Southeast Asian practice of soil reinforcement in ... · Southeast Asian practice of soil...
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soil reinforcement
TC9 specialty session, 12 ARC, Singapore, 2003
Southeast Asian practice of soil reinforcement in combination with other ground improvement methods
byC.R. Lawson
soil reinforcement
Ground improvement techniques used in conjunction with reinforced soil structures
Variety of ground improvement techniques used in conjunction with reinforced soil structuresInternal zone:
Enhancement of the reinforced mass itself
External zones:Required to improve stability and reduce deformations of the structure
soil reinforcement
Ground improvement technique according to time of useNew Construction
Remedial Works
soil reinforcement
Ground improvement techniques used in conjunction with new reinforced soil construction
Internal zone:Stabilization of reinforced fill:
Carried out when poor soils are used and where serviceability is not a requirementDifficult to obtain consistent qualityStill experimental
External – backfill:Nails and anchors:
Used to transfer residual reinforcement tension into hard backfillsUsed where reinforced zone is constrained in extent
External – foundation:Soil replacement:
Used for soft foundations of limited depth
Preconsolidation:Used for deep soft foundations to ensure consolidation occurs before structure is built
Piles, columns, etc:Used to prevent settlements due to deep soft foundationsEnables quick construction
soil reinforcement
Conventional vs constrained reinforced soil walls
Segmentalblockfacing
Segmentalblockfacing
Geogridreinforcement
Geogridreinforcement
Reinforced fillReinforced fill
Retainedfill
FoundationHighly overconsolidatedsoil or rock
Anchors
a) Conventional reinforced soil wall b) Constrained reinforced soil wall
soil reinforcement
Horizontal force coefficient for φ’ = 30°
RigidzoneH
Lt
Ph
W
θ
a) Forces acting behind wall facing with potential failure surfaces
Potential failuresurfaces
b) Horizontal force coefficient for ’ = 30°
Kφ
c) Wedge angles that provide maximum horizontal force coefficient for ’ = 30°
θ
φKmax
0
0.1
0.2
0.3
0.4
0.5
40
50
60
70
80
90
0.2 0.20.4 0.40.6 0.60.1 0.10.3 0.30.5 0.50.7 0.7L Ht/ L Ht/
PH
Kh/½
= γ
2
Wed
ge a
ngle
(d
egre
es)
θ
Ka = 0.333
K for = 45°+ ’/2θ φ
Kmax
θ φ = 45°+ ’/2
soil reinforcement
Distribution of tension in the reinforced fill
Rigid zone
Anchor atlevel j
ωPanj
Passive zoneActive zoneLine of maximumtension
level j
hj
Segmentalblockfacing
θ
Tmaxj
Laj Lej
Geogridreinforcementat level j
TfacejTrearj
Distribution of tensionin geogrid reinforcement
soil reinforcement
Constrained reinforced soil wall
soil reinforcement
Basal reinforced piled embankmentBasal reinforced piled embankments constructed between piled bridge structures and light-weight fill embankments
Piles
Basalgeotextilereinforcement
Concrete connectingbeam
Geogridreinforcement Grassed
side slopesPavement
Pavement
soil reinforcement
Basal reinforced piled embankment
soil reinforcement
Ground improvement techniques used for remedial construction
Internal zone:Nails:
Used to provide additional shear resistance to reinforced fill
Anchors:Used to provide restraint to the reinforced soil mass
Grouting:Provides additional stability to reinforced fillNormally used as a last resortAlso used where loss of reinforced fill occurs
External – top:Waterproofing:
Used to prevent water ingress into reinforced fill
External – face:Buttressing:
Used to prevent movement of structure face and prevent foundation instability
External – backfill:Anchors:
Used to provide restraint to the reinforced soil mass
soil reinforcement
Stages of deformation in reinforced soil structures
In the field, performance is primarily assessed by level of deformation over timePotentially three deformation stages can be reachedPreventing the harmful effects of Stage 2 deformations are where ground improvement techniques are used as remedial measures
The specific technique used depends on the nature and location of the problem
Amou
nt o
f def
orm
atio
n
Time
Structurally stable andfunctionally serviceable
Serviceability limit forassociated structures
Serviceability limit forreinforced soil structure
CollapseStructurally unstable
Structurallystable butstructurallyunserviceable
Structurally stablebut functionally unserviceable
Stage 1deformations
Stage 2 deformations
Stage 3 deformations
soil reinforcement
Remedial works applied to reinforced soil wall
soil reinforcement
Conclusions
Ground improvement techniques used with new construction:
Primarily concerned with foundation treatments Backfill treatments to a lesser extent
Ground improvement techniques used as remedial works:
Primarily concerned with enhancing and maintaining internal stability of reinforced zoneFirst options - nailing, anchoring, buttressingFinal option - grouting