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Collaborating Authors
Stability Analysis for to ppling Failure of Unstable Rock in Three Gorges Reservoir Area, China
Wang, G. L. (Xi’an Center of Geological Survey, China Geological Survey) | Wu, F. Q. (Institute of Geology and Geophysics, Chinese Academy of Sciences) | Ye, W. J. (Xi’an University of Science and Technology)
Abstract As distinguished from the former types of toppling failure (i.e. flexural, blocky, blocky-flexural and secondary), another type of toppling failure developed in interbedded hard rock and soft rock slope is very common in Three Gorges Reservoir region. Based on discrete element method, the failure process of toppling failure can be summarized as erosion notches → tension cracks → toppling failure → gravitational transport and accumulation. According to the toppling failure mode, the computing formula of factor of safety is deduced by means of the method of geo-mechanics. The results of a typical case study show that the factor of safety of toppling failure decreases with increasing of notch depth. Supposing the erosion rate of notches is 1 mm/yr and toppling failure of the unstable rock occurs at a notch depth of 1.45 m, we can calculate the time required for the unstable rock to topple as 50 years. Introduction Toppling failure is one of the most serious and hazardous instability of rock slopes (de Freitras and Watters 1973; Goodman and Bray 1976; Wang 1981; Ishida et al. 1987; Goodman 1989; Aydan and Kawamoto 1987, 1992; Adhikary et al. 1996, 1997, 2007). Many toppling failures are observed in practice and hence toppling is an important failure mode that requires further attention (Wyllie 1980; Liu et al. 2010). In general, this failure can be classified into four principal types: flexural, blocky, blocky-flexural and secondary (Goodman and Bray 1976). Flexural toppling failure occurs due to bending stresses (Amini et al. 2009). However, another mode of toppling failure, which mainly developed in interbedded hard rock (i.e. sandstone) and soft rock (i.e. mudstone, shale and limestone) slope is very common in Three Gorges Reservoir region (Chen et al. 2004; Dong et al. 2010). Field investigation indicates that notches of undercut slopes are formed by differential weathering. Furthermore, tension crack on the top surface will occur due to concentration of tensile stress. As result, the unstable rock begins to topple because of momentum unbalance.
- Asia > China (0.69)
- North America > United States (0.46)
The Characters of Freeze-Thaw Deformation and the Treatment Technics of Road Slopes in Plateau and Mountain Area
Xu, Shuanhai (Xi’an University of Technology, Xi’an Research Institute of China Coal Technology & Engineering Group Xi’an) | Li, Ning (Xi’an University of Technology) | Cao, Zubao (Xi’an Research Institute of China Coal Technology & Engineering Group) | Liu, Dan (Zhengzhou University)
Abstract According to the analysis, there are five types of deformation failure of the slopes along the road which are shallow freeze-thaw creeping of gravel soil slopes in plateau meadow area, cracking of soft rock high slopes by weathering and freeze-thaw cycling, freeze-thaw slump along the planes of consequent rock slopes, freeze-thaw collapse of big colluvial gravel slopes and freeze-thaw slide along basal rock of residual gravel soil slopes. Grassing, water draining, SNS flexible protection net, concrete insert repair, anchored retaining wall or concrete pier, root pile and anti-sliding pile are selected to treat these deformation failures based on different situation. 1 Introduction There is about 200 km distance of Xining-Jiuzhi class II road,which connects Qinghai and Sichuan province, is in a typical alpine environment and it passes through five mountains higher than 4000 meters. This complicated-geological-condition road has several high slopes and ancient landslides. There are many deformation failures, collapses and landslides occur every year along this road because of the rebuilding, freeze-thaw cycling and weathering. 2 Environmental Geological Conditions Along This Road 2.1 Climatic conditions The weather along this road belongs to plateau mountain climate which is dry, cold, windy and hypoxic. The average temperature is 3.4° and the extreme minimum temperature is -36.2° while the day temperature difference is 16°. The amount of precipitation is 400~500mm which concentrates in from July to September. 2.2 Topography and geomorphology Along this road, there are four geomorphic unitswhich are alpine mountain landscape, alpine mountain basin landscape, alpine deep valley landform and alpine alluvial plain landscape. The altitude of this area is between 3100m and 4000 m. Both south and north sides of this area are higher than the middle which appears like a valley between two mountains. The altitude difference is about 500 m. Most of the alpine deep valleys areV type while U type valleys are rare. There are alluvial flat and first terrace in the bottom of the valleys. Meadows spread over the high terraces and plateau hills.
