1. SOIL MECHANICS AND FOUNDATION ENGINEERING-II (CE 311)

2. SAMPLERS AND SAMPLING TECHNIQUES
Generally Samples are collected from bore holes at depth intervals of 1.5m and whenever there is change of soil type observed.
The SAMPLES obtained are varying in the degree of DISTURBANCE they suffer in the process of sampling.

3. TYPES OF SOIL SAMPLES UNDISTURBED SAMPLES: DISTURBED SAMPLES:
In which care is taken to cause minimal disturbance to the density, structure and water content of the soil.
Obtained by carefully designed SAMPLERS.
Can be tested in the LAB to determine both the physical and engineering properties.
DISTURBED SAMPLES:
In which care is taken to ensure that at least the composition of the soil remains unaltered.
Obtained by more rugged but relatively crude.
Can be used to determine mineralogy, grain size distribution and Liquid Limit and Plastic Limits.

4. TYPES OF SOIL SAMPLES (Contd.)
DISTURBED NON-REPRESENTATIVE SAMPLES:
These are not obtained by samplers but are recovered during drilling operation.
They give broad idea of the soil type but can not be used for laboratory testing.

5. TYPE OF SOIL SAMPLERS PISTON SAMPLERS FOIL SAMPLERS
OPEN DRIVE SAMPLERS

6. PISTON SAMPLERS
thin-walled metal tubes which contain a piston at the tip
pushed into the bottom of a borehole, with the piston remaining at the surface of the soil while the tube slides past it
Used for undisturbed samples from soft soils, but are difficult to advance in sands and stiff clays, and can be damaged if gravel is encountered
Livingstone corer is a commonly used piston sampler

7. FOIL SAMPLERS Primarily used for sampling of cohesive soils
Uniquely adapted for sampling of thinly stratified soil and for very soft and semi-liquids soils which frequently occur at harbour bottom

8. OPEN DRIVE SAMPLERS
Called open drive because at the leading end, it is open and soil enters through it.
Cutting edge at leading end
Pushing sampler into the ground displaces the soil of equal volume of the metal of the sampler.
Thicker the volume of metal, greater shall be the disturbance.
Area Ratio (Ar) represents the ratio of soil volume that has to be displaced to the sampled volume.
The displacement of soil either in the sample or outside
OUTSIDE DISTURBANCE is always better

9. Types of OPEN DRIVE Samplers
THIN WALL SAMPLERS
THICK WALL SAMPLERS
COMPOSITE SAMPLERS
SAMPLER WITH CORE CATCHER

10. THIN WALL SAMPLERS
Made up of SEAMLES steel tube and cutting edge is and integral part.
Used when least disturbance needed i.e. undisturbed samples are obtained
Area ratio is 10%
After sampling, the barrel is separated from the head
Then both ends are dipped in molten wax
Placed along length in the laboratory
Cut along its length to give minimum disturbance

11. THICK WALL SAMPLERS
Most Common type of samplers known as SPLIT SPOON SAMPLER
It splits into two halves longitudinally
The soil sample obtained is DISTURBED but Representative

12. COMPOSIT SAMPLERS It is also thick wall sampler
Its barrel is so shaped that a number of liners fit in it.
After the sampling operation, the liners are pushed out of the barrel; the soil remains in the barrel
Samples obtained are DISTURBED Representative

13. IN-SITU FIELD TESTING PENETRATION TESTS GROUND WATER OBSERVATIONS
Standard Penetration Test
Static Cone Penetration Test
GROUND WATER OBSERVATIONS
PERMEABILITY TESTS

14. STANDARD PENETRATION TEST (SPT)
Split spoon sampler is driven by the impact of a hammer under standardized test conditions
We measure number of blows required to achieve a standard amount of penetration.
Sample obtained is UNDISTURBED
Constant energy imparted by each blow is that of 650 N weight falling freely from a height of 750 mm.
The blow count (N) noted down
Where N is number of blows required to push the split spoon sampler from a penetration depth of 150 mm – 450 mm.

15. Factors affecting SPT N Values
Efficiency of Mechanism
Diameter of borehole
The size of the rod to which split spoon sampler is attached
Location of the water table
etc.
BUT the CODES OF PRACTICE do not give correction due to above factors

16. Correction to the N-value
As per the practice, the CODES give following TWO factors for which correction in the N-values should be made.
These are influence of DILATENCY and of OVERBURDEN
OVERBURDEN CORRECTION:
A soil have same c & f will exhibit more strength if it is located deep in the ground.
N´=CN Nobs

17. Correction to the N-value
DILATENCY CORRECTION:
In saturated condition, the impact load gives undrained conditions and develops pore water pressure.
In loose soil, N´ value < 15, positive pore pressure develops thus effective stress decreases: NO CORRECTION IS APPLIED
In dense soil, N´ value >15, negative pore pressure develops thus effective stress increases: CORRECTION IS APPLIED
𝑁´´=15+ (𝑁´−15) 2

18. Problems
An SPT was conducted at a depth of 2m in a sand deposit with a unit weight of 20kN/m3. The water table at this site was 1m below ground level. The N value was observed to be 5. What would be corrected N value?
At the site in Problem 1, the SPT conducted at 15m below ground surface gives N observed as 21. What would be the corrected N-value.
At a site the soil has a unit weight of 18 kN/m3 and the water table is at a depth of 6m. The observed N-values at the site were as follows:
Depth (m)
Nobs
Determine the magnitude and corrected N-values i.e. N“.

19. STATIC CONE PENETRATION TEST (SCPT)
MECHANICAL CONE
ELECTRICAL CONE

20. Electrical Static Cone Penetration Test (ESCPT)
The consists of pushing a standard sized cone having diameter of 35.6 mm with a taper angle 60° into the soil at a rate of 10 to 20 mm/sec
As cone penetrates into the ground, the cone tip resistance, qC and the friction one the sleeve, fC is vey useful for the design of foundations especially piles

21. Comparison of the SPT and ESCPT
PARAMETER
SPT
ESCPT
Nature of load
Impact
Static
Resistance Measured
Dynamic
Frequency of measurement
At intervals
Continuous
Conducted in the Bore Hole
Yes No
Affected by disturbance caused
Skill required to conduct test
Low
High
Utility of Data
More for Shallow Foundation
More for Deep Foundation

22. Presenting Results of Site Investigations
FOUR PARTS:
The Project: Nature of Civil Engineering Work
Results of Site Investigation: Nature of the site, the soil profile and the properties of the soil.
Possible Solution and Analysis: which describes alternative solutions that you have considered and the analysis you conducted to characterize merits of each alternative.
Recommendations: which presents the solution you propose with details of required design parameters.