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Construction design of Hongjiadu concrete face rockfill dam?

What is the specific content of the construction design of Hongjiadu concrete face rockfill dam? Zhong Da Consulting will answer your questions below.

1, project overview

Hongjiadu Hydropower Station dam is a concrete face rockfill dam with a height of 179.5m, a crest length of 427.79m and an aspect ratio of 2.38, which belongs to a high face rockfill dam with narrow riverbed. The rest of the hub buildings are concentrated on the left bank. There are two stone yards upstream and downstream of the dam body on the right bank, with the bottom elevation close to that of the dam top and the horizontal distance from the dam body of 100~ 150m. The cross section of the dam site valley is asymmetrical "V" shape, and the left bank is steep, with 70 ~ 80 limestone steep walls with a height difference of about 300m m.. The right bank is relatively gentle with a slope of 35 ~ 45.

The project is scheduled to cut off water on June 5, 2006, store water on April 6, 2004, generate electricity on June 6, 2004 1 unit, and be completed on September 30, 2005. The total construction period is 5 years and 9 months, in which the power generation period of 1 unit is 4 years and 9 months.

2, dam abutment excavation

Abutment and dam foundation excavation has a large amount of work and complex topographic and geological conditions, among which the left abutment is steep and the excavation slope is as high as 300m, which is one of the key projects in engineering construction. During excavation, stone slag should fall into the river bed as far as possible to block the river course. On the other hand, it is required to excavate as close as possible to the river bed water level before river closure to ensure the straight-line construction period. The excavation of left bank abutment must pass through the entrance of flood discharge tunnel, diversion tunnel and other buildings, which has great construction interference.

2. 1 construction layout

The excavation of the left bank is combined with the excavation of the entrance of flood discharge and power generation diversion system, and the excavated roads are uniformly arranged. 1087.5m,117.5m,147.5m, 1227.5m highways are arranged at different elevations, and the subgrade width is 8 m, in addition, they are upstream of steep slopes.

The excavation road on the right bank is combined with the dam filling road layout of Tiansheng Bridge and Kalazhai Stone Yard, and a total of four layers of excavation roads are arranged, which are located at elevations 1 147.5, 1097, 1050 and 996m respectively. Among them, the 996m highway is connected with the No.3 construction branch tunnel through the traffic tunnel, avoiding the foundation pit of the power plant and leading to the upstream cofferdam in the form of traffic tunnel.

2.2 excavation method and progress

The excavation of the left bank abutment enters the excavation face from the bifurcation branch, and the upstream and downstream are carried out simultaneously at the elevation 1250 and 1 175m respectively. Slope presplitting and 15m one-step millisecond extrusion blasting were used for excavation. In order to reduce the debris flow into the river, the blasting working face should be arranged perpendicular to the river bed as far as possible, and a rock ridge should be reserved near the edge of the steep wall for final blasting. 4m3 excavator, 2~5m3 backhoe and 20~32t dump truck are used to discharge the stone slag in the working face. At the elevation of 1030m, the slag retaining platform and riverbed of the river shall be cleaned with backhoe in time. Slope support and excavation are carried out in parallel. Construction began in May 2000. The excavation ended at 2001100/00 m, which lasted for 18 months, and the stone excavation was 980,000 m3, with an average excavation intensity of 54,000 m3/ month.

Excavate 6~ 15m steps from top to bottom on the right bank abutment. The construction period is arranged to start at the left bank abutment at the same time. Before river closure, it needs to be excavated to an elevation of 996m, which takes 18 months. The stone excavation is 340,400 m3, the overburden is 173 1 10,000 m3, and the average excavation intensity is 29,000 m3/ month.

3. Dam filling

3. 1 dam surface transportation There are two main schemes for dam filling: direct dam surface transportation by dump trucks and combined dam surface transportation by mobile ramp trucks.

(1) Dump trucks are transported directly to the dam. This scheme is simple, safe and reliable, and has been widely used in the construction of concrete face rockfill dam. It can achieve higher transport intensity on a wide river bed. However, for Hongjiadu project located in narrow riverbed, it is difficult to arrange construction roads with 45t dump trucks, so 32t dump trucks are selected as the main transportation equipment for dam materials. The road standard is road width 10m, average longitudinal slope 6%~7% (individual sections 10%~ 12%), and minimum turning radius 15m.

