Underground leakage has always been a difficult problem in underground waterproofing projects. The use of new materials, new processes and new methods plays a key role in improving underground waterproofing. This paper introduces the waterproofing treatment technology of a subway station. The various construction methods and measures described have been applied to the subway station project with high waterproof requirements. The method of rigid-flexible combination and anti-discharge combination is adopted in the project. Several effective methods for the treatment of the external waterproofing parts have achieved good results, and provided a reference for improving the construction quality of the underground outdoor waterproofing.
With the continuous improvement of people's awareness of ecological environmental protection, the widespread application of underground environmental protection projects has received more and more attention from everyone. The construction of underground works such as cross-street tunnels, underground parking lots, high-rise building basements, and subway projects is increasing. The use of new materials, new processes, and new methods plays a key role in improving the underground waterproofing effect, ensuring equipment safety and appearance, and extending the life of the structure. The various construction methods and measures described in this paper have been applied to subway station projects with high waterproof requirements, and have achieved good results.
1 Project Overview
The structure of a subway station is mainly waterproof from the structure. The outer waterproofing is supplemented by the all-inclusive waterproofing method. It is a waterproof structure composed of a flexible waterproof layer and a waterproof reinforced concrete lining. The waterproof area is about 18500m2. The waterproof structure of the main structure of the station is one level, that is, the structure is not leaking, and the surface of the structure shall not have wet stains; the waterproof standard of the entrance and exit passage structure is two-stage, that is, the structure is not leaking, and the surface of the structure is allowed to have a small amount of occasional wet stains. The top of the structure is made of 2.5mm thick YN non-tar polyurethane coating waterproof layer; the bottom plate and the vertical wall are made of 4mm thick YN self-adhesive elastomeric asphalt coil waterproof layer. The waterproof layer is constructed by the “outside defense†method. The vertical wall is protected by YN coil waterproof layer polyurethane film surface 5~6mm thick polyethylene foam board.
2 waterproof design principles and standards
China's "Code for Design of Subways" [1], "Code for Construction and Acceptance of Underground Railway Projects" [2] and "Technical Specifications for Waterproofing of Underground Works" [3] have made special provisions on the waterproofing of subway structures, as follows:
(1) The waterproof design of underground works should follow the principle of “preventing prevention, combining prevention and control, adapting to local conditions, and comprehensive managementâ€.
(2) The waterproof engineering design should follow the principle of “anti-discharge combination†and “water-proof surface defenseâ€, and adopt measures such as “multi-channel fortificationâ€, “composite waterproof†and “node sealâ€.
3 waterproof construction optimization program
3.1 Pretreatment of the waterproof layer construction base
Because the enclosure structure of the project is to use the “bite†manual digging pile to attach three horizontal steel pipe supports as the supporting structure, the waterproof layer is constructed by “external anti-adhesive†method, that is, the bottom plate and the siding are tied. Before the steel bars, the outer waterproofing membrane must be adhered to the backing cushion and the backfill concrete layer between the piles.
YN self-adhesive coils are cold-adhesive coils. As with most waterproof materials, the base layer moisture content of concrete should not exceed 9% for the construction of the base layer. It is relatively easy to achieve the roof of the station or the "outer anti-adhesive" waterproof base surface, but there are certain difficulties for the construction of the base plate of the station and the side wall of the laminated structure. As the retaining piles of the station are excavated with the excavation of the foundation pit and the steel support construction, the pile body will be deformed and deformed, causing cracks between the originally dug holes, and the groundwater can easily penetrate into the interior of the foundation pit along the crack. If there is no inter-pile treatment or inter-pile plugging treatment at this time, the concrete will be backfilled between the piles as usual, and the seepage will seep along the pile edge and the weakest part of the backfill concrete, forming a result of seepage around the surface of the base layer, becoming more Difficult to deal with.
The use of organized drainage treatment methods can solve the embarrassing situation that the blind plugging causes the water seepage. The specific method is as follows: Before the screed layer between piles, first use the cut PVC pipe piece or bamboo piece to make a water-passing passage along the concave position of the pile (see Figure 1), and lead the water seepage between the piles to surround the foundation pit. In the organized drainage blind ditch and collecting well of the surrounding basement, the water is pumped away at the location of the collecting well to reduce the groundwater level, which can solve the problem of seepage in the foundation pit and the screed between the piles, and meet the construction of the YN waterproofing membrane of the bottom plate and the siding The dryness condition ensures the effect of waterproof construction.
3.2 Waterproof construction treatment of expansion joints
The expansion joint is a weak part of the waterproof, mainly due to the complete disconnection of the steel and concrete in the part, and the ring-type rubber waterstop directly resists the groundwater pressure. Firstly, the rubber waterstop and reinforced concrete are two completely different materials, and the expansion ratios are quite different. The bonding ability of the two is poor. The water seepage usually bypasses the setting range of the rubber waterstop. The penetration into the structure is only time. problem. Secondly, the connection quality of the rubber waterstop also directly affects the waterproof effect at the expansion joint, such as the inaccurate position of the rubber waterstop. In addition, the location of the rubber waterstop is not sufficient due to the rigidity of the end template of the fixed waterstop. When the concrete is poured, the template is deformed, and the waterstop is easily squeezed to one side. Finally, the concrete cannot be fully vibrated, resulting in insufficient compactness and the reason why the expansion joint often leaks.
