Introduction
According to the current situation of field investigation and observation, grouting and caulking were used to repair the cracks in the side wall of the tunnel portal. The cracks are sealed and bonded inside by grouting, and the grooves of 3cm wide and 2cm deep are cut out outside by grooves, and special grouting materials are used to repair the cracks, eliminate hidden dangers of safety and quality, and maintain the overall beauty and integrity.
Governance method steps
The method of micro damage — pinhole oblique drilling method of low viscosity modified epoxy resin reinforcement method; Pinhole grouting materials: HK-UW-3 and HK-WG21; Materials: quick-curing solvent-free epoxy resin chemical grouting materials;
Cleaning:
clean the surface with a wire brush, and then blow the surface clean with an air compressor, check and analyze the cracks in detail, and determine the location, spacing and depth of the drilling hole.
Drilling:
Use a drilling tool such as a high-power percussion hammer to drill holes along both sides of the crack. The hole spacing should be between 25 and 30cm and the diameter should be between 10 and 14mm. The drilling Angle should be no more than 45° and the drilling depth should be no more than 2/3 of the structural thickness.
Cleaning joints:
Use an air compressor to blow air into the grouting nozzle to clean the fine dust in the joints, and observe the cracks.
Buried nozzle:
Install the grout nozzle (also known as water stop needle) in the drilled hole, with the structure of check valve), and tighten it with a special hex wrench, so that the expansion bolt behind the needle expands, close the crack surface, and leave the observation hole and pressure relief outlet hole.
The high pressure grouting machine is used to fill the grouting hole (mouth) with epoxy resin slurry, gradually from the bottom up or from one side to the other side. When the adjacent hole or crack surface observation hole begins to produce slurry, keep the pressure for 10-30 seconds, and use the method of control grouting to observe the slurry in the joint before filling
Remove the nozzle:
After grouting is complete, make sure that the epoxy resin is completely cured and remove or knock off the exposed grouting nozzle.
Grooving:
Use a fixed width grooving machine to cut the cracks, and then use special grouting materials to repair the grooves. When its strength and color reach the same requirements of the second lined concrete surface, use a polishing machine to clean the surface and basically restore the original surface color.
Crack prevention and control
1. Improve the design accuracy and strengthen the advance geological forecasting work.
To provide detailed engineering geology and hydrogeology exploration data for the design, improve the quality of the design, at the same time, strengthen the geological forecast work in advance in the construction, to provide accurate data basis for bad areas.
2. Make good entrance of materials and strictly control the quality and technical standards of raw materials
(1) Cement: different brands, different specifications, different batches of cement can not be mixed; The construction site uses ordinary Portland cement, but tries to reduce the amount of cement per unit
(2) Gravel: according to the inner diameter of the pumping pipeline, as far as possible to choose gravel with larger particle size; Strictly control the mud content is not more than 1%, needle and flake content is not more than 15%, the size of 5-31.5mm is appropriate, the maximum is not more than 40mm.
(3) Sand: medium sand with good gradation, fineness modulus of 2.3-3.0, particle size less than 0.135mm, the proportion of content should be 15%-20%, and the mud content should be strictly controlled within 3%; In order to facilitate concrete transportation, pumping and pouring, the sand rate should be 35%-45%.
(4) Water: Drinking water is the best choice.
(5) Admixture: the construction must be carefully selected types and dosage of admixture, high efficiency water reducing agent can effectively reduce mixing water, reduce the heat of hydration, delay the heat of hydration release rate, so as to reduce temperature cracks, but too much admixture will cause swelling and cracking of concrete.
3. Strictly control the construction operation of each tunnel to improve the construction quality
(1) Strengthen the section detection of tunnel excavation, strictly control over and under excavation, and create good conditions for the later lining construction.
(2) On the premise of ensuring that the excavation section forming meets the design requirements, the initial support should be strictly controlled to prevent the spraying concrete from encroachment on the headroom of the secondary lining, resulting in the lining thickness not meeting the design requirements.
(3) Before the construction of invert and low side wall, it is necessary to clean up the foundation slag, debris and water, so as to avoid different degrees of subsidence and deformation of concrete after forming, which may affect the quality of secondary lining in the later stage.
(4) The construction time of secondary lining should be carried out when the deformation of surrounding rock and initial support is basically stable. When the surrounding rock deformation is large and the rheological properties are obvious, the secondary lining needs to be carried out in advance, and the primary support or lining structure must be strengthened.
(5) Secondary lining concrete perfusion, the whole process should be carried out by technical personnel, and it is strictly prohibited to add water to the concrete in the process of transportation and pumping.
4. Control and selection of concrete mix ratio
(1) Measure in strict accordance with the construction ingredients list, and check and calibrate the measuring device regularly; Strengthen sand and stone moisture content detection, timely adjust mixing water consumption.
(2) Improve aggregate gradation, adding fly ash or high efficiency water reducing agent to reduce cement dosage and heat of hydration.
(3) Concrete is mixed with a certain amount of admixtures with water reduction, lengthening, retarding and other functions to improve the fluidity and water retention of concrete mix, reduce the heat of hydration, and delay the occurrence time of heat peak.
(4) Control the mold temperature of concrete; In summer construction, when the temperature is higher than 30℃, the sand and stone mixer should set up a sunshade, wash the gravel with cold water to cool down; Try to arrange for concrete to be poured at night.
