Construction technology of joint grouting for hydropower station?

What is the concrete content of joint grouting construction technology in hydropower station? Here, Zhong Da Consulting will answer your questions.

The basic situation of 1

Hydropower station is located on the main stream of a county, which is a reservoir for cascade hydropower development from the lower reaches of the main stream to the estuary. It is about 75 kilometers away from the urban area and 358 kilometers away from the estuary. The foundation elevation of concrete hyperbolic arch dam of hydropower station is as high as1580m, the crest elevation and maximum dam height are 885m and 305m respectively, the thickness of the bottom and top of the crown beam is 63m and16m respectively, and the arc length of the center line of the crest arch is152m. The maximum central angle is 63. 16 m. Under normal circumstances, the water level of a hydropower station can reach 880m m. According to the actual situation, 25 transverse joints are set, and the dam is divided into16 dam sections. The spacing between transverse joints is 20-25m, and the average width of dam section is 22.6m.. It is difficult to install longitudinal joints in construction. According to the design documents, all transverse joints of arch dams should be grouted.

2 joint grouting construction technology

2. 1 joint grouting technology

Dam joint grouting is more complicated than consolidation grouting and curtain grouting, and most of its work mainly focuses on the preparation stage before grouting and the handling of some special situations. The specific construction process is shown in the following figure.

2.2 Preparation before joint grouting

The preparation work before joint grouting mainly includes: before grouting, the irrigation area shall be fully inspected for water supply, joint opening and grouting temperature according to 80% of grouting pressure.

(1) Comprehensive water inspection. There are two kinds of comprehensive water inspection: boiled water inspection and closed water inspection. Boiled water inspection mainly checks the smoothness of grouting pipes (slurry inlet pipe, slurry lifting pipe and exhaust pipe) and joint surfaces (divided into upstream surface and downstream surface of the dam). During the closed inspection, water is supplied from the slurry inlet pipe and all exhaust pipes are closed. The sealing situation of joint grouting irrigation area is judged by calculating the difference between the water filling amount of pipeline and joint surface and the actual stable water intake.

② Check the opening at the joint. The detection of joint opening is an important index of joint grouting. According to the specific situation of the site, the embedded electronic joint tester can be used for observation, and the water injection quantity estimation method can be used for calculation or one of the methods for inspection.

(3) Check the grouting temperature. Before grouting, the dam concrete in each irrigation area is planned to be tested by embedded thermometer and cooling pipe water stuffy temperature method. When using temperature measuring instruments, observation records are generally made every 7- 14 d, and observation should be strengthened when grouting is near. The latter is to fill the cooling water pipes of each pouring layer of concrete on both sides of the irrigation area with water, and then close the inlet and outlet valves to make the concrete fully exchange heat with the water in the pipes. When reading, put the stuffy water into a thermos cup or a small bucket made of thermal insulation materials, immediately measure the water temperature for three times with a thermometer, and take its average value as the temperature data of the cooling pipe of this layer, and then take the average value of the temperature of each pouring layer as the temperature of the dam block.

(4) Water pressure before irrigation. After the inspection (treatment) of the irrigation area is qualified, the water pressure before irrigation shall be checked, and the water pressure is the same as the grouting pressure. After the completion of water pressure inspection, the irrigation area should be soaked in water for 24 h before joint grouting, and grouting construction can only be carried out after the grouting row is empty or the water in the joint is blown clean by wind.

2.3 Horizontal pressure and water circulation

Before any grouting layer is about to be grouted, horizontal pressure should be applied to the adjacent joints while pressurizing the grouting joints, and the horizontal pressure should ensure that the top pressure does not exceed 0. 2 MPa. Before and during grouting, the upstream irrigation area of the irrigation area keeps water circulation for at least 6 hours after grouting.

2.4 Additional observation

In order to control the expansion degree of transverse joints during grouting, deformation observation devices installed on the downstream surface of the dam or the inner wall of the corridor are used to observe the expansion degree of grouting joints and their adjacent joints during the whole grouting process. When the slurry is closed and the pressure increases, if the increasing trend is obvious and close to zero. 5 mm, the tester will immediately notify the grouting personnel through walkie-talkie or temporary telephone. Grouting personnel should make appropriate adjustments according to the situation, such as reducing grouting pressure and increasing the horizontal pressure of adjacent joints, but the horizontal pressure should not exceed 0. The top of irrigation area is 2 MPa. If all the above measures are ineffective and the openness continues to increase by more than 0. 5 mm, should immediately stop into the slurry, and open the top pipe to discharge slurry, in order to reduce the slurry pressure in the joint. At this time, whether the top pressure has risen to 0 or not. 35 MPa or not, increase 0 at the end of grouting. 5 mm as the control standard.

2.5 Grouting pressure

The grouting pressure is controlled by the pressure of the slurry return tank (slurry discharge tank) at the top of the irrigation area, and the pressure of the slurry inlet (the bottom of the irrigation area) is used as an auxiliary control value. Grouting pressure of transverse joints: 0. Generally, 35 MPa is used at the top of irrigation area.

