###### Abstract  
Arsenic is a metalloid frequently found in contaminated sites due to its easy mobilization in the environment. This has attracted the researchers who have studied this phenomenon from an environmental engineering perspective. Although there is evidence indicating that soil contamination impacts its geotechnical behavior, there is no available information about the changes in the soil's suction after its contamination. The objective of this paper was to evaluate the soil-water retention curve of arsenic-contaminated soil. An unsaturated soil sample was contaminated with arsenic at two different concentrations and a filter paper calibration curve was developed for each contaminant concentration. Soil contamination decreased the BET area and increased its pore sizes. At a saturation rate of 0.8, the matric suction of the contaminated soils decreased (from 1681 kPa to 260 kPa), while the osmotic suction increased (from 23 kPa to 530 kPa), compared with the natural soil's condition. Furthermore, the soil's suction values obtained with the ASTM D5298 calibration curve were higher than those obtained using the calibration curve developed for the contaminated state. Thus, to avoid misunderstanding the mechanical behavior of the unsaturated soils under contaminated conditions, the osmotic suction should be considered and evaluated with the corresponding calibration curve. unsaturated soil; soil suction; arsenic; contaminated soil; environmental geotechnics Article  
Evaluation of the Soil-Water Retention Curve of Arsenic-Contaminated Soil by the Filter Paper Method  
[PERSON], 1 Facultad de Ingenieria, Universidad Autonoma de Queretaro, Cerro de las Campanas S/N, Queretaro 76010, Mexico; [EMAIL_ADDRESS]  
1 Facultad de Ingenieria, Universidad Autonoma de Queretaro, Cerro de las Campanas S/N, Queretaro 76010, Mexico; ismael. and adsorption forces that generate negative pressures on the soil. Surface tension results from an imbalance of attractive intermolecular forces developed in the air-water interface. Such surface tension causes the interface to behave like an elastic curved membrane subjected to excess pressure. These stress forces are known as suction and depend on the water content that is affected by soil structure due to the random interconnections of the pores [11; 12] and can considerably affect soil behavior [13]. Most of the problems that involve unsaturated soils are commonly the result of environmental changes, which can cause the expansion or reduction of the soil volume. Those changes affect the metric (\(\psi_{m}\)) component of the soil suction and cause the osmotic suction (\(\psi_{o}\)) to become essential in the shear strength of the soil when chemical contamination arises [10]. The soil's total suction (\(\psi_{t}\)) corresponds to the sum of the \(\psi_{m}\) and the \(\psi_{o}\). Nevertheless, it is common only to consider the contribution of the \(\psi_{m}\) to the unsaturated soil behavior because the contribution of the \(\psi_{o}\) is negligible. In contrast, it has been proposed that under contaminated conditions, the \(\psi_{o}\) becomes relevant due to the reactions between the soil and the contaminant, which modifies its geotechnical properties and, consequently, the shear strength resistance of the contaminated soil [10]. Moreover, the water flow is affected by the void spaces between solid particles because changes in water content result in changes in the soil's suction [14]. Diverse indirect techniques have been used to measure soil suction, for example, the relative humidity sensor, psychrometer technique, and filter paper method [15].