Stockholm Bypass Research Articles

Förbifart, Bypass Stockholm

AbstractThe Stockholm bypass (E4 Förbifart Stockholm) is being built by the Swedish Transport Administration (Trafikverket) – the office responsible for transport infrastructure in Sweden. The project aims to improve connections between the regional town centres and reduce congestion on the main urban roads. The route, which runs mainly underground, employs numerous contractors and has a planned construction period of 14 years, preceded by a 10‐year planning phase. This article looks at three projects: the FSE 61 Akalla Interchange, the FSE 309 Lovön Interchange and in particular, the FSE 613 Akalla Tunnel. The Akalla Tunnel is driven as a conventional full‐face excavation with pre‐grouting and supported with rock bolts and steel‐fibre‐reinforced shotcrete. The tunnel excavation is followed by the interior work comprising precast concrete walls, a suspended membrane reinforced with shotcrete, ceiling foundations and the carriageway structure.

Drill Monitoring for Rock Mass Grouting: Case Study at the Stockholm Bypass

In tunneling, rock mass grouting is a method applied to reduce water ingress. Grouting is influenced by rock mass conditions, especially apertures, frequency, and continuation of fracturing. These rock mass conditions can partly be determined by rock mass classification systems. At the Stockholm bypass, the Measurement While Drilling (MWD) Fracturing Index was applied to characterize the rock mass for grouting purposes, with a focus on adjusting the grout hole drill plan to minimize environmental impact. This study divided the rock mass in a 1.9 km tunnel into six categories based on rock mass conditions, identifying rock mass quality, apparent fracturing, and grout consumption. These categories were then compared with the mean fracturing index based on the coefficients of penetration rate and rotation pressure variations, as well as grout consumption at each grout umbrella. The fracturing index was 93% successful in assessing favorable and unfavorable rock mass conditions in the studied tunnel and 85% successful in determining grout consumption. Finally, a conceptual method was developed to reduce the grouting activities using the MWD fracturing index and water loss tests. The introduction of this conceptual method for grouting decisions could potentially reduce 59% of the umbrellas found in the case study.

Rock support prediction based on measurement while drilling technology

In tunnelling, rock mass support is designed based on the observed rock mass conditions. These conditions are determined by rock mass characterization. Measurement while drilling (MWD), one such characterization method, acquires drill parameter data during drilling. These data can be used to predict rock mass conditions ahead of the face. In this study, grout-hole MWD data are collected at one of the main tunnels in the large infrastructural project Stockholm bypass tunnels. The normalized and filtered MWD data are correlated to the rock mass characteristics using multilinear regression and the Levenberg-Marquardt method. Although a strong numerical correlation cannot be obtained, the results are promising. As a result, a holistic visual approach, which linked the MWD parameters with the rock mass classification and rock support requirements, was developed.

Application of Measurement While Drilling Technology to Predict Rock Mass Quality and Rock Support for Tunnelling

A tunnelling project is normally initiated with a site investigation to determine the in situ rock mass conditions and to generate the basis for the tunnel design and rock support. However, since site investigations often are based on limited information (surface mapping, geophysical profiles, few bore holes, etc.), the estimation of the rock mass conditions may contain inaccuracies, resulting in underestimating the required rock support. The study hypothesised that these inaccuracies could be reduced using Measurement While Drilling (MWD) technology to assist in the decision-making process. A case study of two tunnels in the Stockholm bypass found the rock mass quality was severely overestimated by the site investigation; more than 45% of the investigated sections had a lower rock mass quality than expected. MWD data were recorded in 25 m grout holes and 6 m blast holes. The MWD data were normalised so that the long grout holes with larger hole diameters and the shorter blast holes with smaller hole diameters gave similar results. With normalised MWD data, it was possible to mimic the tunnel contour mapping; results showed good correlation with mapped Q-value and installed rock support. MWD technology can improve the accuracy of forecasting the rock mass ahead of the face. It can bridge the information gap between the early, somewhat uncertain geotechnical site investigation and the geological mapping done after excavation to optimise rock support.

