Abstract
To collect background information for formulating a description of
the expected soil properties along the tunnel line, in 1987
Storebælt initiated a statistical investigation of the occurrence
and size of boulders in the Great Belt area. The data for the
boulder size distribution were obtained by use of aerial
photographing of cliff beaches with subsequent stereo metric
measurement on the photographs. To get information about the
density of occurrence, a series of continuous seismic scannings
were also made along parallel lines in a corridor with the tunnel
line as about the central line. The data collection part of the
investigation was made on the basis of geological expert advice
(Gunnar Larsen, Århus) by the Danish Geotechnical Institute
(DGI).The statistical data analysis combined with stochastic
modeling based on geometry and sound wave diffraction theory gave
a point estimate and a 95% confidence interval (say) for the
expected number of boulders with largest dimension larger than 1m
(say) per volume unit of till along the tunnel line. Using
quantitatively prudent assessments of the uncertainties of the
seismic measuring method in the calculations, the resulting point
estimate varies linearly from about 35 to about 53 boulders of
maximal size larger than 1 m per 100 000 m3 of till across the
seismic scanning corridor from the south to the north boundaries.
The assessed 95 % confidence interval for the number of boulders
along the north boundary ranges from 22 to 112 boulders.
Contractor and client representatives systematically recorded the
boulders from the first 61 500 m3 of tunnel excavation in the in
the upper till.The observed empirical distribution given in the
range from about 0.5 m to about 1.2 m is well within the 95%
confidence interval. For 1 m it is by interpolation obtained as
about 45, convincingly close to the prediction of 44.
Original language | English |
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Title of host publication | East Tunnel |
Place of Publication | Copenhagen |
Publisher | A/S Storebæltsforbindelsen |
Publication date | 1997 |
Pages | 39-41 |
Publication status | Published - 1997 |