The following is the relevant content about the treatment of water leakage in subway projects brought to you by Zhongda Consulting for your reference.
This article briefly describes the treatment methods for different water leakage situations in subway projects, introduces the correct use of various leakage plugging, grouting, and waterproofing materials in more detail, and points out that measures should be taken according to different leakage situations. Appropriate leakage plugging methods can ensure the waterproofing effect of subway projects.
1 Overview
Water leakage in subway projects is a common engineering defect in China today, especially in areas with rainy weather and high groundwater levels in the south. It is not only related to the surrounding areas of underground projects It is related to the geological and hydrological environment, structural burial depth, waterproof design plan, waterproof materials, etc. It is also related to structural concrete performance, construction plan, construction technology, etc. Since there are many factors that affect the waterproofing effect of subway projects, most subway projects have more or less quality defects such as local leakage after completion. In order to complete the defect repair as soon as possible and put the project into use, subway engineering leakage treatment is particularly important after the project is completed. This article summarizes the construction experience of Guangzhou Metro, Shanghai Metro and Shenzhen Metro, and discusses the treatment of leakage water in subway projects.
2 Reasons for leakage
Generally, the main reasons for structural water leakage are the following:
1) The structure’s self-waterproofing fails.
Structural self-waterproofing is an extremely important waterproofing measure, but it is difficult to achieve in actual projects. The main reason is that structural cracks are difficult to avoid. In addition, due to the particularity of the underground engineering space environment, the uniformity of concrete construction quality is insufficient. Good, there are local defects inside the concrete, which destroys the self-waterproofing ability of the structure.
2) Leakage is caused by poor waterproofing design, improper measures, and imprecise construction techniques at deformation joints, construction joints, and wall pipes in the concrete structure.
3) The waterproofing of the enclosure structure fails.
The waterproofing failure of the building envelope is mainly caused by poor joint processing or leakage caused by defects in the concrete of the structure itself.
4) The outer waterproof layer fails.
Leakage caused by improper selection of materials such as outsourcing waterproof boards and waterproof coatings or poor construction quality.
5) Subway stations built using different construction methods have caused leaks due to improper treatment of special parts.
For example: the cover-and-excavation method is used to construct underground projects, and the piles pass through the concrete floor. Because no reinforced waterproofing measures are taken or the waterproof layer of the floor is discontinuous, and the concrete around the piles is not dense, groundwater flows along the piles. Column roots penetrate into the base plate.
3 Methods for treating leakage water
Through the analysis of the causes of leakage, once leakage occurs, it is proved that there must be defects in the waterproofing of the enclosure structure and the outer waterproof layer, but it cannot be carried out Treatment, leakage problems can only be solved by repairing structural concrete defects. Leak plugging in subway stations mainly uses grouting to seal structural defects. Tunnel waterproofing is mainly achieved through grouting behind the lining and partial grouting inside the lining to repair structural concrete defects.
The leakage conditions in subway stations and sections are mainly point seepage, surface seepage, construction joint leakage, crack leakage and deformation joint leakage. Different leakage situations are divided into different treatment methods.
3.1 Determine the leakage location
Generally, wipe the surface with a dry rag and wait for a while to visually observe the leakage point. If the wet surface is not easy to see, you can use hot air to dry it and observe it. Although surface seepage and leakage from construction joints, cracks, and deformation joints require comprehensive treatment, the leakage situation still needs to be understood through the above methods, such as leakage speed, water seepage amount, seepage point distribution, seepage pressure, etc.
3.2 Treatment methods
3.2.1 Point leakage
The phenomenon of point leakage can be divided into points or cracks less than 5cm. Drill a hole at this point or in the center of the crack with a hole diameter of 10mm and a depth of 6cm. Rinse with high-pressure water and then grout. There must be a certain gap between the grouting pipe nozzle and the bottom of the hole. The orifice and the grouting pipe are fixed with leakage-stopping powder. The cracks on both sides are also sealed with leakage-stopping powder. If the effect is not good, gouge processing is performed.
3.2.2 Surface seepage
Surface seepage is formed by dense point seepage. For example, if the diameter is less than 5cm, the first process can be treated as point seepage, and then in the seepage surface Chisel to a depth of 3cm, clean and apply leak-proofing powder, dry the base surface and apply two-component polyurethane paint, and finally seal it with waterproof mortar.
