Section B

Explain the principles behind the Shear Vane Test

- indirect test to measure strength of the subgrade -A 19mm shear vane blade is pushed into soil and torqued to fail the soil - Undrained shear strength is obtained from a direct reading dial (Su is proportional to torque) - Only works for fine grained cohesive soil - Good for quick evaluation of layer strength but limited to maximum reading of vane which is equal to CBR =7

what are the 3 ways of achieving granular stabilisation?

- mixing of materials from different parts of the deposit at the supply of the source - mixing selected imported materials with insitu materials - mixing two or more selected, imported natural gravels, soils and/or quarry products on site or in a mixing plant

What does pavement life depend on?

- number of repetitions of heavy commercial vehicles (design traffic/ESA) - stiffness of subgrade (CBR/E)

What are bound materials?

- produced through the addition of stabilising agents (using cementitious in nature) to granular materials in sufficient quantities to produce a bound material with significant tensile strength.

How does the primary reaction in cementitous stabilisation work? And what does it enable?

- reaction with water which leads to the formation of cementitious material - these reactions occur almost independently of the soils nature and this is the reason why these agents can be used to stabilise a large range of materials.

How has environmental considerations influenced the use of stabilisers?

- stabilisation helps preserve natural resources by recycling existing materials, which also reduces the need for landfill. - uses industrial run-off such as ground granulated blast furnace slag and fly ash - reduces the amount of haulage to the site, reducing pavement deterioration and vehicle admissions

What does the density of a soil depend on? (3)

- type of soil - compactive effort -water content

What's the application of Sheeps foot roller?

- used to compact subgrade -used for cohesive/fine grained soils It has protrusions which increase the contact stress so greater compaction

How do bound materials behave differently compared to unbound and modified

-Bound materials act like a beam in resisting traffic loading and has considerably increased structural capacity compared with modified and unbound materials.However shrinkage cracking needs to be controlled in pavement base layers. -Modified and unbound materials resist traffic loading via a combination of cohesion and internal friction. -Bound materials have significantly more tensile strength than unbound and modified.

Why would you avoid using cement stabilisation on unsealed roads?

-Cement will cause the pavement to harden and crack -it cannot be maintained -there is no surface layer to protect the cemented layer

Explain the difference between ESA and the legal load limit enforced by police.

-ESA is the number of passes of a standard axle load carried by a pair of dual tyres that would cause the same pavement damage as a single pass of the axle in question. -The legal load limited enforced by police is just the weight of the vehicle and doesn't take into account different axle configurations (different axle configurations distribute load differently and result in different amounts of damage)

Why does granular layer need to be graded?

-Using different sized particles reduces the void space, potential for water to seep into and increases the shear strength (due to greater contact area between particles). -Poor grading = initiate high attrition degradation, breakdown of the aggregates, premature densification and rutting - possible generation of plastic fines and premature shear failure

You expect the soaked CBR values from the field samples to vary significantly along the centreline of the road. What statistical measure will you use determine the design CBR from all these samples?

-soils of similar types are grouped together and analysed statistically. -The 10th percentile value of strength is used. -CBR (design) =CBR (mean) - 1.3 standard deviation

List 6 construction types

1 - Bituminous bound 2 - Unbound = natural gravel pavement 3 - Concrete 4 - Block paving 5 - Lime or Cement stabilised bases or subgrade 6 - Reinforced with geotextiles or geogrids

Name 5 tests that evaluate subgrade strength

1 - California Bearing Ratio (CBR) 2 - Dynamic Cone Penetrometer - 3 - Shear Strength (Shear Vane) 4 - Clegg Hammer (impact resilience) 5 - Deflection/ Curvature measurements

Name 5 material properties that need to be specified for unbound granular aggregates

1 - Grading 2 - Plasticity of the fines in the aggregates 3 - Hardness 4 - Weathering Resistance 5 - California Bearing Ratio (CBR)

