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Questions and Answers
What is the significance of the Linear Shrinkage (LS) in the CBR calculation?
What is the significance of the Linear Shrinkage (LS) in the CBR calculation?
- It influences the calculated CBR value. (correct)
- It is a direct measure of moisture content.
- It affects the plasticity index results.
- It is not related to the CBR calculation.
Which of the following is NOT a factor considered in selecting CBR for moisture conditions?
Which of the following is NOT a factor considered in selecting CBR for moisture conditions?
- Design moisture content
- Thickness of pavement layers (correct)
- Equilibrium conditions
- In-service moisture regime
What is meant by 'in-service' moisture conditions?
What is meant by 'in-service' moisture conditions?
- Moisture is consistent and remains unchanged.
- Moisture conditions are evaluated at the center of the pavement.
- Moisture is influenced by seasonal variations. (correct)
- Moisture conditions are tested solely in dry seasons.
What approach is recommended for CBR testing during adverse climate conditions?
What approach is recommended for CBR testing during adverse climate conditions?
Which equation represents the first estimate for calculating CBR from grading?
Which equation represents the first estimate for calculating CBR from grading?
What does the repeat load triaxial testing provide?
What does the repeat load triaxial testing provide?
What criteria should be considered when selecting the design CBR?
What criteria should be considered when selecting the design CBR?
Which sieve size is relevant for determining the fines content in graded materials for CBR calculations?
Which sieve size is relevant for determining the fines content in graded materials for CBR calculations?
What is the primary purpose of pavement drainage?
What is the primary purpose of pavement drainage?
Which type of asphalt is specifically designed to allow for very high binder content?
Which type of asphalt is specifically designed to allow for very high binder content?
What do table drains primarily do in the context of rural roads?
What do table drains primarily do in the context of rural roads?
What is the significance of California Bearing Ratio (CBR) in pavement design?
What is the significance of California Bearing Ratio (CBR) in pavement design?
What role do cut-off drains serve in pavement engineering?
What role do cut-off drains serve in pavement engineering?
Why is subsoil drainage important when groundwater levels are high?
Why is subsoil drainage important when groundwater levels are high?
Which material can be used in a spray seal application?
Which material can be used in a spray seal application?
What should be considered when selecting materials for batters in pavement design?
What should be considered when selecting materials for batters in pavement design?
For effective pavement drainage, catch pits are used to divert rainwater into what system?
For effective pavement drainage, catch pits are used to divert rainwater into what system?
What is an additional benefit of an excellent culvert beyond passing water?
What is an additional benefit of an excellent culvert beyond passing water?
What is the maximum allowed CBR value for a stabilised subgrade?
What is the maximum allowed CBR value for a stabilised subgrade?
In the example of a subgrade with three layers, what is the thickness of the first layer?
In the example of a subgrade with three layers, what is the thickness of the first layer?
How is the CBR value of the second layer calculated when a subgrade is stabilised to a depth of 0.4m?
How is the CBR value of the second layer calculated when a subgrade is stabilised to a depth of 0.4m?
What must be true about the layers when using the Japan method for CBR calculations?
What must be true about the layers when using the Japan method for CBR calculations?
For a layered subgrade with CBR values, how do you calculate the average CBR?
For a layered subgrade with CBR values, how do you calculate the average CBR?
What is the depth range for the original CBR to be assigned to the remaining material after the stabilised layer?
What is the depth range for the original CBR to be assigned to the remaining material after the stabilised layer?
If a three-layered subgrade has layer thicknesses of 0.2m, 0.5m, and 0.3m, what should the total thickness of layers equal?
If a three-layered subgrade has layer thicknesses of 0.2m, 0.5m, and 0.3m, what should the total thickness of layers equal?
What happens to the CBR of the lower 0.2m of a stabilised subgrade?
What happens to the CBR of the lower 0.2m of a stabilised subgrade?
What should be done if anomalies cannot be explained in pavement analysis?
What should be done if anomalies cannot be explained in pavement analysis?
When designing heavy duty pavements, what value is primarily used for the design CBR?
When designing heavy duty pavements, what value is primarily used for the design CBR?
What is the maximum allowable CBR value typically recommended for sands?
What is the maximum allowable CBR value typically recommended for sands?
Which of the following is NOT a method for treating soft subgrades?
Which of the following is NOT a method for treating soft subgrades?
What is one result of lime stabilisation applied to subgrades?
What is one result of lime stabilisation applied to subgrades?
Which method assigns the CBR for the lower 200 mm of a stabilised layer?
Which method assigns the CBR for the lower 200 mm of a stabilised layer?
What is the purpose of geogrids in pavement construction?
What is the purpose of geogrids in pavement construction?
For good drainage conditions, what is the typical CBR value for sandy clay?
For good drainage conditions, what is the typical CBR value for sandy clay?
