Innovative Applications of Geogrids as Tie-Back Anchors for Vertical Walls
This paper describes three different projects, where the application of flexible, high modulus geogrids
proved to be the best solution. First case: An additional anchoring of an existing sheet pile wall was necessary in Amersfoort, the Netherlands, due to an increase of loading. The use of conventional anchors was technically not feasible. The installation of a geogrid anchoring was a cost-efficient, quick and easy solution, which was installed in less then two days. To keep the deformation of the sheet pile wall to less than 100mm a high modulus geogrid made of Polyvinyl alcohol was used.
Second case: A temporary, 10 m high bridge had to be built over an existing road and railway in Switzerland to support a temporary haul road with heavy construction traffic. The abutments were constructed using a series of Ibeams with open timber polling's. Anchorage of the I-beams was carried out at four different levels using a geogrid from high tenacity polyester. A technical solution for post-tensioning the geogrids after the construction of the abutments to limit the face movements was installed.
Third case: During the construction works of the motorway BAB A20 close to Rostock very bad soil conditions were encountered due to the presence of an infilled lagoon. The soil exhibited very low undrained shear strength (<5 kPa) to a depth of 15 m. The motorway to be built in this section was on an embankment up to 15 m high. A change of the road alignment was not possible. The final solution consisted of slope support combining two rows of 21 m long steel tubes vibrated into the ground as a vertical supporting wall, horizontally anchored by, up to, 28 m long Aramid geogrids.
The paper presented three different projects, where special solutions due to the particular circumstances were required. After evaluation of different conventional solutions the use of geogrids as horizontal anchor elements for the retaining structures proved to be the best solution under the site specific conditions. Measurements and observations demonstrated very small or no deformations, which were all within the design limits. Back-anchoring retaining walls with flexible geogrids allowed cost-efficient, simple and successful innovative solutions to these problems.