This document provides information on three common penetration tests: Standard Penetration Test (SPT), Static Cone Penetration Test (SCPT), and Dynamic Cone Penetration Test (DCPT). It describes the procedures, equipment, corrections, and correlations with engineering properties for each test. The SPT is the most commonly used test and provides data on density and strength. The SCPT gives continuous resistance measurements with depth. The DCPT is fast and inexpensive but resistance values must be correlated to SPT results. Each test has advantages and limitations depending on the soil type and project needs.

1. MODULE 3
SOUNDING AND PENETRATION
TESTS

2. SYLLABUS
• Sounding methods Standard Penetration Test – Procedure –corrections to be applied to
observed N values – Procedure for estimation of representative average N value –
Numerical examples - Factors influencing the SPT results and precautions to obtain
reliable results – Merits/drawbacks of the test – Correlations of N value with various
engineering and index properties of soils
• Static Cone Penetration Test – Procedure – Merits/drawbacks –Correlation of static CPT
results with soil properties
• Dynamic Cone Penetration Test – Procedure – Merits/drawbacks –Critical comparison of
SPT, static CPT and dynamic CPT

3. INTRODUCTION
• Subsurface soundings are used for exploring soil strata of an erratic nature
• Useful for determining
The presence of any soft pockets between drill holes
Density index of cohesionless soils
The consistency of cohesive soils at various desired depth
• Methods of sounding normally consists of driving or pushing a standard sampling
tube or a cone

4. • The devices used – penetrometers as they penetrate the subsoil with a view to
measuring the resistance to penetration of soil strata
• Thereby identifying the engineering properties
• Necessary field test are called penetration tests. Major tests are
1. Standard Penetration Test (SPT) – a sampler is used to penetrate soil
2. Static Cone Penetration Test (SCPT)
3. Dynamic Cone Penetration Test (DCPT)
Cone is used to penetrate soil
Static and Dynamic – mode of penetration
INTRODUCTION

5. STANDARD PENETRATION TEST
• Most commonly used in-situ test
• Especially suited for cohesionless soil as a correlation has been established b/w
SPT value and the angle of internal friction of the soil
• Extremely useful in
 determining relative density, angle of shearing resistance for cohesionless soil
 unconfined compressive strength of cohesive soil

6. APPARATUS AND PROCEDURE
• IS: 2131 – 1963
• SPT is done in a borehole using a standard split spoon sampler
• STEP 1: when the borehole is drilled to required depth , the drilling tools are
removed and the sampler is lowered to the bottom of the hole.
• STEP 2: The sampler is driven into the soil by a drop hammer of 63.5kg mass and
falling through a height of 750 mm at the rate of 30 blows per minute

7. APPARATUS AND PROCEDURE

8. APPARATUS AND PROCEDURE
• STEP 3: The number of blows required to penetrate 150 mm of the sample is
counted (N1).
• STEP 4: The sample is further driven 150 mm and the number of blows are
recorded (N2).
• STEP 5: Likewise, the sampler is once again driven by 150 mm and the number of
blows are recorded (N3).
• STEP 6: The number of blows for the first 150mm are ignored as those are
required for the seating drive. The number of blows required for the next 300mm of
the penetration is recorded as the SPT value

9. APPARATUS AND PROCEDURE
• The Standard Penetration Number is equal to the number of blows required for 300
mm penetration after a seating drive of 150 mm
• N = N2+ N3
• Note:
• If the number of blows for 150 mm drive exceeds 50, it is taken as refusal and
the test is discontinued
• The standard penetration number should be corrected for dilatancy correction
and overburden correction

10. CORRECTIONS FOR STANDARD PENETRATION NUMBER
a) Overburden Pressure Correction
• In granular soils, the over burden pressure affects the penetration resistance.
• Confining pressure in cohesion less soil increases with the depth
• If two soils having same relative density but different confining pressure are
tested, the one with higher confining pressure gives higher Penetration Number
• The Penetration number of soils at shallow depth is under estimated and and at
greater depth is over estimated

11. CORRECTIONS FOR STANDARD PENETRATION NUMBER
a) Overburden Pressure Correction
• For uniformity, the N values obtained from field tests under different effective
overburden pressure are corrected to a standard effective over burden pressure
• Gibbs and Holtz (1957)

