This set of Pavement Design Multiple Choice Questions & Answers (MCQs) focuses on “Highway Materials – Subgrade Soil Properties – 1”.
1. Which of the following is not a desirable property of subgrade soil?
Explanation: The soil must be incompressible in nature otherwise it would keep getting compressed every time the vehicle moves over it. The soil must possess sufficient strength to take the load coming on it. It must be possible to compact the soil easily to ensure that there are no gaps in between and it should be stable enough to resist permanent deformations.
2. ______ properties aid in the classification and identification of soil types.
Explanation: Index properties give an idea about the grain size, consistency of the soil and thus can be used to classify the soil being used. Engineering properties are dry density and moisture. Chemical properties can only give the chemical composition of the soil.
3. Which soil type comes between the grain size of 0.06 mm to 0.002 mm based on the classification?
Explanation: As per the classification of soil type based on grain size, silt comes in the size range between 0.06 mm to 0.002 mm. Gravel has a size greater than 2 mm, sand is in the range of 0.6 mm to 0.06 mm and clay is in the range of 0.002 mm to 0.0002 mm.
4. FSI stands for which of the following?
a) Frost swell index
b) Free soil index
c) Free swell index
d) Frost soil index
Explanation: FSI stands for Free swell index. It is a way to judge the index properties pf subgrade soil. Free swell index gives an idea of the increase in the volume of the soil when it is submerged in water and has no other external constraints.
5. Textural soil classification is based on which of the below options?
a) Grain size
b) Mineral content
c) Grain shape
d) Grain colour
Explanation: Textural classification of soil is done based on the proportion of particles with varying sizes that are present in the soil mix. There can be gravel, sand, silt or clay particles present in the soil mix. Each of these is of varying grain sizes.
6. Dry density is found to increase continuously when the compacting moisture content is increased.
Explanation: When the compaction is carried out, it reduces the gaps between the soil particles and increases the density of soil. Moisture content and dry density vary linearly only up to a certain point. After the optimum moisture content point, an increase in moisture content would decrease the dry density. So, the dry density does not increase continuously.
7. The BIS soil classification has been drafted based on which of the below systems?
a) Compaction classification
b) Public road administration classification
c) Highway research board classification
d) Unified soil classification
Explanation: BIS soil classification system has adopted the classification parameters from the Unified soil classification system. Casagrande had classified the soil in 1942 and it was revised and termed as Unified soil classification system by the US Corps of Engineers and the US Bureau of Reclamation.
8. The numerical difference between plastic limit and liquid limit is termed as ______
a) Liquidity index
b) Flow index
c) Plasticity index
d) Consistency index
Explanation: Plasticity index gives the range of water content over which a soil type is plastic in nature. Liquidity index gives the natural water content of the soil. Consistency index gives an idea of the firmness of the soil. Flow index is obtained as the slope of graph plotted between the number of blows and liquid limit.
9. ______ represents the strength of subgrade soil.
b) Shearing resistance
c) Dry density
d) Moisture content
Explanation: Failure in a soil mass occurs due to slippage between particles when load is applied to it. So, shearing resistance gives a measure of the strength of the soil. Cohesion is a factor affecting shearing resistance. Dry density and moisture content affect the engineering behaviour of the soil mass.
10. In the Highway research board classification system, the groups are named in which of the below formats? (n indicates group number)
c) Soil type-n
Explanation: There are seven groups being classified as per the Highway research board system. They are named in the format A-n, for example, group 4 would be named as A-4.
11. According to the unified soil classification system, what property do the symbols L, M and H indicate?
b) Grain size
Explanation: The symbol L represents soil with low plasticity i.e. it has liquid limit less than 35%. The symbol M represents soil with medium plasticity and has liquid limit in between 35% and 50%. The symbol H represents soil with high plasticity and has liquid limit greater than 50%.
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