Compaction MCQ Quiz - Objective Question with Answer for Compaction - Download Free PDF

Explanation:

Sheep foot roller:

• This type of roller is most suitable for compacting cohesive soils such as clay or silty soils.
• The protruding "feet" help to knead and compress the soil, which is particularly effective for cohesive materials that tend to stick together and require more pressure for proper compaction.

 Additional Information

1. Vibratory roller: Best suited for granular soils (such as sand and gravel) where vibration helps to reduce air gaps and improve compaction. It is not as effective for cohesive soils.

2. Smooth wheel roller: Works well for compacting fine-grained soils (sand or gravel) on the surface but lacks the necessary force for effective compaction of cohesive soils.

3. Pneumatic roller: Has rubber tires that apply pressure and are suitable for compacting granular soils or mixtures. It is not as effective for cohesive soils as the sheep foot roller, which provides more kneading action.

Explanation:

Impact force is used in the soil compaction process to achieve a dense and strong soil structure. When a heavy weight (e.g., a compactor or rammer) is repeatedly dropped onto the soil, it generates an impact force. This sudden compression helps to:

• Reduce void spaces: The particles of the soil are forced closer together, decreasing the air gaps between them, which makes the soil denser and more stable.

• Increase soil strength: By reducing the void spaces and compacting the soil particles, the soil's overall strength increases, making it more stable for supporting structures.

 Additional InformationSoil compaction:

1. Purpose: Soil compaction is done to increase the soil's density and stability by reducing the void spaces between soil particles.

2. Impact Force: It involves the application of impact force (such as from a rammer or roller) to compress the soil, which reduces air gaps and increases the soil’s load-bearing capacity.

3. Types of Compaction:

   • Static Compaction: Achieved by applying continuous pressure, commonly used in heavy machinery like rollers.

   • Dynamic Compaction: Achieved by applying a force in the form of impacts or vibrations.

4. Effects on Soil: Proper compaction improves the soil's strength, reduces permeability, prevents settlement, and ensures that the soil is capable of supporting structures.

5. Applications: Soil compaction is essential in construction, particularly for foundations, roads, and embankments, where a stable and firm base is required. 

Explanation:

According to IS 2720 (Part 8) - 1983, which deals with the determination of the optimum moisture content (OMC) and maximum dry density of soils for compaction, the optimum moisture content (OMC) for cohesive soils (like clay) generally falls within the range of 12–16%.

Additional InformationOptimum Moisture Content

• OMC is the moisture content at which the soil can be compacted to its maximum dry density.

• At this moisture level, cohesive soils exhibit their best compaction characteristics, leading to the highest strength and stability.

• Cohesive soils have a higher OMC compared to non-cohesive soils (like sand), as they require more water to achieve maximum compaction due to their finer particles and adhesive properties.

Explanation:

Compaction of Soil

Compaction is a process used to densify soil, reducing its porosity and increasing its stability by mechanical means. It is crucial in construction to ensure a firm foundation, reduce settlement, and increase the load-bearing capacity of the soil.

Analyzing the Given Statements

1. "Relative compaction is the same as relative density." (Incorrect)

   • Relative compaction refers to the ratio of the field dry density of soil to the maximum dry density obtained in the laboratory, expressed as a percentage.

   • Relative density, on the other hand, is a measure of the compactness of granular soil, comparing the void ratio of a soil to its minimum and maximum void ratios.

2. "Vibroflotation is effective in the case of highly cohesive soils." (Incorrect)

   • Vibroflotation is a ground improvement technique used to densify granular soils, such as sands and gravels, by inserting a vibrating probe into the ground.

   • It is not effective for highly cohesive soils (clays and silts) as they do not allow the free movement of particles required for densification.

3. "'Zero air void line' and 100% saturation line are identical." (Correct)

   • The zero air void line represents the condition where the soil is fully saturated, meaning all voids within the soil are filled with water, leaving no air.

   • This line is also referred to as the 100% saturation line, as it indicates the theoretical maximum dry density of the soil for complete saturation.

Conclusion: Based on the analysis, Statement 3 is correct, and statements 1 and 2 are incorrect. Therefore, the correct answer is:

Option 3

Explanation:

Compaction Methods for Deep Layers of Soil

When constructing embankments and foundations, achieving the desired soil density in deep layers is crucial for ensuring stability and longevity. Various compaction methods are available, but their effectiveness varies depending on the depth and type of soil. Let's analyze the options provided:

1. Rolling Compaction: (Option 1)

   • This method involves using heavy rollers to compact the soil surface. While effective for shallow layers, it is not suitable for achieving desired density in deep layers.

2. Kneading Compaction: (Option 2)

   • This method involves manipulating the soil to compact it, often using sheepsfoot rollers. While effective for certain soil types, it is generally more suitable for cohesive soils and less effective for deep layers.

3. Vibroflotation: (Option 3)

   • This method involves using a vibrating probe to rearrange soil particles and densify the soil. It is effective for non-cohesive soils but requires specialized equipment and may not be suitable for all soil types or very deep layers.

4. Dynamic Compaction: (Option 4)

   • This method involves dropping heavy weights from significant heights to compact the soil. It is highly effective for deep layers as the energy from the impact penetrates deeply, densifying the soil at greater depths.

Conclusion

Based on the analysis, Dynamic Compaction is the most effective method for achieving desired soil density in deep layers for the construction of embankments and foundations.

