With the continuous development of road and bridge construction, the disadvantages of tunnel leakage gradually appear, which will shorten the service life of roads and bring unsafe factors, so waterproof construction must be strengthened. Waterproofing, in addition to construction and technical factors, should also strengthen management. Only in this way can we ensure the construction period and create high-quality projects. This paper analyzes the causes of tunnel water leakage, puts forward the principles of combining dredging with prevention and dredging with blocking, and expounds the measures and methods for treating tunnel water leakage.
Keywords: tunnel; Seepage prevention; Technical factors; Governance measures
First, the main causes of tunnel leakage
There are many reasons for tunnel leakage, and the specific reasons are as follows:
1. Design reason
(1) For some reason, the tunnel was designed in the gully fracture zone or fault zone without waterproof and drainage treatment, and a large amount of surface water was replenished underground, which eventually led to tunnel leakage;
(2) The foundation is unstable and untreated, resulting in uneven settlement of the foundation, resulting in cracks or gaps in the repair structure, resulting in leakage;
(3) Early formwork removal time or excessive surrounding rock pressure exceeding the design load of the lining can make the internal stress of the lining exceed its failure strength, resulting in cracks and joints.
2. Construction reasons
(1) Concrete is not designed and constructed according to drainage grading. In places with high groundwater pressure, water seepage occurs because the impermeability grade is lower than the corresponding water pressure.
(2) The compacted concrete is not dense and forms a honeycomb, so there is more local leakage. In the hardening process of concrete, because of the evaporation of excess water (free water which has no effect on water sliding), a permeable and open capillary channel is formed in concrete, especially in the process of sinking, a part of the concrete mixture precipitated is ready to squeeze towards it, and a part is gathered on aggregate particles to form a permeable tube.
(3) There are sundries in the lining concrete material, which will form cracks or holes after rotting.
(4) The work of pouring concrete is not handled properly or improperly, and the combination is not strict, which causes the gap to leak.
(5) The joints between the arch wall and the back wall or between the first wall and the back arch are not filled, resulting in leakage.
(6) If the reserved holes are not treated according to waterproof requirements, leakage channels will also be formed.
3. The PH value of natural water around the lining exceeds the standard, which is corrosive to the lining concrete. The common ones are carbonation, acid salt and magnesium salt corrosion.
Second, the tunnel waterproof technology and construction measures
1. Waterproof concrete seepage control
Concrete is a heterogeneous material, which is porous from a microscopic point of view and contains many tiny pores of different sizes. These pores can be divided into construction pores (caused by poor pouring and vibrating quality) and structural pores (indexed due to improper proportion). Waterproof concrete is to restrain and reduce the formation of internal pores in concrete from two aspects of materials and construction, change the characteristics (shape and size) of pores, block leakage channels and improve the compactness of concrete itself, so as to achieve the purpose of waterproofing. It can be divided into waterproof concrete, admixture concrete and expansive cement waterproof concrete.
(1) Ordinary waterproof concrete
Ordinary waterproof concrete is a kind of concrete that can improve its compactness and impermeability by adjusting its mixture ratio. In order to prepare high-quality waterproof concrete, we must follow the following technical requirements:
A. the water-cement ratio shall not be greater than 0.6.
B the cement dosage of concrete should not be less than 300kg/m3.
C sand content is 30-40%, and the ratio of lime to sand is 1: 2- 1: 2.5.
(2) Admixture waterproof concrete
Waterproof concrete with admixture is a kind of concrete that relies on adding a small amount of organic or inorganic admixture to improve the workability, compactness and impermeability of concrete to meet the waterproof needs of engineering. According to different kinds of additives, it can be divided into water-reducing agent waterproof concrete, aerated agent waterproof concrete, triol amine waterproof concrete and iron oxide waterproof concrete.
A. waterproof concrete
Water reducing agent has a strong dispersing effect on cement, which improves the workability of concrete. Therefore, after adding water reducer, the mixing water can be greatly reduced, thereby reducing free ions and improving the pore distribution of concrete, and the total porosity of its pore expanding agent is significantly reduced, thus improving the compactness and impermeability of concrete. When in use, the content of calcium lignosulfonate and molasses accounts for 0.2% ~ 0.3% of the cement weight. When it exceeds 0.3%, concrete retarder will be used for excessive retarding.
B. Aerated waterproof concrete
C. triethanolamine waterproof concrete
D. Ferric chloride waterproof concrete
The main components of ferric chloride waterproofing agent are ferric trichloride and ferrous chloride. Adding an appropriate amount of ferric chloride waterproofing agent can greatly improve the impermeability of concrete. It is one of the best waterproof concrete, and there are several common additives.
The dosage of ferric chloride waterproofing agent is generally 3%. Excessive dosage will affect the corrosion of steel bars, drying shrinkage and setting time of concrete. If the dosage is too small, the effect is not obvious, the water cement ratio should not be greater than 0.55, and the water content of the waterproofing agent should be deducted from the mixed water. The dosage of cement is not less than 365,438+00 kg/m3, and the slump is 3 ~ 5 cm. Portland cement should be used when preparing ferric chloride waterproof concrete in winter. In order to accelerate the curing, the dosage of ferric chloride waterproofing agent can be appropriately increased, but it does not exceed 5%.
(3) Expansive cement concrete
Expansive cement concrete relies on cement itself to form a large number of crystals with large volume enhancement during hydration and hardening, and generates certain expansion energy, so as to reduce or eliminate the volume shrinkage of concrete, improve the crack resistance of concrete, and thus improve the waterproof ability of concrete, which is a new way to solve the impermeability of concrete internally.
