Small reservoir construction organization design preliminary discussion?

This paper summarizes the construction organization design of small reservoirs on the basis of the proposed use of pumping for the construction of small reservoirs in mountainous areas diversion, and through the analysis of engineering examples know that the use of pumping can save a large amount of money for the design of small reservoirs in addition to the risk of reinforcement design to provide a practicable construction program.

1Introduction

Small reservoirs have a lot of problems and few funds, in the case of limited funds, as far as possible to complete the design of the de-risking and strengthening of sick reservoirs, which has brought great challenges to the designers, especially the construction of diversion programs, almost every small reservoir construction organization design have encountered this problem, in the process of the design of the authors according to the characteristics of several small reservoirs to summarize . There are mainly two aspects of the problem: First, the reservoir capacity curve is relatively flat,

Construction of the reservoir water level rise is small, this situation is generally used cofferdam way more economical; Second, the reservoir capacity curve is steeper, the reservoir water level during the construction period is rising fast, if the traditional diversion program, using cofferdam type, is a small reservoir total investment of more than 3 million can not afford to meet this situation, the authors think that The use of pumping is more economical and practical. In this paper, Zhushan County, Gujiagou reservoir construction organization design as an example to focus on the second case of construction diversion design.

2 project overview

Gujiagou reservoir is located in Hubei Province, Zhushan County, drumming town, West River Village, the reservoir dam intercepts the West River upstream of the ancient family ditch and Wuchang Temple ditch water, the reservoir above the dam site rain area of 3.2km2, the river is 2.9km long, watershed to the dam site of the main channel average slope drop of 115.2 ‰, the terrain is relatively high. The dam site is 10km away from the drum town, 60km away from Zhushan County. it is a small (1) type reservoir pivot project which is mainly used for irrigation, and also has the function of flood control and water supply and other comprehensive utilization. Reservoir hub project existing buildings include: clay heart wall dam, spillway and water transfer culvert pipe composition. The reservoir has a total capacity of 1,710,000 m3, of which 1,407,000 m3 are profit-making and 63,000 m3 are dead.The reservoir provides irrigation water for 0.3 million acres of farmland in the downstream irrigation area, and also undertakes the flood control tasks of the downstream Drumming Town and 305 Provincial Highway and other facilities, and protects 0.3 million acres of farmland and 1.0 million people. Gujiagou reservoir hub is Ⅳ project, small (1) type scale, its water retention, water discharge, water transfer buildings for the 4-level buildings. Reservoir de-risking and strengthening of the preliminary design project mainly includes: ① the heart wall of the dam part of the filling grouting method to deal with, to solve the heart wall permeability coefficient does not meet the requirements of the problem; dam and spillway bedrock medium permeability layer using curtain grouting; ② for the deformation of the dam slope and berm weathering and crushing of the situation, the upstream dam slope refurbishment, the use of 30cm-thick dry masonry berms, the downstream slopes of the dam in the leveling of the foundation of planting The downstream slope is planted with turf on the basis of leveling to improve the structure of the dam surface; ③ Seal the original water conveyance culvert, and open a new flood relief tunnel upstream of the right bank of the dam, which is also used for irrigation water conveyance. The original spillway will be blocked, demolition and reconstruction of the left wall of the inlet canal and control section, the new 21m long water retaining earth dam; ④ update the opening and closing equipment, additional inlet maintenance gates and outlet working gates.

