ENV - Final Report - TASK 3553 - Reuse of Cleaned … standard optimum Proctor (compaction) PE poly...

Task 3553 : Reuse of Cleaned Sediments

TBT clean 1 ENVISAN N.V.

LIFE02 ENV/B/000341

Development of an integrated approach for theremoval of tributyltin (TBT) from waterways and

harbors :Prevention, treatment and reuse of TBT

contaminated sediments

Task 3553 - Reuse of Cleaned Sediments-----

Geotechnical evaluation of mechanically dewateredsediments and thermally treated sediments for possible

re-use of sediments containing tributyltin (TBT)

Alain Pieters & Lode Goethals

ENVISAN N.V., Tragel 60, 9308 Hofstade (Aalst), Belgiumwww.envisan.com, [email protected], [email protected]



Index

1. Geotechnical tests ......................................................................................................................................... 51.1. Purpose of the investigation.................................................................................................................. 51.2. Description of the samples.................................................................................................................... 51.3. Description of the laboratory tests ........................................................................................................ 6

1.3.1. Grain size distribution................................................................................................................... 61.3.2. Moisture content ........................................................................................................................... 61.3.3. Atterberg limits (the plasticity index) ........................................................................................... 71.3.4. Methylene blue value.................................................................................................................... 81.3.5. Shear strength (according to CMA/2/II/A.4) ................................................................................ 81.3.6. Organic matter content.................................................................................................................. 91.3.7. Lime content (NEN 5752, gravimetric Wesemael)....................................................................... 91.3.8. Tri-axial test CU ........................................................................................................................... 91.3.9. Consolidation test ....................................................................................................................... 101.3.10. Proctor compaction test .............................................................................................................. 111.3.11. The CBR value ........................................................................................................................... 111.3.12. Permeability................................................................................................................................ 11

1.4. Test results and interpretation............................................................................................................. 121.4.1. Results ........................................................................................................................................ 121.4.2. Interpretation of the results ......................................................................................................... 131.4.3. Classification of the soils. ........................................................................................................... 21

1.5. Conclusion of the soil mechanic tests ................................................................................................. 232. On site compaction tests : ........................................................................................................................... 25

2.1. results.................................................................................................................................................. 272.1.1. in situ density.............................................................................................................................. 272.1.2. Bearing capacity of the platform................................................................................................. 29

2.2. Conclusions on site compaction tests.................................................................................................. 303. Consulted literature : .................................................................................................................................. 31



List of abbreviations / definitions

CBR Californian Bearing rationd50 the grain size in µm at which 50 % of the sediment is smallerDM dry matterIp Plasticity indexMBV Methylene blue valueMpa mega PascalOPN standard optimum Proctor (compaction)PE poly electrolite (used as additive for the dewatering of the sediment by

mechanical pressesTBT tributyl tinW chem moisture content (expressed as % water compared to the total wet mass)W sm moisture content (expressed as % water compared to the dry matter)CU (triaxial test) consolidated undrained triaxial test



Executive summary

The purpose of this investigation is to know the soil mechanical properties of the mechanicallydewatered dredged sediment and the cleaned sediment (by using thermal treatment). With thisknowledge, the possibilities of re-use of the dewatered / treated sediment could be assessed for theuse in landscaping, building dikes, constructing waste bodies.The dewatering of the with TBT contaminated sediment has been described in report (“Task 3550 :Sediment dewatering”). The consecutive thermal treatment of these dewatered sediments has beendescribed in the report (“Task 3550 : Full scale thermal treatment of dewatered sediment containingtributyltin (TBT)).Before thermal treatment the mechanically dewatered sediments react as a natural (sandy) loam witha low shear strength, a low bearing capacity and a low permeability. These parameters increase afterthermal treatment.From the triaxial test, the dewatered sediment is best comparable with a loam to clayey material andhas a relatively high cohesion combined with a moderate internal friction angle. After thermaltreatment these parameters increase, especially the cohesion.The compressibility of the sediment dewatered with lime is higher compared to those dewateredwith PE, independent of the treatment. The compressibility increases with 25 to 30 % (resp.lime/PE) after thermal treatment.The optimum Proctor dry density is rather low (1,60 to 1,65 ton/m³; resp. lime versus PE). Afterthermal treatment the optimum Proctor water content decreased from 20 % before to 17 % aftertreatment.The maximum moisture content to reach a CBR value of 8 % is the same before as after the thermaltreatment and only depends on the additive used (resp. 20 and 16 % for lime/PE).From the tests in the lab and the compaction modalities specified in the French SETRA guide wedetermined how the thermally treated material should be compacted under real site conditions. Inorder to check the prescribed compaction modalities a test field has been made on the Envisan’s soiltreatment centre in Ghent. From these on site compaction tests we could conclude that this specificmaterial (class B5) can be easily re-used for land raise. The re-use of this material, as it comes out ofthe thermal treatment installation is however not advised as (under)foundation material for whichthe requirements are more stringent. Therefor the material could be treated with f.e. cement. Thiswas however beyond the scope of this study.



1. Geotechnical tests

1.1. Purpose of the investigation

The purpose of the investigation is to know the soil mechanical properties of the dewateredsediment and the cleaned sediment (by using thermal treatment). With this knowledge, thepossibilities of re-use of the dewatered / treated sediment will be assessed for the use inlandscaping, building dikes, constructing waste bodies or the reuse of the sediment.To determine the soil mechanical properties of the sediment, several laboratory tests are performedin the laboratory of “Verbeke diepsonderingen” except for the shear strength and the grain sizedistribution which have been determined at the laboratory ERC. The following characteristics areinvestigated:

Test Dewateredsediment (lime)

Dewateredsediment (PE)

Cleaned sedimenttherm. treatment;

(lime)

Cleaned sedimenttherm. treatment;

(PE)Dry matter content X X X XAtterberg limits X X X XMethylene blue value X X X XOrganic matter content X X X XGrain size distribution X XLime content X X X XProctor test X X X XCBR-curve X X X XShear strength X X X XTriaxial test : Cohesion,friction angle X X X X

Permeability X X X XOedometer test X X X X

Table 1 : Summary of test programme

The dewatering of the with TBT contaminated sediment has been described in report (“Task 3550 :Sediment dewatering”). The consecutive thermal treatment of these dewatered sediments has beendescribed in the report (“Task 3550 : Full scale thermal treatment of dewatered sediment containingtributyltin (TBT)).

