According to Article 21 of the regulations on Preparation of engineering construction standards, the common requirements of the standards shall be the basic principles related to the whole standard or the basic requirements related to most chapters and sections. When there are many common requirements, the chapter can be formed independently, and the name of the chapter should be "basic provisions". In the chapter of basic provisions of the general code for waterproofing of building and municipal engineering, the basic principles to be followed for waterproofing of building and municipal engineering are specified, including the design working life of Engineering waterproofing, engineering waterproofing category, engineering waterproofing service environment category, engineering waterproofing grade and basic requirements for engineering waterproofing materials.

China has a vast territory, with great differences in rainfall, regional water level, geological conditions and climate temperature difference between the East, West, North and south; From the perspective of the purpose of waterproofing, the project waterproofing includes two major purposes: one is to prevent rain, snow, groundwater and domestic water from spreading to people's production and living space, which is the basic function of the project waterproofing to meet people's production and living requirements; The second is to prevent rain, snow, groundwater and domestic water from invading the engineering structure to damage the main body of the structure and shorten the safe service life of the structure, which is the protective effect on the engineering structure; Engineering waterproofing involves materials, survey and design, construction, quality acceptance, operation and maintenance and other links. Therefore, article 2.0.1 of the general specification stipulates that the waterproofing of the project shall follow the principle of "adjusting measures to local conditions, focusing on prevention, combining prevention and drainage, and comprehensive treatment".

1. Suit measures to local conditions

China has a vast territory. There is a great difference in rainfall, basic wind pressure, groundwater level, engineering geological conditions and climate temperature difference between the southeast and northwest. The southeast coast is rainy, with long rainy season, humid, typhoon and high temperature; The inland areas are dry, with concentrated rainfall, dry and cold, and the same fortification cannot be made under different conditions; The extreme temperature in the severe cold areas of northwest and Northeast China is low. In winter, snow is accumulated and water is accumulated to form ice, which is easy to produce frost heave, with distinctive regional characteristics. For example, Zhejiang Province has a subtropical monsoon climate, with abundant annual rainfall of 1500mm. There is plum rain between June and July, and it is also affected by typhoons every year. These climatic conditions are more likely to cause water leakage of building roofs and exterior walls. The high groundwater level in most parts of the province makes the underground works immersed in groundwater all year round, and there are special requirements for waterproofing and material selection of underground works. Therefore, the difference of waterproofing conditions in different regions determines that waterproofing must be adapted to local conditions.

There are great differences in economic development among different regions in China, and different regions have different requirements for the basic requirements of Engineering waterproofing and the working life of waterproofing design; There are certain differences in construction process habits, production and product supply of waterproof materials, construction technical force, etc. Therefore, measures should be taken according to local conditions in many aspects, such as engineering waterproof design, fortification requirements, structural practices, selection of waterproof materials, etc.

2. Focus on prevention and combine prevention and drainage

Waterproof refers to the use of dense materials to block the holes and joints of the waterproof body to prevent the passage of water; Drainage refers to the removal of incoming water in the shortest time and process, which is one of the most economical and effective methods for waterproofing. The waterproofing of the project shall be based on the specific conditions of different parts of the project, and the principle of "prevention first and combination of prevention and drainage" shall be adopted.

(1) Focus on Prevention

For underground works such as flat roof, building interior, basement and subway tunnel, reliable waterproof fortification shall be provided first, and no leakage is allowed. Methods such as the combination of waterproof main body's own compactness (self waterproofing) and external waterproof layer, the combination of structural self waterproofing, structural waterproofing and material waterproofing, the combination of rigid waterproofing and flexible waterproofing, multi-channel fortification and composite use of multiple materials are often adopted.

