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CPT Guide

Role of the CPT

The objectives of any subsurface investigation are to determine the following:

Nature and sequence of the subsurface strata (geologic regime)
Groundwater conditions (hydrologic regime)
Physical and mechanical properties of the subsurface strata

For geo-environmental site investigations where contaminants are possible, the above objectives have the additional requirement to determine:

Distribution and composition of contaminants

The above requirements are a function of the proposed project and the associated risks. An ideal investigation program should include a mix of field and laboratory tests depending on the risk of the project.

The Cone Penetration Test (CPT) and its enhanced versions (i.e. piezocone-CPTU and seismic-SCPT) have extensive applications in a wide range of soils. Although the CPT is limited primarily to softer soils, with modern larger pushing equipment and more robust cones, the CPT can be performed in stiff to very stiff soils, and in some cases soft rock.

Advantages of CPT:
Fast and continuous profiling
Repeatable and reliable data (not operator-dependent)
Economical and productive
Strong theoretical basis for interpretation

Disadvantage of CPT:
High capital investment
Requires skilled operators
No soil sample
Penetration can be restricted in gravel/cemented layers

Although a disadvantage of the CPT is that no soil sample is obtained during a CPT, it is possible to obtain soil samples using the CPT pushing equipment. The continuous nature of the CPT results provides a detailed stratigraphic profile to guide in selective sampling appropriate for the project.

To receive a complete copy of the CPT Guide, please e-mail your request to Dr. Robertson at: peter@cpt-robertson.com