Seepage prevention supervision of subway station structure?

What exactly does the supervision of subway station structure leakage include? Here, Zhongda Consulting will introduce relevant contents for your reference.

with the rapid development of rail transit construction in Shanghai, Shanghai will build 1 rail transit lines in the next five years, with a total length of more than 2 kilometers, and most of them are underground lines, crisscrossing which has become one of its characteristics. Therefore, the construction depth of subway stations is deepening, and the leakage prevention of subway station projects is becoming more and more difficult, and it is more and more important to do a good job in leakage prevention of the main structure of stations. Taking a subway station structure as an example, the author analyzes the quality control content of supervision in the anti-leakage construction of subway station structure engineering.

1. General situation of the project

A subway station runs east-west, with a total length of 373m, a width of 11m-26.5m and a depth of 16.5m.. The main structure is an overlapping underground two-story structure with the inner lining wall and the retaining structure (underground continuous wall). There are 11 induced joints and 2 construction joints in the main structure of the station. Steel pipes are used to support the foundation pit excavation. There are 58 deep well dewatering holes in the foundation pit, and there are two entrances and exits on the north and south sides, and settlement joints and induced joints are arranged at the joints between the channels and the main structure. The entrance and exit enclosure structure adopts SMW construction method. This project is mainly based on the self-waterproofing of the structure, and the auxiliary is the additional waterproof layer of the roof of the structure.

2. Supervision practice

First of all, implement the control beforehand. The supervision engineer should be familiar with the construction drawings carefully, organize the design disclosure, and make clear the design intention; Carefully review the construction organization plan, prepare supervision rules according to the approved construction plan, and organize internal supervision meetings, so that each supervisor is familiar with the key contents of supervision and inspection of each working procedure. The second is the inspection and approval of good materials. It is strictly forbidden to use materials that have not been submitted for witness sampling and the results of the second interview are unqualified. Third, strictly examine the qualification certificates of special types of work to ensure that the construction personnel are trained and qualified professional construction personnel. Fourth, strengthen the monitoring, especially the on-site supervision of key parts and key processes. Fifth, strictly control the quality of working procedures, and refuse to sign off the working procedures that have not been accepted by supervisors or are unqualified, and it is strictly forbidden to enter the next working procedure. For the quality defects found in the construction process, timely issue a supervision notice, urge the construction unit to rectify, and check the rectification results.

3. Monitoring of leakage prevention of subway station structure

In view of the leakage prevention of subway station structure, we think it is necessary to control it from the following aspects-

3.1 Design

3.1.1 The implementation of mandatory specifications should be checked in the design stage. In architectural design, we should check whether the waterproof grade, waterproof measures and the distance of induced joints meet the requirements of waterproof specifications; Whether the requirements of waterproofing and impermeability are fully considered in the selection of building materials.

3.1.2 structural design should pay attention to sudden changes in the structure, and check whether its stiffness meets the requirements of anti-cracking. Try to avoid structural abrupt changes in design.

3.2 waterproof structure

3.2.1 waterproof main envelope The quality of the main envelope (underground continuous wall) directly affects the self-waterproof effect of the lining structure. The seam of each diaphragm wall is its weak link. In order to ensure the quality of the seam, it is necessary to check the cleaning work of the adjacent groove wall, and there is no caking mud on the wall brush after repeated cleaning. When pouring concrete, the specific gravity of mud in the tank should be controlled within the allowable range of design and specification, and at the same time, the concrete must have good workability; Continuous and compact concrete pouring is required to avoid mud inclusion due to long pouring interval.

3.2.2 Self-waterproofing of main structure

(1) Formwork installation directly affects the quality of concrete. For example, the formwork for transverse induced joints is divided into several blocks with a large number of holes after the installation of buried water stop and reserved steel bars, and the uneven surface of underground continuous wall will cause leakage if it is not handled properly. The installation of formwork at the end of construction joint is the key part of waterproofing. Targeted preventive measures must be taken before construction, and check whether the water stop is damaged when the side formwork is fixed during construction. In a word, the template should be installed tightly, supported firmly, and operated in strict accordance with the determined construction scheme and relevant construction procedures.

(2) Before the construction of the lining wall, the construction party should be required to comprehensively deal with the leakage point of the retaining wall: chisel away the muddy surface of the wall, especially remove the soil embedded in the reinforcement cage of the underground continuous wall. After cleaning, the shallow parts shall be painted with waterproof mortar; For the embedded parts, waterproof fine stone concrete should be used to fill the concave surface; At the same time, the waterproof coating on the wall of the embedded connector should be urged to have a good anti-leakage effect.

(3) In addition to the appropriate amount of ground fly ash, the waterproof concrete needs to be added with the compound waterproof agent of Temes (TMS) with shrinkage compensation function. During the construction, water consumption should be limited, slump should be controlled, plastic film should be used to cover the concrete after setting, and the roof of the structure should be immersed in water to ensure the self-waterproofing effect of the structure.

(4) For some special parts, such as the large openings left in the roof and middle plate during construction, steel fiber reinforced concrete is used to prevent the cracking of the roof concrete at the large openings. According to the requirements of using different concrete in different parts, the supervisor should organize to review the special construction scheme and strictly control the pouring sequence to ensure that the steel fiber reinforced concrete around the roof hole can be well combined with other concrete and prevent cracks in the roof concrete.