Name 4 types of stabilisations and the 3 classifications they can be put into

1 - Granular stabilisation 2 - Cementitious stabilisation 3 - Lime stabilisation 4 - Bituminous stabilisation Classification 1 - Unbound materials 2 - Modified materials 3 - Bound materials

Name 6 factors that influenced the development of road stabilisation

1 - Increased Heavy vehicles 2 - Improved Pavement Design Procedures 3 - Better means of characterising stabilised materials 4 - Environmental considerations 5 - Improved range and effectiveness of binders 6 - Improved plant and equipment

Name and explain 2 ways to measure field density

1 - Sand replacement -Excavate hole and weigh excavated material - Measure volume of hole by filling hole with sand from graduated cylinder 2 - Nuclear density meter - Amount of scatter of radiation measured and is related to density of soil

Name 4 types of rollers for insitu compaction

1 - Smooth wheeled roller 2 - Sheeps foot roller 3 - Rubber tyred roller 4 - Vibratory roller

Name 2 tests that determine pavement strength on existing pavements

1- Falling Weight Deflectometer (FWD) 2- The Benkelman Beam

What are the 4 input variables of the pavement design procedure?

1. Design traffic 2. Subgrade and pavement material properties 3. Environment 4. Construction and maintenance needs

What are the 5 objectives of compacting subgrade soil

1. Increase shear strength by maximising frictional contact between particles 2. Increase permanence by reducing potential for swelling, shrinkage and frost heave because reducing void ratio 3. decrease compressibiity - reducing settlement under traffic loading 4. Decrease void ratio 5. Achieve increased unit weight.

What two tests help us determine the permanence of the soil?

1. Moisture content and density curve (5 samples) 2. Soaked and unsoaked CBR testing

What are the 3 options that an engineer is confronted with on a job with insitu material

1. Produce a design that uses inherent properties 2. Remove the local material and use better imported material 3. Treat the insitu material

what are the benefits of cementitous stabilisation on the material?

1. Reduction in moisture susceptibility - resulting in improved volume and strength stability under variable moisture conditions 2. Development of inter-particle bonds in granular materials, resulting in higher tensile strength and high elastic modulus

What are the 5 main failure mechanisms of a pavement?

1. Rutting in excess of 15mm-25mm caused by subgrade deformation due to repeated ESA 2. Cracking in asphaltic base pavement caused by fatigue strain cracks at the base of the asphaltic concrete from repeated ESA 3. Combination of 1 and 2 4. Rutting due to densification (or shear) in granular base or asphaltic concrete 5. Stripping of thin bitumen seal over granular base the reduces the waterproof and skid resistance

What are the two primary mechanisms of fatigue failure or distress to design against of unbound granular aggregate pavement

1. Subgrade deformation: due to vertical strain generated in the subgrade that results from rutting 2. strength and permanence of the GA - adequate compacted compressive strength and shear strength - high compacted modulus to protect subgrade - significantly is the long term behaviour or the permanence (or durability) of this strength under all physical and environmental conditions.

what is the key information that designers should know about the pavement and the subgrade.

1. The strength and stiffness parameters of these materials which can be used to determine their load bearing properties 2. Variations in the materials parameters due to: - changes in moisture and temp - increases in age -cumulative distress during design period 3. Manner in which they deteriorate and the significant reaction to stress(load) and strain (deformation) 4. Their performance criteria (limiting values of strain and stress which will cause distress.

What are the 3 advantages of a mechanistic design?

1. You can predict actual material stiffness 2. You can take into account unusual loading regimes 3. Examine many different and varied pavement structures

how can lime stabilisation cause issues in the construction process?

1. hydrated lime can cause dust problems even in light winds. Dont use in urban or windy areas. 2. soil moisture: quicklime and hydrated lime are effective in drying out soils because they react with the excess water, but slurry lime can't be used. Slurry limes are suited to dry soil conditions where water may be required to achieve effective compaction 3. Available equipment and expertise are required to achieve good results

what are the two principal methods used to stabilise a material?

