Huangbizhuang Reservoir is an important controlling large-scale water control project in the middle and lower reaches of Hutuo River, with a total storage capacity of121000000 m3, 30km away from Shijiazhuang city, and its geographical location is very important. As early as the early 1980s, especially after the "96.8" project, this reservoir was listed as one of the first 43 key dangerous reservoirs in China. The auxiliary dam of Huangbizhuang Reservoir passes through Sanlian single ditch in Guxian County, passes through Guyunlang River, Yongle ditch and San Ji Canal to Mashan, with a total length of 6,907.3 m, a main elevation of 129.2m and a dam crest width of 6 m. The dam foundation of the auxiliary dam is located on the basis of sandy pebbles and gravels, and the geological conditions are quite complicated. Huangbizhuang Reservoir adopts the combined vertical seepage control scheme of dam crest. The cutoff wall is 0.8m thick and embedded in bedrock 1 ~ 3m. The elevation of the top of the wall is125.5m, and the center is located at the dam axis of 2.9m. The vertical accuracy of construction is required to be 3/ 1000. The construction technology of high-precision cutoff wall in A4+700 ~ A5+700 section is introduced as follows.
2, construction technical problems and countermeasures
2. 1 technical problems
The technical problems encountered in the construction of concrete cutoff wall in this section mainly include: 1 requires high precision, and the verticality is difficult to control during the hole-making process; 2. The geological conditions are complicated and the slurry leakage is serious. There are karst caves in some dam foundation rocks, and there is a risk of dam collapse in the groove section and dam body. 3. The ballast cleaning is not complete, and the sediment at the bottom of the wall is too thick; 4. The joint hole is poorly brushed, the wall is muddy, and the joint leakage is serious; 5. Broken piles reduce the stability and permeability of the wall.
If the above technical problems are not properly solved, the quality of concrete cutoff wall will be seriously affected. In case of catastrophic flood, the risk of dam break may occur, and the quality of internal cutoff wall is poor when Jiujiang levee breaks. Therefore, corresponding countermeasures must be taken to ensure the quality of concrete cutoff wall.
2.2 solutions
2.2. 1 accuracy assurance
At present, due to the low mechanical precision and poor quality of stable liquid, hole collapse, slag accumulation and irregular groove shape often occur. Under the existing mechanical and technical conditions, in order to effectively ensure the accuracy of the cutoff wall, on the one hand, the drilling tools are improved by drilling and splitting, and CZ-30 and CZ-22 impact drills (or impact reverse circulation drills) are used to directly form grooves; On the other hand, the method of two drills and one grab is adopted, that is, the main hole (or pilot hole) is constructed by impact drilling machine, the auxiliary hole (or soil between pilot holes) is grabbed by grab bucket, and then the pebble layer and bedrock layer are constructed into grooves by drilling machine. The slotting accuracy is controlled within 1/2000. The grab bucket adopts 6500 full-automatic computer-controlled hydraulic pressure (with automatic deviation correction system), and various monitoring means are adopted in the construction, which effectively ensures the geometric size and verticality of the trough section. High-quality bentonite mud is used to fix the wall when making holes. The viscosity of the mud should be controlled within 30 ~ 60s, and the specific gravity should be controlled within 1.09 ~ 1.2g/cm3 to ensure the stability and formability of the tank wall.
2.2.2 Anti-collapse and plugging measures
Due to the complex geological conditions of the dam, there are bad strata such as serious seepage layer, strong seepage zone and bedrock karst cave. In order to solve the problem of drilling in complex seepage layer, a new technology of anti-collapse and plugging grouting for large-diameter wall protection pipe was invented (this technology has been patented by the state). The main equipment is: large-diameter wall protection pipe (φ 550,505 505mm) and 2× 100t automatic hydraulic pressure. Main construction methods: when the drilling rig is constructed above the leakage stratum 1 ~ 2m (the depth of this section is generally controlled at 43m, 48 ~ 5 1m), stop drilling, lower the casing, then block the outer wall of the pipe with clay to isolate the inside and outside of the pipe, insert the leakage stratum into the pipe with special drilling tools, and fill it with filling materials (sand, gravel, flocculated concrete, etc. This technology is particularly effective in treating bedrock karst caves, which solves the problem of hole-making in the section with serious slurry leakage of the auxiliary dam and effectively avoids the risk of dam collapse in the section or dam body. This technology fills the technical gap in dealing with serious leakage stratum, strong leakage zone and crossing karst caves in China.
