Summer 2016

In the United States thousands of bridges are in need of repair or replacement. For the construction of bridge abutments, geosynthetic-reinforced foundations can be used in addition to traditional methods. Thanks in part to the use of TenCate Mirafi® HP geotextile, substantial savings can be made in time, costs and inconvenience.
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n 2013 the small town of North Haven on North Haven Island, off the coast of the state of Maine (US) began reconstruction of Beach Bridge. In 2009 this structure had deteriorated and needed to be rebuilt. The bridge provides access to a handful of seasonal homes, an important wharf for local lobstering as well as summertime swimming for tourists. 

brug maine _farm8.staticflickr.com_

The project presented several challenges. North Haven Island is about 20 kilometres from Rockland, the closest mainland connection. All construction materials and equipment had to be transported to the island by boat and barge. Significant daily tidal fluctuations affected the duration of daily construction: at high tide most of the bridge abutments would be under water. Construction had to be completed during the late winter/early spring to minimise the impact on residents, anglers and summer tourists. The retaining walls of the bridge had to withstand the potential impact from boats navigating the waterway. This led the design team to search for a more efficient solution than a typical pile-driven foundation for the bridge abutments. 

West abutment construction; east abutment demolition
Western abutment construction and eastern abutment demolition 

The answer for North Haven and the Maine Department of Transportation was a Geosynthetic Reinforced Soil-Integrated Bridge System (GRS-IBS). And for this they decided to use TenCate Mirafi® HP geotextiles. The Federal Highway Administration, a division of the United States Department of Transportation that specialises in highway transportation, has long championed GRS-IBS. The use of this reinforced soil technology is especially popular with county engineers for its time- and money-saving efficiencies. The existing bridge pier was in good shape and could be integrated into the new structure by installing lightweight concrete beams.

Western abutment nearing completion
The western abutment nearing completion

The limestone wall would join up well with the appearance of the natural surroundings. ‘This is located in one of the most spectacular sailing harbours along the coast of Maine’, said administrator Joe Stone. ‘It was important that the natural scenic beauty of the site should not be damaged by the bridge.’ Redi-Rock-Limestone-GRS-retaining-wall
At the tallest point the abutment walls stand at 15 feet (4.6 metres), of which 1.2 metres are buried. The original centre support no longer provides structural support, but has been retained for historical reasons 

The construction of a GRS-IBS bridge abutment is a three-step process. First, a row of blocks is put into place. Second, a layer of fill is compacted to the height of the facing blocks. Third, a layer of geotextile is extended between the rows of blocks to connect them to the GRS mass. This process is repeated until the wall height is reached. Pre-cast concrete box beams can be placed directly on the GRS abutments without a concrete footing. A GRS wall was by far the cheapest and easiest to incorporate in that type of environment. It is the first time a GRS wall has been used in a marine or tidal environment and also the first time for its use in a two-span bridge arrangement.   

TenCate Mirafi® HP is a range of geotextiles for the construction of support walls and embankments and separation, filtration and reinforcement of ground layers. In North Haven they opted for TenCate Mirafi® HP770.

Blue fabric (Tecawork Blue 65287)