The northern slope of the Orvieto hill (Central Italy) is affected by slow intermittent movements within the overconsolidated clays at depth and in the overlying debris cover. Inclinometer and piezometer (Casagrande) measures show that reactivations are rainfall-induced. This encourages the interest in a predictive seepage model which allows to evaluate rainfall conditions determining pore pressure threshold for reactivation. Since the low permeability of the materials raised doubts on the correlations between piezometer and rainfall data, new boreholes were instrumented with vibrating wire cells. Their time histories are compared to those of Casagrande piezometers and the applicability of the two instruments is discussed. Finally, results of a preliminary model are presented, comparing calculated and measured time series of pore pressure in the shal-lower portion of the slope
