During the winter season, ice causes major problems in many Swedish railway tunnels. Ice, rock and shotcrete in the roof and on the walls may come loose and fall down, installations and cables can break due to ice loads and the tracks can become covered with ice. To maintain safety and prevent traffic disturbances, many tunnels require frequent maintenance. The removal of ice, loose rock and shotcrete is expensive and potentially risky work for the maintenance workers. To reduce maintenance costs, it is important to improve our knowledge of frost penetration inside tunnels and investigate the effect of ice pressure and frost shattering on loadbearing constructions. The aim of this investigation was to gather information about the problems caused by water leakage and its effect on the degradation of a rock tunnel when subjected to freezing temperatures. There are many factors that determine whether frost or ice formations will appear in tunnels. To collect information on ice formation problems, field observations were undertaken in five of Sweden’s railway tunnels between autumn 2004 and summer 2005. For one of the tunnels, follow-up observations also took place in March during the years 2005, 2006 and 2007.

Canals and tunnels in hydropower plants must be able to receive high shock-like flows without damaging either the dam or the rock foundation. Although the canals often consist of rock, erosion can occur when water is released. The natural riverbeds and lakes in Sweden usually run along large faults and other zones of weakness in the rock. This is because the water could more easily erode its way along these weakness zones. Spillways of hydropower dams are generally unlined thereby exposing the bedrock to erosion during floods.This study focuses on block erosion mechanisms and characteristics in unlined spillway canals that comprises hard rock mass systems. Two hydropower dam spillway canals were investigated as case studies; identified as Dam1 and Dam 2. The spillway canals of these two dams have uniquely different bed rock characteristics. At Dam 1 the rock mass is very blocky with visually estimated GSI classification in the range of 50 to 70, while Dam 2 is composed of massive rock mass with visually assessed GSI classification of 70 to 90.The erosion characteristics observed in these two spillway canals are uniquely different. The rock mass is obviously the principal factor contributing to these observations. However, there are also other factors, namely the hydraulic factors, as well as the geometrical factors of the canals. In this report these factors have been described in detail.  Three main mechanisms of block erosion were observed, (i) removal or plucking of rock blocks, (ii) fracturing of intact rock blocks and (iii) abrasion. At Dam 1 spillway canal all three mechanisms were observed to be significantly evident. At Dam 2, abrasion is the dominant mechanism of erosion. Hydraulic parameters, water pressure and velocity, affect the criticality of the erosion.Numerical simulations of the spillway canals were conducted using 3DEC. These simulations show that block displacements greater than 10 m are experienced within 1 to 2 minutes of flow. This observation is consistent with observations made during an actual discharge from a dam. Numerical simulations indicated that blocks with sizes less than 1 m3 would easily be plucked and transported downstream. If they are intact and with unfavourable geometry, they can be easily fractured by the spill water loads. Field investigations support these observations.Remedial measures would first require classification of a spillway canal into erosion domains based on erosion vulnerability. For example, the upstream sections of the channels are typically vulnerable to high intensity erosion. Hydraulic jumps, plunge pools, stilling basins, etc, have been typically used to break up the energy before the water flows downstream. However, erosion still occurs further down since the energy is still very large. Reinforcing the bedrock with artificial supports such as rock bolting, widening and levelling of canals, diverting the flow to less vulnerable areas of the canal, etc, have been some means to reduce block erosion. This study concludes that, remedial measures must start with identifying the mechanisms of block erosion, three of which have been described above. Domaining of the channels into erosion critically domains may also assist in monitoring and application of remedial measures. Empirical methods, such as Pells (2016) can be applied in each domain to identify their erosion potential. This study also concludes that the hydraulic pressure and displacements that occur around a rock block needs to be further investigated, either by field measurements in a spillway or by using physical models. In this way, it will be possible to better understand the conditions around blocks in a spillway and erosion mechanisms during a discharge.

