Underground Excavations Below the Water Table by the Cut-and-Cover Method

Most underground constructions, which are needed to improve mobility and increase available space in urban areas, require excavations that are usually deeper than the water table (e.g., for the construction of stations or underground parking lots). A frequently used technique to develop excavations under these conditions consists in combining the cut-and-cover method with a dewatering system based on deep pumping wells. Retaining walls used for the cut-and-cover method allow excavating between vertical walls and minimizes the inflow of groundwater, while deep pumping wells provide dry and stable conditions. Despite this technique is widely used, some aspects related with the presence of groundwater must be considered to avoid accidents. Dewatering systems must be properly designed to guarantee suitable conditions and to minimize the pumping settlements outside of the working area. In addition, it is required to assess the presence of defects in the retaining walls because the flow of groundwater through them may entail negative consequences. This chapter explains procedures (i) to design efficient dewatering systems considering the working conditions, the stability and the impacts generated in the vicinity of the construction, and (ii) to evaluate the state of the retaining walls by using hydrogeological tools

Parametric assessment of hydrochemical changes associated to underground pumped hydropower storage

Underground pumped hydropower storage (UPHS) using abandoned mines is an alternative to store and produce electricity in flat regions. Excess of electricity is stored in form of potential energy by pumping mine water to a surface reservoir. When the demand of electricity increases, water is discharged into the mine (i.e., underground reservoir) through turbines producing electricity. During the complete operational process of UPHS plants, hydrochemical characteristics of water evolve continuously to be in equilibrium successively with the atmosphere (in the surface reservoir) and the surrounding porousmedium (in the underground reservoir). It may lead to precipitation and/or dissolution of minerals and their associated consequences, such as pH variations. Induced hydrochemical changes may have an impact on the environment and/or the efficiency (e.g., corrosions and incrustations affect facilities) of UPHS plants. The nature of the hydrochemical changes is controlled by the specific chemical characteristics of the surrounding porous medium. However, the magnitude of the changes also depends on other variables, such as hydraulic parameters. The role of these parameters is established to define screening criteria and improve the selection procedure of abandonedmines for constructing UPHS plants. This work evaluates the role of the main hydrogeological factors for three different chemical composition of the porous medium. Results are obtained by means of numerical reactive transport modeling. Potential impacts on the environment (mainly on groundwater and surface water bodies) and on the efficiency of the UPHS plants vary considerably from a hydraulic parameter to another showing the need for a detailed characterization before choosing locations of future UPHS plants.SMARTWATE

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

Ecological Sustainability Assessment of Water Distribution for the Maintenance of Ecosystems, their Services and Biodiversity

Water provision and distribution are subject to conflicts between users worldwide, with agriculture as a major driver of discords. Water sensitive ecosystems and their services are often impaired by man-made water shortage. Nevertheless, they are not sufficiently included in sustainability or risk assessments and neglected when it comes to distribution of available water resources. The herein presented contribution to the Sustainable Development Goals Clean Water and Sanitation (SDG 6) and Life on Land (SDG 15) is the Ecological Sustainability Assessment of Water distribution (ESAW-tool). The ESAW-tool introduces a watershed sustainability assessment that evaluates the sustainability of the water supply-demand ratio on basin level, where domestic water use and the water requirements of ecosystems are considered as most important water users. An ecological risk assessment estimates potential impacts of agricultural depletion of renewable water resources on (ground)water-dependent ecosystems. The ESAW-tool works in standard GIS applications and is applicable in basins worldwide with a set of broadly available input data. The ESAW-tool is tested in the Danube river basin through combination of high-resolution hydro-agroecological model data (hydrological land surface process model PROMET and groundwater model OpenGeoSys) and further freely available data (water use, biodiversity and wetlands maps). Based on the results, measures for more sustainable water management can be deduced, such as increase of rainfed agriculture near vulnerable ecosystems or change of certain crops. The tool can support decision making of authorities from local to national level as well as private enterprises who want to improve the sustainability of their supply chains. © 2022, The Author(s)

Drogas de abuso en las aguas subterráneas urbanas de Barcelona (España)