1. mix-in-place or insitu stabilisation 2. stationary or pugmill

What tests can be used to evaluate granular stabilised materials?

1. particle size distribution 2. sand equivalent properties (checks plastic properties) 3. strength test CBR 4. Ten percent finers test

When can Falling Weight Deflectometer (FWD) be used

3 situations (in decreasing pavement data order) 1 - Individual layer thickness are known 2 - Total pavement thickness are known 3 - No Layer data available - On existing pavements - to assess the subgrade and pavement structure before upgrading. - Used for quality control of new pavements

What are some examples of stabilisation use

1. to improve the working platform for construction traffic in otherwise soft/loose conditions 2. improve the quality of the pavement material so they can be used in higher levels and also to enable the thickness of the pavement to be reduced. 3. To reduce the effects of moisture on the subgrade or lower layers of the pavement

What are some quality control factors?

1. uniformity of the material to be stabilised 2. quantity and uniformity of distribution of the stabilising agent 3. thickness (& uniformity of thickness) of the stabilised layer 4. degree of grading 5. quality of mixing 6. moisture content 7. compacted density 8. surface finish or roughness.

Assuming you take samples on the centre-line of a new road geometry, at what frequency would you do the material sampling in the field?

100m because NZ has very variable soil

What is the design life for flexible pavements?

20 years but if allowing reconstruction the design life can be extended to 40 years - Bituminous bound pavements = 40 year life - Rigid concrete pavement = greater than 40 years

When would you use a cemented pavement composition as opposed to an unbound granular structure.

An unbound granular layer is used in the base-course as a structural layer. It minimizes the stresses on the subgrade to prevent subgrade rutting. It would be used on gravel roads or when you want to address the grading of the pavement. A cemented pavement is used when more strength is required eg when high traffic loads because the cement increases inter-particle bonds so has higher tensile and elastic modulus.

Name and briefly discuss at least THREE factors that may influence the actual damage a specific vehicle causes to the pavement.

Axle Loading - overloading causes damage to increase exponentially Number of Axle Passes - more passes means more damage time between loading- less damage on pavement if longer time between loading Axle Configurations - eg how the load is distributed. A truck with more axles and wheel parts will spread the load more evenly and decrease damage

Which soil compacts more- dry soil or wet soil and why?

A dry soil will compact more because the voids are filled with air not water so upon compaction the air voids are removed. If they are filled with water they cannot be compacted because water is incompressible.

Failure mode definitions (1/5) 1 - define Foundation deformation

A rut excess 15-25mm in pavement wheel path caused by fatigue deformation in subgrade from repetitions of load (ESA)

What does an ESA of 1 mean?

A specific axle has been loaded to the correct reference axle load. Therefore not over or under loaded.

Benefits and limitations of the FWD test

Benefits: FWD units have built in software that instantaneously print out the subgrade modulus (quickly calculate the modulus). FWD method is fast and can cover large distances in a day Can be used on existing pavements and on new pavements Can be used when individual layer thickness is known, total pavement thickness is known or no layer data known -cheap Limitations: -limited by moisture in the soil -indirectly measures the deflection

How does the bituminous stabilisation process work?

Bitumen must be in a fluid state (achieved by heating the bitumen). A light cutter oil or kerosene is added to keep the bitumen fluid at room temperature The fluid bitumen is then mixed with the pavement materials coating the fines and/or coarse material.

What is CBR? What does it depend on?

CBR = Californian Bearing Ratio. It indicates the strength of a material compared to strength of compacted rock eg CBR of 10 means it has 10% strength of the reference material. - depends on degree of compaction and moisture content of the sample CBR < 4 is low and CBR > 10 is high

Explain the principles behind the CBR test? what does CBR depend on?

CBR is an empirical test to directly measure the strength of a soil. You push a standard plunger into a sample at a fixed penetration rate. The amount of force required to penetrate the soil compared to the force required to penetrate compacted rock is the CBR. The CBR depends on the degree of compaction and moisture content of the soil. Usually do soaked tests (soak for 4 days) for fully saturated CBR value.

