Multiple sites in the river-side suburbs near Port of Brisbane have experienced issues with long term differential settlement when loaded with shipping containers and other heavy stored items. The ground conditions in the area typically consist of a very soft compressible soil layer to a depth of 20m. Wagstaff Piling’s mass mixing technique is an ideal solution for this settlement problem.
Wagstaff Piling’s initial design using Plaxis 2D required an unconfined compressive strength of 1.0MPa for the mass mixed material comprising a cement binder. Further design indicated a requirement to increase the tensile capacity of the mixed mass which was achieved by incorporating a geogrid layer between the mass mix subgrade and bitumen layer. During the construction of the mass mix, the drainage was incorporated into the mass mix to reduce the risk of differential movement. A test area was completed to assess the constructability, design assumptions and serviceability of the combined mass mix and geogrid bitumen layer. Main works using a Kemroc mixing head and Soilmec SGM45 batch plant were then completed across the 20,000m2 site to create a 1.2m mass mixed raft in lieu of a piled reinforced concrete slab. The use of mass soil mixing for the improvement of container storage yards with soft compressible soil layers has proven to be a practical and cost-effective engineered solution.