12. CORRECTIONS FOR STANDARD PENETRATION NUMBER
b) Dilatancy Correction
• Silty fine sand and fine sand below WT develop pore water pressure
which is not easily dissipated
• pore pressure increases the resistance of the soil and hence
Penetration Number also increases
• This correction is applied when N > 15

13. CORRECTIONS FOR STANDARD PENETRATION NUMBER
b) Dilatancy Correction
The corrected Penetration Number (Nc),

14. CORRELATION OF N VALUES WITH ENGINEERING
PROPERTIES
• The N value depends upon the density of cohesion less soil and the unconfined
compressive strength of cohesive soils
• If the soil is compact or stiff, the N value is high
• The angle of shearing resistance (Φ) of cohensionless soil depends on N value. In
general, greater the N value, greater is the angle of shearing resistance
• The consistency and unconfnied shear strength of cohesive soils can be
approximately determined from N value

15. CORRELATION OF N VALUES WITH ENGINEERING
PROPERTIES
• The N value depends upon the density of cohesion less soil and the unconfined
compressive strength of cohesive soils
• If the soil is compact or stiff, the N value is high
• The angle of shearing resistance of cohensionless soil depends on N value. In
general, greater the N value, greater is the angle of shearing resistance
• The consistency and unconfnied shear strength of cohesive soils can be
approximately determined from N value

16. CORRELATION OF N VALUES WITH ENGINEERING
PROPERTIES
Sl.no Condition N Dr Φ
1 Very Loose 0-4 0-15% <28˚
2 Loose 4-10 15-35% 28˚-30˚
3 Medium 10-30 35-65% 30˚-36˚
4 Dense 30-50 65-85% 36˚-42˚
5 Very Dense >50 >85% >42˚
Correlation between N, Dr and Φ

17. CORRELATION OF N VALUES WITH ENGINEERING
PROPERTIES
Sl.no Consistency N qu (kN/m2)
1 Very Loose 0-2 <25
2 Soft 2-4 25-50
3 Medium 4-8 50-100
4 Stiff 8-15 100-200
5 Very Stiff 15-30 200-400
6 Hard >30 >400
Correlation between N and qu (clays)

18. FACTORS INFLUENCING SPT RESULTS

19. FACTORS INFLUENCING SPT RESULTS

20. FACTORS INFLUENCING SPT RESULTS

21. FACTORS INFLUENCING SPT RESULTS

22. PRECAUTION TO OBTAIN RELIABLE RESULTS

23. PRECAUTION TO OBTAIN RELIABLE RESULTS

24. ADVANTAGES

25. ADVANTAGES

26. DISADVANTAGES

27. DISADVANTAGES

28. STATIC CONE PENETRATION TEST (DUTCH CONE
TEST)
• Standardised by ISI and given in IS 4968 (Part III) – 1976 – Method for
subsurface sounding for soil.
• Most successful in soft or loose soils like silty sands, loose sands, layered deposits
of sands, silts and clay as well as in clayey deposits.
• Experience indicates that a complete static cone penetration test up to depth of 15
to 20m can be completed in a day with manual operations of the equipment,
making it an inexpensive method of investigation

29. STATIC CONE PENETRATION TEST (DUTCH CONE
TEST)

30. APPARATUS and PROCEDURE
• Apparatus
• consist of a steel cone, a friction sleeve, sounding
rod, a driving mechanism and a measuring
equipment
• The dutch cone has an apex angle of 60º and an
overall diameter of 35.7mm, giving an end area of
10 cm2

32. APPARATUS and PROCEDURE
• Procedure
STEP 1: for obtaining cone resistance, the cone is pushed downward at a steady
rate of 10mm/sec through a depth of 35 mm each time. The cone is pushed by
applying thrust and not by driving.(Qc)
STEP 2: After cone resistance has been determined, cone is withdrawn.
STEP 3: The sleeve is pushed onto the cone and both are driven into the soil and
the combined resistance is also determined (Qt)
STEP 4: The resistance of the sleeve alone is obtained by subtracting the cone
resistance from the combined resistance

