*2.4. Flexible-Wall Hydraulic Conductivity Test*

The unamended, attapulgite-amended, diatomite-amended, and dual-additives (attapulgite 4% and diatomite 1%)-amended compacted clay were prepared with moisture

content of 30% and additives dosage of 5%. The degree of compaction was set as 85%. The specimens of 50 mm in diameter and 50 mm in height were prepared, assembled in a flexible-wall permeameter, and saturated using deaired tap water. Hydraulic conductivity test was conducted in the permeameter using the constant head method as per ASTM D 5084 [42]. All hydraulic conductivity tests in the study were conducted under hydraulic gradients (*i*) of 40 and effective confining stress of 36.7 kPa calculated by Equation (6) as follows [43–45].

$$
\sigma\_c^{\prime} = \sigma\_3 - \frac{1}{3}(p\_2 + 2p\_1) \tag{6}
$$

where *σ<sup>c</sup>* = average effective confining stress; *σ*<sup>3</sup> = cell pressure (50 kPa in this study); *p*<sup>1</sup> = bottom seepage pressure (20 kPa in this study); *p*<sup>2</sup> = top seepage pressure (0 kPa in this study).