(2) Joint transportation scheme of moving ramp vehicles to the dam. The combined transportation system of mobile ramp car consists of two groups of tracks, and each group of tracks is connected with the winch through wire rope and pulley respectively. When the system works, the heavy truck is located on the upper platform of the ramp track and slides down with the ramp truck by gravity. At the same time, the empty car on another track will be pulled to the upper platform, and the braking and speed of the ramp car will be controlled by the motor. The track slope and terrain slope are basically the same. The track extending into the dam will be buried in the dam, and the bottom will adopt a mobile platform. When the system works, the platform and the track will be fixed together and will rise with the rise of the dam. The lowest downward position of the ramp car is controlled by the wire rope. With a 32t dump truck as the carrier, the elevation of the upper platform is 1 147m, and the lower platform is located in the dam, with the lowest elevation of 990m, the maximum height difference of 157m, and the maximum length of the ramp is 320m. The acceleration of the ramp truck will be limited to 0. 1~0.2m/s2. The braking acceleration will be limited to 0.11~ 0.174m/S2, with the maximum running speed of 6.67m/s and the maximum traction of 43t. According to the above parameters, the motor power required for each system is 2×300kW, and each working cycle is 5 ~ 6 min.

Because the direct transportation distance of dump trucks is within 3~3.5km, which belongs to the range of economic transportation distance, the investment in temporary facilities is less, while the engineering quantity and operating cost of temporary facilities in ramp transportation scheme are relatively high. Therefore, the direct dam loading scheme of dump truck is finally recommended.

3.2 Dam filling by stages

Dam staging mainly meets the requirements of dam construction safety, dam flood control mode, power generation ahead of schedule and uniform dam rise.

The best way of flood discharge for dam body is to fill the dam body to the safe flood level in the 1 dry season after river closure, and the dam body will not flow and rely on temporary sections to stop water. Hongjiadu CFRD adopts the diversion method of intercepting cofferdam tunnel. The diversion standard of cofferdam is the once-in-a-decade flood in dry season, and the flood crossing standard (when the reservoir water level is ≥ 1 100 million m3) is the flood with frequency P= 1%, and the corresponding water level is1021.7m. Therefore, after the closure is determined, the first-stage dam filling requirements should reach 1023m before the end of May 2002.

After the diversion tunnel is blocked in the later period, it will be implemented in flood season at P=0.2%, and the highest water level in front of the dam will reach the elevation of 1098m. After the diversion tunnel is blocked, the temporary section of the dam should be above 1098m before the flood season. Considering the risk of retaining water by rockfill at high water level, the panel below 1 100m elevation should also be completed. Therefore, the elevation of 1 102m is determined as the boundary of dam staging, which can meet the requirements of the power generation level of the first generator.

The strength of the upper dam in the narrow river valley is limited, and the elevations of the above two important stages are mainly met by the temporary section, and the rest stages are divided according to the requirements of convenient construction, uniform rise of the dam body and guarantee of construction quality.

3.3 Panel segmented transportation

The principle of panel staging: ① Arrange the construction in low temperature and dry season, and the corresponding dam body should naturally sink for more than 3 months during panel construction, preferably through a flood season; (2) The engineering quantity should not be too large to ensure that the panel construction does not occupy the straight-line construction period; (3) Try to let the dam stop water in advance to generate electricity, so as to improve economic benefits; (4) Avoid the risk caused by high rockfill retaining water; ⑤ Seepage-proof clay and protective stone slag (filling elevation is 1030m) at the upstream of the face slab are constructed under the protection of cofferdam, so there is enough construction time.

According to the above principles, the face slab will be constructed in three phases, the elevation of the first phase is 103 1m, the corresponding rockfill elevation of the second phase is 1033m, the second phase is100m and the third phase is 102m.

3.4 Layout of Upper Dam Road

The valley at the dam site of Hongjiadu Hydropower Station is narrow, and it can only be filled after river closure and foundation excavation. The sources of dam filling materials are scattered, and the processing point of cushion materials, the stacking point of transition materials, protective stone slag and some secondary rockfill materials are all located in the small scouring dump on the upstream of the left bank, so the dam must be placed on the left bank. The remaining main rockfill materials and secondary rockfill materials are sent to the dam from the right bank of the downstream Tianshengqiao and Kalazhai quarry and Wangjiadu slag yard. The principle of road layout is that no matter whether the material source is upstream or downstream, the dam is loaded from downstream, and the whole dam filling construction is controllable. According to this requirement, there are three layers of traffic tunnels in the upper reaches of the left bank, namely: the No.4 branch tunnel leads to the dam body with an elevation of1030m; No.5 branch tunnel leads to the dam back, with an elevation of1055 m; The upper dam traffic tunnel leads to the dam top, with an elevation of1147.5m; There is a five-story highway on the right bank with an elevation of 996,655. According to this layout, combined with the roads in and behind the dam, it can meet the dam filling requirements.

