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Contents
Introduction / Description of the problem
Effect of creep stress level
Creep strains
Laboratorial tests
Effect of binder quantity
Conclusions
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A14 (IP3) soft soil of Baixo Mondego
Introduction / Description of the problem
Creep settlements of an embankment on soft soil (Portugal)
Geotechnical design:couple stability-settlement analysis incorporating time effects
Effects of time on the rheological behaviour of soft soils
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log
time
q C
q B
q A
qC
> qB
> qA
1 3= ' 'q
Material creep - deformation- irreversible- time dependent
Creep Model
Soil creep - sandy soil: rearrangement of soil particles- soft soils: viscosity effects
Failure
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Creep modelation
Volumetric
component
Deviatoric
component
Creep Model
Incorporated into an Elastoplastic Soil Model
Taylors law
C Secondary consol. coefficient
e void ratio
tv volumetric age
( )0/ 2.3
1
t ttv t
v
Cdt
e t
+=
+, m Singh-Mitchells parameters
Singh-Mitchells law
( )( )ult
D31
31
-
- =
deviatoric stress level
td deviatoric age
A,
( )..m
t t dt D is
t d
tAe dt
t
+ =
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Laboratorial Tests
Unstabilized soft soil:- identification and characterization- oedometer tests
Stabilized soft soil with CEM I 42.5R and Slag (75/25):
- preparation of samples with = 70 and 50 mm- oedometer tests
Creep volumetric study by oedometer tests
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GG wwnatnat satsat ee natnat GranulomGranulom .. PlasticPlasticPlastic . OM. OM Unifined c uu(%) ((%) ( kNkN/m/m 33)) (%) (%)(%) (%) (%)(%) Classific. (kPa)(kPa)
2.55 80 14.6 2.1 C = 8 - 12 wwLL = 71 7.7 OH of high < 25M = 71 wwPP = 43 plasticity
S = 17 - 21 IP = 28
Unstabilized soft soil
Soft soil deposit of Baixo Mondego (thickness 20m):- geotechnical properties
- chemical properties
CaOCaO SiOSiO 22 Al Al22OO 33 FeFe 22OO 33 MgOMgO KK22O pH TOC ECECO pH TOC ECEC(%)(%) (%) (%)(%) (%) (%)(%) (%)(%) (%)(%) ((--) (%) () (%) ( cmolcmol +/kg)+/kg)
0.74 62.00 16.00 4.80 1.10 3.00 3.5 2.79 11
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Sample preparation
Based on EuroSoilStab (2001) with the modificationsproposed by Correia (2011)
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Oedometer test
Curing time = 28 days
Vertical pressure applied
during the curing time = 48 kPa( v0 middle of deposit thickness)
Stress ratio adopted:2 loading4 unloading
(each stress increment = 24h)
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Oedometer test
Curing time = 28 days
Vertical pressure applied
during the curing time = 48 kPa( v0 middle of deposit thickness)
Stress ratio adopted:2 loading4 unloading
(each stress increment = 24h)
Creep stress (14 days):
(embankment of 4m high, = 22kN/m 3)136 kPa unstabilized
88 kPa
Unstabilized
embankment
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Oedometer test
Curing time = 28 days
Vertical pressure applied
during the curing time = 48 kPa( v0 middle of deposit thickness)
Stress ratio adopted:2 loading4 unloading
(each stress increment = 24h)
Creep stress (14 days):
(embankment 4m high, = 22kN/m 3)136 kPa unstabilized448 kPa stabilized
(DMC of = 0.8m, spaced 1.5m in
a square pattern)
400 kPa
Stabilized
embankment
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Results
One-dimensional compression curves
0,5
0,7
0,9
1,1
1,3
1,5
1,7
1,9
2,1
1 10 100 1000 10000 100000
'v (kPa)
e
UnstabilizedStabilized
'p =40kPa
'p = 2500kPa
(C r = 0,065; C c =0,57)(C r = 0,032; C c =1,00)Stabilized (C r = 0.032 C c = 1.00)
Unstabilized (C r = 0.065 C c = 0.57)
y = 40 kPa
y = 2 500 kPa
M e t a s t a b l e
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Results
Creep volumetric strains
Stabilized