3.2.3 Waterproofing of induced joints

(1) Externally attached waterstops and embedded waterstops are mainly used for waterproofing of induced joints. Once the outer base surface is uneven, the waterproof function of externally attached waterstops will be greatly weakened. Therefore, in strict accordance with the requirements of design and construction specifications, polymer waterproof mortar should be used to level the base surface, and the internal corners should be chamfered into circular arcs, so that the external-attached water-stop is close to the uneven base surface outside the base surface, which will greatly weaken the waterproof function of the external-attached water-stop Therefore, in strict accordance with the requirements of design and construction specifications, polymer waterproof mortar should be used to level the base surface, and the internal corners should be chamfered into circular arcs, so that the externally attached water stop can cling to the base surface. For the embedded steel edge water stop in the induced joint of each floor and wall body, direct contact between the water stop and the fixed steel < P > reinforcement after the setting reinforcement is installed should be avoided, and measures should be taken to make the concrete under the water stop vibrate and compact. At the closed joint of the embedded steel edge water stop, the manufacturer should send technicians to use special adhesive to deal with it.

(2) In the shallow groove facing the water surface of the roof induction joint, the design depth and width of the groove must be ensured, and polyurethane or polysulfide sealing paste should be used for caulking, with the emphasis on checking the quality of the lap joint between the lap joint and the externally attached water stop protruding from the roof, so as to form an independent and closed external waterproof system at the induction joint.

(3) A through drainage trough is set under the induced joint of the roof to guide the water into the drainage ditch of the station floor. Check whether the reserved holes in the lower beam and column of the slab are in place.

(4) Check whether there is a groove in the induced joint on the inside of the drainage ditch of the hall floor, and fill it with polyurethane waterproof sealant after the settlement of the structure tends to be stable. The key is to control the base surface to be dry and clean, so that the sealing paste can be firmly combined with the concrete contact surface to prevent the accumulated water in the drainage ditch from seeping out of the ground through the induced joint.

3.2.4 Waterproofing of construction joints

(1) Galvanized water-stop steel plates are used for horizontal and longitudinal construction joints, which will be the weak link of water seepage prevention if not handled properly. Therefore, it is required to ensure the tightness when welding the water stop steel plate; The concrete surface should be controlled at half the height of the water stop; Before binding the vertical steel bar, the surface must be roughened, and the sundries at the lower part of the wall should be cleaned before sealing the side formwork. Before pouring concrete, water it and wet it, and lay a layer of cement mortar on the interface surface.

(2) Two lines of defense are used for waterproofing of transverse construction joints, namely, buried water-stop strip and water-stop strip with water-swellable rubber putty. The former has the same treatment requirements as the induced joint, while the latter should pay attention to the smooth base surface pasted as much as possible, and must ensure continuous arrangement, and its lap length should not be less than 5 mm. It is not advisable to paste it too early, and it should be carried out in the dry state of the base surface.

3.2.5 Waterproofing of settlement joint

This joint is located at the entrance and exit connected with the main structure, and external water stop, grouting type embedded water stop and built-in detachable water stop device are used in the project. The requirements of externally attached waterstop are the same as those of induced joint treatment, and the grouting treatment should be carried out after the settlement of the structure reaches stability. When installing the embedded parts with built-in detachable water stop device, check the tightness of welding between the nut and the iron plate of the embedded parts, whether the rust prevention treatment is in place, and whether the drainage pipe in the built-in detachable water stop tank is reserved. Before the water stop is installed, the surface must be cleaned of scum, and the surface must be smooth. Tighten the pressure plate screw to make the water stop stick to the surface.

3.2.6 Waterproofing of entrance and exit envelope and main envelope

The joint between main envelope (underground continuous wall) and entrance envelope (SMW method) is the weakest waterproof link, which can generally be treated by grouting or high-pressure jet grouting pile. When the depth of the foundation pit is shallow, if it is sandy soil, grouting treatment can be taken; When it is deep, it should be treated by high-pressure jet grouting pile, which has good water-stopping effect. In case of water leakage, in order to prevent the scope of water leakage from expanding, the plugging treatment must be carried out in time according to the construction plan.

3.2.7 Waterproofing of other links

(1) The Rachel bar of the formwork for fixing the wall body is a water-permeable part. Before installation, workers with good technical level should be selected to weld the water stop in the middle of the screw, and the supervisor should check the weld by sampling. The width of the water stop is not less than 3 times the diameter of the screw. The tie rod should be vertical to the wall as far as possible, and not in contact with the steel mesh of the lining structure.

(2) The reserved steel supports are waterproof. Because some steel supports can't be removed before pouring concrete for the lining wall, there are usually two kinds of round steel tube supports and H-beam supports, and this part is also the weak point of waterproof. In view of the characteristics of more reinforcing steel bars at the support end and long support installation time, two water-stop rings should be set within the support end before support installation. Before binding reinforcement, the supporting surface must be cleaned, and the reinforcement should be prevented from contacting the external wall. A circular hole is pre-drilled on the web of H-beam, so that the concrete under the H-beam can discharge gas smoothly during vibration. After the support is removed, there is still secondary pouring of concrete in the round pipe, so it is necessary to ensure that the pipe surface is clean and fill the hole with micro-expansive concrete.

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