**2.3. Transmissivity test**

The horizontal permeability, transmissivity, which is the drainage performance of the geonet, was measured using the ASTM Standard Test Method (ASTM D4716/D4716M-14; Standard Test Method for Determining the In-plane Flow Rate per Unit Width and Hydraulic Transmissivity of a Geosynthetic Using a Constant Head) [11]. And this is determined from the relationship between the number of paths per unit area and the in-plane drainage capacity, the compressive strength and the hydraulic gradient.

The short-term transmissivity test of geonet was carried out under various normal stresses and three hydraulic gradient conditions at 0.1–1.0, and the test temperature was 22–23°C. **Figure 3** shows a schematic diagram of the transmissivity test apparatus and the transmissivity value was calculated from the following equation:

$$\Theta = \frac{Q}{B \times \{\Lambda h/L\}} \tag{1}$$

 where *θ* = transmissivity (m2 /s), Q-=volume of discharged fluid per unit time (m<sup>3</sup> /s), L = length of the specimen (m), B-=width of the specimen (m) and h-=difference in the total head across the specimen (m).


**Table 1.** Basic properties of various geonet samples.-

**Figure 2.** Schematic diagram various test parameter for determining the main factor: (a) 3-D, (b) horizontal, and (c) verticle.

**Figure 3.** Schematic diagram of transmissivity test device.
