Brook. These deformations can indicate increased pressures on the
linings resulting in bulges, or the converse can occur where cavities are
created behind the lining causing decreased pressures. The presence of
deformations in the tunnel structure can indicate one of three conditions:-
i) Ihe shape of the tunnel as built.
ii) Changes in pressures during the life of the tunnel, whicn have
since stabilized, or
iii) Changes in pressures still occuring.
The third situation is the one which is the cause for concern. The problem
is to detect these deformations with sufficient accuracy and as cheaply as
possible.
Detection of profile deformations in brick lined tunnels is best done by
recording the profiles at right angles to the axis. Visual inspection,
even with powerful lamps does not reveal deformations, unless they are
prominent, a fact which we have proved by the commercial operation of
our system.
Recording Sections
Many techniques exist for recording tunnel sections, which vary from
decimeter to sub millimeter accuracy. Generally, the more accurate
the method, the more time is required to record the section, and the
more costly the operation. Early and high accuracy methods tend to
be by direct measurement whilst contemporary development has moved
towards remote sensing.
B.K.S. became involved in tunnel sectioning some six years ago. The
original technique used was stersometric photogrammetry, being an
extension and development of our main line of business - aerial
photogrammetry. The technique involved a pair of Wild P32 cameras
mounted on a 1.2 metres base bar with lighting provided by numerous
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