###### Abstract
Total suction can be obtained from [PERSON]'s law, where the free state water energy can be measured in terms of the partial pressure of water vapor present in the gaseous phase existing in the soil (Equation (1)):  
\[\psi_{t}=-\frac{\rho_{w}\cdot R\cdot T}{M_{w}}\ln\left(\frac{u_{v}}{u_{v0}} \right), \tag{1}\]  
where \(\psi_{t}\) is the total suction, \(\rho_{w}\) is water density, \(R\) is the universal gas constant, \(T\) is the absolute temperature, \(M_{w}\) is the molecular mass of water, \(u_{v}\) is the vapor pressure of water, and \(u_{v0}\) is the saturated water vapor. However, the filter paper method is a reliable, less expensive, and frequently used laboratory technique covering a wide range of suction measurements that use a calibration curve for natural soil [15]. The soil suction measurements by the filter paper method evolved in Europe in the 1920s [16]. Since then, several researchers have studied and applied this method due to is relatively low cost and the suction range covered by it, from 0 to 1 \(\times\) 10\({}^{6}\) kPa and 1000-500,000 kPa for the total and matric soil suctions, respectively [17]. Due to this, the filter paper method is currently used to evaluate the total and matric soil suction [18; 19]. This laboratory test method, described by the standard ASTM D5298 [20], allows measuring the \(\psi_{t}\) by a non-contact procedure, and the \(\psi_{m}\) by a contact procedure. In this technique, the water content of an initially dry filter paper comes into equilibrium with the soil either through vapor or liquid flow [16]. The importance of the soil-contaminant interaction lies in the contaminant movement control through the soil and the changes in its geotechnical properties [21; 22; 23]. Different theories have supported those changes (e.g., the diffuse double layer) and provided a guide to study the change in the soil-water retention curve (SWRC) since particle size and permeability changes are related to soil suction [17]. It is known that soil suction describes the potential water retention into the soil's pores. In contrast, SWRC describes the relationship between the degree of saturation of the soil and the soil's suction. When unsaturated soils are subjected to drying and wetting cycles, the SWRC shows hysteretic behavior. This causes the soil to retain more water on the drying path than on the wetting path at the same suction value. Soil's water retention is affected by the void ratio and the pore structure, represented by the pore-size distribution. The SWRC depends on many factors such as soil type and structure, temperature, salts content, and stress state. The SWRC is an essential relationship that provides information about unsaturated soils' mechanical and hydraulic behaviors. The SWRC has a similar role as the consolidation curve for saturated soils mechanics. The SWRC is used to predict the volume change, shear strength, and permeability coefficient for unsaturated soils [9; 14]. Thus, the knowledge of the SWRC of the unsaturated and contaminated soils is a crucial parameter for its analysis [9]. The literature review showed that many efforts have been made to study the contaminated soils' geotechnical behaviors. However, to the best of the authors' knowledge, there is no available information about the SWRC for heavy metal contaminated soils. Hence, the objective of this paper was to evaluate the SWRC of arsenic-contaminated soil. Further, the permeability coefficient of the arsenic-contaminated soil was evaluated through its laboratory measurement and compared with a correlation equation using the consolidation parameters of the soil.