En este estudio se determinaron las concentraciones de drogas de abuso (DAS) y sus metabolitos en el agua subterránea urbana de Barcelona. Para este fin, se recogieron 37 muestras de aguas subterráneas en zonas urbanas y se analizaron 21 medicamentos incluyendo compuestos cocainicos, compuestos similares a la anfetamina, opioides, lisérgicos, cannabinoides y benzodiacepinas (con prescripción médica). Las mayores concentraciones en el agua subterránea (alrededor de 200 ng / L en SAP-4) y el mayor número de detectado el DAS se encuentran en zonas básicamente recargadas por un río que cruza la zona urbana recibe grandes cantidades de efluentes de plantas de tratamiento de aguas residuales (EDAR). En contraste, en el área urbana sin la influencia fluvial se encontraron concentraciones más bajas y un menor número de fármacos, lo que sugiere un origen local. De hecho, la cocaína y su metabolito fueron dominantes en los barrios más prósperos, mientras que el MDMA más barato era el fiscal dominante en los distritos más pobres. Las concentraciones medidas fueron siempre menores que los estimados a partir de la fracción de agua residual en las muestras de agua subterránea, lo que sugiere que el DAS se someten a procesos de eliminación, tanto en la reducción y condiciones oxidantes.This study is concerned with drugs of abuse (DAs) and their metabolites in Barcelona’s urban gr oundwater. To this end, 37 urban groundwater samples were collected and 21 drugs were analyzed including cocainics, amphetamine-like compounds, opioids, lysergics and cannabinoids and the prescribed drugs benzodiazepines. The highest groundwater concentrations (around 200 ng/L in SAP-4) and the largest number of detected DAs were found in zones basically recharged by a river that receives large amounts of effluents from waste water treatment plants (WWTPs). In contrast, the urbanized areas yielded lower concentrations and a smaller number of drugs, which suggests a local origin. In fact, cocaine and its metabolite were dominant in more prosperous neighbourhoods, whereas the cheaper MDMA was the dominant DA in poorer districts. Measured concentrations were consistently smaller than those estimated from the waste water fraction in groundwater samples, suggesting that DAs undergo removal processes in both reducing and oxidizing conditions.Universidad Nacional de La Plat

Towards the construction of representative regional hydro(geo)logical numerical models: Modelling the upper Danube basin as a starting point

Introduction: Pressure on groundwater resources is increasing rapidly by population growth and climate change effects. Thus, it is urgent to quantify their availability and determine their dynamics at a global scale to assess the impacts of climate change or anthropogenically induced pressure, and to support water management strategies. In this context, regional hydrogeological numerical models become essential to simulate the behavior of groundwater resources. However, the construction of global hydrogeological models faces a lot of challenges that affect their accuracy.Methods: In this work, using the German portion of the Upper Danube Basin (∼43,000 km2) we outline common challenges encountered in parameterizing a regional-scale groundwater model, and provide an innovative approach to efficiently tackle such challenges. The hydrogeological model of the Danube consists of the groundwater finite element code OpenGeoSys forced by the groundwater recharge of the surface hydrological model mHM.Results: The main novelties of the suggested approach are 1) the use of spectral analyses of the river baseflow and a steady state calibration taking as reference the topography to constraint the hydraulic parameters and facilitate the calibration process, and 2) the calibration of the hydraulic parameters for a transient state model by considering parameters derived from the piezometric head evolution.Discussion/conclusion: The results show that the proposed methodology is useful to build a reliable large-scale groundwater model. Finally, the suggested approach is compared with the standard one used by other authors for the construction of global models. The comparison shows that the proposed approach allows for obtaining more reliable results, especially in mountainous areas

Drenaje mediante bombeo vs. profundidad de muros pantalla en el control de los asientos del terreno durante excavaciones profundas

