Construction design of Hongjiadu concrete face rockfill dam?

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

1 project overview

Hongjiadu Hydropower Station dam is a concrete face rockfill dam with a height of179.5m, 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. The elevation of the dam bottom is close to that of the dam top, and the horizontal distance from the dam body is100 ~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 300 meters. The right bank is relatively gentle with a slope of 35 ~ 45.

This project is scheduled to cut off water on June 5, 2006, store water on April 6, 2004, generate electricity by 1 unit on June 6, 2004, 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 300 meters, 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 on the left bank is combined with the excavation at the entrance of flood discharge and power generation diversion system, and the excavated roads are uniformly arranged. 1087.5m,117.5m,1147.5m and1227.5m are arranged at different elevations, and the subgrade width is 8m. In addition, the No.4 branch tunnel is arranged at the elevation of1030m on the upstream slope of the steep wall, which is directly connected to the elevation.

The excavation road on the right bank is arranged in combination with the dam filling road of Tiansheng Bridge and Karazhai quarry. The excavation road has four floors, with elevations of 1 147.5, 1097, 1050 and 996 meters respectively. Among them, the 996-meter 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 is carried out simultaneously at the elevation of 1250 and1175m in the upstream and downstream respectively. Slope presplitting and 15m one-step millisecond extrusion blasting were used for excavation. In order to reduce the amount of 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 for stone slag discharge in the working face. The slag retaining platform and riverbed of Xiahe River at1030m 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 time limit for a project is arranged to start at the same time as the left bank abutment. It takes 18 months to dig to the elevation of 996 meters before river closure, with 340,400 m3 of rock excavation, 173 10000 m3 of overburden, and an average excavation intensity of 29,000 m3/month.

3. Dam filling

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

(1) Dump trucks are directly transported 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 realize high transportation intensity in 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 it slides down with the ramp truck through gravity. At the same time, the empty car on the other 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 is basically the same as the terrain slope. The track extending into the dam will be buried in the dam, and the mobile platform will be used at the bottom. When the system works, the platform and the track will be fixed together and will rise with the rise of the dam. The lowest descending position of ramp car is controlled by wire rope. With a 32t dump truck as the carrier, the elevation of the upper platform is1147m, and the lower platform is located in the dam, with the lowest elevation of 990m, the maximum height difference of157m, and the maximum length of the ramp is 320m. The acceleration of the ramp truck will be limited to 0.1~ 0.2m/. The braking acceleration will be limited to 0.11~ 0.174m /S2, the maximum driving speed is 6.67m/s, and the maximum traction force is 43t. According to the above parameters, the motor power required for each system is 2×300kW, and each working cycle takes 5~6min.

Because the direct transportation distance of dump trucks is within 3 ~ 3.5 kilometers, 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 in advance, and uniform dam rise.

In the 1 dry season after river closure, the dam body will store water to a safe flood level, and the dam body will not flow, so it is the best way to discharge water by relying on temporary sections. Hongjiadu CFRD adopts the diversion method of intercepting cofferdam tunnel. The diversion standard of cofferdam is the once-in-a-year flood in dry season 10, while 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. Therefore, after the river closure is determined, the first-stage dam filling requirements should reach1023m before the end of May 2002.

After the diversion tunnel is blocked in the later period, it will be carried out in flood season at the rate of 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 above1098m before the flood season. Considering the risk of rockfill retaining water at high water level, the panel below 1 100 meters elevation should also be completed. Therefore, the elevation of1102m is determined as the dividing line of dam staging, which can meet the power generation grade requirements of the first generator.

The strength of the upper dam in the narrow river valley is limited, so the elevations of the above two important stages are mainly met by temporary sections, 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. During the panel construction, the corresponding dam body should naturally sink for more than 3 months, and it is best to spend a flood season; (2) The construction quantity should not be too large, so as to ensure that the panel construction does not occupy the straight-line construction period; (3) Try to make the dam stop water in advance to generate electricity, so as to improve economic benefits; (4) Avoid the risk of high rock filling and water retaining; 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 basic excavation of foundation pit are completed. The sources of dam filling materials are scattered, and the processing point of cushion materials, the stacking point of transition materials, the protective stone slag and some secondary rockfill materials are all located in the small waste 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 can be controlled. According to this requirement, there are three layers of traffic tunnels in the upper reaches of the left bank, namely: No.4 branch tunnel, which leads to the dam body with an elevation of1030m; No.5 branch tunnel, leading to the dam back, with an elevation of1055m; The traffic tunnel on the upper dam leads to the top of the dam with an elevation of1147.5m. According to this arrangement, combined with the roads inside and behind the dam, the dam filling requirements can be met.

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 the two-lane traffic tunnel is 10m×8m, and that of the single-lane tunnel is 6m×6m. Considering the transportation capacity of 2,000 vehicles day and night, the peak daily 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 adjacent 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, so it is necessary to support the slope during the excavation; The width of the excavation face is 300 ~ 400 meters, and the average thickness is 40 ~ 60 meters. Based on the above factors, the excavation intensity of the material yard is calculated to be 300,000 ~ 400,000 cubic meters/month according to reasonable mechanical equipment configuration and blasting charge control. 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, it is determined that the average construction intensity should 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 290,000 m3/month, and the peak filling strength is 337,000 m3/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 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 rock bank for excavation and blasting the rock bank for the last time is often adopted. This scheme should be used with care. The edge of steep abutment is often weathered and cracks appear, and the rock foundation may not be preserved. After blasting, the block rate of residual rock ridge is very high, which makes it more difficult to remove slag from river bed.

(2) In the canyon area, the dam is transported by road, and the road grade should be determined according to the transportation intensity of the dam and the selection of transportation equipment. Because the road is steep and curved, it is best to choose concrete 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 stages, but also often determines the flood season and power generation period. Therefore, the construction strength should be demonstrated in detail according to the actual situation. If the construction intensity is controlled by quarry mining, 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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