| The under construction Miaowei Hydropower station in Lancang river is located near the JiuZhou Town Miaowei Village in Yunlong County.It is in the Mountain range Rift Valley region of Lancang river. Planning is the most downstream Lancang River upstream of a cascade hydropower stations. The proposed dam is rockfill dam, the maximum height of 139.80 m, reservoir normal water level 1408.0m, corresponding storage capacity 660 million m3, dead water level 1398 m, corresponding storage capacity of 501 million m3, using the power house at dam-toe. Intake slope is the height of 71 m, the width of slope is only about 110 m at EL1370, for an excavation of four diversion tunnel with a diameter of 12 m, so the axis spacing between adjacent tunnel is only 26.5m, the thickness of rock wall is only less than 15 m between the tunnels. In narrow toppling slope caverns excavated are so dense, how to ensuer the stability of the caverns, and how cavern excavation has impact on slope stability has become an important issue in engineering design and construction.Combination of the above problem, this paper takes Miaowei water diversion tunnel and water-intake slope as the research object, using the geological and numerical simulation analysis, further study the stress- deformation characteristics of Intake Slope before and after the diversion tunnel excavation, and the stability of tunnel surrounding rock, meanwhile support measures for evaluation of the deformation are analyzed and recommended. Through systematic research and analysis, this paper has made the following findings and basic understanding :(1) According to preliminary geological survey data, and combined with the field investigation and recheck of the geological conditions during excavation, a systematical analysis is presented of the engineering geological conditions of the project area,especially the characteristics of the rock mass structure and the toppling deformation,the results show that: the slope toe of the left bank is given priority to with soft rock, the central and upper part is interbedded with soft and hard rock; Within the range of the slope, the development of structure surface is mainly with the level of Ⅲ1,Ⅲ2, Ⅲ3,Ⅳ and Ⅴ structural plane; After the slope excavation, only a few of level of A,B1, B2 toppling deformation rock mass and part level of C toppling deformation rock mass is last.(2) Three axis rheological experiment system of soil mass was used to test the mechanical properties of the interlayer fracture zone: Natural shear strength index ofinterlayer fracture zone c is 105 KPa, ? is 47°, saturated shear strength index c is69 KPa, ? is 36. Interlayer fracture zone of slope stress- strain curve can be divided into four stages: compaction stage, the stage of elastic deformation, plastic deformation,destruction phase. The rheological experimental studies of interlayer fracture zone shows that interlayer fracture zone creep deformation characteristics consistent with Burgeers rheological models, the creep constitutive equation is:Interlayer fracture zone flow into the rheological stages long-term shear strength index: c is 46 kpa,? is 27°.(3) Though of the general structure of the intake slope of Miaowei hydropower station hole site, the water inlet slope deformation and stability were studied, the results show that: after excavation of slope, Slope stability is good in natural conditions and it is less likely overall instability, and it is in understable state in the rainstorm conditions,there are local or global instability. And puts forward the optimized support scheme, the monitoring data of intake slope can provide data support for the slope deformation on the basis of the intake slope, the intake slope is in stable state.(4) By means of finite difference FLAC3 D numerical simulation, the deformation characteristics of intake slpoe before and after tunnel excavation were analyzed, the results show that: the deformation of the intake slope before the diversion tunnel excavation mainly concentrated in A zone, after the tunnel excavation it provides new deformation space, leading to the deformation of the slope to the deep development,which affect the stability of the intake slope.(5) Though numerical simulation method, the stability of surrounding rock is analyzed by the safety distance and construction scheme of the tunnel group. The results show that: the proposed design 26.5m spacing can meet the security needs; the quantitative indexes of the numerical calculation of the 3 excavation schemes are basically equivalent, considering the mutual influence of the diversion tunnel, the proposed scheme is the first excavation of 1# and 3# diversion tunnel and after the excavation of the diversion tunnel 2# and 4#. |
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