How to Make a “Floating Road”

floating-road

Credit: PRESTO GEOSYSTEMS
Material from a local crushing operation was used as infill for this “floating road.”

Robert Barrett of Carthage Mills went on in the late 1970s to join forces with the US Army Corps of Engineers in the development of geotechnical fabrics. From their tests in Mobile, AL, fabrics for architectural designs and construction on soft soils were developed, and a whole new frontier was opened for the future uses of filter fabrics.

Although the filter fabrics of Barrett’s days have changed, some of the same strategy is used. In areas of the United Kingdom where roads have to be built across peat-thick lands, or in Canada oil sands where roads are built over very soft, spongy soils, a strategy referred to as “floating roads” is sometimes used. A three-dimensional geocomposite reinforcement is used when a single layer alone won’t prevent weak and soft soils from drifting.

When the gas and oil production construction managers at Devon Canada came to Layfield Group, Alberta, they wanted to find alternatives that would help reduce costs for their lease access roads and drilling pads. The environment is dominated by soft soils and short seasons where the temperatures drop fast.

Their challenges were numerous, but included the need to stabilize the access roads, drilling pads, and platforms over soft soils to reduce the downtime that results from replacing a degraded road or drilling pad.

Devon Canada wanted something that would be easy to deploy, reduce the amount of aggregate needed, allow use of locally available sand, and reduce the amount of operational maintenance required. Floating roads seemed like a good solution to test.

Building over saturated clay and other pliable subgrades didn’t end the challenge for Layfield. In this area, suitable fill material for the access roads is either very expensive to purchase and truck in, or it’s limited. To that end, construction managers at Devon requested that Layfield design a road and demonstrate for them how new technologies could offer significant cost savings. Each test section measured 7.6 meters wide by 340 or 240 meters long.

Layfield knew where to look for a product that could handle the challenges. It had a good history with and recommended Presto’s Geoweb load support system.

Bill Handlos, P.E., director of Presto Geosystems, explains why the Geoweb system offers value for areas like this where available fill alone is unsuitable for the job.

“It’s fast to deploy,” he says. “They can use borrowed material that’s not ­typically acceptable. The Geoweb system also reduces the amount of base necessary, and builders can install the Geoweb geocell throughout the cold of winter. It offers high functional benefit with low environmental impact, and so it’s really an ideal solution for this location.”

The Geoweb three-dimensional ­cellular structure controls shearing, and lateral and vertical movement of infill materials.

“It also reduces environmental impact to a site by reducing site disturbance, critical in environmentally sensitive areas. Onsite waste fill is often acceptable, conserving local aggregate supplies. Sections are manufactured from HDPE, an inert material that does not contaminate or contribute to groundwater issues, and are shipped to a site in compact form, lowering transportation costs,” adds Handlos.

Layfield proposed a design solution and supplied Presto Geosystems GW30V6 and a LP45G geotextile for Devon. Devon had used the product the previous year at Horn River and was happy with its performance there. For this project, Layfield suggested not using aggregate in the road construction, but instead using rejected screening from local crushing operations as the infill material. The material was coarse sand (<5 mm) and would be used for the Geoweb cross section in place of aggregate.

Construction crews used a small skid steer to spread the coarse sand infill material within the Geoweb cells. After compacting, it was leveled to final grade and put into service.

The owners have been impressed with the performance of the test cross sections. The Layfield design saved on infill material by using reject fines and was able to show a reduction in the amount of fill required to construct a project site.

Using the Geoweb system, Layfield was able to demonstrate that a typical 1.5-meter-deep cross section for a haul road over soft subgrades can be reduced to less than 300 millimeters. This satisfied the cost-savings goal for the owners, who are now using the design and materials for future lease and pad construction. EC_bug_web

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