2.6 Grouting water cement ratio

Joint grouting adopts single water cement ratio, and concrete joint surface adopts 0. 45: 1 mud. When superplasticizer is added into the slurry, the 28-day strength of the slurry should not be lower than M40, and the water separation rate of the slurry within 2 hours should not be greater than 3%. ..

2.7 grouting end conditions

When the mud discharged from the exhaust pipe reaches or approaches the density of the thickest mud, and the nozzle pressure or the opening of the joint surface reaches the design value, the injection rate is not greater than 0. Grouting can be completed in 4 minutes and 20 minutes. After grouting, close the valves of each nozzle before stopping the machine, and the grouting time shall not be less than 8 hours. ..

3 the main problems in the construction and treatment methods

In the process of joint grouting construction, special circumstances may suddenly appear for various reasons, and common problems include: slurry leakage, belt crossing, pipeline blockage, interruption for some reason, poor slurry discharge from exhaust pipe, etc. Considering the complexity and importance of joint grouting process, if the above-mentioned common problems occur in the construction process, it is necessary to organize relevant technicians to conduct thorough and detailed cause analysis in time, and use other geophysical detection methods to conduct cause analysis when appropriate, so as to ensure the correct analysis of the causes and the correct use of treatment methods, thus ensuring the quality of joint grouting construction. The main problems that may occur in the construction and the treatment methods are as follows:

(1) slurry leakage. If slurry leakage is found during grouting, construction personnel shall be organized to seal the slurry leakage point from the outside in time. The plugging material can be cement mortar, epoxy mortar or other quick plugging chemical materials mixed with accelerating agent and anchoring agent. If the direct sealing method cannot be used for sealing, a groove should be cut on the surface of the leakage joint, and then epoxy mortar should be used for sealing.

② Slurry stringing in irrigation area. In the process of dam concrete construction, if there are defects in the installation of layered grout stops or the concrete around the grout stops is not compacted during concrete pouring, grouting in the upper and lower irrigation areas is easy to occur during the joint process. During the grouting process, it was found that the upper irrigation area and the lower irrigation area were cross-grouted. When the cross grouting irrigation area has grouting conditions, synchronous grouting should be organized. If there is no grouting condition in the stringing irrigation area, if irrigation is not started for a long time, the irrigation area will be washed with clear water immediately, and grouting will be carried out at the same time when the stringing area has the conditions. If irrigation is started for a long time, adjust the slurry inlet pressure and circulating water pressure at the joint surface of the upper irrigation area to make the pressure as balanced as possible, and consider increasing the slurry concentration to block the leakage channel near the slurry stop, and the circulating water in the upper irrigation area will continue to flow until it is completely clear.

(3) The grouting pipe is blocked. During grouting, if the slurry inlet and return pipes are blocked, the slurry inlet and return directions should be reversed immediately, and the holes should be punched with pressurized air, water or mud in a short time, and then normal grouting can be resumed after dredging. If it still doesn't work, it should be reversed from the exhaust pipe.

(4) Grouting is interrupted. When the grouting process is interrupted for some reason, the pipeline and irrigation area should be washed with clear water immediately to ensure the smooth grouting pipeline and irrigation area. Check the water pressure again before resuming grouting. If it is found that the grouting pipe is not smooth or the single outlet of the drainage pipe is obviously reduced, the following remedial measures can be taken according to the specific situation: ① drill an inclined hole at the top of the irrigation area, which runs through the exhaust slot (this method is suitable for the gambling situation of the exhaust pipe); (2) Drill an inclined hole about 30cm above the top of the slurry inlet pipe, and the inclined hole penetrates the grouting joint surface (this situation is applicable to all slurry inlet pipes).

(5) The mud discharged from the exhaust pipe is not smooth. When the exhaust pipe is blocked or blocked after grouting, according to the design and technical requirements, the grouting pressure should be increased within the limit of joint opening until it reaches the limit. When the injection rate is less than 0. 4L/min, lasting for 20 min, grouting can be completed.

If it doesn't work, reverse flow will be carried out from two exhaust pipes immediately after downstream. Use the thickest mud for backflow. Stop sucking slurry on the joint surface under the pressure specified in the construction drawing, and continue grouting for 10 minute.

(6) The seam opening is small. When the opening of the joint surface is less than 0. 5 mm, can use the fineness of less than 2% cement slurry or fine cement slurry for grouting construction, and increase the grouting pressure within the limit of the joint surface opening, or use chemical slurry for grouting.

4 conclusion

To sum up, in order to control the construction quality of dam joint grouting, it is necessary to carry out all-round control. Not only should we choose the best grouting construction technology, deal with the special situation in the construction process and adjust the construction method, but also we should standardize the installation and protection of layered slurry stop and grouting pipeline in the dam concrete pouring process to ensure the concrete pouring quality.

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