Hydrogeological challenges in a low carbon economy

Hydrogeology has traditionally been regarded as the province of the water industry, but it is increasingly finding novel applications in the energy sector. Hydrogeology has a longstanding role in geothermal energy exploration and management. Although aquifer management methods can be directly applied to most high-enthalpy geothermal reservoirs, hydrogeochemical inference techniques differ somewhat owing to peculiarities of high-temperature processes. Hydrogeological involvement in the development of ground-coupled heating and cooling systems using heat pumps has led to the emergence of the sub-discipline now known as thermogeology. The patterns of groundwater flow and heat transport are closely analogous and can thus be analysed using very similar techniques. Without resort to heat pumps, groundwater is increasingly being pumped to provide cooling for large buildings; the renewability of such systems relies on accurate prediction and management of thermal breakthrough from reinjection to production boreholes. Hydrogeological analysis can contribute to quantification of accidental carbon emissions arising from disturbance of groundwater-fed peatland ecosystems during wind farm construction. Beyond renewables, key applications of hydrogeology are to be found in the nuclear sector, and in the sunrise industries of unconventional gas and carbon capture and storage, with high temperatures attained during underground coal gasification requiring geothermal technology transfer

A Framework for Risk-Based Cost-Benefit Analysis for Decision Support on Hydrogeological Risks in Underground Construction

Construction below the ground surface and underneath the groundwater table is often associated with groundwater leakage and drawdowns in the surroundings which subsequently can result in a wide variety of risks. To avoid groundwater drawdown-associated damages, risk-reducing measures must often be implemented. Due to the hydrogeological system\u27s inherent variability and our incomplete knowledge of its conditions, the effects of risk-reducing measures cannot be fully known in advance and decisions must inevitably be made under uncertainty. When implementing risk-reducing measures there is always a trade-off between the measures\u27 benefits (reduced risk) and investment costs which needs to be balanced. In this paper, we present a framework for decision support on measures to mitigate hydrogeological risks in underground construction. The framework is developed in accordance with the guidelines from the International Standardization Organization (ISO) and comprises a full risk-management framework with focus on risk analysis and risk evaluation. Cost-benefit analysis (CBA) facilitates monetization of consequences and economic evaluation of risk mitigation. The framework includes probabilistic risk estimation of the entire cause-effect chain from groundwater leakage to the consequences of damage where expert elicitation is combined with data-driven and process-based methods, allowing for continuous updating when new knowledge is obtained

Managing hydrogeological risks in underground construction

Groundwater leakage into underground constructions can cause groundwater drawdown and subsequently costly damages to objects impacted by changes in groundwater conditions. In order to reduce the damage risk, risk-reducing measures can be implemented. When implementing measures, society’s limited resources must be carefully managed by balancing the costs and the benefits (e.g. reduced risk) of the measures. Decisions regarding risk-reducing measures must always be taken under uncertainty since the conditions of the hydrogeological system cannot be fully known. In this thesis, a generic framework for management of hydrogeological risks in underground construction is presented (Paper 1). This framework constitutes a structured and transparent approach to the decision process for implementation of risk-reducing measures for groundwater control in underground construction. The framework uses a stochastic and iterative approach for managing the changing level of uncertainty inevitably associated with underground construction. The different modules that constitute the framework are also exemplified by application in a case study (paper 2). The case study focuses on the risk of subsidence damages to the built-up environment (buildings, paved surfaces and pipes) and risk-reducing measures in the form of sealing, artificial recharge and reinforcement measures to houses. The framework and methods used within the framework for the risk analysis and risk evaluation have proven useful as decision support for management of hydrogeological risks. The framework has also proven to be an efficient tool in communication of risks both internally in a project but also between the project owner and stakeholders in the society

The disposal site and underground construction : Part I: The disposal site and the natural barrier : Part II: Preserving the favourable properties of the bedrock during construction

