2114
Proceedings of the 18
th
International Conference on Soil Mechanics and Geotechnical Engineering, Paris 2013
ve
rizontal drainage wells were
ins
m OD, to speed
dr
all in terms of its outward movement
as measured by the inclinometers and the traverse line surveys
working of the quay, consistent with the
cu
. The figure
Fig
ruary 2000 and June
20
ing such structures once
the are perceived to be ‘at risk’, and the need to establish
o overall movements but to
lar where rates of movement
are
The au
nowledge with thanks the permission and co-
rt owners and their engineers in gathering
and
REFERENCE
eck R. B. 1969. Avantages and limitations of the observational method
in applied soil mechanics.
Géotechnique 19
(2), 171-187.
rtical and approximately thirty near-vertical 63.5mm diameter
shear keys into rock beneath the base of the wall.
In addition, a series of sub-ho
talled through the quay wall at a level of +0.0
the ainage of the retained soils.
These works were completed in early 2002.
5
WALL BEHAVIOUR 2002 – 2012
The dewatering wells were shut off in April 2002 and the
wall behaviour was monitored.
The response of the w
is illustrated in Figure 6.
Figure 6. Wall displacements at crest level 2002 to 2012. (Toe
displacements similar but generally smaller.)
Initial wall movements over the first 5-6 months were
between 5 and 10mm at the crest and toe of the wall as the
anchors took up further load. Load increases in the 43
o
anchors
were typically between 50 and 200kN over this period.
By the end of 2002 the movements had stabilised at around
16 to 26mm at the crest, and 15 to 20mm at the toe. These data
confirmed that the predominant mode of movement of the quay
wall in the most active area was by sliding along a plane
coincident with or close to the interface between the base of the
wall and the underlying strata.
Over the next 3 years outward crest movements over the
anchored section had increased to 30 to 40mm relative to the
April 2002 readings and toe movements were between 35 and
40mm
.
Loads in the 43
o
anchors had increased by between 200
and 250kN. It had been planned to complete the main
remediation works within this 3-year timeframe, but the
monitoring works had demonstrated that movements were
remaining controllable. The main works were put on hold,
therefore and a watching brief was maintained on the wall.
Based upon the previous readings, a movement criterion of
10mm/year had been adopted as a signal that further support
works needed to be put in place.
By 2009 the loads in some 43
o
anchors were approaching or
exceeding 1200kN – 15% above their design loads. Any
anchors found to be in excess of this load level were being
relaxed to avoid overstressing.
Outward wall movements over the anchored section
generally continued at a rate of around 3 to 5mm per year.
By 2012, however, inclinometer and traverse line readings
were indicating that outward wall movements were reaching 10
to 12mm per year, and the loads in the 43
o
anchors were
increasing at an average of around 150 to 300kN per year.
Additional interim measures were undertaken at the end of
2012, when a further six 1800kN capacity 43
o
anchors were
installed through the face of the wall over the anchored section.
The aim of these works is to reduce outward movements back to
acceptable levels.
These additional limited-scope works are intended to allow
the continued limited
rrent requirements of the Port. As demand rises or
operational needs change at the Port, then full remediation
works will be implemented to upgrade the South Quay facilities
to meet this demand.
For reference, the data from Figures 4 and 6 have been
combined on Figure 7 to illustrate the relative degrees of
movement measured at the crest of the quay wall over the worst
affected section from 2000 to the present day
clearly shows the rapid, and probably catastrophic, accelerating
rates of movement in 2000, before the dewatering was switched
on, followed by the relatively slow but continuing movements
over the next 9-10 years, but increasing latterly.
ure 7 Wall crest movements between Feb
12
6
SUMMARY AND CONCLUSIONS
The long-term monitoring of this 19
th
Century harbour wall
over the last twelve years in particular, (but with records
extending back over thirty years) has given a unique
opportunity to gain an insight into the behaviour and relative
‘flexibility’ of such structures. The data gained from this work
highlight the importance of monitor
y
‘trigger values’ related not just t
rates of movement, and, in particu
seen to be accelerating over time.
7 ACKNOWLEDGEMENTS
thors ack
operation of the po
and collating the data obtained from these monitoring works
allowing their publication in this paper.
8
P
