1. Introduction Golmud, Qinghai Province is located in the Qaidam Basin and has a typical alpine continental desert climate. It is windy, dry, mostly wind-accumulated yellow sand, with poor soil quality and strong permeability. This anti-seepage reinforcement project has become a part that cannot be ignored in the construction of water conservancy projects. Let’s briefly talk about the anti-seepage reinforcement technology of water conservancy projects. 2. Dam reinforcement technology Different construction methods are carried out according to different parts of the dam. Curtain grouting of the dam body and dam foundation mainly fills loopholes and gaps to prevent leakage and is reinforced by grouting to form an anti-seepage body. This method is suitable for mortar masonry gravity dams. The upstream surface of the dam is consolidated and grouted to plug loopholes and gaps, strengthen the dam body and improve the anti-seepage performance, so as to further improve the load-bearing capacity and integrity of the dam body. ?The downstream surface of the dam is tracked and consolidated grouting. Where there is water leakage or dissolved matter escaping on the downstream dam surface, horizontal holes or oblique holes are formed, and grout pipes are buried for grouting to block the leakage channels and dam body cavities and cracks, and strengthen the dam. body to increase the stability and erosion resistance of the dam surface. This reverse grouting process is very suitable for arch dam and buttress dam projects. It can also be used for gravity dam projects as long as the lifting pressure and drainage holes are provided. When using this method, it is best if there is no water in front of the dam. The dam surface is re-checked and jointed. After the joints are checked, high-grade cement mortar, dry-hard pre-shrunk cement mortar or waterproof material is used to prepare high-grade cement mortar joints to improve the anti-leakage ability of the dam surface and the stability and integrity of the dam body. And resistance to freeze-thaw and wind and wave erosion. This method is the "front blocking, middle interception, and rear tracking" grouting leakage control and reinforcement method. 3. Principles that should be followed when laying out and making holes in dam reinforcement technology: 1. Lay out holes for curtain grouting. In the leaky dam section, along the center line of the dam top, the hole spacing should be 3m and the hole diameter should be 50mm or 75mm, or the hole spacing should be determined according to the test. The hole depth should be drilled to 1m-2m below the leakage site. If there is water leakage in the contact zone or bedrock, the hole can be drilled to lm-2m below the impermeable bedrock. Holes can be made at one time or in sequence. Holes can be made in sections up and down the crushing zone, and sea slurry can be created in sections. At the same time, after the slurry has solidified for 5-7 days, holes can be drilled downward to prevent drilling from getting stuck. A buried drill accident occurred. For the grouting of the contact parts between the dam body and the bedrock and the dam foundation, oblique holes or vertical holes can also be grouted at the upstream dam foot to plug leaks. However, the foundation should be cleared before making holes, and 0.3m-0.5m thick concrete should be poured at the dam foot. Drill holes after solidification. Vertical or inclination angle is less than 5. For the curtain grouting holes, the deviation value of the hole direction shall not be greater than the specified value 2.2.2 Consolidated grouting holes upstream of the dam; in the leakage area, it will be in a "plum blossom" shape, and the drilling spacing and row spacing are lm-3m. Depending on the leakage situation Make sure that the drilling position is selected in the "break" joint of the masonry; at the crack location, one hole can be laid every lm along the crack. The hole diameter is 42mm and the hole depth is 0.7m-1.5m, which is determined according to the actual conditions of the dam body. Trace the holes of consolidated slurry on the downstream face of the dam; place a hole every 1m along the crack at the crack; in other seepage parts, arrange holes according to a "plum blossom" shape, with row spacing and hole spacing of 2m-3m. The location of the holes is In the "T" seam, the holes can also be appropriately densely packed. The hole depth and diameter are the same as those on the upstream side of the dam. 2. Construction requirements: Empty the reservoir first or lower the water level below the grouting site before grouting, and keep records of grouting. Clean the hole; before grouting, the hole wall, hole bottom and cracks should be flushed, using Feng Shui combined flushing method, the water pressure should not be greater than 75% of the grouting pressure of this section, and the time will be determined by the depth of the hole until clean water is returned. Dimensional curtain grouting; ① Adopt the in-hole circulation method, grouting in sections from top to bottom or bottom to top, and finally full hole grouting. When grouting in sections, a rubber plug should be added 0.5m above the grouting section. Through demonstration, the small-diameter bore hole closed grouting method can also be used; ② The grouting length in the dam body is about 5nt for one boat. When the hole depth does not exceed 8m, the whole hole can be grouted at one time; ③ The grouting pressure is controlled according to the design. But it should be lower than the ultimate pressure of the lifting test, generally controlled at 0.2MPa-0.4MPa. Dam surface consolidation and tracking grouting: ① Pre-embed the grouting pipe in the hole, fill it with dry hard cement mortar around the orifice pipe, use a 20mm inner diameter steel pipe, 50cm long, insert 40cm into the hole, 5cm-10cm exposed, pipe head Threads need to be processed to connect with the grout pipe; ② Use a set of four holes in parallel grouting method, or single hole or two holes can be grouted together.