If the surface seepage area is greater than 5cm, drill the base surface 6cm deep, clean and brush the exposed steel bars, and deepen the circumference by 2cm to facilitate water stopping.
1) Apply three coats of leak-stopping powder to the base surface. The consistency of the leak-blocking powder depends on the humidity of the base surface and is subject to operational sensory effects. If the effect of individual points is not good, you can use leak-proofing powder to repair it, with a thickness of 5mm~15mm. 2) Apply 1mm of two-component polyurethane. Before painting, the base surface needs to be air-dried. When applying two-component polyurethane, 2cm should be reserved for the mortar bonding part; 3) Waterproof mortar sealing.
3.2.3 Cracks and construction joint leakage
1) Process flow:
Drill grouting holes → Chise U-shaped grooves → Clean the base surface → Rinse Grouting hole → insert grouting pipe → sealing powder cover → grouting → seal grouting pipe → base surface restoration.
2) Construction technology and requirements:
a. Preset grouting holes.
Depending on the formation of cracks, cracks generally form vertical cracks on the wall, and the grouting holes are preset to ensure the position of the crack after it is dug and to ensure that the space is above the crack. Use a Ф10mm impact drill bit to punch holes with a depth of 10cm and a spacing of 20cm. When forming holes, pay attention to centering the crack, perpendicular to the wall, and add one hole 5cm apart at both ends of the crack.
b. Groove.
Determine the closing position at both ends of the crack and extend it by 15cm as the end position of the groove. In order to ensure the integrity of the groove, first use a steel disc to cut the border (turn in a straight line) to a depth of 1cm and a width of no more than 20cm. Follow the cutting border along the crack to form a U-shaped groove. The depth of the groove is the main reinforcement. Until exposed, the depth principle is that the diameter of the main bar of the steel protective layer is 1cm to fill the space, which can generally reach 7cm.
c. Base surface cleaning.
The cleanliness of the base surface is the key to the combination effect of the leak-proofing powder and the base surface. The base surface must be brushed clean with clean water and a steel brush, and dust, loose layers of scum and other debris are not allowed. Fresh concrete base surfaces should be sealed promptly.
d. Rinse the grouting hole.
The grouting hole is still 2cm~3cm deep from the base surface. You can use the grouting pipe to go deep into the hole and flush it with high-pressure water. Repeat this several times. No debris is allowed to be left in the hole.
e. Embed grouting pipe.
The grouting pipe is embedded in the hole leaving a little space to facilitate the injection of slurry; the orifice is ring-sealed and fixed with leak-stopping powder.
f. Leak-stopping powder cover.
The sealing powder cover is sealed from one end of the crack to the other end. The material must be stirred evenly, the time must be controlled appropriately, and the connection with the grouting pipe must be tight. The water used must not be groundwater or water from crack leaks, but must be tap water. The sealing powder operation is from both sides of the tank to the middle, and from the areas with mild leakage to the areas with severe leakage. The operation is carried out in three layers: the thickness of the first layer is based on the principle of stopping water and is determined according to the size of the water seepage. The thickness of the second and third layers is 2cm~3cm. The surface of each layer is smooth and smooth by hand. There are no bee holes or grainy appearance, and watering is not allowed.
g. Grouting.
Inject grouting the next day after the leak-proofing powder cover is used to observe the effect of the cover. If there is side leakage, it needs to be reworked until the entire cover does not seep.
Before grouting, a test grouting inspection should be carried out. The pressure test has four purposes: to clear the cracks and clean up debris in the joints; to check the penetration of the cracks; to check whether the sealing layer has been broken by grouting. Weak points; determine the grouting flow rate and approximate saturation time. The pressure of the pressure test is generally below 0.3MPa, and detailed records should be kept for analysis and judgment during grouting.
h. Grouting operation method.
When there is no abnormality after pressure test inspection, grouting can be carried out. Grouting starts from the first grouting pipe (No. 1) at the bottom of the crack. When the crack is wide (greater than 0.3mm), the grouting pressure is adjusted to 0.3MPa~0.5MPa. When the crack is less than 0.3mm, the grouting pressure can be adjusted appropriately. Increase the pressure by about 0.5MPa. When the grout is produced from the adjacent hole (No. 2), cut the plastic pipe of No. 1 hole about 5cm from the root, fold it and tie it tightly with a tie, and use the No. 2 grouting hole instead. From bottom to top, pump out one hole and close the other hole until the hole at the top of the crack is blocked. After plugging it, continue to pressurize it stably for 3 minutes until the entire crack is filled with slurry.
