Recently, with the continuous improvement of urban infrastructure construction in China, underground passages have become an important carrier for alleviating surface traffic pressure and connecting urban functional areas. They are widely used in scenarios such as urban roads, subway hubs, and commercial district connections. Underground passages are exposed to underground environments for a long time and are easily affected by groundwater infiltration, surface rainwater backflow, and moisture erosion. As the core defense line to ensure the normal use of underground passages, the construction quality of waterproofing and drainage systems directly affects the service life, user experience, and operational safety of the passages. If the waterproofing is not in place, problems such as wall moisture regain and structural leakage may occur; If the drainage system is not smooth, it can cause water accumulation in the channel, affect traffic safety, and even damage internal facilities.
The construction of waterproofing and drainage systems for underground passages follows the core principles of "combining prevention and drainage, comprehensive treatment, adapting to local conditions, and full process control", which runs through the entire process of construction preparation, on-site construction, post acceptance, and management and protection. The core goal is to build a protective system that can be "prevented and drained smoothly", eliminate hidden dangers of leakage and water accumulation, and ensure the long-term stable operation of underground passages. Industry experts say that waterproofing and drainage of underground passages is a systematic project that needs to balance the sealing of waterproofing and the smoothness of drainage. Based on the geological conditions, hydrological environment, and usage needs of the passage, targeted construction techniques should be selected to accurately control every technical detail in order to achieve long-term protection.
The technical key points of underground channel waterproofing system construction mainly include four core links: pre construction preparation, base surface treatment, waterproof layer construction, and node sealing. Each link must strictly follow industry standards to eliminate leakage hazards from the root, among which node sealing is the top priority of waterproofing construction.
The key technical points in the preparation stage before construction are to do a good job in material control, on-site investigation, and scheme preparation. Waterproof materials are the core carrier of waterproof systems, and their quality directly determines the waterproof effect. They need to be strictly screened and accepted according to design requirements and industry standards. Commonly used waterproof rolls, waterproof coatings, sealing materials, etc. need to be checked for specifications, models, quality certificates, and qualification certificates to ensure that the materials have heat resistance, cold flexibility, anti-seepage, corrosion resistance, and other properties. For waterproof materials in important areas, sampling and retesting are required to test their tensile strength, low-temperature flexibility, and other indicators. Unqualified materials are strictly prohibited from being put into use. At the same time, material storage should be standardized. Waterproof rolls and coatings should be stored in dry and ventilated warehouses to avoid moisture and exposure to sunlight, and to prevent material aging and deterioration. Before construction, a comprehensive survey of the site is required to understand the groundwater level, geological conditions, and characteristics of the channel structure. Hidden cracks, leakage points, and other hidden dangers should be identified. Based on the survey results, a special waterproof construction plan should be developed to clarify the construction process, technical parameters, and emergency measures. After approval, it can be put into implementation.
Base surface treatment is a prerequisite for the construction of waterproof layers, which directly affects the bonding strength and waterproof effect of the waterproof layer. The principle of "clean, flat, and without hidden dangers" should be followed. Before construction, it is necessary to clean the cement slag, dust, sharp debris, etc. on the base surface. Use an angle grinder to smooth out the protrusions and steel bar heads on the base surface, and fill the pits with polymer mortar layer by layer; If there is visible water or slight seepage on the base surface, quick setting waterproof mortar should be used to seal the leak first, and subsequent construction should be carried out after the base surface is dry. For nodes such as internal and external corners, construction joints, deformation joints, and through wall pipe roots, they should be made into circular arcs or 45 ° slopes with a radius of not less than 50mm to avoid tearing the waterproof layer at right angles and lay a good foundation for the construction of the waterproof layer.
The construction of the waterproof layer should be carried out according to the location of the channel structure, and targeted construction techniques should be selected. Common waterproof methods include flexible waterproofing and rigid waterproofing, and the combination of the two can improve the waterproof effect. Flexible waterproofing mainly uses waterproof rolls and waterproof coatings for laying. The construction of rolls requires controlling the laying sequence and overlap width to ensure that the rolls are tightly adhered to the base surface, without problems such as hollowing or warping. The overlap width must meet the requirements of the specifications; Waterproof coating construction should be evenly applied, with controlled thickness and number of coats to avoid omissions and uneven thickness. After application, wait for the previous coat to completely dry before proceeding to the next coat. Rigid waterproofing mainly uses waterproof concrete pouring, and closed structures such as underground passage box culverts can use self waterproof concrete. At the same time, waterproof layers are added to the top surface of the roof and the outer side of the side walls to further enhance the anti-seepage ability.