Explanation:

The range of optimum water content for different types of soil is as follows:

Mostly four types of rollers used are:

1. Pneumatic tired roller
2. Tamping roller/ sheep foot roller
3. Smooth wheel rollers
4. Vibratory Roller

Pneumatic tired roller: Pneumatic tired roller has a number of rubber tires at the front and at the rear end. A pneumatic tired roller can be used for highways, construction of dams, and for both fine-grained and non-cohesive soils.

Tamping roller/sheep foot roller: Sheep foot roller also named tamping roller. The front steel drum of the sheep foot roller consists of many rectangular-shaped boots of equal sizes fixed in a hexagonal pattern. In sheep foot, roller compaction is by static weight and kneading of the respective layer. This makes the tamping roller better suited for clay soils.

Smooth wheel rollers: Smooth wheel roller and vibratory rollers are the same. Both have the same characteristics. Only the difference in both is vibratory equipment. The smooth wheel roller has no vibrator attached to the drum. This makes smooth wheel roller best suited for rolling of weaker aggregates, proof rolling of subgrades, and compacting asphalt pavements.

Vibratory Roller: Vibratory-type rollers have two smooth wheels/drums plus the vibrators. One is fixed at the front and the other one is on the rear side of the vibratory roller. Vibration is to reduce the air voids and to cause densification of granular soils. During the vibration of the soil layer, rearrangement of particles occurs due to the deformation of the granular soil because of the oscillation of the roller in a cycle.

Mistake Points

Sheep foot roller is used for compacting clay soil but here proof rolling subgrades and finishing operation of fills with clayey is asked (only finishing operation as compaction is already done) and for finishing operations and proof rolling subgrades, smooth wheel roller is most suitable not sheep foot roller.

Concept:

Compaction Equipment:

• It is often got by using a vibrating or non-vibrating steel drum roller, a pneumatic-tire roller, a grid or cleated roller, or a sheep-foot roller.

Pneumatic tyred rollers:

• Suitable for soil type: Non-plastic silts and fine sands, not suitable for uniformly graded soil
• Nature of Project: Base, sub-base, and embankment compaction for highways, airfields, etc.

Different compaction equipment with suitable soil is as follows:

Explanation:

(i)The Indian Standard Equivalent of the Standard Proctor Test is called the light compaction test (IS: 2720 Part VII - 1974).

(ii) The Indian Standard Equivalent of the Modified Proctor Test is called the heavy compaction test (IS: 2720 Part VIII - 1983).

In compaction test:

Concept-

Compaction of soil is the pressing of soil particles close to each other by mechanical methods. Air during compaction of soil is expelled from the void space in the soil mass and therefore the mass density is increased.

Compaction of soil is done to improve the engineering properties of the soil. Compaction of soil is required for the construction of earth dams, canal embankments, highways, runways and many other structures.

Effect of Compaction on Soil Structure-

Soils compacted at a water content less than the optimum generally have a flocculated structure. Soils compacted at water content more than the optimum usually have a dispersed structure.

Effect of Compaction of Soil on Permeability

The permeability of soil depends upon the size of voids. The permeability of soil decreases with an increase in water content on the dry side of optimum water content.

Given Data and Analysis-

The optimum moisture content of clay soil is 24%, whom compaction test is conducted at 30% moisture content.

The moisture content is more than the optimum moisture content, so the soil will have a dispersed structure of the soil.

Explanation

Vibratory Roller: Vibratory type rollers have two smooth wheels/drums plus the vibrators. One is fixed at the front and the other one is on the rear side of the vibratory roller. Vibration is to reduce the air voids and to cause densification of granular soils. During the vibration of the soil layer, rearrangement of particles occurs due to the deformation of the granular soil because of the oscillation of the roller in a cycle.

Suitability of Compaction Equipment

Using the relation,

\({\gamma _d}_{max} = \frac{{G{\gamma _w}}}{{1 + e}}\)

\(1.65 = \frac{{2.65 \times 1}}{{1 + e}}\)

e = 0.606

Using the relation

se = wG

s = \(\frac{{0.205 \times 2.65}}{{0.606}}\)

s = 0.896

a_c + s = 1

where, a_c = air content

a_c = 0.104 = 10.4 %

Concepts:

S1: True- As the compaction effort is increased; the maximum dry unit weight of the compaction is also increased.

Explanation:

Maximum Dry Density (MDD) with minimum moisture content (OMC) depend on impact energy (compactive effort) given to soil specimens. Higher the impact energy, higher will be MDD and lower OMC.

S2- False The co-efficient of consolidation generally decreases as the liquid limit of soil increases

Explanation:

The coefficient of consolidation of clay is given as:

\(C_v = \frac{K ( 1 + e_0)}{a_v γ_w }\)

On increasing the liquid limit, the compressibility increases due to which coefficient of compressibility (a_v) increases which in turn reduces the C_v as C_v ∝ 1/a_v. 

Concept:

Effect of compaction on properties of soil:

Hence,

The soil at 'A' will have more swelling potential and less shrinking upon moisture variation, compared to 'B'.

The Indian Standard Equivalent of the Standard Proctor Test is called the light compaction test (IS: 2720 Part VII - 1974).

The Indian Standard Equivalent of the Modified Proctor Test is called the heavy compaction test (IS: 2720 Part VII - 1983).

In compaction test:

∴ Option 2 is more appropriate.