USE OF ELECTRIC TRANSDUCERS FOR CONTINUOUS MONITORING OF GROUNDWATER LEVEL VARIATIONS IN A LANDSLIDE AREA

This paper concerns the instability processes of peri-urban slopes in Caramanico Terme, a hilltop town located in the Apennine Mountains of the Abruzzi region (central Italy). The Caramanico area is characterised by a long record of historical landsliding typical of a high mountainous setting subjected to a relatively high average rainfall and seismic activity. Furthermore, there are indications that 20th century human alterations to the local environment have resulted in an increase of landslide activity. So the causes of the slope instability seem to be related to the interaction of climatic, human and seismic factors. However, most of the recent landslides and slope deformations seem to have been triggered by long periods of high precipitation. Following previous landslide surveys and a careful evaluation of slope movements case records, we argue that a systematic and periodic monitoring of both ground deformation and causal factors of instability using integrated ground based techniques, including subsurface monitoring, GPS surveys and EO based techniques, is necessary to advance understanding of such recurrent landslide hazards. In particular, in order to gain some more insight on local groundwater level and pore water pressure variations, two sites have been investigated: Case Pastore and Case Mancini. In the first one, which is the upslope area of an active landslide, a borehole was instrumented with an open pipe piezometer equipped with an electric transducer (48 m depth) in order to investigate groundwater table variations within a 47 m thick limestone megabreccia caprock. An electric piezometer was also installed in the same borehole at 52 m depth to monitor pore water pressure changes within the uppermost weathered part of the mudstone substratum below the caprock. In the second one, located within an apparently inactive deep-seated landslide, a borehole was equipped with a Casagrande piezometer logging by means of an electric transducer. The cell was positioned at 14 m depth to measure groundwater pressures in remoulded landslide material. All the instruments are recording in continuous with an acquisition timestep of 6 hours and the data are transmitted to data-loggers located at ground surface. The initial data suggests that systematic groundwater field control may give useful informations for identifying those areas which may be most susceptible to future landsliding. This paper mainly concentrates on the functioning of the various sensors of the described piezometers within the different lythotypes and soil conditions and on their response to the variations of the slope boundary conditions in terms of time lag and reliability.