The Buffer and Backfill Handbook

Svensk Krnbrnslehantering ABSwedish Nuclear Fueland Waste Management CoBox 5864SE-102 40 Stockholm SwedenTel 08-459 84 00

+46 8 459 84 00Fax 08-661 57 19

+46 8 661 57 19

Technical Report

TR-02-20

The Buffer and BackfillHandbook

Part 1: Definitions, basic relationships,and laboratory methods

Roland Pusch

Geodevelopment AB

April 2002

This report concerns a study which was conducted for SKB. The conclusionsand viewpoints presented in the report are those of the author and do notnecessarily coincide with those of the client.

The Buffer and BackfillHandbook

Part 1: Definitions, basic relationships,and laboratory methods

Roland PuschGeodevelopment AB

April 2002

3Foreword

Part 1 of this Handbook is focused on description of fundamental issues of soil physicaland chemical arts and on soil mechanical definitions and relationships. Part 2 comprisesa material data basis including also preparation and field testing methods. Part 3provides a collection of physical and mathematical models and examples of how theycan and should be applied.

The present document, which has been prepared by Geodevelopment AB inco-operation with Scandia Consult AB and Clay Technology AB, Sweden, and withTVO, Finland, makes up Part 1. Most of the data and information emanate from thework that Geodevelopment AB and Clay Technology AB have performed for SKB buta number of results from experiments made in and for other organizations have beenincluded as well. A significant number of experimental procedures and ways ofcharacterizing buffers and backfills are included.

The experience from the comprehensive international Stripa Project, concerning bothsystematic material investigations in the laboratory and the full-scale field experiments,has contributed significantly to this report. However, similar and additional informationgained from later work in SKBs sp Hard Rock Laboratory and from NAGRA andalso from other waste-isolation projects have helped to make this document of assumedinternational interest.

5Contents

1 Symbols and definitions 91.2 Definitions 10

1.2.1 General 101.2.2 Mass relationships 101.2.3 Consistency parameters 131.2.4 Strength parameters 171.2.5 Rheological parameters 181.2.6 Transport properties 21

1.3 References 22

2 Soil characterization 232.1 Introduction 232.2 Soil classification 23

2.2.1 General 232.2.2 Definitions 262.2.3 Classification with respect to mode of formation 272.2.4 Classification according to grain size composition 302.2.5 Classification according to mineral composition 332.2.6 Classification according to organic content 342.2.7 Classification according to geotechnical properties 34

2.3 References 36

3 Mineral constituents 373.1 Introduction 373.2 Rock-forming minerals 373.3 Clay minerals 38

3.3.1 Main minerals 383.3.2 The kandite group 403.3.3 The hydromicas (illite) 423.3.4 The smectites 433.3.5 Chlorite 473.3.6 Mixed-layer minerals 483.3.7 Appearance 483.3.8 Occurrence 523.3.9 Characteristic properties 55

3.4 Experimental 563.4.1 General 563.4.2 Rock-forming minerals 563.4.3 Clay minerals 58

3.5 References 69

4 Organic constituents 714.1 Introduction 714.2 Primary organic species 724.3 Secondary organic matter in sediments 774.4 Implications with respect to the performance of organics in

buffers and backfills 81

64.5 Experimental 824.5.1 General 824.5.2 Experimental 82

4.6 References 84

5 Porewater chemistry 855.1 General 855.2 The electrochemical potential 855.3 pH 865.4 Eh 865.5 Electrolyte content 875.6 Experimental 90

5.6.1 pH 905.6.2 Porewater composition 925.6.3 Precipitation from porewater 93

5.7 References 94

6 Soil structure 956.1 Introduction 956.2 Granulometry 95

6.2.1 Size 956.2.2 Size determination 966.2.3 Shape 1026.2.4 Accuracy 1056.2.5 Specific surface area 105

6.3 Clay microstructure 1076.3.1 Structure-forming factors and processes 107

6.4 Experimental 1176.4.1 Scope and comprehension 1176.4.2 Granulometry 1176.4.3 Microstructure 121

6.5 References 126

7 Density, water content and porosity 1297.1 Introduction 1297.2 Density 129

7.2.1 General 1297.2.2 Bulk density 1337.2.3 Dry density 1367.2.4 Specific (grain) density 136

7.3 Porewater density 1377.4 Gas density 1387.5 Water content 1387.6 Experimental 143

7.6.1 Bulk density and dry density 1437.6.2 Grain density 1457.6.3 Porewater density 1477.6.4 Water content 1477.6.5 Degree of water saturation 1487.6.6 Porosity and void ratio 149

