Centrifuge modelling of capillary rise

This paper reports results from centrifuge tests designed to investigate ca pillary rise in soils subjected to different gravitational fields. The expe rimental programme is part of the EU-funded NECER project (Network of Europ ean Centrifuges for Environmental Geotechnic Research), whose objective is to investigate the appropriateness of geotechnical centrifuge modelling for the investigation of geoenvironmental problems, particularly with referenc e to partially saturated soils. The tests were performed at the geotechnica l centrifuge laboratories of Cardiff. Bochum. Manchester, and LCPC in Nante s. The aim was to determine the scaling laws of capillary rise under both e quilibrium and transient conditions. In all laboratories, column wetting tests in fine poorly graded sands (Cong leton Sand, Bochum Normsand, HPF5 Sand, and Fontaineblau Sand) were perform ed. Capillary rise above the phreatic surface of the sand model was disting uished in a continuous capillary zone (completely saturated) and a disconti nuous capillary zone (partially saturated). The Cardiff Geotechnical Centrifuge Laboratory used matrix potential probes to follow the capillary rise of the continuous zone and, therefore, determ ine the suction above the phreatic zone during centrifuge testing. Ar Bochu m, two cameras were used for optical and volumetric measurements, in order to follow the rise of the visible wetting front (upper limit of discontinuo us zone) in the sand within the sample column. At Manchester. the movement of the wetting front was observed by video cameras over periods up to 8 h, whereas in LCPC pore pressure transducers recorded the changes in pressure caused by capillarity. A simple centrifuge similitude law for capillary rise in these sands has be en established and the kinetic phenomena have been measured as a function o f the gravitational field. The results from these experiments verify that b oth the continuous and discontinuous capillary zones are scaled at a factor 1/N whereas the time for rise seems to be scaled at a factor 1/N-2. This r esearch suggests that capillary phenomena can be modelled using a geotechni cal centrifuge. Therefore, centrifuge testing can be a useful tool for futu re modelling of boundary value problems involving complex transport phenome na. (C) 2001 Elsevier Science B.V. All rights reserved.