1 geological conditions
The reservoir area is inclined plate, and the strata include sandstone of Yujiang Formation of Middle Devonian, limestone of Donggangling Formation, limestone of Liujiang Formation of Upper Devonian and shale. Geologically, it is south-central oblique, and most folds and faults are north-south and parallel to rivers. Therefore, although most of the reservoir area is located in soluble carbonate rocks, there is no frequent leakage area around the reservoir after impoundment, and the groundwater in the reservoir is not deep and the surface water flow is rich, so it is a good reservoir.
2 design description
2. 1 orifice plate design
1) Selection of discharge mode The main discharge modes of gravity dams are open flow and orifice overflow. In addition to flood discharge, the former can also remove ice or other floating objects. When the gate is set, the elevation of the gate top is almost flush with the normal high water level, and the elevation of the weir top is low, so the water level and flow can be adjusted by the opening height of the gate, which is suitable for large and medium-sized projects. Therefore, in order to make the reservoir have greater flood discharge capacity, open overflow is adopted in the design.
2) Determination of the total length of overflow dam section The pier thickness is preliminarily determined, with the middle pier thickness d=7m and the side pier thickness t=5.5m, so the total length B0 of overflow dam section is: B0 = Nb+(n-1) D+2t = 5×12+(5-1).
3) Determination of gate height = normal high water level-weir crest elevation+(0.1~ 0.2) =182-176+(0.1~ 0.2) = 6+(0./kloc-)
4) Determination of final design head The maximum head on the weir Hmax= check flood level-weir crest elevation, i.e. HMAX =184.73-176 = 8.73m. The final design head HS = (7.5m% ~ 95%) HMAX = 6.5475 ~ 8.2935. ..
5) Check the discharge capacity of overflow weir with weir flow formula Q=σmmξB(2g)0.5H0 1.5, and the calculation result is |(Q, -q)/q|.
2.2 Drainage hole design
In this design, the power generation hole is designed with pressure hole, the irrigation hole is designed without pressure hole, and the power generation tail water is used for water supply. Design of pressure drainage hole The entrance of power generation hole is equipped with trash rack and emergency gate (also used as maintenance gate), and the exit is equipped with working gate. The cross section of the hole is circular, and the hole is lined with steel plates. There are four power generation holes * * *, which is the water supply mode of the unit.
1) The suggested maximum power generation flow of aperture D is 87.687m3/s, and * * has four units, calculated according to formula D=(4Q/πVp)0.5. Where: q is the flow led out by multiple power generation holes, m/s; Vp is the allowable velocity in the hole, m/s, and VP of the power generation hole = 3m/s ~ 3.6m/s; Then d = [87.687/3.14× 3] ~ [87.687/3.14× 3.6] = 3.05m ~ 2.785m, and D=3m.
2) The shape design of the water inlet adopts an elliptic curve at the top of the water inlet, and the equation is x2/a2+y2/b2= 1, where: a is the long semi-axis of the ellipse, and when the water inlet is circular, a is the diameter of the circular hole; For rectangular entrance, the top curve a is the hole height h, and the side curve a is the hole width b; B is the semi-axis of ellipse, and when the entrance is circular, b = 0.3a For rectangular entrance, the top curve b = (1/3 ~ 1/4) a and the side curve b=a/5. Where a=3 and b=0.3a= 1, then x/9+y= 1.
3) Set trash rack, plane emergency gate and plane working gate at the entrance of gate and gate slot. The emergency gate is arranged near the upstream dam face, and the gate slot is a rectangular gate slot with a size of 0.8m×0.5m.
4) A gradual change section is set behind the intake gate, which adopts fillet transition, and the length is (1.5 ~ 2.0) d, which is 5m here.
5) The slope pressing section of 1: 10 is adopted before the outlet of the water outlet, and the outlet section is 85% ~ 95% of the hole section. Since the cross-sectional area of the hole is A=π(D/2)2=7.065m2, the cross-sectional area of the outlet is 6.005m2 ~ 6.7 165438. The outlet section is square, with a size of 2.5m×2.5m and an area of Ac=6.25m
6) Check the discharge capacity. The discharge capacity is calculated according to the pipe flow formula Q=μAc(2gH). Where μ is the flow coefficient; Ac is the cross-sectional area of the outlet of the drainage hole, m2; H is the height difference between the reservoir water level and the outlet water level. If the discharge coefficient μ=0.85, then q = 0.85× 6.25× (2× 9.8× 39) 0.5 =146.878m3/s.
7) Non-pressure drainage hole design The working gate of the irrigation hole is arranged at the water inlet, and the top of the rear orifice of the working gate is raised to form a free surface flow. The shape design of the water inlet is composed of inlet curve section, inspection gate slot and slope pressing section. The entrance curve also adopts an elliptic curve of 1/4, followed by a straight slope press section with a slope of 1: 5, with a length of 6m.
3 construction technology
3. 1 dam crest structure
1) gate arrangement The working gate is arranged slightly downstream of the overflow dam section to prevent the water tongue from leaving the dam surface to form negative pressure when the gate is partially opened. The gate is a plane steel gate, the gate size is 5m× 12m, there is a maintenance gate at the upstream of the working gate, and the clear distance between the two gates is 2m.
