Civil Engineering Reference
In-Depth Information
Geotechnical interpretation
The layering of the subgrade encountered was obviously based on the local
geology. Here a differentiation is made between a cohesionless and a cohe-
sive subgrade.The Boom clay is part of the cohesive subgrade, whereas the
glauconitic sands are classified as cohesionless subgrade.
The geotechnical layering is the result of the interpretation and correlation
of all the results of the drillings, cone penetration tests and laboratory tests
carried out.
Geotechnical layering
The geotechnical layering of the non-cohesive subgrades is reflected in
Figures 7.9
and
7.10.
Layer ZK1 (in which Z stands for sand and K for clay)
does not show full cohesionless behaviour because of the considerable clay
content, but being a layer containing sand as the main ingredient, it was clas-
sified as an cohesionless subgrade. The opposite applies for layer KZ1. This
involves a considerable sand content so that the layer does not show full
cohesive behaviour. However, being a layer that contains clay as the main
ingredient, KZ1 has been classified as a cohesive subgrade.The geotechnical
profile was then drawn up on the basis of the geotechnical layering.
Pas van Terneuzen
Everingen
Z1
0
0
KZ1
K1
K1
10 m
KZ1
Z1
Z1
10 m
Z1
KZ
1
Z1
26
1
20 m
20 m
30 m
ZK1
ZK1
BK1
25
BK1
2
30 m
Z1
Cross connections
BK2
9
10
11
8
12
2
4
13
15
40 m
3
14
23
BK2
40 m
16
17
7
18
22
20
19
21
GZ1
50 m
GZ2
6
50 m
60 m
4
BK2
BK1
5
GZ1
60 m
K2
GZ2
BK2
70 m
70 m
approx. 6,600 m
Zeeuwsch-
Vlaanderen
Axis
of
tunnel
Pas van Terneuzen
Everingen
Zuid-
Beveland
Middelplaat
In Everingen - the secondary fairway at the northern end of the trajectory -
the extensive soil investigation brought to light a number of erosion chan-
nels situated in the Boom clay. These channels were not identified during
the four deep drillings with the seismic research which were previously
undertaken. Due to the presence of the glauconite in the sand in the erosion
channels, the seismic reflecting image was interpreted as Boom clay. The
layer Z1 which lies above GZ1, does not contain glauconite and is therefore
interpreted in the seismic reflecting image as sand. This meant that a con-
siderable portion of the boring trajectory was not positioned fully in the
Boom clay, but in a transition zone between Boom clay and glauconitic sand.
Furthermore, it appeared that particularly the bottom of the Boom clay con-
tained siltish to clayish sand deposits with a thickness varying from a few
decimetres to 2 metres.These sand deposits have the character of sand lenses
and don't continue.
Fig. 7.8
Profile and research
locations (see chart
showing 'geotechnical
layering' for
clarification of
abbreviations)
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