Benefits of Including CPTu in Geotechnical Investigation Program—A Case Study

Modern testing technologies such as electric cone penetration test with pore water pressure measurement and SPT energy transfer measurements can generate reliable geotechnical parameters for foundation design that is usually somewhat higher than that justified from conventional borehole data only. A case study of an industrial grain silo project is presented here that illustrates the savings that can be achieved by including electric cone penetration test with pore pressure measurement (CPTu) and SPT energy transfer measurement in the scope. Various engineering parameters, such as undrained shear strength of cohesive soils, angle of internal friction of granular soils, bulk density, over-consolidation ratio, modulus of elasticity, constrained modulus, etc., have been computed from the cone tip resistance values using published correlations developed by Robertson which are proven and used worldwide. Detailed foundation analysis was performed to determine the safe bearing capacity and settlement of foundations by conventional analysis using borehole data and compared with the safe bearing pressures that can be justified by use of CPTu results. The significantly higher safe bearing pressures justified resulted in considerable economy in foundation cost. The need for ground improvement by stone columns for the silo raft could be eliminated resulting in substantial savings in the foundation cost.