Evaluating the Reference Geological Model (RGM) is crucial during the design and construction of underground tunnels. It enables accurate assessment of technical and financial risks, as well as environmental hazards that may arise from potential interactions between underground works and water resources, such as water tables, lakes, or springs. In contrast, inaccurate geological forecasts may compromise the tunnelling project, even if it is impossible to eliminate all uncertainties affecting geological models. This paper focuses on the geological model drafted for the Abatemarco underground tunnel project. The project consisted of excavating a 6.270 km-long tunnel, through the Coastal Range (Calabria, Southern Italy), to capture two springs (Favata and Nascejume springs) capable of furnishing a water flow rate of 200 l/s to Cosenza settlement and 25 neighbouring municipalities located at a distance of 70 km from the tunnel. The latter is located at an altitude of 622 m on the Coastal Range east flank and 657 m on the west flank, crossing the central portion of the Mula massif with a N140° direction. The excavation works began in November 1979 and were completed in December 1982. The project planned excavation works without water inflow, as it involved mainly impermeable phyllite rocks and a small portion of carbonate rocks, both part of the sedimentary succession of the S. Donato Unit (Ietto & Barillaro, 1993). The S. Donato Unit, Triassic in age, consists of three main intervals in stratigraphic contact (Barca et al., 2010): 1) Basal Terrigenous Complex, made up of siliciclastic sediments (phyllites) with limestone intercalation; 2) Intermediate Carbonate Complex, consisting of a shelf margin limestone sequence; 3) Upper Marly Dolomitic Complex, characterised by a dolomitic succession. Contrary to the original geological model, abundant water flows were recorded at 1500 m of excavation. The water flow reached up to 874 l/s with a pressure of 12 atm, ultimately stabilising at a flow rate of approximately 500 l/s. Consequently, the tunnel project was modified from a water transport tunnel to a drainage tunnel. A latest detailed geological field survey, coupled with the analysis of data collected during the tunnel excavation phases, led to the development of a new geological model. The model reveals the existence of a monocline fold, not recognised within the original geological model. The fold structure has an axis in the N120° direction, dips to the NE, and consists of carbonate rocks and phyllites that form the core of the fold structure. Consequently, the abundant water flows in the carbonate rocks, recorded during the excavation works, were due to water circulation within the reverse flank of the fold structure, forming a confined aquifer with phyllite rocks at the top. This case study emphasises the importance of an accurate Geological Model in engineering projects to identify and manage excavation risks while reducing costs.
The importance of a Reference Geological Model in underground tunnel construction: the Abatemarco water pipeline case study (Cosenza, Southern Italy)
Ietto F
2025-01-01
Abstract
Evaluating the Reference Geological Model (RGM) is crucial during the design and construction of underground tunnels. It enables accurate assessment of technical and financial risks, as well as environmental hazards that may arise from potential interactions between underground works and water resources, such as water tables, lakes, or springs. In contrast, inaccurate geological forecasts may compromise the tunnelling project, even if it is impossible to eliminate all uncertainties affecting geological models. This paper focuses on the geological model drafted for the Abatemarco underground tunnel project. The project consisted of excavating a 6.270 km-long tunnel, through the Coastal Range (Calabria, Southern Italy), to capture two springs (Favata and Nascejume springs) capable of furnishing a water flow rate of 200 l/s to Cosenza settlement and 25 neighbouring municipalities located at a distance of 70 km from the tunnel. The latter is located at an altitude of 622 m on the Coastal Range east flank and 657 m on the west flank, crossing the central portion of the Mula massif with a N140° direction. The excavation works began in November 1979 and were completed in December 1982. The project planned excavation works without water inflow, as it involved mainly impermeable phyllite rocks and a small portion of carbonate rocks, both part of the sedimentary succession of the S. Donato Unit (Ietto & Barillaro, 1993). The S. Donato Unit, Triassic in age, consists of three main intervals in stratigraphic contact (Barca et al., 2010): 1) Basal Terrigenous Complex, made up of siliciclastic sediments (phyllites) with limestone intercalation; 2) Intermediate Carbonate Complex, consisting of a shelf margin limestone sequence; 3) Upper Marly Dolomitic Complex, characterised by a dolomitic succession. Contrary to the original geological model, abundant water flows were recorded at 1500 m of excavation. The water flow reached up to 874 l/s with a pressure of 12 atm, ultimately stabilising at a flow rate of approximately 500 l/s. Consequently, the tunnel project was modified from a water transport tunnel to a drainage tunnel. A latest detailed geological field survey, coupled with the analysis of data collected during the tunnel excavation phases, led to the development of a new geological model. The model reveals the existence of a monocline fold, not recognised within the original geological model. The fold structure has an axis in the N120° direction, dips to the NE, and consists of carbonate rocks and phyllites that form the core of the fold structure. Consequently, the abundant water flows in the carbonate rocks, recorded during the excavation works, were due to water circulation within the reverse flank of the fold structure, forming a confined aquifer with phyllite rocks at the top. This case study emphasises the importance of an accurate Geological Model in engineering projects to identify and manage excavation risks while reducing costs.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
