Soil treatment The French approach Jean-François Corté · Essai d’aptitude (NF P 94-100) 37 ......
Transcript of Soil treatment The French approach Jean-François Corté · Essai d’aptitude (NF P 94-100) 37 ......
Objective:
Improve materials with poor characteristics or increase their performance in order to make them suitable for appropriate fields of application from low volume roads to infrastructure subject to the heaviest loadings (roads, airports, industrial platforms, etc.).
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Amélioration ou stabilisation ?
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Capping layer
Fill
Pavement course
Treatment
After
improvement
Before
improvement
Stabilisation(Medium / long term)
Improvement(Short term)
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1. Effects of treatment additives on soils
2. Brief history of use of soil treatment in France
3. Limits to soil treatment
4. Methodology of treatment design
5. Soil improvement for fill construction
6. Soil stabilisation for capping layers
7. Concluding remarks
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1. Effects of treatment additives on soils
1.1. Effects of lime
1.2. Effects of cement and hydraulic road binders
2. Brief history of use of soil treatment in France
3. Limits to soil treatment
4. Methodology of treatment design
5. Soil improvement for fill construction
6. Soil stabilisation for capping layers
7. Concluding remarks
1.1 Effects of lime
wikipedia
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Reaction of hydration of quicklime
CaO + H2O Ca(OH)2 + 15,5 kcal
hydration of the quicklime (320 l/ton CaO)
vaporisation of water by the heat produced
addition of dry bulk (slaked lime) which reduces the weight ratio (water / dry material)
Effect of lime on the soil moisture content
1% of quicklime D w - 1%
1% of slaked lime D w - 0,3%
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increase of the plastic limit wp
(wl remains almost unchanged)
• increase in shear resistance
• modification of compaction characteristics
Effect of lime on the clay fraction
Interaction of the lime with the electrical charges of clayparticles floculation
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Proctor and CBR curves
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Proctor & CBR curves
before lime treatment
Natural moisture content
before lime treatment
Modified moisture content
after lime treatment
Proctor & CBR curves after
lime treatment
CB
R I
mm
ed
iat
Moisture content (%)
Dry
de
nsity
Low resistance
Moisture content (%)
Easier compaction
Increased bearing capacity
Long-term effects of lime treatment
Pozzolanic reaction (*) between lime and clay minerals
Formation of liaisons between limestone aggregates or
soft saturated calcareous materials.
(*) Silice + Alumine + Lime + Water Hydrated Calcique Hydraté +Hydrated Aluminate Calcique
SiO2 + (Al2O3 , SiO2) + Ca(OH)2 + H2O → CSH , CAH , CASH
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1.2 Effects of cement and hydraulic road binders
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Composite binders obtained by mixing and/or crushing of
Portland clinker (K) and by-products from industry (slag (S),
flyash (V), calcinated schists (T)) or natural pozzolans (Z) ,
calcareous rocks(L), sometimes lime.
Hydraulic road binders (HRB)
Example of naming
HRB 10, S 55, V 25, L 15
Class of strength 10 : Rc56j between 10 and 30 Mpa
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hydration of the binder
vaporisation of water by the heat produced
addition of dry bulk which reduces the weight ratio (water / dry bulk)
Effect of cement and HRB on the moisture content
1% of HB LHR Δw - 0,3 to - 0,5%
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Medium and long-term effect of cement and HRB
Setting reaction the kinetic of which depends on the
composition of the binder (formation of hydrated ferro-
silico-aluminates) and to some extend on the soil.
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• Example of evolution of Rc with a silty soil as a function of time and of binder
Soil Dmax % < 80 μ % < 2 μ Ip
A1 0,2 mm 96 24 7
7 9028 365
Untreated
Time (days) 1,5% CaO + 4,5% ciment
Soil treated with lime
(Slow hardening)Soil treated with cement
(Rapid hardening)
Time (days)
Selection of treatment additive – French context
• Improvement quicklime1 to 3% depending on the soil and moisture content
With some nuances:
Mixed treatment, lime-cement, of
clayey soils.
