1. Site exploration and characterization
structural engineers know the engineering properties (strength, modulus of elasticity, etc.) of the material (steel, concrete) they are working with, based on the material they are using.
however, geotechnical engineers work with soil, which is a natural material with unknown engineering properties.
thats why geotechnical engineers spend most of their time identifying the types of soils on a site and evaluating their engineering properties (i.e. strength, consolidation characteristics, compaction characteristics, hydraulic conductivity etc.)

2. Site Exploration
The elements of a site investigation generally should provide the following:
Information to determine the type of foundation required (shallow or deep)
Information to allow the geotechnical consultant to make a recommendation on the allowable load capacity of the foundation
Sufficient data/laboratory tests to make settlement predictions
Location of the ground water table
Informatin so that identification and solution of construction problems (sheeting and dewatering or rock excavation, etc..) can be made
Information to identify potential problems (settlements, existing damage, etc..)
Information to identify environmental problems
but how do we accomplish those goals?

3. Site Exploration
Possible construction problems in advance (sheeting, dewatering, slope instability etc.)

4. Site Exploration
Possible construction problems in advance (sheeting, dewatering, slope instability etc.)

5. Site Exploration
Potential geotechnical problems concerning adjacent structures

6. Site Exploration Phases
Planning
The desk study and walk-over survey
Subsurface exploration:
boring, drilling, probing and trial pitting
engineering geophysics
Sampling and sample disturbance
Laboratory testing
In situ testing
Writing a report

7. Location, number and depth of borings
Where should be the b.h’s drilled?
Importance of the building
Shape and size of the structure
Cost is affordable
Depends on soil conditions
General rules for required depth of borings
Reach to stable layers, penetrate through all stable layers (Be careful when stiff and dense layers are underlain by soft deposits)
If structures are to be built on a deep soft deposit, the borings must penetrate to a certain depth where consolidation settlement is negligible.
Bedrock (if accessible) should be differentiated from boulders (penetrate into bedrock for a minimum depth of 2*3m)
The following rules may be used as guide for required depth of exploration below various structures

8. Location, number and depth of borings
General rules for required depth of borings?
The depth of exploration should not be less than 10 m below the actual foundation level unless rock is encountered.

9. To Make a Decision of
Remember that there is not a “unique” answer regarding the number and depth of borings.
Depth of bore holes depends on
type of superstructure
loads of superstructure
envisaged type of foundation
depth of borings are usually selected such that the effective vertical stress change due to the new construction is insignificant (i.e. less than 10% of the initial vertical effective stress-De Beer’s Rule).
Number of bore holes depends on
importance degree of superstructure
knowledge about site soils (soil variability)
budget for site investigation
size of the project
try to locate the borings where structural loads are expected.

11. Determination of Soil Profile
SAND h1
CLAY h2
SAND h3 h4
2~3 m
TP-1
~1 m
Number of borings
Coordinates of borings
Topographic plan
BH-1
BH-3
BH-5
TP-2
BH-2
BH-4

12. Location, number and depth of borings
For a building with a width of 30m

13. Augering

14. Washboring

15. Exploratory Borings
usually subsurface explorations are performed using a drilling rig to drill borings.
these borings typically are
8cm-60cm in diameter, and
3m-30m deep.

16. Truck mounted drilling
caving occurs when the sides of boring fall in (could occur in sandy soils, hollow stem auger could be used).
squeezing occurs when the soil moves inward reducing the diameter of the boring (could occur in soft saturated clays, casing could be used).

17. Subsurface Exploration: boring, drilling, probing

18. Soil sampling
disturbed sampling (bulk or bag samples): obtained from cuttings emerged from the drilling operation.
Grain size analysis
Determination of liquid and plastic limits
Specific gravity of soil solids
Organic content determination
Classification of soil
Cannot be used for consolidation and shear strength tests
undisturbed sampling: intact soil samples in terms of soil fabric, obtained by shelby tubes shown in the figure.

19. Sampling and Sample Disturbance
Generally, samples of two types are specified
Undisturbed samples; generally taken by cutting blocks of soil or rock, or by pushing or driving tubes into the ground.
Disturbed samples; are taken from cuttings produced by the drilling process.
Soil disturbance can occur during
drilling
sampling
transportation and storage
preparation for testing
The mechanisms associated with this disturbance can be classified as
changes in stress conditions
mechanical deformation
changes in water content and voids ratio
chemical changes

20. Sampling and Sample Disturbance
Undisturbed sampling techniques
Drive samplers are pushed into the soil without rotation, displacing the soil as they penetrate.
They generally have a sharp cutting edge at their base.
In contrast, rotary samplers have a relatively thick and blunt cutting surface, which has hard inclusions of tungsten or diamond set into it.
The sampler is rotated and pushed gently downwards, cutting and grinding the soil away beneath it.
Undisturbed sampling is generally not possible in granular soils.
Shelby type tube

21. Laboratory Testing Classification Tests Strength and Stiffness Tests
Particle size distribution test
Hydrometer test
Plasticity test
Specific gravity determination
Strength and Stiffness Tests
California bearing ratio (CBR) test
Franklin point load test
Laboratory vane test
Direct shear test
Unconfined compression test
Triaxial test
Consolidation Tests
the oedometer (Terzaghi 1923; Casagrande 1936)
the triaxial apparatus (Bishop and Henkel 1962)
the hydraulic consolidation cell (Rowe and Barden 1966)

23. Determination of gwt
location of gwt is very important in foundation design.
you can simply install an observation well, once gwt level becomes stable, lower a probe and determine the gwt depth.

