Hydrogeological Prognoses in Infrastructure Projects: A Case Study of Stockholm Bypass, Hjulsta Norra

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IN THE FIELD OF TECHNOLOGY DEGREE PROJECT

ENERGY AND ENVIRONMENT AND THE MAIN FIELD OF STUDY ENVIRONMENTAL ENGINEERING, SECOND CYCLE, 30 CREDITS STOCKHOLM SWEDEN 2021,

Hydrogeological Prognoses in Infrastructure Projects

- A Case Study of Stockholm Bypass, Hjulsta Norra

FRIDA GRENHOLM

KTH ROYAL INSTITUTE OF TECHNOLOGY

SCHOOL OF ARCHITECTURE AND THE BUILT ENVIRONMENT

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Hydrogeological Prognoses in Infrastructure Projects

- A Case Study of Stockholm Bypass, Hjulsta Norra

FRIDA GRENHOLM

Supervisor

BO OLOFSSON

Examiner

BO OLOFSSON

Supervisor at NCC CECILIA MONTELIUS

Degree Project in Environmental Engineering and Sustainable Infrastructure KTH Royal Institute of Technology

School of Architecture and Built Environment

Department of Sustainable Development, Environmental Science and Engineering SE-100 44 Stockholm, Sweden

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ii TRITA-ABE-MBT 20788

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Sammanfattning

I och med urbaniseringens framfart har stadsplanering och utnyttjande av mark blivit komplexa men viktiga frågor för samhället. En stad som står inför dessa utmaningar är Stockholm

(Stockholms stad, 2018). Städernas utbyggnad kan leda till höga priser för mark vilket därför kan resultera i ett ökat intresse för att bygga infrastruktur under marknivå. Dock kan undermarksbygge påverka miljö och konstruktioner över mark. En av utmaningarna med konstruktion under

marknivå är grundvattenhantering. Grundvatten existerar i fyllda jordporer och hålrum i berg under grundvattennivån och kan eventuellt läcka in i schakt och undermarkskonstruktioner. Dock kräver omledning av grundvatten ett tillstånd från mark- och miljödomstolen i Sverige (SGU, 2017).

Syftet med detta examensarbete är att undersöka hur väl en hydrogeologisk prognos

överensstämmer med utfallet i ett specifikt infrastrukturprojekt; entreprenaden Hjulsta Norra i Förbifart Stockholm. Arbetet har delats upp i fyra olika delmål för att uppnå detta syfte. Arbetet har skrivits med hjälp av litteraturstudier av relevanta ämnen och även dataanalys som är specifik för entreprenaden Hjulsta Norra.

Litteraturstudien syftar till att förklara hur hydrogeologi och infrastruktur hör ihop, hur

byggprocessen fungerar, hur miljölagstiftningen ser ut och vad som är syftet med en hydrogeologisk prognos. Fallstudien har gjorts för en av entreprenaderna av Förbifart Stockholm som tillhör NCC;

Hjulsta Norra. Förbifart Stockholm är ett infrastrukturprojekt som huvudsakligen syftar till att öka tillgängligheten i och runt Stockholmsområdet (Trafikverket, 2020a). Entreprenaden omfattar konstruktion av ett tråg och två betongtunnlar (NCC Infrastructure, 2017a) och byggprocessen är uppdelad i flera faser (Montelius, 2020). Entreprenadområdet består av varierad geologi, men mestadels gnejs eller granit som överlagras av friktionsjord och fläckvis lera. Friktionsjorden ligger delvis under grundvattennivån och därför kan två olika grundvattenmagasin identifieras inom studieområdet; Järva 6 och Järva 7 (Runesson, 2014). En hydrogeologisk prognos har utvecklats av NCC i syfte att undersöka hydrogeologiska effekter i studieområdet, hur grundvattennivåer kan uppehållas och ifall artificiell infiltration behövs för att behålla dem. Prognosen har till stor del centrerats kring friktionsjordens permeabilitet och att modellera olika fall för denna då det påverkar grundvattenförhållandena i området (Lundgren, 2017a; Lundgren, 2017b).

Resultatet presenteras i tre olika sektioner. Första sektionen undersöker vilka olika komponenter som kan vara en del av en hydrogeologisk prognos baserat på litteraturstudier. Den andra delen utvärderar den hydrogeologiska prognosen utvecklad av NCC och den tredje är en jämförelse av det verkliga utfallet och prognosen. Diskussionen är huvudsakligen centrerad kring fallstudien och slutsatser som kan dras från denna. Prognosen är förenklad och presenterar homogena

hydrogeologiska miljöer vilket resulterar i en enkel konceptuell modell. Skillnaderna mellan prognosen och utfallet varierar i omfattning, men en av de största skillnaderna är det bedömda behovet av artificiell infiltration in Järva 6. Risker som uppstår under utvecklingen av en prognos identifieras och de kan sammanfattas till risker kring kommunikation mellan olika faser av byggprocessen, homogenitet i prognosen och att basera resultat på erfarenhet snarare än utredningar. Vidare undersöks hur fallstudiens prognos kunde utvecklas.

Slutligen tas ett antal slutsatser fram ur fallstudien som är överlåtelsebara för hydrogeologiska prognoser i andra projekt. Dessa slutsatser handlar om risk- och osäkerhetsanalys, kommunikation mellan olika projektfaser, lärdomar av andra typer av prognoser, att kombinera metoder för att samla och analysera data samt att göra prognosen lätt att utvärdera och jämföra.

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Abstract

As cities expand, urban planning and efficient land use becomes more important and presents new challenges. A city that is exposed to these challenges is Stockholm, Sweden (Stockholms stad, 2018).

The expansion of the city can lead to expensive acquisition of land above ground, which therefore results in an increase of subsurface infrastructure being constructed. The construction below ground level also imposes challenges affecting our urban environments above ground. One of the challenges when working below ground level is the management of groundwater. The groundwater exists in filled pores of soil and rock below the groundwater table and can potentially leak to a subsurface construction. However, redirecting the groundwater requires permission from the environmental court (SGU, 2017).

The purpose of this thesis is to examine how well a hydrogeological prognosis corresponds to the outcome of a specific infrastructure project; the contract Hjulsta Norra in the Stockholm Bypass.

More specifically, the thesis has been divided in four different objectives relating to the main purpose. The thesis has been conducted through literature studies of reports and studies within relevant subjects as well as specific data analysis for the case of Hjulsta Norra.

