Estimation of vertical subgrade reaction coefficient from CPT investigations: applications in Christchurch

The vertical subgrade reaction coefficient Kv is extensively used by structural engineers for the design of shallow foundations. The value of the coefficient is usually estimated by the geotechnical engineer by three possible ways: in situ testing, laboratory testing and bibliography. In this paper a methodology is proposed for estimating the subgrade reaction coefficient KCPT from cone penetration test. The continuous nature of CPT results provides a detailed stratigraphy that can be used for delineating the coefficient with depth which could be invaluable for both structural and geotechnical engineers. Comparison of results from one CPT with the corrected (N60) SPT values from an adjacent borehole constructed on a site in Christchurch indicates that the results of the proposed method may be of some use. The collection of further results from site investigations is recommended for verifying the validity of the proposed method in sands of any state of packing.