Use of mixed binders (lime plus
hydraulic components) for some
clayey and/or humid soils.
Stabilisation of plastic soils with
lime.
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• Stabilisation HRB3 to 7% depending on soil and expected performance
Choix du liant : chaux ou ciment ?
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%lim
e%
HR
B
Clay content of the soil
0 %
Single
treatment
Single treatmentMixed
treatment
HRB LimeLime+
HRB
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1. Effects of treatment additives on soils
2. Brief history of use of soil treatment in France
3. Limits to soil treatment
4. Methodology of treatment design
5. Soil improvement for fill construction
6. Soil stabilisation for capping layers
7. Concluding remarks
Treatment of humid silts
(North of France)
Standard solution:
Remove and dispose the wet silts (w : 17-23%)
Replace by schists for the capping layer (80 cm) and the fills
Variant:
Treatment of the silts with 2 to 4% of quicklime
Benefit: 40 %
First applications (mid-60ies)
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Motorways A-13 A-15 (Normandy)
Treatment of wet silts:
with quick lime for the fills
1,5% of quicklime and 5% of cement for the capping
layer
First applications (mid-60ies)
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Reduction of the contractual deadlines for theconstruction of conceded motorways
Necessity to find solutions permitting almost all –timetrafficking of the earthwork equipment in order to meetthe contractual deadlines.
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Example – A 26 (Chalons - Troyes)
chalk treated with 6% CLK 45 (over 33 cm)
modulus of the platform > 80 MPa
“graveluche “ a limestone treated with 4 to 5 % HRB
(over 33 cm)
Modulus of the platform > 120 MPa
Improvement of the bearing capacity of pavement
subgrade by soil treatment
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Optimisation of the whole design (earthworks/capping layer/pavement)
Pavement courses
Treated capping layer
Treated subgrade
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improve the homogeneity and quality of the subgrade to support all-time trafficking of the worksite
increase the stiffness of the capping layer and hence the bearing capacity of the platform which supports the pavement courses
Reduction in thickness of the pavement courses
The approach : Make the best use of the least
expensive materials
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Sandy capping layer treated with 1% lime (au déblai) +6 % cement in plant
Example : A-11 (Angers - Le Mans)
Deflexion, after 28 jours,
< 12/100 mm
Rtd > 0.3 MPa
130 kN
40 cm
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From Chaussées d’Autoroutes Infos n°11 - 1988 9 %
-165-120Total
-350-150Economie on cost of the pavement courses
+185+30 FF/mSurcoût capping layer
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A-11
7 cm
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25
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Sand
5% cement
GC
Sand
6% cement
Sand
6%
cement
GNTGNT
GB GB GB
In situ In plant
7 cm
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20
35
7 cm
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15
40
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Necessity to valoriser local materials for environmentalreasons
(reduction of borrow pits and disposal areas)
and economical reasons
(extraction of materials and cost of transportation)
Very strong drivers for the development of soil treatment for fills and capping layers
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Volume of earthworks 50 à 100 Mm3/an
Consomption of lime 0,4 à 0,5 Mt/an
Consomption hydraulic binders 0,9 à 1,1 Mt/an
Volume treated 25 à 35 Mm3/an
Number of stabilisation plants 150 à 200
Soil treatment in France
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1. Effects of treatment additives on soils
2. Brief history of use of soil treatment in France
3. Limits to soil treatment
4. Methodology of treatment design
5. Soil improvement for fill construction
6. Soil stabilisation for capping layers
7. Concluding remarks
• Grading:
Dmax < 125 à 150 mm : compatibility with capacity of the blenders
• Plasticity:
In France : treatment is currently done if
o Ip < 40 : in fill and capping layer
o Ip < 20 : in sub-base
• Moisture content:
Case of high moisture content:
o The limit is that preventing equipment to move and correct treatment with the target to reach optimum compaction conditions (Proctor Normal)
Case of low water content:
o Addition of water is a necessity, in addition to the treatment, in order to reach optimum compaction condition
Limits associated with geotechnical characteristics
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• Sulphates and sulphides
In combination with calcium and alumine of the binder formation of a swellingcrystalline: ettringite
• Phosphates and nitrates
inhibit or at least retard the hydraulic set
• Chlorides
Speed up setting with possible swelling as chloro-aluminates are formed
• Organic chemicals
Pre-emptively use part of the binder to neutralise acidity. A pre-treatment withlime can sometimes be used.
