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