July 17, 2017

CT Construction Digest Monday July 17, 2017

Soil wall is just the latest modern marvel on Interstate 84

WATERBURY – A subcontractor building a soil nail wall along a massive earth cut on the Interstate 84 reconstruction project was so proud of its work, it hung a banner near the top of the concrete face advertising its company name.
National Shoring of Stonington is completing work on a 900-foot long soil nail wall between Harpers Ferry Road and Scott Road, and beneath Calvary Cemetery. The height varies, but its peak is 55 feet tall. It contains roughly 1,500 soil nails.
“I’m not saying it’s the largest soil nail wall in the state, but it’s got to be among the largest,” said Christopher Zukowski, project engineer for the Department of Transportation, which is overseeing the project.
The soil nail wall is a temporary earth-retaining system used while a permanent retaining wall is built. The soil nail wall gets its strength from large nails, or pins, that workers drive as deep as 60 feet into the soil.
Workers pump grout into the hollow nail to fill the void around the nail, while adhering it to the surrounding earth, Zukowski said. Mesh reinforced shotcrete is applied to the exposed face and steel plates are placed over the nails while large nuts secure them in place, he explained.
Inspectors check the GPS coordinates of the nails regularly to ensure the wall hasn’t moved. So far, it hasn’t.
In several locations, the soil nail wall was built around boulders embedded in the soil. For one rock, workers had to drill nails 15 feet before reaching soil on the other side. From there, the nail extends another 45 feet into the earth.
Although the soil nail wall is strong enough to hold back thousands of tons of earth under Calvary Cemetery, it’s not a permanent fixture.
As National Shoring finishes the soil nail wall, the state DOT’s primary contractor, I-84 Constructors, is erecting a permanent retaining wall designed by DoubleWal of Plainville.
The wall consists of pre-cast concrete modular blocks as large as 24 feet deep, weighing 27,000 pounds each. The largest blocks are on the bottom because they support the most weight. The blocks get smaller as they reach the top. The blocks are interlocked, held together like jigsaw puzzle pieces.
“There’s a key in each of the units that interlocks,” Zukowski said.
MORE THAN 650 BLOCKS WILL BE USED. They have a decorative face with a rectangular cut-stone form liner finish, designed to look like stone blocks rather than concrete.
When the retaining wall is finished, the soil nail wall will be de-tensioned. Compacted free draining gravel will be placed between the soil nail wall and retaining wall, which is designed to support the weight of the soil. CLICK TITLE TO CONTINUE