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Matakuliah: S2094 / Rekayasa Pondasi

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... Objectives Determine location and thickness of soil and rock strata ... must be determined during geotechnical investigation Can be accomplished by ... – PowerPoint PPT presentation

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Title: Matakuliah: S2094 / Rekayasa Pondasi


1
Pertemuan 03Penyelidikan Tanah
  • Matakuliah S2094 / Rekayasa Pondasi
  • Tahun 2005
  • Versi 1.1
  • Media referensi video DrillingAndSampling.wmv
    minicone.wmv

2
Site Exploration and Characterization
  • Subsurface material properties cannot be
    specified they must be deduced through
    exploration.
  • Charles Dowding (1979)

3
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

4
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7

Site Exploration General Strategy
  • Project Assessment
  • Literature Search
  • Field Reconnaissance
  • Subsurface Drilling and Sampling
  • Laboratory Testing of Soil Samples

8

Project Assessment
  • Type, location and approximate dimensions of the
    proposed development
  • Existing topography and any proposed grading
  • Any previous developments

9

Literature Search
  • Geologic Maps
  • Soil Survey Reports
  • Geotechnical Reports
  • Historic Groundwater Data

10
  • Geologic Maps

11

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

12

Field Reconnaissance
  • Any previous developments, grading etc.
  • Site topography, any signs of slope instability
    (landslides, soil creep)
  • Site drainage conditions
  • Rock outcrops
  • Site access

13
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

14

Field Exploration
15
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)

16

How Many Borings?
17

How Deep?
18
Look Up and Live!
  • Safety Awareness
  • Regular Emphasis

19
Drilling and Sampling of Soils
  • Subsurface Drilling
  • Auger Drilling
  • Solid Stem Auger
  • Hollow Stem Auger
  • Rotary Drilling
  • Bucket Auger
  • Percussion (or Cable Tool) Drilling

20
Auger Drilling
21
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

22
Hollow-Stem Augers
23
Air or Mud Rotary Drilling
  • http//www.redi-drill.com/ms-index.htm

24
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

25
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

26
Rock Drilling, Coring, Augering
  • http//www.globaldrilsup.com/cat-index.html

27
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

28
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

29
Soil Samplers
  • Standard Split Spoon Samplers
  • Shelby Tube Samplers
  • Piston Samplers
  • Heavy Wall Samplers

30
Standard Split Spoon Samplers
  • Thick wall (0.25in) cylinder
  • Sampling tube is split along the length
  • Hammered into the ground

31
Shelby Tube (Thin-wall) Samplers
  • Thin wall (1/16in) sampling tube
  • Sampler pushed into the ground hydraulically
  • Sample extruded from tube

32
Piston Samplers
  • Minimizes sample disturbance caused by
    back-pressure

33
Heavy-Wall Samplers
  • Thicker walls provide better strength
    durability
  • However, it creates more disturbance
  • Sampler pounded into the ground

34
Groundwater Monitoring
  • Groundwater level must be determined during
    geotechnical investigation
  • Can be accomplished by leaving selected soil
    borings open

35
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

36
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 countblows for 2nd 6 inch penetration
    blows for 3rd 6inch penetration

37
Standard Penetration Test (SPT)
38
Standard Penetration Test (SPT)
39
Types of SPT Hammers
40
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)

41
SPT Correction Factors
42
SPT Overburden Correction
43
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
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