1,4
1,5
1,6
1,7
1,8
0 , 0 1
0 , 1 0
1 , 0 0
1 0 , 0 0
1 0 0 , 0
0
1 0 0 0
, 0 0
1 0 0
0 0 , 0 0
1 0 0 0
0 0 , 0 0
time (min)
e
UnstabilizedStabilized
(C =0,023)(C =0,00075)
Unstabilized
C = 0.023
C = 0.00075
Stabilized
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Results : effect of creep stress level(binder quantity = 125kg/m 3)
One-dimensional compression curves
0,6
0,8
1,0
1,2
1,4
1,6
1,8
2,0
2,2
1 10 100 1000 10000 100000 'v (kPa)
e
Unstabilized
Stabilized100 kPa
1,690
1,695
1,700
1,705
1,710
1,715
1,720
100 1000 10000
'
creep = 100 kPa
creep
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One-dimensional compression curves
0,6
0,8
1,0
1,2
1,4
1,6
1,8
2,0
2,2
1 10 100 1000 10000 100000 'v (kPa)
e
Unstabilized
Stabilized100 kPa248 kPa448 kPa
1,670
1,675
1,680
1,685
1,690
1,695
1,700
100 1000 10000
'
creep = 448 kPa
creep
Results : effect of creep stress level(binder quantity = 125kg/m 3)
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One-dimensional compression curves
0,6
0,8
1,0
1,2
1,4
1,6
1,8
2,0
2,2
1 10 100 1000 10000 100000 'v (kPa)
e
Unstabilized
Stabilized100 kPa248 kPa448 kPa848 kPa
1248 kPa1648 kPa
1,650
1,655
1,660
1,665
1,670
1,675
1,680
100 1000 10000
'
creep = 1648 kPa
creep
Results : effect of creep stress level(binder quantity = 125kg/m 3)
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Creep volumetric strains
0,000
0,005
0,010
0,015
0,020
0,025
0,030
0,0350,01 0,1 1 10 100 1000 10000 100000
Time (min)
e100 kPa248 kPa448 kPa848 kPa1248 kPa1648 kPaEOP
C = 0.00075
C = 0.00102
C = 0.00160C = 0.00274
C = 0.00292
C = 0.00051
Results : effect of creep stress level(binder quantity = 125kg/m 3)
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C = 1.67x10-6 . ' creep + 322.7x10
-6
(R = 0.970)
0
0,001
0,002
0,003
0,004
0 250 500 750 1000 1250 1500 1750
' creep (kPa)
C
Secondary consolidation coefficient vs creep stress
Results : effect of creep stress level(binder quantity = 125kg/m 3)
creep < y
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Results : effect of binder quantity(creep stress = 448kPa)
One-dimensional compression curves
creep
0,6
0,8
1,0
1,2
1,4
1,6
1,8
2,0
2,2
1 10 100 1000 10000 100000 'v (kPa)
e
Unstabilized
75 kg/m3125 kg/m3Stabilized
1,610
1,620
1,630
1,640
1,650
1,660
100 1000
75 kg/m3
creep
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Results : effect of binder quantity(creep stress = 448kPa)
One-dimensional compression curves
creep
0,6
0,8
1,0
1,2
1,4
1,6
1,8
2,0
2,2
1 10 100 1000 10000 100000 'v (kPa)
e
Unstabilized
75 kg/m3100 kg/m3125 kg/m3250 kg/m3400 kg/m3
Stabilized
1,300
1,310
1,320
1,330
1,340
1,350
100 1000
400 kg/m3
creep
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Creep volumetric strains
0,00
0,02
0,04
0,06
0,08
0,10
0,12
0,01 0,1 1 10 100 1000 10000 100000
time (min)
e
75 kg/m3100 kg/m3125 kg/m3
250 kg/m3400 kg/m3EOP
C = 0.00636
C = 0.00149C = 0.00102C = 0.00062C = 0.00055
Results : effect of binder quantity(creep stress = 448kPa)
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Secondary consolidation coefficient vs binder quantity
0
0,002
0,004
0,006
0,008
0 100 200 300 400 500
Binder quantity (kg/m3
)
C
Results : effect of binder quantity(creep stress = 448kPa)
250
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Chemical stabilization stronger and stiffer material(metastable behavior)
Conclusions
Chemical stabilization creep volumetric strains decrease
Chemical stabilization linear relationship C and creep stress level(for creep < y)
Chemical stabilization C decreases with the increment of thebinder quantity
Although creep volumetric strains are smallthese should not be disregarded
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Aknowledgements
CIMPOR
(Cements of Portugal)
FCT(Foundation for Science
and Technology - Portugal)
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