Validation of Double Constant and Falling Head Permeameter for Determination of Hydraulic Conductivity of Soils in the Laboratory

The objective of this research was to validate alternative equipment for determining the hydraulic conductivity of saturated soil (Ksat) in laboratory settings. The aim was to develop a single piece of equipment that could be used to carry out tests using both the constant-head permeameter (CHP) and the falling-head permeameter (FHP) methods with minimal disturbance to the samples. To this end, undisturbed soil samples were collected (in volumetric cylinders with 100 and 250 cm3) from three soil profiles with different textures to evaluate the sensitivity of the double permeameter (DP) in determining Ksat, considering the method, the sample size, and the textural class of the soils. To assess the efficacy of the DP in estimating Ksat, the coefficient of variation (CV) was determined for the two methods (CHP and FHP), the sample size (100 and 250 cm3), and the applied hydraulic head (cwc) (constant: 1.5 and 2.5 cwc; falling: Δhi, upper limit, h1 = 67.6 and h2 = 57.6 cwc; Δhii, medium limit, h1 = 49.3 and h2 = 39.3 cwc; and Δhiii, lower limit, h1 = 31.3 and h2 = 21.3 cwc). The results indicate that the DP may be employed as an alternative permeameter for Ksat tests employing the CHP and FHP methods. The most favorable statistical coefficients were observed in tests conducted with samples of a sandy texture (Profile 3, Ap horizon), particularly those with a larger volume (250 cm3), for both the CHP and FHP methods, irrespective of the applied hydraulic head. The equipment can be utilized within the full range of methodological limits employed in this study, and the appropriate limit must be selected according to the physical properties of the soil to be employed in the tests.