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Waterproofing Solution for Sichuan Tunnels

Southeast Asia Construction – September 2009

In 2006, a superhighway project in Sichuan province, China, became a major focus for the government. Spanning more than 180 km, the new expressway was developed to run along the Yangtze River from Sichuan’s capital city Chengdu to Leshan.

Construction of the superhighway involved building five pairs of tunnels in a mountainous region of the province. While the tunnels were completed in early 2007, the soil and rock conditions paired with heavy seasonal rainfall quickly contributed to cracking and water leakage within the structures. Only a few months after completion, the tunnels needed to be repaired. With approximately 125,000 sq m of surface area throughout the tunnels, the waterproofing repair work was a significant undertaking.

Kryton was selected by the China Highway Authority to perform this task. The company supplied its Krystol concrete waterproofing system, which can transform concrete into a permanent, water-resistant barrier. Using integral crystalline waterproofing technology, Kryton’s system keeps concrete structures dry by becoming a part of the concrete matrix. When combined with water and concrete, proprietary chemicals react with unhydrated cement particles to form millions of needle-like crystals. Over time the crystals grow, filling naturally occurring pores and voids in concrete and providing permanent waterproof protection.

In mid 2007, approximately 250 t of Kryton’s products were manufactured in Canada and shipped to China. Once they arrived in port, they were transported inland by truck, then transferred onto smaller flatbed trucks to be delivered to the jobsite in the Sichuan mountains.

The remote work location not only called for extensive planning, but also required contractors who could live on-site for a long period of time. Kryton’s local distributor in Chengdu, Chengdu Kaidan Underground Works Ltd, put together a team of workers that would live in the area for at least 12 weeks. Due to the scope of the project, all workers had to complete a preliminary training in Chengdu as well as a comprehensive on-site, hands-on training with Kryton staff to ensure that they would be prepared to handle any challenges that could arise.

Because the leaking tunnels had already been built out of cast-in-place concrete, Kryton’s team recommended using its Krystol T1 and T2 surface applied crystalline slurry coat system. Krystol T1/T2 is a two-step, brush-applied system that prevents water intrusion, repairs cracking and maintains existing concrete structures. T1 seals the concrete against permeating water and T2 protects the surface of the structure from moisture. Once applied, the chemicals are absorbed into the concrete creating a water barrier. It takes 28 days for most of the active crystalline chemicals to migrate into the concrete. After that time, the surface-applied slurry can be completely removed from the surface with no impact on its waterproofing abilities.

Before using the product, the tunnels’ surfaces needed to be carefully prepared to ensure that the waterproofing system would be effective. A high-pressure washer was used to remove dust and other loose particles from the wall surface, and additional water was applied to make sure the surface was adequately saturated. Kryton’s crack repair system was also used to mend static structural cracks.

Due to the size of the project, 6 m high scaffolding was assembled to assist in the product application. When all preparations had been completed, the project team began applying Kryton’s T1/T2 slurry coating. All 250 t of T1/T2 were used to waterproof the 125,000 sq m of tunnel walls. About 2 t of Kryton’s crack repair system material werealso used to mend the 1,200 lineal metres of cracked and leaking concrete.

The entire waterproofing project took about 18 weeks to complete. Keeping the application process and workers on-site forthe duration of the project helped to meet the tight deadline.

The China Highway Authority signed off on the completion of the tunnels in late 2007.