Despite extensive grouting efforts to prevent water from leaking into tunnels, water seepages remain. When exposed to freezing temperatures, ice formations occur. During the winter, the Swedish Transport Administration's railway tunnels are affected by major problems caused by ice, such as icicles from roof and walls, ice loads on installations, ice-covered tracks and roads, etc. To ensure safety and prevent traffic disruptions, many tunnels require extensive maintenance. Improved knowledge about frost penetration in tunnels is required to reduce maintenance of the tunnels. Frost insulated drain mats are often used at leakage spots to prevent ice formation along the tunnels. To find out which parts of a tunnel are exposed to freezing temperatures, the University of Gävle and the Royal Institute of Technology in Stockholm conducted a laboratory model test on behalf of the Swedish National Rail Administration (now the Swedish Transport Administration). The laboratory model test aimed to find a method to determine the expected temperature conditions along a tunnel to decide which parts of the tunnel require frost insulation to protect the drainage system from freezing and prevent ice formation. To evaluate the laboratory model test, the Swedish Transport Administration in collaboration with Luleå University of Technology have performed field surveys in two Swedish railway tunnels. The field measurements involved monitoring temperatures in air, rock surfaces and rock mass, as well as measuring wind direction, wind and air velocity and air pressure. The measurements in the tunnels show that the frost penetrates further into the tunnels than was expected from the laboratory model test, which was based on a completely uninsulated tunnel. Frost insulated drains do not only prevent the cold air from reaching the rock mass, but also prevent the rock from emitting geothermal heat that warms up the cold tunnel air. Consequently, the frost penetrates further into the tunnel than it would do if the heat from the rock mass was allowed to warm up the outside air on its way into the tunnel. The number of frost insulated drains and how much of the tunnel walls and roof are covered thereby affect the length of the frost penetration.

Rock tunnels excavated using drilling and blasting technique in jointed rock masses often have a very uneven and rough excavation surface. Experience from previous studies shows that the unevenness of a rock surface has a large impact on the support effect of shotcrete lining. However, clear conclusions regarding the effect of 2D and 3D uneven surfaces were not obtained due to limited studies in the literature. The numerical analyses reported in this paper were made to investigate the influence of the surface unevenness of a circular tunnel opening on the support effect of shotcrete using a 3D numerical code (3DEC). The models were first calibrated with the help of observations and measured data obtained from physical model tests. The influential factors were investigated further in this numerical study after calibration had been achieved. The numerical analyses show that, in general, the unevenness of a tunnel surface produces negative support effects due to stress concentrations in recesses (compressive) and at apexes (tensile) after excavation. However, shotcrete sprayed on a doubly waved uneven surface has better support effect compared to shotcrete sprayed on a simply waved tunnel surface. The development of shear strength (specifically frictional strength) on the uneven interface between the shotcrete and the rock contributes to this effect, in the condition where bonding of the shotcrete does not work effectively. The interface is a crucial element when the interaction between the rock and shotcrete is to be simulated. When an entire tunnel surface is covered by shotcrete with high modulus, more failures will occur in the shotcrete especially when rock surface is uneven. Based on the numerical model cases examined, some recommendations on how to incorporate tunnel surface conditions (2D or 3D unevenness) in the design of a shotcrete lining are given.

This paper presents the result of the research carried out on the effect of temperature on the Bushveld Igneous Complex (BIC), South Africa. The BIC has high virgin rock temperature. If the platinum mines advance to ultra-deep levels, then the virgin rock temperature at a depth of 5 km will be approximately 140°C. Hence, there is a need to improve the understanding of the behaviour of rock under high temperatures. Five rock types were tested in a 2600 kN servo-controlled testing machine. The testing was done at a controlled loading rate and a confining pressure 0, 10, and 30 MPa within temperature range of 20–140°C. Comparison was made between the results obtained from the laboratory experiments and numerical modelling. It was observed from the stress–strain behaviour of the samples that an increase in temperature results in the reduction of the Young’s modulus and peak strength. 

