Sub Grade Soil (Code: 443)
1. What is the levelled surface of earth or rock that supports a foundation called?
The sub-grade is the prepared and levelled surface of natural earth (soil) or rock that forms the foundation for a structure, such as a road pavement or a building's foundation. It's the layer that ultimately supports all the loads imposed upon it.
2. What does the sub-grade refer to in transport engineering?
In transport engineering, the sub-grade specifically refers to the in-situ or native soil that lies beneath the constructed layers of a road, pavement, or railway. The performance of the entire structure heavily depends on the strength and stability of this underlying sub-grade.
3. What is the term for the relative proportions of solid particles, water, and air voids in soil?
The soil phase system is the conceptual model used in soil mechanics to represent soil as a three-phase material. It illustrates the relative proportions and relationships between the three phases: solid particles, water, and air, by volume and weight.
4. What is the term for the ratio of the volume of voids to the volume of solids in soil?
The void ratio (e) is a fundamental property that defines the volume of voids (spaces filled with air and/or water) relative to the volume of the solid particles in a soil mass. It's a key indicator of the denseness or looseness of a soil, expressed as \(e = \frac{V_{voids}}{V_{solids}}\).
5. What is the term for the percentage of voids occupied by water in soil?
The degree of saturation (S) represents how much of the void space in a soil is filled with water. It is expressed as a percentage: \(S = (\frac{V_{water}}{V_{voids}}) \times 100\%\). A completely dry soil has S=0%, and a fully saturated soil has S=100%.
6. What is the term for the ratio of the volume of air to the volume of voids in soil?
The air content ($a_c$) is the ratio of the volume of air voids to the total volume of voids in a soil mass. It represents the proportion of the void space that is occupied by air. Note that Air Content + Degree of Saturation = 1 (or 100%).
7. What is the term for the ratio of the volume of air to the total volume of soil?
The percentage air voids ($n_a$) is the ratio of the volume of air voids to the total volume of the soil mass, expressed as a percentage. This differs from air content, which is relative to the volume of voids only.
8. What is the term for the mass of water per unit volume of soil?
Water content (w), or moisture content, is defined as the ratio of the mass (or weight) of water to the mass (or weight) of the solid particles in a soil sample. It is usually expressed as a percentage (\(w = \frac{W_w}{W_s}\)).
9. What is the term for the weight of soil per unit volume of soil?
Unit weight ($\gamma$) is the standard term in geotechnical engineering for the weight of a soil per unit of its total volume. It can be bulk unit weight, dry unit weight, or saturated unit weight depending on the soil's condition.
10. What is the term for the ratio of the weight of soil solids to the weight of an equal volume of distilled water at 4°C?
The specific gravity of soil solids ($G_s$) is the ratio of the weight of a given volume of soil solids to the weight of an equal volume of distilled water at 4°C. It is a dimensionless quantity indicating how much heavier the soil particles are than water.
11. What is the term for the ratio of the weight of solids per unit of total volume?
The dry unit weight ($\gamma_d$) represents the weight of only the solid particles within a soil mass divided by the total volume of that mass (solids + voids). It is a key measure of how densely the solid particles are packed.
12. What is the term for the ratio of the total weight of soil mass per unit volume?
The bulk unit weight ($\gamma$), also known as total unit weight or moist unit weight, is the total weight of a soil mass (solids + water) divided by its total volume. This is the unit weight of the soil in its natural state.
13. What is the term for the ratio of the total weight of saturated soil mass per unit volume?
The saturated unit weight ($\gamma_{sat}$) is the bulk unit weight of a soil when all its voids are completely filled with water (i.e., the degree of saturation is 100%).
14. What is the size range of silt particles according to the Indian Soil Classification System (ISCS)?
According to the Indian Soil Classification System (ISCS), soil particles are classified as silt if their size falls within the range of 0.002 mm to 0.075 mm.
15. What is the size range of fine sand particles according to the Indian Soil Classification System (ISCS)?
According to the Indian Soil Classification System (ISCS), sand is classified as fine sand if its particle size is in the range of 0.075 mm to 0.425 mm.
16. What is the size range of medium sand particles according to the Indian Soil Classification System (ISCS)?
According to the Indian Soil Classification System (ISCS), sand is classified as medium sand if its particle size is in the range of 0.425 mm to 2 mm.
17. What is the size range of coarse sand particles according to the Indian Soil Classification System (ISCS)?
According to the Indian Soil Classification System (ISCS), the correct size range for coarse sand is 2 mm to 4.75 mm.
18. What is the size range of gravel particles according to the Indian Soil Classification System (ISCS)?
According to the Indian Soil Classification System (ISCS), particles are classified as gravel if their size is larger than 4.75 mm. Among the given options, >2 mm is the best choice, as it correctly places gravel as being larger than sand.
19. What is the term for the minimum water content at which soil flows under its own weight?
The liquid limit (LL) is the minimum water content at which a fine-grained soil will begin to flow like a liquid. It represents the boundary between the plastic and liquid states of the soil.
20. What is the term for the minimum water content at which soil can be rolled into a 3 mm diameter thread without breaking?
The plastic limit (PL) is the minimum water content at which a fine-grained soil can be rolled into a thread of 3 mm diameter without crumbling. It represents the boundary between the semi-solid and plastic states.
21. What is the term for the water content at which soil stops shrinking when dried further?
The shrinkage limit (SL) is the specific water content below which a soil will no longer decrease in volume as it dries. At this point, the soil particles are in their closest possible packing.
22. What is the term for the range of water content in which soil behaves plastically?
The plasticity index (PI) is the range of water content over which a soil exhibits plastic behaviour. It is calculated as the difference between the liquid limit and the plastic limit: \(PI = LL - PL\).
23. Match the following:
List I:
A. Well-graded gravels or gravel-sand mixtures with little or no fines
B. Well-graded gravel or gravel-sand mixtures with clay binder
C. Silty-graded or poorly graded gravel-sand silt
D. Clayey gravels poorly graded gravel-sand-clay mixtures
List II:
1. GC
2. GM
3. GW
Codes:
The correct matching is:
A. Well-graded gravels...with little or no fines is GW (3).
B. Well-graded gravel...with clay binder is GC (1).
C. Silty-graded...gravel-sand silt is GM (2).
D. Clayey gravels... is GC (1).
24. Match the following:
List I:
A. Poorly graded gravels or gravel sand mixtures with little or no fines
B. Well-graded sand or gravelly sands with clay binder
C. Well-graded sand or gravelly sands with little or no fines
D. Clayey sand, poorly sand-clay mixtures
List II:
1. SW
2. SC
3. GP
Codes:
The correct matching is:
A. Poorly graded gravels... is GP (3).
B. Well-graded sand...with clay binder is SC (2).
C. Well-graded sand...with little or no fines is SW (1).
D. Clayey sand... is SC (2).
25. Match the following:
List I:
A. Silty sands or poorly graded gravel-sand silt
B. Poorly graded sands or gravel sands with little or no fines
C. Silt and very fine sand; rock flour, silty to clayey fine sands with low plasticity
D. Gravelly clays, sandy clays, silty clays, lean clays of low plasticity
List II:
1. SP
2. ML
3. SM
4. CL
Codes:
The correct matching is:
A. Silty sands... is SM (3).
B. Poorly graded sands...with little or no fines is SP (1).
C. Silt and very fine sand...with low plasticity is ML (2).
D. ...clays of low plasticity is CL (4).