TBM BORED IN-USE cable tunnel grout repair & extension of life

Water-stop reinforcement technology for TBM bored cable tunnel

1. PROJECT BACKGROUND

A cable tunnel in use was constructed using the TBM method. After a period of use, water leakage of various amounts occurred in wells, corridors, linings, flexible joints, ring segments and inverts. The pre-designed guttering in the tunnel was sufficient to eliminate water leakage. However, there was a need to prevent the internal components and reinforced concrete structure from having service life reduced due to the humidity of the environment, and to prevent leakage becoming more serious in the future. Specialists were entrusted to carry out leakage prevention and reinforcement work to improve the environmental quality in the tunnel.

2.SOLUTION

After undertaking this project, the company immediately assigned engineers with relevant experience to conduct on-site investigation. They surveyed and mapped the location of the leakage site and the dampness condition. After compiling the data, the proposed solution was as follows:

(1) Lining and concrete cracks leakage prevention. Second-degree grouting adopted using inclined holes, and self-expanding and non-expanding rigid polyurethane resin to stop leakage and bond concrete cracks.

(2) Construction joints leakage stop. After the second-degree grouting is used to stop leakage, the old filling material to be knocked out, and then the construction joint repaired with elastic joint filler.

(3) Ring segment interfaces to prevent leakage. The blind cover sheet runs through the opening and is filled and sealed with elastic non-expanding polyurethane resin.

(4) Flexible joints and wells are to be reinforced for leakage prevention. Fill the water leakage points with elastic polyurethane resin in the inclined holes or side holes to stop the water, and pour with foaming concrete grout to fill the gap after cleaning.

(5) Invert reinforcement. Use foaming concrete grout to fill the gaps under the invert to enhance the rigidity of the pathway.

3.  WORKS DESIGN

Because the water leakage points of this project are distributed in different locations, the fracture properties are also different. There are 4 types of works methods:

(1) Second-degree filling with polyurethane resin using inclined holes. Oblique drilling is adopted at an appropriate angle; the intersection of the drill holes and crack is at about 1/2 of the wall thickness. The holes are drilled in a staggered arrangement at about 10 cm on both sides of the cracks; the center of each hole is 35 to 45 cm apart. First use self-expanding non-solvent resin to seal water seepage from bottom to top, and then use rigid non-expanding resin to bond cracks.

(2) Polyurethane resin is poured forward. Install a 2-point backstop injector on the blind cover or backfill grouting hole cover of the RC rings and steel segments, and refill the gap behind the segments with elastic non-expanding resin.

(3) Foaming concrete grouting. First knock out the old fillers, silt, detritus, etc. in the shafts, inverts, flexible joints, etc., then use drilling or direct pouring to fill in the gaps and holes.

(4) Treatment of concrete surface and expansion joints. Knock out the deteriorated concrete, expansion joint filler and infiltrated silt, etc., rinse with high pressure water and dry with compressed air, fill the gaps with elastic caulk, and repair the concrete surface with resin mortar. 

4.PROJECT PROCESS

The works sites of this project were all located in underground tunnels, and there was no need for extensive communication during the works process. Polyurethane resin second-degree leak-stop grouting is also often used in tunnel engineering, and there were no special difficulties in the implementation process. Only in the process of pouring foaming concrete into flexible joints, wells, inverts, etc., in order to ensure good adhesion between the old and new interfaces, high-pressure water and high-pressure air was used to carefully clean up the filling materials and sludge in the early stage of cleaning. In addition, when pouring the foaming concrete, the infiltrated groundwater had to be pumped out in accordance with the current situation to ensure that the water-cement ratio of the foaming concrete met the requirements.

5.  RESULTS

The works process of this project went smoothly. According to the second-degree grouting technology of polyurethane resin imported from Germany, it was used with the Tipor series of high-quality resins produced in Taiwan authorized by the original factory. The water-stopping effect was very good after the grouting. The project was submitted to the owner for acceptance. The results met the requirements of the contract for water-stop reinforcement, and showed that the grouting repair and extension of life works of the TBM bored cable tunnel were a success.