Project Description

This project involved construction of a 9.3 km long dual carriageway expressway to facilitate traffic between the 2 sides of the Usk river.

Due to the height of the foreseen embankment (up to 10 m), and to the poor quality of the ground (4 m of made ground followed by 10 to 12 m of very soft alluvium), the direct construction of the road was not possible.

Additionally, classical wick drains and preloading treatment were not feasible due to the presence of various facilities (underground cables and pipes, etc.).

Finally, the presence of an old tip area made the soil treatment very sensitive to environmental concerns.

DGI-Menard proposed the use of the Controlled Modulus Column (CMC) techniques. The concept of CMC is to install columns made of mortar in the existing soil so as to form a complex soil + inclusion behaving as a uniform soil having good geotechnical properties.

A complete FEM analysis was developed in order to model the improved soil and to ensure a good long term behavior of the road.

Three rigs were mobilized on site in order to assure an average production rate of 1,500 lm per day.