Table 7.20.

Cone penetration tests (CPT)

Cone penetration tests (CPT)MethodApplicationsLimitations
Graphic
  • Rapid probing tool using an instrumented electric cone pushed directly into ground from surface using a hydraulic penetrometer rig;

  • The penetrometer rig may be mounted on trucks or crawler units, long reach backhoe excavator booms and marine jack-up platforms;

  • Sea-bed CPT rigs for marine investigations.

  • Preliminary soil profiling;

  • Data may be used for semi-empirical design methods;

  • Derivation of soil parameters;

  • Piezocones may be used to assess groundwater profile, permeability and soil characteristics;

  • Minimal disturbance of sensitive soft soils or water-bearing silts/sands.

  • Difficult to penetrate coarse granular fill and natural deposits, and rock;

  • The characteristics of some soils and weathered rock are difficult to interpret without control boreholes;

  • Does not permit sampling of strata unless used in parallel with a Mostap sampler.

Cost factor: low, but medium or high if deployed over water.
Relevance to glacial/periglacial depositsProbing technique routinely used onshore and offshore for the investigation of glacial deposits. Will penetrate most massive tills and interbeds or pockets of sands and gravels. Can penetrate past cobble beds but will refuse on boulders, bedrock, extensive layers of dense granular deposits and sometimes in over-consolidated massive diamicton tills. Cone resistance, side friction and porewater pressures allow interpretation of soil units and basic geotechnical parameters providing valuable lower-cost data points between boreholes. CPT pushes often placed adjacent to boreholes to confirm depths of lithofacies boundaries, particularly useful for identifying the depth and texture of granular lenses and beds encountered which may have been disturbed during drilling. Can be used to aid the positioning of boreholes after a preliminary investigation phase. Depths and variation in glacial deposits determined by CPT can be used by cable percussion and rotary drillers to plan operations, reduce risks associated with using these techniques and enhance the quality of samples taken.