Transient surges in one of the overhead conductors, due to direct lightning strikes, causes crosstalk [C.R. Paul, Analysis of Multiconductor Transmission Lines, John Wiley & Sons, Inc., 1994; C.R. Paul, Introduction to Electromagnetic Compatibility, John Wiley & Sons, Inc., 1992] in other adjacent conductors. It is a common electromagnetic interference (EMI) phenomenon observed in power lines, communication lines and electrified railway lines. In this paper we investigate the crosstalk in multiconductor transmission lines (MTLs) above finitely conducting ground as a function of ground conductivity, heights of the receptor conductor and the terminal loads. For receptor conductor close to the ground, compared to the emitter conductor [C.R. Paul, Analysis of Multiconductor Transmission Lines, John Wiley & Sons, Inc., 1994; C.R. Paul, Introduction to Electromagnetic Compatibility, John Wiley & Sons, Inc., 19921, the decrease in ground conductivity increases the crosstalk peak currents at near end (end near to the source in the emitter conductor) of the receptor conductor, but at the far end it could either increase or decrease depending upon the line height and ground conductivity. It is found that the ground impedance [J.R. Carson, Wave propagation in overhead wires with ground return, Bell. Sys. Tech. J. 5 (1926) 539-554; Y.J. Wang, S.J. Liu, A review of methods for calculation of frequency dependant impedance of overhead power transmission lines, Proc. Natl. Sci. Cone. ROC (A), 25 (6), (2001) 329-338; E.D. Sunde, Earth conduction effects in transmission systems, 1st ed., Dover Publications Inc., New York, 1968; A. Deri, G. Tevan, A. Semlyen, A. Castanheira, The complex ground return plane a simplified model for homogenous & multilayer earth return, IEEE Trans. PAS 100 (8) (1981) 3686-3693; K.C. Chen, K.M. Damrau, Accuracy of approximate transmission line formulas for overhead wires, IEEE Trans. EMC 31 (4) (1989) 396-397; A. Semlyen, Ground return parameters of transmission lines an asymptotic analysis for very high frequencies, IEEE Trans. PAS 100 (3) (1981) 1031-1038; E.F. Vance, Coupling to Cable Shields, Wiley Interscience, New York, 1978; J.R. Wait, Theory of wave propagation along a thin wire parallel to an interface, Radio Sci. 7 (6) (1972) 675-679; R.G. Olsen, J.L. Young, D.C. Chang, Electromagnetic wave propagation on a thin wire above earth, IEEE Trans. Amen. Propag. 48 (9) (2000) 1413-1418; M. D’Amore, M.S. Sarto, Simulation models of a dissipative transmission line above a lossy ground for a wide-frequency range. I. Single conductor configuration, IEEE Trans. EMC 38 (2) (1996) 127-138; M. D’Amore, M.S. Sarto, Simulation models of a dissipative transmission line above a lossy ground for a wide-frequency range. II. Multiconductor configuration, IEEE Trans. EMC 38 (2) (1996) 139-149; F. Rachidi, C.A. Nucci, M. Ianoz, C. Mazzetti, Influence of lossy ground on lightning induced voltages on overhead lines, IEEE Trans. EMC 38 (3) (1996) 250-264; F. Rachidi, C.A. Nucci, M. lanoz, Transient analysis of multiconductor lines above a lossy ground, IEEE Trans. Power Deliv. 14 (1) (1999) 294-302; FM. Tesche, M.V. Ianoz, T. Karisson, EMC Analysis Methods and Computational Models, John Wiley and Sons Inc., 1997; A.K. Agrawal, H.J. Price, S.H. Gurbaxani, Transient response of multiconductor transmission lines excited by a nonuniform electromagnetic field, IEEE Trans. EMC 22 (2) (1980) 119-129] has profound influence in all the crosstalk cases studied here. Hence, a brief review and comparison of different closed form ground impedance expressions under the limits of transmission line approximation [EM. Tesche, M.V. lanoz, T Karlsson, EMC Analysis Methods and Computational Models, John Wiley and Sons Inc., 1997] and its behavior at both high and low frequencies is presented. It is shown that low frequency approximation of ground impedance is not sufficient for lightning transient studies involving ground conductivities lower than 10 mS/m. The observations presented in the paper have important implications in EMI studies of large distributed outdoor systems, such as the railway network, subjected to lightning strikes.