3.5 Construction intensity and construction period

The main factors affecting the construction intensity are: transportation intensity, dam surface operation intensity and quarry mining intensity.

(1) transport intensity. The road standard for the dam is Grade III, concrete pavement, road width 10m, maximum longitudinal slope 12%? The cross section of two-lane traffic tunnel is 10m×8m, and the cross section of one-lane tunnel is 6m×6m. Considering the capacity of 2000 vehicles day and night, the daily peak strength of 32t dump truck can reach 32,000m3, and the peak strength can reach 720,000m3/month.

(2) Operation strength of dam surface. Mechanized flow operation, reasonable mechanical equipment configuration, dam surface zoning and efficient organization and management, the intensity of dam surface operation should generally be greater than the transportation intensity.

(3) Mining intensity of the material yard. This is determined by geological and topographic conditions and the size of the working face. The horizontal distance between the two rockfill yards and the dam is only 100 ~ 150m, and the downstream of Karazhai quarry is close to landslide 1, so the influence of blasting vibration on landslide must be considered when mining the quarry. The terrain slope of the two quarries is 25 ~ 35, and the dip angle of rock strata is basically the same as that of the surface, and the dip angle is slightly smaller than that of the surface, so it is along the slope; There is a weak interlayer in the excavated rock, and the slope is required to be supported during excavation; The width of the excavation face is 300 ~ 400m, and the average thickness is 400 m. Based on the above factors, the excavation strength of the material yard is calculated to be 300 ~ 400,000 m3/ month according to the reasonable mechanical equipment configuration and the control of blasting charge. Therefore, the main factor that determines the dam filling strength of Hongjiadu Hydropower Station is the stone mining strength. According to the construction period requirements of Hongjiadu Hydropower Station in September 2004, the average construction intensity is determined to reach 300,000 m3/ month.

4. Arrangement of dam filling by stages

The dam filling design of Hongjiadu Hydropower Station is divided into seven stages, and the face slab construction is divided into three stages. The total filling time is 3 1.5 months, the average filling strength is 290,000m3/month, and the peak filling strength is 337,000m3/month. See figure 1 and table 1 for the design dam filling stage.

5. Conclusion

Hongjiadu Hydropower Station was officially started on June 8, 2000 +065438+, and all the work is being carried out in an orderly manner according to the construction plan. Judging from the constructed sections, the construction scheme is reasonable in terms of construction scheme, overall layout, road system planning, and node construction period arrangement. Through the preliminary design and construction practice, the experience is as follows:

(1) It has always been a difficult problem to excavate the riverbed under the rubble at the steep abutment of the rockfill dam in the canyon area. In order to reduce the riverbed under the stone slag, the scheme of reserving the rock sill for excavation and blasting the rock sill for the last time is often adopted. This scheme should be used with care. The edge of steep dam abutment is often weathered and cracked, and the bedrock may not be preserved. The retained rock sill has a high lump rate after blasting, which makes it more difficult to discharge slag from the river bed.

(2) In the canyon area, the transportation on the dam adopts highway, and the road grade should be determined according to the transportation intensity and the selection of transportation equipment on the dam. Because there are many steep bends, it is best to choose cement pavement. The scheme of mobile tilting rail car using gravity transportation is technically feasible, and it is a subject worthy of study in areas with large height difference.

(3) Diversion and flood discharge are the main factors that determine the dam filling stage; The construction intensity not only determines the stage, but also often determines the flood season and power generation period. So the construction strength should be demonstrated in detail according to the actual situation. If the construction intensity is controlled in quarries, it can be adjusted by preparing materials in advance.

(4) The panel construction stage also directly affects the filling stage. Panel construction should be arranged in the right season to ensure the quality of the panel; Panel construction does not occupy a straight-line construction period; Rock filling must be higher than the height of the corresponding panel by stages to ensure the construction quality of the panel.

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