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Terms in this set (10)

Method When considering long underground structures (tunnels) an unsupported cavity without supporting influence of the face has to be assumed. Sequential excavation steps are not considered in this phase. The following influencing factors are usually considered for the evaluation of the Ground Behaviour:
Ground Type (GT)
Virgin stress conditions
Shape and size of the underground structure (final shape and size)
Position of underground structure in relation to surface or existing structures
Relative orientation of the underground structure and discontinuities as a basis for kinematical analyses, and the assessment of the stress redistribution
Boundaries between different ground types
Ground water, seepage force, hydraulic head For the determination of the ground behaviour the following evaluations are rec-ommended:
Kinematics: Kinematical analyses for the determination of discontinuity con-trolled overbreak and sliding of wedges Methods: Key Block Theory [18], analyses using stereographic projection [19, 20]
Ground utilization: evaluation of the ratio between the strength of the ground and the spatial stress situation in the vicinity of the underground opening. Methods: analytical and numerical methods [21, 22, 23], 24] Failure mechanisms: possible failure mechanisms of the ground have to be analyzed and described at least qualitatively (for example: spalling, shearing along discontinuities as result of stress release, shear failure, etc.) Guideline for the Geotechnical Design of Underground Structures with Conventional Excavation 14 Austrian Society for Geomechanics Methods: model tests, analytical analyses, numerical analyses, which allow the modelling of discrete failure planes, case histories. When influencing factors cannot be determined with sufficient accuracy, a para-metric study considering the spread of parameters shall be made. Analytical and/or numerical methods are to be used, which provide appropriate modelling methods for the characteristics of the ground types under the given boundary conditions. The Ground Behaviours resulting from the analyses have to be assigned to one of the categories listed in Table 2. In case more than one Behaviour Type is identified in one of the general categories, sub types have to be assigned (for example 2/1, 2/2 for a ground with a different potential for overbreak with different combinations of joint sets or orientations). If combinations of behaviours are identified in the same section, all behaviours have to be shown. The assignment to the general categories is done according to the behaviour type considered dominating (for ex-ample: discontinuity controlled overbreak and swelling of invert BT 2+10). Ground with frequently changing strength and deformation characteristics, as can be found in fault zones are assigned to the general behaviour category 11. The characteristics and behaviours have to be described project specifically.