| In recent years, in the process Of development the Tibetan Plateau hydropower resources, more and more engineering-geology problems of hydropower slope are revealed. This paper focuses on the cataclastic loose rock mass, which is one of the typical examples. Carry out in-depth research on developmental characteristics, engineering features, causes and the stability of the engineering Slope, will have a more science practical significance and engineering value.On the right bank of a hydropower station on Lancang river, where development four large cataclastic loose rock mass. To identify the scope of their development and distribution, structure of rock mass deformation and failure phenomenon, causes and engineering geological characteristics and stability on slopes, a large number of field investigations and more in-depth study waste carried out. This paper draws the following main conclusions:(1)Through field reconnaissance surveys, aerial drones, 3D laser scanning and indoor study, the rock mass structure characteristics and cataclastic loose rock mass distribution range was investigated, delineated and checked. The four cataclastic loose rock mass SL18, SL20, SL22 and SL24 mainly developed in ? bridleways above,whose natural slope angle is about 30 degrees to 55 degrees. In addition,the SL24's estimate volume is the biggest, which is about 13.5 million cubic meters and development on the abutment slope.(2) The rock mass structure in study area can be mainly classified into granular structure, fragmented structure, mosaic structure and block structure. The cataclastic loose rock mass, which is defined by considering the field engineering geological conditions, is a kind of particularly rock mass.This kind of rock mass usually has a triple rock structure, which is block fracture, cataclastic structure and granular structure, and the surface of rock mass is given priority to cataclastic structure to granular structure. Its structure is mainly fragmented structure and granular structure and this kind of rock mass has a unstable feature, which may deformation and failure by collapse, topping or slide.(3)There are four groups of preferred plane in study eare. In accordance with the specification requirements and engineering experience, the structural plane in the study area is divided into levels grade ? to grade ? five categories. The grade ? structural plane, which is closely related to the development features of the cataclastic loose rock mass, has two sets of the joint. The occurrence of fist Anti-dip joints strike 281°~323°and the dip 191°~233°?73°~90°.The occurrence of second bedding joints strike 284°~330°and the dip 14°~60°?69°~90°.(4) Site investigation found that the high rock slope unloading conditions in study area is very different from conventional large-scale hydro power projects' slope. In accordance with the specification requirements and existing research results, this paper proposed the classification criterion of the extremely strong unloading zone, which has two types of boundaries. One class of boundary is a kind of joints whose open width is generally greater than 10 cm, with tensile or shear properties of unloading fissure, and the other is stretching width is several meters to tens of meters repose of unloading rock mass distribution zones. In addition, during the process of surveying the cataclastic loose rock mass and the unloaded zone, a strong correlation was found, that is, theirs developmental depth is similar.(5)Field survey results show that there are three main types of deformation and failure of rock mass in the study area. The first type is toppling, which has the characteristics of brittle failure and widely developed. The deformation and failure depth of the slope is shallow, and significant impacted by the primary columnar joint and unloading crack. What's more, this pattern can be further divided into block toppling and shallow toppling. The second mode, controlled by the gentle inclination joints, which consists of sliding and compression cracking, sliding and fracturing, steplike slide. The third form is accumulation body failure, whose sliding surface is bedrock-cover discontinuity or circular-arc-shaped.(6)To study the cause of cataclastic loose rock mass, rock structure, evolution of the valley, highland stress, meteorology and hydrology and other several geological lithology controlling factors were analyzed. Studies have shown that the specific causes of this type of rock mass, is under internal and external factors' long-term effects caused by its own structure, evolution of the valley, the ground stress field, freezing and thawing actions, and the complex coupling produced it.(7)A more in-depth study on the engineering properties of cataclastic loose rock mass was carried out by rock uniaxial compression test, triaxial compression test and creep test. The test results shows it's a kind of solid rock, which has many micro-cracks and whose mechanical strength index significantly less than the fresh Dacite. The creep characteristics of such rock mass is not obvious. By comparing the long-term strength index between the conventional triaxial strength index, the strength reduction was not significant and the cohesion and angle of internal friction is only reduced 6.7 percent and 7.7 percent. Thus the cataclastic loose rock mass creep properties may be appropriate to considered during the design and construction process.(8) Though qualitative evaluation of slope stability, and numerical simulation based on discrete element method, finite difference method and rigid limit equilibrium method research, the key research was carried out on the SL24, which mainly development on the abutment slope.The overall stability of the abutment slope in the natural state is good, the rock mass deformation and failure mainly in the form of topping during the future evolution of this slope, which mainly developed in the cataclastic loose rock mass.Meanwhile,the granular structure of cataclastic loose rock mass' s local stability is adverse in the vicinity of the slope surface, which may partial slides under unfavorable conditions.The abutment slope has a better stability after excavation without support measures, and the obvious deformation and failure phenomenon appers partial near the excavation face, which proves the designed excavation is feasible.However, a rational design of the excavation steps and spray anchor support measures should be noted. |
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