3. Construction Organization Design

Gujiagou Reservoir is located in the watershed area is a subtropical continental monsoon climate, with warm and humid, four distinct seasons, abundant rainfall, abundant light and other characteristics. Frost-free period of about 250 days, the average annual temperature of 10.2 ℃ ~ 15.6 ℃, the extreme minimum temperature of minus 9.9 ℃, the extreme maximum temperature of 43.4 ℃. The average rainfall in the regional reservoir area is 849.5mm, the average runoff depth is 353mm, and the average volume of water is 4.29 million m3. Floods in the basin are generated by torrential rains, and the time of occurrence of torrential rains is generally from July to October, and the formation of torrential rains is mostly due to the low vortex shear and frontal rain surfaces, and the number of typhoons that form large torrential rains in depth is very small. The duration of heavy rainfall is generally 1 to 3 days, the scope of heavy rainfall is generally throughout the entire basin, rainfall is characterized by concentrated rainfall, intensity, flood peaks, high volume, steep rise and fall. The multi-year average maximum wind speed at the dam site is 13m/s, and the wind direction is generally northeast.3.1 Construction diversion standardThe permanent buildings of this project are class 4 buildings. According to the Specification for Construction Organization Design of Water Conservancy and Hydropower Projects (SL303-2004) and the specific conditions of this project, the level of temporary buildings for diversion is set at level 5. Combined with the diversion requirements of this project, the 5-year flood in dry water period is selected as the diversion standard.3.2 Construction organization designAccording to the project volume and project characteristics, one dry water period is used to complete the reinforcement of the dam pivot project and the construction of management facilities, i.e., the total construction period is set at 12 months. July of the first year for the construction of the preparatory period, the preparatory period to build, improve the construction of roads, make good preparations for the yard, to ensure that the construction period has qualified soil and good construction roads. In early August of the first year, the main project started in full swing, first of all, the excavation of the section 0+010～0+080 of the water transfer tunnel, which is the key project to control the construction period. The tunnel outlet excavation is carried out first, and the hole excavation is carried out at the end of the excavation, and the stone excavation of section 0+010～0+080 of the tunnel is completed in 3 months, and then the concrete lining and backfill grouting of the roof of the tunnel are completed in 3 months. In early November of the first year, the construction of the 0+000～0+010 section of the tunnel inlet will start immediately after the water level of the reservoir is lowered, and then in mid-February of the second year, the construction of all the flood relief tunnels will be completed. At the same time can be completed inlet and outlet gatehouse, outlet canal construction. In early November of the first year, the dam can also be remediation of the top of the dam, the upper and lower reaches of the dam slope leveling and masonry construction. At the same time to complete the dam body curtain grouting construction. In the second year in mid-February after all the tunnel lining work can be carried out after the original low water culvert sealing, using 1.5 months to complete all the sealing work. At the same time the very spillway reinforcement and other projects can be carried out. By the end of April of the second year, the construction of the dam's upstream slope protection, downstream slope improvement and most of the main works as well as the installation and commissioning work of the metal structure and the opening and closing equipment will be completed; in May of the second year, all the construction work, the construction of the road on the top of the dam and the construction of the dam management facilities will be completed; and the project will be closed down and the clearing of the site will be carried out in June of the second year.3.3 Construction FloodsAccording to the analysis on the rainfall characteristics within the basin, the flood season of the Gujiagou Reservoir occurs from April to October every year, and the dry water period is from November to March every year. According to the design of the construction organization, the time period for the construction of the diversion is the dry water period (November to March), and the flood standard of the diversion building is one in five years. The total amount of runoff in each month with the corresponding frequency is calculated according to the deep discharge frequency of runoff from 1956 to 2000***45 years in the fourth level area of the plug river basin. According to the measured maximum 24-hour precipitation data of Jushan meteorological station from 1980 to 2006***27 years during the dry period year by year and month by month, the results of design flood calculation during the construction period are obtained. The results of the calculation of runoff during the dry period are shown in Table 1, and the results of the design flood during the construction period are shown in Table 2.

