Field verification tests of the newly developed flow cone tool—In-situ measurements of hydraulic soil properties

Abstract

Hydraulic soil properties, and in particular the hydraulic conductivity, is important in a number of geotechnical design cases. However, attention is often drawn towards the method of analysis rather than the quality and validity of the hydraulic properties used as input. Intact samples of sand or silt are difficult or impossible to obtain, and prediction of hydraulic soil properties from available in-situ tools represents a challenge. With the aim of quick and reliable in-situ measurements of hydraulic properties of sands and silts, NGI developed a prototype tool referred to as the flow cone. The tool combines the widely used cone penetration test with an add-on pumping system that allows water to flow into the surrounding sediments during cone penetration and stand-still. By measuring flow rates and pore water pressures, the hydraulic properties of the surrounding soil can be estimated. The flow cone prototype was tested at the NGTS sand site (Øysand, Norway) in September 2018. The aim of this paper is to present the measured and interpreted results. The results are evaluated within the context of available data from the sand site including cone penetration tests, in-situ falling head tests, grain size distributions and constant head tests from laboratory. Recommendations for further work and potential applications in engineering practice are discussed.

Keywords

• hydraulic conductivity
• hydraulic fracturing
• sand
• silt
• ngts sand site
• cptu