Explain the fundamental concept of equivalent standard axle (ESA) loads

ESA is the number of passes of a standard axle load carried by a pair of dual tyres that would cause the same pavement damage as a single pass of the axle in question. Different HCV have different loads and axle configurations so ESA is used to normalise them.

Explain the difference in the fundamental behaviour of cemented versus unbound granular pavement structures.

Cemented pavement have a large amount of cementitious material added so the cement increases the inter-particle bonds so a higher tensile and elastic modulus can be achieved. -cement also fills voids so reduces the moisture susceptibility. Unbound granular pavement structures strength comes from the cohesion and internal friction forces between the particles, and does not have much tensile strength.

How do you assess pavement failure?

Failure is defined as a rut depth greater than 15-25mm. Can also measure failure by measuring roughness of the road ie number of bumps. 150/km indicates sufficient deterioration to be considered failure

For a given soil what does the density depend on and how can we control this?

Depends on: 1. compactive effort 2. Water content Controlled by: 1. Good/ heavy compaction 2. Ensuring the subgrade is at or near OMC

What are the main differences in construction techniques of an unbound pavement and a cemented pavement.

Cemented pavement: layers beneath the cemented pavement should not deform much otherwise it will lead to cracking. Therefore those layers need to be compacted to near OMC. -need to provide cement/cementitious material and water so the cement can react with the water. Unbound pavement: can mix the aggregate together by: -mixing different grades at the source -mixing imported materials with insitu materials -mixing imported materials at site

Why do we need to consider both the longitudinal and transverse direction of the pavement in terms of failure

Failure of a pavement occurs by rutting or by excess roughness. Rutting occurs transversely while roughness occurs longitudinally along the road. Therefore need to check both directions.

What are the 5 main materials that roadbase is usually comprised of?

Basecourse - high quality aggregate (typical in NZ) Asphalt (AC) Cement or lime bound (lean mix). Becomes flexible composite pavement when combined with bituminous overlay Concrete continuous or slab continuously reinforced. Becomes rigid composite pavement with combined with bituminous overlay. Should be resistant to permanent deformation or cracking.

Why is there no failure criterion for the granular base layer?

Because a good granular layer will have insignificant vertical strains compared to the subgrade. Instead the layer is treated as a simple elastic filter of strains for the subgrade.

Why do round pebbles have less shear resistance?

Because of their rounded shape, they have less frictional contact with surrounding particles and therefore less shear strength.

Why is cementitious stabilisation suitable for a range of materials?

Because the primary reaction (stabilising agent with water to form cementitous material) occurs independent of the nature of the soil.

What is the difference between modification of material and stabilisation?

Modification is adding a small amount of stabilising agent such that there is not a significant increase in tensile strength but still corrects a material deficiency. It alters the chemical properties of the unbound material. -stabilisation is adding large amounts of stabilising agent resulting in a significant increase in tensile strength and structural capacity.

What is the primary purpose of pavement?

Reduce the stresses imposed on the pavement to an acceptable level of stress which can be supported by the subgrade

What design adjustment(s) will you make to cater for the high tyre pressures?

High pressure tyres increase the stress on upper layers so need to increase the strength of upper layers so less stress is filtered to the subgrade. Can do this by: -increasing thickness of upper base course layer -increasing total thickness -stabilising the subgrade/ pavement layers

Explain how high tyre pressures will impact on your design

High pressure tyres means the contact area between the road and vehicle is reduced. Therefore greater pressure on the upper layers of pavement = more damage and greater stress filtered on the subgrade = more deformation.

What does compaction do to subgrade soils

It's the process of densification of soil by mechanical means (roller) by reducing air voids at constant water content (not consolidation)

Benefits and limitations of the Benkelman Beam test

Limitations: Procedure is slow and only suitable for short lengths of pavements, Expensive Benefits: Directly measures the peak deflection and gives high accuracy

In relation to CBR test values what happens when the test is done on a soil with MC lower the OWC? greater than the OWC? what range should be aimed for?

