Blast damage in tunnels is usually regulated in Swedish infrastructure contracts as it can influence the quality and lifecycle cost for tunneling projects. The topic is important for underground constructions with a long operation period such as tunnels for public transport, permanent access tunnels in mines or underground repositories for nuclear waste. This paper aims to evaluate the influence of design and geology variables on the resulting blast fracture length and frequency by means of multivariate data analysis. The analysis was based on data from five field investigations carried out at tunnel sites in Sweden and Finland where emulsion explosives were used. Data was compiled and analyzed using Principal Component Analysis (PCA). Charge concentration was found to be the most influential design variable and hole spacing had limited influence on blast fracturing. Results from the PCA suggest that blast fractures length could be dependent also on geology and natural fractures. Three main groups of fracture patterns were identified, one group with relatively few and short blast fractures, a group with several longer blast fractures and a group with few or a single long blast fracture. The result shows differences in fracture length between the column and bottom charge part of the contour holes, with blast fracture lengths up to approx. 40 cm for the column charge and up to approx. 60 cm for the bottom charge.

Numerous aspects of underground construction, from structural stability to construction costs, depended on the tunnel quality, including blast damage and the Excavation Damage Zone. Accurately quantifying the extent and severity of damaged rock is a problem. Recent technical developments in the field of Measurement While Drilling (MWD), including software for on-board logging and on-site analysis, have shown potential for rock-mass characterization. Ground Penetrating Radar (GPR) and P-wave velocity measurement have also improved and show similar potential. This paper explores the use of MWD, GPR and P-wave velocity measurements and uses them in techniques for excavation damage characterization and prediction. The paper is based on data collected from a small underground wastecollection site in central Stockholm, Sweden. The data is correlated against rock-mass characteristics and their responses are evaluated. Results indicate potential for excavation damage characterization for all tested techniques, which could minimize blasting damage and improve the over-all tunnel quality.

This paper presents two recent studies on the extent of blast damage after excavation in crystalline rock. The Swedish Transport Administration and the Swedish Nuclear Fuel and Waste Management Company (SKB) are both under regulations to limit excavation damage during construction of tunnels. SKB is also required to limit the Excavation Damage Zone (EDZ), as this could be a potential flow path for radionuclides in the planned repository for spent nuclear fuel.Presented in this paper are investigations of blast damage from three tunnel sites, a road tunnel, an experimental tunnel in Äspö Hard Rock Laboratory and an underground subway depot.As expected the fractures resulting from the bottom charge are both longer and more frequent then those mapped in the column charge. The results show that the requirement to limit blast damage according to Swedish regulations was fulfilled for the column charge at the three studied sites.

A project was initiated by SKB and Forcit Sweden AB to investigate blast damage from emulsion explosives in two experimental tunnels in Äspö HRL. The new tunnels were excavated with emulsion explosives (Kemitti 810) and charging was done with a Forcit charging unit model 201. Extensive documentation of the excavation works was conducted, so that charge concentration per hole is traceable in contour, floor and helpers. Contour and floor holes were charged with concentration 0.35 and 0.5 kg/m respectively. In order to study blast fractures, five slots were excavated in the wall and floor. The results from mapping of the slots shows a longest blast fracture of 24.5 cm for the 0.35 kg/m charge and 24.1 cm for the 0.5 kg/m charged holes. Generally, there is a large spread in the results with few fractures longer than 20 cm.

Det finns ett behov inom berg- och tunnelbranschen i Sverige av en praktiskt tillämpbar skadezonstabell för moderna emulsionssprängämnen. Behovet är tydligast när krav ställs på minimerad påverkan på kvarstående berg. Minimerad sprängskada i tunnlar kan reducera mängden överberg, oönskade bergutfall samt skrotningsbehov, både under bygg- och driftskede. Den här rapporten redovisar resultat från det första projektsteget i BeFo-projektet Underlag till skadezonstabell för emulsionssprängämne i bergtunnlar, som är ett sammarbetsprojekt mellan Svensk Kärnbränslehantering AB (SKB) och Forcit Sweden AB. Steg I omfattade sammanställning av befintlig laddningsdata mot sprängsprickor för två experimenttunnlar som byggdes i Äspölaboratoriet under 2012. Tunnlarna drevs med emulsionssprängämne (Kemitti 810) och dokumentation av bergarbetena under entreprenaden var omfattande. Mängden emulsionssprängämne per hål är därför spårbart i kontur, sula och hjälpare. I Steg II planerar projektet att komplettera och data från steg I med data från en annan site för att ta fram ett mer komplett underlag till en framtida skadezonstabell för emulsionssprängämne.För att studera sprängsprickor i vägg och sula har 5 slitsar sågats ut i två av de nya experimenttunnlarna på -410 m nivån i Äspölaboratoriet. Snitten lokaliserades genom kontroll av data från sprängning, GPR-reflektorer samt synliga borrpipor. Projektets ambition har varit att data skall ha hög tillförlitlighet och att hela processen skall vara väldokumenterad. Slitsarna karterades med avseende på både sprängsprickor och geologiska sprickor. Karteringsdata har sedan satts samman med laddningsdata från utbyggnadsprojektet. Kontur- och sulhål i de aktuella tunnlarna laddades med 0,35 respektive 0,5 kg/m. Resultatet från karteringen av sprängsprickor visar på en längsta radiell spricklängd om 24,5 cm för laddningskoncentrationen 0,35 kg/m och 24,1 cm för laddningskoncentrationen 0,5 kg/m. Generellt visar resultatet stor spridning med få sprickor längre än 20 cm.Resultatet är mycket bra för laddning med strängemulsion och den begränsade sprickbildningen tyder på en mycket bra borrnoggrannhet, en låg laddningskoncentration och att hålen detonerat momentant. Kontur- och sulhålen har initierats med elektroniska sprängkapslar och dessa har en mycket låg tändspridning vilket tidigare undersökningar visat ge kortast sprickbildning (Olsson och Ouchterlony, 2003).

