Soil treatment The French approach Jean-François Corté · Essai d’aptitude (NF P 94-100) 37 ......

1

Soil treatment – The French approach

Jean-François Corté

[email protected]

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.).

2

Amélioration ou stabilisation ?

3

Capping layer

Fill

Pavement course

Treatment

After

improvement

Before

improvement

Stabilisation(Medium / long term)

Improvement(Short term)

4

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

5


1.1. Effects of lime

1.2. Effects of cement and hydraulic road binders







1.1 Effects of lime

wikipedia

6

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%

7

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

8

Proctor and CBR curves

9

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

10

1.2 Effects of cement and hydraulic road binders

11

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

12

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%

13

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.

14

15

• 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.

16

• Stabilisation HRB3 to 7% depending on soil and expected performance

Choix du liant : chaux ou ciment ?

17

%lim

e%

HR

B

Clay content of the soil

0 %

Single

treatment

Single treatmentMixed

treatment

HRB LimeLime+

HRB

18








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)

19

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)

21

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.

22

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

23

Optimisation of the whole design (earthworks/capping layer/pavement)

Pavement courses

Treated capping layer

Treated subgrade

24

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

25

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

26

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

32Comparison/solution 1

A-11

7 cm

15

25

35

Sand

5% cement

GC

Sand

6% cement

Sand

6%

cement

GNTGNT

GB GB GB

In situ In plant

7 cm

16

20

35

7 cm

14

15

40

27

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

28

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

29

30








• 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

31

• 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

32

33








Technical guidelines

Soil treatment with lime and/or hydraulic binders.

Application to the construction of fills and capping layers

34

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

35

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

36

Essai d’aptitude (NF P 94-100)

37

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)

38








Objective of soil treatment in fills:

mainly to improve too wet soils pso that they can be used under acceptable engineering and cost conditionis.

39

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

40

Construction techniques

41

Soil preparation in the case of chalks

42

Spreading of the binder

43

Treatment is usually done in the cut

Scrap

44

Mixing plants

45

46








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

47

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

48

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

49

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

50

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

51

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

52

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

53

Mechanical characteristics for pavement design

54

Construction techniques and plant

55

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

58

Compaction

Grading

61

Final grading

Autograder guided by laser

tolerance on level 2 cm

62

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

63

• 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

64

65








• 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…

66

• 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

67

Thank you for your attention

Soil treatment The French approach Jean-François Corté · Essai d’aptitude (NF P 94-100) 37 ......

Documents

Transcript of Soil treatment The French approach Jean-François Corté · Essai d’aptitude (NF P 94-100) 37 ......