Boat-towed radio-magnetotelluric and controlled source audio-magnetotelluric study to resolve fracture zones at Äspö Hard Rock Laboratory site, Sweden

SUMMARY Boat-towed radio-magnetotelluric (RMT) measurements using signals between 14 and 250 kHz have attracted increasing attention in the near-surface applications for shallow water and archipelago areas. A few large-scale underground infrastructure projects, such as the Stockholm bypass in Sweden, are planned to pass underneath such water zones. However, in cases with high water salinity, RMT signals have a penetration depth of a few metres and do not reach the geological structures of interest in the underlying sediments and bedrock. To overcome this problem, controlled source signals at lower frequencies of 1.25 to 12.5 kHz can be utilized to improve the penetration depth and to enhance the resolution for modelling deeper underwater structures. Joint utilization of boat-towed RMT and controlled source audio-magnetotellurics (CSAMT) was tested for the first time at the Äspö Hard Rock Laboratory (HRL) site in south-eastern Sweden to demonstrate acquisition efficiency and improved resolution to model fracture zones along a 600-m long profile. Pronounced galvanic distortion effects observed in 1-D inversion models of the CSAMT data as well as the predominantly 2-D geological structures at this site motivated usage of 2-D inversion. Two standard academic inversion codes, EMILIA and MARE2DEM, were used to invert the RMT and CSAMT data. EMILIA, an object-oriented Gauss–Newton inversion code with modules for 2-D finite difference and 1-D semi-analytical solutions, was used to invert the RMT and CSAMT data separately and jointly under the plane-wave approximation for 2-D models. MARE2DEM, a Gauss–Newton inversion code for controlled source electromagnetic 2.5-D finite element solution, was modified to allow for inversions of RMT and CSAMT data accounting for source effects. Results of EMILIA and MARE2DEM reveal the previously known fracture zones in the models. The 2-D joint inversions of RMT and CSAMT data carried out with EMILIA and MARE2DEM show clear improvement compared with 2-D single inversions, especially in imaging uncertain fracture zones analysed in a previous study. Our results show that boat-towed RMT and CSAMT data acquisition systems can be utilized for detailed 2-D or 3-D surveys to characterize near-surface structures underneath shallow water areas. Potential future applications may include geo-engineering, geohazard investigations and mineral exploration.

The Stockholm Bypass – Design and execution of grouting works

AbstractThe E4 Stockholm Bypass is a new route for the European highway (E4) past the Swedish capital Stockholm. The bypass will connect the southern and northern parts of Stockholm. To reduce the impact on the surroundings, 18 km of the total of 21 km of the Stockholm Bypass are being constructed in tunnels. The Bypass will be one of the longest road tunnels in the world, with a construction cost of 3.1 billion Euro (2009 prices).The challenges have been many, for example how to evaluate the hydraulic rock mass properties for such a vast tunnel stretch and then find the most suitable grouting design, the contractor's ability to deliver proper grout properties and suitable grouting equipment, the time and resources needed for QA/QC of the grouting works and the need for adaption of the grouting works to true geological conditions. Not to mention the complexity of monitoring water ingress during construction for the Client to show that the sealing demands are being met according to the environmental permits for water works operations. The Stockholm Bypass is by far the largest rock fissure grouting operation undertaken for road tunnels in Swedish history.

Integrating evacuation research in large infrastructure tunnel projects - Experiences from the Stockholm Bypass Project

Large infrastructure projects often involve important decision about evacuation safety measures, e.g., emergency exit portals, alarm systems, etc, that need to be taken in spite of limited information and knowledge about the topic. This has been shown to sometimes lead to design mistakes, but these mistakes can potentially be avoided if research is linked to the project at an early stage. This paper discusses how research can be connected to large infrastructure tunnel projects, and illustrates the process using the Stockholm Bypass Project as an example. In addition, the results of a research project, which was linked to the Stockholm Bypass Project, are presented and relevant additional publications are given.