• Acid soil
An excess of acidity causes overconsomption of binder. In this case considerpre-treatment with lime.
Limits associated with composition of the soils
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1. Effects of treatment additives on soils
2. Brief history of use of soil treatment in France
3. Limits to soil treatment
4. Methodology of treatment design
5. Soil improvement for fill construction
6. Soil stabilisation for capping layers
7. Concluding remarks
Technical guidelines
Soil treatment with lime and/or hydraulic binders.
Application to the construction of fills and capping layers
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A – General concepts
Materials
Effects of treatment additives on the soil
Methodology of soil treatment design
Construction plant for soil treatment
Quality assurance
B – Soil improvement in fill construction
Soil improvement applied to the use of too wet soils
Other applications
C – Soil stabilisation for the construction of capping layers
Design
Construction techniques and plants
Quality assurance
Appendices
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Parameters for soil nature
• Plasticity
• Proportion of specific chemicals particulières
(sulphates, sulphites, organic matters...)
• Grain size distribution
Parameters for soil condition
• Moisture content
• In-situ density (for limestone, chalk)
Parameters for performance
• Fragmentation of large particles
• Abrasion of granular fraction
Based on technical guidelines
Construction of fills and capping layers
for the characterisation of the soils
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Essai d’aptitude (NF P 94-100)
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Accelerated test for the detection of the presence of deleterious substances
(gypsum, organic chemicals, etc.)
Test Rit Measure of volume swelling
Without gypsum
With
gypsum
Treated soil sample
D = 5 cm, H = 5 cm
Assessment of soil suitability for treatment(Essai d’aptitude d’un sol au traitement NF P 94-100)
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1. Effects of treatment additives on soils
2. Brief history of use of soil treatment in France
3. Limits to soil treatment
4. Methodology of treatment design
5. Soil improvement for fill construction
6. Soil stabilisation for capping layers
7. Concluding remarks
Objective of soil treatment in fills:
mainly to improve too wet soils pso that they can be used under acceptable engineering and cost conditionis.
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Test : Instant bearing index IPI
a CBR test performed without surcharge nor prior immersion
Criteria for treatment
Soil classes Sols (NF P 11 – 300)
A1, C1A1, C2A1
A2, B6, C1A2, C2A2, C1B6, C2B6, R34
A3, C1A3, C2A3
B4, C1B4, C2B4
B2, B5, C1B2, C2B2, C1B5, C2B5
R12 R13
IPI value below which treatment can be considered
8 5 3 15 12 15 10
Target IPI on treated material
10 à 20 7 à 15 5 à 10 20 à 40 15 à 30 15 à 30 10 à 20
Plasticity Index 12 12 à 25 25 à 40
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Construction techniques
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Soil preparation in the case of chalks
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Spreading of the binder
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Treatment is usually done in the cut
Scrap
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Mixing plants
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1. Effects of treatment additives on soils
2. Brief history of use of soil treatment in France
3. Limits to soil treatment
4. Methodology of treatment design
5. Soil improvement for fill construction
6. Soil stabilisation for capping layers
7. Concluding remarks
insensitive to water
resistance to crushing under worksite traffic
no swelling in freezing weather (if applicable)
Objective of the treatment of soils for capping layers:
Improve the soils to make them suitable to be used in a capping layer
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Limitation of volume swelling in water
Minimum resistance in traction
Suitability for treatment
Treatment type
Suitability of the soil
Volume swelling Gv(%)
Brazilian strength Rtb (Mpa)
HRB & HRB + lime
Suitable Marginal
Unsuitable
5
5 Gv 10
10
0,2
0,1 Rtb 0,2
0,1 Lime alone Suitable
Marginal Unsuitable
5
5 Gv 10
10
Not considered, setting too slow
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Small jobs (up to 5000 m3)
standard binder contents are proposed
Medium and large jobs
3 levels of study as a function of the importance of the job
• Level 1 : verification (soil and interaction with binder are well-known from former jobs)
• Level 2 : 1 + sensitivity study