The literature studies attempt to explain how hydrogeology relates to infrastructure, the building process, environmental legislation and the hydrogeological prognoses purpose. The case study is conducted for a part of the Stockholm Bypass that is developed by NCC; Hjulsta Norra. The Stockholm Bypass project is developed to increase accessibility around the Stockholm region (Trafikverket, 2020a). The contract consists of the construction of a tray and two concrete tunnels (NCC Infrastructure, 2017a) and the building process is divided into several stages (Montelius, 2020). Geologically, the area of the contract Hjulsta Norra is varied but mainly consists of gneiss or granite overlaid by friction soil and sometimes clay. The friction soil layer is partially below the groundwater level and therefore two different groundwater storages are found within the study area; Järva 6 and Järva 7 (Runesson, 2014). A hydrogeological prognosis has been developed by NCC for the purpose of investigating hydrogeological effects in the study area, how to maintain groundwater levels and if artificial infiltration is required to maintain the groundwater levels. The prognosis has been largely focused around attempting to model different cases of friction soil hydraulic conductivity, as this is a parameter that largely affects the groundwater levels in the area (Lundgren, 2017a; Lundgren, 2017b).

The results are presented in three sections. The first results present different components that may exist in a hydrogeological prognosis based upon literature studies. The second part evaluates the hydrogeological prognosis developed by NCC and the third part compares the actual outcome to the prognosis. The discussion is mainly focused around the specific case and the conclusions that can be drawn for the case study is that the hydrogeological prognosis is simplified and presents rather homogenous hydrogeological environments that results in a simple conceptual model. The differences between the prognosis and outcome are larger in some respects than others; among which the largest differences are the need for artificial infiltration in Järva 6. Some risks for

development of the prognosis are brought forward relating to communication between stages of the building process, homogeneity in the prognosis and replacing investigated results with experience.

Further, some possibilities for the development of the case study prognosis have been identified.

Finally, in accordance with the objectives, some transferable conclusions have been found in the case study that can be used in other projects. These conclusions relate to risk and uncertainty analysis, communication between stages of the building process, learning from other prognoses, combining methods of data gathering and analysis as well as making the prognosis easy to evaluate and compare.

Keywords

Infrastructure, hydrogeology, groundwater, prognoses.

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Acknowledgements

This master thesis is the result of a collaboration between NCC Infrastructure (Stockholm) and the Royal Institute of Technology (Stockholm) during the fall 2020. The thesis is the final examination and last part of my Engineering degree from the program Energy and Environment including a master’s degree from the program Environmental Engineering and Sustainable Infrastructure.

The thesis was written with the help from my supervisor Cecilia Montelius (NCC) and supervisor and examiner Bo Olofsson (KTH).

I would like to thank my supervisors Cecilia Montelius and Bo Olofsson for supporting my work throughout this process, providing valuable feedback and opinions. I am grateful that you have shared your expertise and knowledge to create an effective learning-environment for me.

Further, I would like to thank contributors at NCC for aiding my work throughout this fall. I want to thank Staffan Hintze and Tomas Widehag for helping me to find and start writing a thesis at NCC. I would also like to thank Blanca Sandoval Ferro for answering my questions and explaining the work process on site within the contract Hjulsta-Norra. Finally, I would like to thank my co-workers at NCC for providing a nice and comfortable work environment during this time.

Stockholm, June 2020 Frida Grenholm

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Definitions

- Aquifer. A body of groundwater contained in rock or soil underneath the groundwater table (Robins, 2020).

- Artificial infiltration. Infiltration of good-quality water used to increase the groundwater recharge through controlled and managed infiltration of water to soil and/or rock. The practical procedure can be done in many ways (Powers, et al., 2007).

- Environmental Impact Analysis (EIA). A legal document regulated by the

environmental code, providing information about the operation to be conducted and what environmental impacts may arise from the operations (Naturvårdsverket, 2019a).

- Excavation water (länshållningsvatten). Water that may require to be redirected from an excavation. Mainly consists of process water, direct precipitation and groundwater leaking into the excavation (Montelius, 2020).

- Groundwater. Water that is stored underground in pore spaces of sediments and voids in rocks (Robins, 2020).

- Hydraulic conductivity. Describes an aquifers ability to transmit groundwater horizontally (Robins, 2020).

- Object Technical Description (OTD). Report compiling demands and expectations on a project’s construction from the client’s perspective. Part of tender documents (Runesson, 2014).

- Performance contract. A procurement form in which the client is responsible for the planning phase but hires a contractor to perform the construction itself (Nordstrand, 2008).

- Permeability. Like hydraulic conductivity, permeability describes an aquifers ability to transmit groundwater through connected pores in the medium. It depends on pore size, connectivity of pores and the viscosity of the water it transmits (Robins, 2020).

- Porosity. The porosity of a soil can be defined as the percentage of the soil volume that is voids. This depends on the soil particle size and shape as well as range of the soil particles (Powers, et al., 2007).

- Process water. Water used to operate machinery used in an excavation (Montelius, 2020).

- Technical Site Investigation Report (TSIR). Report compiling field- and laboratory investigations done in a contract area. Part of the tender documents (Hellgren, 2016).

- Turnkey contract. A procurement form in which the contractor is responsible for both the planning phase and performing the construction (Nordstrand, 2008).

- Water-related works (vattenverksamhet). A legal term that describes operations that include construction in water bodies, redirection of surface- or groundwater or in some other way altering water environments. To operate any water-related works, permissionis needed from the County Administrative Board (Enheten för mark- och vattenskydd, n.d.).

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Introduction

This introduction will introduce the background to this thesis, the purpose and aims of it, its limitations and the method used to develop it.

Background

Stockholm is a growing city, facing many challenges in terms of urban planning and upcoming infrastructure projects. The visions for Stockholm from the municipality involve a good public environment, as well as a resilient and climate smart city. These goals demand an efficient urban structure and puts high demands on the existing and future infrastructure. Among the established demands are to have an efficient land use as well as an efficient transportation system. These demands should be met sustainably according to the municipal general plan (Stockholms stad, 2018).

Combining the demands requires innovative solutions, among which one is to preserve land use above ground level by building transport infrastructure underground. However, underground construction faces many challenges that are not to be discarded. The spatial access to the underground is, alike that of the ground level, finite. One of these mentioned challenges is to not impose hazardous effects on water supply and the built environment above ground (SGU, 2017).

A substantial part of the Swedish water supply is dependent on groundwater of good quality (SGU, 2017). Groundwater is the water found in parts of geological formations that are completely saturated with water and are directly in contact with the ground level or underlying soil layer. The groundwater fills pores of soils and the cavities. Due to its existence below ground level, it is an important factor to consider during subsurface construction.