Lower than OWC: soaked CBR value decreases due to swelling and permanence is compromised Higher than OWC: soil is relative permanent (low swell) but the CBR value is too low Optimal range: OWC + 5%

What are unbound materials

Materials such as natural gravels, crushed rock and fine grained soils which don't exhibit significant tensile strength. They resist traffic loading through a combination of cohesion and internal friction between particles.

What type of materials usually require granular stabilisation?

Materials which have poor cohesion and internal friction so cannot resist traffic loading. eg poorly graded products (low internal friction), or high plasticity materials such as clay. Once stabilised behave like conventional unbound materials

Explain how the Falling Weight Deflectometer (FWD) tests are undertaken.

Measures the deflection indirectly by dropping weights from a given height and measuring the deflection. The weight has a spring at the bottom to slow down the momentum of the weight so it is applied gradually and rebounds. This recreates the passing of a moving vehicle over the pavement. FWD uses geophones to measure sound waves to measure the deflection bowl.

What do the material properties of the aggregate in UGA pavement need to ensure? What properties are measured?

The strength/stiffness (modulus) of the aggregate in the pavement needs to be adequate during the in service life of the pavement. Measured by looking at: 1. Grading 2. Plasticity of the fines in the pavement 3. Hardness 4. Weathering resistance 5. CBR

Why is compaction specification using air voids more preferable than with water content?

There is a wide range of soil types so compaction specification using water content is meaningless. Air voids are a more consistent property and less effected by the range of soil types.

What influences the thickness of the subbase? What material is it usually made of?

Thickness influenced by: CBR of subgrade, traffic volume/load over life of pavement (ESA) Dense unbound crushed aggregate material but can be open graded to improve drainage

What is the basecourse/roadbase?

This is the structural layer of the pavement. Thickness depends on CBR of subgrade and traffic volume of the lifespan.

How do you test the resilient modulus?

Using the repeated load triaxial testing.

Why does it require more energy to compact a soil with a lower water content?

When the soil is dry it has the greatest amount of contact area between the particles so the shear strength is large. Therefore a large force is required to compact it. When water is added it lubricates the particles so it is easy to compact

Define stabilisation

a process that improves the load-bearing capacity and/or stability of a material

What is the effect of clay in pavement

clay absorbs water leading to swelling. Particles lose friction so pavement reduces in shear strength

What advantages arise from mixing the bitumen with the pavement materials?

adds cohesion to the material due to the cohesive properties of the bitumen. makes the material less permeable and therefore less susceptible to moisture because bitumen fills voids.

What water content should we measure a pavements CBR/modulus at?

at the highest water content likely to occur during its design period.

What materials can be used in bituminous stabilisation?

hot bitumen cut back bitumen bitumen emulsion any of the above combine with cementitious binders

Name the TWO layer properties that need to be determined for the mechanistic design of pavements.

layer thickness and stiffness/strength

What is the subbase?

lower structural layer of the pavement and provides working platform for the upper layers.

What is lime stabilisation?

mixing proportion of lime with the proposed subgrade or pavement materials. Material being treated must have clay particles or pozzolanic materials for the lime to react with

Does the type of lime used in stabilising affect the long term structural process of the material?

no but it influences the construction process

When is lime stabilisation particularly effective? When is it not effective?

plastic soils - improves both workability and strength. Not effective: cohesionless or low cohesion soils because nothing to react with the lime (without adding pozzolanic additives)

What is the structure of clay

plate like - not very strong -either tetrahedron or octahedron

what is the principal function of a unbound aggregate in a granular flexible pavement

robust (high compacted modulus) filter of stresses such that the subgrade has the stress conditions suitable for the design traffic loading (no. of ESA's) to avoid subgrade rutting.

