Research On The Effect Of Narrow Channel Covered In Wide Valley On High Gravity Dam And Treatment Scheme Of Longkaikou Hydropower Station

The highest section of high concrete gravity dam, as well as the largest loading is located in the river bed.Because of the water and quaternary system coverage, the riverbed is relatively weak zone of exploration and test.Therefore. It’s hard to reveal some large hidden engineering geological problems under dam foundation of modern riverbed. Once exposed during construction period, the problems often affect the whole project seriously, which cause huge losses. To find out the origin, engineering geological conditions of geological problems and chooses the optional manage scheme can reduce the damage to a minimum.This paper takes the Longkaikou Hydropower Station of the Jinsha River as an example, where the riverbed of dam axis is wide and flat. The narrow channel is revealed during construction period when most of the dam has been constructed. The large-scale deep channel is 40m in depth and 6m in width of narrowest site, which is similar to the micro gorge. The deep groove has typical characteristicand not tectonic origin. It’s very particular that such a deep-narrow long channel covered in such hard rock of the middle reaches of Jinsha River.The engineering characteristics of channel rock changed during the process of its formation. The deep narrow channel is filling with tens meters of sand and gravel layer, time of project is limit as well, so the conventional exploration methods cannot be used here. It’s hard to survey and evaluate the rock of the narrow channel. This paper use the large amounts of data on spot and the data of relatively large hydropower, taking comparative thinking and citation, to clarify the quickly and various survey technology, as well as to analysis the origin of the narrow channel. In the aspect of mechanical parameters of rock mass, use the analogy to analyze rock mass structure, rock grade and mechanics parameters.Use numerical analysis to study the management of the channel. The specific contents are as follows:(1)Unconventional exploration technology of deep channel lurked in modern riverbed. Basing on dynamic train of thought, use consequent of Longkaikou dam basement, investigation on spot, and seismic CT, inclined borehole, slot borehole and vertical borehole to find out the channel rock. Layout boreholes layer by layer in the initial survey period and the construction stage. Complete the follow-up evaluation of engineering geological characteristics of channel rock mass from initial to final phase, which provide important geological information for design and construction measures for further engineering;(2)Engineering geological condition and availability evaluation based on Unconventional exploration technology of deep channel, which include space form, engineering geological condition and availability evaluation.Reveal the deep-narrow channel space distribution accurately by inclined borehole, seismic CT. As revealed continuously, modify the groove space distribution gradually. Comprehensively analyze the spatial distribution characteristics of the narrow channel from the horizontal, vertical and horizontal direction. Finish the three-dimensional spatial distribution model of the deep-narrow channel.Carry out rapid, multiple means to ascertain the rock structure, weathering extent, unloading zone of the deep groove. Measure the fracture in groove wall and platform revealed. Using lots of borehole and fast integrity assessment, considering the research experience of Longkaikou and other related hydropower, basing on the characteristics of deep groove, obtain the evaluation method and standard of deep groove, the division of rock mass structure, weathering and unloading zone as well;Use the large number of holes to identify the quality of deep groove rock. Comprehensively study the rock quality and mechanical parameters of the groove by relatively rock evaluation techniques, technology, achievements of earlier research on Longkaikou basement. According to the construction schedule, follow-up evaluate and revise the deep groove rock layer by layer, and constantly predict the rock mass quality, changes of mechanics parameters and availability.Research into evaluation of deep rock mass by the rock mass evaluation standards of Longkaikou high gravity dam foundation, providing important data for design and construction;(3)On the base of regional geological environment of the deep groove, data of relative big hydropower, the structure of middle reaches of Jinsha River Valley, the stacking feature of quaternary in riverbed, valley morphology, lithology, tectonic conditions, fully reveal the characteristics of deep groove.Combin with the riverbed morphology, structure, lithology, existence of lake varve to study the origin of the deep groove covered in Longkaikou modern riverbed;(4)Based on geological characteristics of the deep groove, choose the suitable treatment scheme. Considering the engineering safety, investment, construction period and other factors, select reasonable treatment scheme-deep groove-crossed board,then excavate-backfill. Analyze the whole process of selected scheme based on ANSYS.Analyze stress, strain, stability and the influence of superstructure on deep groove rock during construction period and normal operation:to simulate the manage scheme construction of deep groove step by step, to analyze the effect on the upper structure and foundation of different construction step, to use overload coefficient method and strength reduction method to evaluate the stability of gravity dam. Simulate the complete basement, basement with deep groove untreated and basement with deep groove treated to research the impact of narrow-deep channel on concrete dam and effects of treatment scheme.