Testing for soil thermal resistivity determines how well the earth can conduct or release heat. When designing and installing underground pipes and transmission cables, it is crucial to fully comprehend the thermal characteristics of the soil or artificial ground layer to prevent premature failures. Whether a buried electrical line overheats or stays cool depends on the soil’s thermal resistance.

Heat accumulation surrounding the cable can lower transmission efficiency or, in the worst situation, melt the cable. Therefore, an underground utility cable needs to have the heat it produces from the current adequately dissipated. Geotechnical soil testing can help detect possible issues. Corrective thermal backfills can be installed in the cable trench, or the insulation and capacity of the cables can be changed as remedial procedures for any issues.

Thermal resistivity testing applications

There are many applications of soil thermal resistivity testing, which we will discuss below:

Design and selection of pipeline and cable routes

It is crucial to comprehend the thermal behavior of the soil when designing and insulating pipelines and cables. The information helps determine the necessary insulation thickness in designing cable alignments and choosing backfill materials. Why is this important?

  • It aids in choosing the appropriate cable backfill material.
  • It defines the minimal amount of insulation necessary to reduce heat loss.
  • It helps make decisions about going above or below the ground.

Thermal resistance as a proxy for other geotechnical characteristics

Thermal resistivity often represents other geotechnical characteristics like unit weight, void ratio, and moisture content. This is so because each characteristic affects how well the material conducts heat.

Keeping an eye on soil property changes

Soil thermal resistivity testing creates enduring recordings of alterations in soil properties that are useful for evaluating the effects of soil modifications on infrastructure.

How is soil thermal resistivity testing done?

Testing for soil thermal resistance occurs before the actual wire layout, and it should ideally take place at the installation’s anticipated cover depth. Although there are a few other techniques for thermal testing, the transient heat approach is the most widely utilized. This entails monitoring the temperature change when an electrical current goes through the porous materials. The standard configuration is a portable device that complies with IEEE 442 and ASTM 5334 criteria and consists of a needle with a temperature and heater sensor inside.

A current is run through the heater while the probe is lowered to a predetermined depth in the earth. Over time, the system keeps track of the sensor’s temperature. The temperature sensor’s analysis determines the surrounding material’s soil thermal resistance. The goal is to minimize thermally triggered water movement and shorten reading times by keeping heating durations as short as feasible. Accuracy in temperature measurement is one-thousandth of a degree. The analysis results are expressed as follows: C.m/W, where W is equal to watts and C is equal to degrees Celsius.

Summing up

Thermal resistance measures the capacity of a material to conduct heat. This characteristic holds significance in numerous engineering applications, including ascertaining the appropriateness of materials for insulation purposes and forecasting heat transfer through soils. Thermal resistivity testing can determine the thermal characteristics of soils, rocks, concrete, and asphalt for different applications.

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