As part of the redevelopment of an urban site near the centre of a small rural town, a working platform is needed to accommodate a SF47 CFA piling rig. Based on an engineering appraisal of the manufacture’s specification, BSEN 996:1995 & A3:2009 and the loading spread sheet of the Federation of Piling Specialists, the characteristic loadings for the plant were as shown in the Table below (Table Q4): Table Q4 Piling Rig Loading Load Case No & loading Pressure (kPa) Effective Track Width (m) Effective Track Length (m) LC1.0: 100 0.70 4.25 LC2.0: 320 0.70 2.40 Based on a review of the boreholes across the site, the near surface deposit below all contaminated ground (top 2.0 m which is removed) was denoted as a soft glacial till with constant undrained shear strength of 24 kPa (Characteristic) to a depth of 6 m. Thereafter the site is underlain by medium dense gravels and sands over stiff glacial till. As part of the engineering team designing the tracked plant platform for the site (BRE Report BR 470 2004), evaluate the following: 

(i) The minimum characteristic undrained shear strength for the platform design,

(ii) The minimum depth of platform for the loading using just a stone platform composed of recycled stone, (iii) The revised depth of platform for the site if a geosynthetic grid is used on site

. The Contractor has in storage a suitable grid with an ultimate tensile strength of 45 kN/m. 

Information It was decided to reuse the onsite concrete in the platform design. After sorting (removal of rebar & unsuitable material) the concrete was crushed and tested to ensure that the material could be used as a secondary aggregate. Based on shear box testing, the concrete gave a minimum internal angle of friction θ’ of 40o. The material has a minimum bulk density of 20.0 kN/m