Investigations on Fluid Flow Properties of Fine-Grained Soil

Abstract

Infrastructure development over quaternary unlithified, unconsolidated sediments is quite critical and poses geo-hydro-engineering challenges. The challenges are more perceptible near high groundwater table areas and increase with the depth of construction. In this study, long-duration (t ≤ 40 h) permeability experimentation on fine-grained soil sample is conducted under varying confining stress (σ3) and fluid flow pressure (fp) employing a flexible wall permeameter to simulate the behavior of fluid flow under the stress conditions equivalent to a depth of approximately 40 m below the earth's crust. The obtained result indicates a nonlinear relationship between discharge, q (m3/s), and time, t (s), there is a rapid reduction in q up to t (≤16 h), which becomes almost constant after attaining steady-state flow and complete saturation. The q linearly increases with an increase in fp and follows Darcy’s law; however, q significantly decreases with an incremental change in σ3. Further, a nonlinear relationship exists between k and σeff. The percentage variation in qavg with changes in fp (=40–80 kPa and 80–120 kPa) corresponding to σ3 (=200 kPa) is about 50% and 70%. respectively. There is less change (5%) in qavg, corresponding to incremental change in σ3 from 100 to 200 kPa; however, the change is quite significant and rapid (about 28%) on an increase in σ3 from 200 to 300 kPa. Further, slow or negligible change can be observed beyond σ3 (=300 kPa). This research highlights the significance of σ3 over fp on the behavior of fluid flow through fine-grained soil and demarcates the flow boundaries, namely unsteady-state, critical-state, and steady-state flows, specific to unsaturated or partially saturated clayey–sandy–silty soil. The research provides quantitative assessment of the behavior of fluid flow through fine-grained soil under varying confining stress and fluid flow pressure conditions, which may be valuable in optimizing the design and construction of any civil or geoengineering projects especially where the depth of construction has significance. The research clearly highlights the flow boundaries, namely unsteady-state, critical-state, and steady-state flow boundaries, specific to unsaturated or partially saturated clayey–sandy–silty soil and provides the relationship among discharge, time, confining stress, and fluid flow pressure, which may assist in developing accurate predictive models to investigate fluid flow through fine-grained soil.