Resolution and sensitivity of boat-towed RMT data to delineate fracture zones – Example of the Stockholm bypass multi-lane tunnel

The resolution and sensitivity of water-borne boat-towed multi-frequency radio-magnetotelluric (RMT) data for delineating zones of weaknesses in bedrock are examined in this study. 2D modeling of RMT data along 40 profiles in joint transverse electric (TE) and transverse magnetic (TM) as well as determinant mode was used for this purpose. The RMT data were acquired over two water passages from the Lake Mälaren near the city of Stockholm where one of the largest underground infrastructure projects, a multi-lane tunnel, in Europe is currently being developed. Comparison with available borehole coring, refraction seismic and bathymetric data was used to scrutinize the RMT resistivity models. A low-resistivity zone observed in the middle of all the profiles is suggested to be from fracture/fault zones striking in the same direction as the water passages. Drilling observations confirm the presence of brittle structures in the bedrock, which manifest themselves as zones of low-resistivity and low-velocity in the RMT and refraction seismic data, respectively. Nevertheless, RMT is an inductive electromagnetic method hence the presence of conductive lake sediments may shield detecting the underlying fractured bedrock. The loss of resolution at depth implies that the structures within the bedrock under the lake sediments cannot reliably be delineated. To support this, a synthetic data analysis was carried out providing useful information on how to improve and plan the lake measurements for future studies. Synthetic modeling results for example suggested that frequencies as low as 3kHz would be required to reliably resolve the bedrock and fracture zone within it in the study area. The modeling further illustrated the advantage of a fresh water layer that acts as a near-surface homogeneous medium eliminating the static shift effects. While boat-towed RMT data provided substantial information about the subsurface geology, the acquisition system should be upgraded to enable controlled-source data acquisition to increase the penetration depth and to overcome the shortcomings of using only radio-frequencies.

Radio Magnetotelluric (RMT) measurement over lake Mälaren, Sweden a case study

Over the past few decades the application of frequency domain radio Magnetotelluric (RMT) have been well established and utilized in the studies of near surface geophysics. This method uses the distance radio transmitter in the frequency range 15 to 250 kHz as source and acts as a tool to model the variation of electrical resistivity of the subsurface. In practice, three component magnetic and two component electric data are measured and recorded. These measured quantities are then used to estimate the earth’s electromagnetic transfer functions called impedance tensor and tipper vector. The transfer function carries the information related to resistivity variation of the subsurface. The present study was carried out in an urban setting which is a challenging environment for this method. The Swedish Road Authorities (Trafikverket) has proposed and planned several infrastructure project to cater the immense overload of traffic in the Stockholm city due to growing population. One such project initiated by Swedish road authorities is the Stockholm bypass project that is a ten year construction plan of 21 km long motor way and to reduce the impact on the environment 18 km will be located in tunnel. The main objective of this study is thus to identify potential fracture zones and faults as well as the general geological settings. The proposed tunnel will be at a depth of 60m and will pass under Lake Malaren at three areas. This raised an opportunity and challenge to explore the applicability of the land RMT measurement system called EnviroMT (Bastani 2001). This acquisition system developed in Uppsala University has already proved to be a robust tool for land survey. To make it applicable in shallow water environment, an improvisation of existing EnviroMT system was pioneered by Geological Survey of Sweden (SGU). The prototype acquisition system was successfully tested in April 2012 by Geological Survey of Sweden (SGU) on Lake Malaren. The new system did not only turned out to be appropriate for such a challenging environment, but it was also much more efficient as compared with land surveys. The survey extensively covered all the three water passages. In three days, fifty two lines including 1160 stations with an average spacing of 15m were covered. Urban environment have its own adverse effect on the RMT data. Such cultural noises had to be identified and removed to obtain more accurate and realistic model. Parametric representation combined with a Truncated Singular Value Decomposition (TSVD) regularization described in Bastani and Pedersen (2001) was used to carry out the processing of the noisy data. Strike analysis of all the profile lines suggested the structure to be mostly 2D except for some region where multiple strike direction was observed suggesting a 3D structure. Thus the data were inverted to obtain 2D resistivity models using EMILIA (Kalscheuer et al., 2010) for all the lines and 3D models using WSINV3DMT (Siripunvaraporn and Egbert, 2000) for a few selected region. The resistivity models of all the lines had consistent features in term of water depth, sediments thickness and the depth to the bedrock (Mehta S et.al 2014). A coherent low resistivity is observed across all the lines and it coincides well with the low velocity zone suggest by the available seismic refraction survey in the same region. This is an indication of a possible fracture zone in the bedrock. The comparison of 3D slices with the 2D resistivity models along the lines further increases the certainty of the fracture zone.

