OWNER:
Peveril Homes
ENGINEER:
Heathcote & Associates
GENERAL CONTRACTOR:
Bridge Bank Ltd
MAIN FIGURES:
2,004 Controlled Modulus Columns (CMC) installed
4,821 Vibro Stone Columns (VSC) installed
Project Details
The project consisted in a new residential development comprising 157 plots of single to double storey houses in Alfreton, Derbyshire. Menard has been approached at early stage to find a ground improvement solution to deal with the local soil conditions comprising backfilled open cast quarries with up to 30m+ of made ground and presence of various high walls.
Ground Conditions
The site footprint came across a former open cast quarry backfilled in an uncontrolled manner with colliery spoil. Due to the presence of various high walls, the made ground thickness was varying between 5m and over 38.5m, overlying a bedrock made of Sandstone. The colliery spoil was mainly silty, with a consistent layer of dense granular material between 8 and 10m in the deep quarry areas.
Solution
The initial proposed piling solution being not economically viable, Menard had been tasked to design a ground improvement solution to mitigate risk of differential settlements below the housing plots and associated externals.
After additional SI comprising CPTs and thorough desk study analysis, Menard proposed a combination of Controlled Modulus Columns (CMC) under the ground bearing houses rafts and Vibro Stone Columns (VSC) below the garages rafts and access roads. Both techniques were proposed as partial depth treatment of the made ground in the deep quarry areas. Creep settlements had been assessed on the back of the SI laboratory tests and site historical observation and allowed for in the design.
Collaborative works with the structural engineer to define achievable performance of the infrastructure and with the warranty provider to relax standard performance criteria have been undertaken to reach a cost effective yet robust ground improvement solution.
Sustainable Development
The use of a VSC and CMC combination in lieu of a dig out and replace with lime and cement stabilisation and piles brought a significant reduction in the overall embodied carbon footprint of the overall project.
