Civil - Foundation Engineering - Site Investigation And Selection Of Foundation
SITE INVESTIGATION AND SELECTION OF FOUNDATION
1. What are the information obtained in general exploration?
Preliminary selection of foun.bndation type depth of water,
Depth, extent and composition of soil strata
Engineering properties required disturbed or partly disturbed
samples approximate values of strength and compressibility
2. Define significant depth?
Exploration depth, in general it should be carried out to a depth upto which increase in the pressure due to structural loading is likely to cause shear failure, such depth is known as significant depth. For footing, depth of exploration =1.5B
3. What are the types of soil samples?
Disturbed soil sample
Undisturbed soil sample
4. What is the difference between disturbed and undisturbed soil sample?
Disturbed soil sample
Natural structure of soils get partly or fully modified and destroyed
Undisturbed soil sample
Natural structure and properties remain preserved
5. What are the disadvantages of wash boring?
It is a slow process in stiff soil
It cannot be used effectively in hard soil, rocks ,etc.
6. What are design features that affect the sample disturbance?
Area ratio, inside clearance, outside clearance, inside wall friction, method of
7. What are the corrections to be applied to the standard penetration number?
? Overburden pressure
? Correction dilatancy correction
8. What are various methods of site exploration?
Open exacavation, borings, geophysical methods, sub-surface soundings
9. What are the methods of boring?
Auger borings, shell boring, wash boring, rotary boring, percussion boring.
10. Define area ratio?
Area ratio is defined as the ratio of maximum cross sectional area of the cutting edge to the area of the soil sample
11. Define liquefaction of sand?
The mass failure occurs suddenly, and the whole mass appears flow laterally as if it were a liquid such failure is referred to as liquefaction.
12. How will you reduce the area ratio of a sampler?
By increasing the size of the soil sample.
13. What is meant by a non- representative sample?
Name the laboratory tests that could be conducted on this sample.
Soil sample consists of a mixture of soil from different soil strata is called non- representative sample and the size of the soil grains and mineral constituents have changed.
14. Write the uses of Bore log Report.
(i) Used to record the change of layer’s depth.
(ii) Used to record the water level.
(iii)Used to record the water quality in deeper levels.
15. Define detailed exploration.
Detailed exploration follows as a supplement to general exploration when large engineering works, heavy loads, and complex and costly foundations are involved. A detailed exploration is meant to furnish information about soil properties such as shear strength, compressibility, density index, and permeability.
16.What are the limitations of hand augers in soil exploration?
1. Hand augers are not suitable for sands and gravels above the water table.
2. The sample is distributed and suitable for identification purposes only.
17. What are the guidelines in terms of inside clearance and outside clearance for obtaining undisturbed sample?
An undisturbed sample is that in which the natural structure and properties remain preserved. The inside clearance should lie between 1 to 3 percent and the outside clearance. The walls of the sampler should be smooth and should be kept properly oiled.
18. List the various methods of soil exploration techniques.
1. Pits and trenches
2. Boring a) augur boring b) wash or water boring c) rotary boring d) percussion boring
3. Geophysical methods a) seismic refraction b) electrical resistivity
4. Standard penetration test
5. Static cone penetration test
19. Write short notes on Augur boring.
An augur is a type of tool which is used for understanding the characteristics of the subsurface soil. Generally there are two types of augurs, a) Manually operated augur b) Mechanically operated augur
20. Define standard penetration number.
The number of blows required to penetrate 300 mm of the split spoon sampler beyond a seating drive of 150mm is known as penetration number (N).
21. List the various corrections to be carried out in SPT test.
The two corrections are
a) Dilatancy correction ( Silty sand)
b) Over burden pressure correction ( Granular soil)
22. What are the uses of soil exploration?
a) To select type and depth of foundation for a given structure
b) To determine the bearing capacity of the soil of the selected foundation c)
c) To investigate the safety of the existing structure
d) To establish ground water level
23. What is soil exploration?
The process of collection subsoil sample by an appropriate method to a needed
depth and check those samples for knowing the properties is called soil exploration.
24. List the different types of samplers.
a) Standard split spoon sampler
b) Shelby and thin walled tube sampler
c) Denison sampler
d) Piston sampler
e) Scraper bucket sampler
25. List the various parameters affecting the sampling disturbance.
a) Area ratio
b) Inside clearance
c) Outside clearance
d) Inside wall friction
e) Position of non return wall
f) Recovery ratio
g) Methods of applying force
26. Write the advantages of SCPT over SPT.
a) There is no need of hammering action, just pushing into the ground. b)
b) No need of bore holes, it is carried out on the ground
c) Engineering properties of the soil like permeability, Shear strength,
strength, Compressibility can be evaluated.
27. Write short notes on spacing of bore holes.
The spacing of bore holes depends upon the variation of subsurface soil in the horizontal direction. The factors influencing the spacing of bore holes are,
a) Type of soil
b) Fluctuation of water table
c) Load coming from structure
d) Importance of the structure.
e) Economical feasibility.