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Abstract Ground penetrating radar (GPR) is a non-destructive electromagnetic method widely used in civil engineering surveys and investigations. GPR applications can be used to analyse rock mass integrity and to detect geological and geometric features such as lithological unit interfaces, fractures, shear zones and voids. Typically, GPR studies have relied on laboratory values of relative dielectric permittivity for calibration. These are effective (homogeneous) medium values for a system that differs from the instrument that is actually used in the field, measured from small samples. In order to investigate GPR signal propagation in the rock mass, a slab of 100 × 90 × 30 cm (width × height × depth) was sawcut from a larger intact rock block of largely homogenous grey granite from Kuru, Tampere, Finland. Point like GPR measurement with central frequency of 1600 MHz were carried out in a grid on both 100 × 90 cm slab surfaces. Altogether 63 points per side were measured with approximately 250 scans per point. Average relative dielectric permittivity of the rock slab was 4.82, which was also the median value. Relative dielectric permittivity varied from 4.74 to 4.90, giving a range of 0.16 (3.3 % of the mean value). Average attenuation of the signal in the rock slab was -16.39 dB/m, with a range from -16.08 dB/m to -16.67 dB/m, or 0.59 dB/m (3.6 %). This study provides information on true attenuation and dielectric properties, as measured with a device to be used in the field, in an actual, relatively homogeneous rock mass. They can be used to obtain more accurate information on the location and size of e.g. fractures, fracture zones, inclusions or altered zones within the rock mass. Furthermore, the process described here can be applied elsewhere to obtain similar, localised and device specific attenuation and relative dielectric permittivity values. 1 Introduction Ground penetrating radar (GPR) method is widely used in civil engineering surveys and investigations. GPR is a non-destructive electromagnetic method, the use of which requires understanding of the signal behaviour in the medium. Along the traditional GPR reflection interpretation the GPR signal analysis provides valuable information of the medium properties. Signal behaviour and interaction in the medium is governed by the electromagnetic properties of the investigated material. Changes in rock mass electromagnetic properties can be related to mechanical and hydrological properties. GPR applications can be used to analyse rock mass integrity and to detect geological features such as lithological unit interfaces, fractures, shear zones and voids. For example, reflected GPR signal frequency content can be linked to the damage level in the rock due to drill and blast excavation.
ABSTRACT: Understanding of EDZ formation, properties and significance has increased recently. EDZ has been evaluated as long term safety issue in spent nuclear fuel disposal. The objective of the study was to characterize EDZ in varied blasting designs. D&B excavations were performed using emulsion explosive Kemiitti 810. GPR EDZ method was used in measuring EDZ extent. Five blasting rounds were excavated in crystalline rock. Blasting and geology relates studies were performed along the visual inspections. The difference in EDZ extend was almost nonexistent. Emulsion explosive Kemiitti 810 with nominal charge 400 g/m is suitable for sites requiring maximum EDZ extent of 400 mm. The GPR EDZ results were well in line with visual inspections. NDT method is suitable in EDZ extend definition. Formed EDZ has safety and economical perspective in mining and civil construction as well. Future investigations concentrates on time evolving EDZ due to rock mechanical pressure in the underground facility. 1 INTRODUCTION Excavation Damaged Zone (EDZ) has been noticed to have impact to underground construction work as well as working safety. Overall understanding of the EDZ formation, properties and significance has increased recently. Posiva Oy and Swedish Nuclear Fuel and Waste Management Co (SKB) as well as other companies involved in spent nuclear fuel disposal research have evaluated the EDZ as a long term safety issue. Various testing methods in EDZ investigation has been tested and evaluated. Series of studies have been made to characterize and evaluate the significance of the EDZ. This project named as LOVA was designed by group of companies working in excavation related field. Project participants are Posiva Oy (Posiva), Swedish Nuclear Fuel and Waste Management Co (SKB), Oy Forcit Ab (Forcit), Sandvik Mining and Construction Oy (Sandvik), EDZ-consulting AB and Geofcon as project leader. All of the participants bring different expertise to the project crew. The objective of this project was to characterize EDZ in varied drill and blasting (D&B) blasting designs applying Kemiitti 810 emulsion explosive by Forcit. Ground Penetrating Radar (GPR) based GPR EDZ method was the central tool in measuring the EDZ extent.