1.2. Description of the samples

All samples are mixed samples. A summary of the tested samples is given in the following table:

Sample code Type of material Sample 'composition'Kalk/pers Dewatered sediment Mix of dewatered sediment with Lime

additionPE/pers Dewatered sediment Mix of dewatered sediment with PE

additionKalk/therm Cleaned sediment (Therm. treatment,

lime)Mix of dewatered sediment with Limeaddition; thermally cleaned at 400°C

PE/therm Cleaned sediment (Therm. treatment,PE)

Mix of dewatered sediment with PEaddition; thermally cleaned at 400°C

Table 2 : Summary of samples



1.3. Description of the laboratory tests

1.3.1. Grain size distribution,The following fractions have been determined :< 2 µm2 - 16 µm16 - 32 µm32 - 50 µm50- 63 µm63 - 80 µm80 - 125 µm125 - 250 µm250 - 500 µm500 µm - 1 mm1 mm - 2 mm> 2 mm.

The grain size distribution of the largest particles (to a limit of 50 µm) is reached by wet sieving(according to the standard NF P 94-050).The grain size distribution of the fine particles (< 50 µm) is determined by performing asedimentation test (according to the standard NF P 94-056).

1.3.2. Moisture content

Moisture contentThe moisture content is determined by measuring the mass loss of a sample after drying the sampleduring a period of minimum 24 hours in an oven at a temperature of 105 °C. Care have to be takento all moisture content values determined by “Verbeke Diepsonderingen”. As is common ingeotechnical analysis the moisture content is expressed as the amount of water compared to theamount of dry matter, while in environmental and chemical analysis (ERC laboratory) the moisturecontent is expressed as the amount of water compared to the total (wet) amount of sample :

• Moisture content wsm - soil mechanics definitionThe moisture content w is calculated as follows:

Gwwsm = 100 . Gd

with:w = moisture content (%)Gw = weight of water (= mass loss after drying)Gd = weight of solids (= weight after drying)

• Moisture content wchem - chemical definitionThe moisture content w is calculated as follows:

GwWchem = 100 . Gd + Gw

with:w = moisture content (%)Gw = weight of water (= mass loss after drying)Gd = weight of solids (= weight after drying)



Dry volume weight and wet volume weightThe wet volume weight of the material is determined by pushing a special mould with a known massand volume in the sample. Therefore the mould is equipped with a sharp edge.The mould is weighed together with the sample.From the mass of the sample together with the volume, the wet volumic mass of the material isdetermined:

Gn�n = V

with:�n = wet volumic mass (g/cm³)Gn = mass of the wet soil (g)V = volume of the mould (cm³)The wet volume weight is determined by the following equation:

�n = �n . g

With�n = wet unit weight (kN/m³)g = acceleration due to gravity (9,81 m²/s)The samples are weighed with a precision of 0,01 g.The dry unit weight �d (kN/m³) is calculated from the moisture content wsm and the wet unit weight �n

in the next equation:�n�d = wsm1+

100

1.3.3. Atterberg limits (the plasticity index)

Liquidity limitThe liquidity limit of a soil is the moisture content of the soil at the moment of the conventional limitbetween liquid and plastic state. It is represented by the symbol WL.The test is performed on the soil fraction smaller than 425 µm. The liquidity limit is determined withthe apparatus of Casagrande. This apparatus has a metal plate where a soil sample is built in. In thissample a groove of normalised dimensions is created and the sample is shaken by dropping thesample of a specific height (ca. 1 cm) on a hard underground. The number of drops necessary toclose the groove is noted.A specific sample is treated in this way with different moisture contents around the liquidity limit.When the moisture content at a linear scale is presented in a graph with the number of drops at alogarithmic scale, a linear relation is visible. The liquidity limit is defined as the moisture contentwhere the groove closes at 25 drops.

Plastic limitThe plastic limit of the soil is the moisture content of the soil at the moment of the conventional limitbetween the plastic and the semi-solid state. It is represented by the symbol WP.The plastic limit is determined by measuring the moisture content by which a soil thread with adiameter of 3 mm starts to break down.

Plasticity indexThe plasticity index Ip is by definition the difference between the liquidity limit and the plastic limit.

Ip > 25 clay

25 > Ip > 15 loam, clay15 > Ip > 5 loam, clay sand, loamy sand

5 > Ip silt, sand



Figure 1 : Apparatus (Cassagrande tool) for the determination of the Atterberg limits.

1.3.4. Methylene blue valueThe Methylene blue value is an indication of the amount and the activity of the clay in a sedimentsample.Methylene blue is a large polar organic molecule which is absorbed onto the negatively chargedsurface of clay minerals. The amount of methylene blue absorbed by a given mass of clay depends onthe relative concentration of negatively charged sites on the clay particle surfaces, and on the surfacearea of the clay per unit of mass. Because methylene blue molecules are preferentially absorbed ontothe negatively charged sites which may otherwise attract cations, titration with methylene blue canalso be considered to give a relative measure of the cation exchange capacity of a clay soil.

1.3.5. Shear strength (according to CMA/2/II/A.4)

The shear strength of the soil depends on different soil characteristics such as for instancethe granular composition, the humus content , the humidity etc. The shear strength isdetermined after compaction of the soil in a mould by means of a vane.

Figure 2 : Vane test laboratory apparatus



1.3.6. Organic matter contentThe organic matter content is determined by adding H2O2 to the sample. The organic matter isoxidised and is transformed in H2O and CO2. The organic matter concentration is calculated bygravimetric determination of the weight loss. The organic matter content is an important factor forthe behaviour of the soil since it determines the compressibility of the sediment.

1.3.7. Lime content (NEN 5752, gravimetric Wesemael)The lime content is determined by adding acid to the soil.

1.3.8. Tri-axial test CU

GeneralTo determine the strength parameters an isotropic consolidated undrained tri-axial test is performed(CU).

