Treatment and prevention measures of concrete cracks in flood discharge tunnel of hydropower station
1.1 Overview of the flood discharge tunnel project of the Shuanghekou Hydropower Station in the Mengjiang River Basin
The flood discharge tunnel of Shuanghekou Hydropower Station in the Mengjiang River Basin of Guizhou Province adopts the shape of a city gate. The whole tunnel is 528 m long, and the entrance and exit floor elevations are 536.65 and 494.2 m respectively. Among them, after the first water storage of Shuanghekou Hydropower Station , After on-site inspection, it was found that when the water level in the reservoir area was higher than the elevation of the top of the plug arch of the flood tunnel, the construction joints and the concrete cold joints of the bottom plate of the long-headed inclined shaft produced water seepage, and the water seepage amount was accompanied by the water level in the reservoir area. rising and continuing to increase. At the same time, water seepage also occurs in the side wall concrete cold joints and construction joints in the inclined shaft section of Longzhuang. After investigation and research by relevant personnel, it was found that the main causes of water seepage in these parts were due to the poor geological conditions of the rock strata in these tunnels, the unsatisfactory treatment of construction joints, the generation of cold joints during the concrete pouring process, and the poor consolidation and grouting of the duxun tunnel plugs. Jia et al. To this end, the relevant personnel proposed the method of chemical grouting on the seepage area to effectively inhibit the seepage and treat the cracks.
1.2 Treatment of the cracks in the flood discharge tunnel of the Shuanghekou Hydropower Station in the Mengjiang River Basin
All the scoured parts of the flood discharge tunnel of the Luding Hydropower Station are made of HFC40 concrete, and most of the cracks caused by the dam construction of the hydropower station are distributed here. According to statistics, the cracks are mainly concentrated in the 0+180~0+600 section of the dam. The main location of the cracks is the side wall with a distance of 1~7m from the bottom plate, and most of the widths are about 0.1 mm, especially for each warehouse. The middle part of the distribution is the most. Among them, the angle of occurrence of cracks and the horizontal angle remain greater than or equal to 45. , the shape is cracked and irregular, and the cracks that produce water seepage usually have a small amount of water seepage, while most of the cracks only appear wet on the joint surface and watermarks appear on the concrete surface, but there are very few obvious water seepage marks. There are hardly any traces of slight running water. By observing the development time of the cracks, it is known that the cracks will appear when the formwork is removed 24 hours after the concrete pouring in the early stage, and then these cracks will gradually reach the peak period about 7 days after the removal of the formwork. It will not stop developing slowly until l5-20 d after demolding.
2. Treatment and effective prevention of concrete cracks in flood discharge tunnels of hydropower stations
2.1 Chemical grouting method for spillway tunnel of Shuanghekou Hydropower Station
2.1.1 Introduction, characteristics and configuration of materials
The material of chemical slurry is PCI-CW high permeability modified epoxy resin. The material has high cohesive force, and can be cured at room temperature, with less shrinkage after curing, and at the same time, it has the characteristics of high mechanical strength and stable heat resistance, so it has good water-stop and leak-stopping effects. This kind of reinforcing grouting material is widely used in the repair and reinforcement of water conservancy projects. In addition, the material also has the advantages of simple process, excellent environmental protection performance, and no pollution to the environment.
2.1.2 Construction steps
First, look for seams and drill holes. Clean the cracks found in the spillway with high-pressure water and reverse the concrete base surface, and check the cause of the cracks and the direction of the cracks. And adopt the method of combining the slit hole and the inclined hole for drilling. After completing the drilling of the inclined hole, it is necessary to use high-pressure air and high-pressure water gun to check the hole and crack, and complete the data collection of the crack size.
Secondly, cloth holes, sealing holes and sealing seams. Once again, use high-pressure air to clear the grouting hole to be constructed, and remove the sediment deposited on the bottom of the ditch and on the wall of the hole, and then install the grouting hole blocker and mark it at the pipe hole. Identification of grout and vent holes. After the grouting holes are arranged, use PSI-130 quick plugging agent to seal the cavities, and use epoxy cement to further strengthen the sealing of the cavities. After closing the opening, it is necessary to chisel a groove of 2cm wide and 2cm deep along the direction of the concrete crack. After cleaning the chiseled groove and the retrograde pressure water, use the quick plugging to seal the groove.