Infrastructure projects constructed underground may be subjected to groundwater inflow. As groundwater is an important resource, there are legal demands in any project that causes drainage (or other environmental effects) of it. These demands are regulated mostly by the environmental code and requires the owner of a project executing the mentioned drainage to apply for their

planned operation to be permitted by the environmental court (SGU, 2017). The permission process requires multiple steps before a permission application is heard before the court (Enheten för mark- och vattenskydd, n.d.). The court ruling can further regulate specific demands for each project to follow, such as leakage regulations and/or demanding certain groundwater levels to be maintained (Mark- och miljööverdomstolen, 2018). These regulations set the limitations for substantial parts of the project and is therefore of great importance to the executor of the construction.

Purpose and Objectives

The purpose of this thesis is to investigate how well hydrogeological prognoses correspond to the actual hydrogeological outcome in a project performed at NCC Infrastructure. Through literature studies and analysis of existing prognoses and outcome, the subject has been examined. The project aims to provide an understanding for the accuracy of hydrogeological prognoses in relation to their outcome. Further, the aim is to draw conclusions from the relationship between prognoses and outcome that can be useful in future projects. The thesis will include a case study on one of NCC Infrastructures existing projects; the Stockholm Bypass, Hjulsta Norra, and evaluate the

hydrogeological prognosis accuracy.

The objectives of the thesis can be summarized to the following:

1. Define possible components and contents of a hydrogeological prognosis used in an infrastructure project.

2. Present the actual outcome from the project Stockholm Bypass, Hjulsta Norra, in a way that is comparable to the hydrogeological prognosis developed for the project.

3. Evaluate and compare the hydrogeological prognosis in Stockholm Bypass Hjulsta Norra to the actual outcome and the method used to develop the prognosis.

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2 4. Develop transferable conclusions from the case study and literature that can be used to

develop future prognoses.

Limitations

The thesis is limited in time to 20 weeks of full-time studies. The limitations of this thesis are set to investigate infrastructure projects concerning hydrogeology. The thesis further aims to discuss hydrogeological prognoses and is limited to only the prognosis within the realm of hydrogeology.

Geographical boundaries to keep in mind for this thesis are for the legal system determined to Sweden and the Swedish legislation. For the literature study, limitations have been set to investigate road/railway projects in soil (and potentially cut by rock). For investigation of the case study of the Stockholm Bypass, the contract named FSE 502 Hjulsta Norra will only be considered. However, this thesis will not consider two parts of the project; the redirection of Akallalänken and the rock tunnel Hästa, this is due to the difference in contract form, different demands on the leakage into the tunnel, limiting amounts of data and for the purpose of limiting the project.

Method

This thesis has been provided by NCC Infrastructure and the methods used to have been mainly literature studies and data processing which will be further explained in this chapter.

Introduction

This thesis is written for NCC Infrastructure within the project of Stockholm Bypass. The bypass itself is divided into many contracts, among which NCC is responsible for two of them; Hjulsta Norra and Häggvik. The contracts themselves involve constructing two new interchanges requiring complex and sustainable solutions (NCC, n.d.). This thesis will focus on the interchange Hjulsta Norra and more specifically the hydrogeological aspects of the project. The thesis has been conducted with the help of NCC Infrastructure, that has provided a material basis for the thesis, support via supervisors and site visits to the contract site.

This thesis report consists of 6 chapters. Following is a description of each chapter and its contents.

Chapter 1: Introduction. The introduction presents background knowledge to the project, the purpose of the thesis, its limitations and a method describing how the thesis was developed.

Chapter 2: Literature Studies. The literature studies present relevant information gathered on relevant subjects for this thesis such as hydrogeology, environmental legislation and

hydrogeological prognoses.

Chapter 3: Case Study. The chapter presents specific information that relates to the Stockholm Bypass and more specifically the contract Hjulsta Norra that NCC is responsible for.

Chapter 4: Results. The results chapter will be divided into three sections, Hydrogeological Prognoses in Literature, Evaluation of Detailed Engineering and Design Prognosis and Detailed Engineering and Design Prognosis and Outcome.

Chapter 5: Discussion. This part of the thesis will be divided into four sections, among which the first three are the same as those presented in the results. The fourth part will discuss the further development of a detailed engineering and design prognosis.

Chapter 6: Conclusions and Recommendations. This part of the thesis will present transferable conclusions that can be learned from the case study and relate further to the development of hydrogeological prognoses.

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3 Literature Studies

Literature studies have been conducted for the purpose of investigating the connection between hydrogeology and infrastructure projects. More specifically - what role hydrogeological questions have in infrastructure projects, the building process of an infrastructure project, the legal aspects in an infrastructure project and what a hydrogeological prognosis is. The literature study was done more general and did not focus on the specifics of the case investigated in this thesis. It was done with the help of various literature found mainly via the KTH database Primo.

Further literature was studied to investigate the case, which was done mainly through the study of inhouse documents from NCC. The purpose of the case study chapter is to provide a technical and hydrogeological background of the area needed to understand the prognosis and its outcome.

Data Collection and Processing

To fulfil the second and third objective of this thesis, the outcome from the actual project had to be compared to the prognosis. To achieve this, four types of main data was collected;

• Precipitation data from 2008-2020. Collected from SMHI database for the measurement station in Vasastan, Stockholm (SMHI, 2020).

• Groundwater level data for measurement pipes in the project Hjulsta Norra 2008-2020.

Collected from the NCC project portal (NCC Infrastructure, 2020a).

• Infiltration data for infiltration pipes in the project Hjulsta Norra 2018-2020. Collected from the NCC project portal (NCC Infrastructure, 2020b).

• Data on incoming water and outgoing water (to a sedimentation pool) in the project Hjulsta Norra 2018-2020. Collected from the NCC project portal (NCC Infrastructure, 2020c).

All mentioned data was collected in Microsoft Excel. The precipitation, groundwater level and infiltration data were plotted as point data in time series and results from the prognosis was added to the plots for comparative studies. The data on incoming and outgoing water was used to estimate the groundwater leakage to the excavation in Hjulsta Norra as point data in time series. This was done through subtracting outgoing water from the incoming water volumes (used for infiltration and process water) for a corresponding time period. Further, direct precipitation entering the excavation for each time period was estimated and subtracted. Existing plots and time series (for all data) were systematically studied and compared to the outcome using statistical analysis. Lastly, a qualitative analysis was done using the data in order to understand the hydrogeological situation and the changes between the outcome and prognosis.

Literature Studies

The following chapter will present the literature studies conducted for the thesis.

Hydrogeology in Infrastructure Projects

The following chapter will introduce the topics of groundwater, how it relates to sustainability and geology, the mechanisms, effects and measures taken when working with groundwater.

What is Groundwater?

To understand the concept of groundwater, the hydrological cycle can be a helpful tool. Fig. 1 below is a simplification that illustrates the basic processes that together constitutes the hydrological cycle.

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4 Fig. 1: Illustrated simplification of the hydrological cycle.

