(SEM V) THEORY EXAMINATION 2019-20 GEOTECHNICAL ENGINEERING

GEOTECHNICAL ENGINEERING (RCE-501)

B.Tech (SEM-V) – AKTU

SECTION A

(Attempt all questions – 2 × 7 = 14 marks)

Q1 (a) Explain index properties of soil.

Index properties are basic properties of soil used for identification and classification. These include water content, specific gravity, void ratio, porosity, degree of saturation, consistency limits, and particle size distribution. Index properties help in understanding soil behavior and engineering suitability.

Q1 (b) What are the basic structural units of clay minerals?

The basic structural units of clay minerals are silica tetrahedra and alumina octahedra. These units combine to form different clay minerals such as kaolinite, illite, and montmorillonite, which influence soil plasticity and strength.

Q1 (c) List the factors affecting permeability of soils.

Permeability of soil depends on grain size, void ratio, soil structure, degree of saturation, viscosity of water, and presence of impurities. Coarse-grained soils generally have higher permeability than fine-grained soils.

Q1 (d) Define critical hydraulic gradient.

Critical hydraulic gradient is the hydraulic gradient at which upward seepage force equals the submerged weight of soil, causing soil particles to lose effective stress and leading to boiling or quick condition.

Q1 (e) Differentiate between compression index and expansion index.

Compression index represents the slope of virgin compression curve and indicates soil compressibility under load. Expansion index represents the slope of swelling curve during unloading and indicates rebound characteristics of soil.

Q1 (f) What are the different types of slope failure?

Slope failures include rotational failure, translational failure, wedge failure, and flow failure. These failures depend on soil type, slope geometry, and water conditions.

Q1 (g) Describe various types of pile foundation.

Pile foundations are classified as end-bearing piles, friction piles, combined piles, sheet piles, and compaction piles. They transfer loads to deeper soil layers and are used where shallow foundations are unsuitable.

SECTION B

(Attempt any three – 7 × 3 = 21 marks)

**Q2 (a) Prove that dry unit weight of soil is

γᵈ = (Gs γw) / (1 + e)**

Dry unit weight is defined as weight of solids per unit volume of soil mass.
Using relationship between void ratio, specific gravity, and unit weights, the expression is derived showing that dry unit weight depends on specific gravity and void ratio. This formula is useful in compaction and field density calculations.

Q2 (b) Explain effective stress principle.

Effective stress principle states that total stress in soil is shared by soil particles and pore water pressure. Effective stress governs soil strength, deformation, and permeability. Mathematically, effective stress is equal to total stress minus pore water pressure.

Q2 (c) Explain consolidation of soil.

Consolidation is the gradual reduction in volume of saturated soil due to expulsion of pore water under sustained load. It occurs in stages: immediate settlement, primary consolidation, and secondary consolidation.

SECTION C

(Attempt any two – one from each unit, 7 × 2 = 14 marks)

Q4 (a) A granular soil deposit is 7 m deep over an impermeable layer. Plot variation of stresses with depth.

Total stress increases linearly with depth due to soil weight.
Pore water pressure depends on water table position and capillary rise.
Effective stress is obtained by subtracting pore water pressure from total stress. Variation shows effective stress reduces near water table and increases below it.

Q5 (a) Describe Standard Proctor test and Modified Proctor test.

Standard Proctor test determines optimum moisture content and maximum dry density using light compaction effort. Modified Proctor test uses higher compaction energy and is suitable for heavily loaded structures. Both tests help in field compaction control.

Q6 (a) Explain Skempton’s pore pressure parameters in detail.

Skempton’s pore pressure parameters A and B relate pore water pressure changes to applied stress. Parameter B indicates degree of saturation, while parameter A depends on soil type and stress conditions. These parameters are important in undrained soil analysis.