Long-Term Deformation Analysis and Treatment Measures for Layered Soil Slopes in Dam Reservoirs: A Case Study
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During the construction of Jinsha River Wudongde Hydropower Station, we encountered problems affecting the safety and stability of the mountain, such as the development of laminated geological formations, poor integrity of the slope surface rock, and even slippage and large deformation. In order to strengthen the deformation and stability control of the layered rock body of the side slope and ensure the safety of the dam project, we tracked and analyzed the actual measured displacement data. Taking the flood relief tunnel rock body and slope as the main research object, we analyzed the valley deformation and development trend in key areas, and summarized the spatial and temporal distribution law of valley deformation in different areas. At the same time, a three-dimensional geological model is established by numerical simulation method, and the finite difference combined with the reduction method is used to calculate the stability of the slope of the flushing pool. The deformation monitoring and numerical simulation results reveal the deformation characteristics of the valley and the stability of steep slopes in the early stage of water storage, and explain the evolution mechanism of slope deformation based on geological structure characteristics. It is found that: the laminated slopes in the reservoir area of the dam are prone to deformation under the joint action of long-term construction disturbance and fracture water seepage; construction disturbance has a high degree of influence on the artificial excavation area below 1070m in elevation, with the maximum rock deformation and surface displacement reaching 92.2mm and 312.5mm, respectively; however, the mountain above 1070m in elevation is limitedly affected, and the valley deformation of the mountain on the left bank of the reservoir area is higher than that on the right bank, the accumulated deformation on the left and right still does not exceed 20mm; seepage has a more obvious effect on the displacement of the top of the slope, and excavation and other disturbances have a more obvious effect on the displacement of the artificial slope; for the deformation of the valley of the water pad pond behind the dam increases more slowly, the deformation data at the site is basically consistent with the change trend of the numerically calculated data, and generally shows a contraction trend, the maximum contraction of the simulated calculation is close to 20mm, located at an elevation of 990m. On-site slope displacement monitoring, with high precision and real and reliable data, is of great significance for hydropower plant construction and long-term safe operation after completion.Accretionary wedge
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Fluvial fans represent one of the dominant sedimentary systems at the active margins of non-marine foreland basins. The Puig-reig anticline at the north-eastern margin of the Ebro Foreland Basin (SE Pyrenees, Spain) exposes continuous outcrops of Late Eocene-Early Oligocene fluvial deposits, from proximal to medial fluvial fan environments. The proximal deposits are found in the north limb of the anticline, especially in the northwest zone. These deposits are characterised by conglomerates with minor interbedded sandstones, with thick and wide sheet-like geometries with unscoured or variably scoured basal surfaces. These are interpreted to be the deposits of unconfined flash floods and wide-shallow channel streams. The medial deposits, covering the rest of the anticline, consist of interbedded conglomerates, sandstones and claystones. These are interpreted to have been deposited from braided to meandering channel streams and overbank areas. Distal deposits are found towards the south, beyond the anticline, and are characterised by sandstone and clay deposits of terminal lobes and lacustrine deltas. This study assesses the impact of the primary depositional characteristics, diagenesis and deformation of the most heterolithic portion of the system, with implications for increasing our understanding of folded fluvial reservoirs. Diagenetic processes, mainly mechanical compaction and calcite cementation, resulted in overall low intergranular porosity, with limited relatively high porosity developed in sandstone lithofacies in the medial deposits. Deformation associated with thrusting and fold growth resulted in the formation of abundant fractures, with relatively high fracture intensities observed in sandstone lithofacies in the anticline crest. This study shows that post-depositional processes can both improve and diminish the reservoir potential of basin proximal fluvial deposits, through the development of fracture networks and by compaction-cementation. The comparison of the Puig-reig anticline with other similar settings worldwide indicates that foreland basin margin locations may be potential areas for effective reservoirs, even in the case of low intergranular porosity.
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Pennsylvanian foreland deformation associated with the Ouachita orogene reactivated a west-northwest-east-southeast Cambrian basement trend, the southern Oklahoma aulacogen, to form the Wichita uplift, southwest Oklahoma. The 30-km-wide subsurface Frontal fault zone separates the uplift from the Anadarko basin to the north. Horizontal shortening across this fault zone is estimated at 7-15 km (20-40%), vertical displacement totals 9-10 km from the uplift to the basin. Folds are mapped on an interformational scale within the Frontal fault zone, and on an intraformational scale (Cambro-Ordovician Arbuckle Group) in the Slick Hills, southwest Oklahoma. Additional shortening occurred along southwest dipping mountain flank thrusts and on bedding plane thrusts, respectively. Hanging wall blocks of major faults contain the shallow dipping limb and anticlinal hinge zone of the interformational scale folds. Oil and gas production is generally restricted to these anticlinal crests within Paleozoic rocks. Deep wells (> 6000 m) that have penetrated footwall imbricates of the mountain flank thrusts have drilled through steep-overturned beds and tight recumbent folds before passing through faults into a normal stratigraphic sequence. Basement thrust loading of the southern margin of the Anadarko basin controlled the trend (west-northwest-east-southeast) of the axis of maximum deposition within the basin during the Pennsylvanian.
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