Structural design verifications, structural analysis of tunnels - Tunnel Engineering: Basics and Additional Services for Design and Construction - page 97

3.2 Ground pressure theories

The construction of a tunnel disturbs the existing equilibrium in the rock mass. The type
and magnitude of the action of this technical intrusion are the result of a complex interac-
tion of rock mass and tunnel construction. The rock mass is provided with all its proper-
ties. The construction of the tunnel structure is involved in the interaction, which causes
the loading of action and reaction of ground mass and tunnel, particularly through the
selection of a construction process and the associated or decisive decision about its depth,
cross-sectional dimensions and construction. The construction of the tunnel is particularly
drawn into the interaction between the loading of action and reaction of rock mass and
tunnel by the selection of a construction process and the associated or decisive decisions
about the vertical alignment, cross-sectional dimensions and construction.

3.2.1 Historical development
Since the construction of the important rail tunnels in the previous two centuries, numer-
ous engineers and geologists have published their analyses of the loading on tunnels and
rock mass.
Qualitative statements. A. Heim [89], writing in 1878 and 1905, considered the load-
ing, which he mostly discovered in the form of damage to tunnels with open inverts, to
result from a ground pressure acting equally all around the cavity, similar to hydrostatic
pressure: the hydrostatic pressure corresponds to the weight of the rock mass overbur-
den. The prompt installation of a closed tunnel tube prevents damage by activating the
internal friction of the rock mass. The lining tube should therefore by fully mortared to
the rock mass.
W. H. Trompeter [246], writing in 1899, assumes from his observations in coalmines that
the excavation of coal seams forms spatial protective envelopes, which relieve the cavity
when the depth is sufficient, particularly in the longitudinal direction.
E. Wiesmann [258] repeated in 1912 the view that a protective envelope is formed across
the tunnel, since the loading on deep tunnels from overburden pressure would otherwise
be so high that such tunnels would “have to be left alone”.

R. Maillart [152] in 1923 extended the theory of Heim with the view that the horizontal
pressure and the vertical pressure can be of different magnitudes and the lining of the tun-
nel increases the strength of the surrounding rock mass “because the strength of a body
is not solely a function of the largest pressure acting in a certain direction, but is also the
minimum pressure acting in one of the other dedicated main axes”.
Quantitative statements. After the more qualitative considerations (A. Heim, W. H.
Trompeter and others) about ground pressure, which were summarised by E. v. Willmann
[259] and E. Wiesmann [258], the ground pressure was then regarded as an external load
parameter and introduced into structural calculations. To start with, the ground pressure
was considered as a fill covering acting on the tunnel structure with the full surcharge
weight. Later, this ground pressure was reduced, W. Ritter, K. Culmann [259]. For the
magnitude of ground pressure for calculation purposes, observations of crown settlement
from O. Kommerell [113] and the influences of tunnel dimensions and rock mass structure
from K. Terzaghi [241] were taken into consideration.