Temperature measurements in the soil

The aim of measuring the temperature in the soil under the foundation slab is to verify the thermal properties of the soil that affect heat loss through the floor structure. Temperature sensors for monitoring of the temperature in the soil are located in 4 positions (S1-1 to S1-4) under the foundation slab of the object (see Fig. 3.8). Three temperature sensors are incorporated in three depth levels below the upper surface of the floor (±0.000 m) at each position in the soil:

1) -0,7 m,
2) -1,5 m,
3) -3,0 m.

Floor plan location of temperature

In-depth location of temperature probes in the soil under the foundation slab

The measuring temperature sensors had to be incorporated into the soil when earthwork was executed. Figure 3.10 and Figure 3.11 illustrate the installation of the sensors into the soil.

Preparation for placing the sensors at the dept of 3.0 m below the ground surface

Sensor location at the depth of 1.5 m below the ground (level of the foundation base)

Figure Sensor location at the depth shows the course of the average monthly temperature in the soil between December 2012 and November 2013. The temperatures in the soil show more stable values with increasing depth and they fluctuate depending only on the position of the probe under the foundation slab and depending on the season of the year. The average temperature moved between 5.5°C and 17.41°C at the depth of 0.7 m below the ground surface at the edge of the foundation slab, while temperatures between 11.2°C and 15,2°C were achieved under the centre of the slab. The average temperature at the depth of 3.0 m below the ground surface varied between 7.7°C and 13.2°C at the edge of the foundation slab during the year, while under the centre of the foundation slab the temperature range between 10.0°C and 13.1°C. While the lowest average outdoor air temperature was reached in January (- 2.7°C), the lowest average temperature in the soil was reached as late as in the months of March (at the a depth of 0.7 m, the edge of the slab) and April (at the depth of 3.0 m, the edge of the slab) – and this was due to the specific heat capacity.

Course of the average air temperature and the temperature of the soil in two depth levels at the edge of the foundation slab (S1 – 1) and under the centre of the foundation slab (S1 – 4)

The highest average outdoor air temperature was reached in July (20.8˚C). In the soil, the highest average temperature was reached in the months of August (at the depth of 0.7 m, the edge of the slab) and September (at the depth of 3.0 m, edge of the slab).