file 3 method of investigation
TRANSCRIPT
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Method of geotechnical investigation
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Preliminaryinvestigation
Detailedinvestigation
General investigation
Simple methods
Low cost
Wide area
Specific problems
Sophisticated methods
High cost
Specific area/soil type
Very detailed
investigation
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Which investigation methods do
you know?
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Preliminary investigation
Literature search
Existing data of boreholes, wells, and other soil investigations
Information on nearby structures such as foundation types, sizes, depths,settlements, and inclinations
Reconnaissance site visits
Geological reconnaissance (observation of outcrops at cut slopes along roads andexposed rocks on river beds; identifying problematic geology for foundation construction)
Terrain observation for landslides and problematic topography for bridge
construction
Geophysical investigations
Seismic prospecting for depths to the bed rock and for extent of weathering anddevelopment of cracks
Echo sounding for depths to sea bed
Borehole investigation and trial pits excavation
Boreholes for deep bearing strata; to study soil stratification and depth ofgroundwater table; to select suitable bearing strata based on , as an example, the
standard penetration tests (SPT); to estimate permeability and compressibility of theground based on various laboratory soil tests performed on SPT soil samples.
Trial pit excavations for shallow bearing strata
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Detailed investigation
Borehole investigationSoil sampling
SoundingSoil/rock tests
Groundwater investigationLoad tests
Geophysical prospecting and loggingPoisonous gas and Oxygen poor air
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Method of Soil Investigation
Boring
Standard Penetration Test (SPT)
Undisturbed soil sampling
Rock Coring
Full scale tests
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SPT
Standard Penetration Test
Standard split sampler (50mm in diameter)
Standard hammer (65.0kg, free falling from
a height of 760mm)
Blow counts (150+300+50mm)
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Sand Cohesionless soil,
granular soil)
SPT Relativedensity
0-4 Very loose
4-10 Loose
10-30 Medium
30-50 Dense
50- Very dense
Terzaghi, Peck and Mesri 1996) BS Classification
SPT Consistency Unconfinedcompressive
strength
kPa)
Consistency
Unconfined
compressiv
e strength
kPa)
0-2 Very soft Less than 50 Very soft Less than40
2-4 Soft 50-100 Soft 40-80
4-8 Medium 100-200 Firm 80-150
8-15 Stiff 200-400 Stiff 150-300
15-30 Verystiff
400-800 Very stiffor hard
Greaterthan 300
30- Hard Greater than800
Clay Cohesive soil) by
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Undisturbed soil sampling
What does undisturbed mean?
What are problems of disturbed soil
samples?
How to take undisturbed soil samples?
Soft clay, stiff clay
Loose sand, dense sand
Evaluation methods
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Rock Coring
Cylindrical pieces of rocks are retrieved during drilling in rocks. The rockcoringisthe act of taking these pieces of rocks with intention of full recovery in goodcondition for visual, physical and chemical examination.A tool to take the rock pieces consists of a bit and steel tube. The bit cuts the rockinto cylindrical form. The tube retains the rock pieces inside. The rock pieces arethen called coreor rockcore.The tool is called corebarrel.The most simple type ofthe core barrel is single core barrel which is essentially a steel tube with a bitattached to one end. There are double tube and triple tube core barrels, which canretain more rock cores than the single tube core barrel.Core recovery ratio is a measure for rock quality. It is the ratio of the cumulativelength of the cores recovered to the length of actual core-run. It is affected not onlyby the rock quality but also the tool used to take the cores and the skill of drillingoperator.Another measures for rock quality is RQD (Rock quality designation). The RQD is
the ratio of the sum of the length of intact rock pieces that are more than 10cm ineach length, to the length of the actual core-run. RQD is 100% if the rock cores arefully recovered with each piece longer than 10cm. However, RQD is 0% if each pieceis shorter than 10cm even if the recovery is 100%.Rock quality is important factor in design where tensile conditions are induced inrock mass such as excavation and tunneling. However, the rock quality is less
important where the rocks are under compressive stresses.
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Rock core
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Full scale tests such as pile load tests, platebearing tests, pull-out tests of anchors, testembankments on soft ground are conductedin two aspects; one as a part of design andthe other for quality assurance duringconstruction.
Full scale tests
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