What are the distress modes and causes for flexible pavement and what materials are affected

rutting - due to densification - all except cemented cracking - extra high load, repetitions of normal load, shrinkage - asphalt and cemented roughness - due to variability of density and material properties - all

What could an alternative approach to a subgrade improvement layer be?

the existing subgrade soil could be improved through stabilisation.

Insitu testing needs to be undertaken so that the pavement designer has the neccessary information about....

the variability of the subgrade and the representative properties of each subgrade material in both cut and fill

What's the application of Rubber tyred roller?

used to compact surface of asphalt pavements by applying a kneading action

What are the CBR values for a soft soil? Firm soil? What is a good CBR range for soils?

soft soil - CBR < 4 Firm soil - CBR > 4 In NZ good subgrades have CBR range of 4-7.

What is the subgrade? How is its strength defined?

subgrade is the insitu material compacted at near OMC and is the most significant part of the pavement. All other layers are designed to reduce stress on subgrade. Strength is defined in terms of CBR

Name the 3 elastic parameters needed for elastic mechanistic pavement

- Vertical Elastic Modulus = Ev (MPA) = 10 x CBR - Horizontal Modulus = Eh (MPA) = 0.5 x Ev - Shear Modulus = F - Poisson's Ratio (v) = 0.45 cohesive soils and 0.35 for non cohesive soils

How to determine Design Traffic

- existing traffic mix and trends - future needs and changes to the network or land use - load factors and HCV vehicle design and suspension factors

Explain the principles of the Clegg Hammer test

- A plunger in a sleeve is dropped onto the soil surface - Deceleration is measured as the clegg impact value (CIV) - Value obtained from a direct dial reading and CBR is found from known relationship - Test can be done in fine and coarse soils with aggregates size up to 19 mm. -Good for quick evaluation of dense coarse grained soils

Why is Weathering Resistance of granular material important?

- Aggregate shouldn't degrade under the environment so must meet minimum chemical weathering criteria. Low grade weathering resistance will cause premature attrition degradation, breakdown of the aggregate and generation of plastic fines

How does water effect pavement design

- Effects the behaviour, strength and overall life of pavement. Should measure CBR/Modulus at highest water content that is likely to occur during design period

How does the environment influence pavement design?

- Environment can change material moisture and temperature properties. Need to use site specific moisture and temperature values

Additional layer - Strain alleviating Membrane Interlayer characteristics

- Highly elastic (won't crack) - Used to resist cracking

Explain Granular stabilisation

- Improving one material by blending it with one or more granular materials. This alters the particle size distributions and may change plasticity

Explain Cementitious stabilisation

- Mixing proportion of cement or cementitious materials with the proposed subgrade/pavement material to improve material properties.

What traffic features determine the performance of the pavement

- Number of axle passes - Axle loadings - Axle configurations

How is hardness of aggregate measured?

- Tested using 'ten per cent Fines test' to meet hardness criteria - the load that causes 10% of unbound crushed aggregates to pass 9.5mm sieve -Specified as crushing resistance (kN)

How is plasticity of the fines in the aggregate measured?Why is it important?

- Use Sand Equivalent Test to specify plasticity - Low SE indicates plastic fines which combined with with water will lead to premature shear failure. Can be fixed using lime stabilisation. -SE > 40 specified for base course aggregate

What are the consequences of poor grading?

-Initiate high attrition degradation -breakdown of the aggregate (from excess rock to rock stresses), -premature densification and rutting - also possible generation of plastic fines and premature shear failure.

Explain the principles of the Dynamic Cone Penetrometer (scala)

-Used to test strength of insitu soil. A 20mm diameter cone driven by a falling weight penetrates the pavements. - Indicates insitu CBR in fine grained soils (not good in coarse soils) - Good for quick evaluation of layer thickness and strength

What is the Influence of heavy vehicles on stabilisation

-gross vehicle mass has been increasing -demand for higher strength pavements -can be difficult to achieve economically with traditional unbound pavement materials

What are the three commonly used limes in lime stabilisation?

