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Curved Section of Reservoir Discharge Channel Lining Repair Case

Curved Section of Reservoir Discharge Channel Lining Repair Case-Special Tunnel Damaged Steel Liner Repair Method

1.  PROJECT BACKGROUND

A reservoir discharge channel suffered serious damage to the lining of a curved section after a period of use.

In order to avoid the expansion of tunnel damage during the upcoming flood period, and even affect the normal discharge function, the maintenance unit and design unit invited experts from all walks of life to discuss repair countermeasures and to propose an implementation plan.

When design work was completed, the contractor was to dispatch personnel for emergency repair as soon as possible.

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2. SOLUTION

The inner diameter of the discharge tunnel of this reservoir was about 3.9m. The steel liner was designed with backfill concrete.

The damaged area was located in the curved section. The steel liner was deformed, cracked, and fallen off. In order to repair the lining of this section while reducing the frequency of future damage, a non-solvent two-component non-expanding rigid polyurethane resin with high compression resistance, high bend strength and fast curing time to be used for pressure infusion.

In addition, the thickness of that area of steel liner to be increased, when selecting backfill materials and construction methods. It also had the functions of completely filling the gaps behind the lining and bonding and strengthening the original backfilled concrete cracks and bedrock joint surfaces that might exist.

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3. WORKS DESIGN

A. Site layout: clean up the silt, damaged lining, broken concrete and loose rock in the discharge channel, erect work platforms, stairways and various safety protection equipment. And after the preparation work is completed, move the equipment and materials to the construction location as soon as possible.

B. Drill core sampling: In order to confirm the rock formation conditions and meet the requirements of the core mechanics test, continuous sampling of 3″ diameter cores is carried out in the section where the lining damage occurred, and the sampling depth to exceed 3m behind the lining. The core tests are to be arranged in a special core box according to the sampling depth, and RQD judgment is performed immediately and the sampling is sealed and sent to the designated laboratory for related tests.

C. Embedded grouting pipe: Designed with a single-stage grouting method, drilling and burying the grouting pipe at the designed position. The depth of the grouting pipe embedded into the rock layer is not less than 2m, depending on the extent of the rock layer joints in the block.

D. Lining repair: hoist the processed steel lining to the predetermined position, and after cleaning up and cutting around the existing lining fracture surface, the steel lining is welded and fixed in place.

E. Infusion of grout: non-solvent two-component non-expanding rigid polyurethane resin is selected as the filling and infusion material for cross-hole pressure grouting. The curing time of the grout is controlled to about one minute, and the final compressive strength of the grout to be not less than 35000kPa.

F. Surface treatment and site clean up: wait for the grout to solidify and then plug the grouting holes. At the same time, the residual grout and attachments on the surface of the steel lining are cleaned and the surface of the steel lining is coated with anti-rust. After all the work is completed, remove all equipment and construction frames, and thoroughly clean up the construction site.

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4. WORKS PROCESS

The geological conditions of the reservoir were dominated by argillaceous sandstone. The rock structure was complete with only a few joints, and the geological condition was good enough to support the discharge channel structure and discharge impact.

When carrying out repair, the main tasks were the backfill grouting of the discharge channel and the replacement and repair of the steel liner surface. All works had to be completed before the flood season.

The internal space of the discharge channel was narrow and winding, a large number of construction frames and stairways need to be erected to reach the working positions when moving machinery and materials.

The preparation work is time-consuming, and the construction time was very tight. In addition, the poor working environment in the pipeline required temporary ventilation systems, lighting systems, wired communication systems and safety protection equipment to ensure the safety of construction workers, which added to the difficulty and workload of the repair work.

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5. RESULTS

As the advance survey and planning work was perfect, the operation went relatively smoothly in accordance with the procedures of the construction plan.

With the concerted efforts of all team members, the repair of the damaged lining of the discharge channel and the filling and reinforcement of the voids, concrete and rock layers behind the steel liner were successfully completed within the scheduled time.

After inspection by the maintenance unit and the design unit and the actual discharge use during the flood season, the overall function was in line with the expected results, and the “repair of the lining of the curved section of the reservoir discharge channel” had been successfully completed.

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Curved Section of Reservoir Discharge Channel Lining Repair Case

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