24. Laboratory Testing Classification Tests Casagrande cup apparatus
Fall cone
apparatus
Plastic limit test
Set of sieves
Drying oven
Specific Gravity test
Precision balance

25. Unconfined compression test
Laboratory Testing
Strength and Stiffness Tests
Point load test
Laboratory vane test
CBR test
Direct shear test
Unconfined compression test

26. Laboratory Testing
Triaxial Tests

27. In-Situ Testing
there is always the question of which is better, laboratory testing or in-situ testing for geotechnical investigation of a site. Both have advantages and disadvantages.
advantages of in-situ testing:
even though we called “undisturbed”, there is some amount of sample disturbance depending on the type of soil during sampling for lab tests. e.g. for sandy soils it is very difficult or very expensive to obtain “undrained” samples.
in-situ testing is usually less expensive compared to lab tests.
test results are available immediately
disadvantages of in-situ testing:
variable or unknown boundary conditions such as drainage conditions, and confining pressure.
in-situ test results are most frequently converted to geotechnical parameters such as internal friction angle, unit weight etc. via empirical(tecrubeye dayanan, gozlemsel) correlations that may not be accurate.

28. FIELD TESTS MAJOR FIELD TESTS Standard Penetration Test (SPT).
Cone Penetration Test (CPT).
Coring of Rocks
Vane shear test (VST).
The Pressure-meter Test (PMT).
The Plate Load Test (PLT).
Geophysical Methods

29. FIELD TESTS

30. Standard Penetration Test (SPT)
one of the most commonly used in-situ test, but also one of the least accurate due to the variations in procedure and poor workmanship.
procedure for the SPT:
drill a 60mm to 200mm hole to the depth of interest,
attach the SPT sampler (see figure below) to the drill rods and lower it to the bottom of the hole,
63.5kg hammer is raised 76cm and allowed to repeatedly fall freely to drive the sampler into the bottom of the hole. Record the number of hammer blows to drive the sampler in to the ground for the intervals of 15cm (15 cm,30cm and 45cm). Stop the test if more than 50 blows are required for any of the intervals, or if more than 100 total blows are required. Either of these events is known as ‘Refusal’ and is so noted on the boring log.
compute the N value by subtracting the blow counts for the first 15cm from the total number of blow counts (for 45 cm),
remove the SPT sampler from the bore hole and save the soil sample. Note that samples obtained by SPT sampler are considered as “disturbed” samples.
drill the boring to the next test depth and repeat the procedure.

31. The Standard Penetration Test (SPT)

32. The Standard Penetration Test (SPT)
SPT spoon

33. The Standard Penetration Test (SPT)
The boring log shows refusal and the test is halted if
1. 50 blows are required for any 150-mm increment.
blows are obtained (to drive the required 300 mm).
3. 10 successive blows produce no advance.
When the test carried out in very fine sand or silty sand below the water table the measured N value, if greater than 15, should be corrected for the increased resistance due to negative excess pore pressure set up during driving and unable to dissipate immediately. The corrected value is given by:
N’ = 15+1/2(N-15)

34. The Standard Penetration Test (SPT)
The standard blow count N60 can be computed from the measured N as follows:
N=measured SPT N value
N60= SPT N value corrected for 60% energy efficiency and field procedures
(N1)60 = SPT N value corrected for 60% energy efficiency and field procedures, and overburden correction
CN = correction factor for overburden pressure
σv´is the effective overburden pressure of the test location (in kPa)
ER = hammer energy ratio
CB = correction factor for borehole diameter
CS = correction factor for samplers with and without liners
CR = correction factor for rod length

35. The Standard Penetration Test (SPT)

37. Uses of SPT data and correlations
remember that SPT is an in-situ test, which does not directly measure any of the engineering properties or design parameters for a soil.
but there are empirical correlations available between SPT blow count and different soil properties such as Dr or f' .
suspect and be cautious when using SPT correlations, especially in clayey soils. Remember that all of such correlations are very approximate.

38. The Standard Penetration Test (SPT)
The SPT has been used in correlations for unit weight g, relative density Dr , angle of internal friction f, and undrained compressive strength qu.