3.4 Construction diversion method According to the design requirements of the current remediation project, construction diversion is required for the upstream slope renovation of the dam, the inlet section of the tunnel, and the construction of the very spillway. The original culvert excavation and removal and backfill blocking and other construction must also be emptied of reservoir water before construction. According to this construction characteristics, combined with the actual layout of the project, the construction of this project adopts two-phase construction diversion. The first phase directly utilizes the original low water conveyance culvert to release and discharge water. In late October of the first year through the original water culvert will be lowered to the original dead water level of 549.49m elevation, in early November of the first year, the use of low water for the upstream slope of the dam dry masonry berm refurbishment of the construction and flood relief tunnel inlet section construction. The second phase of the tunnel construction process using the necessary means for the construction of diversion, excavation and lining of the flood relief tunnel, the original culvert excavation and removal and blocking and other construction projects. According to the size of the project intake and construction arrangements, the design of the construction period (November of the first year to March of the second year) **** 5 months of incoming water to consider two sets of construction diversion program for comparison: Program 1: pump drainage program, that is, the first year November to March of the second year, all the incoming water through the pump to pumping. According to Table 2: During the construction period, the peak flow rate of a rainstorm with flood frequency P=20% is 5.1m3/s, and the total amount of flood water is 58,000 m3. The original dead storage capacity of 58,000 m3 can be pumped out in the pre-construction period of the inlet section of the tunnel to serve as the reserved flood protection storage capacity for a flood of the design standard (P=20%). The total amount of incoming water is calculated according to the monthly runoff frequency (P=20%), and the total amount of incoming water in 5 months is about 222,800 m3, that is, the total amount of water needed to be pumped out in this project is 222,800 m3 The design pumps (with a head of 16m) are pumped out according to the flow rate of 600m3/h (0.167m3/s), and the pumps are considered according to the 2 pumps, which can meet the requirements of the construction pumping out. Calculated, each pump according to the power of 45Kw, pumping period *** need electricity 10530Kw-h, the program investment 0.96 million yuan. Program 2: cofferdam water blocking program, that is, the use of cofferdam water blocking, reservoir storage of all the water during the construction period, check the reservoir capacity curve, get the corresponding design level 556.3m, consider the safety plus high, take the cofferdam top elevation of 556.8 m. Cofferdam around the water intake arrangement, and with the dam site near the mountain connected to the formation of a closed flood control system. The cofferdam adopts stone slag mixture as weir body, clay inclined wall seepage control cofferdam structure type, weir top elevation of 556.8m, weir height of 14.25m, weir top width of 3.5m, the slope of the water surface adopts 1:3, and the slope of the water surface adopts 1:1.5, the length of the cofferdam is 50m, the main project quantity: filling earth and stone cofferdam 12150m3, clay 7123m3, construction road 0.3km, the investment of this program is 39.38million yuan. 393.8 million Yuan. Scheme 1 is more effective than Scheme 2 in utilizing the existing dead storage capacity, avoiding the filling cofferdam to cause a large amount of excavation and filling work, which reduces the construction risk and construction period, and there is no construction road, and is not affected by the construction of the upstream slope of the dam. Comparing the two direct investment scheme one saves 384,200 Yuan compared with scheme two, so it is recommended to choose scheme one as the second phase of construction diversion program. According to Table 1 and Table 2, during the construction period of the entire flood relief tunnel and the original culvert blocking project (November to March), the peak flow rate of a rainstorm with a flood frequency of P=20% is 5.1m3/s, and the total amount of flood water during the period is 222,800m3. Considering the financial constraints and the inconvenience of constructing construction roads and cofferdams upstream, the construction process of the entire flood relief tunnel excavation and lining, the removal of original culvert excavation and blocking project will not be carried out. During the construction of the entire flood relief tunnel, the original culvert excavation, removal and blocking project, no construction cofferdams, directly using submersible pumps will be discharged to the downstream through the newly built water transfer tunnel, the use of five months to complete the flood relief tunnel and the original culvert excavation, removal and blocking of the construction.

4. Conclusion

Small reservoir rehabilitation design due to their own geographic conditions and supporting the limitations of the funds, in the design of the construction of diversion, especially in the mountainous areas of small reservoirs in the vast majority of cases can not be used in the way of conventional cofferdams diversion of the construction of the diversion, and the use of pumping is not only to save investment but also can be very well implemented.

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