The 21st century is a century in which humans have vigorously developed and utilized underground space. Underground engineering waterproofing technology has become a hot issue of concern to the academic and engineering communities. Underground engineering is a hidden project, and it is long affected by changes in groundwater level or surrounded by water. Once the waterproof measures are improper or fail, it will not only be difficult to repair, affect the normal use of the project, but also cause the main structure of the project to be corroded. Seriously endanger the safety of buildings.

1 Waterproof Structure Design for Underground Works Waterproof structure design for underground works must define the basic conditions and requirements for waterproofing projects, properly select and reasonably use waterproof materials, follow the principles of multi-channel protection, rigid-flexible combination, and comprehensive prevention and control, and apply the combination of prevention and drainage. The method of “advocating sparseness” is based on the specification, combined with the actual situation, refines the joint construction method, selects new construction techniques, and pays attention to the design of the protective layer of waterproof.

The waterproof design of underground works includes the main body waterproof design and the node waterproof design. The main body of waterproof is divided into structure waterproof and additional waterproof. Self-waterproofing of the structure must be adopted. Additional waterproofing is selected according to the waterproof grade of the project. Additional waterproofing is also called "other waterproofing layer". The waterproofing of the joints mainly includes the construction of the cast-in-place, post-casting belts, deformation joints, pipelines through the wall, waterproofing of the column tops, etc. The node waterproofing is also called "detailed structural waterproofing", and different waterproofing measures may be selected according to the waterproof level of the project and the actual situation.

1.1 Waterproof design of the main body 11 Self-waterproof design of the structure The self-waterproof design is a concrete or reinforced concrete structure that has a certain degree of waterproof capacity by increasing the compactness of the concrete itself. Concretely, measures such as adjusting the mix ratio of concrete, adding concrete admixtures, limiting the maximum particle size of the aggregate, etc., make the concrete composition the most compact and the smallest porosity structure, and thus have a good waterproof performance.

In the self-water-proof design of underground engineering structures, the key is to control the generation of cracks in reinforced concrete and its width. Once cracks occur in concrete structures, seepage of water is difficult to avoid. There are two types of cracks in reinforced concrete, one is the crack caused by the load, which reduces the bearing capacity of the structure. It can be controlled according to the standard design calculation and reasonable use, so that it does not appear or limit the width of its development. The other type is cracks caused by constrained structural deformation. Such cracks, for most practical projects, currently have no accurate calculation method. Therefore, design can only take appropriate measures to prevent them according to relevant regulations and principles, such as adopting improved constraints and selecting smaller shrinkage rates. Cement and aggregates use compensated shrinkage concrete to reduce the temperature drop of concrete, increase the tensile strength of concrete, and strengthen curing.

1.1.2 Additional waterproof layer design The use of self-waterproof structures alone in underground construction is not appropriate. It is unscientific to exaggerate the role of additives (such as water reducers, early strength agents, and micro-expansion agents) on the market. Structural self-waterproof concrete is not absolutely impervious to the material. In view of the concrete's own protection and durability, it is necessary to design an additional waterproof layer. In underground projects with high waterproof and moisture-proof requirements, even if the groundwater level is not high, an additional waterproof layer should be provided on the surface of the concrete structure. Additional waterproof layer commonly used materials include waterproof mortar, waterproof coating, polymer waterproof membrane, and other waterproof materials.

1.2 Node Waterproof Design In addition to doing the main body self-waterproof design, the underground works must achieve good waterproof effect as well as handle the waterproof problem at the node. The waterproofing of the nodes mainly includes the waterproofing of the construction joints, the post-casting belts, the deformation joints, the through-wall pipelines, and the column tops.

1.2.1 Construction Joints Construction joints are joints formed by the planned interruption of construction and are mainly cast-in-place concrete. Usually, the construction joints should be left in the parts where the shear force of the components is small and the construction is convenient. In the treatment, flat seams, step joints, convex joints, and concave joints can be used. The waterproofing of construction joints is generally set to 1~2 lanes. Excessive set-ups are economically unreasonable and the actual results are rather poor (too much material will affect the compaction of the concrete). The traditional construction joints and the steel sheet waterstops, in principle, extend the water seepage route, which is equivalent to increasing the thickness of the concrete, but reducing the construction quality of the concrete. See also.

