Civil Engineering Reference
In-Depth Information
12
Design Methods
12.1
Introduction
There are different views with regard to rock engineering design. The most frequently
applied design methods are based on:
- rock mechanical models
- assessment of the rock mass behavior
- classification systems.
The first design method is mainly based on the results of comprehensive geotechnical in-
vestigations, stability analyses and monitoring results during construction (Section 12.2).
This design method has been successfully applied for several decades by WBI (Wittke
1990, Wittke 2000b, Wittke et al. 2002, Wittke et al 2006) and other designers and consult-
ants. One of the main objectives of this topic is to provide the fundamentals of this design
method. Examples of completed projects carried out according to this design method are
presented in Part D of this topic.
The second kind of design method is based on rock mass behavior types and hazard
scenarios and is applied mainly in Austria and Switzerland (Section 12.3).
A characteristic attribute of the third design method, based on classification systems, is
that rock mass properties and other influencing factors such as stresses and groundwater
conditions are condensed to a single numerical value referred to the “rock mass rating
index”. As stated by Bieniawski (1989), the developer of the “rock mass rating (RMR)”
system, which was one of the first empirical classification systems, “a classification sys-
tem is not intended to replace analytical modeling, site investigations and monitoring but
should be used in conjunction with these tools of rock engineering design” (Bieniawski
1989). According to this view, classification systems should not be used as self-contained
design methods. However, the development and promotion of a number of new and more
refined classification systems in the recent past has given rise to their use as self-contained
design methods (Section 12.4). The risks that are associated with the use of classification
methods as self-contained design methods are emphasized in Sections 12.5 to 12.7.
12.2
Design Based on Rock Mechanical Models
A characteristic feature of rock engineering design is the iterative procedure in which
individual phases of work may be repeated several times, if necessary.
The design has to be adjusted to the type of rock mass and local conditions in the
project area. The following instructions must therefore be treated as general guidelines.
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