Abstract Rantatunneli is a project of moving highway 12 into a tunnel in the city of Tampere. The excavation work was finished in the summer 2015. The tunnel will be operational in 2017. The twin tunnel will be the longest highway tunnel in Finland with the length of 2.3 kilometres. The project included in-situ stress measurement campaigns, stability analyses and rock displacement monitoring during the excavation phase. The stress measurements were conducted with hydraulic fracturing method. In this paper, the test results and their analysis are presented. Comparison of the predicted and the observed displacement behaviour of the rock mass are discussed. Introduction The city of Tampere, which is the third largest city in Finland, is located on an isthmus between two lakes and thus space is limited. Tampere is also a national traffic nexus as it houses key rail and road connections including three national highways and Helsinki-Oulu railway. All these have originally run through the city center, but two highways have so far been partially rerouted to a ring road running south of the central isthmus. The Rantatunneli project aims to transfer the third highway, national Highway 12, into a tunnel under the city centre. After completion, the tunnel will free up the land on central Tampere northern areas for urban development. The excavated rock is used to fill in the water body for a new park in the future Ranta-Tampella district. Rantatunneli is built as 2.3 km long twin tunnel which will be the longest highway tunnel in Finland. The tunnel starts from Santalahti in west and ends at Naistenlahti in east. A short concrete tunnel section is built at Santalahti. The tunnel passes under Tammerkoski rapids at midway, and houses a space reservation for a possible underground junction. The span of a single tunnel is 13... 15 m and height 9,2 m (Figures 1 and 2). The thickness of rock cover varies from 8 to 27 m (Figure 3). The total excavated volume for the two tunnel tubes is 650.000 m. The project was realised as an Alliance scheme between the key organisations, and the design work started in July 2012. An overall cost target was set in mutual understanding. The construction works started in autumn 2013 with excavation of the access tunnels. Tunnel excavations were finished by Midsummer 2015. The construction work is currently in progress, and the tunnel is scheduled to open to traffic in November 2016, few months ahead of schedule. The work will continue after this with construction of a new multilevel junction at Santalahti, landscaping and finishing works. The project is to be completed in 2017.
Abstract Theoretical calculation methods generally exaggerate the extent of the EDZ and used formulas do not apply to most rock types. This study comprises of correlating the theoretical to the realized extend of the EDZ on drill and blast (D&B) excavation surface. Generally when excavation is designed, applied theoretical EDZ extend origins from explosive manufactures material to fulfill the EDZ requirements of the blasted surface. Well known theories and formulas have been used to calculate the failure of the rock. In this work actual EDZ extend was defined and correlated to the theoretical extend when using Kemiitti 810 bulk emulsion explosive. The results were compared to realization using nitroglycerin based pipe charge F-pipe 17 × 500. All together 20 m of tunnel was excavated in crystalline granodiorite in Tampere test mine and numbers of small granite blocks were blasted in Kuru dimensional stone quarry. Realized EDZ extend definition was done visually on core samples and saw cut surfaces. Definition of theoretical EDZ extend requires rock mechanical testing of the site rock as well as borehole pressure data on used charges. Required and laboratory defined rock mechanical measures were the unconfined compressive strength, dynamic Young's modulus and Poisson's ratio. Also borehole pressure was defined in series of tests. Measured pressure values were compared to the calculated values based on ideal detonation, though it is known that in commercial explosives detonation is nonideal. The larger the charge diameter is, the more ideal explosion comes. When calculated borehole pressures were compared to the measured values it was noticed that the constant applied in the formula should vary along the charge diameter. Revised formula demonstrates how the EDZ extend can be calculated in crystalline rock when using explosives charges less than 600 g/m. The result is more realistic EDZ extend values.
Abstract Parking facility P-Hamppi under central Tam pare has now been in use for few years. During completion, it was the first large span cavern in Tampers city centre with a span of 32 m and a volume for 972 cars. Due to the demanding conditions i.e. large cavern close to the ground surface above lively city centre and fractured rock the project included an in-situ stress measurement campaign and rock mechanics stability studies, e.g. 2D and 3D numerical analyses and rock monitoring during construction. Rock stresses play often an important role in the rock engineering projects in Finland in the underground facilities near the rock surface. Horizontal stresses can be utilized in stabilizing rock caverns and may then allow wide caverns to be excavated. Hence the stress measurements were also conducted in the P-Hamppi project with hydraulic fracturing method. This paper describes how the results were analysed, utilized in the stability analyses and compared with the behaviour predicted by modelling and the observed behaviour. Introduction The city of Tampere which is the third largest city in Finland is located on a cliff rise, and Tampere's main street Hameenkatu follows its highest ridge. Because of this, the opportunities for building underground in Tampere are outstanding. Growing city of Tampere had started to place more emphasis on the issues of pedestrians and on light and public transport. The planning of a parking facility underground served this development. The developer of the P-Hamppi is Finn park Ltd, which is a Tampere-based parking services developer and operator owned by the City of Tampere. P-Hamppi with a length of 650 m is located at the depth of around 30 m under the main street Hameenkatu and between the Tammerkoski rapids and the railway station (Figure 1). The span of the P-Hamppi is 32 m, the height is 10m and its excavated rock volume was around 210 000 m3 and the capacity for 972 cars (Figure 2). Planning of the facility started in the end of 2007, the rock construction took place in 2009–2011 and the first cars drove into P-Hamppi in November 2012. P-Hamppi received EPA Award 2013 to be the best new parking facility in Europe.