- Asia > China > Sichuan Province (0.24)
- Asia > China > Qinghai Province > Xining (0.24)
- Geology > Geological Subdiscipline (1.00)
- Geology > Structural Geology > Tectonics (0.48)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock > Mudrock (0.32)
- Transportation > Ground > Road (0.57)
- Automobiles & Trucks (0.57)
Abstract The pregnant and sliding mechanism of rock landslides was firstly obtained, comparative analysis of modern typical rock landslides information. Then, the failure mechanism of rock landslides was simulated selected a typical rocky bedding landslide as prototype, which damaged mainly by goundwater pressure. The test was to maintain the true latent slip surface and seize the main factors causing the landslide. Major stress magnitude, direction and distribution was basically the same with the prototype in the test. Finally, the prototype landslide hydraulic start critical value was calculated, in accordance with the easily slip over dip slope stability model and its hydraulic start value formula. The rock mechanics parameters and structural parameters of the prototype rock landslide was obtained from the inversion analysis. The simulation test results show that the experimental critical values was coincide with the theoretical critical values, and verify the correctness of the test method. 1 Introduction Rocky bedding landslides are widely developed disastrous landslides. For example, the Shaoxi landslide in Zhong county, Chongqing, which damaged in July 16, 1982 (Xichang CHEN et al. 2009a). And the Niujiaodong landslide in Yunyang county, Chongqing, which damaged in July 18, 1982 (Xichang CHEN et al. 2009a). And theVajont landslide near the Vajont reservoir dam banks in the Italian, which damaged in October 9, 1963 (Anderson. J.G.C. & Trigg. C.F. 1986, LanshengWANG2007). And the Qianjiangping landslide in the China Yangtze River Three Gorges Project reservoir bank, which damaged in July 13, 2003 (Shirong XIAO et al. 2010, Baoping WEN et al. 2008, Shouding LI et al. 2008). And so forth. The first two landslides are occurred in the easily slip over dip slope, and the latter two landslides are occurred in the chair-shape cataclinal slope (Xichang CHEN et al. 1993b). Both the two rock landslides have a high degree of similarity on slopes structure, inducing factors, deformation and failure characteristics. In this paper, the pregnant and slide mechanism of the rock landslides was first analysis, and was simulatd on the basis of the slope structure and inducing factors of rocky bedding landslides.
ABSTRACT Due to the construction excavation and heavily raining, resulted in serious creep deformation on the Mayanpo slope. Through the analysis of the deformation monitoring material, together with the in situ detail geological survey results, this paper present the deformation characters of the slope rock mass. As an effective numerical method used in analysis the discontinue surface of geotechnical material such as fault, bedding plane and joints, DEM (Discrete Element Method) was used in this paper. With the two-dimension DEM software UDEC, this paper analysis the deformation characters and mechanism in detail. Three cases were used in the numerical modeling. First, an initial static loading is applied in this model to simulate the prevailing rock mass conditions at the site. Second, excavation cutting of the slope was simulated. Third, heavily raining was simulated by saturated the joint condition. In doing so, the model simulates the effect of degradation of discontinuities in the rock mass. This study has provided some insight into the deformation mechanism of the Mayanpo slope. The simulation results indicate that the deformation of Mayanpo slope rock mass was mainly controlled by weak interlayer, while the construction cutting and raining are the external inducing factors. The results of this paper can provide some reference to the similar engineering. 1. INTRODUCTION The Mayanpo slope lies near a hydropower station under construction in southwest of China, it's the right place to provide materials to the hydropower station under construction according to the designed layout. In June 2006, parts of the Mayanpo slope excavation were carried out, including road cutting and basement excavation for engineering structure, which cause some parts of the rock mass near toe of the slope were removed. In July 2006, cracks appeared at the top of the slope and some blocks have the trend to slide. From August 2006, due to several heavily raining, the sliding velocity of blocks speed-up, and the gap of the joint become wider and wider, staggered joint appeared at parts of the surface of the slope, road, enclosing wall and building. The volume of the creep deformation rock mass at Mayanpo slope is estimated to be 5,600,000m. Discrete element method (DEM, Cundall, 1987) is an effective numerical method to analysis rock mechanical problems with discontinuities. Several authors have used this method to analysis slope stability problems. For example, Marc-Andre Brideau et al. (1999) used the above method to investigate the failure mechanism of the East Gate Landslide happened in 1997 in Canada; Rajinder Bhasin, et al. (2003) studied a 700-m high rock slope in western Norway using both static and dynamic methods by the numerical method of DEM, the results indicate that, the entire slope does not become unstable and that down-slope sliding and rotation of blocks occur mainly on the top layers of the slope. Zhang Chuhan, et al. (1997) used discrete element method to study the dynamic behaviors of three gorges shiplock slope in China, the numerical results agrees well with field measurements.
