Comprehensive Guide to Underground Waterproofing Construction
1. Concrete Structure Waterproofing Method
Basements, underground pump rooms, water tanks, underground passages, and other waterproof structures in general industrial and civil buildings utilize the density of concrete for waterproofing, possessing a certain self-waterproofing capability. They all use monolithic concrete or reinforced concrete structures, combining waterproofing and load-bearing functions.
Waterproof concrete structures include ordinary waterproof concrete, waterproof concrete with admixtures, and expansive cement waterproof concrete.
2. Cement Mortar Waterproofing Layer
Cement mortar waterproofing layers are divided into two types: cement mortar waterproofing layers with admixtures and rigid multi-layer waterproofing layers. They are generally used as waterproofing layers on the inner or outer surfaces of underground engineering structures or as reinforcement layers for waterproof concrete structures.
3. Rolled Waterproofing Membrane Layer
Due to the good toughness of rolled waterproofing membranes, they can adapt to certain lateral pressures, vibrations, and deformations, achieving good results in corrosion resistance and impermeability, and the material source is relatively sufficient. Generally, two methods are used: external waterproofing with external application and external waterproofing with internal application. However, since externally applied membranes can protect underground engineering structures from the harmful effects of groundwater erosion, penetration, and capillary action, externally applied membranes are still widely used.
4. Waterproof Coating Membrane Layer
Waterproof coatings are developing rapidly, with high-end options including polyurethane, acrylic, and silicone rubber, used for brushing or spraying on the inner or outer surfaces of underground engineering structures. Coating waterproofing also has the characteristics of good integrity and easy handling of irregular parts, so the coating waterproofing layer can serve as one of multiple waterproofing layers.
The external coating of waterproofing can protect the structure from the harmful effects of erosive media in groundwater, or be used for moisture isolation and humidity reduction to decrease the moisture dissipation of underground engineering structures.
The internal coating of waterproofing can be used as an anti-seepage material for liquid storage and water tanks.
Construction Case Analysis
The Ningxia Grand Theater is the largest, most functionally complete, and most advanced large theater building in the history of public cultural facility construction in our region. It is a landmark building rich in regional characteristics, an important window to showcase the achievements of spiritual civilization construction in the autonomous region, and an important symbol of the cultural and social development level of the autonomous region!
Waterproof coatings are developing rapidly, with high-end options including polyurethane, acrylic, and silicone rubber, used for brushing or spraying on the inner or outer surfaces of underground engineering structures. Coating waterproofing also has the characteristics of good integrity and easy handling of irregular parts, so the coating waterproofing layer can serve as one of multiple waterproofing layers.
The external coating of waterproofing can protect the structure from the harmful effects of erosive media in groundwater, or be used for moisture isolation and humidity reduction to decrease the moisture dissipation of underground engineering structures.
The internal coating of waterproofing can be used as an anti-seepage material for liquid storage and water tanks.
The Ningxia Grand Theater is located on the east side of People's Square in Jinfeng District, Yinchuan. Together with the Ningxia Museum, Ningxia Library, and Yinchuan Cultural Arts Center, it forms a beautiful square. The east side of People's Square is called the "grand living room" of Ningxia culture by out-of-town media, and the Ningxia Grand Theater is the finishing touch of this "grand living room."
As an important window to showcase the achievements of spiritual civilization construction in the autonomous region, this project is an important symbol of the cultural and social development level of the autonomous region. It was invested and constructed by the Department of Culture of Ningxia Hui Autonomous Region, with a total construction area of 48,600 square meters, including an underground construction area of 14,000 square meters. Beijing Zhuobao Waterproof Engineering Co., Ltd. is responsible for the waterproofing work.
The design service life of this project is 100 years, and the underground waterproofing protection level is Class I. The waterproofing method adopts a combination of concrete structural self-waterproofing and flexible waterproofing membrane layers. The concrete in the underground engineering part uses C30-C40 impermeable concrete with an impermeability grade of S6-S10, and the flexible waterproofing layer uses "3 mm+3 mm" double-sided self-adhesive rubber asphalt waterproofing membrane.
Key Points of Waterproofing Construction
Basement Floor Slab: Loose-laid Method
Construction process: Substrate acceptance → Node reinforcement treatment → Positioning and line marking → Loose-laying the first layer of waterproofing membrane → Self-adhesive second layer of waterproofing membrane → Inspection and acceptance → Peel off the isolation film on the upper surface of the second layer of waterproofing membrane.
The waterproofing reinforcement layer is constructed using the spot-bonding method, i.e., applying a primer or cement slurry in strips at node locations for temporary fixation and bonding.
Basement Exterior Wall and Roof: Wet-laid Method
Construction process: Substrate acceptance → Moistening the substrate → Positioning and line marking → Applying plain cement slurry and laying the first layer of waterproofing membrane → Air exhaust and drying → Overlap edge treatment → Node reinforcement treatment → Self-adhesive second layer of waterproofing membrane → Membrane termination and sealing → Inspection and acceptance.
Embedded Grouting Pipe Construction
Since part of the project has 3 underground floors and some underground corridors, there will be certain settlement deformation in the later stage. Therefore, grouting conduits are embedded in deformation joints and vibrating construction joints for later waterproofing maintenance.
Embedded grouting pipe construction process: Clean concrete joints → Install embedded grouting pipe → Install water-swelling waterstop adhesive → Inspection and acceptance → Structural concrete construction → Inject elastic polyurethane grout or acrylate grout.
1) Use a wire brush, putty knife, and brush to clean the hardened cement laitance, dust, and other debris on the concrete surface.
2) Cut the required length (5-6 m) of the full-section grouting pipe, smooth the end by rotating, insert it into the blue bell mouth connector and ensure it is tightened securely, then attach the reinforced PVC grouting conduit to the thinner end of the blue bell mouth. Place the grouting pipe tightly against the concrete surface and fix it with cement nails and fixing clips at intervals of 200-300 mm.
The PVC conduit must be led out of the concrete structure to facilitate later grouting construction;
The PVC conduit should be led out at about 200 mm from the construction joint; it is strictly prohibited to lead it directly from the construction joint;
Adjacent grouting pipe loop connections should be staggered and tightly overlapped with an overlap length of 20-30 mm.
3) Place the water-swelling waterstop adhesive into the extrusion gun, cut a 10 mm outlet at the top of the aluminum bag, and install the grouting nozzle while covering the gun cap; cut the nozzle width according to design and construction requirements, and the nozzle cross-section should be cut at an angle.
4) Check whether the full-section grouting pipe is installed securely. Adjacent grouting pipe loop connections should be staggered and tightly overlapped with an overlap length of 20-30 mm. The reserved grouting pipe must directly contact and cover the entire length of the concrete joint. The water-swelling waterstop adhesive should be continuous, uniform, and straight, and firmly bonded.
5) Inject elastic polyurethane grout or acrylate grout. When concrete curing is completed and later shrinkage is finished or water seeps in later, use this embedded device for grouting and water stopping. If there is no leakage at the joint, no grouting treatment is required for the time being.
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