39. The Standard Penetration Test (SPT)

40. Cone Penetration Test (CPT)
developed in Europe in early 20th century and becoming increasingly popular,
a truck-mounted cone is pushed into the ground at constant rate.
two things are measured
cone resistance (qc)
cone side friction (fsc)
pore pressures (u) can also be measured with a “piezo cone”
in practice side friction could be expressed in terms of friction ratio, Rf
Rf (%)= fsc /qc .100
note that no soil sample is recovered during CPT, hence inspection of soil samples is not possible.
can not be used in gravelly soils.

41. The Cone Penetration Test (CPT)
The cone penetration test is carried out in its simplest form by hydraulically pushing a 60° cone, with a face area of 10cm2 (35.7mm dia.), into the ground at a constant speed (2 ± 0.5 cm/s) whilst measuring the force necessary to do so.
Both electrical and mechanical means of measuring cone resistance and side friction are currently used, with the shape of the cone differing considerably according to the method in use. The cone is driven from ground surface, without making a borehole, using a special mobile hydraulic penetrometer rig.
CPT is an invasive soil test that defines soil strata type, soil properties, and strength parameters. It is highly repeatable, insensitive to operators, and best suited for uncemented soils, sands, or clay.

42. The Cone Penetration Test (CPT)

43. The Cone Penetration Test (CPT)

44. The Cone Penetration Test (CPT)

45. correlations with CPT data
the good thing about CPT is that you can take continuous measurements through different soil profiles (unlike SPT)

46. The Cone Penetration Test (CPT)

47. The Cone Penetration Test (CPT)
CPT data correlated to soil type and equivalent SPT-N. (After Robertson, P.K. and Campanella, R.E., 1983,Canadian Geotechnical Journal, Vol. 20, No. 4)

48. Uses of CPT data and correlations
similar to SPT, CPT is an in-situ test, which does not directly measure any of the engineering properties or design parameters for a soil.
but there are empirical correlations available between CPT resistance and different soil properties such as Dr , f' , soil classification.
CPT data can also be used in deep foundation design as well.

49. The Cone Penetration Test (CPT)

50. The Cone Penetration Test (CPT)
In cohesive soils, the CPT is routinely used to determine both undrained shear strength and compressibility. In a similar way to the bearing capacity of a foundation, cone resistance is a function of both overburden pressure (σv) and undrained shear strength (cu):
Nk is not a constant, but depends upon cone type, soil type, overconsolidation ratio, degree of cementing
The Nk value in an overconsolidated clay will be higher than in the same clay when normally consolidated. Therefore it is normal to use area-specific values of Nk to calculate cu. Typically, Nk varies from 15 to 20 (Bowles, 2002).

51. Field Vane Test
Early geotechnical engineers found difficulty in determining the shear strength of very soft and sensitive clays by means of laboratory tests, as a result of the disturbance induced by poor-quality samplers. These difficulties led to the development of the vane shear test. This device made it possible for the first time to determine the in situ shear strength and sensitivity of a soft clay.
Once the vane has been pushed into the ground, it is rotated at a slow rate. Torsional force is measured, and is then converted to unit shearing resistance by assuming the geometry of the shear surface, and the shear stress distribution across it.

52. Field Vane Test

53. Field Vane Test cuv-design = l . cuv
Undrained shear strength from vane test; cuv
cuv = Tmax/(πD2 (H/2+D/2)),
H/D is usually kept as 2 so;
cuv = 6 Tmax/ 7π D3
cuv-design = l . cuv

54. Field Vane Test

55. Field Vane Test

56. Pressuremeter Test
The pressuremeter was developed in France in the early 1950s (Ménard 1957). In its earliest form it was (and remains today) a simple, robust mechanical tool, well-adapted to use in routine investigations.
Pressuremeter tests can be carried out both in soils and in rocks. The pressuremeter probe, which is a cylindrical device designed to apply uniform pressure to the ground via a flexible membrane, is normally installed vertically, thus loading the ground horizontally.
The aim of pressuremeter test is to obtain information on the stiffness, and in weaker materials on the strength of the ground, by measuring the relationship between radial pressure and the resulting deformation.

57. Pressuremeter Test

58. Pressuremeter Test

59. Pressuremeter Test

60. Field Load Test

61. Field Load Test
The ultimate load capacity and allowable bearing capacity of foundation can be effectively determined.
Generally referred as ‘Plate Load Test’
The plates used in the tests are made of steel generally with the dimensions of :
25mm thick and 150 to 722 mm in diameter Or
square plates with 305x305 mm

62. Field Load Test
A hole is excavated with a minimum diameter of 4B (B=diameter of the test plate) up to a depth of Df (Df=depth of the proposed foundation)
Load is applied in steps by means of a jack
At least 1 hour elapses after application of each step load before the next load is applied
The test should be conducted until failure or at least until the plate has gone through 25 mm of settlement.
qu(F)=ultimate bearing capacity of the proposed foundation
qu(P)=ultimate bearing capacity of the test plate
SF= settlement of foundation
SP=settlement of plate

63. Field Load Test
For tests in clay;
qu(F)=qu(P)