Additional test informationFrom the soil, compacted in a Proctor mould 3 identical cylindrical test samples (diameter Di ≈ 38mm and height H i ≈ 90 mm) are taken and built in a tri-axial cell.With the remaining material (identical to the material of the test samples in saturation degree,density, texture, etc.) the moisture content wsm is determined. From the sample itself, the wet massMn is determined.In the same way, the wet mass Mn and the dry mass Md is determined after the execution of the test.From these data, the moisture content w, the dry volumic mass ρd and the saturation degree isdetermined. The dry volumic mass ρd is determined by the dry mass Md and the volume V. Thevolume V is determined by the initial volume V(i) and the change in volume Vcons duringconsolidation with an isotropic cell pressure σc and the change in volume during the execution of thetest. The moisture content w is determined by drying the sample after the execution of the test in adry oven at a temperature of 105°C, during a period of minimum 24 hours.

ConsolidationAfter the samples are built in, the air and water enclosed in the pores, is stabilised under a uniformcell pressure of 0.102 MPa while applying a pore water pressure ui of 0.100 MPa. This means aneffective uniform stabilisation pressure of 0.002 MPa.The pore water pressure ui of 0.001 MPa that is applied during consolidation phase serves a bettersaturation of the sample.After stabilisation of the sample the uniform back pressure in the cell is increased to an in advancedetermined value σ'c increased with the value of the constant initial pore water pressure ui

(0.100 MPa).

Test procedureAfter the consolidation the axial (vertical) mean stress σ1 is increased, with a constant lateral(horizontal) mean stress σ3. The value of the vertical speed of deformation is deduced from the time-settlement behaviour of the hydrodynamic phase of the consolidation. The test is executed drainedwith a permanent registration of the variation of the volume V.

Failure criteria, CD-testsThe maximum value of the deviator stress (σ1 - σ3) is defined as the failure criterion. Sometimes thefailure is induced by a much smaller strain than the one during the maximum deviator stress. In thesecases this failure mechanism is defined as the failure criterion.The found stress situation allows drawing the circles of Mohr for each of the 3 soil samples duringfailure in terms of effective stresses.The envelope of the circles gives the effective (c', ϕ') strength parameters.



Boundary conditionsThe consolidation stresses during these triaxial tests are 70 kPa, 170 kPa and 270 kPa. During thetests an excess water pressure (backpressure) of 200 kPa internal and external is applied to thesample to ensure a better saturation.

Figure 3 : Triaxial apparatus

1.3.9. Consolidation test

Test procedureA cylindrical test sample with known dimensions (diameter D ≈ 60 mm; Height hi ≈ 20 mm) is takenfrom a soil sample and placed in a compression test cell to determine the consolidationcharacteristics of the soil. The formula of Terzaghi, valid for a lateral enclosed soil sample, is asfollows:

h p2C (or A) =dh(ordh’)

. lnp1

With:C = compression constantA = decompression constanth = height of the sample after consolidation under stress p1

dh = compression of the sample after increase of the stress from p1 to p2

dh'= swelling of the sample during decrease of the stress from p2 to p1

This formula allows to determine the compression constant C for each increase of pressure and thedecompression constant A for each decrease of pressure for a lateral enclosed soil sample.Loading and possible unloading is executed in several steps. An additional load is applied after oneweek or as soon as the settlement during 24 hours is smaller than or equal to 4 µm.In a compression diagram (where the strains are shown in a linear scale and the stress variation in alogarithmic scale) the results are visualised. The slope of the curve in this graph is a measure for thecompression constant C or the decompression constant A, in the case of a discontinuum material thatreacts as a friction material, as most soils do.Using the above mentioned formula the compression constant C or the decompression constant A canbe determined. The height of the sample after consolidation under a stress p1 is determined by:h = h(i) – dh(i)With:h(i) = the height of the sample after the built-in in the compression apparatusdh(i) = the total variation in height compared with h(i) of the sample due to the pressure stress p1



Figure 4 : oedometer apparatus

1.3.10. Proctor compaction testThe main purpose of the Proctor compaction test is the determination of the optimal moisture contentnecessary to obtain a "maximum" degree of compaction by applying a standard amount of energy perunit of compacted volume. The standard Proctor compaction test uses a compaction energy of600 kNm per m³ soil. With known (measured) values of:

w = moisture content of the soilp = weight of the compacted soilV = volume of the mouldγk = specific weight of the grains

The volume weight γn, the dry unit weight γd and the pore volume n is deduced.The variation of γd in relation to the moisture content w is visualised in a graph (5 different moisturecontents). The shape of the proctor-curve gives an indication of the sensitivity of the investigated soilto the moisture content by which it is compacted.The maximal dry weight gives insight in the possibility to compact the soil with a specific amount ofcompaction energy that is applied in a standard way. This maximal dry weight γd,opt is in this Proctorcompaction test only reached if the compacted soil reaches a specific moisture content, its optimalmoisture content wopt. For clays, this behaviour is visualised in a narrow graph. This means thedegree of compaction is very sensitive to the present moisture content of the clay. For sandy soils,the graph will show a less sensitive behaviour.

1.3.11. The CBR valueAt each of the 5 different moisture contents of the Proctor curve the CBR value is determined bypressing a cylinder in the compacted material at a constant speed. The force needed to penetrate thecylinder 2,5 mm and 5 mm in the soil is measured. Both strengths are compared to standard valuesand the highest ratio (in %) is the CBR value.

1.3.12. PermeabilityThe permeability is determined with the 'falling head' method on a disturbed sample, compacted withthe standard Proctor compaction energy at the natural moisture content. A cylindrical test sample istaken from the compacted sample. This test sample, with a height of approximately 50 mm and adiameter of 31,2 mm, is built in the permeameter.



1.4. Test results and interpretation

1.4.1. Results

The results are presented in the table below.

Table 3 : results of the soil mechanical tests

Lim

e/de

wat

ered

PE

/dew

ater

ed

lime/

ther

mal

trea

t.

