Stability of shallow seated constructions in hard rock
There is a tendency of increased use of the underground space for railroads, roads, sewers, telecommunication and high voltage cables. These constructions are in many cases situated in urban areas and at shallow depth. The mechanical properties and the state of stress in the shallow parts of the earth’s crust are much more sensitive to anomalies in the rock mass than at depth. This makes it harder to estimate and measure these properties.
Approach: The first part of the project is a literature study dealing with shallow tunneling, where the state of stress, the distribution of strength and stiffness with respect to geographical location and depth, and the influence of large geological structures on the stability and deformations is studiesd.
Thereafter conceptual numerical analyses are performed which include a preliminary study of a few chosen factors leading to a first indication of the sensitivity for the chosen factors. The next step is to perform numerical analyses of real cases and formulation of guidelines for data acquisition during pre-investigations.
Aim: The aim is to increase the understanding of excavations at relatively shallow depth by identifying factors influencing the behavior and the stability of shallow underground constructions. Some pertinent questions are:
How accurately must virgin state of stress be known to be able to perform feasible realistic analyses?
How are the results from a stability analysis affected by the precision/uncertainty of other properties like strength, stiffness, geological variations, blast damage, and loads from buildings on the ground surface?
In what way will the uncertainty of the virgin state of stress, stiffness, strength, and the other factors affect the design of tunnels and rock caverns and the reinforcement of these?
Are detailed geomechanical models of the rock mass necessary? What degree of details is necessary?
How should pre-investigations be conducted to decrease the total costs of a project? What parameters need to be determined with most precision – Young’s modulus, stress and/or strength and their variations with consideration of the position in the rock mass, etc?
Project period: 2003-2006 | Contact: Erling Nordlund
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