Las excavaciones profundas que afectan a acuíferos pueden ser realizadas mediante la combinación de métodos como son el drenaje por bombeo en pozos con la construcción previa de muros pantallas y excavación posterior (cut and cover method). Estos muros pantalla pueden ser continuos (pantallas de hormigón) o pilas de Jet-grouting. Los muros pantalla a menudo se alargan más de lo que es estructuralmente necesario, lo que disminuye el riesgo levantamiento de fondo de la excavación y así se reducen los asientos del terreno causados por la propia excavación y el drenaje, pero por el contrario, se incrementan mucho los costes de ejecución Se analizó la eficacia de impermeabilización de un recinto a excavar mediante pantallas de hormigón y pilas de jet-grouting en un terreno de sedimentos preconsolidados. Se ha aplicado a dos excavaciones de grandes pozos verticales (Shafts) durante la construcción del túnel del tren de alta velocidad en Barcelona situado junto a la Basílica de la Sagrada Familia. La impermeabilización de las pilas de Jet-grouting o muros pantalla se han cuantificado mediante ensayos hidráulicos antes y después de la construcción del recinto. Se han analizado diversos escenarios de drenaje en el que la variable a considerar han sido la profundidad de los muros pantalla. En estos escenarios se han comparado los caudales, los descensos de nivel y los asentamientos en relación a la profundidad de las pantallas a construir.Deep excavations in aquifers may be constructed by combining pumping with the cut and cover method. These enclosures are often lengthened more than is structurally necessary, which diminish the risk of heave, in order to reduce settlements caused by pumping and the involved discharges. Jet-grouting piles are sometimes adopted for lengthening. We analysed the water-proofing efficiency of jet-grouting and the need for water isolation in preconsolidated sediments. We used data obtained from two shaft excavations during the construction of the high speed train tunnel in Barcelona located adjacent to the Sagrada Familia Basilica. Jet-grouting was characterised using pumping tests before and after the construction of the enclosure. A number of dewatering scenarios were considered at the two shafts by varying the depth of the enclosures. The flow rate, drawdowns and settlements at the different scenarios were compared to observe the efficiency of lenghtened the enclosures.Universidad Nacional de La Plat