To study the behaviour of shotcrete under dynamic load, a non-destructive laboratory experiment was set up with P-wave propagation along a concrete bar, with properties similar to rock. Cement-based mortar with properties that resemble shotcrete was applied to one end of the bar with a hammer impacting the other. The shape of the stress waves travelling towards the shotcrete was registered using accelerometers positioned along the bar. Finite-element modelling was used to verify the test results, which showed that the laboratory model with an impacting hammer could be used to initiate the same type of stress waves that result from blasting in good-quality rock. Previously recommended maximum allowed peak particle vibration velocities were verified.

During blasting in tunnels and mines, the interaction between shotcrete (sprayed concrete) and rock is influenced by propagating stress waves. Shotcrete support in hard rock tunnels is studied here through numerical analysis using three different modelling approaches. The stress response in the shotcrete closest to the rock when exposed to P-waves striking perpendicularly to the shotcrete–rock interface is simulated. The first model tested is a structural dynamic model that consists of masses and spring elements. The second is a model built up with finite element beam elements interconnected with springs. The third is a one-dimensional elastic stress wave model. The models give comparable results, although the definition of the dynamic loads is different. The analysis results can be used to estimate whether the shotcrete will fail or not for a prescribed distance to detonating explosives inside the rock.

An elastic finite element model is used tosimulate theinducedstress waves from blasting, propagating in rock towards shotcrete on a tunnel wall. Due to the inhomogeneous nature of the rock, the stress wavesattenuate onitsway from the point of explosiontowardsthe shotcrete on the rock surface. Material damping for the rock-mass is estimated from in-situ measurements. The vibration resistance of the shotcrete-rock support system depends on the material properties of the shotcrete. Age-dependent material properties are varied to investigate the behaviour of young shotcrete subjected to blast loading. Finally, finite element analysis results are presented and verified through comparison with other numerical models, measurements and observations.

The effect on shotcrete from blasting operations during tunnelling is studied, with focus on young and hardening shotcrete. A finite element model specially adapted for analysis of the shotcrete behaviour is tested, it is able to describe stress wave propagation in two dimensions which is important for cases where shear stresses are dominant. The modelling results are compared with in situ measurements and observations, from construction blasting during tunnelling through hard rock. The comparison shows that the model gives realistic results and can be used to investigate the vulnerability of shotcrete, aiming at compiling recommendations and guidelines for practical use. The given recommendations emphasize that blasting should be avoided during the first 12 h after shotcreting and that distance and shotcrete thickness are important factors for how much additional time of waiting is possibly needed.

Numerical modelling in combination with in situ measurements, observations and laboratory testing will be important to future establishment of reliable guidelines for efficient civil and engineering work involving concrete casting close to e.g. blasting operations. Results from laboratory tests with impact loaded young concrete prisms are here evaluated using a 3D finite element model. Solid elements are used and a non-linear material model implemented, capable of describing cracking during stress wave propagation. The position of cracks and measured particle vibration velocities are calculated and compared with laboratory test results. The damaging effect of impact vibrations is evaluated using crack width and fracture energy as damage criteria. Alternative geometry for the test prisms, with a notched section, is analysed. This will give one wide crack at the centre of the prism instead of two or three cracks distributed over its length which will make future laboratory test more efficient and reliable. Recommended damage limits at concrete ages of 4, 6, 8 and 12 h are given, based on numerical calculations for concrete strength class C25 and C50.