The knowledge of flow and transport phenomena in fractured rocks is very important in hydrogeologic engineering in order to optimize clean up and monitoring strategies, to carry out risk assessment and to manage interventions in aquifers. Recently, understanding, characterizing and modeling physical and chemical interactions within fractured aquifers has acquired increasing importance, especially with regard to the question of water resources development and groundwater contamination. Sometimes the equivalent porous medium approach fails to reproduce flow and transport patterns in such complex geological formations. Critical emerging issues for fractured aquifers are the validity of the Darcian-type “local cubic law” which assumes a linear relationship between flow rate and pressure gradient to accurately describe flow patterns and of the classical advection-dispersion equation to describe the propagation of solute. Most studies of transport through discrete fractures are still based on simpler flow models which has limited the interpretation of solute breakthrough curves. Experimental data obtained under controlled conditions such as in a laboratory allow to increase the understanding of the fundamental physics of fluid flow and solute transport in fractures. In this study hydraulic and tracer tests on artificially created fractured rock samples of parallelepiped (0.60×0.40×0.8m) shape have been carried out. The volumes of water passing through different paths across the fractured sample for various hydraulic head differences and breakthrough curves for saline tracer pulse across different pathways have been measured. The above experiments are aimed at understanding the relations existing between the applied boundary conditions, the geometry of the system and the occurring flow and transport phenomena. The experimental results have shown evidence of non linearity in flow and concentration profiles that cannot be described by conventional solute transport models. In fact, the classical advection-dispersion equation -used as a benchmark for comparison in a numerical model- poorly describes the experimental breakthrough curves of the tracer propagation. A comparative analysis of the obtained results has allowed to study the behavior of flow and transport in the investigated medium on the one hand, and to evaluate possible improvements to the experimental setup on the other.

La conoscenza dei fenomeni di flusso e trasporto nelle rocce fratturate è molto importante al fine di ottimizzare strategie di bonifica e di monitoraggio, effettuare analisi di rischio e gestire convenientemente le risorse idriche di tali acquiferi. Recentemente sia la comprensione delle modalità di circolazione delle acque sia la caratterizzazione e modellazione delle interazioni fisico-chimiche all’interno di acquiferi fratturati stanno acquisendo sempre più importanza, specialmente per la necessità di pervenire ad una corretta gestione delle risorse idriche o anche per implementare corrette strategie di monitoraggio, o per garantire la qualità delle stesse, sia in termini di prevenzione da possibili inquinamenti che di recupero nel caso di contaminazione in atto. Talvolta l’ approccio del mezzo poroso equivalente non è in grado di riprodurre le condizioni di flusso e trasporto in tali complesse formazioni. Questioni critiche emergenti per gli acquiferi fratturati sono: la validità della “legge cubica locale” che assume una relazione lineare tra portata e gradiente idraulico (legge di Darcy), nel caso si voglia descrivere con precisione le condizioni di flusso; l’uso dell’equazione classica di advezione-dispersione ove si voglia descrivere la propagazione del soluto. La maggior parte degli studi sul trasporto attraverso fratture discrete sono tuttora basati su modelli di flusso molto semplici, cosa che ha limitato l’ interpretazione delle curve di avanzamento (breakthrough curve) del soluto. I dati sperimentali ottenuti sotto condizioni controllate come quelle di laboratorio permettono di migliorare la comprensione delle fisiche fondamentali del flusso di falda e del trasporto di contaminante nelle fratture. In questo studio sono state effettuate prove idrauliche e di tracciamento su un campione di roccia fratturata di forma parallelepipeda (0.60×0.40×0.8m) creato artificialmente. Sono stati misurati i volumi di acqua passanti attraverso differenti percorsi attraverso il campione fratturato per varie differenze di carico idraulico; inoltre sono state misurate le curve di avanzamento relative ad un tracciante salino immesso ad impulso per vari percorsi. I suddetti esperimenti sono finalizzati a comprendere le relazioni esistenti tra le condizioni al contorno applicate, la geometria del sistema ed i fenomeni di flusso e trasporto in atto. I risultati sperimentali hanno mostrato evidenza di non linearità nel flusso e profili di concentrazione che non possono essere descritti da modelli di trasporto di soluto tradizionali.Infatti, la classica equazione di advezione-dispersione, usata come benchmark per confronto in un modello numerico, non descrive in maniera sufficientemente accurata le curve sperimentali relative alla propagazione del tracciante. Un’ analisi comparativa dei risultati ha permesso da una parte di studiare il comportamento del flusso e del trasporto nel mezzo indagato e dall’ altra di valutare possibili miglioramenti al setup sperimentale.

A laboratory physical model to analyse flow and transport processes in a fractured rock sample at bench scale level / Cherubini, C.; Giasi, Concetta Immacolata; Pastore, Nicola. - In: ITALIAN JOURNAL OF ENGINEERING GEOLOGY AND ENVIRONMENT. - ISSN 1825-6635. - STAMPA. - 2013:1(2013), pp. 19-32. [10.4408/IJEGE.2013-01.O-02]

A laboratory physical model to analyse flow and transport processes in a fractured rock sample at bench scale level

GIASI, Concetta Immacolata;PASTORE, Nicola
2013-01-01

Abstract

The knowledge of flow and transport phenomena in fractured rocks is very important in hydrogeologic engineering in order to optimize clean up and monitoring strategies, to carry out risk assessment and to manage interventions in aquifers. Recently, understanding, characterizing and modeling physical and chemical interactions within fractured aquifers has acquired increasing importance, especially with regard to the question of water resources development and groundwater contamination. Sometimes the equivalent porous medium approach fails to reproduce flow and transport patterns in such complex geological formations. Critical emerging issues for fractured aquifers are the validity of the Darcian-type “local cubic law” which assumes a linear relationship between flow rate and pressure gradient to accurately describe flow patterns and of the classical advection-dispersion equation to describe the propagation of solute. Most studies of transport through discrete fractures are still based on simpler flow models which has limited the interpretation of solute breakthrough curves. Experimental data obtained under controlled conditions such as in a laboratory allow to increase the understanding of the fundamental physics of fluid flow and solute transport in fractures. In this study hydraulic and tracer tests on artificially created fractured rock samples of parallelepiped (0.60×0.40×0.8m) shape have been carried out. The volumes of water passing through different paths across the fractured sample for various hydraulic head differences and breakthrough curves for saline tracer pulse across different pathways have been measured. The above experiments are aimed at understanding the relations existing between the applied boundary conditions, the geometry of the system and the occurring flow and transport phenomena. The experimental results have shown evidence of non linearity in flow and concentration profiles that cannot be described by conventional solute transport models. In fact, the classical advection-dispersion equation -used as a benchmark for comparison in a numerical model- poorly describes the experimental breakthrough curves of the tracer propagation. A comparative analysis of the obtained results has allowed to study the behavior of flow and transport in the investigated medium on the one hand, and to evaluate possible improvements to the experimental setup on the other.
2013
A laboratory physical model to analyse flow and transport processes in a fractured rock sample at bench scale level / Cherubini, C.; Giasi, Concetta Immacolata; Pastore, Nicola. - In: ITALIAN JOURNAL OF ENGINEERING GEOLOGY AND ENVIRONMENT. - ISSN 1825-6635. - STAMPA. - 2013:1(2013), pp. 19-32. [10.4408/IJEGE.2013-01.O-02]
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11589/1033
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