Preserving History, 150-year-old Brick Storm Drains Rehabilitated with Trenchless Technologies
In Victorian London, civil engineering practices that are nowadays considered standard in terms of maintaining basic health and sanitation, had yet to be developed.
Without toilets and a network of sewage tunnels to carry away human and animal wastes, putrid water gathered in foul-smelling cesspools or gutters, before eventually flowing into the River Thames. Receiving over 400,000 tonnes of sewage every day, the river was soon contaminated, and London became a breeding ground for diseases, including cholera, which killed over 10,000 residents in 1853.
Only when the problem degenerated into the “Great Stink” of 1858, did something get done about it. The Parliament brought in its top engineer, Joseph Bazalgette, and tasked him with building London’s first underground sewage system. At a cost of GBP 4.2 million, an enormous sum at the time, Bazalgette and his team built 82 miles of intercepting sewers running parallel to the Thames and 1,100 miles of street sewers.
According to the BBC, the project was a triumph of Victorian engineering. It used 318 million bricks and dug up 2.8 million cubic metres of earth, a job made harder by the fact that the system was built at the same time as underground and above-ground railway lines were being constructed. Upon completion, the sewers served a population of 4 million.
Today, Bazalgette’s handiwork can still be seen all over London, where many of the city’s brick sewage tunnels have been maintained. Some of the Victorian pumping stations can even be described as grandiose, such as Abbey Mills and Crossness, whose ornate ironwork interior was influenced by Moorish imagery.
In Victoria, British Columbia, the same masonry techniques that were used to build sewage tunnels in London and other major metropolitan areas, were employed when the nascent British colonial settlement on the southern tip of Vancouver Island was being constructed.
The nearly 10 kilometres of brick storm drains were originally combined sewers – designed to carry both wastewater and stormwater – but have since been separated out to handle only stormwater. While the storm drains have held up reasonably well after an incredible 150 years of use, they have not been regularly maintained.
Parts of the system have been slowly crumbling, with several sections showing the effects of traffic, construction projects and weathering. In 2012, the City of Victoria contracted AECOM to assess the condition of the storm drains and to map out a plan to rehabilitate them. There was a particular desire on the part of the City to look for rehabilitation approaches that would result in a minimum level of disruption to many well-established and historic neighbourhoods.
Some inspection work using conventional CCTV technology had been done from 2006 to 2008, but the 2012 program went into more detail, using multiple sensors, to determine problem areas and when the damage might have occurred. From the condition assessment, AECOM prioritized the areas most in need of rehabilitation.
Rehab methods selected
Trenchless rehab work began in 2012 and is in the third year of a 15-year, $30 million rehabilitation program involving cured in place pipe (CIPP), CIPP with reinforced felts, and segmental glass-reinforced plastic (GRP) technologies.
Segmental GRP, a niche form of trenchless pipe rehab, is necessary due to the large number of egg- and arch-shaped cross sections, which range in height from 914 to 2,100-mm, to between 2,100 and 2,855-mm wide. The concrete and brick structures were built in layers, some sections up to six layers deep.
According to Mike Brady, project manager with the City of Victoria Brick Storm Drain Condition Assessment and Rehabilitation Program, about a third of the inventory looks “pristine or near pristine,” with the rest in various states of decay. Construction overtop or near existing sewer drains was a primary factor in breaking down the original brickwork.
“The thing about brick sewers is they’re sensitive to parties working around the pipes,” Brady explained. “Over time the mortar that was put in the bricks can break down and the rings can lose compression, the soil structure starts to alter around them and they can fall down. Some of them show evidence of structural instability and some show evidence of very good structural stability despite their age.”
Pipe relining projects are gratifying to civil engineers because they prolong the lives of pipes that would otherwise need to be dug up and replaced. With the Victoria brick drain rehab, the project has the added benefit of preserving a piece of history that would otherwise be lost.
Chris Macey, an expert in condition assessment and rehabilitation of linear infrastructure who works out of AECOM’s Winnipeg office, said trenchless technologies were chosen for the project for their low impact. He estimated the cost of re-lining to be around $1 million to $3 million each year for the duration of the 15-year program. In comparison, replacing the inventory through traditional open-cut construction would cost up to $90 million. “That’s a lot of money,” he said, “and it would be hellishly disruptive.”
One of the biggest challenges for AECOM in rehabilitating the century and a half-old brick storm drains was dealing with the unconventional shapes of the structures. While CIPP is effective for regular circular pipes, the technique can run into trouble when working around Victorian-era brick sewers, which tend to be shaped like upside-down eggs (wide at the top and narrow at the bottom to maximize flow), and arches which are efficient at distributing loads.
To deal with the vast majority of the “eggs” and “arches”, the installation companies have been very successful in using CIPP, a relatively recent technology that has only been used in North American since the 1980s. However, to deal with some of the larger sections the best solution was to use segmental glass reinforced plastic liners.
“You have the ability to get very desirable strength-to-weight ratios, very lightweight pieces with good structural characteristics, and we make them in segments so that you can site-specifically manufacture them to any cross section,” Macey explained. “GRP technology has been very successful.”
Another issue for the CIPP and GRP installers is accessing the storm drains, which do not necessarily follow the current road system. Some segments are running under houses and one section goes under the historic Ross Bay Cemetery, which has been functioning since 1872. Through trenchless technology, however, the access issues can be overcome.
“The cemetery has a very challenging section to go through. That’s on the 15-year list and that is likely going to be a pure GRP job, but it’s certainly accessible,” says Macey.
The vast majority of the job will be done without resorting to open-cut construction, with the exception of a few areas where services are found to be crisscrossing the top of the brick drains and have to be excavated and rerouted.
“Occasionally we have to add a new manhole to get a launching section, but the areas under the houses should be pretty easy to do by CIPP,” Macey said.
The brick drain inventory traverses a wide range of native soils ranging from cohesionless soils with a high water table to cohesive soils and rock cuts.
Macey said the soil structure’s ability to handle frequent rain events is a strong correlator of which sections tend to deteriorate fastest.
“A 150-year-old brick sewer is not watertight anymore,” he said. “The biggest risk to the pipe is that when it rains and water runs inside the pipes and goes through the cracks in the pipe, those soils don’t exhibit cohesion. They’re more easily eroded, and they compromise the overall pipe soil structure integrity.”
Pipe relining projects are gratifiying to civil engineers because they prolong the lives of pipes that would otherwise need to be dug up and replaced. With the Victoria brick drain rehab, the project has the added benefit of preserving a piece of history that would otherwise be lost.
According to Macey, while the aesthetic quality of the brick drains will no longer be there for people with the opportunity to probe the city’s subterranean reaches, knowing they will be preserved provides a certain satisfaction.
“I’m in awe of brick masonry structures from that vintage, the ones that are intact are a marvel of art. They’re really beautiful,” he said. “We will have compromised their aesthetics from that perspective, but I would argue that we’re preserving them, it’s like we're putting a little seal on them so they don’t go anywhere soon.”
Brady agrees. “I think it’s strategic and very fulfilling because this is in fact what we and the City of Victoria’s program are all about, going in there and preserving infrastructure with the minimum environmental footprint.”
Conventional cured-in-place pipe, a trenchless rehabilitation method, works for almost all of Victoria’s brick egg-shaped sewers and many of its arched ones. The use of more advanced composite materials will be required for a number of the larger pipe structures.