Geothermal energy as a tool for groundwater remediation

Peer reviewe

Interaction between groundwater and underground constructions

Underground constructions below the water table may be problematic if the role of groundwater is not properly acknowledged. Difficulties worsen in urban environments. Two aspects should be taken into account in the interaction between underground constructions and groundwater, 1) the impacts caused by the construction in the aquifers and 2) the difficulties that groundwater causes during the construction. Therefore, the design of an underground construction must be minimize the impacts in the underground environment as well as guaranteeing the safety of the workers and the integrity of adjacent structures. The adopted measures must not complicate the development of the construction and must not increase the total cost. To sum up, the construction must be efficient. These questions arose during the construction of the High Speed Train (HST) tunnel in Barcelona, which passes next to the Sagrada Familia. This thesis proposes answers to the questions which came up. Two problems may arise when a construction intersects an aquifer, the drain and the barrier effect. While the former has been widely studied, the second has not been adequately formalized and this is the first aim of the thesis. Analytical solutions are obtained to compute the head variations caused by an underground impervious structure. The solutions allow computing of the impact under different circumstances and to design corrective measures. The proposed equations were verified by using the data from real underground constructions. Subsidence caused by dewatering processes of deep excavations is feared. This fact affects the design. One option to reduce subsidences consist on deepen the enclosures (diaphragm walls, piles, jet-grouting piles) in order to avoid or minimise the dewatering. The second objective is to discuss the effectiveness of this measure, which rise the cost of the constructions, since drawdown caused by pumping are usually small and less dangerous (poorly differential) than is expected. Moreover, the pumping stabilizes the bottom of excavations. Therefore, to deepen the enclosures may be less efficient than combining short enclosures with deep pumping wells. Both alternatives must be compared. Thus, a number of dewatering scenarios, where the depth of the enclosures and the pumping wells are varied, are compared considering the safety, the outside affectations and the cost. Results show that combining deep pumping wells with short enclosures can become the most efficient method to perform excavations in preconsolidated soils. ii Regardless of the method used to perform an excavation, the enclosure, always, plays an important role since it guarantees the stability of the excavation walls and prevents the entrance of lateral flow. The presence of small defects may lead to disastrous consequences, which would invalidate all the previous work oriented to develop an efficient construction. Therefore, given that the defects are relatively common, that the techniques used to detect defects are limited and that the groundwater behaviour taking into account underground structures can be predicted, the third objective of the thesis is to develop hydraulic methods to assess the state of an enclosure. These methods, specifically the Watertightness Assessment Test (WTAT), are used as much to estimate the effective parameters of the enclosure as to locate the defects. Finally, the steps followed during the construction of the HST tunnel in Barcelona demonstrate the importance of the geological characterisation. If the soil is well known, all the aspects associated with the construction can be predicted accurately, which is crucial for designing an efficient underground construction. The geology, the hydrogeology and the historical processes suffered by the soil must be characterized accurately.Las construcciones subterráneas realizadas por debajo del nivel piezométrico pueden ser problemáticas si no se reconoce el papel del agua subterránea. Las dificultades aumentan en ambientes urbanos. La interacción con el agua subterránea tiene lugar en las dos direcciones 1) los impactos causados por la construcción sobre el acuífero y 2) las dificultades que, durante la construcción, causará la presencia de agua subterránea. Por ello, el diseño de una construcción subterránea debe minimizar los impactos en el medio subterráneo y garantizar la seguridad de los trabajadores y la integridad de las estructuras adyacentes. Las medidas adoptadas no deben complicar en exceso el desarrollo de las obras ni sobrecargar el coste total de la obra. En resumen, la construcción debe ser eficiente. Estas preguntas surgieron durante la construcción del túnel para el Tren de Alta Velocidad (HST) en Barcelona, adyacente a la Sagrada Familia. En esta tesis se proponen respuestas a las mismas. Los impactos sobre el acuífero pueden ser de dos tipos: el efecto dren y el efecto barrera. Mientras que el primero ha sido ampliamente estudiado, el segundo no ha sido formalizado adecuadamente, lo que constituye el primer objetivo de esta tesis. Para calcular las variaciones de nivel causadas por una estructura subterránea impermeable, se derivan ecuaciones para diversas condiciones de obra y para medidas correctoras. Se han verificado con datos de construcciones reales. La subsidencia causada por el drenaje de excavaciones profundas es uno de los temores más condicionantes del diseño. Una de las maneras de reducirla, consiste en profundizar los recintos (pantallas, pilotes, columnas de jet-grouting) con el fin de evitar o minimizar el bombeo. El segundo objetivo de esta tesis es cuestionar la eficacia de estas medidas, que aumentan el coste de la construcción, ya que los asientos causados por el bombeo suelen ser pequeños y menos peligrosos (poco diferenciales) de lo temido. Además, el bombeo estabiliza la base de las excavaciones. Por