Using Driving Simulators in Road Design–A Road Safety Study of Merging Traffic in Tunnels

The present study describes a simulator study on the merging of traffic from entry-ramp tunnels into the main Stockholm bypass tunnel. The present study focuses on two of the five junctions with connections at Lovo and Vinsta. Three research questions were formulated relating to 1) Is there a difference in the subjective and/or objective measures between the two different entry-ramp tunnels (Lovo, 1.5 km and Vinsta, 0.5 km)? 2) Is driver performance when merging affected by the drivers’ experience when entering the main tunnel from the entry-ramp tunnel? 3) Does traffic intensity and its subsequent effect on the gap size between vehicles influence the frequency and character of hazardous situations such as late merging? Twenty-one participants completed the study. The main results of the reported study suggest that the merging zones were too short for some of the drivers in order to merge comfortably and safely. The merging zones are found at the point where the entry-ramp tunnel merges with the main motorway tunnel. For the Vinsta (0.5 km) merging zone with heavy traffic the distance-to-wall measure (the measure that gauges how much of the merging zone remains at the time of merge-completion) is particularly concerning from a road traffic safety perspective because more than 25% of the drivers completed the merging manoeuvre with less than two seconds of Time Headway (THW) remaining before the end of the completion section. Two seconds of travel before the ending of the tapered completion section of the merging zone was considered to be the bare minimum in terms of safe driving and safe merging. Two seconds equates to 44.4 m when travelling at 80 km/h. The completion section of the merging zone also tapers to the width of a car (approx. 2 m) 40 m from the end of the merging zone.

Driver distraction in an unusual environment: Effects of text-messaging in tunnels

Text messaging while driving can be distracting and significantly increases the risk of being involved in a collision. Compared to freeway driving, driving in a tunnel environment introduces factors that may interact with driver attentional resources to exacerbate the effects of distraction on driving safety. With planning and design of the 18km Stockholm Bypass tunnel ongoing, and because of the potentially devastating consequences of crashes in long tunnels, it is critical to assess the effects of driver distraction in a tunnel environment.Twenty-four participants (25–50 years) drove in simulated highway and tunnel road environments while reading and writing text messages using their own mobile phones. As expected, compared to driving alone, text messaging was associated with decrements in driving performance and visual scanning behavior, and increases in subjective workload. Speeds were slower compared to baseline (no text-messaging) driving when participants performed the text-messaging tasks in the tunnel environment compared to the freeway, suggesting that drivers may have attempted to compensate more for the increased text-messaging-related workload when they were in the tunnel. On the other hand, increases in lane deviation associated with the most complex text-messaging task were more pronounced in the tunnel compared to on the freeway. Collectively, results imply that driver distraction in tunnels is associated with generally similar driving decrements as freeway driving; however, the potential consequences of these decrements in tunnels remain significantly more serious. Future research should attempt to elucidate the nature of any differential compensatory behavior in tunnel, compared to freeway, driving. In the meantime, drivers should be advised to refrain from text messaging, especially when driving in tunnels.