Geology Reference
In-Depth Information
2010). The barrettes were cracked by high-pressure water injection
down pre-installed pipes whilst the concrete was still at low
strength. Once the concrete had reached its 21-day strength, high-
pressure grouting was carried out through the cracked path around
the barrettes, metre bymetre from the base to improve the skin frictional
resistance.
Caissons are large box structures formed of steel or concrete and are
used as a common solution for bridge foundations offshore. The box is
typically constructed onshore then
floated and towed to its location
where it is sunk. Sometimes caissons are sunk into the ground by
driving and digging, elsewhere they just sit on a prepared surface on
the sea
floor. Different types are illustrated schematically in
Figure 6.13.
Once the caisson is in place/sunk to the required depth,
then it is back
lled with rock and concrete. Caissons are also often
used to form sea walls for reclamation schemes, the boxes are formed
on land then
floated and towed to position where they are sunk onto
prepared foundations and then back
lled.
Open
(Top & bottom)
Pneumatic
(Closed at top)
Box or Floating
(Open at top)
Soil excavated by
grab buckets
Maximum depth water 40m for
manned excavation
Constructed on land,
sunk onto prepared
foundation
Air &
access
Sink under
own weight
as soil is
excavated
Muck
(soil) out
Floated
to
position
May need
internal
strutting
during
towing
Soil
Working
chamber
Rip rap to
prevent
scour
Prepared base
May construct within
dewatered coffer dam or on
artifical, temporary sand
island
1874 Eads Steel Arch
Bridge, Misssissippi
(15 died, 79 severely
afflicted by 'caission
disease')
Akaishi Kaikyo, Japan
Rion-Antirion, Greece
Busan-Geoje
− Mostly concrete or steel
− Good for mixed soil that might hinder
driven piles
− Resistant to scour and impact (boat / ice)
− Resist lateral forces (earthquakes)
− Filled with soil / rock fill / concrete
− May be any shape to suit structure
2007 Second Tacoma
Suspension Bridge (span
925 m Tower Caissons 40
m × 25 m × 70 m deep)
1993 Rainbow Bridge,
Tokyo − used robot
excavators
Humber Bridge, UK