PE

/ther

mal

trea

t.

Methylene blue value g/100g dry s 2,23 2,82 0,73 0,99Proctor

W sm w% 43,82 35,5 25,34 20,31dry density T/m³ 1,2 1,33 1,41 1,51CBR % 1,8 1,35 5,97 9,82

shear strengthDry matter chem % 68,5 72,9 78,9 80,7Wchem % 31,5 27,1 21,1 19,3Wsm % 46 37,2 26,7 23,9Wet density kg/dm³ 1,78 1,69 1,99 1,95Dry density kg/dm³ 1,56 1,57 1,49 1,56Shear strength kN/m² 70,0 40,0 48,3 98,0

permeability m/s 8,67E-10 < 8,93E-11 3,47E-08 1,53E-05grain size distribution

< 80µm % 44,7 27,7< 2µm % 12 9,9

class (according to NF P 11-300) A1-A2 B5Atterberg limits

Plasticity index (Ip) % 14,4 16,8 - -liquidity limit (WL) % 54,8 56,5 31,8 30,8plastic limit (Wp) % 40,4 39,7 - -

Oedometer testVoid ratio e0 1,165 1,096 1,046 0,992Porosity (n) % 53,82 52,29 51,13 49,8Compressibility ( C )

50 kPa - 60.3 52.5 80.8 76.575 kPa - 33.9 31.3 46.0 44.1100 kPa - 41.8 33.3 46.3 45.3200 kPa - 20.9 22.7 30.5 31.7400 kPa - 19.0 15.1 23.9 19.7

triaxial testW sm w% 45,52 33,82 17,3 17,5Cohesion c kPa 12,65 19,74 22,51 28,22Internal friction angle � ° 17° 59 19° 93 21° 20 22° 25



1.4.2. Interpretation of the results

1.4.2.1. Grainsize distribution

The original sediments contains 54 % sand. With such sand content it is economically interesting toseparate the sand from the sediment, however earlier tests showed that the sand is not clean enough(to much TBT) and furthermore the sand consists mostly of very fine sand (sand between 63 and 125µm) which is not interesting from a geotechnical point of view. The sediment contains 30,6 % loam(between 63 and 2 µm) and 15,4 % clay (< 2 µm). The d50 of the original sediment is 89 µm.After thermal treatment the sand fraction increases to 74,8 % sand. The loam and clay fractiondecrease to resp. 15,5 and 9,7 %. The d50 becomes 130 µm.

Table 4: grainsize distribution of the sediment before and after thermal treatment.

original fraction mesh diameter before before after

µm dewatering thermal treatment thermal treatmentcumulatif % cumulatif % cumulatif %

sand 2000 0,77 0,87 1,41000 2,97 2,37 3,9500 4,67 3,67 6,3250 7,97 7,67 17,3125 39,97 40,67 54,380 52,97 54,67 72,363 53,97 56,17 74,8

loam 50 55,17 59,47 74,832 70,17 76,47 82,516 72,57 79,97 85,12 84,57 87,57 90,3

clay < 2 99,57 99,57 100,2

% % %sand 2000-63 54,0 56,2 74,8loam 62-2 30,6 31,4 15,5clay < 2 15,4 12,4 9,7

dewatered TBT sediment



Graph 1 : grain size distribution of the original sediment, the sediment after dewatering and after thermaltreatment.

1.4.2.2. The Atterberg limits, the plasticity index

Before treatmentThe liquid limit (the limit between solid state and the plastic state) is around 40 % (W sm).The plastic limit (the limit between the plastic and the liquid phase) is around 56 % (W sm)The plasticity index varies between 14 and 17 %, typical for a loam with a medium clay content.The moisture content of the filter cakes (dewatered sediment) is between 41 and 46 % (Wsm),therefor the dewatered sediment is in a plastic state.Apparently the addition of lime has no influence on the plasticity (only 3 % difference).

grain size distribution dewatered sludge before and after thermal treatment

0102030405060708090100

110100100010000

sieve diameter in µm

% p

assi

ng (c

umul

.)

original sediment

dewatered

after thermaltreatment

��

��

��

� �� 0 10 20 30 40 50 60 70

� �� 0 9,1 16,7 23,1 28,6 33,33 37,5

� � �� 100 90,9 83,3 76,9 71,4 66,67 62,5



After treatmentThe liquid limit (the limit between solid state and the plastic state) is around 31 %.The plastic limit (the limit between the plastic and the liquid phase) could not be determined andtherefor the plasticity index could not be calculated.

Dewateredwith lime

Dewateredwith PE

Afterthermal

treatmentLime

Afterthermal

treatmentPE

Unit

Moisture contentWsm

41,36 45,8 26,6 22,9 % (Wsm)

Plasticity limit PL 40 40 - - % (Wsm)Liquid limit LL 55 57 31,8 30,8 % (Wsm)

Plasticity index Ip 14 17 - - % (Wsm)

Table 5 : plasticity index results

1.4.2.3. The methylene blue value (MBV)

The methylene blue value of the dewatered sludge is between 2,23 and 2,82 g blue/100 g dry soil.After treatment these values diminish to 0,73 and 0,99. This means that the thermal treatment makesthe dewatered sediment less plastic and/or coarser. These MB-values are coherent with the plasticityindex results.

Dewateredwith lime

Dewateredwith PE

Afterthermal

treatmentlime

Afterthermal

treatmentPE

Unit

Methylene bluevalue

2,23 2,82 0,73 0,99 g blue/100gdry soil

Table 6 :MBV results

Graph 2 : methylene blue value before and after thermal treatment

methylene blue value (MBV) before and after thermal treatment for PE and LIME

0

0,5

1

1,5

2

2,5

3

Lime/dewatered PE/dewatered lime/thermaltreat.

PE/thermal treat.