Groundwater can be explained as the water that is abundant in the areas of soil pores and rock cavities that are saturated with water. In Sweden, the conditions for extraction and storage of groundwater are good as the geology and climate allows it. Commonly, groundwater can be found in one of many Swedish eskers, for example where surface water is infiltrated through layers of sand and gravel to further add to a groundwater resource in some geological formation (SGU, n.d. a;

Powers, et al., 2007).

Geological formations that are porous and permeable enough to allow for a flow of, or extraction of groundwater are called aquifers (SGU, 2018). The characteristics of these geological formations affect properties of the groundwater and its movement. Important characteristics affecting groundwater movement is hydraulic conductivity (the water’s ability to travel through porous media), porosity and permeability of the geological formation the water is travelling through.

Groundwater also tends to be affected by general conditions in the vicinity of the formation and generally takes the path of least resistance. Hence, groundwater often follows topography of the ground level and tends to move rather towards more permeable structures. If the groundwater does not have a natural path to follow to exit the ground, like a spring or any other surface water, it tends to stay in aquifers (if not extracted). Therefore, aquifers and groundwater movement are commonly affected by extraction rates caused by pumping water out of the aquifer (Powers, et al., 2007).

Yet another process that is central in terms of movement and the existence of groundwater is the concept of recharge. Recharge is a process that takes part in the hydrological cycle and can occur naturally or caused artificially through anthropogenic activities. Naturally occurring recharge can be water from a precipitation event, moving through the ground via infiltration and percolation down to the groundwater level and saturated zone. This concept is called diffuse recharge and occurs widely spread over an area. Localized recharge on the other hand, also occurs naturally but stems from surface water bodies that leak water that further moves to the saturated zone and ground water level. The artificial recharge can be intentional or unintentional but is often caused by surplus surface water or by recovered wastewater (Alley, 2009).

Groundwater and Sustainability

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5 Water is a finite resource and so also groundwater, making the usage of it highly important. Of all available water in the world, less than 1% is available for drinking water. Of that portion,

approximately 95% is groundwater. Hence, groundwater is commonly used as potable water for drinking and is often found pure and potable without the need for treatment of any kind (SGU, n.d.

a). Therefore, knowledge about groundwater, where to find it and how to manage it is of utmost importance. This fact is also firmly established by the Swedish parliament, as one of the 16 Swedish Environmental Objectives. The goal is formulated accordingly;

“Groundwater must provide a safe and sustainable supply of drinking water and contribute to viable habitats for flora and fauna in lakes and watercourses”

It is summarized under the heading “Good-quality groundwater”. The authority that is responsible for the goal is the Geological Survey of Sweden (SGU) (Swedish Environmental Protection Agency, 2018). This further establishes the status of groundwater as a subject to consider when discussing sustainability.

Climate change and global warming effects groundwater in multiple ways, according to the SGU.

This will affect the hydrological cycle and may be observed as for example increased evaporation rates or more intense precipitation events causing flooding. Increasing temperatures globally leading to melting ice caps will introduce a sea level rise that increases the risk for saltwater intrusion along coastal areas. Other effects on the quality of groundwater are observable as

increased precipitation and flooding events cause more surface water to encounter the groundwater.

This can possibly lead to contamination of groundwater, as surface water has not gone through the same purification process. Overall, climate change can be stated to both increase and decrease groundwater levels as well as affect the overall groundwater quality (SGU, n.d. b).

Groundwater and Geology

Groundwater is a topic that can be studied within the realm of hydrogeology, or geohydrology (Springer Nature, 2020a). The name of the topic itself reveals the close connection to geology – the study of Earth and other planetary bodies (Springer Nature, 2020b). Groundwater affects and is affected by different geological settings and structures. Whilst most conclusions about groundwater varies between rock and soil types, there are some geological structures that have similar impacts regardless of the geological environment they are presented in (Fitts, 2012).

The porosity of a media has large effects on how water moves and how much can be stored in the media. Porosity in soil and bedrock is usually correlated with grain size distribution – the more well-sorted soils and bedrocks generally have a higher primary porosity. Secondary porosity, however, depends on the existence of structures like fractures and faults. If the porous cavities are not filled, the media will be able to transmit water in the cavities if conditions are right. A coarser material with both high primary porosity (well-sorted) and high secondary porosity (many fractures and/or faults) is more permeable and will be able to transmit more water than its opposite (Fitts, 2012).

Unconsolidated material often forms deposits that can yield large amounts of groundwater and is often located shallowly and connected to some surface water body, making them yield large amounts of groundwater. Stratification, deposition pattern and other properties of these types of deposits can also govern the movement and storage of groundwater. Certain unconsolidated material, like clay and finer silts, can prohibit the movement of water in a geological structure and act as boundaries that confine aquifers. Clays can be very sensitive to the surrounding

environmental conditions and shear strength of the material can decrease rapidly due to

disturbances. Among the unsorted soils, till is an example, consisting of different soil types ranging from boulders to clay (Fitts, 2012).

Mechanisms of Groundwater Lowering

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6 Fig. 2 illustrates three different zones in which water can be found, as well as an overlaying zone through which water percolates to reach the groundwater table; the unsaturated zone. Groundwater can be considered as existing in three different environments that can make up the saturated zone; a saturated soil zone, a shallow groundwater zone in rock and a deep groundwater zone in rock. The contact between these three zones are crucial for determining groundwater movement. Lowering of the groundwater in the shallow groundwater zone in rock must occur for lowering in the saturated zone to occur. The contact between the shallow and deep groundwater in rock varies depending on local conditions; if fractures or fracture systems exists in the interface between them, they will influence each other, otherwise they will not. Hence, these three systems may all be connected and influence each other, or they may be isolated from each other (or some combination) (Axelsson &

Follin, 2000).

Fig. 2: Zones of the subsurface.

Subsurface construction usually occurs at the depth of the shallower groundwater zone in rock, apart from, for example deep geological repository that is stored in the deeper groundwater zone.

During construction of the subsurface infrastructure (in the shallow zone), parts of the rock are removed (by different methods) causing leakage of water to occur to some degree. The amount of water leaking into the construction varies and depends on many factors. It is largely dependent on the fractures and fracture systems that are intercepted during construction and another factor contributing is the total availability of water in the rock and specifically the availability in the intercepted fracture systems. As construction progresses and more rock is removed, the fractures and/or fracture systems that are intercepted will be drained, causing the groundwater levels closest to the construction to lower. The larger the groundwater storage is in the surrounding rock, the smaller the lowering becomes on the entire storage, and vice versa. If there is contact between the shallow groundwater zone, being drained, and the saturated soil zone, the water in the latter will flow toward the subsurface facility through the drained fractures. This will further cause a local lowering in the saturated zone above, that will be lower just above the facility and level off further away. The shape of the water table caused by this drainage is referred to as a cone of depression (Axelsson & Follin, 2000).