Preface This report is a summary compilation of the findings of STUK’s expert reviewers in the area of geosciences and the natural barrier to support STUK’s evaluation of Posiva’s Construction License Application (CLA) for the planned spent nuclear fuel repository at Olkiluoto. The Core Group of reviewers has advised STUK over the period since the Decision in Principle to proceed with geological disposal of spent fuel at Olkiluoto. Members of the team have reviewed numerous documents developed by Posiva over the last decade or more, have made frequent visits to the ONKALO facility with STUK’s inspectors and have attended topical workshops at which issues have been discussed in detail with Posiva staff and expert contractors. This latest round of review and evaluation has assessed the suite of documentation provided by Posiva in support of its TURVA Post-Closure Safety Case, which is a major component of its CLA, submitted in 2012. Each reviewer in the Core Group has assessed the documentation relevant to their own area of expertise, with considerable overlap between the reviewers. Reviewers compiled their own comments and findings in an identical template, developed by STUK. This report consolidates and summarises the separate template reports. In the process, material has been significantly condensed and edited to provide a more readable Consolidated Review Report. Discussions between the Core Group members in May 2014 allowed identification of the key issues arising, enabled common positions to be reached and facilitated the subsequent consolidation of comments and conclusions. The consolidation was carried out by the Key Consultant for the Natural Barrier area (Professor Neil Chapman) and the resulting report was approved by the other members of the Core Group. It thus represents a consensus view of this group. The review work was supported by specialist evaluations in the fields of fractured rock hydrogeology, seismology, structural geology, hard rock construction and climate and glaciology. These expert reviewers assessed specific reports and subsequent workshops were held with Posiva on some of these topics to clarify issues. The findings and suggestions of these workshops, which were agreed between the specialist reviewers present, have been incorporated into this report.Tiivistelmä Tämä raportti on yhteenveto Säteilyturvakeskuksen (STUK) käyttämien ulkopuolisten geotieteiden asiantuntijoiden arvioinneista, jotka teetettiin Posivan rakentamislupahakemuksen tarkastuksen yhteydessä STUKin oman arvioinnin tueksi. Työhön osallistunut arviointiryhmä on toiminut STUKin tukena Posivan käytetyn ydinpolttoaineen loppusijoituksen ensimmäisestä periaatepäätöksestä lähtien. Ryhmän jäsenet ovat arvioineet useita Posivan raportteja viimeisen kymmenen vuoden aikana, he ovat vierailleet Onkalossa useita kertoja STUKin tarkastajien kanssa ja he ovat osallistuneet useisiin STUK järjestämiin aiheeseen liittyviin työpajoihin, joissa arviointihavainnoista on keskusteltu Posivan ja Posivan konsulttien kanssa. Viimeisimmällä arviointikierroksella ryhmä on keskittynyt Posivan TURVA-raporttikokonaisuuteen (pitkäaikaisturvallisuus), joka on keskeinen osa vuonna 2012 toimitettua rakentamislupahakemusta. Jokainen ryhmän jäsen on keskittynyt arviossaan omaan erikoisalueeseensa. Arviointihavainnot ja kommentit on kirjattu STUKin valmistelemaan arviointiraporttipohjaan. Tämä raportti tiivistää ja vetää yhteen erillisten arviointiraporttien havainnot. Alkuperäisiä yksittäisten konsulttien arviointiraporttien tekstejä on tiivistetty ja editoitu, jotta yhteenvetoraportista on luettava kokonaisuus. Toukokuussa 2014 järjestetyn työpajan keskusteluissa arviointiin osallistuneet asiantuntijat tunnistivat ja keskustelivat tärkeimmistä arviointihavainnoista. Yhteenvetoraportin on koonnut professori Neil Chapman, joka toimi STUKin avainkonsulttina paikkatutkimuksiin liittyvissä asioissa. Kaikki arviointiryhmän jäsenet ovat hyväksyneet raportin, joten se edustaa arviointiryhmän jäsenten näkemystä. Arviointityöhön osallistui vakiojäsenten lisäksi erikoisosaajia seuraavilta aloilta: rakoilleen kallioperän hyrdogeologia, seismologia, rakenteellinen geologia, kalliorakentaminen, ilmasto ja jääkaudet. Nämä erikoisasiantuntijat arvioivat oman erityisalansa raportteja ja osallistuivat niiden aihealueista järjestettyihin työpajoihin, joissa tutkimushavainnoista keskusteltiin Posivan kanssa. Työpajoissa kirjatut havainnot ja ehdotukset on sisällytetty tähän yhteenvetoraporttiin.1. paino

Advanced Geological Prediction

Due to the particularity of the tunnel project, it is difficult to find out the exact geological conditions of the tunnel body during the survey stage. Once it encounters unfavorable geological bodies such as faults, fracture zones, and karst, it will bring great challenges to the construction and will easily cause major problems, economic losses, and casualties. Therefore, it is necessary to carry out geological forecast work in the tunnel construction process, which is of great significance for tunnel safety construction and avoiding major disaster accident losses. This lecture mainly introduces the commonly used methods of geological forecast in tunnel construction, the design principles, and contents of geological forecast and combines typical cases to show the implementation process of comprehensive geological forecast. Finally, the development direction of geological forecast theory, method, and technology is carried out. Prospects provide a useful reference for promoting the development of geological forecast of tunnels