- Geology > Geological Subdiscipline > Geomechanics (0.67)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock (0.36)
ABSTRACT: The Qianjiangping landslide, located in China's Three Gorges Reservoir(TGR), occurred on 13th July 2003 , one month after the first impoundment to 135m a.s.l. of TGR water level. This is the first reservoir triggered landslide in TGR. This huge landslide was a high speed dip rockslide with a volume of 15 million m³, a maximum sliding velocity of 16m/s. The maximum surge height was 24.5m,and the sliding process was finished in less then 1 minute. The catastrophic landslide caused 10 people died, 14 people disappeared, destroyed 129 houses and 4 factories , and left 1200 people homeless . After the landslide, the author continued research on the high speed slide mechanism in order to be able to predict the same kind of landslide disaster in the TGR area and elsewhere in the world. On the research effort on the high speed slide mechanism seen in the Qianjiangping landslide is based on geologic analysis and numerical computations, concluded that the Qianjiangping landslide had a typical geological structure needed to gestate a high speed landslide; the great decline in shear strength in the shear zone (from peak to residual) is the essential cause for the high initial sliding speed; and the potential energy of the high slope and the liquefaction of the shear zone accelerated the sliding. 1. INTRODUCTION The Qianjiangping landslide, located in China's Three Gorges Reservoir(TGR), occurred on 13th July 2003 , one month after the first impoundment to 135m a.s.l of TGR water level, has been the first reservoir triggered landslide with the maximum slide velocity of 16m/s and the volume of 15 million m3 in TGR area[1]. The sliding process was finished in less then 1 minute, which was too fast for 13 citizens on the slope to escape. The landslide made maximum surge height of 24.5m [2],which killed 11 fishermen in the nearby river area. Study on the high-speed sliding mechanism of the Qianjingping landslide has a certain academic and practical significance for landslide disaster prevention and mitigation. Research on high-speed landslides from theory to experiment, began in the 1930s, has yielded fruitful research results in recent years [3~14].But in literature on high-speed sliding mechanism of Qianjiangping landslide is still not going far enough. Wu et al.(2006) simulated the Qianjiangping landslide sliding process by DDA method, drawing the biggest landslide sliding velocity of 5m/s for the conclusions, which was clearly inconsistent with the actual[15]; Wu et al. (2007) analyzed that Qianjiangping landslide had nurtured the typical structural features of high-speed slide, with the liquefaction features of the slip zone, but did not analyze the mechanism of high-speed sliding in detail[16]. The Qianjiangping landslide is very similar with Vaiont landslide in Italy in October, 1963, the latter's slide velocity was 15-30m/s. Regarding Vaiont landslide high speed mechanism, Skempton.
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock (0.68)
- Reservoir Description and Dynamics > Reservoir Characterization > Reservoir geomechanics (0.48)
- Reservoir Description and Dynamics > Reservoir Characterization > Exploration, development, structural geology (0.46)
- Reservoir Description and Dynamics > Reservoir Characterization > Geologic modeling (0.34)