MB

V (g

/100

g dr

y m

atte

r)



1.4.2.4. Shear strength and CBR value at actual moisturecontent

The shear strength of the dewatered sediment was 70 and 40 kN/m² (resp. for lime and PE) which ismore than enough to transport it to a dumping site (minimum should be 10 kN/m²). The dry densityof the compacted material in the mould was 1,56 and 1,57 ton/m³ (resp. for Lime and PE).After thermal treatment the shear strength was resp. 48 and 98 kN/m² (Lime/PE). The dry densitywas resp. 1,49 and 1,56 ton/m³.The Californian bearing ratios (or CBR) of the dewatered sediment are very low (resp. 1,8 and1,35%) due to the high water content. After the thermal treatment the CBR value has increased to 6and 9,8 %.The shear strength and the bearing capacity of the dewatered sediment cannot easily be raised sincethe maximum dry matter content that can be reached with mechanical dewatering is 60 to 65 %. Themoisture content of the thermally treated material can however be adapted easily in order to get theoptimum moisture content. By diminishing the moisture content the shear strength and the bearingcapacity can be raised.

Dewateredwith lime

Dewateredwith PE

After thermaltreatment

lime

After thermaltreatment

PE

Unit

Dry matter chem 68,5 72,9 78,9 80,7 %Moisture contentWchem

31,5 27,1 21,1 19,3 %

Moisture contentW sm

46 37,2 26,7 23,9 %

Wet density 1,78 1,69 1,99 1,95 kg/dm³Dry density 1,56 1,57 1,49 1,56 kg/dm³Shear strength 70 40 48,3 98 kN/m²

CBR (%) 1,8 1,35 5,97 9,82 %

Table 7 : CBR and shear strength results on the samples at natural moisture content

Graph 3 : CBR-values before and after thermal treatment

CBR value before and after thermal treatment for PE and LIME at actual moisture content

0

2

4

6

8

10

12

Lime/dewatered PE/dewatered lime/thermaltreat.

PE/thermal treat.

CB

R (%

)



1.4.2.5. Lime content and organic matter content

The original lime content is 9,9 % Approximately 2% of quick lime was added to the sediment fordewatering (cfr. 120 g/kg dry soil). After thermal treatment the lime content is around 9%.The organic matter content of the original sediment varies between 8,6 and 7,5 %. After thermaltreatment only 4,3 to 4,7 % remains. The rest has been burned in the desorber of the TDU.

Dewateredwith lime

Dewateredwith PE

Afterthermal

treatmentlime

Afterthermal

treatmentPE

Unit

Organic matter 8,6 7,5 4,3 4,7 % O.MCaCO3 120 99 86 92 g/kg dry soil

Table 8 :organic matter and CaCO3 content before and after treatment

1.4.2.6. Tri-axial tests

The complete results of the tri-axial CU test are given in attachment.Normally the tri-axial test is performed on disturbed samples compacted at optimum Proctormoisture content. This method procedure has been followed for the thermally treated material, sincethis material has a moisture content close to the optimum Proctor moisture content. The dewateredsediments however, will be re-used at their actual moisture content (which is much higher comparedto the optimum Proctor moisture content). Therefor the tri-axial tests on the dewatered filter cakeswas performed at the actual moisture content.A summary of the results of the triaxial tests are given in the following table.

Dewateredwith limeAt actualmoisturecontent

Dewateredwith PEAt actualmoisturecontent

Afterthermal

treatmentLime atWOPN

Afterthermal

treatmentPE atWOPN

Unit

Wsm 45,52 33,82 17,3 17,5 %Cohesion c 12,65 19,74 22,51 28,22 kPaInternal friction angle � 17° 59 19° 93 21° 20 22° 25 °

Table 9 : triaxial test result before and after treatment

The obtained results are high. These values can be compared with several known values of differentsoil types in the following table.

Cohesion c(kPa)

Internal friction angle

Sand, clean 0 35 – 40Loam, a bit sandy 5 – 7,5 27,5 – 35Clay, clean 25 – 30 17,5 – 25

Table 10 : Common strength parameters



The results for the sediment treated with PE are always higher compared to those treated with lime.The cohesion is approximately 6 to 7 kPa higher. The internal friction angle is only slightly higher (1to 1,4 °).The dewatered filter cakes have triaxial results that can be compared to loam or clayey material andhas a good cohesion and a moderate internal friction angle.After thermal treatment the cohesion of the material increases from 12,7 to 22,5 kPa (lime) and from19,7 to 28,2 kPa (PE). The internal friction angle increases from an average of 18,8° to 21,7°.The thermal treated material gives thus a better stability when used in a land raise.

1.4.2.7. Consolidation tests

As for the triaxial test the thermally treated material has been compacted at a moisture content equalto the optimum Proctor moisture content, while the mechanically dewatered sediments have beencompacted at their natural moisture content before the execution of the consolidation tests.The summary of the consolidation results is given in the following tables.

Dewateredwith lime

Dewateredwith PE

Afterthermal

treatmentLime

Afterthermal

treatmentPE

Unit

Moisture content (Wsm) 43,5 35 17 17 %Void ratio e0 1,165 1,096 1,046 0,992 -Porosity (n) 53,82 52,29 51,13 49,8 %Dry density 1,224 1,264 1,295 1,33 Ton/m³Wet density 1,756 1,707 1,515 1,557 Ton/m³

Table 11 : Summary of the results for the porosity , the void ratio and the moisture content before applicationof the pressure

Graph 4 : Summary of the results for the void ratio of the sediment before and after treatment

From these data it is clear that void ratio is 5 % lower in the sediments treated with PE compared tothe sediments treated with lime (before and after the treatment). After thermal treatment the voidratio of the sediment decreases with 10 %.

void ratio before and after thermal treatment for PE and lime

0,9

0,95

1

1,05

1,1

1,15

1,2

kalk/pers PE/pers kalk/therm PE/therm

void

rat

io (e

0)



Compressibility ( C )Pressure in kPa Dewatered

with limeDewatered

with PEAfter

thermaltreatment

lime

Afterthermal

treatmentPE

Unit

50 60.3 52.5 80.8 76.575 33.9 31.3 46.0 44.1

100 41.8 33.3 46.3 45.3200 20.9 22.7 30.5 31.7400 19.0 15.1 23.9 19.7

Table 12 : Summary results consolidation tests (compressibility in function of the pressure applied).