ello realizar recintos más profundos puede ser menos eficiente que combinar recintos cortos y pozos de bombeo profundos. Es obvio que ambas alternativas deben compararse adecuadamente. Para ello, se han estudiado una serie de escenarios de drenaje que son comparados teniendo en cuenta la seguridad, las afecciones externas y el coste. Las variaciones entre los diferentes escenarios son las profundidades de los recintos y de los pozos de bombeo. Los resultados muestran que combinar pozos de bombeo profundos con recintos cortos es el método más eficiente para llevar a cabo excavaciones en suelos preconsolidados. Independientemente del método utilizado para llevar a cabo una excavación, el recinto, siempre juega un papel importante, ya que garantiza la estabilidad de las paredes de la excavación y evita la entrada de flujo lateral. La presencia de pequeños defectos puede tener consecuencias desastrosas, lo que haría inútil todo el trabajo previo orientado a desarrollar una construcción eficiente. Por lo tanto, dado que los defectos son relativamente comunes, que las técnicas utilizadas para detectar defectos son limitadas y que el comportamiento del agua subterránea puede ser predicho teniendo en cuenta las estructuras subterráneas existentes. El tercer objetivo de la tesis es desarrollar métodos hidráulicos para evaluar el estado del recinto de una excavación. Se muestra que estos métodos y, en particular, el ensayo de caracterización de impermeabilización permiten tanto estimar los parámetros efectivos del recinto como localizar los defectos. Por último, los pasos seguidos durante la construcción del túnel para el Tren de Alta Velocidad en Barcelona evidencian la importancia de una buena caracterización geológica. Si el suelo es bien conocido, todos los aspectos asociados con la construcción pueden ser estimados con precisión, lo que resulta crucial para diseñar una construcción subterránea eficiente. La geología, la hidrogeología y los procesos históricos sufridos por el suelo deben ser bien conocidos.Les construccions subterrànies realitzades sota el nivell piezométric poden ser problemàtiques si no es reconeix el paper de l'aigua subterrània. Les dificultats augmenten en ambients urbans. La interacció amb l'aigua subterrània té lloc en els dos sentits 1) els impactes causats per la construcció sobre l'aqüífer i 2) les dificultats que, durant la construcció, causarà la presència d'aigua subterrània. Per això, el disseny d'una construcció subterrània ha de minimitzar els impactes al medi subterrani i garantir la seguretat dels treballadors i la integritat de les estructures adjacents. Les mesures adoptades no han de complicar en excés el desenvolupament de les obres ni sobrecarregar el cost total de l'obra. En resum, la construcció ha de ser eficient. Aquestes preguntes van sorgir durant la construcció del túnel per al Tren d'Alta Velocitat a Barcelona, adjacent a la Sagrada Família. En aquesta tesi es proposen respostes a les mateixes. Els impactes sobre l'aqüífer poden ser de dos tipus: l'efecte dren i l'efecte barrera. Mentre que el primer ha estat àmpliament estudiat, el segon no ha estat formalitzat adequadament, la qual cosa constitueix el primer objectiu d'aquesta tesi. Per calcular les variacions de nivell causades per una estructura subterrània impermeable, es deriven equacions per a diverses condicions d'obra i per a mesures correctores. S'han verificat amb dades de construccions reals. La subsidència causada pel drenatge d'excavacions profundes és un dels temors més condicionants del disseny. Una de les maneres de reduir-la, consisteix a aprofundir els recintes (pantalles, pilotis, columnes de jet-grouting) amb la finalitat d'evitar o minimitzar el bombament. El segon objectiu d'aquesta tesi és qüestionar l'eficàcia d'aquestes mesures, que augmenten el cost de la construcció, ja que els seients causats pel bombament solen ser petits i menys perillosos (poc diferencials) del temut. A més, el bombament estabilitza la base de les excavacions. Per això realitzar recintes més profunds pot ser menys eficient que combinar recintes curts i pous de bombament profunds. És obvi que ambdues alternatives han de comparar-se adequadament. Per a això, s'han estudiat una sèrie d'escenaris de drenatge que són comparats tenint en compte la seguretat, les afeccions externes i el cost. Les variacions entre els diferents escenaris són les profunditats dels recintes i dels pous de bombament. Els resultats mostren que combinar pous de bombament profunds amb recintes curts és el mètode més eficient per dur a terme excavacions en sòls preconsolidats. vi Independentment del mètode utilitzat per dur a terme una excavació, el recinte, sempre juga un paper important, ja que garanteix l'estabilitat de les parets de l'excavació i evita l'entrada de flux lateral. La presència de petits defectes pot tenir conseqüències desastroses, la qual cosa faria inútil tot el treball previ orientat a desenvolupar una construcció eficient. Per tant, atès que els defectes són relativament comuns, que les tècniques utilitzades per detectar defectes són limitades i que el comportament de l'aigua subterrània pot ser predit tenint en compte les estructures subterrànies existents. El tercer objectiu de la tesi és desenvolupar mètodes hidràulics per avaluar l'estat del recinte d'una excavació. Es mostra que aquests mètodes i, en particular, l'assaig de caracterització d'impermeabilització (WTAT) permeten tant estimar els paràmetres efectius del recinte com localitzar els defectes. Finalment, els passos seguits durant la construcció del túnel per al Tren d'Alta Velocitat a Barcelona evidencien la importància d'una bona caracterització geològica. Si el sòl és ben conegut, tots els aspectes associats amb la construcció poden ser estimats amb precisió, la qual cosa resulta crucial per dissenyar una construcció subterrània eficient. La geologia, la hidrogeologia i els processos històrics soferts pel sòl han de ser ben coneguts