In the above scenario, the saturated zone may be an isolated system of water, perhaps divided from the shallow groundwater zone by a layer of impermeable or low-permeability soil. Then, the groundwater in the soil will be less affected by the construction. However, that would cause a larger lowering in the rock, as it is not refilled by the above water (and the total permeability of rock usually is quite small). Other factors that affect the lowering of the groundwater table in is the

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7 recharge to the groundwater, that can slow down the process of lowering. It may also be important to consider if there are any sensitive ecosystems that are connected to water bodies through which groundwater from any of the three groundwater zones is flowing out (Axelsson & Follin, 2000).

Effects and Risks of Groundwater Lowering

Any project conducted in contact with or affecting groundwater in any way may encounter risks connected to groundwater. In general, the subsurface can be unpredictable and there is no explicit summary of the built underground, making facilities underground difficult to locate (SGU, 2017).

This complicates other existing risks even further.

Lowering of the groundwater table can affect the surroundings substantially, both due to natural lowering such as seasonal variations due to less precipitation and due to leakage in infrastructure projects. Agriculture and forest landscapes as well as other sensitive ecological environments are sensitive to water depletion and can be very affected from groundwater lowering. This can also affect areas that act as buffer zones during seasonal droughts, like wetlands (Naturvårdsverket, 2019b). Pilipovic states, referencing the STA, that if here is contact between soil and rock

groundwater storage, vegetation and smaller streams may be drained due to groundwater lowering (Pilipovic, 2018).

Agriculture and water consumption have also shown to be negatively affected by groundwater lowering in terms of yielding less crops and wells drying. In the project Hallandsåsen, where depletion of water storages was substantial and had large effects on surroundings, project employees feared groundwater levels would not recover for decades. However, even though large lowering’s could be observed, the recovery of the groundwater levels occurred faster than predicted, rather in months than decades. During the execution of the ecological control-program, that is the focus of the report regarding Hallandsåsen, the effects on nature remaining from the project (that caused lowering during the 1990s’) were stated to be very limited or non-existing (Annertz, 2016).

However, the project is an example of a project of unexpected groundwater effect that proved to contribute to the price of the project increasing tenfold compared to the initial calculations (Magnusson, 2015).

Construction itself affects and is affected by lowering groundwater levels. One effect that can occur on ground level due to lower groundwater levels, is subsidence. In saturated, finer soils, capillary forces hold water in the soil pores and contribute to maintaining the pressure needed for the ground to handle the weight from overlaying buildings. As groundwater levels decrease, so does the internal pressure in the soil, leading to consolidation of the grains. The overlaying structures weight then entirely allocates the grains themselves. This diminishes both the volume of the soil and the abrasion resistance of it, leading to subsidence of the soil. This type of movement in the soil can occur at different paces, but most often causes damage to buildings (and utilities) and have economic consequences (Pathan & Michalak, 2013). Other effects in terms of construction can be caused due to wooden structures that initially are built below the groundwater table. If the structures are then exposed to oxygen as groundwater levels decline, they may be caused to rot (Statens geotekniska institut, 2019).

Lowering groundwater levels can also lead to issues regarding groundwater quality and contamination. The quality can be affected by an increase of chemical substances in the

groundwater as the levels decrease (SGU, n.d. b). As the natural fluctuations in groundwater are disturbed, changes can be caused in flow patterns that affects areas of discharge and recharge to change functions. Hence, groundwater chemistry can be altered having ranging effects. For example, changes in reduction and oxidation-reactions and the carbonate systems can occur (Olofsson, 1991).

In coastal areas there is a risk for saltwater intrusion as well as microbial contamination when groundwater levels decline (Giglio, et al., 2015). Closer to coastal areas, aquifers tend to store water from the closest waterbody, which in this case contains saltwater. This can, in an unconfined (or partially confined) aquifer create an interface in which the salt groundwater in the aquifer meets the fresh groundwater that exists further inland. If the groundwater flow in the aquifer is not in

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8 equilibrium, the interface will be disrupted, and the two waters will mix partially. Since the

saltwater density is higher, the saltwater will be positioned below the freshwater. When the water table declines and extraction from the aquifer continues, the saltwater may interact even further and maybe also become extracted (USGS, n.d.).

The risks and effects of groundwater lowering can be substantial to the surroundings. It is also important to note that problems caused by, or involving, groundwater can lead to delays and become very expensive during construction of infrastructure. As stated, by Pilipovic (2018) it is crucial to identify risks and carefully plan and organise the project with the influence of these risks.

Infrastructure and the Building Process

The building process for larger road or railway infrastructure projects is complex and often consists of parallel processes, as is illustrated by Fig. 3. The figure illustrates an overview on significant processes that govern the construction and planning process for some transport infrastructure projects. The processes are in most cases adjusted to fit a specific project and are therefore individual for each project and can include processes that are not depicted in this figure (Vestin &

Öste, 2016).

There are some main concepts that are important to understand regarding the planning process.

Consultation is a stage initiated in the beginning of the planning process and further continued until the promulgation and review. The consultation is required by legislation and the purpose is to provide involved actors with information and a forum for discussion regarding localisation alternatives, formation of the project and environmental effects of the project. The consultation should be documented and accounted for in the consultation documents. The County

Administrative Board (CAB) should early in the project use the consultation and consultation material to hear if the project will cause significant environmental impact. The decision made by the CAB should be motivated and the effects on the environment should be described in an

environmental impact assessment (EIA) (Trafikverket, 2014a; Stockholms läns landsting, 2017).

The construction process is initiated in parallel with the planning process. Its extent and detailed description are determined largely by the contract form. The most common contracts are turnkey contracts and performing construction, among which the latter is the most common. In a turnkey contract, the property developer is also responsible for development of general and detailed engineering & design. In performing construction projects, the client is responsible for the general and detailed engineering & design. This is often developed with the help of consultants (Eriksson &

Hane, 2014).

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9 Fig. 3: Timeline Overview for Larger Road/Railway Infrastructure Projects.

Groundwater and Construction

Effects and changes on groundwater levels can be divided into two categories, namely; natural and anthropogenic. Naturally, seasonal and climactic variations have always been abundant in

groundwater storages. Recent changes in land use, for example an increased agricultural land use, can also increase the need for irrigation and hence use groundwater storages. Anthropogenically, there are multiple factors causing altering groundwater levels. These include the increased domestic water use that further contributes to increased pumping of groundwater (International Association of Hydrogeologists, 2016). Another abundant factor that is man-made is effects from construction on groundwater levels (Cashman & Preene, 2014).

