Developers eyeing scheduling delays and a morass of mud where they need stabilizing fill have been finding a solution to getting their projects back on track with the help of Kerr Contractors. Turns out the answer is right at their feet or stuck to their boots. Treating soil with a specified dose of powdered cement can be much more efficient that excavating and removing soil and then trucking in rock fill.
Helping to Reduce Delays
Brent Kerr, President of the Woodburn, Oregon - based company, described one such situation, at a site west of Portland International Airport (PDX). The developer is building a large distribution center, with two buildings, each covering over 400,000 square feet.
"The client wanted to start the project last June (2014)," said Kerr, but permitting and other delays pushed the start back to October "when the rains had already set in."
"In the process of the doing the project we moved initially 200,000 cubic yards of mud and cement treated that mud," said Kerr. His team used Challenger tractors and Eject pull scrapers on the project. Kerr points out that rubber track tractors are key to being able to move material in the mud.
Kerr's team stripped off the ground cover, and moved the structural fill into place. "Then we used our two Wirtgen 2500 Pulverizers to cement treat that material into a hard fill material," said Kerr.
"The process is to take a spreader truck which is usually a six-wheel drive truck which has got a box on the back kind of like a sanding truck for snowy roads," explained Kerr. "You go out and meter the amount of cement that's designed into the project and you spread it out over the mud." Then roto-tillers are used to till it into the designed depth. "When that's done you compact it and get ready for the next lift. So it's a pretty simple process."
After completing the initial building pad of 400,000 square feet, half of that surface area was surcharged with 100,000 cubic yards of earth and left to sit for 90 days. Then they moved that surcharge onto the other half of the building pad to be surcharged. As of June 2015, they moved back in to make the fill underneath the next 400,000 square foot building. Then they moved the surcharge sitting on the first building pad over to the second building pad, completing the same two-step process. "That's all there is to it, " said Kerr. "After the pads are done we've got a lot of underground utilities to put it and some off-site road improvements to do and away you go."
A Special Advantage
Kerr said the process is one "we use a lot here in Oregon," where the plentiful rain makes for plentiful mud.
"It's an advantage that Kerr Contractors has that we can do the cement treatment and we also can move the mud," said Kerr. He cites an example of an apartment complex project Kerr Contractors had taken on the previous winter. "With the dirt work contractor the owner was looking at having to haul the mud off and bring rock in to keep the project moving. They called us and asked if we could help them out," he recalled. "We said sure we can move the material, cement treat it for a third of the cost of what he was planning on spending." Having the rubber track tractors and the pull scrapers along with the cement treatment equipment sets up Kerr for this work. "We're a nice go-to company when clients get stuck in that position of having to move forward with a project over the winter," said Kerr.
He adds that powdered cement is not cheap but the process is a very economical alternative compared to hauling mud away and hauling rock back, "especially with dump fees going up and dump sites getting farther away from the metropolitan area."
Technology Adds to Productivity
The Colwood job also featured the extensive use of GPS technology. Kerby McGinnis, LSIT, Survey/ Grade Control Manager for Kerr Contractors said, "We set up two out of the four or five Challenger scrapers we had with GPS. We also had our motor grader, excavator and John Deere 850K Dozer set up with GPS as well."
"We've invested a lot in that and company-wide have nine excavators wired up, we have four graders, eight dozers and three scrapers," McGinnis said. Kerr Contractors uses Topcon GPS equipment, with most of what we have set for Topcon's 3D MC-2 system. "All of the graders and the three 850k dozers have the 3D MC-2 system," said McGinnis. "That sets everything up on the screen for us, so it's all stake-less."
McGinnis estimates the use of the GPS increases efficiency by 30 to 40 percent on any kind of fine grade. "When we're removing grade-checkers on the ground that saves dollars per day," he added, "and more importantly it's safer."
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