High permeability sand/gravel trenches surrounding utility pipes are deemed to create preferential pathways for water in the subsurface of urban environments. Although this can be true when both trench filling material and surrounding soils are fully water saturated, the same is not obvious in the unsaturated zone. This study explores the behavior of these anthropogenic features in the unsaturated zone and their role in the formation of the urban karst with specific interest to the fate of water leaked from utility pipelines and its potential to affect urban aquifers. A series of 3D steady state numerical simulations was performed assuming two groups of nearby utility trenches hosting a water pipeline, up to 6 concurrent leaks, different leak rates, native soil properties, slopes of the utility trenches, and initial water saturation profiles. The analysis showed that utility trenches in the unsaturated zone are more likely an obstacle to water flow originated from leaking water utilities. Indeed, they served as capillary barriers rather than sinks in the simulations, although with a limited diversion capacity. Nevertheless, a pronounced lateral spreading of leaked water within the trenches was predicted in some scenarios, which suggests that there is still potential for the urban karst effect to occur when native soil properties are not that far from those of the trench filling material, although high initial effective water saturations would be required in this case.

Utility trenches: sinks or barriers? Modeling the fate of leaked water in a crowded subsurface

Andrea D'Aniello
Primo
;
Luigi Cimorelli
Secondo
;
Domenico Pianese
Ultimo
2022

Abstract

High permeability sand/gravel trenches surrounding utility pipes are deemed to create preferential pathways for water in the subsurface of urban environments. Although this can be true when both trench filling material and surrounding soils are fully water saturated, the same is not obvious in the unsaturated zone. This study explores the behavior of these anthropogenic features in the unsaturated zone and their role in the formation of the urban karst with specific interest to the fate of water leaked from utility pipelines and its potential to affect urban aquifers. A series of 3D steady state numerical simulations was performed assuming two groups of nearby utility trenches hosting a water pipeline, up to 6 concurrent leaks, different leak rates, native soil properties, slopes of the utility trenches, and initial water saturation profiles. The analysis showed that utility trenches in the unsaturated zone are more likely an obstacle to water flow originated from leaking water utilities. Indeed, they served as capillary barriers rather than sinks in the simulations, although with a limited diversion capacity. Nevertheless, a pronounced lateral spreading of leaked water within the trenches was predicted in some scenarios, which suggests that there is still potential for the urban karst effect to occur when native soil properties are not that far from those of the trench filling material, although high initial effective water saturations would be required in this case.
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Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/11588/893004
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