Groundwater can cause many problems during construction of infrastructure facilities. The result of these groundwater problems often induces large costs, major delays or even involves the re-design of the facility (Powers, et al., 2007). During excavation, groundwater can cause many technical problems that result in instable constructions. This will be further discussed in the chapter Measures Against Groundwater Lowering in Construction.

Tunnel Construction

The construction of a tunnel can be characterized by aspects concerning hydrogeology in relation to function, geology and environment. The following aspects have been identified by Gustafsson and Wallman (1995) as important contributors for the tunnelling. Functionality is highly affected by water quality of the leaked water and grouting of the permeable rock areas. Geologically, tunnel construction requires a relatively homogenous rock type, well identified fracture sets and zones, low permeability, grouting possibilities and control as well as good water quality. Finally, the

environment poses the following demands; groundwater lowering cannot induce too large settlements temporarily or permanently and the project cannot be too closely located to other facilities or bad rock coverage (Gustafson & Wallman, 1995).

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10 In tunnel construction, there are three main categories. The first one is in-situ tunnels, which is a tunnel built without affecting the ground on top of the tunnel, through removal of in-situ material below ground. Secondly, cut and cover tunnels are built by creating trenches and further covering the trench. Finally, there are tunnels built below or in water bodies called immersed (Lundman, 2011). Overall, it should be stated that tunnelling in rock generally is easier than in soil, although rock is harder to penetrate. The cause of this is the difficulty of upholding the structure of soil during and after construction (Hemphill, 2012).

Measures Against Groundwater Lowering in Construction

During construction in soil or rock, as mentioned in the chapter Mechanisms of Groundwater Lowering, there is a substantial risk for groundwater lowering. The local lowering can be crucial for the construction stability and is especially important when constructing in soil (Powers, et al., 2007). However, as the drawdown spreads further from the construction site, the negative effects of groundwater lowering may appear. To prohibit this, environmental courts sometimes puts demands on groundwater control and reduction of the lowering in the surroundings. These demands can regulate permanent lowering of groundwater levels or levels during construction (Mark- och miljödomstolen, 2017).

In rock, excavation of rock caverns will abstract natural water flow paths and cause the water to leak if preventative measures are not implemented. Leakage will be extensive and concentrated to fractures and fracture zones (Olofsson, 1991). The prevention of leakage in rock can be done before constructing or after. Grouting is done through injecting drilled holes with some injection

substance, allowing it to set and further block water (Vägverket, 2000). Lining facilities made of concrete can also be implemented in rock to further grout and is highly effective for rocks that are fractured extensively (Axelsson & Follin, 2000).

Soil around, and in an excavated area, should be useful for engineering purposes, which creates difficulties regarding groundwater. Groundwater has a large impact on soil stability and other soil properties which can be problematic when excavating below groundwater level. Groundwater in soil can cause a reduction of strength in the material and due to high porewater pressure on excavation slopes, this could even lead to collapse. Uplift pressure from groundwater on the bed of the

excavated area can cause risks for piping failures. Finally, groundwater can cause pressure on supporting structures of built facilities that may damage the entire facility. The mentioned all contribute as reasons to dewater during construction (Calin, et al., 2017). However, there are several risks that can come as an effect of dewatering, as mentioned in the chapter Effects and Risks of Groundwater Lowering.

There are several methods to approach these problems; one is by using cut-off methods to prevent groundwater from entering an excavation. One cut-off structure that can be used is sheet piling, which serves as a classic excavation support (often constructed in steel) that also partially seals the excavation from groundwater. The installation requires driving the sheeting piles into the soil surrounding an excavation, before it has begun and using interlocks between the piles to maintain the structure. Slurry trenches are another effective measure that can be taken to exclude water from entering an excavation. The slurry trench involves the digging of a narrow trench under slurry and further filling the excavated trench with less permeable material. Usually, this material is a mixture between soil and bentonite and the methods of installation vary depending on site conditions (Powers, et al., 2007).

Other methods for abstraction of groundwater is grouting and ground freezing. There are many different types of grouting techniques in soil, among which two are permeation grouting and jet grouting. Permeation grouting allows for grout flow into soil pores while still maintaining the initial composition and structure of the soil. This is either done in the purpose of preventing water from passing, decreasing the permeability of soil or strengthen the soil. Grouting against water using the permeation grouting is extensive and done with chemical grouts like sodium silicates or with particulate grouts that are cement-like material. Jet grouting is a more aggressive method based upon high-pressure jets used to mix, replace or erode soil or weak rock with soil and cement

mixtures. The purpose can be to lower the permeability of the mixed, replaced or eroded material. It

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11 is more commonly done in soils where grouting is not appropriate, but groundwater control is necessary. Finally, ground freezing involves freezing of groundwater in soil pores, which thereby freezes the soil mass surrounding it. This is done through the usage of circulation systems of cold liquid, constructed using freeze pipes in drilled holes of the soil. The purpose of the freezing is again to either increase strength or decrease permeability of the ground (or both) (Powers, et al., 2007).

Artificial Infiltration

Artificial infiltration, or artificial recharge is a method used for prevention of effects from lowering groundwater levels either during construction or permanently. The practical procedure can be done in many ways, but the main goal is to increase the groundwater recharge through controlled and managed infiltration of water to soil and/or rock. The procedure itself is more complex than extraction of water from the aquifer as the infiltrated water should be of good quality and may require pre-treatment (Powers, et al., 2007).

A few different methods for artificial infiltration are filter wells, infiltration in ditches and infiltration in filter pipes. Filter wells are often easily controlled but as their function can be

summarized as opposed to that of an extraction well (that is pumping water to the aquifer), they can be susceptible to clogging. Filter wells are good for deep infiltration and are generally designed like the typical extraction well, with a few minor alterations. Ditches or trenches are used for artificial recharge as water levels in them are maintained constant (through artificially adding water to them). Ditches used should be placed in areas that can infiltrate water naturally quite quickly, that is, areas with soil of high permeability. This option for infiltration is quite low cost but has a few limitations. Like most other infiltration methods, the quality of the water should be high, but the method also requires maintenance, is limited to shallow aquifers and requires large amounts of land. Filter-dressed pipes on the other hand, can be installed to penetrate deeper aquifers, but requires the surface area of the pipe to be maximized. It also requires that the pipes are installed down to the most permeable part of the aquifer to ensure good contact directly. However, they are easily controlled as the water is added directly to the pipes (which also requires water of good quality) (Powers, et al., 2007; Lundgren, 2017a; Lundgren, 2017b).

The Environmental Code and Water Rights Judgement

This chapter will examine how the Swedish legislation and court view groundwater in infrastructure projects.

