Unloading Zones And Rock-mass Quality Classification Study Of Dam Slope Area Of Lianghekou Hydroelectric Power Station In Yalong River

Based on a large number of field investigations, testing, and indoor data analysis together with the geological conditions of the dam's location, this paper introduces the formation lithology, landform, physiognomy, rock structure, deformation and damage modes of the dam slope. Then through qualitative analysis and qualitative testing method, unloading zones features are illustrated. Comprehensive classification is conducted for the rock mass quality using the experience grading system and multi-factor rock mass quality classification method. Rock mechanical parameters are given by means of a comprehensive analysis of the correlation between in-situ test data and rock mass quality classification index. Details and results are as follows:(1) Rock structure of the dam slope is summarized by the field investigation data. Dam structure is divided into classⅢ,ⅣandⅤ. Small faults (F1～F30)areⅢclass with a primary strike direction of NWW and NEE to next best.89 interlayer extrusion dislocation interfaces found in the adits areⅣclass.Ⅴclass structural plane is mainly composed by a various types of intermittent extended fracture structural planes. They appear a lot in the rocks with a random distribution.(2) The slope deformation modes in different parts of the dam diversified. Left abutment slope is mainly wedge-shaped slip tension crack deformation, developed with two unloading tension crack rocks: 1 and 2; Slopes in the right abutment and diversion entry of the right bank are mainly slip tension crack and slip tension crack deformation; Qingda River slope shallow surfaces are mainly dumping-bending tension crack, slip tension crack and flexural slumping deformation,with slip tension crack or tension crack deformation along the low-angle structural planes in the deep part, developed two unloading tension crack rocks (Q1,Q2).(3) River valley epigenetic-surface reformation is controlled by rockmass stru cture,but weathering and unloading of rockmass is the direct cause which leads to different epigenetic-surface physical geology phenomena, for example,collapse, landslide, incline, dynam-relaxed and so on.Together with the division criteria and characteristics of unloading zone, rock mass unloading zone's development factors are summarized as the following: primary factors are topography, landform, formation lithology, rock structure and stress field characteristics. Other factors include weathering conditions, groundwater occurrence and so on.(4) Combination qualitative and quantitative method, studying synthetically on the abutment slope off-load zoning and spatial distribution rule. In aspect of quantitative division, synthetically apply the test achievement of RQD and rebounding test, radon survey, acoustic wave test results etc.(5) By summarizing the main factors which impact the rock mass quality. The rock mass quality level of abutment slope is divided by the qualitative judgment and 3 rock mass quality classification methods (BQ, RMR and CSMR after adjusted). It comes to the conclusion that the rock mass quality level of abutment slope is::①Rock mass quality are mainlyⅢandⅣclasses. Especially for the abutment slope in two banks,ⅢandⅣclass rock mass accounts for the proportion of more than 93%.Ⅴclass occupies only a small percentage.TheⅣlevel rock mass is generally distributed approximately within tunnel adit to 60 meter limits in the superficial slope spot.②Qingda river left bank side slope rock mass quality haveⅤclass accounts for 35%;Ⅳclass accounts for 36.3%;Ⅲclass accounts for 28.7%.Ⅴclass rock mass mainly concentrates in a distortion more intense region, the rock mass is better toward the slope, the whole later the rock mass relatively will be generally complete to 100 meter, most will beⅢclass rock mass. On the basis of this analysis, Rock mechanical parameters and engineering geological properties are given then.