Ballasted tracks are common in the railway system as a means of providing the necessary support for the sleepers and the rails. To keep them operational, tamping and other maintenance actions are performed based on track geometry measurements. Ballast particle rearrangement, which is caused by train load, is one of the most important factors leading to track degradation. As a result, when planning maintenance, it is vital to predict the behaviour of the ballast under cyclic loading. Since ballast is a granular matter with a nonlinear and discontinuous mechanical behaviour, the discrete element method (DEM) was used in this paper to model the ballast particle rearrangement under cyclic loading. We studied the performance of linear and nonlinear models in simulating the settlement of the sleeper, the lateral deformation of the ballast shoulder and the porosity changes under the sleeper. The models were evaluated based on their ability to mimic the ballast degradation pattern in vertical and lateral direction. The linear contact model and the hysteretic contact model were used in the simulations, and the effect of the friction coefficient and different damping models on the simulations was assessed. An outcome of this study was that a nonlinear model was proposed in which both the linear and the hysteretic contact models are combined. The simulation of the sleeper settlement and the changes in the porosity under the sleeper improved in the proposed nonlinear model, while the computation time required for the proposed model decreased compared to that required for the linear model.

Ground support systems are commonly used to mitigate the potential consequences of rockburst in burst prone mines. To assess the capacity of ground support systems when subjected to dynamic loading, simulated rockburst tests using blasting were conducted at the Kiruna Mine. In this study, a numerical simulation for one of the field tests was conducted using the LS-DYNA code to investigate the dynamic response of the ground support systems including shotcrete and rockbolts. The numerical results showed a similar particle vibration pattern and a crack pattern to those of the field measurements. The effects of the detonator position and the charge configuration on the dynamic response of ground support systems are also discussed. Numerical results indicated that the peak particle vibrations on the tested panel increase along the direction of detonation propagation. It is difficult to use different charge concentrations in one borehole to investigate the effect of different dynamic loads on the dynamic response of support systems. Numerical results also indicated that 2D numerical modeling for simulated rockburst experiments could overestimate the dynamic response of ground support systems.

Back analysis for evaluation of the merits of the short-term seismic hazard indicators (precursors) used in the mines and their potential application for early warning was carried out for fourteen seismic events that potentially caused damage in Kiirunavaara Mine, Sweden, selected according to our designed criteria. Five short-term hazard indicators: Seismic Activity Rate (SAR), Cumulative Seismic Moment (CSM), Energy Index (EI), Cumulative Apparent Volume (CAV) and Seismic Apparent Stress Frequency (ASF) were tested. The behaviour of the indicators was studied using the parameters of all seismic events within a sphere around the hypocenter location of the analyzed seismic source within one month before the main (damaging) event. The size of the sphere equals the estimated radius of the analyzed seismic source (area of inelastic deformation). mXrap software (Australian Centre for Geomechanics) was used for data visualization, manipulation, analysis and extraction. The results from the main analysis showed a good agreement between the expected and actual behaviour of the SAR, CSM and CAV indicators. In overall, CSM and CAV ranked the highest positive/expected behaviour followed by SAR (Table 3). The EI and ASF ranked lowest and showed to be sensitive to the number of events within the source sphere. The rate of false warnings and missed warnings was also investigated for the 25 days-long period before the damaging events. A similar trend was observed as for the main analysed event. The results from this study can be used for further improvement of the short-term hazard estimations and early warning system in deep underground mines.

In rock tunnels in regions with colder climates, the load-bearing structure, including the rock and the reinforcing elements, is exposed to repeated destructive freezing and thawing cycles during the winter. If water accumulates in cracks or in the interface between rock and shotcrete, frost shattering may occur. If there is adequate adhesion between the rock and shotcrete, degradation of the shotcrete as a reinforcement element due to frost shattering should not present a problem. However, if adhesion is poor, a small void will form between the rock and the shotcrete where water can accumulate. If the water in these voids is subjected to freeze-thaw cycles, ice will develop, thus exerting pressure on the interface and causing the shotcrete to crack and degrade. In tunnel sections with complex water conditions, for example, relatively water-bearing open joints and weak zones, the adhesion of the shotcrete and its stability and reinforcing effect may be strongly affected when exposed to freezing temperatures. This article describes a laboratory study that comprised freeze-thaw tests on shotcreterock panels with the objective of studying how water migration affects the growth of ice and the ice pressure in the shotcrete-rock interface to better understand the degradation of the reinforcing effect of shotcrete