2.2.3 Siltation at the bottom of the hole
The construction method of reverse circulation combined with sand suction pipe cleaning is adopted, and the sand components at the bottom of the hole are cemented with cementing materials (such as cement and bentonite). During construction, the cementing material is tied to the bottom of the drill bit and then placed at the bottom of the hole for drilling. After a certain period of time, the cementing material cemented the fine sand together, and the sand was pumped out by the sand pumping barrel, so that the fine sand components were pumped out, and the deposition thickness at the bottom of the hole 1h was ensured to be within 10cm, thus ensuring the effective connection between concrete and bedrock.
2.2.4 Connection technology
On the premise of effectively controlling the verticality of the joint hole, the "new technology of joint pipe method" is adopted. This technology is to put the connecting pipe with the same diameter (800mm) and wall thickness into the connecting hole before the first stage of concrete pouring. After the concrete pouring reaches a certain strength, the connecting pipe is pulled out with a 2×308t automatic hydraulic pipe puller to form the connecting hole. The new seam pipe technology saves concrete raw materials at the seam hole, and the seam hole can be directly formed without drilling concrete at the seam hole. This technology can significantly improve the construction efficiency of the joint hole of the cutoff wall, greatly reduce the construction cost, and the construction quality is reliable. It is a fast, efficient, energy-saving and low-consumption construction technology. It has been successfully used for many times in the construction of cutoff wall in this section, and the depth of tube drawing of 30m and 40m has been successfully tested, and successful experience has been obtained. Before pouring concrete in the secondary tank section, use multipole brush bit to scrub the joint of hole wall for a long time until there is no debris on the brush bit. Because the joint hole adopts the new technology of joint pipe, the hole wall is regular, which ensures the scrubbing quality, and the concrete of the first-class tank section and the second-class tank can be closely connected to ensure the good impermeability of the wall.
2.2.5 pouring quality control
Set conduits in strict accordance with the specification requirements, and control the blanking speed and amount of each conduit during the pouring process, so that the rising speed and height of concrete in the tank section are basically the same, and local concrete is prevented from being mixed with mud; Control the removal speed and buried depth of the conduit, avoid the conduit floating, and prevent the concrete aggregate of the wall from being concentrated and broken. During pouring, the traditional method of lifting the conduit by drilling rig was changed, and the conduit was lifted by 1.5t electric hoist gantry crane, which made the conduit lift smoothly and effectively avoided the conduit lifting.
Quality inspection
After a period of construction, the concrete cutoff wall was tested by drilling coring method and CT. It is found that the concrete of cutoff wall is evenly distributed in orthopedics, and no honeycomb pits are found. The settlement at the bottom of the hole is generally within 8cm, and the joint concrete is closely connected without mud inclusion, especially within the scope of joint pipe construction, and there is no obvious joint at the joint joint. Check by water injection test. Practice has proved that the construction quality of concrete seepage prevention is guaranteed by the above construction methods.
3. Economic analysis of adopting new technologies and new processes
3. 1 Economic benefit analysis of "New grouting technology for anti-collapse and plugging of large-diameter wall protection pipe"
During the construction of the cutoff wall of the auxiliary dam of Huangbizhuang Reservoir, there were four pit collapses, and the dam broke 1 time, resulting in a direct economic loss of about 30 million yuan. Using this new technology in the section with serious slurry leakage between pile numbers A5+300 ~ A5+450, the hole-making of cutoff wall and concrete pouring were successfully completed, and there was no pit collapse and dam collapse, which saved huge funds. Moreover, the construction task was completed six months ahead of schedule, which was praised and praised by the Engineering Construction Bureau.
3.2 Analysis of economic benefits of adopting new takeover technology
The joint hole constructed with this joint pipe is about 2500m, saving 2000m3 of concrete, and the direct benefit is about 1 10,000 yuan. In addition, the indirect benefits of supporting projects such as waste residue removal, clay and mud consumption will exceed 654.38+500,000 yuan.
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