Groundwater characterization of a heterogeneous granitic rock massif for shallow tunneling

Shallow tunneling may encounter a number of problems, the most important of which is high water inflows in transmissive areas that are often associated with fractures or discontinuities. Moreover, research into shallow tunneling may be limited by the duration and cost of the civil engineering works. Two important aspects that are often overlooked are: variable groundwater behavior of faults (conduit, barrier, conduit-barrier), and role of groundwater connectivity between fractures that cross the tunnel and the rest of the rock massif. These two aspects should be taken into account in the geological and groundwater characterization to correct the tunnel design and minimize hazards. A geological study and a preliminary hydrogeological characterization (including a prior steady state investigation and cross bore-hole tests) were carried out in a granitic sector during the construction of Line 9 of the Barcelona subway (B-20 area). The hydrogeological conceptual model was constructed using a quasi-3D numerical model, and different scenarios were calibrated. Faults and dikes show a conduit-barrier behavior, which partially compartmentalized the groundwater flow. The barrier behavior, which is the most marked effect, is more prominent in faults, whereas conduit behavior is more notable in dikes. The characterization of groundwater media entailed a dewatering plan and changes in the tunnel course. This enabled us to construct the tunnel without any problems

Parametric and numerical modeling tools to forecast hydrogeological impacts of a tunnel

The project of interest involving a hydroelectrical diversion tunnel through a crystalline rock massif in the Alps required a detailed hydrogeological study to forecast the magnitude of water inflows within the tunnel and possible effects on groundwater flow The tunnel exhibits a length of 9.5 km and is located on the right side of the Toce River in Crevoladossola (Verbania Province, Piedmont region, northern Italy). Under the geological framework of the Alps, the tunnel is located within the Lower Penninic Frappes in the footwall of the Simplon Normal Fault, and the geological succession is mostly represented by Antigorio gneiss (metagranites) and Baceno metasediments (metacarbonates). Due to the presence of important mineralized springs for commercial mineral water purposes, the above mentioned hydrogeological study focused on both quantity and quality aspects via rainfall data analysis, monitoring of major spring flow rates, monitoring of hydraulic heads and pumping rates of existing wells/boreholes, hydrochemical and isotopic analysis of springs and boreholes and hydraulic tests (Lefranc and Lugeon). The resulting conceptual model indicated dominant low-permeability (aquitard) behavior of the gneissic rock masses, except under conditions of intense fracturing due to tectonization, and aquifer behavior of the metasedimentary rocks, particularly when interested by dissolution. Groundwater flow systems are mainly controlled by gravity. The springs located near the Toce River were characterized by high mineralization and isotopic ratios, indicating long groundwater flow paths. Based on all the data collected and analyzed, two parametric methods were applied: 1) the Dematteis method, slightly adapted to the case study and the available data, which allows assessment of both potential inflows within the tunnel and potential impacts on springs (codified as the drawdown hazard index; DHI); 2) the Cesano method, which only allow assessment of potential inflows within the tunnel, thereby discriminating between major and minor inflows. Contemporarily, a groundwater flow model was implemented with the equivalent porous medium (EPM) approach in MODFLOW-2000. This model was calibrated under steady-state conditions against the available data (groundwater levels inside wells/piezometers and elevation and flow rate of springs). The Dematteis method was demonstrated to be more reliable and suitable for the site than was the Cesano method. This method was validated considering a tunnel through gneissic rock masses, and this approach considered intrinsic parameters of rock masses more notably than morphological and geomorphological factors were considered. The Cesano method relatively overestimated tunnel inflows, considering variations in the topography and overburden above the tunnel. Sensitivity analysis revealed a low sensitivity of these parametric methods to parameter values, except for the rock quality designation (RQD) employed to represent the fracturing degree. The numerical model was calibrated under ante-operam conditions, and sensitivity analysis evaluated the influence of uncertainties in the hydraulic conductivity (K) values of the different hydrogeological units.The hydraulic head distribution after tunnel excavation was forecasted considering three scenarios, namely, a draining tunnel, tunnel as a eater loss source, and tunnel sealed along its aquifer sectors, considering 3 levels of K reduction. Tunnel impermeabilization was very effective, thus lowering the drainage rate and impact on springs. The model quantitatively defined tunnel inflows and the effects on spring flow at the surface in terms of flow rate decrease. The Dematteis method and numerical model were combined to obtain a final risk of impact on the springs. This study likely overestimated the risk because all the values assigned to the parameters were chosen in a conservative way, and the steady-state numerical simulations were also very conservative (the transient state in this hydrogeological setting supposedly lasts 1-3 years). Monitoring of the tunnel and springs during tunnel boring could facilitate the feedback process