• Level 3 : overall design (pavement / capping layer / earthwork)
Determination of binder content
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Determine the mean and standard deviation of the natural moisture content
Determine the scatter (2σ/m) of ρdOPN
Acceptable up to 8% for most situations and to 10% for small to medium jobs
Number of tests depends on current knowledge of the deposit and its volume (from a few ones to several tens)
Assessment of the uniformity of the deposit
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minimum IPI on the treated soil at the maximum natural moisture content
Final moisture content of the treated soil prepared at the minimum natural moisture content must be not less than 0.90 wOPN
Target characteristics of the treated soil
Class IPImin
A3 – C1A3 10
A2 – C1A2 – B6 – C1B6 15
A1 – B5 – C1A1 – C1B5 20
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IPI
IPImin
IPI curve of the
treated soil
traité
IPI curve of the
natural soil
Interval of natural moisture content
0.9 wOPNwOPN
wf
wi
Proctor curve of
the natural soil
Proctor curve of
the treated soil
d
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Age at which traffic can be allowed on the treated soil
Rc 1 MPa
Resistance to water immersion at young age
- if VBs 0.5
Rci 0.8 Rc60j
- if VBs > 0.5
Rci 0.6 Rc60j
Resistance of treated soil on probable onset freezing weather
Rtb 0.25 MPa
Rci : 28 days of standard cure followed by 32 days of immersion
in water at 20 °C
Target mechanical characteristics for soils reated with hydraulic binders
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Mechanical characteristics for pavement design
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Construction techniques and plant
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rate of binder spreading interlocked with speed forward
binder strip width control
Spreading of binder
Control of weight of binder per unit area spread
coefficient of variation < 10 %
discrepancy between average mass spread and design
mass of binder better than 5 % 56
Control of binder spreading
Mixing plant
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Compaction
Grading
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Final grading
Autograder guided by laser
tolerance on level 2 cm
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Suitable for construction of capping layers with clayey and humid soils
Pre-treatment with lime to reduce the moisture content and produce floculation of clay particles
Treatment with the hydraulic binder to improve the mechanical characteristics (modulus, tensile strength) of the treated soil
Mixed treatment with lime and hydraulic binder
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• Spreading, light rolling for surface closure and preliminarygrading of the delivered capping layer material
• Spreading of lime
• Mixing (one passe of pulviriser)
• Preparation before treatment with the hydraulic binder:- rolling (2 to 4 passes)- grading with a grader- scarification and wetting
• Spreading of the hydraulic binder
• Mixing
• Partial compaction with vibratory roller
• Fine grading
• Chipping
• Final compaction
Mixed treatment lime & hydraulic binder
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1. Effects of treatment additives on soils
2. Brief history of use of soil treatment in France
3. Limits to soil treatment
4. Methodology of treatment design
5. Soil improvement for fill construction
6. Soil stabilisation for capping layers
7. Concluding remarks
• There is a long-standing international experience of soil treatment
• Some countries make an extensive use of soil treatment because of the economic benefit derived from the use of local materials which wouldn’t be suitable to road construction in their natural condition
• Practical experience has been translated into technical guidelines
• BUT, there shouldn’t be hastive transpositions of foreign experience. Studies are necessary to take into account local soils, the traffic loads, the climatic context…
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• Réalisation des remblais et des couches
de forme (GTR)SETRA / LCPC, 2000 (2ème édition)
• Traitement des sols à la chaux et/ou aux
liants hydrauliques Application à la réalisation des remblais et
des couches de forme (GTS)SETRA / LCPC, 2000
• Traitement des sols à la chaux et/ou aux
liants hydrauliques Application à la réalisation des assises de
chaussées (GTS Assises)SETRA / CFTR, 2007
• Retraitement en place à froid des
anciennes chausséesSETRA/LCPC, 2003
French technical guideliness
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Thank you for your attention