Geological & Geothermal

Granular and unconsolidated materials such as soils and aggregates are best characterized using the Transient Line Source (TLS) method, which inserts a needle probe directly into the sample so the line source is in intimate contact with the granular medium. TLS testing follows ASTM D5334 and is well-suited to packed, moist, or loosely consolidated samples where flat-surface contact methods would otherwise struggle.

Moisture content has a strong effect on the measured thermal conductivity of porous and granular materials — water has a much higher conductivity than air, so saturation generally raises the measured value substantially. Because of this sensitivity, C-Therm recommends testing soils, grouts, and aggregates at the moisture content representative of in-service conditions and reporting the saturation state alongside the result.

Thermal conductivity governs how efficiently heat is exchanged between a borehole heat exchanger and the surrounding ground, so mapping conductivity across the relevant strata directly determines borehole length, spacing, and overall system sizing. Accurate, site-specific data reduces oversizing margins, lowers capital cost, and de-risks long-term performance for ground-source heat pump and geothermal projects.

Transient methods on the Trident Thermal Conductivity Instrument typically deliver thermal conductivity results within a few percent reproducibility on well-prepared samples, with method-specific accuracy detailed in the ASTM and ISO standards each method conforms to. Performance depends on sample type, geometry, and conditions — C-Therm is happy to share method-specific specifications for your application on request.

Yes — the Trident is a compact, single-instrument platform that suits both fixed-lab and near-field deployments, and the TLS needle probe is widely used in mobile and field workflows for soils, sediments, and grouts. For walk-up screening of prepared samples, the Modified Transient Plane Source (MTPS) method, exclusively available on the Trident, completes a non-destructive measurement in under a minute.

Geothermal grouts are most commonly characterized using the Transient Line Source (TLS) method per ASTM D5334, with the needle probe inserted directly into the cured or curing grout to measure thermal conductivity in a geometry representative of borehole installation. TLS handles the high water content and paste-like consistency of grouts well, and the same approach supports formulation work on bentonite- and silica-enhanced mixes.

Rock and sediment preparation depends on the chosen method. For the MTPS/TPS method, a flat, smooth surface on a core or cut slab gives the fastest, non-destructive measurement; for the TLS method, intact cores can be drilled to accept the needle probe, and unconsolidated sediments can be packed into a sample holder. C-Therm provides prep guidance specific to your sample type during application scoping.

Bentonite-based grouts are widely used as the backfill between the pipe and the borehole wall in vertical ground-loop heat exchangers, where they provide hydraulic sealing while carrying heat between the working fluid and the surrounding ground. Thermal conductivity of the grout — often enhanced with silica sand or graphite — is a primary lever on overall borehole thermal resistance, making it a key target for measurement and formulation work.

C-Therm’s methods conform to the relevant international standards for each technique:

1. MTPS to ASTM D7984
2. TPS to ISO 22007-2, ISO 22007-7, and ASTM E3088 and
3. TLS to ASTM D5334 (geological / soils) and ASTM D5930 (polymers)

These are complemented in industry by steady-state standards such as ASTM C177 (Guarded Hot Plate) and ASTM C518 (Heat Flow Meter).

Thermal conductivity sets the rate at which heat moves through rock, soil, grout, and engineered materials, so it directly drives the sizing and efficiency of ground-source heat pumps, geothermal wells, borehole thermal energy storage, and subsurface infrastructure. Reliable conductivity data reduces design margins, supports better project economics, and is increasingly expected as part of feasibility and permitting documentation.

Yes — High-Pressure TLS extends the Transient Line Source method to elevated pressure and temperature, with the line source probe rated to a maximum of 14,500 psi, enabling characterization of subsurface materials, polymer melts, and metal hydrides. High-Pressure MTPS and TPS, exclusively available on the Trident, similarly extends method capabilities into high-pressure and vacuum environments.

No. Trident is not limited to thermal conductivity. Depending on the selected method, it can also measure thermal effusivity and other thermal properties relevant to material characterization. This allows users to obtain more comprehensive thermal data depending on their application needs.