Environmental Code: Water-related Works

The Swedish legislation concerning water and environment is called the Environmental Code (Ministry of the Environment, 2000). In chapter 11, 3§ (SFS 2020:75, 1998), of the legislation, the term water-related works (vattenverksamhet) includes (but is not limited to) any construction that redirects or adds water that contributes to groundwater alterations. The actor responsible for this

“water-related works” is also responsible to monitor any environmental effects and take measures to improve them. The legal definition of water-related works can include anything from the

construction of a water power plant to the drilling of a drinking water well (Enheten för miljöskydd, n.d.). Concerning hydrogeology however, the following functions are considered water-related works by the 11^th chapter, 3§ (SFS 2020:75, 1998), of the environmental code;

• Altering, construction, or evulsion of a facility in a water district

• Piling or filling in a water district

• Redirecting groundwater or constructing a facility for that purpose

• Blasting or excavating in a water district

• Performing measures in an area that aims to change water depth or position

• Adding water to increase groundwater levels or constructing a facility for that purpose or performing some other measure for that purpose

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12 In a construction project where groundwater may be affected, there are three options regarding legislation of water-related works; applying for approval, claiming exemption or reporting the activity. The approval of water-related works is sought for in the land and environmental court and is a multi-step process. This process includes for example consultation with the CAB and the establishment of an EIA. If the function is smaller and less significant for environmental effect, it may only be required to report the function to the CAB (Enheten för miljöskydd, n.d.). This is however, not possible to do if the function involves redirecting groundwater according to the environmental codes 11^th chapter, 3$ and 9$ (SFS 2020:75, 1998). Exemption is given to any function when it is apparent that there are no public or private interests are affected by it. However, the evidential burden of the stated exemption lies on the function operator (Enheten för mark- och vattenskydd, n.d.).

Multiple actors are involved in the permission of water-related works. The land and environmental court are responsible for approval of water-related works and are the issuers of the verdict allowing the function to operate under some decided conditions. Mentioned are also the CAB that is not only the authority to report the function to, but they may also be the regulatory authority (Enheten för mark- och vattenskydd, n.d.). The institute SGU is the administrative authority for the

environmental objective groundwater of good quality and is therefore often consulted in similar matters. Their role is to guide and provide support in groundwater questions and often be involved in different parts of the application process and directly in the land and environmental court (SGU, 2019; SFS 2020:75, 1998).

The Permission Process

When constructing an infrastructure project of substantial size, many permits may be required from the land and environmental court. Different cases of similar nature are applied for in separate permission applications but may be addressed simultaneously in court (Trafikverket, 2014b). The permission process for water-related works in the land and environmental court can at large be summarized into seven necessary steps, assuming the effect on the environment is assumed to substantial (Enheten för mark- och vattenskydd, n.d.). The steps are summarized in Fig. 4 below.

Fig. 4: Permission process for large infrastructure projects requesting permission for water-related works.

The permission process requires an initial consultation to determine whether the project will imply significant environmental impact, which is unnecessary if the applicant already has determined that this is correct. Further the opinions heard from the consultation should be compiled to provide material for the decision regarding significant environmental impact. The delimitation consultation aims to voice opinions required to produce an Environmental Impact Assessment (EIA) (see next chapter about EIA). The application is proclaimed and the main hearing (sometimes including site visits) is initiated and the court further determines the verdict with accompanying terms. The verdict can be appealed after it is determined which results in the extraordinary court of appeal for land and environment will take on the case (Enheten för mark- och vattenskydd, n.d.).

Water-Rights Judgement

For each project applying for permission of water-related works, a water-rights judgement

(vattendom) is issued (by the land and environmental court) once the project has been through the permission process. The water-rights may permit the function to operate but might also require certain conditions to be followed according to the 16^th chapter of the environmental code (2§) (SFS 2020:75, 1998). These water-rights judgement is specific for a project and may determine smaller

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13 details, like the level of lowering of the groundwater that is permitted at a certain location and for a certain time-span. The water-rights judgement can also determine conditions to be set during construction regarding environmental effects and groundwater or demands regarding control programs (Mark- och miljödomstolen, 2017).

In the permission process (see Fig. 4), an EIA is conducted in the purpose of determining the environmental effects arising from the project itself. Certain projects accompany the EIA with specific investigation about hydrogeology that more in depth investigates the present and

potentially arising hydrogeological conditions of the project. The main effects on the groundwater is often summarized and added to the EIA itself. These hydrogeological investigations (or appendices to them) include calculations, prognoses and/or modelling results performed to estimate

hydrogeological effects from the project implementation (Sundkvist & Wallroth, 2016; Golder Associates, 2017). As part of the EIA, the hydrogeological investigations and their appendices are therefore used in the court as a basis for the water-rights judgement (Enheten för mark- och

vattenskydd, n.d.) (SMHI, 2016). Court procedures requires a technical advisor to be present during the hearings and take part in the judgement according to the second chapter of the law of land- and environmental court (1-2§) (Justitiedepartementet DOM, 2010) . The technical advisor should have a scientific education within the subject on trial according to the law.

Hydrogeological Prognoses in Infrastructure Projects

There are multiple definitions of a hydrogeological prognosis. This chapter will provide an overview of several different definitions and theories regarding the layout of a prognosis, its role in the planning process and identify the different actors that are involved in the creation of the prognosis.

General Definition of a Prognosis

The general, broad description of the word prognosis is “a prediction about how something […] will develop” (tyda.se, n.d.).This very broad definition can be applied to a range of subjects, from overall geotechnical prognoses to specific prognoses regarding injection design for example. A prognosis can be developed by several actors and in multiple stages of the building process. Following is a gathering of more common prognoses done in correlation with infrastructure projects.

The usage of the prognosis in an EIA is common as the prognosis often involves predicting effects of the construction (Naturvårdsverket, 2019b). The legal process of applying for permit to redirect groundwater requires an EIA if a project is considered to influence groundwater conditions according to the 11^th chapter of the environmental code (SFS 2020:75, 1998). These documents often include some prognoses on the effect on the groundwater levels from the infrastructure facility. Methods used for development of the prognoses could be a simple water balance, but also advanced modelling tools depending on what type of facility is being built and what the

hydrogeological conditions are (Werner, et al., 2012).

Olofsson (1991) describes two types of prognoses in the report Impact on Groundwater Conditions by Tunnelling in Hard Crystalline Rocks; prognosis of drawdown and water leakage in rock caverns and tunnels. A drawdown prognosis, according to Olofsson, is based on idealistic situations where water flow is estimated based on homogenous and isotropic conditions. The second prognosis is often carried out through site investigation methods, sometimes in combination with numerical models. The methods referred to in the report, used a continuum approach in order to provide regional values of leakage per unit length that excluded permeable zones (that were calculated separately).