-hydrated line (dry fine powder) -quicklime (very granular and dry ) -slurry lime

Explain the principles behind vibratory rollers

-used to compact subgrade. Can be attached to other 3 types of rollers to increase compaction effort. -Used for granular soils (don't use on clays cause vibrations force carried by pore water pressure)

Explain the principles behind smooth wheeled roller and when are they used

-used to compact the subgrade . -used for granular material (road pavement) - asphalt pavements

Explain the principles of the Benkelman Beam test

-used to measure the peak deflection of the pavement - A pivoted beam rests on two supports and as the vehicle drives forward over the beam (the beam is wedged in between the dual tyres) the deflection induced by the tyres of a twin wheel truck at the midpoint is measured. -the beam will deflect and the angle the beam makes with the pavement is the deflection angle.

What is the quality management rule of thumb?

A deficiency in the order of 10% in either the density or thickness in bound layers could lead to a decrease in performance of the order of 90%

Explain how and what the deflection bowl is used for during the pavement design process.

A deflection bowl is the deflection shape of the pavement under loading. It is used to quickly determine the modulus of the sub-grade by back analyzing the deflection shape through the mechanistic elastic analysis. The larger the deflection the weaker the pavement layer, so the deflection bowl indicates strength of the pavement.

What equipment is required for insitu stabilisation?

Additive spreader and stabilising mixer

Explain the relationship between achieved density, moisture content and compaction energy with the aid of a sketch of moisture/density curves.

As the moisture content increases the dry density increases because the water lubricates the particles and allows them to compact more. At the OMC the max compaction occurs. As the moisture content increases further dry density decreases because swelling occurs. More compaction energy is required to compact a soil with a low water content.

How can we increase the dry density of the subgrade?

By ensuring good compaction ie heavier + more energy - ensuring the soil is near OMC

What is bituminous stabilisation?

Coating particles with bitumen to increase cohesion and reduce permeability.

Why do we need to consider construction and maintenance when designing pavement

Construction/maintenance will influence the type of pavement structure because many material properties depend on the construction type eg level of compaction

Failure mode definitions (2/5) 2 - define Loss of Structural Slab Action (crack)

Cracking in asphaltic base pavement caused by fatigue strain cracks on the base of the asphaltic concrete layer from repetition of load (ESA)

List the type of pavements range

Range from heavy duty eg aircraft runway -> light eg access roads

Difference between empirical pavement design and mechanistic approach?

Empirical design is observing existing pavements and doing full- scale trials (traditional method). Mechanistic approach is analysing the pavement as a structure and estimating material properties (modern method)

Explain the THREE aggregate properties that influence the shear strength of materials.

Grading - Well graded materials have greater contact area between aggregate so greater shear strength. Amount of plasticity of the fines in the aggregate- large amount of fines mixed with water = premature shear failure. Shape of aggregate- rounded particles have less contact area vs angular therefore less shear strength. It is easier for rounded particles to slip over one another while a greater force is required to shear angular particles.

When is cementitious stabilisation not suitable?

In materials that contain a high amount of deleterious salts (sulphates, organics and chlorates) because these materials retard cementitious reactions Cohesive materials requires more cement because the clay absorbs cement during initial reaction so very expensive. Better treated with lime. Inefficient when treating one sized materials because it requires increased quantities of cement.

Failure mode definitions (4/5) 4 - define Within in pavement Shear and pavement densification failure

Rutting due to densification (or shear) in a granular base or asphaltic concrete base (unusual in a well-constructed pavement)

in a cemented granular pavement there are two primary fatigue failure mechanisms. What are they and where do we need to test for these failure mechanisms?

Rutting due to subgrade deformation from fatigue strains (repeated ESA ) - need to test vertical compressive strains on the subgrade below the centre of the wheel load. Cracking in the cemented or asphalt layer due to fatigue strains from repeated loadings -need to check tensile strain at the bottom of cemented layer below wheel and centre of wheel path.

Why is stabilisation undertaken?

