What is thermal backfill?

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Fluidized Thermal Backfill (a trademark of Geotherm, Inc.) is a form of controlled low-strength material composed of certain types of stone, sand, fluidizing agents and cement specifically designed to dissipate the heat generated by underground electric transmission cables within city streets or on rural wind farms.

What is thermal sand?

Thermal Sand is an insulative form of sand widely used throughout the power industry to improve underground electrical performance. Electrical cables are typically thought of as a conductor which is limited by the temperature in which insulation materials can withstand.

What is soil thermal resistivity?

Soil thermal resistivity testing measures the capacity of the ground to conduct or dissipate heat. A correct understanding of the thermal properties of a soil or layer of made ground is important for the design and installation of underground pipelines and transmission cables, to avoid premature failures.

What is a good thermal resistance?

These resistances are referred to as Rsi and Rso respectively with common values 0.12Km²/W and 0.06Km²/W for the internal and external surfaces, respectively. This is the measure that is always within Building Regulations. The lower the U-value is, the better the material is as a heat insulator.

What material is used for backfill?

Backfill materials can generally be graded as: Coarse grained soils – gravelly and sandy soils ranging from clay to gravel. Fine grained soils of low to medium plasticity – inorganic clays of low to medium plasticity, inorganic silts and very fine sands of low plasticity.

What is sand slurry?

Sand Slurry is a self-compacting form of Controlled Density Fill (CDF) primarily used for filling tanks and large voids in excavation. A small portion of cement may be used in order to help firm up the mix and dissipate the large volume of water typically in the mix.

How do you find the thermal resistivity of soil?

The probe is inserted into the ground to a specified depth and a current passed through the heater. The system monitors the temperature of the sensor over a period of time. Analysis of the sensor temperature determines the soil thermal resistivity of the material surrounding the probe.

Is a higher thermal resistance better?

Thermal resistance is calculated by dividing the thickness of the material by its thermal conductivity, giving an R-value specific to that thickness. As a rule of thumb, the higher the thermal resistance the better, because there is a greater resistance to heat transfer.

What is the best material to use for fill?

Sand is often used for fill material in and around ponds, septic tanks, and other damp areas.

Is sand good for backfilling?

Sand is a key component of a properly backfilled hole or trench in that it provides drainage and compacts well, especially when damp. Above the rock bedding is a layer of felt to prevent the sand from washing into the rock bed, sand and top soil. Properly layering these materials prevents sinking after the backfill.

What is a fluidized backfill?

This fluidized backfill was selected for its low and stable thermal resistivity, as well as for its free flowing property which made backfilling in the restricted space an easy and efficient task (Croall and others 1981).

What is the temperature of thermal backfill around transmission cables?

Howver for transmission cables, it is assumed that the “thermal backfill” placed around the cables will have a thermal rho of less than 90°C-cm/W. However many soils, especially uniform sands, can dry substantially when subjected to heat from the cables.

What is a cable backfill?

This backfill, after solidification (settling and hardening), forms a low thermal resistance and mechanically strong envelope for the cable. This technique will practically do away with the compaction required for soil-type backfills.