A GIS based mass flow model was used to simulate debris flow triggering and evolution: a saturated/unsaturated soil water model was used to simulate the distribution of soil water and the generation of excess pore pressure leading to slope instability during a rainfall event. The model is able to detect potential instability due both to the development of a perched watertable at the colluvium/bedrock interface, and to the development of a saturated top layer because of the direct infiltration of rainfall during an intense event. Stability conditions are evaluated at the bottom of the saturated zones, i.e. at the wetting front and at the soil-rock contact. The safety factor, ratio of stabilizing forces or shear strength to destabilizing forces or shear stress, is calculated assuming the infinite slope model. The geotechnical parameters c' and phi can be introduced with uncertainty (mean value and variance); confidence intervals are calculated using a first order second moment (FOSM) method. This also allows to the estimate the failure probabilities. A flow routing model is then used to simulate the spreading and deposition of the mud/debris mixture on the hillslopes: once a landslide has been predicted, the location and released volume are used as inputs to a second model to simulate the spreading of the debris on the hillslope. The dynamic model has been built with PCRaster Software, based on the Bingham rheological expression. This model is applied to simulate the debris flow triggering and evolution in the Cardoso Torrent basin (Upper Versilia, NW Tuscany - Italy), where an extremely heavy rainstorm (about 500 mm within 12 hours) hit some restricted areas on June 19th, 1996, involving a few basins of the Versilia and Garfagnana areas and inducing various effects on the slopes (soil slips and debris flows). A large number of data is available thanks to detailed surveys, which provided the characterization of the main factors (pluviometric, hydrogeological, geological, geomorphological and geotechnical) contributing to the landslide triggering. In particular, some factors were recurrent in the landslide sites: bedrock features (impermeable bedrock, discontinuity dipping downslope), slope morphology (hollow shape), geotechnical characteristics (fine, scarcely permeable cover material).
Modelling the initiation and runout of rainfall induced debris flows in the Cardoso basin (Apuan Alps, Italy)
GIANNECCHINI, ROBERTO;D'AMATO AVANZI, GIACOMO ALFREDO;PUCCINELLI, ALBERTO
2005-01-01
Abstract
A GIS based mass flow model was used to simulate debris flow triggering and evolution: a saturated/unsaturated soil water model was used to simulate the distribution of soil water and the generation of excess pore pressure leading to slope instability during a rainfall event. The model is able to detect potential instability due both to the development of a perched watertable at the colluvium/bedrock interface, and to the development of a saturated top layer because of the direct infiltration of rainfall during an intense event. Stability conditions are evaluated at the bottom of the saturated zones, i.e. at the wetting front and at the soil-rock contact. The safety factor, ratio of stabilizing forces or shear strength to destabilizing forces or shear stress, is calculated assuming the infinite slope model. The geotechnical parameters c' and phi can be introduced with uncertainty (mean value and variance); confidence intervals are calculated using a first order second moment (FOSM) method. This also allows to the estimate the failure probabilities. A flow routing model is then used to simulate the spreading and deposition of the mud/debris mixture on the hillslopes: once a landslide has been predicted, the location and released volume are used as inputs to a second model to simulate the spreading of the debris on the hillslope. The dynamic model has been built with PCRaster Software, based on the Bingham rheological expression. This model is applied to simulate the debris flow triggering and evolution in the Cardoso Torrent basin (Upper Versilia, NW Tuscany - Italy), where an extremely heavy rainstorm (about 500 mm within 12 hours) hit some restricted areas on June 19th, 1996, involving a few basins of the Versilia and Garfagnana areas and inducing various effects on the slopes (soil slips and debris flows). A large number of data is available thanks to detailed surveys, which provided the characterization of the main factors (pluviometric, hydrogeological, geological, geomorphological and geotechnical) contributing to the landslide triggering. In particular, some factors were recurrent in the landslide sites: bedrock features (impermeable bedrock, discontinuity dipping downslope), slope morphology (hollow shape), geotechnical characteristics (fine, scarcely permeable cover material).I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
