group of structural planes intersects with the slope surface at a small angle,which is the controlling structural plane for the stability of the slope.2.A multi-angle UAV close to photogrammetry scheme is proposed to measure the structural plane of high and steep rock slopes finely.In view of the special conditions of high,steep slopes and complex structural planes in the study area,for the first time,the multi-angle observation method was combined with UAV close-to-photogrammetry technology.The millimeter-level resolution images of the structural plane were obtained from all directions,which improved the coverage of close-in photogrammetry images,improved the problem of insufficient local accuracy of conventional close-in photogrammetry,and realized high-precision non-contact measurement of high-steep rock slope structural planes,which lays a foundation for the accurate identification and further application of rock mass structure information.3.A three-dimensional fracture network based on non-contact measurement(large window structural surface data)is constructed.The structural plane of high and steep slopes obtained by non-contact measurement has a large window as its basic feature.In view of the geometric distribution characteristics of this special structural surface,the paper constructs an analytical scheme for the derivation of the diameter of the large window structural surface,and corrects the occurrence frequency and density of the structural surface,and constructs a data suitable for the non-contact large window structural surface.3D fracture network simulation method.In addition,the steps of this method are relatively simple,the calculation is simple and the precision is high,and it has certain application and promotion value.4.A scheme for determining the most dangerous sliding surface of high and steep fractured rock slopes controlled by non-penetrating structural planes is constructed.The number of non-penetrating structural planes inside high and steep rock slopes is extremely large and the development is random and complex,and the bottom boundary of slope deformation and failure(the most dangerous sliding surface)has not been well determined.In this paper,the determination scheme of the most dangerous sliding surface of high and steep fractured rock slopes is constructed from two aspects of geometry and mechanics.First,based on the basic idea of"structural cybernetics",the search of the most dangerous sliding surface is transformed into the search problem of the shortest path,and the geometric search of the most dangerous sliding surface is realized by the Dijkstra algorithm;secondly,the particle flow discrete element PFC2D is used to construct The geomechanical model of the fractured rock slope is established,and the method for determining the most dangerous sliding surface of the slope considering mechanical factors is constructed through the quantitative analysis of the stability of the rock slope described in(5).Through the comparative study of the two,it is found that the two have a high degree of coincidence and are suitable for the determination of the most dangerous sliding surface of high and steep rock slopes controlled by non-penetrating structural planes.5.A method for quantifying the stability of high and steep rock slopes controlled by non-penetrating structural planes is proposed.The tip of the non-penetrating structural plane inside the high and steep rock slope often produces stress concentration,and the resulting crack initiation and expansion are an important factor leading to the formation of the sliding plane and the failure and instability of the rock mass.In this paper,a particle flow discrete element rock slope geomechanics model is constructed to study the stress response of the non-penetrating structural plane and the whole process of crack initiation-expansion-penetration,so as to reflect the influence of the non-penetrating structure on the macro-mechanical behavior of the rock mass.The traditional method for calculating the safety factor of rock slopes cannot consider the influence of non-penetrating structural planes.In this paper,the limit equilibrium method is combined with the PFC2D safety coefficient calculation principle,and a rock slope improvement gravity suitable for the control of non-penetrating structural planes is proposed.Analytical formulas for the increase method and the strength reduction method.Analytical analysis shows that there are differences in the stress conditions at the crack tip under the two methods,and there are errors in the calculated safety factors.In view of the improved gravity increase method can better reflect the collapse and instability characteristics of rock slopes,this method is selected to determine the safety factor of fractured rock slopes,and the quantitative analysis of the stability of high and steep rock slopes controlled by non-penetrating structural planes is realized. |
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