Abstract

Traditional design methods for mining, tunneling and public underground constructions use deterministic approaches. Reliability requirement for these constructions became very high and deterministic approaches lead to introduction of overpriced Factors of Safety (FS). It is more appropriate to select an optimal support based on the risk focused management approach. The Monte-Carlo method for statistical simulation is recommended for the design of underground constructions. As the first step we use simplified approach based on a plausible assumption that variation in the stress and the strength of rock mass, rock pressure manifestation, and support capacity can be described by the normal distribution law.

1 Introduction

Karl Terzaghi was one of the first specialists who underlined the importance of risk management in the design of geotechnical structures (Terzaghi 1982). He considered risk management as a process of balancing economy and safety. During the last 50 years of quantitative analysis of probability failure for different constructions was developed and discussed in numeral workshops and international conferences (Whitman 1984, Baecher & Christian 2003, Chowdhury & Flentje 2008). However, application of modern probabilistic solutions in design practice is still limited because of rather poor current statistical estimates of the initial data and results. These solutions can not adequately describe the complicated multifactorial process of rock deformations around underground openings and interaction support with rock mass. Risk management for the design of underground construction shall take into account uncertainties associated with the stress and the strength of rock mass as well as uncertainties of construction and technology:

• Uncertainties of the initial geological, geomechanical parameters:

• strength and creep properties of the rock mass around opening

• stress state in the rock mass

• dip angle of the rock seams

• Uncertainties of the technological condition:

• dimension of the opening cross-section

• rate of opening driving

• opening direction in respect to strike direction

• type of construction: drill-and-blast or TBM

• distance and time support installation from the face

• type of support: concrete, anchor or yielding support

• contact condition: full contact or contact with rubblework behind contour

• type of opening: separate, chamber, parallel or junction of the openings

• Uncertainties of the strength and deformation characteristics of the support

• Uncertainties of the design methods

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