Once again, after checking the ventilation of the buried pipeline, start the grouting operation. During the grouting process, the odd-numbered oblique holes are first filled, and the number of holes is arranged according to the length of the actual construction process. When grouting, it is necessary to fully consider the grouting condition of adjacent holes. Once the adjacent holes have grouting, all the water in the grouting holes needs to be drained, and then connected to the grouting pipe and grouted. According to the above method, each hole is grouted from top to bottom and bottom to high.
Treatment and prevention measures of concrete cracks in flood discharge tunnel of hydropower station
Finally, the grout ends standard. The pressure standard for chemical grouting of concrete cracks in the spillway is the standard value provided by the design. Generally speaking, the maximum grouting pressure should be less than or equal to 1.5 MPa. The determination of the end of grouting is based on the amount of injection and the size of the grouting pressure. The basic requirement is that after the grouting pressure reaches the maximum, the grouting will no longer enter the hole within 30mm. At this point, the pipe tying and slurry closing operation can be performed.
Causes and treatment measures of cracks in flood discharge tunnel of Luding Hydropower Station
2.2.1 Analysis of the causes of the flood discharge tunnel of Luding Hydropower Station
First, the raw materials have poor compatibility and stability. Secondly, the amount of cement in the mix ratio is large, which causes the concrete to generate too much heat of hydration. Secondly, due to the large thermal expansion coefficient of rock aggregates in river basins, when the temperature changes, the aggregates and the so-called coagulating materials will dislocate. Thirdly, HF concrete has high construction technology requirements, it is difficult to master in the construction process, and the control of vibrating time and method cannot meet the standard requirements. In addition, because the flood discharge tunnel of Luding Hydropower Station is penetrated, strong air flow occurs, resulting in a low temperature inside the tunnel, resulting in a large temperature difference between the concrete and the external environment.
2.2.2 Treatment and prevention measures for cracks in flood discharge tunnel
(1) In order to reduce the ventilation in the tunnel and protect the temperature of the concrete, so as to reduce the temperature difference between the concrete and the external environment, the bent frame can be set up at the exit of the spill tunnel, and a canvas curtain can be hung.
(2) Under the premise of meeting the strength requirements, the proportion of concrete should be adjusted, the amount of cement should be reduced as much as possible, and the amount of fly ash should be increased at the same time, so that the heat of hydration of concrete can be reduced, so as to reduce the internal and external heat of concrete. temperature difference.
(3) Use the computer to control the amount of water added, so that the water-cement ratio is strictly controlled in the process of mixing concrete. It should be noted that during mixing, in order to reduce the temperature of the raw material outlet, it is necessary to adopt a relatively low temperature. When transporting concrete in summer, corresponding thermal insulation and cooling measures should be taken to effectively reduce the heating of concrete during transportation.
(4) The vibrating process needs to be strictly controlled in the construction process, and the vibrating operation is strengthened by using flexible shaft vibrating rods with diameters of 100 mm and 70 mm.
(5) Strictly control the speed of concrete entering the warehouse, so that its rising speed is less than or equal to 0.8 m/h.
(6) Extend the time for concrete formwork removal to 1 times the original time, that is, from 24 h to 48 h.
(7) After dismantling the formwork, send special personnel to do the spraying maintenance work on the concrete project in time. The maintenance water should be kept at 20℃ or above warm water, and the concrete surface should be kept moist.
(8) The thermometer is buried in the concrete warehouse, the temperature inside the concrete is monitored, and the relationship between the concrete temperature change and the crack generation is effectively analyzed.
By analyzing the causes and treatment methods of the flood discharge tunnel of Shuanghekou Hydropower Station and the flood discharge tunnel of Luding Hydropower Station, it is known that the former is due to poor geological conditions, unsatisfactory treatment of construction joints, cold joints and duxun caves during concrete pouring. The cracks in the flood discharge tunnel caused by poor plug consolidation and grouting can be effectively suppressed by chemical grouting with high-permeability modified epoxy resin materials; the latter cracks caused by the excessive heat of concrete hydration, Cracks can be treated and effectively prevented by reasonably reducing the amount of cement and using polycarboxylate superplasticizer and C9035 concrete materials.
Post time: Jan-17-2022
