A Device for the Simultaneous Determination of the Water Retention Properties and the Hydraulic Conductivity Function of an Unsaturated Coarse Material; Application to a Green-Roof Volcanic Substrate

The determination of the water retention curve (WRC) and hydraulic conductivity function (HCF) of a specific volcanic coarse granular material used as a substrate for urban green roofs in Europe was carried out on a newly developed specific device in which low suctions, typical of coarse granular materials, were controlled. Smaller suctions (up to 32 kPa) were imposed by using a hanging column system, and larger suctions (between 32 and 50 kPa) were imposed by using the axis translation technique in the same cell. The changes in suction during the tests were monitored by using a high accuracy differential pressure transducer. They were also used to determine the HCF by means of both Kunze and Kirkham’s and Gardner’s methods. The former technique was used at low suctions (