7.7 References 150

78 Consistency 1518.1 Introduction 1518.2 Consistency states 1528.3 Consistency limits 153

8.3.1 Definition 1538.3.2 Preparation of samples 153

8.4 Liquid limit 1548.4.1 Percussion liquid limit 1548.4.2 Fall-cone liquid limit 1648.4.3 Reliability 1708.4.4 Comparison between the percussion liquid limit and the

fall-cone liquid limit 1708.5 Plastic limit 170

8.5.1 General 1708.5.2 Determination of the plastic limit 1708.5.3 Reliability 172

8.6 Shrinkage limit 1738.6.1 Method principles 1738.6.2 Reliability 176

8.7 References 176

9 Transport properties 1779.1 General 1779.2 Hydraulic conductivity 177

9.2.1 Definition of hydraulic conductivity, K [m/s] 1779.2.2 Microstructural implications 1789.2.3 Influence of hydraulic gradient and prewater chemistry 1859.2.4 Influence of the mineral content 188

9.3 Gas conductivity 1889.3.1 General mechanisms 188

9.4 Ion diffusivity 1899.4.1 Mechanisms and basic relationships 1899.4.2 Dependence of soil density 1919.4.3 Unsaturated conditions 192

9.5 Gas diffusivity 1939.6 Experimental 193

9.6.1 Hydraulic conductivity 1939.6.2 Gas conductivity 1979.6.3 Ion diffusivity 200

9.7 References 205

10 Thermal properties 20710.1 Introduction 20710.2 Mechanisms in heat transfer 210

10.2.1 General 21010.2.2 Heat conduction 21010.2.3 Influence of soil structure 211

10.3 Experimental 21310.3.1 General 21310.3.2 Equipment 21410.3.3 Performance 21410.3.4 Evaluation 21510.3.5 Accuracy 216

10.4 References 216

811 Rheology 21711.1 General 21711.2 The effective stress concept 218

11.2.1 General 21811.2.2 Relevance of the effective stress concept for smectitic clays 219

11.3 Basic relationships 22011.3.1 Definitions 22011.3.2 Compression properties 22411.3.3 Shear strain 22911.3.4 Shear strength 23311.3.5 Swelling 23511.3.6 Swelling pressure 236

11.4 General material model 24011.5 Experimental 243

11.5.1 General 24311.5.2 Compressibility and swelling 24311.5.3 Shear strain, creep 24411.5.4 Undrained shear strength 24711.5.5 Drained shear strength 248

11.6 References 249

12 Routine methods for quality assurance of large quantitiesof buffer clay and ballast 251

12.1 General 25112.2 Criteria 25112.3 Routine characterization scheme 254

12.3.1 General 25412.3.2 Scheme for characterization 255

12.4 References 263

91 Symbols and definitions1

ac = activityaz = swelling indexA = cross section, creep

parameter, weightpercentage

As = contact areab = soil structure

coefficient, load factorB = creep parameterBs = solid phase modulusBw = bulk modulusc, c = cohesionC = heat capacity,

concentrationCc = compression index,

gradation coefficientCu = uniformity coefficientd = diameter, distance,

sample thicknessd10, d60 = grain diametersDa = apparent diff.

coefficientDe = effective diff.

coefficientDp = pore diffusivityDs = surface diffusion

coefficiente = void ratioE = modulus of elasticityF = forceg = gravitygo = organic contentg1, gc = ignition lossG = shear modulush = settling distancei = hydraulic gradient,

activityIP = plasticity indexIC = consistency indexIL = liquidity indexk = (hydraulic)

permeability,colorimeter reading

K = hydraulic conductivity,compression modulus

Kd = sorption factorl = sample length (height)

lc = content of particleswith an equivalentstoke diameter smallerthan 2 m

LS = linear shrinkagem = mass, modulus

numbermj = modulus number (ref.)ms = mass of solid mattermw = mass of waterM = oedometer modulusMI ,MII,M III = metal cationsn = porosityp = normal stresspS = swelling pressureP = vapor pressureq = deviator stressR = molar gas constant,

roundnessRS = shrinkage ratios = salt content of pore

fluid, scale factorS = expansion

(rebounce),sphericity

Sr = degree of watersaturation, vol %

St = sensitivityt = timeT = temperatureu = porewater press. = Poissons ratioV = bulk volumeVd = volume of dry soil

sampleVp = pore volumeVs = volume of solid

matterVS = volumetric shrinkageVw = volume of waterVg = volume of gasw = water content (ratio)wL = liquid limitwP = plastic limitwS = shrinkage limitx = variabley = variable

1 Only major ones are listed

10

= heat expansioncoefficient

s = swelling index = stress exponent = strain = shear strain = constitutional

parameter = viscosity = heat conductivity = Poissons ratio = bulk densityd = dry densitys = density of solid

particlessat = density of fluid-

saturated soil

w = density of water = pressure1 = effective press.c1 = preconsolidation

pressurej = reference stress = shear stressfu = undrained shear

strengthr = remoulded shear

strength = electrical potential, = friction anglel = shortening of sample

with length (height) l

Note 1 on Grain sizeIn literature the grain size distribution is expressed as Percentage finer than, percent finerby weight, weight percent passing etc. They appear in various diagrams quoted fromliterature sources.

Note 2 on SymbolsSome additional symbols that appear in the Ha