Geotechnics / soil thermal route analysis

Hukseflux is market leader in “thermal needle” thermal conductivity sensors. The main application of these sensors is in measurement of soil thermal conductivity and resistivity.
There are two product categories: the first consists of scientific systems (needle types TP02 and TP08, with system type TPSYS02). The second category is systems designed for robustness rather than accuracy, with systems FTN02, MTN02 and TNS02.
Watch our video to see systems for soil thermal conductivity measurement at work:

Soil thermal route surveys

When designing infrastructure, the thermal properties of the soil may play a role. Thermal conductivity is a material property. It expresses how well a material conducts heat under steady state conditions.
Soil thermal conductivity matters for example when designing:
During the design phase of a project, often the soil thermal properties of the entire trajectory or the location are measured.

What is measured

The measured quantity is thermal conductivity in W/(m·K). Users may also call this the “K-Value”. Other users talk about the thermal resistivity. The latter is simply the inverse of the thermal conductivity in m·K/W.
There are standards for measurement of soil thermal conductivity. The most commonly used are:
Both methods rely on thermal needles. These needles are inserted into the soil.
You may measure:
During collection, also other parameters are taken down:
After the measurement, in particular in the laboratory, many users will determine:
When preparing for the high voltage power cables, the main consideration is that the temperature of the plastic insulation must remain below 80 °C. It is important to establish the most dangerous situation; i.e. the thermal conductivity of the dry soil.


What you must know about thermal conductivity of soils:

Table 1 Reported soil thermal conductivity, as known to the author, in different soil types in W/(m·K).

Range of all reported values for granular soils0.15 to 4
Saturated soil0.6 to 4
Sand perfectly dry0.15 to 0.25
Sand moist0.25 to 2
Sand saturated2 to 4
Clay dry to moist0.15 to 1.8
Clay saturated0.6 to 2.5
Soil with organic matter0.15 to 2
Solid Rocks2 to 7
Tuff (porous volcanic rock)0.5 to 2.5
What you must know about thermal needle measurement

Selecting a sensor or measuring system

a typical checklist is:

What we contribute

Hukseflux has been designing soil thermal conductivity measurement sensors and systems for over 20 years. In the course of the years, we have added many sensors to our product range. We also offer measuring services and rent out equipment.
Hukseflux offers the following measuring systems:
For thermal needle types TP07 (used in MTN02) and TP08 and TP02 Hukseflux 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. Hukseflux is also capable of supplying custom designed models (heavy duty, pressure resistant) for field or offshore applications.
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.
For field experiments, Hukseflux 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 metres below the soil surface. FTN02 includes a 1.4 metre 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.

How to request a thermal conductivity measurement service

How to rent a thermal conductivity measuring system


Hukseflux is a leader in thermal conductivity measurement. We offer:
Take a look at our selection of suitable sensors:



High-accuracy thermal conductivity measuring system
Measurand thermal conductivity, thermal resistivity
Measurement range 0.1 to 6 W/(m·K)

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Multi-purpose thermal needle system for thermal resistivity / conductivity measurement
Measurand temperature, thermal conductivity, thermal resistivity
Measurement range 0.1 to 6 W/(m·K) (all common soils)

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Field thermal needle system for thermal resistivity / conductivity measurement
Measurand thermal conductivity, thermal resistivity
Measurement range 0.1 to 6 W/(m·K) (all common soils)

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Thermal needle set for thermal resistivity / conductivity measurement
Measurand temperature, thermal conductivity, thermal resistivity
Measurement range 0.1 to 6 W/(m·K) (all common soils)

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Non-steady-state probe for thermal conductivity measurement

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Small size non-steady-state probe for thermal conductivity measurement

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Heat flux plate
Measurand heat flux
Measurement range -2000 to +2000 W/m²
Sensitivity (nominal) 60 x 10⁻⁶ V/(W/m²)

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