Best-in-Class Performance in Modern Digital CPT Tools
Gregg’s main business focus is to provide uncompromising industry-leading CPT data collection technology, processes, and equipment to maximize the value we bring. Gregg works to published standards, high-quality management processes, and uses precision state-of-the-art tools that provide the data our clients can rely on to support their engineering decisions.
How does one ensure they are using in-situ tools that are unparalleled in performance? This job begins by going to Holland, “where CPT all began” and seeking out the best tooling. Gregg is proud to offer a line of equipment that is built and serviced by the best in industry. These state-of-the-art digital in-situ tools produced by A.P. van den Berg offer best-in-class performance with respect to any modern digital CPT tools on the market. We work directly with the manufacturer to obtain equipment that is unmatched in performance, reliability and repeatability. The A.P. van den Berg tools deliver advantages through efficiency by using a fully down-hole digital system with next-generation temperature compensated sensors, real-time sensor readout and high-speed data communication to meet the exacting standards that we require, and our clients demand. These tools are second to none in terms of quality and are used by contractors around globe, both on and off-shore.
Whether its international test reference standard ISO 22476-1 or ASTM D5778 for CPT or numerous other test reference standards, our clients can expect that our quality processes, review and training, meet client’s requirements. Our quality management activities are coordinated by two key personnel, our Vice President (Mr. Shane Kelly) and our Senior Technical Director (Dr. Peter Robertson).
Additional In-situ Measurement with CPT
It is Gregg’s experience that a “CPT Project” can include a wide range of required in-situ measurements beyond the standard tip, sleeve, pore pressure and tilt measurements requested from a generic CPT program. It is not uncommon for additional in-situ measurements to be required, such as temperature, resistivity (or conductivity), or seismic Shear and Compression wave velocities. Gregg deploys all these systems in a module style approach and has experience on projects in all environments with them.
Gregg uses component-based systems to efficiently and accurately collect this additional data. Note that in addition to the components, Gregg uses a variety of CPT probes to suit the expected site conditions, whether they be very soft (i.e.. very-low capacity compression style probes to provide resolution of small loads), or very hard conditions (i.e.. high capacity subtraction probes to withstand hard conditions and tip pressures up to 100 MPa).
Examples of module based systems include seismic data collection as set out below.
Seismic Cone Penetration Testing (SCPT) can be conducted at various intervals during the Cone Penetration Test. Shear wave velocity (Vs) and compression wave velocity (Vp) can then be calculated over a specified interval with depth. A small interval for seismic testing, such as 1 to 1.5m (3’ to 5’) allows for a detailed look at the shear wave profile with depth. Conversely, a larger interval such as 3 to 6m (10’ to 20’) allows for a more average shear wave velocity to be calculated. Gregg operates CPT systems with horizontally active and vertically active sensors located behind the main tip and sleeve areas of the cone. Using components such as seismic, as well as, conductivity modules can be accomplished on the same profile to collect standard CPT data, seismic velocity data and even temperature profiling and conductivity – all at the same time. Conductivity probes are regularly used to examine saltwater intrusion in aquifers, but can also be used to examine differences in tailings streams using the variation in conductance across layers.
In seismic velocity testing Gregg continues to advance the practice. Typically to conduct the seismic shear wave test, the penetration of the cone is stopped, and the rods are decoupled from the rig and a source sends a shear wave into the soil. The distance from the source to the seismic module is calculated knowing the total depth of the cone and the horizontal offset distance between the source and the cone. In pseudo-time data collection, to calculate an interval velocity in a given layer, a minimum of two tests must be performed at two different depths (i.e. listen for a separate inbound signal at two locations). In this approach the arrival times between two separate wave traces are compared to obtain the difference in time (∆t). The difference in depth is calculated (∆d) and velocity can be determined using the simple equation: v = ∆d/∆t. Multiple wave traces can be recorded at the same depth to improve quality of the data. A complete reference on seismic cone penetration tests is presented by Robertson et al. 1986 and Lunne et al. 1997.
In the true-time approach to seismic velocity testing, a second seismic module is included above the first, either at a 0.5 m or 1.0 m spacing. During data collection, the seismic wave arrival at each depth is measured by both modules (at two depths), essentially simultaneously – different only by the interval time between the two receivers. True-time approach reduces uncertainty in analysis as the same waveform is present across two modules – this allows for field-level review at the tool-face of seismic wave velocity.
