Guanfeng (Andy) An, chief engineer of Guangzhou Municipal Group, was searching for an effective solution to apply to the rehabilitation of a 200-ft stretch of an arch tunnel on a stormwater collection line in the old town section of Guangzhou. The City was formerly known as Canton, and is the capital of Guangdong Province of the People’s Republic of China.

Root intrusion and corrosion had caused severe damage to the brick-and-masonry structure, which is more than a century old.

Root intrusion and corrosion had caused severe damage to the brick-and-masonry structure, which is more than a century old.



Root intrusion and corrosion had caused severe damage to the brick-and-masonry structure, which is more than a century old. The City’s Pearl River is just a block away, creating a high groundwater table. Its hydraulic pressure had collapsed the weakened line, causing severe leaking. Heavy silt covered more than 30 percent of the pipeline’s bottom.

The City was seeking a structural rehabilitation and infiltration control solution, with a 50-year service life. Guanfeng compared four possible rehabilitation methods and chose SprayWall, a spray-applied liner from Sprayroq Inc. SprayWall was chosen for its durability, waterproofing and especially its structural characteristics, to hold up against further hydraulic pressure.

Guanfeng had first been introduced to Sprayroq protective and structural coatings at an ASCE Pipeline conference industry conference in Xiamen, China, in 2011. At the conference, Xiamen Anyue Trenchless Technology Engineering Ltd., Southeast China’s Sprayroq Certified Partner (SCP), performed an onsite Sprayroq process demo to the conference attendees. Guanfeng was impressed by the demonstration, and began spending considerable time learning about both the protective and structural properties of Spraywall’s material, the application process and the expected service life.

He believed this trenchless rehabilitation project would be an ideal opportunity to demonstrate the efficacy of Sprayroq products to the city’s utility departments.
As the project’s general contractor, Guangzhou Municipal Group contracted Xiamen Anyue. They would be responsible for inspection, cleaning and rehabilitation of the tunnel. Sprayroq and Xiamen Anyue personnel provided onsite consultation on specific technology, installation and design issues.

Comprehensive Planning and Prep


The tunnel’s irregular shape, an 800-mm (31.5-in.) square at the bottom and an 800-mm diameter rounded top, created an unusual design challenge that lent itself well to a spray-applied solution. Less than a yard in diameter, the tunnel constituted a relatively small size line to accommodate man entry, which would be necessary for the application process.

Traffic is heavily congested in this city, an important national transportation hub and trading port about 75 miles northwest of Hong Kong, with a population in excess of 13 million. Though the project was trenchless, it was still going to significantly affect the crowded downtown location, therefore work could not begin until after 8 p.m. For the same reason, all equipment — which occupied one traffic lane — was required to vacate the jobsite each day before 6 a.m.

Xiamen Anyue fielded a total 10-person crew for the two-month job. Half a month was spent in planning, cleaning and prep work took a month, and the final spray application of the SprayWall product took about 10 days.

They started the project’s physical work with the bypassing of the tunnel flow. A temporary masonry wall was built in the upstream manhole, sealing it off from any new flows. Flexible pipe was installed with a submersible pump to bypass the water to a downstream manhole.

Confined Space Inspection and Cleaning


Next came line inspection and cleaning by a five-member crew, including a supervisor. A city representative was also on hand to view this new rehabilitation process.

The line was inspected using the QuickView manhole and pipeline survey system. This system allows a single-operator survey from street level, saving the expense of a CCTV van and crew, and making it ideal for entering the smaller line. The process took about three hours.

Once the inspection had ascertained the exact nature of the work that would be required, the process of cleaning out the line began. Larger cleaning equipment wouldn’t fit in the line, so hand methods were used. Alternating power washing and mechanical brushing were employed to loosen the worst areas, and 51.8 tons of silt were shoveled out by hand and transferred to a landfill. The whole cleaning process took about 10 days.

This cleaning revealed some deteriorated areas in the vault, where tree roots had pushed aside the masonry sidewall. This collapsed section was removed using hand pick and impact drill, and the waste was removed by wheelbarrow.
Once the inspection had ascertained the exact nature of the work that would be required, the process of cleaning out the line began. Larger cleaning equipment wouldn’t fit in the line, so hand methods were used. Alternating power washing and mechanical brushing were employed to loosen the worst areas, and 51.8 tons of silt were shoveled out by hand and transferred to a landfill. The whole cleaning process took about 10 days.

Repair and Finally, Lining


The sidewall was rebuilt by hand using traditional masonry techniques with brick, stone and mortar. This patch was reinforced with a 4-mm, arched stainless steel plate that measured a bit more than 8 sq ft, attached with expansion bolts. This process took about five days.

The entire surface was then repaired with micro-grouting where needed, then troweled-on concrete to form an even substrate for the spray liner. The entire surface, with special attention paid to the pipe bottom, was then thoroughly dried using hot air blowers.

After the surface was deemed adequately dry, application of the Spraywall structural coating commenced. The engineer specified 6 mm to achieve the rigid, waterproof structural thickness that would also help maintain strength against repeat hydraulic load failure. Actual spray application time was one week.

Following cure time, the building inspector performed testing of peel strength, which was determined to meet local building code #50728. The bypassed line was returned to service after the application’s final inspection, 24 hours later. Spraywall cure time is immediate, and in most applications, the asset can be immediately returned to service. However, in this case, it was decided to wait a day before final installation inspection to be sure the high groundwater table was adequately dealt with.

The tunnel’s irregular shape, an 800-mm (31.5-in.) square at the bottom and an 800-mm diameter rounded top, created an unusual design challenge that lent itself well to a spray-applied solution.

The tunnel’s irregular shape, an 800-mm (31.5-in.) square at the bottom and an 800-mm diameter rounded top, created an unusual design challenge that lent itself well to a spray-applied solution.


Expectations Exceeded


It was, and city officials marveled at the unique working properties, quick setup time and smooth cure surface of the Spraywall product, according to Guanfeng. He expects this project will lead to many others for Sprayroq’s protective lining products, including applications in basements, potable and wastewater lines, other stormwater tunnels, subway and road tunnels.

“We’re even looking at it (Sprayroq products) to rehabilitate bridge bases and beams,” he says. This follows a trend for Sprayroq, whose liners are increasingly being employed in DOT infrastructure rehabilitation projects stateside.

“We’re hoping that reactive thinking will expand to foresight,” says Sprayroq business development director Chip Johnson. “It’s great that our products work so well in rehab applications, but just think how much money could be saved if they were applied to new asset installations, preventing structural deterioration in the first place.”
John Dickson is a marketing representative with Sprayroq.