Posted Jun 9, 2021, 1:55 AM
|
|
Registered User
|
|
Join Date: Dec 2015
Posts: 15,683
|
|
Not directly related but sort of.
Quote:
“The geotechnical conditions are pretty good from the Lougheed area to the north end of the bored tunnel [in Port Moody],” says Preece, explaining that this section is considered mainly glacial till. But the area between Port Moody and Coquitlam is the legacy of old debris flows, old forests and logging areas and wetlands, plus ground where artesian pressures are a concern. “The area is very challenging,” he says.
“The conditions have caused engineers to look at alternative solutions to stabilize areas that must meet seismic requirements,” says Preece.
In Coquitlam, just east of Port Moody, engineers have found highly unstable soils. “We had a situation where soil conditions were highly liquefiable,” says Preece. The solution was to use timber densification on the soil. A 10-metre wide swath measuring 700 metres in length will have 12-15-metre long timbers driven into the ground at 1.2 metre intervals. A total of over 6,000 timber piles will be used to create seismic stability for the line’s guideways. While the technique of timber densification is not new and has also been used on the South Fraser Perimeter Road, “this is probably the most timber that has been used on a transit project,” he says.
Originally, the contract called for not using timbers because of a fear they would degrade. But EGRT was able to demonstrate that by ensuring the timbers in the ground remained wet, they would not be affected. The decision to use the timbers was made in collaboration with the province after other solutions did not provide the stability that was needed.
The technical director for the Province of B.C., Raymond Louie, says the solutions being implemented on the new line will “help our knowledge here” on rapid transit construction. One such application is soil mixing, which is more common in the U.S. but is having its first application in the Lower Mainland’s new transit line. Its use again arises from the need to bring sites in the Port Moody and Coquitlam area up to the seismic standards required. The process involves an on-site batch plant for low-strength concrete. The concrete is injected into the ground in columns, with the boring machine’s head able to inject the concrete and mix it with soil beginning at the bottom. The ensuing column will not only prevent the ground from moving but also provide vertical support for the guideways.
Soil mixing, which costs less than timber piles for soil stabilization, is being used on the portion of grade-level guideway by Golden Spike Lane that runs through Port Moody by the CPR tracks. Timbers are being used on a 750-foot stretch by rail tracks book-ended by the Balmoral Drive area through to Bond Street in Coquitlam.
|
https://www.canadianconsultingengineer.c...footing-metro-vancouvers-evergreen-line/
|
Prev
Linear Mode