2) The upstream of pier head is semicircular, and the downstream is streamlined. The working bridge is arranged upstream, and the top elevation is taken as the elevation of non-overflow dam, that is, 176m, with the middle pier being 7m thick and the side pier being 5.5m thick. The parting of the overflow dam is located in the middle of the sluice hole, so there is no combined pier. The working gate has a groove depth of 0.532 1m and a width of 1m, and the maintenance gate has a groove depth of 0.5m and a width of 0.8m..
3) The side pier of the water guide wall extends downstream to form the water guide wall, and its length extends to the end of the nose sill. The height of the side pier should be 0.5m ~ 1.5m higher than the aerated water depth. The estimation formula of aerated water depth in straight section is hb=h( 1+ξv/ 100). Where: H and hb are the water depth before and after aeration, m; V is the average flow velocity of the calculated section before aeration, m/s; ξ is the correction coefficient, generally 1.0 ~ 1.4m/s, v >；; 20m/s, whichever is larger. Then the height of the water guide wall HB =1.8× (1+1.4× 22.887/100) = 2.377m, 2.377+0.6=2.977m, and the water guide wall needs to be split, with the spacing.
3.2 dam joint and water stop
1) transverse joints are arranged perpendicular to the dam axis, with a joint distance of 19m, a joint width of 2cm, and a water stop inside. 2) The dam body is provided with two water stop pieces and an anti-seepage asphalt well. The water stop is made of copper with a thickness of 1.0mm, and the first water stop is 1.0m away from the upstream dam surface. The distance between the two waterstops is 1m, and there is an asphalt well with a diameter of 20cm in the middle. The lower part of the water stop is 30cm deep into the bedrock, tightly embedded with concrete, and the upper part reaches the dam crest. 3) The longitudinal joint is a temporary joint with a keyway. After the concrete is fully cooled, grouting should be carried out before the reservoir is filled with water. The longitudinal joint is perpendicular to the dam surface, and the joint distance is 20cm. 4) The thickness of concrete pouring blocks for horizontal construction joints is 4m, the horizontal joints of adjacent dam blocks on both sides of longitudinal joints are staggered, and the interval between the upper and lower concrete pouring layers is 5d. Before pouring the upper concrete, chisel and rinse the lower concrete, and lay 2cm thick cement mortar.
3.3 Corridor system
1) The corridor bottom of the foundation corridor is 4m away from the dam foundation surface, the elevation of the corridor bottom is 147m, and the upstream side (center point) is 4m away from the upstream dam surface; It is shaped like a city gate cave, with a bottom width of 2 meters and a height of 3.5 meters. There is a drainage ditch in the upstream and a collecting well in the lowest place. Parallel to the dam axis, the corridor gradually rises along the topography on both banks, and the slope is not more than 40.
2) Starting from the foundation corridor, the dam corridor is provided with one floor every 18m along the dam height, with two floors in total. The bottom elevations are 16 1m and 179m, respectively, which are in the shape of a city gate cave. The upstream side (center point) is 4m away from the upstream dam face, with a bottom width of 2m and a height of 3m. There is an exit on the left and right banks.
3.4 dam seepage control and drainage
1) The upstream surface, overflow surface and downstream surface of the dam body below the highest water level are impervious, and the impervious facilities of the dam body adopt a layer of concrete with impermeability of 2m thickness.
2) The dam drainage is 5m away from the upstream surface of the dam, and a row of vertical drainage curtains is set along the dam axis. The inner diameter of the pipeline is 20cm, and the spacing is 2.5m m. The upper end of the pipeline is connected to the dam crest and the lower end is connected to the corridor, which is vertically arranged. The drainage pipe adopts sand-free concrete pipe.
3.5 dam concrete strength grade
Dam concrete should meet the requirements of strength, impermeability, frost resistance, erosion resistance, erosion resistance, low heat resistance, crack resistance and volume reduction when hardening. In order to use materials reasonably, dam concrete can adopt different strength grades according to different parts and working conditions. The thickness of upstream surface is greater than that of downstream surface, and the thickness of foundation concrete (area IV) is 0. 1B(B is the width of dam bottom), and there should be a good contact zone between concrete with different strength grades of not less than 3.9m.
3.6 Foundation treatment
1) Anti-seepage curtain and drainage hole curtain are drilled in the grouting gallery of dam foundation anti-seepage treatment, and their center lines are 3m and 5m away from the upstream dam heel respectively. The impervious curtain adopts expansive cement slurry as grouting material, which is arranged on the dam foundation and both banks near the upstream dam surface. The depth of the curtain is 10m~30m ~ 30m, and the riverbed is deep, and the banks gradually become shallow. Grouting holes are 80mm in diameter, vertical, 2m apart, and arranged in a row.
2) The drainage hole curtain of dam foundation is located downstream of the anti-seepage curtain, inclined downstream, with an included angle 10 with a hole spacing of 3m, an aperture 130mm and a hole depth 10m ~ 15m, and arranged in a row along the dam axis.
Before construction, the project must be carefully analyzed and the best construction method should be selected according to the actual situation of the project. At the same time, during construction, the construction management personnel must coordinate and arrange, strictly control the construction technology, and the construction personnel should do a good job in quality control and acceptance of key working procedures to ensure the engineering quality.
I believe that after the above introduction, everyone has a certain understanding of dry goods sharing and dam construction. Welcome to Zhong Da for more information.
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