Which statement is TRUE regarding composites in pavement construction?
Which statement is TRUE regarding composites in pavement construction?
What is the typical effective depth for road pavements below the top of the subgrade?
What is the typical effective depth for road pavements below the top of the subgrade?
Which test is used to measure the California Bearing Ratio (CBR) for surface levels only?
Which test is used to measure the California Bearing Ratio (CBR) for surface levels only?
What is one of the properties that should be tested for subgrade classification?
What is one of the properties that should be tested for subgrade classification?
What is the purpose of soaking a sample for 4 days during a CBR test?
What is the purpose of soaking a sample for 4 days during a CBR test?
How is the CBR determined from load and penetration?
How is the CBR determined from load and penetration?
Which method is NOT an insitu test for determining subgrade CBR?
Which method is NOT an insitu test for determining subgrade CBR?
What corrective action is needed when the CBR curve is initially concave up?
What corrective action is needed when the CBR curve is initially concave up?
Which of the following measurements helps find the soil type using the Electric Friction Cone Penetrometer?
Which of the following measurements helps find the soil type using the Electric Friction Cone Penetrometer?
What is an essential factor to be considered during the CBR test that may affect the accuracy of results?
What is an essential factor to be considered during the CBR test that may affect the accuracy of results?
What is a key characteristic of industrial pavements in terms of effective depth?
What is a key characteristic of industrial pavements in terms of effective depth?
Which factor primarily influences the classification of subgrades?
Which factor primarily influences the classification of subgrades?
Which type of CBR test focuses on fully saturated conditions?
Which type of CBR test focuses on fully saturated conditions?
What effect do polymer materials have before CBR testing?
What effect do polymer materials have before CBR testing?
Which formula approximates the CBR from the Clegg Impact Value (CIV)?
Which formula approximates the CBR from the Clegg Impact Value (CIV)?
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Study Notes
CBR and Pavement Stabilisation
- CBRmax ≤ 20 for cement-stabilised subgrades.
- Subgrade layers must decrease in CBR and be thicker than 0.2m, totaling 1.0m for stability.
- Example involves 3 layers with CBR values: Layer 1 (0.2m, 8%), Layer 2 (0.5m, 4%), Layer 3 (0.3m, 2%) resulting in an average CBR of 3.8%.
Japan Method for CBR Calculation
- Utilises weighted average of layer CBR and thickness to determine the effective CBR.
- Involves calculating CBR based on multiple layers, assessing only top two layers when used for certain depths.
- In case of stabilised subgrades, the original and stabilised CBR must be averaged for the lower 0.2m layer.
Heavy Duty vs. Road Pavements
- Road pavements are typically designed with an effective depth of 1m, while industrial pavements may extend to 2-3m due to heavier loads.
- Variances in behavior and requirements for heavy duty due to unregulated axle loads.
Subgrade Characterisation
- Subgrades vary significantly based on natural soil properties, requiring geological mapping and systematic sampling.
- Essential properties like Particle Size Distribution, Atterberg Limits, and California Bearing Ratio (CBR) must be tested.
CBR Testing Methods
- Insitu tests include the CBR Test, Dynamic Cone Penetrometer, and others.
- Laboratory tests include Undisturbed CBR and Triaxial tests, highlighting that variability across labs is common.
CBR Testing Procedure
- Tests performed in a compacted sample, soaked if required, with load applied via a piston to determine resistance.
- Corrected load values at specified penetration depths are used for accurate CBR determination.
Equipment and Measurements
- Static/Dynamic Cone Penetrometers and Clegg Hammers provide quick field estimates of CBR by measuring penetration resistance.
- Falling Weight Deflectometers assess pavement response to dynamic loads, estimating subgrade modulus.
Drainage in Pavement Design
- Effective drainage systems are critical to manage surface water and prevent pavement failure.
- Proposed methods include table drains and culverts, ensuring both aquatic life passage and road integrity.
Subgrade Support and Strength
- CBR values influence pavement thickness design; maximum CBR values are suggested (e.g., sands CBRmax = 10).
- Soft subgrades with CBR < 5 may require special construction techniques and groundwork stabilization.
Moisture Balance and CBR Selection
- Moisture conditions (equilibrium, in-service, and design) impact subgrade behavior; field tests should reflect worst-case scenarios.
- Statistical methods facilitate CBR estimates based on measured results, with adjustments for soil variability.
Treatment of Soft Subgrades
- Strategies for soft subgrades include drainage, replacement of material, stabilisation, and geotextile applications to enhance performance.
Lime Stabilisation and Geotextiles
- Lime stabilisation addresses soil stiffness, permeability, and water sensitivity, influenced by lime demand testing.
- Geotextiles provide separation and reinforcement, while geogrids enhance structural integrity when laid under pavement.
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