## 2 Construction of the Energy Slab in a Test Bed
### Overview of Test Bed  
The test bed is located in Dangjin city, South Korea. The construction site consists of low hilly land with the mountains dominating. The ground formations are composed of quartzite, quartz  
Figure 3: Sectional view of energy slab. (**a**) Wall slab; (**b**) Floor slab.  
Figure 2: Schematic diagram of constructed energy slab.  
arenite and granite. A boring investigation was carried out from 0.0 to 10.0 m in depth, in order to assess the composition of ground formations at varying depths. According to the investigation results, the bedrock mainly consists of metamorphic rocks. In the colluvium layer from depth 0.0 to 2.7 m, sandy silt mixed with gravel is predominant, while sandy gravel with silt is present in some sections of 1.7 to 2.7 m depth. The color tones of this layer are dark gray to grayish brown. The weathered soil layer, ranging from 2.7 to 9.8 m in depth, is mostly composed of silty sand with the color tone of grayish brown. Meanwhile, the weathered rock layer, from 9.8 to 10.8 m in depth, is the entire weathering zone of biotite granite, and the composition of the parent rock is evident. The hard rock and soft rock layer are composed of biotite granite with the color tone of grayish gray.  
The thermal conductivities of surrounding media were measured by field and laboratory tests. The specifications of measuring equipment are summarized in Table 2. First, KD2-pro complying with the transient hot probe method was adopted to measure the thermal conductivity of ground formations [17] in the field. The thermal conductivity of ground formations was measured at three different locations under the energy slabs (refer to Figure 4). As a result, the average thermal conductivity of ground formations was estimated to be 1.232 W/mK. Meanwhile, the thermal conductivity of concrete slabs was measured from laboratory tests with the aid of QTM-500 complying with the transient hot-wire method [18]. In the laboratory tests, two different concrete specimens were prepared to match up strengths with the constructed concrete slabs. The strength of the wall slab was designed to be higher than the floor slab in order to withstand the pressure of backfill soil. The concrete specimens were cured in dry and saturated conditions for four weeks before measuring thermal conductivity, which corresponded to the moisture content expected in the field. Table 3 summarizes the laboratory measurements for the thermal conductivity of concrete specimens. The concrete specimen cured in the saturated condition shows about 8% higher thermal conductivity than the specimen cured in the dry condition. The average thermal conductivity of concrete specimens was estimated to be 2.05 W/mK.  
Figure 5 shows the comprehensive construction procedure of energy slabs. Four types of energy slabs were constructed in the test bed (refer to Table 1). First, heat exchange pipes were arranged in the floor and wall slabs as shown in Figure 5a, b. In this step, steel reinforcements were additionally installed in the wall slab to stand against the earth pressure exerted by the sand backfill. Then, concrete was cast-in-place in the floor and wall slabs. Before finishing work, a thermal insulation layer (PF board) was installed in the floor-type energy slab (refer to Figure 5g). Finally, in order to induce heat exchange between the wall-type energy slabs and ground formations, the backside space of the wall slab was backfilled with sand, and so resembled the in-situ ground conditions (refer to Figure 5i). Figure 6 shows the views of energy slabs at the end of construction.