2. All kinds of gaps are leak-proof
There are generally three kinds of cracks in concrete lining, namely construction joints, expansion joints and settlement joints. This crack is the main part of underground tunnel leakage and must be handled carefully.
Construction joint (1) is caused by intermittent pouring of lining concrete, which is one of the weak links in waterproof engineering. Generally, before pouring the second layer of concrete, the joint surface of the first layer of lining is scrubbed clean and covered with 20 ~ 25m thick cement mortar.
(2) Settlement joint, also called deformation joint, is set to prevent lining cracking caused by uneven settlement. Expansion joint is a gap set by considering the thermal expansion and cold contraction of concrete. These two kinds of cracks are also the main channels of water leakage. Waterproofing measures include asphalt waterproofing, asphalt slab waterproofing or rubber belt waterproofing. Among them, rubber waterproofing is suitable for lining engineering with strict requirements.
Step 3 drain water
For the leakage of common surrounding rock cracks, corresponding drainage measures should be taken to extract groundwater to reduce the pressure of groundwater on the lining structure, which is conducive to better waterproofing. The concrete methods are often blind ditch, drainage ditch in the hole and open caisson.
Third, the construction of waterproof concrete engineering
The quality of waterproof concrete engineering depends not only on the concrete itself and its proportion, but also on the quality of each working procedure in the construction process. Therefore, in the process of construction, we must strictly control the construction links to avoid all possible hidden dangers of leakage.
(1) The mixture ratio of materials must be carefully determined according to the design requirements.
(2) Strictly inspect and test all kinds of raw materials to ensure the quality of materials.
(3) The waterproof concrete construction shall be completed at one time as far as possible, and the length of each build by laying bricks or stones shall be lengthened as far as possible to reduce construction joints.
(4) Do a good job of foundation pit drainage to prevent groundwater and surface water from flowing into the foundation pit to cause water accumulation, which will affect the normal hardening of concrete and lead to the decrease of concrete strength and impermeability.
(5) During concrete transportation, segregation and slump loss should be prevented.
(6) Concrete must be vibrated and compacted. When mechanical vibration is used, insert plug-in vibrators, and the spacing is not more than 1.5 times the effective radius. Undervibration, vibration leakage and excessive vibration shall be avoided, and the vibrator shall not touch the formwork, water stop and embedded parts.
(7) In order to strengthen the curing of concrete, it is not advisable to dismantle the formwork prematurely to prevent cracks on the concrete surface.
Fourth, the leakage treatment construction technology
1. Check the wall, mark the leaking parts, and determine the treatment scheme according to the leaking situation.
For leaks and cracks, planing and plugging scheme is adopted; For surface leakage, according to the degree of leakage, plugging and grouting schemes are adopted respectively; For the leakage of construction joints, grouting scheme will be adopted. But it is not absolute. According to the specific situation, the causes of water leakage should be comprehensively analyzed and the most suitable treatment scheme should be adopted.
2. Leakage plugging construction technology
(1) For the leakage of cracks, a groove with a width of 20mm and a depth of 40mm should be carved along the cracks; For the leakage point, drill a hole with a diameter of 10 ~ 30 mm and a depth of 20 ~ 40 mm with the leakage point as the center, and try to keep the hole perpendicular to the base surface. In addition, the groove of the continuous wall should be deepened and widened appropriately, depending on the degree of looseness on both sides of the joint.
(2) Thoroughly clean and wash the grooves and holes;
(3) Take a proper amount of plugging material, add water and stir it into slurry, rub it into a strip or cone shape, quickly stuff the cement into the groove (hole), squeeze it hard to make it dense, and stand still for 45-60 seconds.
(4) In case of serious water leakage, grouting construction scheme shall be adopted.
3. Grouting and drainage construction technology
Grouting is mainly at the construction joint, mainly because it is at the end of the formwork when pouring concrete. Some construction joints can't be completely filled with concrete due to poor operation by workers, especially in the vault. In this way, the expansion water stop there can't stop the water. Similarly, due to the irregular installation of water stop, it is also common that the whole section of construction joint leaks. Therefore, the method of mining grouting can achieve good results.
(1) Check the leakage point.
After the surface of the base is dry, immediately spread a layer of dry cement evenly. If there are wet spots or wet lines on the surface, they are leaking holes and joints, so as to determine the leaking parts.
(2) Chiseling and drilling
First, drill a hole with a diameter of about 100mm and a depth of about 40mm around the leakage point. Then drill a 20mm hole Ⅰ from the leakage point to the concrete with a depth of 200 ~ 300 mm with an impact drill or special drilling equipment, and drill holes in the vault of the same section in the same way.
Verb (abbreviation of verb) conclusion
Through the construction practice, the above construction technology has well controlled the leakage phenomenon of the structure, and accumulated some experience for the leakage treatment of similar tunnel engineering structures. In addition to construction and technical factors, strengthening management is also a crucial factor for tunnel waterproofing. In the long run, only by strengthening management and improving the overall technical level can we guarantee the construction period, create high-quality projects, achieve good economic and social benefits and develop enterprises.
refer to
1. Technical Specification for Waterproofing of Underground Engineering (GB 50108-2001)-published by China Industry Press.
2. Compilation of Building Materials Standards-Building Waterproof Materials 2003- Published by China Standards Publishing House.
3. Highway tunnel construction. People's Communications Press, 200 1.
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