| 1. |
- Eitzenberger, Andreas, et al.
(författare)
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Numerical simulation of train-induced vibrations in rock masses
- 2012
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Ingår i: Harmonising rock engineering and the environment. - Leiden : CRC Press/Balkema. - 9780415804448 ; , s. 1189-1194
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Konferensbidrag (refereegranskat)abstract
- The vibrations generated by a moving train in a tunnel will radiate into the surrounding ground which, in densely populated areas, will reach nearby buildings and its residents. Analyses are commonly made where the aim is to estimate the ground-borne noise and vibrations levels that may occur in nearby buildings. A common assumption is to treat the rock mass as an isotropic, homogeneous, and linear elastic material. Thus, the influence of discontinuities on the propagation of waves is not considered in the analyses. Within this study, numerical simulations were performed to study the propagation of low-frequency waves through a rock mass near a tunnel. A single period sinusoidal wave was applied as dynamic source on the floor of the tunnel. Observation points were located on the ground surface and around the tunnel. The influence on wave propagation from overburden, position of a discontinuity in relation to the tunnel, and normal and shear stiffness of the discontinuity, was studied by using the Universal Distinct Element Code (UDEC). The results show that increasing overburden reduces the vibration levels on the ground surface. Furthermore, the influence of the normal and shear stiffness of discontinuities depends on where the horizontal discontinuity is positioned in relation to the tunnel. If the horizontal discontinuity is positioned above the dynamic source (e.g. above tunnel or in the tunnel wall) the vibration levels on the ground surface will be reduced but if the horizontal discontinuity is located below the dynamic source (e.g. below the tunnel) the vibration levels on the ground surface will be enhanced. In our analyses, discontinuities only have an impact on the wave propagation if the normal and shear stiffness of is ≤10 GPa/m.
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| 2. |
- Saiang, Christine, et al.
(författare)
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Effects of heat on the mechanical properties of selected rock types : A laboratory study
- 2011
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Ingår i: Harmonising Rock Engineering and the Environment. - Leiden : CRC Press/Balkema. - 9780415804448 ; , s. 815-820
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Konferensbidrag (refereegranskat)abstract
- A laboratory study was conducted to study the effect of heat on the mechanical properties of diabase, granite and quartzitic schist at temperatures of 400◦C, 750◦C and 1100◦C. Unheated samples were also studied. The reasoning behind this study was to understand the effect of elevated temperatures on the rock mass, such as in the event of a fire in a rock tunnel. Samples from the aforementioned rock types were heat treated at temperatures shown above, cooled slowly to room temperature and then subjected to uniaxial compression and Brazilian tests. Thin sections were extracted from the heat treated samples for microscopic analyses, which assisted in explaining the reasons for the mechanical behaviour observed from the mechanical test results. The uniaxial compression test showed that the strength of the rock specimens increased by 6% for granite to 29% for diabase at 400◦C when compared to the UCS values of the unheated specimens. From 750◦C to 1100◦C the decay in the strength was very rapid. From the microscopic analyses it was concluded that the increase in the strength of the rock specimens at 400◦C is attributed to the initial reaction of the rock forming minerals, hence the rock specimens were less brittle but more plastic. The rapid drop in the strength from 750◦C to 1100◦C is attributed to the mineralogical changes, micro-cracking and dehydration due to the loss of crystal bound water. At 1100◦C the rocks were highly friable and crumbled very easily when tested mechanically. The effect of mineralogical changes was obvious in diabase where the physical appearance of the samples mimicked that of natural iron, which is believed to be due to the alteration of pyroxene. The result was an increase in strength by 29% at 400◦C compared to the unheated specimens. Even at 750◦C the strength was slightly higher than unheated specimens. In summary; the mechanical behaviour of the rock specimens depended on the temperature level and the mineralogical and physical changes that occur at that temperature.
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| 3. |
- Shirzadegan, Shahin, et al.
(författare)
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Rock support subjected to dynamic loading : Field testing of ground support using simulated rockburst
- 2011
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Ingår i: Harmonising rock engineering and the environment. - Leiden : CRC Press/Balkema. - 9780415804448 ; , s. 1269-1273
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Konferensbidrag (refereegranskat)abstract
- Increasing the mining depth at LKABs Kiirunavaara mine located in the northern part of Sweden is leading to higher stress magnitudes, resulting in increased seismic activity and more rockburst damage. The effectiveness of various ground support systems under dynamic loading conditions has therefore become of prime interest to LKAB for successful and safe mining at deep levels. Therefore, a series of rockburst simulations will be conducted, using explosives to generate the dynamic load, on a number of support systems. This paper covers the results from the first trial test called Zero test-1. The test included ground motion measurements with a number of accelerometers, fracture investigation, ground and support motion imaging, as well as the deformation measurements. The methodology used to simulate rockbursts is discussed and the issues met in these tests are also addressed for further improvement.
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