The new quarrying techniques and the reject stone recovery system induce new geomorphological hazard scenarios in the Carrara Marble Basin. This work analyses the recent landsli des and debris flows occurred in the Marble Basins, stressing their relationships with the quarrying activity. In the open space quarries, the progressive lowering of the working base level determines the formation of steep and high (more than 100 m) slopes carved in densely fractured rocks. In correspondence of these cliffs, several landslides occurred in the last years, in some cases mobilizing more than 30,000 m3 of rock. The triggering causes were the rainfall hourly intensity (even 60 mmllh) and the antecedent rainfal is (up to 80 mm in the 34 antecedent hours). The main land slides kinematic analysis highlighted that they are a structu ral collapse of high rocky bench, with rupture phenomena at the base, differential slides and local toppling. As regard the quarry dump deposits (locally called ravaneti), the temporal evolution of quarrying techniques determined the overlapping along the slopes of two layers with different granulometric and permeability characteristics. The deepest layer, with multi-decimetres blocks and scarce fine matrix, corresponds to the typical ravaneto of the 1t29h0 centuries crossing period. The active surface ravaneto, with decimetres blocks and abundant fine matrix, is the consequence of the new diamond wire cutting methods, introduced in the ‘70s. Nowadays, fine material is added to the ravaneti also by the reject stones sieving, in order to produce C3.aCO In the last years, several debris flows affected the ravaneti. The rainfall recording analysis shows a relative low threshold for debris flows triggering, with events occurred with 60 mmJ5 h of rainfall and with a maximum intensity of only 14 mm/i h. The mobilization occurs by means of initial soil slip that, with a progressive fluidification, becomes a debris flow. The increased frequency of the events in the last years can be referred to fine material added to the ravaneti that forced the saturation processes. In the Carrara Marble Basins, the highest geomorphological hazards for the workers and the infrastructures are represen ted by the abandoned sub-vertical and densely fractured slo pes, and the increased concentration of fine fractions in the ravaneti, induced by the new quarrying techniques and the reject stone recovery.
Il rischio geomorfologico indotto dall’attività estrattiva nei bacini marmiferi apuani (Alpi Apuane, Toscana)
BARONI, CARLO;RIBOLINI, ADRIANO
2002-01-01
Abstract
The new quarrying techniques and the reject stone recovery system induce new geomorphological hazard scenarios in the Carrara Marble Basin. This work analyses the recent landsli des and debris flows occurred in the Marble Basins, stressing their relationships with the quarrying activity. In the open space quarries, the progressive lowering of the working base level determines the formation of steep and high (more than 100 m) slopes carved in densely fractured rocks. In correspondence of these cliffs, several landslides occurred in the last years, in some cases mobilizing more than 30,000 m3 of rock. The triggering causes were the rainfall hourly intensity (even 60 mmllh) and the antecedent rainfal is (up to 80 mm in the 34 antecedent hours). The main land slides kinematic analysis highlighted that they are a structu ral collapse of high rocky bench, with rupture phenomena at the base, differential slides and local toppling. As regard the quarry dump deposits (locally called ravaneti), the temporal evolution of quarrying techniques determined the overlapping along the slopes of two layers with different granulometric and permeability characteristics. The deepest layer, with multi-decimetres blocks and scarce fine matrix, corresponds to the typical ravaneto of the 1t29h0 centuries crossing period. The active surface ravaneto, with decimetres blocks and abundant fine matrix, is the consequence of the new diamond wire cutting methods, introduced in the ‘70s. Nowadays, fine material is added to the ravaneti also by the reject stones sieving, in order to produce C3.aCO In the last years, several debris flows affected the ravaneti. The rainfall recording analysis shows a relative low threshold for debris flows triggering, with events occurred with 60 mmJ5 h of rainfall and with a maximum intensity of only 14 mm/i h. The mobilization occurs by means of initial soil slip that, with a progressive fluidification, becomes a debris flow. The increased frequency of the events in the last years can be referred to fine material added to the ravaneti that forced the saturation processes. In the Carrara Marble Basins, the highest geomorphological hazards for the workers and the infrastructures are represen ted by the abandoned sub-vertical and densely fractured slo pes, and the increased concentration of fine fractions in the ravaneti, induced by the new quarrying techniques and the reject stone recovery.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