1.2.2 Post-pouring zone The post-pouring zone refers to the temporary temperature shrinkage deformation joints that remain in the cast-in-place monolithic reinforced concrete structure only during construction. After a certain period of time, it is filled and closed, and then cast into a continuous whole. structure. Since the post-pouring belt only exists during construction, it can be considered as a special construction joint. Therefore, its waterproof design is basically the same as the waterproof design of the construction joints. It is generally set with water-expanded putty strips or rubber waterstops. In addition, the post-pouring belt should adopt the micro-expansion cement as the filling material, and the strength grade of the concrete should be higher than the strength level of the original structure. It is also possible to use a disposable steel mold with a scaled hole or several layers of steel mesh, or to seal the water Disposable steel molds are used in combination.

1.2.3 Deformation Joints Deformation joints are mainly composed of expansion joints, settlement joints, gap joints, etc. They are recognized as weak links in structural waterproofing. It is difficult to deal with the difficulty of waterproof treatment. It is not only necessary to consider the settlement of structures, the telescopic displacement deformation, but also must be In the deformed condition, the watertightness is guaranteed. Of all the underground waterproof design nodes, deformation joints are the most complex and the failure rate is also the highest. Therefore, in general, there should be as little or no deformation joint as possible. In fact, the deformation joints are mainly settling joints, generally do not consider setting temperature deformation joints and seismic joints. The width of deformation joints should not be too large. If it is more than 40mm wide, it should be used with caution, and it should be avoided in multi-layer underground works. Settlement joints are located in the multi-layer section where there is peace and where the sections are complex. See also.

When deformation joints need to be set up, reasonable construction types and proper spacing and good reinforcement materials should be selected. According to previous investigations, the following conclusions have been drawn: "Seam-joint type* (asphalt-mastic caulking, rubber tube caulking, angle-filled asphalt, etc.) deformation joints with arc-shaped galvanized iron sheet-type "deformation joints" and "buried copper in the middle" The film "deformation joint waterproof effect is poor: "Inside the steel plate detachable" deformation joints and "intermediate buried rubber water stop type" deformation joint waterproof effect is very good. The same reasonable deformation joint spacing can avoid or reduce the structure does not produce more than the allowable crack width in the construction process and use, but currently there is no systematic theoretical calculation basis, the existing design is mostly based on the existing engineering practice experience, Combined with the construction conditions selected.

1.2.4 Induced joints In view of the special nature of deformation joints, induction joints are considered instead of deformation joints. Induced joints and deformation joints are identical in function, but from the analysis of waterproof construction, the concrete at the induced joints can be continuously poured, and the deformed joints must support the formwork, stop the concrete from pouring, and remove the formwork after the concrete has hardened. Continue structural concrete construction. Moreover, the setting of deformation joints is more complicated than induction joints and the construction cost is high. Therefore, the setting of induced joints can reduce the number of deformation joints and reduce the cost.

Induced joints are specifically designed to provide several weak joints along the longitudinal length of the wall. The amount of longitudinal reinforcement at the joint is a percentage of the longitudinal reinforcement content at the non-induced joint. When the structure changes due to temperature difference or concrete shrinkage, etc. The induced joint cracks first, which controls the cracks in the concrete structure. According to the actual situation of existing projects, the setting of induced joints achieves very good results. The waterproof structures are generally made of two materials, waterstops and caulking seals. Leakage principle. When the induced joint is set, the wall joints of the underground wall should be aligned as much as possible so as not to be constrained when the structure is deformed, resulting in cracking of the inner lining.

1.2.5 Through-wall pipelines in underground pipeline projects, including the water stop rings used for supporting bolts, are recommended to be used in combination with water-swelling water-stopping belts. Measures should be taken to prevent the rotation of the wall pipe, line and bolt. Large diameter pre-embedded casing should be properly opened to prevent the concrete from being empty here. The casing and pipe must be recessed at the concrete surface. The groove is sealed with a sealing material, and the sealing ring can be welded with a sealing ring. The sealing ring and the sealing ring are to be tightly welded. When concrete is poured, special care should be taken to reinforce the concrete at the bottom of the pipe; The group of pipes should be centralized and installed in the embedded steel box. After the pipes are installed, concrete shall be poured in the box. The side of the box facing the water surface shall be added as a flexible waterproof coating; it shall not be directly on the concrete. Leave the hole at the top and mix the concrete in the reserved box or reserved hole.

