australian geomechanics society mini-symposium sydney october 2005 soil loads on cut and cover...
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Australian Geomechanics Australian Geomechanics Society Mini-symposium Society Mini-symposium Sydney October 2005Sydney October 2005
Soil Loads on Cut and Cover Tunnels Under High Fills
Doug Jenkins
Interactive Design Services
Overview:Overview: Influence of high fills on structural
actions Design of foundation structures for high
vertical loads Longitudinal differential settlement Longitudinal loads Examples Conclusions
Influence of high fills on structural actionsInfluence of high fills on structural actions Axial loads
High fill = high axial load Effect of foundation stiffness on axial load
Influence of high fills on structural actionsInfluence of high fills on structural actions Bending moments and shear forces
Effect of foundation stiffness on axial load Lower bound stiffness may not be conservative
Influence of high fills on structural actionsInfluence of high fills on structural actions Bending moments and shear forces
Effect of arch profile on arch actions Morwell Tunnels - alternative cross sections
Influence of high fills on structural actionsInfluence of high fills on structural actions Bending moments
-8 -6 -4 -2 0 2 4 6 8
X-Axis
-800
-700
-600
-500
-400
-300
-200
-100
0
100
Ben
ding
Mom
ent;
kNm
ActualCircularElliptical
Morwell TunnelsComparison of Arch Shapes
Bending Moments
Influence of high fills on structural actionsInfluence of high fills on structural actions Shear Forces
-8 -6 -4 -2 0 2 4 6 8
X-Axis
-1000
-500
0
500
1000
She
ar F
orce
; kN
m
ActualCircularElliptical
Morwell TunnelsComparison of Arch Shapes
Shear Forces
Influence of high fills on structural actionsInfluence of high fills on structural actions
Use finite element analysis. Consider the effect of boundary conditions in
the model. Consider the effect of upper and lower bound
stiffness values in the foundation materials Model the footing structure accurately Optimise the arch shape for the fill height
Essential Features of Finite Element Essential Features of Finite Element ModelModel
Include foundation layers. Add arch fill in layers, modelling the
actual construction sequence. Allow slip at the arch/soil interface. Non-linear Mohr-Coulomb soil model.
Design of foundation structures for high Design of foundation structures for high vertical loadsvertical loads
Morwell Conveyor Tunnels Alternative foundation treatments
Design of foundation structures for high Design of foundation structures for high vertical loadsvertical loads
Detail of finite element mesh Alternative simplified model
Design of foundation structures for high Design of foundation structures for high vertical loadsvertical loads
Design actions in actual raft under maximum load
-3 -2 -1 0 1 2 3
-1000
-500
0
500
1000
Bas
e Fo
rces
; kN
,m
Moment
Shear
Axial
Type A Raft
Design of foundation structures for high Design of foundation structures for high vertical loadsvertical loads
Comparison of bending moments in flat and tapered rafts
-3 -2 -1 0 1 2 3
-2000
-1500
-1000
-500
0
500
1000
Ben
din
g m
om
ents
; kN
m
Flat raft
Actual raft
Bending MomentFlat raft vs. Actual
Design of foundation structures for high Design of foundation structures for high vertical loadsvertical loads
Alternative raft models: bending moments
-3 -2 -1 0 1 2 3
-200
-100
0
100
200
300
400
500
600
Raf
t M
omen
ts;
kNm
REPL FEA
Strand7 FEA
Strand7 simplified
Bending MomentAlternative analysis methods
Design of foundation structures for high Design of foundation structures for high vertical loadsvertical loads
Alternative raft models: axial forces
-3 -2 -1 0 1 2 3
-900
-800
-700
-600
-500
-400
-300
-200
-100
0
Axi
al F
orce
; kN
REPL FEA
Strand7 FEA
Strand7 Simplified
Axial LoadAlternative analysis methods
Design of foundation structures for high Design of foundation structures for high vertical loadsvertical loads
Larger spans
Design of foundation structures for high Design of foundation structures for high vertical loadsvertical loads
Larger spans
Longitudinal Differential SettlementLongitudinal Differential Settlement Long Section - Morwell TunnelsLong Section - Morwell Tunnels
Longitudinal Differential SettlementLongitudinal Differential Settlement Morwell conveyor tunnels analysis Deep brown coal deposits + uncompacted fill
Vertical SettlementVertical Settlement
Horizontal MovementsHorizontal Movements
Longitudinal Differential SettlementLongitudinal Differential Settlement
-200 -100 0 100 200
X-Axis
-2.5
-2
-1.5
-1
-0.5
0
Se
ttle
me
nt D
Y,
m
-0.2
-0.1
0
0.1
0.2
Ho
rizo
nta
l Mo
vem
en
t, D
X, m
DX
DY
Settlement and Longitudinal MovementMinimum stiffness all layers
-200 -100 0 100 200
X-Axis
-0.8
-0.7
-0.6
-0.5
-0.4
-0.3
-0.2
-0.1
0S
ettl
em
en
t DY
, m
-0.15
-0.1
-0.05
0
0.05
0.1
Hor
izon
tal M
ove
me
nt,
DX
, m
DXDY
Settlement and Longitudinal MovementMaximum differential stiffness
Longitudinal Differential SettlementLongitudinal Differential Settlement
Longitudinal LoadsLongitudinal Loads Steep fill slopes above the structure Segmental structures on steep slopes Longitudinal spreading of foundations under
high fills Longitudinal differential settlement effects on
continuous structures
Longitudinal LoadsLongitudinal Loads
Longitudinal LoadsLongitudinal Loads Use wider precast elements Provide shear connectors between adjacent
elements and/or strengthen crown beam Provide movement joints in the crown beam
and footings Design for variation in axial load Detail robust crown joints
Examples - Morwell Conveyor TunnelsExamples - Morwell Conveyor Tunnels
Examples - Mt Arthur, Olympic DamExamples - Mt Arthur, Olympic Dam
Examples - SpainExamples - Spain
ConclusionsConclusions High axial loads, possibly high bending
moments and shear forces Consider upper and lower bound foundation
stiffness Design raft foundations for soil-structure
interaction Consider longitudinal effects:
– Differential settlement– Foundation spreading– Longitudinal loads due to fill slopes and/or inclined
structure