UNDERGROUND ENGINEERING - Introduction to Soft Soil Geotechnique: Content, Context and Application - page 258

The resulting force of this approximate stress distribution is worked out; the
components are

2

Q x = 0 x sin Rd = 0 (15.25a)

2 R 2

Q z = 0 z cos Rd = (15.25b)

t

It shows that the force Q corresponds to the cavity weight. Verruijt showed by
comparison of this approximate stress state according to (15.23) and (15.24) to an
exact analytical solution for a rigid cavity with a vertical force in a semi-infinite
elastic space that it reveals good agreement for cavity depths H > R . The
evaluation of induced stresses during boring is, however, more complicated.
During this process extensive monitoring, proper understanding of the measured
data and adequate mitigating measures are therefore inevitable.

10 20 30 10 20 30

- 41

-48

INTERFACE BOOM CLAY
AND GLAUCONITIC SAND

CPT39

CPT31

2m

Figure 15.9 Western Scheldt Tunnel alignment; geological-geotechnical conditions

E TUNNEL BORING DESIGN AND CONSTRUCTION
The design and the construction of the Western Schelde tunnel in the
Netherlands opened in March 2003, started in 1995. It was at the limits of the state
of the art: a bored twin tunnel of 6600m length with diameters of 11m reaching as
deep as 60m below sea level under difficult geological conditions, in particular the
loose sands and stiff clays of extraordinary composition (Fig 15.9). The public-
private nature of the consortium, with the private organisation NV Westerschelde
(NVW), responsible for the construction and access roads, as well as for the