Soil thermal conductivity selection guide

The right instrument for your application

Hukx offers a wide range of products for material characterization and measurement of soil thermal conductivity, or its inverse value thermal resistivity. Hukx sells a range of measuring systems which include “thermal needles”. All systems comply with ASTM D5334-14, D5930-97 and IEEE 442-1981 standards. Thermal needles are suitable for repeated insertion into various specimens or into undisturbed soil.

These sensors and systems can be divided in:

• high-accuracy measuring systems, using models TP02 and TP08 thermal needles, and measuring system TPSYS02
• systems more focused at robustness during field use, compromising on accuracy (FTN02 / MTN02 and TNS02 systems) with thermal needles TP09 and TP07
• a special model for long term monitoring, foil type sensor model TP01
   

Table 1 Soil thermal conductivity measurement.

Measuring systems using thermal needles: what we offer

Hukx offers the following measuring systems:

• FTN02:  a 100 % field instrument
• MTN02:  for mixed field/laboratory use
• TPSYS02: a scientific measuring system typically for the laboratory, but also useful in case you are only working with soft sediments and dry out experiments

For thermal needle types TP07 (used in MTN02) and TP08 and TP02 Hukx offers stainless steel “guiding tubes”. Using these tubes it is possible to measure in hard materials such as cements and thermal backfill (heavy clay) and dried-out soil by casting them into specimens.
For all models there are Calibration Reference Cylinders available, providing a traceable reference material. Hukx is also capable of supplying custom designed models (heavy duty, pressure resistant) for field or offshore applications.

High-accuracy measuring systems

TP02 and TP08 are primarily intended for use in the lab providing the highest possible measurement accuracy.

Although intended for indoor measurement, TP02 and TP08 may be taken outdoors for on-site testing, provided that care is taken during operation. Operation in soft soils, such as sediments is easy.  In harder soil holes must be pre-drilled, or guiding tubes may be used. TP02 and the smaller TP08 may be purchased as a single needle or a as part of a complete turnkey system TPSYS02. Models TP02 or TP08 can be operated using "standard" electronics, found in most measurement laboratories.

The user should carefully consider which probe to use. The standard model is TP02. This offers the highest accuracy, the lowest sensitivity to external influences and the best performance at higher or lower temperatures.

In case the specimen size for TP02 (typically 150 x 10^-3 m height) is not available, use of TP08 should be considered. TP08 is shorter than TP02, but its general operation is identical to that of TP02. A special sample container (TP08-CO) is available for use with TP08. TP08 is also often used in analyses of sediment cores in offshore experiments. Many times insertion of TP08 from the side of the core is possible.

Robust measuring systems for field use

For field experiments, Hukx offers measuring systems FTN02, MTN02 and the combined TNS02. These “heavy duty” systems are equipped with robust thermal needles suitable for penetrating soft as well as harder soils. The FTN02 system is designed for field use, in particular surveys for high voltage electric cables (not during operation) typically measuring at a depth of 1.5 meters below the soil surface. FTN02 includes a 1.4 meter long lance (model LN02) at the tip of which a very robust (6.3 x 10^-3 m diameter) needle (model TP09) is mounted. Using a lance rather than digging trenches saves time.

The MTN02 system is suitable for laboratory experiments as well as field experiments. The 3.5 x 10^-3 m diameter needle (model TP07) is mounted on a small insertion tool (IT03).

Models TP07 and TP09 are more robust than TP02 or TP08; however, the attainable measurement accuracy is considerably lower.