IEEE 442:2017 pdf free download – IEEE Guide for Thermal Resistivity Measurements of Soils and Backfill Materials
5.1.1 Installation of field probe
The thermal probe with multiple temperature sensors should be carefully inserted in the earth. The probeshould be inserted such that the middle temperature sensor is located at the depth that the cable is to beinstalled.Resistivities could then be determined at the cable depth and 300 mm above and below that depth. If,due to soil conditions, insertion of the probe is difficult, a pilot hole should first be made.Under no conditionsshould the thermal probe be hammered or inserted with excessive force into the soil. When a pilot hole isneeded, a pilot rod of slightly smaller diameter than the thermal probe should be driven into the soil using aslide hammer and guide (Annex C), or another appropriate device.Similar means should be used to removethe pilot rod.If insertion of the thermal probe is difficult, because of unusual soil conditions, the pilot rodshould be reinserted and removed again.This process can be repeated until the hole is just enlarged enough toaccommodate the probe to minimize the contact resistance at the probe/soil interface. If the soil is extremelyrocky, an electric drill may be used to facilitate producing a pilot hole. In any event, if the ambient temperatureis raised as a result of this process, enough time should be allowed for the ambient temperature to return andstabilize at the initial condition.This may be several minutes to over an hour.
5.2.1 Sample preparation and installation of laboratory probe
The laboratory thermal probe is used primarily to determine the effects of changes in density and moisturecontent on the resistivity of soil and backfill materials. It can be used for both undisturbed tube samples aswell as reconstituted or re-moulded samples. If the soil is to be tested at the maximum density, ASTM D698,ASTM D1557, or ASTM D2049′ should be followed to determine the moisture content required at which themaximum density can be obtained. For most soils, the sample is mixed to the desired moisture content andthen compacted to the desired density. Silty soils artificially moistened should be allowed to equilibrate forat least 12 h in an airtight container prior to sample preparation and testing. The soil should be compactedin 25 mm thick layers so that the density of the soil in the container remains relatively uniform. The sampleshould be placed in a rigid cylindrical container with a minimum inside diameter of 100 mm. The height of thecontainer would vary depending on the length of the thermal probe used.
There are some sands that contain chemical deposits which form light bonds between sand particles as thesand dries. These bonds may lower the thermal resistivity of the sand due to the reduction in contact resistancebetween sand particles. Thus sand that is compacted at zero percent moisture could have a higher resistivitythan sand that is compacted at a higher moisture content and then dried to zero percent moisture. Sand shouldbe compacted to the condition in which it will be installed in the cable trench.
Care should be taken in inserting the thermal probe into the sample.Ilf insertion of the probe is difficult, then aprobe of slightly smaller diameter may be inserted into the soil to make a pilot hole.