The compressibility of the sediment dewatered with lime is higher compared to those dewatered withPE, independent of the treatment. The compressibility (at a pressure of 400 kPa) increases with 25 to30 % (resp. lime/PE) after thermal treatment.These values obtained for the compression constant C can be compared with the following commonvalues.

Soil type Known values for compression constant CSand 50 – 500Loam 25 – 50Clay 7.5 – 25Peat 2.5 – 7.5

Table 13 : Known values compression constant

From this table it is clear that according to the compression constant C the sediments can becategorised as a clay material for the higher pressures and a sandy to loamy material for the lowerpressures.The results can further be used to calculate the settlement of a future land raise.

Graph 5 : compressibility in function of the pressure applied for the mechanically dewatered sediment beforeand after thermal treatment.

Compressibility in function of the pressure applied

10

100

1000

0 20 40 60 80 100

compressibility (C)

pres

sure

app

lied

(kP

a)

kalk/persPE/perskalk/thermPE/therm



1.4.2.8. Proctor curves

The results of the Proctor curves are given below.

Dewateredwith lime

Dewateredwith PE

Afterthermal

treatmentLime

Afterthermal

treatmentPE

Unit

Optimal Proctorwater content(Wsm)

20,0 % 21,0 % 17 17 %

Optimal Proctordry density (γd)

1,60 1,65 1,65 1,65 Ton/m³

Actual moisturecontent Wsm (%)

41 46 26,6 22,9 %

Wsm for aCBR=8%

20 15 20 16 Wsm (%)

Table 14 : Proctor results

Dewatered sediment before thermal treatment

The optimal Proctor water content is 20 to 21 % (for the filter cakes treated with lime compared tothe ones treated with PE). The optimum Proctor density is the maximum dry density that can bereached on site for this type of material. It is equal to resp. 1,60 and 1,65 ton/m³ (lime versus PE).From the moisture content after dewatering (41 and 46 %) we see that we are far from the optimumwater content. In those conditions the density that can be reached is only 1,2 or 1,33 ton/m³(lime/PE).The CBR curves give us an indication at what moisture content we can have a certain minimumbearing capacity. A CBR value of 8 % is considered to be sufficient to give a landfill with a goodbearing capacity. The filter cakes with lime should have a moisture content lower or equal to 20 %(Wsm) in order to reach a CBR equal to 8% (see CBR curves). The filter cakes with PE should havea moisture content of 15 % or lower (Wsm). This is a typical effect of the lime addition.

After thermal treatment

The optimum Proctor water content is the same for both batches (lime/PE) namely 17 %. Theoptimum Proctor dry density is the same as before the thermal treatment (1,65 ton/m³). Themaximum moisture content to reach a CBR value of 8 % is the same as before the thermal treatment(resp. 20 and 16 % for lime/PE).



Graph 6 : Proctor curves of the sediment before and after thermal treatment.

Graph 7 : CBR curve of the sediment before and after thermal treatment.

1.4.3. Classification of the soils.

In order to re-use the sediments they have been classified according to the French standard NF P 11-300. This standard uses the results of the grain size distribution to classify soils into categories calledA till D (class “ A” being the fine soils and “ D” the coarsest soils. A further subdivision is madeaccording to the amount and the activity of the clay fraction that is expressed by the methylene bluevalue or the plasticity index. For the ‘A-class’ soil for example 4 subdivisions are made: namely A1,A2, A3 and A4. For each subclass a further subdivision is made for the moisture conditions of thesoil. Therefore the moisture content is compared to the optimal Proctor moisture content. By doingso the subclasses gets a supplementary index; from ‘very wet’ over ‘wet’ , ‘medium’ , ‘dry’ to ‘verydry’ ; ‘medium’ being the optimal moisture content range for compaction of this specific material.The ‘Technical guide of SETRA’ 1gives for each subclass the compactions modalities, in function of:• the layer thickness

1 Technical Guide SETRA : “ Réalisation des remblais et des couches de forme” , Fascicule 1 : principesgéneraux, et Fascicule 2 : Annexes techniques. L.C.P.C. (Laboratoire central des ponts et chaussées, France.

Proctor curves before and after thermal treatment

1,2

1,3

1,4

1,5

1,6

1,7

1,8

0 10 20 30 40 50

moisture content (W sm %)

dry

dens

ity (t

on/m

³)beforeafter

CBR curve (CBR ifo moisture content)

0

5

10

15

20

25

30

0 10 20 30 40 50

moisture content (W sm %)

CB

R v

alue

%

beforeafter



• the type of compactor used• the speed of the compactor• the intensity of the compaction etc.

According to the French standard the mechanical dewatered TBT-sediment can be classified as a‘loams with low plasticity, alluvial silt, fine sands with little fines, …’ and belongs to the class ‘A2’ .Once this sediment is treated thermally the soil becomes coarser, the plasticity decreases and isclassified as ‘sand or highly loamy gravel’ (class ‘B5’ ).

Dewatered filter cakes (class A2) :The moisture content (30 to 35 % of water) of the dewatered sludge is far to high to get a goodcompaction of these filter cakes and the bearing capacity of such material is very low (CBR = 1,3 to1,8%). This material is classified as ‘A1-th’ (or ‘very wet’ ). The re-use of the filter cakes as such in awork is impossible. In order to re-use them anyway, additives (like lime and/or cement) should beadded to enhance the bearing capacity by decreasing the moisture content further.

The thermally treated material (class B5) :The treated material belongs to the class B5 and with a initial moisture content of 26,6 % (Wsm)they belong to the class B5-th (‘very wet’ ). Luckily the material looses easily it’ s water and on themoment of the compaction field test the moisture content had diminished to 14,3 % (Wsm) so thatthe material could be re-used without any addition of lime or cement to diminish the moisturecontent. These B5-type of materials are however very sensible to the meteorological conditions at thetime of compaction. Any rain can stop all works. This kind of material can not be used as afoundation material as such, therefor it is to sensible (a combination of a cement and lime treatmentshould be used).

Graph 8 : classification of the sediments before and after thermal treatment according to the French standardNF P 11-300.

