Deformation of Geogrid Reinforced River Bank using a Laser Scanner

Geogrid reinforced structures (GRS) have been constructed and monitored since the 1980s, but deformation data for real industry case studies is often limited in scope, quality and quantity. With the recent advance of laser scanning technology, obtaining detailed deformation data, has become much more efficient, with the latest scanners capable of surveying thousands of individual measurements every second. Laser scanning is unobtrusive, negating the need for targets attached to the face and indiscriminate, allowing analysis to be undertaken post-survey, saving time. The system is particularly suited to surveying horizontal deformation, during or after construction, as it can measure profiles of GRS to within a noise range of ±5 mm. As part of infrastructure development on a former forge site, in the Kirkstall area of Leeds, to facilitate access to a new rail halt, new highways were proposed to the North and South banks of the River Aire together with a new road bridge. The embankments on both sides of the river were constructed with HUESKER Fortrac® T uniaxial high tenacity polyester geogrids, in combination with Allan Block segmental blocks. This project also utilised a new positive connection system, for connecting geogrid to block. The reinforced concrete bank seats, for the new stitch bridge, are supported on reinforced soil structures to the North and South of the river. A terrestrial laser scanner was used to survey multiple stages of construction of the Northern section of the reinforced embankments, to determine any change in profile, due to the overlying layers and bridge deck. The most critical cross-sections were extracted from the virtual 3D model of the embankment, and detailed in the paper. The paper starts with a brief introduction to GRS, before discussing how laser scanning is well suited to the surveying of horizontal deformation. The case study details are then outlined, along with the laser scanning results, showing small deformation levels, despite the high increased loading from the bridge, between scans. Finally, the last section discusses the success of the application of laser scanning for this project.