The State Council's Opinions on Further Promoting Ningxia's Economic and Social Development promoted Ningdong to "National Key Development Zone", determined the strategic orientation of "three national bases and one demonstration zone", and demanded that Ningdong be built into an important national large-scale coal base, coal chemical base, "power transmission from west to east" thermal power base and circular economy demonstration zone. The first phase of Ningdong water supply project, known as lifeline project, consists of two parts: water source project and distribution network project. Construction started on February 26th, 2003, and passed the acceptance on February 28th, 2008. The daily water supply reached 400,000 tons, reaching the limit of the first phase. The second phase of Ningdong Water Supply Project started in 2065,438+02, and the dam adding project of the reservoir started in 2008. Yazidang Reservoir is an industrial water storage reservoir. After the reservoir is completed, it will store water for a long time, and the secondary dam can only be added behind the dam. After adding the dam, the maximum dam height above the riverbed of the main dam is 29m, the length of the dam crest axis is 2332m (the length of the dam in the same period), the dam crest elevation is 1258m, and the dam crest width is 8.0m The engineering grade is Grade II and other large (2) projects, with a total storage capacity of 44.07 million m3, an increase of 23.54 million m3 compared with the first phase. According to the situation of soil materials, the dam body is divided into impervious body, filter layer, dam shell, drainage body and slope protection. The part above the elevation of phase II 1247.5 is used as the impervious body, and the impervious body is filled with fine-grained soil; 1247.5 fill pebbles below the elevation; A chimney drainage body is arranged between the primary dam body and the secondary dam body, which is communicated with the raft drainage body at the lower part of the secondary dam body to form a vertical drainage system, and a drainage prism is arranged at the outer side of the lower dam shell behind the dam.
Construction technology and quality control
Dam foundation drainage
Due to the long-term seepage of the first-stage dam, the dam foundation is clear to the design elevation, and the water level is higher than the dam foundation surface. Drainage ditch excavation and drainage are adopted to reduce and drain the foundation surface. The original toe drainage ditch and the newly excavated drainage ditch are used to form a well-shaped drainage ditch for dewatering, and a faucet pit is set outside the dam foundation surface for pumping and drainage. The drainage effect is good, but the dam foundation surface is damaged by the excavated drainage ditch and needs to be treated. After the drainage ditch at the toe of the original dam is cleaned, gravel with the same particle size as the drainage prism of the first-stage dam (particle size 50- 120 mm) is backfilled at the bottom of the ditch, and the drainage material at the upper part of the ditch is rolled, and the relative density is greater than 0.75; Other temporary construction drainage ditches on the foundation surface shall be cleaned, backfilled and rolled with drainage materials, and the relative density shall be greater than 0.75.
Determination of drainage materials
The natural graded gravel with a particle size of 2-60 mm was sampled in the surrounding material yard for grading test. The material content below 10mm was low, and the grading was discontinuous. The material below 10mm exceeded the upper envelope of the designed particle grading curve, which could not meet the drainage material index. By using the method of mixing 5- 10 mm crushed stone, it is determined that the volume ratio of natural graded crushed stone and 5- 10 mm crushed stone is 10:7, which can meet the grading requirements of drainage materials and solve the source problem of drainage materials.
Treatment of concentrated leakage parts of dam body in the first stage
After the foundation cleaning is completed, it is found that there is a relatively concentrated seepage zone at the toe pile number 1+300 ~ 1+400 of the first phase project. Through field observation and field geological logging, it is confirmed that there are 18 leakage points at the pile number 1+000 ~ 65438+400 of the dam foundation of the first phase project. *** 12, the main reason is that the dam foundation of section 1+300 ~ 1+400 is located on the coarse sand layer, and all the water seepage comes from the coarse sand layer. In order to ensure the long-term safe and stable operation of the dam, the plastic concrete cutoff wall is used for the foundation of the first-stage dam1+300 ~1+415.
Selection of dam filling materials
Coarse gravel materials are used for filling below the elevation of1247.5m. The design physical indexes of coarse gravel materials are: the particle content greater than 5mm is 57-77%, the particle content less than 0.075mm is 12-20%, the relative density is greater than 0.75, and the dry density is 2. 10g/cm3. Due to the large soil layer in coarse gravel yard, in order to ensure that the content of particles larger than 5mm is 57-77% and that of particles smaller than 0.075 mm is 12-20%, after a large number of field sampling, screening, compaction and rolling tests, the content of particles smaller than 0.075 mm can be relaxed to 12-35%.
Special dam foundation treatment
After the dam foundation cleaning is completed, there are special sections such as weak interlayer, high water content, silt and gypsum interlayer in the dam foundation. The acceptance meeting decided to deal with these parts, dig out these bad soil, backfill the deep large area with the same soil material as the dam foundation and the same compactness as the dam filling material, and fill the shallow small area with drainage material with the same compactness as the drainage material.
Building filling method
In order to ensure a large filling surface and meet the requirements of some mechanized construction, leveling construction method is often used in dam surface construction, which can reduce the procedures of slope connection and slope cutting in the construction process. It is particularly worth mentioning that leveling construction can reduce the interference to the drainage area during material transportation.
Processing and treatment of soil materials
The dam is filled with fine earth materials above the elevation of 1247.5 m, and the selection of fine earth materials mainly depends on the optimal water content (generally 2%). The moisture content of the selected soil yard is about 5%, and the optimum moisture content of the test is 14%. Only by breaking the ridge in the yard and adding water to prepare the soil, the amount of water added is calculated and controlled according to the original moisture content of the soil and the optimal moisture content of the test.
The construction quality of reservoir dam project is strictly controlled, all kinds of records are complete, and all procedures meet the design requirements, which has accumulated useful experience for improving the construction technology of earth-rock dam. By adding a dam, the water storage capacity of the reservoir is not only improved, but also the leakage of the left and right abutments and the middle section of the old dam is eliminated.
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