IP

fraction < 2 mm

100%

70%

MBV

A1 A2

B5

B3

B1 B2

B4

A4A3

B6

D1

D2

12 %

12 %

0 %

35 %

100 %

25 % 40 %

0,1 0,2 82,5

before treatment

after treatment



1.4.3.1. PermeabilityThe permeability test is performed with a compacted sample according to the standard proctorcompaction test on a sample at actual moisture content.A summary of the results of these tests are given in the following table.From this data it is clear that after thermal treatment the permeability increases with a factor 40 inthe case of sediment dewatered with lime. The permeability of the sediment dewatered with PEincreases much more, namely 168500 times.

Permeability kin m/s

Watercontentwsm (%)

Dewatered samples Kalk/pers PE/persAfter thermal treatment Kalk/therm PE/therm

8,7 10-10

8,9 10-11

3,5 10-8

1,5 10-5

45,335,5

26,622,9

Table 15 : Summary results permeability tests

The values obtained for the dewatered samples from the falling head permeability tests can becompared to the Flemish legislation (Vlarem). The maximum permeability of a mineral sealing layer(in a top cover layer as well as in a bottom sealing layer) should be 1.10-9 m/s. Compared with thisvalue, the obtained results are sufficient for the reuse of the dewatered sediment as a mineral sealinglayer (according to the Flemish legislation).On the other hand the thermally treated material contains to much fines to be used as drainage sand.

1.5. Conclusion of the soil mechanic testsBased on the several soil mechanic tests performed in this study, the following conclusions can bemade.From the grain size distribution tests it is clear that the crude sediment contains approximately 54%of sand, 30,6 % of loam and 15,4 % of clay. The d50 of the original sediment is 89 µm. After thermaltreatment the sand fraction increases to 74,8 % of sand. The loam and clay fraction decrease to resp.15,5 and 9,7 %. The d50 becomes 130 µm. No explanation has been found for this change in grainsize.The methylene blue value (MBV) and the plasticity index, both indications of the amount and theactivity of the clay fraction, give results for the dewatered sediment comparable to a natural loam ora loamy sand. After the thermal treatment the plasticity decreases with a factor 3.The shear strength varies between 40 and 98 kN/m². The CBR value (at the actual moisture content)is low after dewatering (1,8-1,35 %) but increases to 6 and 9,8 % (lime/PE) after thermal treatment.The original lime content is 9,9 %, the organic matter content varies between 8,6 and 7,5 %. Afterthermal treatment only 4,3 to 4,7 % organic matter remains.From the triaxial test, the dewatered sediment is best comparable with a loam to clayey material andhas a relatively high cohesion combined with a moderate internal friction angle. After thermaltreatment these parameters increase, especially the cohesionThe compressibility of the sediment dewatered with lime is higher compared to those dewatered withPE, independent of the treatment. The compressibility (at a pressure of 400 kPa) increases with 25 to30 % (resp. lime/PE) after thermal treatment. From the compression data, the sediments can becategorised as a clay material for the higher pressures and a sandy to loamy material for the lowerpressures.



The optimal Proctor water content is nearly the same for the filter cakes treated with lime comparedto the ones treated with PE (20 % instead of 21 %). The optimum Proctor is equal to resp. 1,60 and1,65 ton/m³ (lime versus PE). After thermal treatment the optimum Proctor water content decreasedfrom 20 % before to 17 % after treatment. The optimum Proctor dry density is 1,65 ton/m³ (PE andlime).The maximum moisture content to reach a CBR value of 8 % is the same before as after the thermaltreatment and only depends on the additive used (resp. 20 and 16 % for lime/PE).The values obtained from the falling head permeability test are much higher after the thermaltreatment of the sediments. The permeability of the dewatered material is sufficiently low in order tore-use the filter cakes as a mineral sealing layerAccording to the French standard NF P 11-300 the sediments can be classified as ‘A2th’ (beforetreatment) and ‘B5th’ (after thermal treatment).



2. On site compaction tests :

From the tests in the lab and the compaction modalities specified in the French SETRA guide wedetermined how the thermally treated material should be compacted under real site conditions. Inorder to check the prescribed compaction modalities a test field has been made on the Envisan’ s soiltreatment centre in Ghent.Before compaction the thermally treated material has to be brought to the right moisture content. Inorder to have a good compaction the moisture content should be as close as possible to the optimumProctor moisture content determined in the lab. The French technical guide foresees a moisturecontent between 0,9 and 1,1 times the optimum Proctor moisture content (which corresponds to the“ medium moisture class” ). Therefor the moisture content of the material was determined in our sitelab after the soil was spread out on site in a layer with a thickness of 50 cm. The moisture contentwas then adjusted by sprinkling the necessary water amount. Since the permeability of the materialwas rather high, we waited only for half an hour for the water to penetrate the whole layer.Consecutively the material was compacted with a single vibrating drum roller. This compactor (aBomag 219 DH3) is a heavy compactor (19 tons) which belongs to the highest class (class V5according to the standard NF P 98-736) in its kind. Prior to its use the tachygraph of the vibratingrole was calibrated; The speed was only out for 3 %.The following compaction modalities are given in the French Technical SETRA Guide for a B5sediment in the medium moisture class compacted with a V5 compactor :� Number of passes : 7� Speed : 2 km/hour� Layer thickness : maximum 0,75 m.For the tests the layer thickness was reduced to 50 cm. Therefor the number of passes at 2 km/hourcan be recalculated and is 4,2. This number is rounded to 5 passes.The degree of compaction of the material on site was checked by using a nuclear density gaugewhich measures the wet in situ density and the moisture content. From these data thegammadensimeter calculates the in situ dry density and the compaction degree (in % compared to theoptimum Proctor density). By measuring the in situ dry density after 1, 3, 5 and 7 passes of thecompactor the optimum number of passes was checked and the maximum density achievable on siteis determined.Indeed the density in the layer increases with an increasing number of passes until the moment that amaximum is reached. With further compaction the in situ density decreases again.On the field 95 % of the optimum Proctor dry density determined in the lab should be reached(namely 95 % of 1,61 ton/m³ = 1,53 ton/m³). This means that the moisture content should be inbetween 13,5 and 20,5 %. Initially the moisture content of the treated material was 26,6 % (Wsm).When the material was spread on site the moisture content had decreased to 14,34 %. In order tosimulate an optimum compaction the moisture was raised to a moisture content close to the optimum(= 17%). This was done by spraying water over the spread layer.



picture 5 : adjustment of the moisture content of the test field (right side)

Picture 6 : compaction of thermally treated sediment with the V5 single drum vibrating roller.