Single-hole key grouting should be adopted for key holes at leakage points behind the dam. The grouting pressure is controlled according to the design, generally 0.2MPa-0.25MPa. Concentration of slurry; when grouting, the principle should be followed from thin to thick, and the concentration should be changed step by step according to the pressure water test. When the amount of slurry injected into the dam body is greater than 30L/min, it can become thicker by leaps and bounds. When a certain level of grout perfusion exceeds 400L, and there is no significant change in the grouting pressure and grout suction volume, the grout filling can be changed to a thicker level of grout. The grout water-cement ratio generally adopts nine levels of weight ratio: 8:1, 5:1, 3:1, 2:1, 1.5:1, 1:1, 0, 8:1, 0.6:1, and 0.5:1. According to the design, fly ash, sand, quartz powder, aluminum powder, etc. can also be mixed if necessary. During the grouting process, the specific gravity of the grout should be measured every hour. When grouting, grouting should be done in 2-3 sequences, and regrouting must be carried out at the same time. Under the design pressure, when the slurry suction volume is no more than 0.4L/mio, the filling can be completed for another 30 minutes. The grouting holes are sealed; when curtain grouting is used, the vertical holes are sealed using the mechanical conduit method, and 1:2 cement mortar is gradually lifted and sealed from the bottom of the hole upwards; the horizontal holes are sealed with consolidation grouting on the dam surface, and low water cement is used. The cement mortar ratio is 1:2 and manually filled and compacted. The best sealing material is expanded cement mortar. 4. High-pressure jet grouting technology In embankment anti-seepage projects, high-pressure jet grouting technology can reduce project costs to varying degrees compared with conventional concrete anti-seepage walls. It has the advantages of small excavation volume, convenient construction, less land occupation, and is very harmful to adjacent buildings. It has the characteristics of small physical impact. This technology has greatly improved the anti-seepage and disaster resistance capabilities of rivers, lakes, reservoirs and canals, reduced flood control pressure, and will play a positive role in ensuring the safety of people's lives and property as well as social and economic development. Its social benefits are Very obvious. The technical parameters used in construction vary depending on the method of high-speed spraying used. The lifting speed is also different depending on the grouting pressure used. For all types of strata, if the same construction method is used, the water pressure, air pressure, and slurry pressure will not change much. Only the lifting speed will change greatly, which is the main factor affecting the quality of high-speed spraying. Under normal circumstances, the following issues should be paid attention to when determining the lifting speed: it varies depending on the stratum. The lifting speed can be slightly faster in the sand layer, and slower in the sand and pebble (gravel) layer, which contains large particle sizes (above 40cm). Strata where blocks or blocks are more concentrated should be slower; this varies depending on the sequence. The lifting speed of the first holes can be slightly slower, and that of the later holes can be relatively faster; when it is found that the amount of back slurry in the hole is reduced during high-speed spraying construction, the lifting speed should be slowed down.
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