ORIGINAL PAPER Permeability of granular soil employing flexible wall permeameter Srikanth Kandalai 1 & Purnendu Narayan Singh 1 & Kunal Kumar Singh 2 Received: 23 October 2016 /Accepted: 26 December 2017 # Saudi Society for Geosciences 2018 Abstract Understanding the changes in permeability of soil, when soil is subjected to high confining pressure and flow pressure, which may alter the textural and geomechanical characteristics of soil, is of great importance to many geo-engineering activities such as, construction of high-rise buildings near the coast or the water bodies, earthen dams, pavement subgrades, reservoir, and shallow repositories. It is now possible to evaluate the changes in permeability of soil samples under varying conditions of confining pressure and flow pressure using flexible wall permeameter (FWP). In the present study, investigation was carried out on a cylindrical sample of granular soil employing FWP under varied conditions of confining pressure (σ 3 )—50–300 kPa, which can simulate the stress conditions equivalent to depth of about 20 m under the earth’ s crust, and a flow pressure (f p )—20–120 kPa, which is mainly present near the small earthen embankment dams, landfill liners, and slurry walls near the soft granular soil with high groundwater table. The obtained results indicate a linear relationship between hydraulic conductivity (k) with effective confining pressure (σ eff. ), k, decreasing linearly with an incremental change in σ eff. . Further, k increases significantly with an increase in f p corresponding to each σ eff. , and q increases significantly with increase in the f p corresponding to each (σ 3 ). It was also observed that corresponding to the low f p of 20 kPa, the reduction in k is nonlinear with σ 3. The percentage reduction in k is observed to be 9, 13, and 27% corresponding to σ 3 of 50–100, 100–200, and 200-300 kPa, respectively. Keywords Granular soil . Confining stress . Permeability . Hydraulic conductivity . Hydraulic gradient . Flexible wall permeameter List of symbols k Hydraulic conductivity (m/s) i Hydraulic gradient ( Δh l ) Δh f p γ w: f p Flow pressure(in kPa) (Difference in pressures ap- plied at top and base of sample) γ w Unit weight of water (9.81 kN/m3) A Area of the sample (m 2 ). σ 3 Confining stress(kPa) Q Cumulative volume (ml) μ Dynamic viscosity of water (8.90 × 10 -4 kg/m s at 25 °C) ρ Fluid density (997.05 kg/m 3 at 25 °C) b p Base pressure (kPa) t p Pressure applied on top of the sample (kPa) l Length of the sample (m) d Diameter of the sample (m) q Discharge (m 3 /s) FWP Flexible wall permeameter RWP Rigid wall permeameter u Pore water pressure b h1 Initial water level in base burette b h2 Change in water level in base burette t h1 Initial water level in top burette t h2 Change in water level in top burette Introduction Permeability is the property of the material which measures its ability to transmit fluid/gases through the interconnected void * Kunal Kumar Singh karfuekunal@gmail.com Srikanth Kandalai srikanthkandalai@gmail.com Purnendu Narayan Singh purnendu.singh@gmail.com 1 Department of Civil Engineering, VNR Vignana Jyothi Institute of Engineering and Technology, Hyderabad 500090, India 2 Geological Survey of India, Bandlaguda, Nagole, Hyderabad, Telangana 500068, India Arabian Journal of Geosciences (2018) 11:28 https://doi.org/10.1007/s12517-017-3352-y