Knowledge about the Excavation Damaged Zone (EDZ) is essential for underground construction design, underground facility layout, work environment issues and analysis of post-closure safety for a final repository for nuclear waste. The EDZ is defined as the zone around a tunnel where the damage is not reversible. The EDZ can be caused by the excavation method as well as by the actual strength–stress conditions.SKB has chosen the Forsmark site for disposal of spent fuel. The site conditions include hard crystalline rock and fairly high stresses. However, analyzes prior to site selection found that the risk for stress induced development of an EDZ is limited. The aim of this paper is to outline the blast design concept and quality control measures to ensure that the excavation method fulfills the requirements. Strategies for blast design and QA/QC measures for tunnel excavation were applied during construction works for the Äspö HRL expansion 2012. This provided an opportunity to demonstrate methods for tunnel excavation and verify that requirements on minimizing the EDZ could be met during the construction of the planned Swedish final repository for spent fuel.

SAMMANFATTNING:SKBs krav på bergschakt, som tillämpades i utbyggnadsprojektet på Äspö, är relaterade till KBS-3 metoden för deponering av använt kärnbränsle. Metoden innebär deponering av använt kärnbränsle i kopparkapslar, 500 m under mark i ett system av deponeringstunnlar som sedan återfylls med bentonitlera.Under 2012 byggdes Äspölaboratoriet ut för att tillgodose behovet av utrymmen för experimentplatser. Nya tunnlar byggdes på -410 och -450 m nivån. Tunnlarna drevs med emulsionssprängämne (Kemitti 810) och laddning utfördes med en laddutrustning modell Forcit laddenhet 201 med slangdragare för strängladdade håltyper. Omfattande dokumentation av bergarbetena har gjorts under projektet så att mängden emulsionsprängämne per hål är spårbart i kontur, sula och hjälpare.För att studera spränginducerade sprickor i vägg och sula planeras ett antal sågsnitt i två av de nya experimenttunnlarna på -410 m nivån i Äspölaboratoriet. Ambitionen är att bidra till kunskap om sprängskadezon (EDZ) orsakad av emulsionssprängämne under realistiska förhållanden vid tunneldrivning. Försök planeras också med Forcits nyutvecklade laddenhet ECMII.

The unique requirements on post-closure safety related to the construction of a disposal facility for spent nuclear fuel demands measures to control and verify the construction process. The Swedish Nuclear Fuel and Waste Management Company (SKB) have selected the Forsmark site for construction of a repository facility. Traceability in all work steps is necessary in order to verify that requirements for post-closure safety on the underground openings are met. This puts high demands on the construction of the deposition tunnels, as well as on the documentation of the construction works.The Äspö Hard Rock Laboratory (HRL), Sweden, is used by SKB for research and development of technology required for the final repository for spent nuclear fuel. During 2012 the HRL was expanded with 308 meters of new main and experimental tunnels. This was a good opportunity for SKB to apply requirements related to control, traceability and verification of the drill and blast excavation method. The tunnels were excavated using a factory new drilling jumbo and emulsion explosives, both with modern logger equipment, in order to receive a good control and documentation of drilling and charging works. The control plans for the work included additional measures to control, document and verify the process and results of the excavation. This paper aims to describe and exemplify the process of blast design, quality control, documentation and verification of the excavation works together.

This paper presents experiences from the conducted grouting works regarding low-pH grout, grouting equipment, control and quality assurance which were acquired during the Äspö HRL expansion project. Companion papers describe the strategy for geoscientific investigations and modelling (Morosini and Hultgren, 2013) and the grouting strategy using the observational method (Olofsson et al., 2013a). Äspö HRL was expanded during 2012 in order to create new experimental sites as well as to develop and verify SKBs methods for tunnel construction. One of the objectives for the Äspö expansion project was to apply a full-scale industrialized test with low-pH grouting material. During complementary grouting in the fans intersecting water bearing fractures plastic plugs of grout were pushed out of the grouting boreholes due to hydraulic connections between holes and slow shear strength development in the low-pH grout. Grouting each fan in two steps and extended time for hardening during the excavation cycle proved to be the most efficient measures to handle the problems related to the slow hardening process of the low-pH grout.