THE PROBLEM
A dredged material disposal lagoon with deposits up to 8m deep and with water content of up to 350% and shear strength of only 0.7–1.0kPa needed capping for environmental reasons and also to permit the creation of a freeport car parking storage area. The original proposal, requiring frozen ground during construction was impracticable and inefficient.
THE SOLUTION
A Tensar mechanically stabilised layer (MSL) incorporating Tensar geogrids and granular fill was used to provide increased load spread and bearing capacity over the deposits to create a layer which was structurally safe. The Tensar system also meant that the construction could take place in all temperature conditions and did not require the deposits to be in a frozen state.
For this project the client opted for a Tensar design and supply package in which Tensar took the role as designer and creator of an outline method statement for the installation.
PROJECT DESCRIPTION
180,000m2 of very soft ground had to be covered to create a firm standing area. The original proposal did not include a consideration of the critical installation stage and so frozen ground would have been required during construction.
Tensar International proposed and designed a Tensar MSL which included one or two layers of Tensar geogrids, depending on the ground strength, the construction activity and the future intended use. This solution did not require frozen ground. The base geogrid layer was factory bonded to a geotextile and supplied as a geocomposite which provided both reinforcement and also separation between the aggregate and the highly mobile fine deposits. A trial area proved the effectiveness of the system and the full project construction followed on immediately.
The hard standing area has been subjected to various in-service loadings in the years following construction and continues to perform well.
The versatility, reliability and efficiency in mechanically stabilising aggregate over varying subgrade conditions, including super-soft deposits is based on Tensar’s more than 30 year experience.
