Influence of dynamic loads 913531 Ground vibration associated with tunnel construction New, B M Proc Tunnel Construction '90, London, 3-4 April 1990 P6776. Publ London: IMM, 1990 Vibrations from tunnelling works are generally of a temporary nature, but the disturbance caused may result in permanent damage to property and substantial nuisance to the local population. At the present time, predictions of vibration by analytical methods are often rather hit or miss affairs and in many instances they are not carried out at all. A report on the investigations that have been undertaken to improve techniques for the prediction and control of ground vibrations caused by civil engineering tunnelling works is presented.
913532 Synthetic seismogram analysis of locally-recorded mine tremors McGarr. A: Bicknell, J Proc International Symposium on Rock at Great Depth, Pau, 28-31 August 1989 V3, PI407-1413. Publ Rotterdam: A A Balkema. 1989 Matching of synthetic seismograms to locally recorded data is an effective method of defining seismic source parameters and focal mechanisms of mine tremors. Using data from a single 3component station plus a seismic location network, and trial and error calculations of synthetic seismograms until observed ground surface motions arc matched, a comprehensive description of the seismic source process is possible. Applications in the Vaal Reefs Gold Mine, South Africa, are illustrated.
913534 Notch acuity effects on the fracture toughness of freshwater ice Wei, Y; DeFranco, S J; Dcmpscy, J P Proc 9th International Conference on Offshore Mechanics and Arctic Engineering, Houston, 18-23 February 1990 V4. P253257. Publ New York: ASME, 1990 One of the most important aspects in fracture toughness testing is the fabrication of a truly sharp crack for linear elastic fracture mechanics to apply. Since there is no standard method available for the fracture toughness testing of ice, different methods for inducing cracks have been introduced. The effects of notch acuity (crack tip sharpness) on the fracture toughness of ice were investigated using six groups of single edge-notched-bend specimens with cracks fabricated by different methods. The apparent fracture toughness of each group was determined as well as their mean values and standard deviation. 913535 Cyclic loading of saline ice: initial experimental results Cole, D M Proc 9th International Conference on Offshore Mechanics and Arctic Engineering, Houston, 18-23 February 1990 V4. P265271. Publ New York: ASME. 1990 Experiments were carried out in order to map out some of the general characteristics of saline ice response under fully reversed loading, concentrating on stress amplitude and frequency effects. The results of these experiments using a newly fabricated system for performing reversed direct stress tests on 100mm diameter ice specimens are presented. 913536 Is minimum creep rate a fundamental material property? Sinha, N K Proc 9th International Conference on Offshore Mechanics and Arctic Engineering, Houston, 18-23 February 1990 V4. P283288. Publ New York: ASME. 1990
Snow and ice mechanics
Ice engineering problems require solutions in terms of specific design stress, strain, or damage limits. Interdependences between stress, strain,damage state, and time for a given ice body at a given temperature distribution and loading history must be known. Common practice when determining the mechanical properties of ice is to evaluate the rate sensitivity of maximum stress or the stress dependency of minimum creep rate. New directions given by the examination of the physical phenomena governing creep deformation and the kinetics of creep damage are discussed.
913533 Preliminary mixed mode fracture experiments on 52 columnar freshwater ice DeFranco. S J; Dempsey. J P Proc 9th International Conference on Offshore Mechanics and Arctic Engineering, Houston, 18-23 February 1990 V4, P247252. Publ New York: ASME. 1990
9 ! 3537 Crack nucleation in polycrystalline ice - a comparison of two nucleation criteria Wu, M S; Sunder, S S Proc 9th International Conference on Offshore Mechanics and Arctic Engineering, Houston, 18-23 February 1990 ;/4. P273282. Publ New York." ASME, 1990
Preliminary experiments were performed on three different specimen geometries each known to produce, at the crack tip, a mixed mode stress field of varying intensity. Observations were made concerning the angle of crack initiation. These geometries are shown theoretically to have different levels of mode mixity at the crack tip. Observations made from preliminary experiments on 52 freshwater columnar ice samples are presented. Discrepancies between theory and observations are discussed in terms of material anisotropy, eccentricity of loading. and specimen stability.
The mechanical behaviour of polycrystalline ice in the ductileto-brittle transition region at moderate to high strain rates (or stress) is significantly influenced by the nucleation of cracks. Comparison of the nucleation stresses for uniaxial and biaxial loading conditions in porous,isotropic, polycrystalline ice with those obtained from the use of a critical strain energy density (SED) factor is made in order to characterize the local material resistance. The results, synthesized into biaxial nucleation surfaces, are compared with the limiting tensile strain criterion.
Subjects Peripheral to Geomechanics
FC: 1991 Pergamon Press plc. Reproduction not permitted