(SEM VI) THEORY EXAMINATION 2022-2023 FOUNDATION DESIGN

FOUNDATION DESIGN (KCE-064)

Important Questions & Answers – Section-wise

SECTION A

(Attempt all questions – 2 × 10 = 20 marks)

a. Factors affecting bearing capacity of soil

The bearing capacity of soil depends on soil type, cohesion, angle of internal friction, unit weight of soil, depth of foundation, size and shape of footing, position of water table, and loading conditions. Proper assessment of these factors ensures safe foundation design.

b. Different types of samplers

Samplers are classified as disturbed and undisturbed samplers. Disturbed samplers include split spoon sampler, while undisturbed samplers include thin-walled Shelby tube and piston samplers used for accurate laboratory testing.

c. Major criteria for foundation design

Foundation design must satisfy safety against shear failure, permissible settlement limits, and structural stability under applied loads. Economy and constructability are also important considerations.

d. Pressure bulb

A pressure bulb is the zone of soil below a foundation that is affected by applied loads. The intensity of stress decreases with depth and lateral distance from the footing.

e. Disturbed vs Undisturbed samples

Disturbed samples lose natural structure during sampling, while undisturbed samples retain original soil structure and moisture content, making them suitable for strength and compressibility tests.

f. Efficiency of pile

Pile efficiency is the ratio of load carrying capacity of a pile group to the sum of individual pile capacities. It depends on pile spacing, arrangement, and soil type.

g. CURB in well foundation

Curb is the cutting edge at the bottom of a well foundation. It facilitates sinking by cutting soil and providing a sharp edge for smooth penetration.

h. Shapes of well foundation

Well foundations may be circular, rectangular, double-D, dumbbell, or twin wells depending on load and site conditions.

i. Soil stabilization

Soil stabilization is the process of improving soil properties such as strength and durability by mechanical compaction or chemical additives like lime, cement, or bitumen.

j. Soil reinforcement

Soil reinforcement improves soil strength by introducing tensile elements such as geotextiles, metal strips, or geogrids to resist tensile stresses.

SECTION B

(Attempt any THREE – 10 × 3 = 30 marks)

Q2(a) Site investigation and stages of sub-surface exploration

Site investigation determines soil conditions for safe foundation design. Stages include desk study, site reconnaissance, preliminary exploration, detailed soil investigation, laboratory testing, and preparation of soil report.

Q2(b) Circular footing bearing capacity (Numerical)

Given footing diameter, soil parameters, depth, and bearing capacity factors, ultimate bearing capacity is calculated using Terzaghi’s equation for circular footing. Factor of safety is obtained by dividing ultimate bearing capacity by applied pressure.

(In exam, write formula → substitute values → final answer clearly)

Q2(c) Design of precast concrete pile (Numerical)

Pile capacity is calculated considering skin friction using adhesion factor and pile surface area. Required pile length is determined by equating safe load to allowable capacity with given factor of safety.

Q2(d) Well sinking and control measures

Well sinking is the process of lowering a well foundation to required depth. Control measures include kentledge loading, water jetting, soil dredging, air jetting, and correction of tilt using eccentric loading.

Q2(e) Geotextiles for filtration and drainage

Geotextiles act as filters allowing water to pass while retaining soil particles. They also provide drainage paths, prevent clogging, and enhance stability in embankments and foundations.

SECTION C

Q3(a) Boring methods for soil exploration

Boring methods include auger boring, wash boring, percussion boring, and rotary drilling. Each method is selected based on soil type, depth, and accuracy required.

Q3(b) Seismic refraction method

Seismic refraction determines soil layer depth by measuring wave travel time. It is useful for rock depth estimation but is limited in layered soils with irregular profiles.

Q4(a) Strip footing bearing capacity (Numerical)

Ultimate bearing capacity is calculated using Terzaghi’s equation for strip footing considering cohesion, surcharge, and bearing capacity factors.

Q4(b) Effect of water table on bearing capacity

Net ultimate bearing capacity is computed using Terzaghi’s method by adjusting unit weight of soil based on water table position relative to footing base.

Q5(a) Pile group capacity (Numerical)

Allowable load on pile group is calculated by comparing individual pile capacity and block failure capacity, and the lesser value is adopted.

Q5(b) Types of pile foundation

Piles are classified as end bearing, friction, compaction, tension, sheet, and batter piles based on structural behavior.

Q6(a) Methods to control tilts in well foundations

Tilts are corrected using eccentric loading, water jetting, pulling techniques, and soil excavation. These methods restore vertical alignment.

Q6(b) Shapes and components of well foundation

Well foundations consist of curb, steining, bottom plug, sand filling, and top plug. Shapes include circular, rectangular, and twin wells.

Q7(a) Advantages and types of soil reinforcement

Soil reinforcement increases bearing capacity, reduces settlement, and improves slope stability. Types include geotextiles, geogrids, and metallic strips.

Q7(b) Applications of soil reinforcement

Soil reinforcement is used in retaining walls, embankments, road subgrades, slope stabilization, and foundation improvement.