Extension of the A14 Trunk Road: Slope Protection Mesh saves Time and Money

Near the city of Cambridge in Great Britain, the trunk road between Girton and Histon is being widened by one lane per direction. The A14 is an important national highway that connects the Port of Felixstowe on the east coast with the British road network.

A number of steep sidehill cuts had to be comprehensively stabilized within the scope of the A14 widening. Soil nails were installed top down in accordance with the side hill cuts that were carried out in individual stages, and the cut face was secured immediately as construction progressed. The GEWI® Soil Nails supplied by DSI Great Britain were ideal for top down construction in this project because they provide a permanent, safe and economic reinforcement of slopes without the requirement for additional support.

The GEWI® Soil Nails installed featured galvanized protection in accordance with EN 1537, which provides comprehensive corrosion protection for soil nailing applications. Galvanizing ensures a top coating of zinc over the zinc alloyed layer of the bar, which is fully integrated with the base metal. In order to achieve the lifespan required for the soil nails, additional protection was provided by sacrificial corrosion allowance. The calculated loss of section was taken into account in advance during the proof of load bearing capacity by thickening the soil nail during the design stage. DSI supplied the soil nails to the jobsite just in time complete with spacers, tremie pipes, articulating wedge bosses and bearing plates and carried out the necessary anchor tests on site.

To install the 1,490, 25mm Ø, 9-15m long GEWI® Soil Nails, the bore holes were drilled with two rigs working concurrently to maintain progress consistent with the tight time frame. Afterwards, the GEWI® Soil Nails were installed using spacers to centralize the bars within the holes, and then grouted via a tremie pipe from the bottom to the mouth of the borehole. This ensured full column bonding of the soil nail to the ground. The protruding ends of the soil nails were trimmed back to 120mm on the surface.

Afterwards, the sidehill cuts were stabilized using Greenax Mesh. This new product offers superior strain stiffness and can be installed up to twice as quickly as standard mesh. The olive green Mesh has a higher performance than comparable products and blends with the environment.

Greenax Mesh consists of a high strength chain link mesh with an integrated polypropylene erosion mat on its underside. With a higher strength of 53kN/m as opposed to 50kN/m for standard mesh, Greenax Mesh ensures reduced deflection of the slope face over its complete lifespan.

The installation of Greenax Mesh is two times quicker than that of conventional hex meshes, as it neither rolls back nor springs. Since the mesh is supplied in 3.9m roll widths, which is nearly twice as wide as conventional mesh roll widths, the number of vertical seams is reduced by 50%. Each Greenax Mesh panel features an exposed mesh seam of 50mm on the right hand side and a 150mm overrun of erosion mat, thus ensuring full continuity of the erosion mat and the protection mesh at each seam. In total, DSI Great Britain supplied 3,000m² of Greenax Slope Protection Mesh, complete with connection clips.

After installing the mesh, the GEWI® Soil Nails were installed with 300 x 300 x 12mm bearing plates, wedges bosses and domed nuts. Angle compensation of the bearing plate was achieved using special articulating wedge bosses. Thanks to this component, large angles can be accommodated and variation of angle on the soil nail is possible as the slope face undulates. The bearing plates featured a slot, as opposed to a circular hole, to achieve a maximum degree of articulation.

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