2.1. results

2.1.1. in situ density

The in situ density, measured with the nuclear density gauge, are given below. The compactiondegree is given in % of the optimum Proctor density determined in the lab (=1,61 ton/m³). Each valueis the average of 4 measurements points (spread over the compacted surface).

1 pass 3 passes 5 passes 7 passesAverage in situ drydensity (ton/m³)

1,41ton/m³

1,41ton/m³

1,43ton/m³

1,41ton/m³

Moisture contentWsm(%)

20,1% 20,55% 18,08% 18,17%

Compaction degree in%; compared to theoptimum Proctor drydensity in the lab

85,9 % 85,9 % 88,8 % 87,6 %

Table 16 : results of the test field measurements : in situ dry density measured with the nuclear density gauge,the measured moisture content, the compaction degree (= the in situ dry density measured on the test fielddivided by the optimum Proctor dry density determined in the lab times 100).

The data are presented in the graphs below.

Graph 9 : in situ measured dry density in function of the number of passes with a V5 compactor.

in situ dry density in function of the number of passes (for B5 material; a V5-compactor; speed : 2 km/hour, layer thickness =

50 cm)

1,40

1,41

1,42

1,43

0 2 4 6 8

number of passes of the compactor (n)

in s

itu d

ry d

ensi

ty

(ton

/m3)



Picture 7 : measurement of the in situ density of the compacted sediment with a nuclear density gauge.

Graph 10 : in situ measured compaction degree in function of the number of passes.

The average moisture content (after adjusting) was very close to the optimum. Nevertheless it wasnot possible to obtain the 95 % compaction degree on the test field. The average compaction degreereached was 89 % (compared to the optimum Proctor dry density) with 5 passes of the compactor,which corresponds to a in situ dry density of 1,43 ton/m³.

compaction degree in function of the number of passes (for B5 material; a V5-compactor; speed : 2 km/hour, layer thickness =

50 cm)

80,0082,0084,0086,0088,0090,0092,0094,00

0 2 4 6 8



The rather low compaction degree reached can be due to the following facts :� The water addition was not completely effective due to the fact that water did not penetrate until

the bottom of the layer. To solve this problem furrows can be ploughed in the spread sedimentbefore the adjustment of the moisture content.

� Instead of using a single drum vibrating roller a pneumatic tyred roller is probably moreappropriate for the compaction.

� The relative small dimensions of the test field

From the test fields we can conclude that the thermally treated dredged material is rather difficult tocompact and that for a layer thickness of 50 cm 5 passes of a V5 compactor are necessary. Thiscorresponds very well with the prescribed number of passes of the French Technical SETRA guide.Better compaction results are probably reachable with a pneumatic tyred roller

2.1.2. Bearing capacity of the platform

The bearing capacity of the compacted material has been measured by means of plate tests. TheBelgian standard prescribes a test with a plate of 750 cm² (standard OCW 50.01). The bearingcapacity should be at minimum 11 MPa in the core of a land raise and 17 MPa in the upper meter ofa land raise.In order to evaluate the bearing capacity of the compacted layer we first tested the bearing capacityof the existing underlying layer (see picture below). Three plate tests have been performed on thislayer. The bearing capacity ranged between 33 and 77 MPa.The bearing capacity on the compacted (treated) layer ranged between 13,0 and 17,7 MPa.

Picture 8 : measurement of the bearing capacity of the platform with the plate test (plate of 750 cm²).



Bearing ofreceivingplatform(Mpa)

Bearing ofcompacted

treatedmaterial(Mpa)

Point 1 77,28 12,99Point 4 33,24 17,66Point 5 52,39 13,44

Table 17 : results of the test field measurements : bearing capacity in MPa..

2.2. Conclusions on site compaction tests

The thermally treated sediments can be compacted with a V5 type vibrating roller compactor in alayer of 50 cm by executing 5 passes at 2 km/h. The maximum compaction degree reached was 88,8% which corresponds to an in situ dry density of 1,43 ton/m³ at a moisture content close to theoptimum Proctor moisture content. Care should be taken to the adjustment of the moisture content.The bearing capacity on the compacted (treated) layer ranged between 13,0 and 17,7 MPa. Mostprobably the use of a pneumatic tyred roller is more appropriate for the compaction of this type ofmaterial.From these on site compaction tests we can conclude that this specific material (class B5) can beeasily re-used for land raise. The re-use of this material, as it comes out of the thermal treatmentinstallation is however not advised as (under)foundation material for which the requirements aremore stringent (plate bearing capacity must then be higher than 35 MPa and the compaction degreeshould be higher than 97,5 %). Therefor the material could be treated with f.e. cement. This washowever beyond the scope of this campaign.



3. Consulted literature :

� LCPC, 2000. Traitement des sols à la chaux et/ou aux liants hydrauliques. Application à laréalisation des remblais et des couches de forme. Guide technique.

� LCPC, 1992. Réalisation des remblais et des couches de forme. Fascicule I : Principesgénéraux. Fascicule II: annexes techniques.

� AFNOR.. NF P 11 300 : Execution des terrassements. Classification des matériaux utilisablesdans la construction des remblais et des couches de forme d’infrastructures routières.

� OCW,. Handleiding voor het grondmechanisch onderzoek van wegentracés. Deel IV,Laboratoriumproeven..



Attachment 1 : report on site plate bearing tests (750cm²)

Attachment 2 : report on site measurements in situ dry density (nucleardensity gauge)

Attachment 3 : lab report geo-technical parameters

These attachments can be found on separate files.

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