Due to the difficulty of waterproofing in underground projects such as building basements and subway tunnels, considering the reliability of waterproofing, backup drainage systems are often set in underground projects to prevent the inconvenience of production and life caused by waterproofing failure. This will also be taken by some engineering and technical personnel as the reason why it is difficult to "focus on prevention" in underground engineering. From the strategic perspective of sustainable development, in order to reduce the adverse impact on the ecological environment and resource consumption caused by being forced to set up a permanent drainage system due to the failure of waterproofing works, the principle of "prevention first" should be emphasized in the waterproofing works of underground works in areas where groundwater resources are scarce or in cities.

(2) Anti drainage combination

Waterproofing and drainage are two aspects of the same problem. Drainage is the other side of waterproofing, which is the most economical waterproofing method. While considering waterproofing, drainage should be considered. The water should be drained smoothly and quickly first, without ponding, so as to reduce the pressure on the waterproof layer. Therefore, any waterproof design should fully consider the possibility of draining water, which is the most effective waterproof.

The waterproofing of flat roof is mainly based on prevention, supplemented by drainage. First of all, there must be reliable waterproofing and no leakage. However, it is an effective way to reduce leakage to drain the roof rainwater quickly within a certain period of time, which requires a certain drainage slope on the roof. According to the technical code for roof engineering GB 50345, the flat roof slope shall not be less than 2%, which is to reduce the thickness of material slope making and reduce the load and cost. In engineering practice, it is difficult to accurately grasp the 2% slope during construction, and it often causes ponding or poor drainage within the allowable error range of construction. Therefore, the specification proposes that when the building allows, that is, when there is ceiling in the top floor or indoor slope is allowed, structural slope making shall be first adopted, and the slope shall not be less than 3%. Gutters and eaves gutters are the places where rainwater flows through intensively, and water often accumulates due to poor drainage. Therefore, the specification stipulates that the longitudinal gradient of gutters and eaves gutters shall not be less than 1%, and the transverse gradient shall also be corresponding; The water drop at the bottom of the ditch shall not exceed 200mm, which stipulates that the drainage line shall not be too long, and the maximum length shall not exceed 20m. If the drainage line is long, there will be fewer downspouts, the longitudinal slope will be less, and the drainage will not be smooth. Therefore, these requirements must be carefully considered in the design to make the drainage as smooth as possible. It is easy to accumulate water around the water outlet. Therefore, it is required to increase the slope within 500mm around the water outlet. It is required that the drainage slope should not be less than 5% to make this place a pit for drainage.

If the underground works have natural drainage conditions, the possibility of drainage should be considered. The terrain elevation difference can be used to lead the water into the drainage pipe network, and the filter layer, drainage ditch and blind ditch can be set to drain the water as much as possible, so as to relieve the pressure of groundwater and reduce the difficulty of waterproofing. There should also be a reasonable drainage slope and direction in the room, so that the water can be discharged quickly. On the other hand, good drainage is also the guarantee to improve the waterproof capacity and reduce leakage.

(3) Comprehensive management

A perfect waterproofing project requires reasonable waterproofing design, high-quality waterproofing materials, careful construction organization, in place project management, and perfect maintenance during use. It is a systematic project, and each link is a comprehensive project. Waterproofing design includes the determination of the importance of waterproofing of the project, investigation of the use environment of waterproofing of the project, application of standards, specifications, Atlas, review of design scheme, structure and node design, joint review of design drawings and other aspects; Waterproof materials include the consistency between the variety, specification, performance requirements and design of materials, the adaptability between material performance and engineering use environment, and the matching between the durability of materials and the working life of engineering waterproof design; Waterproofing construction involves confirmation of construction environmental conditions, base conditions and technical conditions, acceptance of materials, selection of construction process, determination of construction sequence, professionalism of waterproofing construction team, technical level of operators, quality inspection of waterproofing works and other factors. Therefore, the project waterproofing should be guided by policy, based on materials, based on design, based on construction, and guaranteed by strengthening management and maintenance, so as to comprehensively improve the quality of waterproofing projects.

Author Zhang Wenhua

Professor, School of civil engineering, Zhejiang University of Technology