Another report, Hydrogeological modelling in the geotechnical forecast (Gryaznova, 2018), states that a geotechnical forecast should contain a hydrogeological forecast, as determined by national regulatory documents. The hydrogeological prognosis is determined to provide an estimate of quantitative potential alterations in the groundwater conditions when designing construction. In the geotechnical prognosis, the following hydrogeological components should be included (Gryaznova, 2018);

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14

• Assessment of hydrogeological conditions of the construction site and its surroundings,

• A geofiltration model,

• Prognosis of hydrogeological conditions and a timeframe for the construction and use of the underground structure planned,

• Assessment of alternative prevention measures due to changes in the groundwater conditions.

The hydrogeological prognosis is further in the report verified and partially results in a forecast map for groundwater level changes in the construction area. Based upon the developed hydrogeological forecast, the author gives a recommendation regarding the future construction project (Gryaznova, 2018).

Specific Prognosis from a Hydrogeological Perspective

There are also smaller prognoses that can be made for more specific purposes, an example of this is a geological prognosis related to rock grouting design. A Swedish pair of researchers have developed a prognosis which includes a description of the hydraulic behaviour of rock masses. The rock mass is further divided into hydraulic domains, representing flow regimes of the different domains.

Finally, the prognosis included need for measures for prohibition of leakage in the construction project and the leakage to the construction was estimated (Kvartsberg & Fransson, 2013).

Wilén et al. (2014) proposes to use the concept of “behovsprövad injektering” (roughly a synonym to selective grouting) where grouting is performed in the zones where a need has been identified by investigations or prognoses. To determine these zones of need, a hydrogeological prognosis is developed through accomplishing some objectives related to model concept. This hydrogeological model is based on parameter values that have been estimated either quantitatively or qualitatively through a hydrogeological description of the area. The results from the conceptual model is a prediction of where grouting is required and how it is to be performed (Wilén, et al., 2014).

A methodology is presented in the report by Wilén et al. (2014) where model concepts were used to determine areas containing objectives leading to the prognosis. The conceptual model resulting in a prognosis can be seen in the Fig. 5 below (Wilén, et al., 2014).

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15 Fig. 5: Conceptual model leading to a hydrogeological prognosis according to Wilén et al. (2014).

The process above, leading to the hydrogeological prognosis was in the report part of the

preliminary investigation program. Input data to the program was investigation material which was further characterised and used as a basis for development of the model concepts. Further, the prognosis was developed according to Fig. 5 and a more detailed prognosis was developed and used as a basis for executing the grouting needed. Between the process of bringing forth the

hydrogeological prognosis and determining the classification and possibilities for grouting, a permission process was ongoing. This process further contributed to the detailed and general prognosis and involved the following information to be determined (Wilén, et al., 2014):

• Identification of objects subjected to damage

• Investigation of leakage and groundwater lowering (including identification of an area under influence of these effects)

• Identifying consequences for objects subjected to damage

• Developing guidelines for allowed leakage values

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16 Swedish Transportation Administration (STA) Prognosis from a Hydrogeological Perspective The Swedish Transportation Administration (STA) has a thorough explanation of a prognosis. The agency defines two different types of prognoses, with different purposes; one geological engineering (ingenjörsgeologisk) and one technical rock (bergsteknisk) prognosis. The product of the

preliminary investigations is portrayed in these prognoses. The purpose of the geological engineering prognosis is mainly to lay a foundation for planning of technical solutions including uncertainties. The technical rock prognosis, on the other hand, aims to continue from the geological engineering prognosis in order to lay a foundation for an economical offer (anbudsräkning) and execution during the construction. It is a simplified version of the engineering geological prognosis but including a specification of technical solutions (Lindfors, et al., 2019).

Investigating the tunnelling project City Line, in Stockholm, the consultants Swindell and Rosengren (2007) found two definitions of prognosis like that of the STA. The engineering geological (ingenjörsgeologisk) prognosis aims to make a basis for decisions regarding valuation and design of different measures. It is based upon the pre-investigation report and should account for uncertainties in the geological conditions, but it is not to be included in the tender documents.

The rock technical (bergsteknisk) prognosis aims to make a basis for the tender phase and for the execution of the tunnelling project. In comparison to the engineering geological prognosis, this is a simplified or generalised version. However, it also includes information regarding reinforcement and grouting measures and should be part of the tender documents (Swindell & Rosengren, 2007).

Fig. 6 below illustrates the use of the different prognoses in the planning process of the STAs prognoses (discussed in the section above) (Lindfors, et al., 2019).

Fig. 6: Flow chart of process from Preliminary Investigations to finished construction documents (blue) according to the Swedish Transportation Administration.

The geological engineering prognosis is an interpretation of the geological conditions from an engineering perspective. This interpretation follows two steps. Firstly, an overview of the geological conditions and tectonic development in the area is established through studies of relevant data.

Secondly, sources are further studied in detail to understand geology and changes in rock character of the area. This leads to a division of the rock mass into different domains that can account for rock types, rock quality, structure and finally hydrogeological conditions. The number of domains the rock mass is divided into depends on the complexity of the rock mass and of the construction. Both prognoses should be presented in text and layout drawings or a digital model (Lindfors, et al., 2019).

In a report from the Swedish Transport Administration (STA) (Malmtorp & Lundman, 2010), the purpose of a prognosis is to make a characterisation and classification to be able to evaluate the execution of the project regarding tunnelling, reinforcement and grouting. The characterization and classification follow in every step of the planning and building process and is followed by mapping during the initiation of construction. The latter being an important tool for evaluation of the characterizations done in the prognosis (Malmtorp & Lundman, 2010). The STA refers to Lundman (2006), regarding more detailed definitions within rock prognoses. Characterisation is done to find rock mass properties when the rock mass itself is undisturbed whilst classifications also consider geometric factors, stress conditions, etc. (Malmtorp & Lundman, 2010).

In the report, data from several tunnels, such as Ådalsbanan, has been used. The preliminary investigation methods that have been used in these cases, were used to generate prognoses. The

Hydrogeological Prognoses in Infrastructure Projects: A Case Study of Stockholm Bypass, Hjulsta Norra

Hydrogeological Prognoses in Infrastructure Projects

- A Case Study of Stockholm Bypass, Hjulsta Norra

FRIDA GRENHOLM

Hydrogeological Prognoses in Infrastructure Projects

- A Case Study of Stockholm Bypass, Hjulsta Norra

FRIDA GRENHOLM

Supervisor

BO OLOFSSON

Examiner

BO OLOFSSON

Supervisor at NCC CECILIA MONTELIUS

Sammanfattning

Abstract

Acknowledgements

Table of contents

Definitions

Introduction

Literature Studies