1.2.6 The top waterproofing pile is waterproof. It is indispensable for the top waterproofing pile. For high-rise buildings, the requirements of the structure and the top of the pile fixed on the platform can be waterproofed with polymer cement mortar. The waterproof layer of the pile top is rigid, and the flexible additional waterproof layer of the bottom plate should be connected with the sealing material at the interface of the cushion layer. The item should not be leveled with cement mortar, and the top of the pile that is connected with the steel column should be embedded with a water-expanded water stop at the periphery of the steel section.

1.3 Waterproofing the outer wall and floor The underground works also need waterproof materials applied to the outer wall and floor. The coils, paints, mortars, etc. are often used. The outer waterproof and inner waterproof are classified according to the location of the waterproof material. Outsourcing waterproofing is to put waterproof material on the water surface, that is, the outside of the wall and the bottom of the bottom, waterproof effect is good, more used, but maintenance is difficult, the defect is difficult to find; inside the package is to waterproof waterproof material back surface, that is, the external wall The advantages of the inside and the bottom of the floor are that the construction is simple and easy to maintain, but the waterproof effect is poor, and it is mostly used for repairs.

2 underground structure waterproof material According to the underground project waterproof design, the underground project waterproof material choice is also very important. Select flexible waterproof material, should pay special attention to the requirements of the material, pay attention to whether it has good durability, water resistance, corrosion resistance, penetration resistance, perforation resistance and other technical indicators, and increase the thickness of the material as appropriate and improve product quality .

In addition, among the three technical indicators of the tensile strength, low-temperature bending (flexibility), and elongation at break (break elongation) of flexible waterproof material products, the first two items should be particularly emphasized. Because the main structure of underground engineering is gradually in a stable state after completion, the non-penetrating cracks produced early on the surface of the structural concrete do not require a high elongation rate for the flexible waterproof material.

In addition, due to the relatively humid environment during the construction of underground works, the material selection should pay attention to the construction of the material under the conditions of moist base surface, that is, whether the material and the base layer can have good adhesion and the sealing of the lap joints. Sex. GB50108-2001 "Technical Specifications for Waterproofing of Underground Works" stipulates that the waterproofing layer for laying coils on the floor cushions of underground works may be paved or glued, but there must be no clear water on the base surface, and the waterproofing layer must be laid on the main wall. It is completely bonded and therefore requires a sufficient dryness of its base layer. From the current material varieties, the use of polymer modified bituminous waterproofing membranes that can be used for hot melt construction and PVC waterproofing membranes constructed by welding are more reliable, even if winter construction (-10T:above) does not Affect the quality of the waterproof layer.

3 Construction Quality Control of Underground Works Waterproofing Waterproofing projects are ultimately achieved through construction. At present, construction waterproofing construction is mostly manual. Leakage may occur if there is slight negligence. The investigation results of leakage engineering at home and abroad all prove this. a little. According to China's statistics on more than 80 surveys in previous years, it shows that the construction causes 45% of the leakage. This shows that construction is the main aspect and is the key.

Because construction is mostly done by hand, the construction methods and personnel quality of waterproof construction are very important. Only the external wall and floor waterproofing is taken as an example. When formulating the waterproofing construction process, detailed practical measures should be made in accordance with the shape characteristics of the grass-roots level and the actual conditions of the detailed structural nodes, in accordance with the requirements of relevant regulations and regulations. The actual construction on site depends on the technical level of the personnel at the construction site. To ensure the construction quality of waterproofing works, it is necessary to use high-quality construction teams, skilled workers, and strictly follow the design plan and specifications. At the same time, the on-site management personnel must be clear about the technical disclosure, and should not only focus on the progress and lightness of quality. The inspection must implement the assessment standards, and the quality education of workers must also be strengthened.

In ensuring the above aspects, we must also pay attention to the on-site construction environment. Conditions such as excessive wind and low temperatures will also affect the quality of the project. This requires that appropriate protective measures must be taken. In this way, the impact of human factors and the Reasonable waterproof solutions and qualified waterproof materials can guarantee the waterproof quality is absolutely safe.

4 Conclusion In summary, underground engineering waterproofing is a very important systematic project. It will involve design, construction, material selection and many other aspects. The design is the foundation of underground engineering waterproofing. It is the control of crack generation and crack width. key. Therefore, in accordance with the requirements of structural waterproofing and the environment in which it is constructed, the self-water-repelling ability of the underground engineering structure is enhanced, and from the viewpoint of dynamics, the durability of the material, the adaptability of the material, and the global compatibility between different waterproof materials are applicable to the selection of waterproof. Materials, in accordance with the design requirements of construction, can effectively improve the reliability and durability of waterproof underground structures.

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