After construction, clean the tools with acetone immediately to prevent the slurry from being unable to be removed after solidification.
4 Reasonable selection of leakage plugging materials
4.1 Leakage plugging materials
1) Application parts and functions. The grouting orifice is blocked, the open water is blocked, and the tank is temporarily sealed to create waterless working conditions for grouting, coating waterproofing and membrane waterproofing.
2) Technical requirements for leak plugging materials.
Leak-stopping materials should generally meet the following technical requirements: rapid setting, adjustable setting time; high strength, no cracking in a short period of time; good impermeability, strong adhesion, and can be operated with water.
4.2 Waterproof materials
1) Technical requirements for waterproof materials. It has strong waterproofing and impermeability, and the coating material does not crack; it is non-corrosive and corrosion-resistant, and has good durability; it has sufficient strength, has strong bonding force with the concrete base surface, and can form an integral part with the structure; the waterproofing material does not contain leachables; Simple operation, easy inspection, no pollution.
2) Commonly used waterproof materials. Cement-organic quick-setting agent: such as R1 waterproof coating, this material can quickly plug leaks and can be used as permanent waterproofing.
Synthetic waterproof materials: such as Sepas, PQ-200, etc. This type of material cannot be used as a quick leak plug, but can only be used as a durable waterproof coating.
High molecular polymer waterproof mortar: This type of material cannot be used in quick leak plugging and can only be used as a durable waterproof coating with good bonding.
KS series repair agent cannot be used as a leak-stopping and waterproofing material because it is a sintered powdery material that stimulates cement, and its K2O content is as high as 19.73%. If used in projects containing active aggregates, it will greatly promote the alkali-aggregate reaction of concrete, and there will be a lot of dissolved matter, forming a seepage channel.
4.3 Grouting materials
1) Mechanism of action. Fill the voids, pores, and cracks in the concrete, seal the leakage water channels, and replace the position of groundwater in the concrete.
2) Material performance requirements. Good permeability and pourability; non-corrosive and corrosion-resistant, no pollution; sufficient strength, good durability, no leachables, no shrinkage; integrated with the structure, the material has good adhesion, and is resistant to train vibrations The lower material will not separate or take off the body.
3) Optional materials. The inorganic grouting material should be ultra-early strength self-leveling cement, which has the functions of reinforcing and plugging. Polymer grouting materials are preferably modified epoxy resins, such as EAA and KS-7 modified epoxy resin chemical grouting fluids. Single-component water-soluble polyurethane slurry should not be used. The main reason is that it has poor durability, poor bonding ability with concrete, self-shrinking, repeated grouting cannot be used during construction, and false plugging defects are prone to occur during grouting plugging.
4.4 Materials for controlling water leakage from deformation joints
The grouting materials for water leakage from deformation joints must not use grouting materials with high strength and stiffness, such as inorganic grouting materials, modified grouting materials, etc. Resistant epoxy grouting materials, etc. It is prohibited to use leak-stopping agents to plug leaks.
Grouting materials with fast setting time (adjustable), low strength, low viscosity, good groutability, and good waterproofing effect in a short time should be used first. Acrylic grouting materials are commonly used grouting and water-stopping materials for deformation joints, but they can only be used as temporary water-stopping materials.
5 Conclusion
Leakage in subway stations is mainly point seepage, cracks and construction joint leakage, and the amount of water leakage is not large, and most of it is slow seepage. If the amount of leakage is relatively large during plugging, grouting will be used to plug the leak. If it is slow seepage, use plugging powder to directly seal it.
Leakage in the interval is mostly caused by point seepage and crack leakage caused by local looseness of the concrete in the arch. The main method of plugging the interval is backfill grouting. The backfill grouting must have sufficient pressure to ensure that the backfill of the arch is dense, and grouting must be done multiple times. Grouting can reduce leakage parts by more than 90%. The remaining leakage parts are mostly point seepage, and grouting is the main method for interval point seepage.
In short, leakage plugging must be tailored to local conditions, and appropriate methods must be adopted according to various leakage situations in order to be targeted. Each process of plugging leaks must be done carefully, and each process cannot be sloppy, otherwise it will inevitably lead to failure.
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