Matakuliah
Tahun
Versi
: S2094 / Rekayasa Pondasi
: 2005
: 1.1
Pertemuan 03
Penyelidikan Tanah
•Media referensi video :
DrillingAndSampling.wmv
minicone.wmv
Site Exploration
and Characterization
“Subsurface material properties cannot be
specified; they must be deduced through
exploration.”
Charles Dowding (1979)
Objectives
Determine location and thickness of soil
and rock strata (subsurface soil profile)
Determine location of groundwater table
Recover samples for laboratory testing
Conduct lab and/or field testing
Identify special problems and concerns
Site Exploration; General
Strategy
Project Assessment
Literature Search
Field Reconnaissance
Subsurface Drilling and Sampling
Laboratory Testing of Soil Samples
Project Assessment
Type, location and approximate
dimensions of the proposed development
Existing topography and any proposed
grading
Any previous developments
Literature Search
Geologic Maps
Soil Survey Reports
Geotechnical Reports
Historic Groundwater Data
Geologic Maps
Remote Sensing
Conventional Aerial Photographs
Geologic features (landslides, faults),
topography, drainage patterns
Site history
Infrared Aerial Photographs
Springs, seepage zones
Useful in slope stability investigations
Field Reconnaissance
Any previous developments, grading etc.
Site topography, any signs of slope
instability (landslides, soil creep)
Site drainage conditions
Rock outcrops
Site access
Field Exploration
Site Boring Layout
Test Borings or Test Pits?
It depends on the type of materials, and
what you want to know.
Number and Frequency of Borings
Depth, Sampling Methods and Field
Testing
Field Exploration
III. Subsurface
Exploration/Sampling
 Borehole Spacing
Site conditions/uniformity
type of structure (bridge, building, landfill)
typically one borehole/2500 ft2
Also see Table 4.1 (p.108)
Borehole Depths
Magnitude of loading/soil conditions
Also see Table 4.3 (p.109)
How Many Borings?
How Deep?
Look Up and Live!
Safety Awareness
Regular Emphasis
Drilling and Sampling of
Soils
Subsurface Drilling
Auger Drilling
Solid Stem Auger
Hollow Stem Auger
Rotary Drilling
Bucket Auger
Percussion (or Cable Tool) Drilling
Auger Drilling
Auger Drilling
Hollow Stem Auger
Casing with outer spiral
Inner rod with plug/or pilot
assembly
For sampling, remove pilot
assembly and insert sampler
Typically 5ft sections, keyed,
box & pin connections
Maximum depth 60-150ft
Hollow-Stem Augers
Air or Mud Rotary Drilling
 http://www.redi-drill.com/msindex.htm
Rotary Drilling
Bit at the end of drill rod
rotated and advanced
Soil/rock cuttings removed
by circulating drilling fluid
Common drilling fluid;
bentonite in water with
slurry density 68-72pcf
Air may be used as drilling
fluid
Cable Tool Drilling
 Not common in US in
geotechnical explorations
 Heavy impact drilling tools
lifted and dropped
 Impact loosens soil and rock
 Cuttings removed with a bailer
 Slow process; Used in
environmental explorations
where drilling fluid is not
permitted
Rock Drilling, Coring,
Augering
http://www.globaldril
sup.com/catindex.html
Soil and Rock Sampling
Disturbed samples
In-place structure is not preserved
Okay for determination of soil index
properties
“…Estimating the nature of the formation
from the cuttings is like identifying the
cow from the hamburgers.”
G.F. Sowers
Soil and Rock Sampling
Undisturbed samples
Minimizes effects from potential disturbance
Needed for determination of in-situ density,
in-situ permeability, soil shear strength and
compressibility
Soil Samplers
Standard Split Spoon Samplers
Shelby Tube Samplers
Piston Samplers
Heavy Wall Samplers
Standard Split Spoon
Samplers
Thick wall (0.25in) cylinder
Sampling tube is split along the length
Hammered into the ground
Shelby Tube (Thin-wall)
Samplers
Thin wall (1/16in)
sampling tube
Sampler pushed into
the ground
hydraulically
Sample extruded
from tube
Piston
Samplers
Minimizes sample
disturbance caused
by back-pressure
Heavy-Wall
Samplers
Thicker walls provide
better strength &
durability
However, it creates
more disturbance
Sampler pounded
into the ground
Groundwater Monitoring
Groundwater level
must be determined
during geotechnical
investigation
Can be accomplished
by leaving selected
soil borings open
In-situ Testing
When it is difficult to obtain
“undisturbed” samples
Cohesionless soils, Sensitive clays
In-situ Test Methods
Standard Penetration Test (SPT)
Cone Penetration Test (CPT)
Pressuremeter Test
Flat Plate Dilatometer Test
Standard Penetration Test
(SPT)
140 lb (63.5 kg) Hammer
30in (76 cm) free fall
Drive sampler over 18 inches
Record no. of blows per each 6 inch
penetration
SPT blow count=blows for 2nd 6 inch
penetration + blows for 3rd 6inch
penetration
Standard Penetration Test
(SPT)
Standard Penetration Test
(SPT)
Types of SPT Hammers
Corrections to SPT blow
Counts
Factors affecting SPT blow count:
Hammer Efficiency (See Table 4.3)
Borehole diameter (See Table 4.4)
Type of sampler (See Table 4.4)
Rod length (See Table 4.4)
SPT Correction Factors
N 60




E m C BCS C R N

0.60
hammer efficiency (Em) …. Table 4.3
bore hole diameter (CB)…….Table 4.4.
sampler correction (CS) ……Table 4.4
rod length (CR) ………Table 4.4
SPT Overburden Correction
( N1 ) 60  N 60
2000 lb / ft
 z
( N1 ) 60  N 60
2
100 kPa
 z
(Customary )
(SI)
Use of SPT Data
 To Determine Relative Density, Dr
From AASHTO Chart
From Eq. (4.3) p.122
 To determine 
From Figure 4.11 (p.123)
 To determine C
From AASHTO Chart