Hydrogeological impact assessment by tunnelling at sites of high sensitivity

A tunnel for the High Speed Train (HST) was constructed in Barcelona with an Earth Pressure Balance (EPB) Tunnel Boring Machine (TBM). The tunnel crosses Barcelona and passes under some famous landmarks such as the Sagrada Familia and the Casa Mill Both monuments are UNESCO world heritage sites and a committee appointed by the UNESCO acted as external observers during the construction. Concerns about soil settlements and the hydrogeological impacts of the construction were raised. These concerns were addressed during the design stage to forestall any unexpected events. The methodology consisted of 1) characterising the geology in detail, 2) predicting the impacts caused in the aquifer, 3) predicting the soil displacements due to water table oscillations produced by the construction, and 4) monitoring the evolution of groundwater and soil settlements. The main estimated impact on groundwater was a moderate barrier effect. The barrier effect, the magnitude of which matched the predictions, was detected during construction. The monitoring of soil settlements revealed short and long term movements. The latter movements matched the analytical predictions of soil displacements caused by the groundwater oscillations. This paper proposes a realistic procedure to estimate impacts on groundwater during tunnel construction with an EPB. Our methodology will considerably improve the construction of tunnels in urban areas. (C) 2015 Elsevier B.V. All rights reserved.Peer ReviewedPostprint (author's final draft

Impactos hidrogeologicos causados por la construccion del AVE en el entorno de la Sagrada Familia (Barcelona)

El tunel del AVE que atraviesa Barcelona fue construido con una tuneladora tipo EPB. El trazado del túnel pasa bajo la Sagrada Familia (declarada patrimonio de la humanidad por la UNESCO), y debido a los riesgos que entrañaba la construcción, un comité designado por la UNESCO actuó como observador externo durante la excavación del túnel. Las dos principales preocupaciones era los movimientos del suelo producidos por la construcción y los impactos causados por la obra sobre el acuífero. Ambas se tuvieron en cuenta durante la fase de diseño del túnel para evitar eventos inesperados durante la construcciónPostprint (published version

Impactos hidrogeologicos causados por la construccion del AVE en el entorno de la Sagrada Familia (Barcelona)

El tunel del AVE que atraviesa Barcelona fue construido con una tuneladora tipo EPB. El trazado del túnel pasa bajo la Sagrada Familia (declarada patrimonio de la humanidad por la UNESCO), y debido a los riesgos que entrañaba la construcción, un comité designado por la UNESCO actuó como observador externo durante la excavación del túnel. Las dos principales preocupaciones era los movimientos del suelo producidos por la construcción y los impactos causados por la obra sobre el acuífero. Ambas se tuvieron en cuenta durante la fase de diseño del túnel para evitar eventos inesperados durante la construcció

Sm-Nd isotope whole rock and garnet from the Southwestern Grenvillian Oaxacan Complex, Mexico: a review of garnet closure temperature and structural implications

The Oaxacan Complex represents the largest outcrop of late Mesoproterozoic age, granulite-facies metamorphic rocks in Mexico. The southwestern Oaxacan Complex was studied using the Sm-Nd isotopic system in whole-rocks and garnets. The use of garnet for dating granulites is a good approach because garnet is usually a rock-forming mineral in this facies, it strongly prefers heavy over light rare earth elements, and its closure temperature is close to the range of the granulite facies. Since the studied garnets display resorbed borders, they are interpreted as pre- or syn- Grenvillian-age granulitic peak. Their closure temperatures, calculated using the Dodson equation and the Nd diffusion coefficients, are 720–770ºC (5– 30ºC/my). The whole-rock Sm-Nd evolution lines intersect the depleted mantle model at ca. 1.4–1.7 Ga, although two paraderivate samples intersect at 2.1–2.2 Ga, suggesting a protolith from an older continental crust. In nearby outcrops, Sm-Nd isochron garnet-whole rock ages follow a certain NW-SE trend, displaying two hypothetical age groups: old ages (954–976 Ma) and young ages (907–920 Ma). The younger age garnet's group display Ti and LREE-MREE rim enrichments with respect to their cores that imply diffusional resetting processes. Folding and faulting structures suggest that these two age groups correspond to different structural levels during the early cooling history of the Oaxacan Complex.The Oaxacan Complex represents the largest outcrop of late Mesoproterozoic age, granulite-facies metamorphic rocks in Mexico. The southwestern Oaxacan Complex was studied using the Sm-Nd isotopic system in whole-rocks and garnets. The use of garnet for dating granulites is a good approach because garnet is usually a rock-forming mineral in this facies, it strongly prefers heavy over light rare earth elements, and its closure temperature is close to the range of the granulite facies. Since the studied garnets display resorbed borders, they are interpreted as pre- or syn- Grenvillian-age granulitic peak. Their closure temperatures, calculated using the Dodson equation and the Nd diffusion coefficients, are 720–770ºC (5– 30ºC/my). The whole-rock Sm-Nd evolution lines intersect the depleted mantle model at ca. 1.4–1.7 Ga, although two paraderivate samples intersect at 2.1–2.2 Ga, suggesting a protolith from an older continental crust. In nearby outcrops, Sm-Nd isochron garnet-whole rock ages follow a certain NW-SE trend, displaying two hypothetical age groups: old ages (954–976 Ma) and young ages (907–920 Ma). The younger age garnet's group display Ti and LREE-MREE rim enrichments with respect to their cores that imply diffusional resetting processes. Folding and faulting structures suggest that these two age groups correspond to different structural levels during the early cooling history of the Oaxacan Complex.The Oaxacan Complex represents the largest outcrop of late Mesoproterozoic age, granulite-facies metamorphic rocks in Mexico. The southwestern Oaxacan Complex was studied using the Sm-Nd isotopic system in whole-rocks and garnets. The use of garnet for dating granulites is a good approach because garnet is usually a rock-forming mineral in this facies, it strongly prefers heavy over light rare earth elements, and its closure temperature is close to the range of the granulite facies. Since the studied garnets display resorbed borders, they are interpreted as pre- or syn- Grenvillian-age granulitic peak. Their closure temperatures, calculated using the Dodson equation and the Nd diffusion coefficients, are 720–770ºC (5– 30ºC/my). The whole-rock Sm-Nd evolution lines intersect the depleted mantle model at ca. 1.4–1.7 Ga, although two paraderivate samples intersect at 2.1–2.2 Ga, suggesting a protolith from an older continental crust. In nearby outcrops, Sm-Nd isochron garnet-whole rock ages follow a certain NW-SE trend, displaying two hypothetical age groups: old ages (954–976 Ma) and young ages (907–920 Ma). The younger age garnet's group display Ti and LREE-MREE rim enrichments with respect to their cores that imply diffusional resetting processes. Folding and faulting structures suggest that these two age groups correspond to different structural levels during the early cooling history of the Oaxacan Complex