The node area is a weak link in waterproof construction and also a high-risk area for leakage, and it is necessary to focus on strengthening sealing treatment. Waterstops or strips should be installed for construction joints and deformation joints. Before pouring horizontal construction joints, the surface floating slurry should be removed, and a layer of 30-50mm thick 1:1 cement mortar should be laid first before pouring concrete; The deformation joint shall be filled with polyethylene foam plastic rod, and the surface shall be filled with polysulfide sealant or silicone sealant to form multiple protection. The wall penetrating pipe root needs to first chisel grooves around it, fill them with sealant, and then extend 200-300mm around the pipe root as a waterproof additional layer to ensure that there is no gap between the pipe root and the concrete. In the construction of the underground passage at Donghu Park Station on Guangzhou Metro Line 6, the construction team first grouted and stopped the leakage points in response to high groundwater pressure scenarios, and then laid a waterproof additional layer, effectively solving the problem of structural leakage.
The technical key points of underground channel drainage system construction are to ensure smooth drainage and no water accumulation, covering three core links: drainage system design, drainage facility construction, and drainage capacity verification. The design principle of "high water, high discharge, low water, low discharge" must be strictly followed.
The design of the drainage system should take into account the length, slope, catchment area, and hydrological conditions of the underground passage, and set up an independent drainage system to ensure the reliability of the outlet. When designing the longitudinal section of the underground passage, it is necessary to set up a slope at the starting points of both ends of the approach, with an elevation of 0.2m~0.5m higher than the ground. At the same time, the drainage of the approach road surface should be strengthened, and interception ditches should be set up on both sides of the joint between the approach road and the underground passage to prevent rainwater from flowing back from the ground. There should be a drainage longitudinal slope of not less than 0.3% to 0.5% between the roadside ditch rainwater outlets in the underground passage. When there is no rainwater outlet in a shorter underground passage, the longitudinal slope should not be less than 0.5%; The roadway surface inside the approach road and underground passage should have a cross slope of no less than 2% to ensure that rainwater quickly collects into the drainage facilities.
The construction of drainage facilities requires controlling key points such as pipeline laying, rainwater inlet installation, and pump station setup. The drainage pipeline should be made of sturdy and corrosion-resistant materials, with a diameter of no less than 150mm. When laying, the slope of the pipeline should be controlled, generally not less than 3%, to avoid a too small slope affecting drainage efficiency; The pipeline connection needs to be sealed tightly to prevent water leakage. After the installation is completed, a hydrostatic test should be conducted to ensure that the pipeline is leak free. The setting and selection of rainwater outlets should adapt to the characteristics of fast and urgent water collection, and reasonably determine the spacing based on the runoff coefficient of the approach channel to ensure rapid collection of rainwater. When the underground passage cannot self drain, a pumping station should be set up for drainage. The pumping station should be designed with a rainfall recurrence interval greater than the road standard to ensure that there is no water accumulation in the underground passage. After the installation of the pumping station, a trial operation should be carried out to verify the drainage capacity.
In addition, auxiliary methods such as blind ditch drainage can be used for underground channel drainage to reduce the pressure of groundwater on the structure. Blind ditch construction requires the use of materials with good permeability to ensure reliable drainage. In humid areas of the south, the drainage pipeline area needs to be adjusted according to the local rainfall intensity. The values of q ₅ and ₁₀ can be set at 2.5-3.0mm/min; The value of 0.5-1.5mm/min can be set in the dry northwest region to ensure that the drainage system is suitable for the regional climate characteristics.
The quality control and later management of underground channel waterproofing and drainage system construction are equally crucial, and are important supports to ensure the long-term effectiveness of the project. During the construction process, it is necessary to strictly follow industry standards such as CJJ11-2011 "Code for Design of Urban Bridges", strengthen the control of material quality and construction technology, conduct strict acceptance of incoming materials, monitor key indicators such as coating thickness, pipeline slope, and node sealing in real time, keep good construction records, and ensure traceability of the construction process. After the waterproof construction is completed, a closed water test needs to be conducted. After the drainage system is completed, a water test needs to be conducted to verify the waterproof and drainage effects. Unqualified parts need to be rectified within a specified period of time, and can only enter the next process after passing the re acceptance.
In the later stage of management and maintenance, it is necessary to establish a sound management and maintenance mechanism, regularly inspect waterproof coatings and sealants, and promptly repair damaged parts; Regularly clean the debris in the drainage pipes and rainwater outlets to prevent pipe blockage; Regularly inspect the drainage pump station to ensure its normal operation. At the same time, intelligent monitoring methods can be used to monitor the humidity and water accumulation in underground passages in real time, timely warn of leakage and water accumulation hazards, and improve management and protection efficiency.
The reporter learned that with the continuous deepening of urban underground space development, the waterproofing and drainage technology of underground passages is also continuously optimized. The application of active drainage technology and new environmentally friendly waterproof materials has further improved construction efficiency and protective effects. Industry experts remind that the construction of underground channel waterproofing and drainage systems is related to traffic safety and engineering durability. Construction units need to strictly implement the quality responsibility system, strengthen full process control, optimize technical solutions based on actual engineering conditions, strengthen professional training for construction personnel, and improve standardized operation levels. In the future, we will further promote the refinement and intelligent development of waterproofing and drainage technology, improve technical standards and management mechanisms, provide strong guarantees for the high-quality construction of urban underground passages, and help create safe, convenient, and durable urban underground transportation facilities.
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