This set of Pavement Design Multiple Choice Questions & Answers (MCQs) focuses on “Highway Materials – Subgrade”.
1. Which of the below materials are used to construct subgrade?
a) Bitumen
b) Cement
c) Soil
d) Aggregate
View Answer
Explanation: Subgrade is the bottom layer of pavement and it is made by compacting the soil in the area. Bitumen is used as a binder and weathering course. Cement is used in rigid pavement top layer. Aggregates are used in sub-base and base course.
2. Which of the below IS codes gives the recommended practice for construction of subgrade for road works?
a) IRC 36
b) IRC 27
c) IRC 2
d) IRC 25
View Answer
Explanation: IRC 36 gives guidelines for recommended practice for construction of earth embankments and subgrade for road works. IRC 27 gives specifications for bituminous macadam. IRC 2 gives details on signs for National highways. IRC 25 gives details on designs for boundary stones.
3. If the soil available for construction of subgrade is weak, then which one of the following can be used?
a) Increasing thickness
b) Providing additional silt
c) Additional base layers
d) Dehydrate the soil
View Answer
Explanation: Additional base layers can be spread over a large area of the subgrade to strengthen it, but care should be taken to check that the thickness doesn’t increase a lot. There is no use of increasing thickness of a weaker soil unnecessarily. Silt cannot be compacted easily; it requires high water to do so. Dehydrating the soil would make it difficult to compact it.
4. Clay soils are the best to prepare subgrade.
a) True
b) False
View Answer
Explanation: Most soils are prone to undergo volume changes when exposed to conditions of high moisture content. Clay soils are known to exhibit high shrinking and swelling as and when the moisture conditions change. So, it is not recommended for use as subgrade material.
5. Which of the below is a function of the subgrade?
a) Distribute wheel load
b) Support wheel load
c) Provide binding
d) Ensure drainage
View Answer
Explanation: The main function of the subgrade is to support the weight of overlying layers and the wheel load coming on them. The top layers and base course help in distributing wheel load to subgrade. Binding is provided by the binder course. Drainage is ensured by the sub-base course.
6. What is the first step involved during the construction of subgrade?
a) Compaction
b) Excavation
c) Levelling
d) Removal of vegetation
View Answer
Explanation: It is important to remove vegetation and topsoil containing organic content before starting the construction. Excavation of high spots and subsequent levelling is done after the removal of vegetation. Compaction is done after the above are completed.
7. What type of section does the below figure represent?
a) Fill section
b) Upward section
c) Cut section
d) Downward section
View Answer
Explanation: In the figure, the subgrade is above the ground level, indicating that the subgrade was prepared by filling the ground level. Trimming of excess material is done in case of a cut section.
8. Which type of compaction roller is unsuitable for well-graded soils?
a) Sheep foot roller
b) Vibratory roller
c) Power rammer
d) Smooth wheeled roller
View Answer
Explanation: Sheep foot roller is only suitable for the compaction of cohesive soils. All other types of rollers can be used for compaction of well-graded soils. Sheep foot rollers are made of steel drum and have many round or rectangular projections on the drum.
9. Compaction ______ the bearing capacity of the soil.
a) Doesn’t affect
b) Reduces
c) Disturbs
d) Increases
View Answer
Explanation: Compaction of the subgrade essentially removes the air and moisture present in voids and the soil particles are pushed closer to one another. This reduces the voids and increases the density which in turn increases the bearing capacity of the soil.
10. Subgrade layer is not present in an airport pavement.
a) True
b) False
View Answer
Explanation: Subgrade layer is the basic bottom layer that is present in all types of pavements. It is present in highway pavements, airport pavements and railway lines. It forms an important layer for the construction of further layers of the pavement.
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