Thermal Resistivity is more than a number. We understand the entire process and provide expert guidance throughout the design process. Trust the team at Geotherm when you are performing Ampacity Calculations for your Underground Cable System.
Our equipment was single-purpose developed, with the support of EPRI, to help electrical engineers design underground transmission and distribution (T&D) systems and is IEEE 442-2017-compliant.
Accurate Data. Better Designs.
Optimal Performance.
The first step in designing your underground electrical system is to understand the existing thermal conditions along the entire route.
A thermal survey is the first step in designing a reliable underground cable system. By evaluating the thermal and geotechnical properties of the proposed cable route, Geotherm provides the data needed to optimize cable ampacity and long-term system performance.
Our surveys include measurements of ambient soil temperature, in-situ thermal resistivity, and ASTM-compliant soil sampling to accurately characterize subsurface conditions and support confident design decisions.
We survey the entire route to determine soil conditions and thermal properties for design considerations. Field personnel perform In-Situ measurements at various depths and collect samples for laboratory testing.
Performed using a barge or a boat, utilizing a vibracore or a conventional soil drill rig. Our thermal probe is attached to a standard drill rod and pushed into the seabed/sediment where measurements of ambient temperature and thermal resistivity are determined.
Geotherm works with your engineering team during the iterative design process to establish Rho (ρ) values and evaluate other design parameters in your ampacity program to optimize the design for cost, constructability and system longevity.
Thermal gradients in a radial field are inversely proportional to the distance from the heat source. Therefore, the thermal resistivity of soil/backfill adjacent to cables is crucial and must be taken into consideration.
Uniform size soil particles (i.e. low soil density) provide fewer contacts for heat conduction.
Variety of particle size reduces air spaces and provides many contacts for heat conduction.
At our state-of-the-art facility, we perform bench scale testing to determine the optimal mix design for each component. Designs are created utilizing materials that are locally available to the project to minimize cost.
Trench backfilling with native soils involves returning the excavated dirt into the trench after utility installation. Mix designs and means and methods of placement are provided to optimize thermal properties.
Concrete encasement provides structural support, shielding from heavy loads, heat dissipation, and visual identification during future excavations. Designs for both cast-in-place and precast concrete.
An engineered, flowable slurry of aggregate, sand, cement, fly ash, and water that is often substantially more efficient than backfilling with native soils.
Thermal grouts are used to infill annular space between casing and conduits that carry electrical transmission cables, typically in jack & bore as well as horizontal drilling applications (HDD).
Geotherm works collaboratively with manufacturers, contractors and project teams to verify material properties and field conditions-providing added confidence that the completed system will perform in accordance with the engineer's design.
Verification of the thermal properties of precast duct-bank concrete is an important step in confirming that the installed system meets the engineer's design parameters. Geotherm provides independent thermal-resistivity testing and documentation for precast concrete used in duct-bank systems. Our technicians can coordinate sample collection at the precast manufacturing facility, or representative samples from each duct-bank production run can be submitted directly to Geotherm's laboratory for testing.
Field QA/QC and laboratory verification help confirm that the installed material will perform as assumed in the electrical design. Geotherm's field personnel can observe placement, coordinate and collect representative samples, document installation conditions and submit samples for thermal-resistivity testing at our laboratory. Samples may also be collected by the project team and shipped directly to Geotherm for independent verification.
When native soils are incorporated into the thermal design, their composition, density and moisture condition can significantly affect the performance of the underground electrical system. Native soil placed above and around duct banks or electrical conduits in accordance with Geotherm's mix design and installation recommendations should be verified throughout construction. Geotherm's field technicians can evaluate soil composition, moisture content and in-place density, and collect representative samples for thermal-resistivity testing.
Geotherm provides THERMAL STABILITY TESTING to evaluate how existing underground cable systems will perform under new operating conditions.
These changes can affect cable temperature, ampacity, reliability, and service life.