SUMMARY: In Tampere, an underground air-raid shelter is being built where two ice-hockey rinks will be placed for civilian use. It consists of a single hall with a span width of 32 m, a maximum height of 9.2 m and a length of 134 m. The Site investigations included different types of geological mapping, diamond core drilling and rock stress measurements. The final cross-sectional profile was chosen on the basis of BEM and FEM calculations. The need for strengthening was mainly determined by the shelter specifications. The Strengthening consists of a combination of rock bolts, steel net and shotcrete. Rock mass Conditions are followed with precise levellings and extensometers during and after the construction stage. ZUSAMMENFASSUNG: InTampere baut man eine Gebirgsschutzraum, wo zwei Eishockeybahnen fuer Zivilgebrauch liegen werden. Sie ist eine Einzelhalle mit einer Spannweite von 32 m, einer Höhe von 9.2m und einer Lange von 134 m. Die Platzuntersuchungen enthielten geologlsche Kartierung auf verschiedenen Weisen, Kern- bohrundgen Gebirgsspannungsmessungen. Der endgueltige Querdurchschnitt war auf der Grunde der Grenzelement- und Finite-elementberechnungen gewahlt. Das Befestigungsbeduerfnis war hauptsachlich von Schutzraumgebrauch festgesetzt. Die Be- festigung besteht aus einer Kombination von Felsankern, Stahlnetz und Spritzbeton. Die Gebirgsmassenverhaltnisse sind mit genauen Abwagungen und Extensometern unter und nach Abbau gefolgt. RESUME: A Tampere on est en train de construire un abri souterrain contenant deux patinoires Pour Ie hockey sur glace. Il embrasse une simple halle avec une portee de 32 m, une hauteur de 9.2 m et une longueur de 134 m. Les investigations in situ embrassont des etudes geologiques variees, des forations au Diamante pour Ie carottage et des mesures de l ' etat de contrainte des roches. La section transversale finale a ete choisie sur la base de calculations par les methodes des ele- ments de bord et finis. Le besoin de renforcer etait principalement determine par l' usage d' abri. Le renforcement consiste en boulons, en filet d' acier et en beton projete combine. Les conditions dans Ie massif rocheux sont observees par 1es mesures geodetiques et par les extensometres pendant et apres la construction. CIVILIAN USE FOR AIR-RAID SHELTERS According to the Finnish legislation a town district of 10 to 30 thousand inhabitants has to have air-raid shelters from 1 to 3 hectares (30 000 m2) altogether. To- day thls is an investment of up to 100 million Finnish marks (25 million USD), only for exceptional use. To utilize these investments more effectively a civilian use is always tried to find'' for these spaces. In larger spaces one has of course more alternatives to choose. Alternative uses Nearby all of the larger air-raid shelters have been built in rock since the beginning of the 1960-es (Vuorela and Tervila,1980). The Finnish bedrock is usually of good quality and the soil cover is thin. The first bedrock shelters were mainly used for storages or car parking. Today there are much more possibilities, e.g. gymnastics and tennis halls, running tracks, swimming halls, cinemas, bowling halls etc., not to speak of training rooms for pop groups. The most important restriction to the civilian use is the demand that the shelter has to be able to be changed to its original purpose in 24 hours. PRELIMINARY INVESTIGATIONS At the middle of the 1970'es such good experiences had been obtained on bedrock shelters that an idea was arisen to place an ice-hockey rink underground into a bedrock air-raid shelter. After some discussions with the Finnish Ice-hockey Association it was found out that the minimum acceptable width for an ice-hockey rink was 28.5 m. This again supposed a bedrock shelter with a span width of minimum 32 m. (Figure in full paper) The planning of the first bedrock shelter with a span width of 32 m was started in 1977 in the town of Turku (Holopainen and Oksanen, 1980). The second one was started a year later in Hervanta, in the town of Tampere (Fig. 1). This one is discussed in more details here. The third one will probably be started this year in the vicinity of Helsinki. The capacity planned for the bedrock shelter of Hervanta is 3 000 persons, which means a hall area of 134 × 32 m in a single hall (Fig. 2). Geological investigations The investigations in Hervanta were started with aerial photogeological mapping and surface geological mapping in summer 1978. On the basis of the information obtained from these the shelter was preliminary placed in a larger block in the bedrock (Fig. 2). The shortest distance to the nearest fault zone was about 2S0 m (N-NW from the shelter). The shelter axis was in the direction of the bedrock block. The rock type in the block was homogeneous, coarse-grained, unaltered porphyric granite.