3.2.1 Reinforced seam pre-embedded PVC grouting tube treatment
Check and clean the rubber waterstop before pouring concrete to prevent the concrete and rubber waterstop from forming gaps in the slag; strengthen the concrete vibration of the expansion joint, make the rubber waterstop and the concrete bond dense, prevent the concrete at the bottom of the rubber waterstop Produce vacancies and leak water. In addition, before the concrete is poured, a pre-embedded PVC tube is added to the water-repellent surface of the expansion joint rubber waterstop. The tube can be made of Φ20 PVC pipe, drilled with a pistol with a diameter of Φ8mm, staggered every 20~30cm on the PVC pipe, and the hole is wrapped with cement bag paper to prevent the concrete from being grouted before being grouted. The slurry will be smashed, and after the structural concrete has been shrunk to a certain stage, the flower tube is pressure-grouted, and the flexible waterproof material is injected with water-soluble polyurethane to fill the fine gap between the concrete and the rubber waterstop, and the weakened part of the waterproofing is strengthened. .
Practice has proved that this is a good solution to fill tiny pores. It can be applied not only to expansion joints, but also to anti-seepage and plugging measures at construction joints. It is used by the design department for station and section construction joints and expansion and contraction. Seam construction process.
3.2.2 Top plate expansion joint position empty shop treatment
The waterproof wall panel of a subway station adopts YN self-adhesive coiled material, and the top plate adopts non-tar polyurethane waterproof coating. This is a more sensible choice, which can fully exert the characteristics of strong adhesion between polyurethane and main roof, and give full play to two types. The advantages of materials, to achieve strengths and avoid weaknesses. Due to the insufficient adhesion of the self-adhesive coil and the top plate, when the earth is backfilled, it is easy to cause the coil to be rolled and arched, which causes the coil interface to be pulled and leaked. The top plate is made of non-tar polyurethane, which can not only exert the strong adhesive force of polyurethane, but also prevent the waterproof material from being damaged by the roll, and can achieve the all-inclusive waterproof effect.
A 20 mm wide gap is reserved at the expansion joint. Since the polyurethane elongation at this point is not sufficient to accommodate the shrinkage deformation of the overall structure, the cracking of the polyurethane coating sometimes occurs. Taking advantage of the fact that the longitudinal tensile strength of YN coil is stronger than that of polyurethane, the 400mm wide YN waterproof coiled material is longitudinally laid in the longitudinal direction of the expansion joint, and 20mm folding marks are reserved in the expansion joint, and a certain amount of expansion and contraction is reserved. The polyurethane waterproof coating can greatly reduce the situation that the waterproof material at the expansion joint is cracked and the groundwater seeps into the expansion joint.
3.3 Structure self-waterproof treatment
Concrete is a heterogeneous porous material that is often subjected to temperature changes and swelling and shrinkage to produce volume changes. Frequent changes in temperature and humidity make cracks and leaks inevitably occur in large-volume concrete members. Cracks in structures are inevitable, and the requirements for self-waterproof design of structures are increased. Construction joints are weak parts of structural self-waterproofing. If it is not handled properly, it is easy to cause leakage.
(1) The main structure concrete shall be segmented and the blocks shall be discontinuously poured. When the concrete has a pre-drying period of 4 to 5 days, the intermediate block concrete is poured to reduce the concrete shrinkage stress, which can reduce the crack generation.
(2) The steel pipe putty water stop belt is used in the construction joint to replace the traditional BW water stop strip. Due to the width of the steel plate putty water stop, the seepage path of the ground water is prolonged, and the waterproof capacity of the construction joint is enhanced.
(3) Special treatment for horizontal and vertical construction joints, horizontal construction joints are strictly in accordance with the standard chiseling treatment, and vertical construction joints adopt “quick and easy†closing nets to strengthen the bonding and biting ability of new and old concrete and reduce the occurrence of cracks. .
(4) After the scientifically blended concrete, the maximum amount of cement is strictly controlled, the water-cement ratio is <0.45, and the “double-osmosis†technology is applied to the concrete, and the appropriate amount of high-quality fly ash and Pu'erli water reducing agent are blended. , reducing the amount of cement, reducing the water-cement ratio, reducing the generation of hydration heat, so that after the concrete solidifies, the temperature difference between the inside and the outside is reduced, reducing the possibility of cracks in the concrete.
(5) Mixing concrete with ice water to directly reduce concrete slump and mold temperature, reduce concrete cooling and shrinkage, and improve the self-waterproof ability of the structure.
4 Conclusion
The subway station project is mainly waterproof from the structure, and the outer waterproofing is supplemented by the all-inclusive waterproofing method. It is a waterproof structure composed of a flexible waterproof layer and a waterproof reinforced concrete lining. The top of the structure is made of 2.5mm thick YN non-tar polyurethane coating waterproof layer, and the bottom plate and the vertical wall are made of 4mm thick YN self-adhesive elastomeric asphalt coil waterproof layer. The waterproof layer is constructed by the “outside defense†method. The vertical wall is protected by YN coil waterproof layer polyurethane film surface 5~6mm thick polyethylene foam board. Due to the use of various waterproof optimization schemes, compared with the previous basement project, the internal structure of the metro station structure is significantly reduced compared with the same type of basement; especially the waterproofing of construction joints and expansion joints, through relaxation treatment and pressure injection The slurry treatment and anti-seepage have achieved ideal results, and provide a reference method for the large-scale underground outdoor waterproof construction of the same type in the future.
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