Study on Stability of Deformation Body of Material Yard Slope of a Pumped Storage Power Station

Abstract

The stability of granite deformation body in a pumped storage power station is studied in the paper, and the research includes field geological survey data collection, analysis of distribution law of structural plane, study on failure model of deformed body and prediction of deformation body stability. Based on that, the failure modes and stability of deformed bodies are studied in detail. According to the regional topographic map of deformed body, a two-dimensional limit equilibrium model is established. The three-dimensional model is established by using 3DEC discrete element software. The stress, strain and displacement under natural and rainstorm conditions are calculated and analyzed respectively, and the accuracy of the calculated results is determined by comparing with the monitoring data, so as to predict the deformation direction and rate of the deformed body. The longest movement distance of the deformed body along the shear outlet of different elevations is simulated separately to determine the affected area, which provides a reliable basis for making preventive measures for the construction site. Introduction The research on the stability of deformed slope is one of the key topics of Engineering geology, so many scholars at home and abroad have carried out in-depth studies [1-6]. The engineering geological conditions of the deformed body are complex, such as fissures, weak interbeds, faults and intersections of various structural planes distributed in the deformed body. At present, the stability evaluation of deformed body includes qualitative evaluation method, quantitative evaluation method and analysis and judgment method based on slope deformation material [8]. A deformed body is located above the slope of the material yard. The excavation at the foot of the slope has caused many tension cracks at upper part of slope and local collapse, which has a further slide tendency. Slope instability not only affects the normal operation of material yard construction, but also poses a serious threat to the safety of personnel, buildings and equipment at the foot of the slope. Therefore, it is urgent to reasonably evaluate the stability of the deformed body and accurately predict its possible degree of damage. Meanwhile, the research has far-reaching significance to ensure the smooth progress of the project construction. Taking the deformed body caused by excavation of a material yard as an example, this paper systematically evaluates the stability of the deformed body and the influence range of its failure by analyzing its deformation characteristics and utilizing the limit equilibrium theory and three-dimensional numerical simulation method, which provides a theoretical basis for the safe operation of the project. Engineering Geological Conditions Topography and Landform The deformed body area is located in the high mountain area of the Yanshan Mountains in Fengning, where the terrain is undulating and the landform belongs to the high mountain and hilly area. The slope inclines towards the southwest, with an overall slope of about 40 degrees, steep terrain and well-developed vegetation. 182 Stratigraphic Lithology The stratum is fine-grained monzonitic granite of Mesozoic Liyaozigou unit (Th). The rock is light flesh red, with few fine-grained granite texture and massive structure and the grain size is generally 1-2 mm. The surface is partly covered with landslides and sediments, generally less than 2m in thickness, mainly bedrock weathered sand, gravel and other loose structures. Geological Structure The Kangbao-Weichang deep faults along the 42°C line north of Weichang County Town are the active belt of the Inner Mongolia-Daxing'anling geosynclinal fold system. The Archaean base debris in the area are generally transformed by migmatization, and the gneiss are obscure, sporadically covered with late Jurassic-like moras construction and Late Jurassic volcanic rock formation. Earthquake The overall characteristics of neotectonic movement in the engineering area are mainly uplifted as a whole, the Quaternary fault activity is not obvious, and the modern seismic activity is weak. No historical destructive earthquakes have been recorded in the near field, and the basic intensity of the site earthquakes is 6 degrees. Failure Characteristics of Deformed Bodies On March 24, 2018, when inspecting the slope of Liyaozigou material yard, it was found that there were longitudinal penetrating cracks in the middle of the slope of Area II and horseway drainage ditch cracking at 1200m elevation. Cracks in the beams above the excavation slope (about 1340m elevation) are circular chair-shaped, the width of the tension cracks at the rear edge is about 1.5m and its falling height is about 2m. The concrete spray layer of the excavation slope at the front edge is swelling and falling off locally (Figure. 1). Figure 1. Back Edge Tension Crack and Bulging and Shedding of Concrete Shotcrete Layer. There are two faults and three groups of fissures in the deformed body. Among them, fault F1 (NE40°SE∠4°) and fault F2 (NW290°NE∠60°) are the left and right boundary of the deformed body. The two dominant structural planes (NE40°SE∠55°and NE30°SE∠35°) constitute the bottom slip surface of the deformed body. Stability Analysis of Deformation Body Physical and Mechanical Parameters of Deformed Rock Mass The recommended values of geophysical and mechanical indexes are shown in Table 1. Table 1. Values of Physical and Mechanical Parameters of Rock Mass for Stability Analysis of Deformed Bodies. Rock Mass Type Φ(°) c(kPa) Natural Density (kN/m 3 ) Saturated Density (kN/m 3 ) Poisson ratio Modulus of elasticity (×10 4 MPa) Quaternary System (Collapse, Slope Deposit) 20 20 20 21 / / Strongly Weathered Granite 27 50 24.1 24.6 0.38 0.5 Weak Weathered Granite 31 350 25.0 25.3 Micro Weathered Granite 45 1050 26.0 26.2