33. STATIC CONE PENETRATION TEST RESULTS
• Cone penetration resistance qc = Qc/Ac
Where Qc = Total driving force acting on the cone
Ac = base area of the cone
• Sleeve friction resistance, qf = Qf/Af
Where Qf = force required to push the friction sleeve
Qf = Qt – Qc
Qt = total force required to push the cone and friction sleeve together
Af = surface area of the friction sleeve

34. STATIC CONE PENETRATION
FRICTION RATIO
• The ratio between sleeve friction and tip resistance, measured as a percentage
• Friction ratio (Rf) = qf / qc
Where qf = sleeve friction
qc = point cone resistance
• Measured at the same depth

35. STATIC CONE PENETRATION
FRICTION RATIO

36. CORRELATION OF CPT VALUES TO ENGINEERING
PROPERTIES
• If cone penetration results are related to the SPT number N, indirect correlations
are obtained between the cone test results and the engineering properties of soil
• Correlation b/w Point Resistance of Cone (qc) And SPT Value N
Type of soil qc (kN/m2)
Gravels 800N to 1000N
Sands 500N to 600N
Silty Sands 300N to 400N
Silty & clayey silts 200N

37. CORRELATION OF CPT VALUES TO ENGINEERING
PROPERTIES
• Approximate relationship b/w relative density of fine sand, SPT, the static cone
resistance and the angle of internal resistance
State of sand N Dr qc (kN/m2) Φ
Very Loose 0-4 0-15% <2000 <28˚
Loose 4-10 15-35% 2000 - 4000 28˚-30˚
Medium 10-30 35-65% 4000 - 12000 30˚-36˚
Dense 30-50 65-85% 12000 - 20000 36˚-42˚
Very Dense >50 >85% >20000 >42˚

38. ADVANTAGES
• CPT gives a continuous record of variation of both cone resistance and friction
resistance with depth
• Unlike SPT and DCPT, this test measures static resistance of the soil
• Data from CPT is often used to estimate the point bearing resistance and skin
friction resistance of a pile foundation and length of pile
• In granular soils, correlation has been established b/w qc and N

39. DISADVANTAGES

40. DYNAMIC CONE PENETRATION TEST(DCPT)
• Standardised by ISI and given in IS:4968
(Part I) -1976 –Method for subsurface
sounding for soil.
• The equipment consists of a cone, driving
rods, driving heads, hoisting equipment and
a hammer.
• The number of blows for driving the cone
through a specified distance is a measure of
dynamic cone resistance

41. DYNAMIC CONE PENETRATION TEST(DCPT)
Procedure
• The test is conducted by driving the cone by blows of hammer.
• Tests are performed either using a 50 mm cone without bentonite slurry or by using
a 65 mm cone with bentonite slurry (when depth>6m)
• When bentonite slurry is used the set up should have arrangements for circulating
slurry so that friction on the driving rod is eliminated

42. DYNAMIC CONE PENETRATION TEST(DCPT)
Procedure
• The driving energy is given by a hammer of 65 kg falling through a height of
750mm
• The number of blows for every 100 mm is recorded
• The number of blows required for 300 mm of penetration is taken as the dynamic
cone resistance (Ncbr)
• If the skin friction is to be eliminated, the test is conducted in a cased borehole

43. CORRELATION OF Ncbr WITH SPT NUMBER (N)
When 50 mm diameter cone is used
Ncbr = 1.5N for depth < 3m
Ncbr = 1.75N for depth b/w 3m and 6m
Ncbr = 2.0N for depth >6m

44. CORRELATION OF Ncbr WITH SPT NUMBER (N)
When 65 mm diameter cone is used with bentonite slurry
Ncbr = 1.5N for depth < 4m
Ncbr = 1.75N for depth b/w 4m and 9m
Ncbr = 2.0N for depth >9m
• The above relations are applicable for medium to fine sand

45. ADVANTAGES

46. DISADVANTAGES

47. COMPARISON
Parameter SPT SCPT DCPT
Borehole Required Not required Not required
Soil type Cohesive and cohesionless
soil
Clayey deposits Gravels and dense sand