The Forth Replacement Project is currently on track to be delivered in 2016 and will replace the current Forth Road Bridge as the main route for cross-Forth traffic. Road alignments have been revised with the creation of new junctions both north and south of the Forth estuary. On the north part, Embankment B981 and FC side roads run over weak soils made of soft organic alluvial deposits reclaimed many years ago. The vertical alignment of these structures creates an embankment up to 16 m high. The direct construction of such embankment without any reinforcement is not possible as it would have led to circular slope failure and unacceptable post-construction settlements. To comply with technical specifications, innovative soil improvement solutions have been developed, considering both soil conditions (nature, compressibility and thickness) and embankment characteristics (symmetrical or side long and height). Controlled Modulus Columns (CMC) and Trenchmix walls (TM) have thus been constructed, separately in some places or in combination in other places. Advanced design of those solutions based on 2D and 3D finite elements calculations and on BS 8006 verifications provided a very competitive alternative solution to the piled-embankment solution initially considered. The paper will first describe the execution methods of CMC and TM walls, and then focus on the main design principles to finally provide the jobsite results: actual bearing capacity of CMC from plate load tests, soil mixing compressive strength from laboratory tests and embankment settlements.
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