Work Package 3 – Hydrogeological methods, drainage and grouting

Ground works such as deep excavations and foundation works performed in soft clay can cause damage to neighbouring buildings and structures. Drainage causes pore pressure lowering, followed by consolidation settlements. The costs related to settlement damage can be substantial and there is a considerable potential for reducing these costs. The risk of settlement damage caused by drainage and pore pressure reduction can be reduced during the early design phase of a project by undertaking the correct type of investigations and understanding the hydrogeological conditions. Furthermore, one may select construction methods, which reduce risk of drainage. In case the selected construction solution yields an unacceptable risk for settlement damage to surrounding buildings and infrastructure, remedial measures may be designed to mitigate the effects, followed by implementation and monitoring during the construction phase. This report provides State-of-the-Art related to hydrogeological investigation methods, hydrogeological modelling and numerous measures to mitigate the effects of drainage to excavations. In addition, governing Norwegian rules and regulations are discussed, as well as the causes of drainage to excavations in Norwegian ground conditions.Norges forskningsråd / The Research Council of Norwa

Dynamic estimating the karst tunnel water inrush based on monitoring data during excavation

The tunnel water gushing has long been a difficult hydrogeological problem, especially in karst areas. It affects the entire process of tunnel construction, operation and maintenance. In view of the complex disaster-causing mechanism and difficult quantitative predictions of water inrush, several theoretical methods are adopted to realize dynamic assessment of water inrush in the progressive process of tunnel construction. According to a survey conducted in the Zoumaling tunnel near Chongqing, China, 62% of its total length, e.g., 1525 m is associated with karst（including a fault fracture zone). On the basis of collecting real-time monitoring data about water inrush in the excavated section of the Zoumaling tunnel, a fuzzy data analysis method has been used to analyze the content of seven common ions in the inflow water, which makes it possible to classify the groundwater types and to establish the hydrogeological model of the tunnel site. In order to forecast the possibility and quantity of water inrush, it is essential to accurately model the groundwater system spatially. The preliminary forecasting result about untapped section reveals a small possibility of a sudden water inflow disaster and 35,000 m3/d water inflow, which is close to the ultimately measured quantity of water. This study provides a theoretical reference for the prediction of water inrush during tunnel construction, and the main characteristic of this study is reflected in the real-time prediction of tunnel water inrush according to actual tunnel inflow of excavated sections. This approach can be applied in similar situations for the prediction of tunnel water inrush in other karst regions.Key words: karst region, tunnel water inrush; dynamic estimate; fuzzy cluster analysis.Pričakovana dinamika vdora vode v predore na podlagi meritev med njihovo gradnjoPojav vdiranja vode v predore je že dolgo časa poznana težava, še posebej na kraških območjih. Pojavlja se med celotno gradnjo predorov, njihovo uporabo in vzdrževanjem. Za proučevanje potencialnega pojava nesreč in težavnega napovedovanja količine vdora vode je bilo preizkušenih več različnih teoretičnih metod. Te omogočajo oceno dinamike vdora vode med celotnim procesom gradnje predorov. Pri predoru Zoumaling v bližini mesta Chongqing (Kitajska) približno 62 % dolžine predora (1525 m) poteka na območju krasa in čez prelomna območja. Na podlagi v realnem času zbranih podatkov o vdorih vode v izkopanih odsekih predora Zoumaling se je naredila analiza mehkih množic. Ta je bila uporabljena za analizo sedmih v vodi najbolj značilnih ionov in je omogočila razvrstitev podzemne vode v različne skupine, s tem pa izdelavo hidrogeološkega modela neposredne okolice predora. Za analizo verjetnosti vdora vode in njene možne količine je izdelava natančnega modela vodonosnika zelo pomembna. Prvi rezultati, ki se nanašajo na en še nedokončan odsek, kažejo na majhno možnost nenadnega vdora vode. Največja možna dnevna količina vdora je ocenjena na 35.000 m3, kar je blizu najvišje izmerjene dnevne količine dotoka. Pričujoča raziskava vzpostavlja teoretično podlago za napoved vdora vode v času gradnje predora, glavna posebnost pa je napoved vdora v realnem času na podlagi izmerjenega dotoka v že izkopanih odsekih predora. Predstavljen postopek in napovedi, ki jih omogoča, se lahko uporabijo v podobnih primerih tudi na drugih kraških območjih.Ključne besede: kraško območje, vdor vode v predore, pričakovana dinamika, analiza mehkih množic.