1. SEMBODAI RUKMANI VARATHARAJAN ENGINEERING COLLEGE DEPARTMENT OF CIVIL ENGINEERING FOUNDATION ENGINEERING BY KARTHIVELU

2. SITE INVESTIGATION & SELECTION OF FOUNDATION
Scope and objectives
Methods of exploration
Depth of boring – Spacing of bore hole
Sampling techniques
Penetration tests (SPT and SCPT)
Bore log report – Data interpretation
strength parameters and Liquefaction potential
Selection of foundation based on soil condition.

3. Site Investigation It decides suitability
construction material & method
It needs for
Efficient
Safe
Economic -design & construction
It involves
(i) Site reconnaissance
(ii) Site exploration

4. (i) Site Reconnaissance
Inspection of the site
Topographical features
Excavation, cutting
Quarry, escarpment
Water level in the well & stream
Evidence of erosion on land slides

5. (ii) Site Exploration Detailed information about
Occurrence & extant of soil & rock strata
Nature & engineering properties of soil & rock
Location & variation of ground water
Types:
General
Detailed

6. General Exploration
approximate picture of sub-soil condition (low cast) by test pits & boring, sub surface penetration & sounding and geophysical methods.
It gives
Depth, extent & composition of soil strata
depth of rock
Water level
Approximate strength & compressibility
Preliminary selection of foundation
Engineering properties by disturbed sample

7. Detailed Exploration For large engineering works
when heavy loads, complex & costly foundations involved
Soil properties- shear strength, compressibility, density index, permeability by testing undisturbed sample (lab) & by field test

8. Ground Water Level Important for deep foundation & water-logged areas
Identified by
Open well
Bore hole
Uncased- observation after Hr
Cased- casing raised to 30 cm & observed after 24 Hr

9. Depth Of Exploration
Significant depth: depth up to which the increase in pressure due to structural loading likely to cause perceptible settlement or shear failure.
Significant depth-
Net increase in vertical pressure <10% of initial
1 5 or of surface intensity press bulb of a isobar
to 2 times the width of loaded area

10. Depth Of Boring
1. Determine the net increase of stress, under a foundation with depth as shown in the Figure.
2. Estimate the variation of the vertical effective stress, ', with depth.
3. Determine the depth, D = D1, at which the stress increase  is equal to (1/10) q (q = estimated net stress on the foundation).
4. Determine the depth, D = D2, at which /' = 0.05.
5. Unless bedrock is encountered, the smaller of the two depths, D1 and D2, just determined is the approximate minimum depth of boring required. Table shows the minimum depths of borings for buildings based on the preceding rule.

11. For Hospitals And Office Buildings

12. Isolated spread footing or raft = 1 1 2 W
Pile foundation=10-30m, at least width of base structure
Retaining wall=greater of width of base height of 𝑠𝑡𝑒𝑚

13. Number & Spacing Of Holes
For small & less important building- one at centre
For 0.4 hectare building- one at each corner
For large area- penetration test at every 100m in grid pattern
For road- in z profile along centre line & pitch line at 100m (30m-500m)
For dam- at 50m spacing along one or both abutment top line in upstream side & few holes in down line

14. Approximate Spacing of Boreholes
There is strict rules for spacing of bore holes.
The above values can be changed by considering the subsoil condition

15. Method Of Site Exploration
Open excavation
Boring
Sub surface sounding
Geophysical method

17. Open Excavation Pits & trenches
Suitable for shallow depth (3m) & all type of soil
Lateral support requires when depth increases or water exists
Cost increases with depth

18. Boring For more depth Methods Auger boring Auger & shell boring
Wash boring
Percussion boring
Rotary boring

19. Post hole Auger Helical Auger
(i) Auger Boring
Suitable in cohesive & soft soil
Highly disturbed sample
Used in highway projects
Type
Hand operated upto 6m
Mechanically operated more than 6m
Post hole Auger Helical Auger

23. (ii) Auger & Shell Boring
Suitable for soft to stiff clay
Undisturbed sample
For stiff & hard clay – shell
For sandy soil – sand pump
For rock – chisel pit with drill rod
Types
Hand operated- upto 25m
Mechanically operated–upto 50m
Generally hole requires casing
Sand Pump

24. (iii) Wash Boring Simple & fast method
Suitable for all type of soil other than boulders & rock
Drill rod is raised & dropped & also rotated - chopping
Water is forced under pressure - jetting
Soil stratification guessed by colour of wash water & rate of progress

25. (iv) Percussion Boring
Suitable for soil & rock
Heavy chisel or pit suspended by cable or drill rod
Water is added if not present
Slurry is bailed out in interval
Disturbed sample

26. (v) Rotary Boring Very fast method Suitable in soil & rock
A drill pit fixed to lower end of the drill rod & rotated (lowered continuously)
Water solution of bentonite forced in to the hollow drill rod
Returning water contains the cuttings
Usually no casing requires

28. Water solution of bentonite inside the drill rod
Slurry of solution & broken rock
casing
Drill pit