1. Piezocone Penetration
M R Selamat

2. Piezocone Machine

3. Piezocone Penetration (CPTU)
Advantage
- Able to carry out tests at depths and unlike in boring, on relatively undisturbed soils, cost effective
Disadvantage
- No samples retrieved, cannot penetrate hard layer or rock like boring can
Why?
- To gain a relatively quick information of soil to 30 m depth

4. Piezocone - CPTU Observe how soil changes with depth
Observe how soil resistances (skin and end) change with depth
Observe how water pressure changes with depth
Cannot get samples
Cannot do field tests (other than those done by the cone)

5. 35.6 mm
Sleeve
Cone

6. Sleeve Resistance = Sleeve Friction = fs
Cone Resistance = qc

7. Sleeve Resistance (Friction) corrected for pore pressure effects = ft
Cone Resistance corrected for pore pressure effects = qt
Friction Ratio = Rf = fs/qc = ft/qt = fs/qt

8. Sleeve (150 cm2)
Porous Stone (Filter Element)
Cone (600, 10 cm2)

9. Pore (water) Pressure = u

10. Pore Pressure Ratio = Du/(qt – svo)
Where:
Du = Excess pore (water) pressure = (u – u0)
u0 = In situ equilibrium (static) pore (water) pressure
svo = In situ total vertical stress = S(gihi)

11. Dissipation
U = Percentage Dissipation (Degree of Dissipation)
ut – u0
U = %
ui – u0
It is frequently recommended that Dissipation be continued to at least U = 50%
ut = u at time t
u0 = In situ equilibrium (static) pore (water) pressure
ui = Immediate (initial) in situ pore (water) pressure at t=0
ui = Up to 26 u0 in clays

12. Rate of Penetration
20 mm/s + 5 mm/s (International Society of Soil Mechanics and Foundation Engineering)
Depth interval between reading
>200 mm (ISSMFE)
10-50 mm (most system)
>20 mm (Norwegian Oil Company)
Saturation of piezocones
Filter, filter-transducer tubing, and transducer cavity must be saturated using silicon oil or glycerin
Calibration
Effects of temperature

13. Soil Description vs. Soil Classification
The description of soils as drilling progresses is not soil classification (such as USCS) but mere layman’s description such as: Sand, Yellow Sand, Clay, Clay and Sand, Yellow Clay, Dense Sand, Loose Sand, Stiff Clay, etc.
True soil classification is done when a sample has been subjected to lab tests and the results produced. Some examples of classification names are MH, SM etc.
A piezocone test also describes soils and appoint names but with another and different procedure, unlike in a drilling or in a soil test.

14. Soil Classification
CPT chart cannot be expected to provide accurate predictions based on USCS, ASSHTO etc
Charts of page 53, 54, 55, and 56
Coefficient of Consolidation
Ch versus t50 is given in page 79

15. SPT in Boreholes Names of Test: Standard Penetration Test, SPT
Data: Standard Penetration Test Number, SPT(N), Standard Penetration Resistance
Hammer Weight: 63.5 kg (140 lb)
Hammer Lift: 760 mm (30 in)
Dimensions of Sampling Tube: 35 mm inside diameter, 50 mm outside diameter, 650 mm length
Procedure: Number of blows per 75 mm advance is recorded for 6 consecutive advances starting at the bottom of a borehole. Numbers of blows of the last 4 advances (300 mm, 12 in, foot) are summed and is called SPT(N). Numbers of blows of the first two advances are discarded due to disturbance of the soil layer by washing and boring. Maximum number of blows per foot to record is 50.

16. How to get SPT(N) number
5.4 of MS1056
N30 is blows/30 cm
N60 is blows/30 cm assuming 60% hammer efficiency
Some demand blows/7.5 cm
Discard the blows of the first 15 cm (2x7.5)
Read blows for every 7.5 cm
So readings of 2, 3, 6, 7, 10, 19, 20 will give N30 = 42
Normally read taken for every 1.5 m interval

17. SPT(N) versus f correlation for cohesion-less soils (Old JKR Document)
SPT(N) versus f correlation for cohesion-less soils (Coyle and Castello, 1981)
SPT(N) versus f correlation for cohesion-less soils (Old JKR Document)

18. SPT(N) versus f correlation for cohesion-less soils (McCarty, David F, 1998)10 20 30 40 50 60 32 35 38 42

20. SPT(N)
c, kPa 2 4 8 15 30 14 25 50
100
200

21. SPT in Sand
Angle of Friction
Description
0 – 4
0 – 28 degree
Very Loose
4 – 10
20 – 30
Loose
10 – 30
30 – 36
Medium
30 – 50
36 – 41
Dense
> 50
> 41
Very Dense

22. SPT in Clay
Cohesion (c), kPa
Description
< 2
0 – 14
Very Soft
2 – 4
14 – 25
Soft
4 – 8
25 – 50
Medium
8 – 15
50 – 100
Stiff
15 – 30
100 – 200
Very Stiff
> 30
> 200
Hard

23. END