Ingeniero Civil

A Study of Strength Parameters in the Reinforced Ground by
Rock Bolts
Sebastiano Pelizza1, Sang-Hwan Kim2, Jong-Soo Kim3
1

TUSC, Tunnelling and Underground Space Center, Dipartimento di Georisorse e Territorio,
Politecnico di Torino, Italy.
2
Dept. of Civil Engineering, Hoseo University, Asan, Korea, 336-795
3
Civil Engineering Division, Hyundai Development Company, Seoul, Korea,135-881

ABSTRACT
In general, the strength parameters of the ground around a tunnel will be changed by the ground
reinforcement during tunnel excavation. In this case, the concept of tunnel design, such as supporting
system, excavation, lining and so on, should be modified based on the failure criteria of the ground
changed by the reinforcement. This paper presents the new mechanism of changingthe strength
parameters of the reinforced ground by rock bolts. In order to perform this research, theoretical and
experimental works were carried out. It was clearly found that the cohesion of strength parameters is
only increased by reinforcement of ground. That is, it could be seen that the rock bolts have more
effects on the increase of cohesion (c) than on internal friction angle (φ).
1.INTRODUCTION
In recent, the tunnel construction has been increasing in railway and road projects. Therefore, effort is
being put into the technology development of a fast, safe, and economical tunnel construction by
analyzing the term and economical efficiencies of tunnel works.
In the recent tunnel design process, the tunnel support patterns, additional reinforcement and
excavation methodare independently determined according to the grade of ground. That is, the design
of individual items is done without any consideration of the combination of these items. In practice,
however, the tunnel could be expected the combined behaviour rather than individual behaviour due to
these tunnel systems. Since the difference between design and practice, uneconomical issues partially
exist inmost tunnel constructions.
In order to minimize these issues, it is necessary that the new approach of combined tunnel
support design method should be developed to reduce the construction costs. It is also needed that the
new tunnel support design method, namely “Combined Tunnel Design Method” should be simplified
to use as tunnel design technique in practice.
This paper presents the newmechanism of changing the strength parameters of the reinforced
ground by bolts. In order to perform this research, theoretical and experimental works were carried
out.
2. LOAD BEARING CAPACITY IN THE REINFORCED GROUND
2.1 Application of Flexibility ratio and Compressibility ratio
Ground behaviour immediately adjacent to the tunnel is influenced by the stiffness of the lining. Peck
et al (1972)suggested that tunnel lining could be classified as either flexible of stiff according to the

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interaction behavior between ground and lining. It is clear, however, that a tunnel lining which is stiff
with respect to a soft ground may behave as flexible lining in a hard ground. To characterize the
stiffness of a liner, therefore, it is necessary to adopt suitable ratios of liner to soilstiffness.
A flexible lining supports the soil stresses applied to it primarily by ring compression. The normal
stresses acting on the lining would be expected to be approximately uniform and any bending moments
will be relatively small. A stiff lining, however, will tend to support the ground stresses by bending action
although hoop stresses will also be present.
Peck et al. (1972) suggestedthe use of the compressibility and flexibility ratios as a means of
defining tunnel liner stiffness, based on the analytical work by Burns and Richards (1964) and Höeg
(1968) in soil-structure interaction. The compressibility ratio, C, is the ratio of a measure of the
compressive stiffness of the soil relative to the hoop stiffness of the liner, and the flexibility ratio, F, is
defined as...