Should be used when it is more economical to use an additive to improve a readily available pavement material than to use a higher quality and higher cost material from elsewhere

Failure mode definitions (5/5) 5 - define Loss of waterproofness and surface attrition

Stripping of thin bitumen seal over granular base that reduces waterproofing and skid resistance

Name the layers of pavement from top to bottom (5 layers)

Surface wearing course Base course Subbase Subgrade improvement layer Subgrade

How do you directly measure the modulus of unbound granular layers? and what are the benefits?

Test using a triaxial cell under repetitive loading. Benefits - obtain modulus but also permanent deformation under long term loading and potential for rutting can be evaluated.

How is weathering resistance of granular material measured?

Testing the breakdown of the aggregate after being soaked in a solution of sodium sulphate = the ' Sodium Soundness Test). It is a qualitative weathering index.

Why is Hardness of granular material important?

The aggregate must not degrade under the traffic loading so must meet minimum hardness criteria. Low crushing resistance (CR) will lead to premature attrition degradation breakdown of aggregate and bring premature densification and rutting

What is the equilibrium water content? And what conditions do we assume for pavements?

The average long-term water content in a pavement subgrade after construction In NZ we assume fully saturated conditions for all pavement layers and all design parameters are obtained from a soaked CBR test (in which the sample is soaked for 4 days)

What is the purpose of the additive spreader in insitu stabilisation?

The purpose of the spreader is to hold and distribute the additive. It is spread through a vane feeder on the ground in front of the stabilizing mixer.

Explain stationary stabilisation

This plant blends a number of materials as well as additive through a pugmill which is then discharged into a truck and laid on site by a paver. Care needs to be taken that the additive has a sufficient working time to allow for the haul distance and compaction.

What is the purpose of the stabilizing mixer in insitu stabilization

To mix the additive into the host material so the stabilising agent is uniformly distributed into the pavement.

What is the purpose of the surface wearing course

To provide a smooth impermeable high skid resistant surface. Made from chipseal or open graded asphalt. (not a structural layer).

what would be your strategy to compact soils at the dry and wet side of the optimum moisture content?

Too dry = hard to compact so need to increase compaction energy by increasing weight of roller, number of passes or add vibratory efforts. Too wet = easy to but cannot compact as much so use drains to allow water to flow out or allow wet soil to dry out. -add quick or hydrated lime to dry out the soil

What are modified materials? How do they behave structurally?

Unbound materials to which small amounts of stabilising agent have been added to: 1. correct a structural deficiency (reduce plasticity), without causing a significant increase in structural stiffness 2. increase strength 3. reduce moisture susceptibility of fine grained soils to form a working platform or lower subbase layer Structurally: they behave the same as unbound materials, although they do gain sufficient strength with time an in the long term can be considered as bound materials

When/where is the most critical loading in an airport

When airplane is parked on the tarmac waiting because loading is static -at touchdown aircraft is light because lost fuel during flight -during takeoff aircraft gradually transfer weight so non critical

Why do the aggregates need to meet the hardness criteria?

because they must not degrade under the action of traffic. A low crushing resistance CR results in: premature attrition breakdown degradation breakdown of the aggregate, bring on premature densification and rutting.

What is the structure of kaolinite vs montmorillerite and its effect

kaolinite has 1:1 structure so doesn't absorb much water while montmorilerite has 2:1 structure so absorbs lots of water.

When would you use bitumen stabilisation

to introduce cohesion into non plastic materials or to reduce moisture sensitivity in cohesive soils

Why and when do we use a subgrade improvement layer

used if the strength of subgrade is too low ie less than 4 CBR and subgrade likely to swell due to inflow of water. Subgrade improvement layer is used to improve the strength of the foundation and is cheaper than a subbase.

When is stationary plant used?

when the material is sourced close to the site and the haul distance is relatively short to site.

What is the consequence of having plastic fines? How is this alleviated?

with water in the aggregate can cause premature shear failure. This can be alleviated through stabilization techniques.