Foundation engineering related to civil engineering

Education purpose for civil engineering

1. UNIT –I
SUBSOIL EXPLORATION

2. SUBSOIL EXPLORATION
Selectionofthetypeandthedepthoffoundation
suitableforagivenstructure.
Evaluationoftheload-bearingcapacityofthe
foundation.
Estimationoftheprobablesettlementofastructure.
Determinationofpotentialfoundationproblems(for
example,expansivesoil,collapsiblesoil,sanitary
landfill,andsoon).
Establishmentofgroundwatertable.
Predictionoflateralearthpressureforstructureslike
retainingwalls,sheetpilebulkheads,andbracedcuts.
Establishmentofconstructionmethodsforchanging
subsoilconditions.

3. PLANNING OF SOIL EXPLORATION
It depends upon
Nature of Sub-soil,
Type of Structure,
Importance of Structure.
Thecostofsiteinvestigationsgenerallyvariesbetween0.05
to0.2%ofthetotalcostoftheentirestructure.Insome
unusalconditions,thecostmaybeevenupto1%.

4. STAGES IN SUB-SURFACE EXPLORATION
RECONNAISSANCE:-
Collection of data about the project
Geologic study of the site
Site inspection.
PRELIMINARY EXPLORATION: -
Depth, extent, and composition of critical soil strata,
Ground –water level and its Fluctuations,
Depth of bed rock, when necessary,
Estimate of engineering properties of soil,
Initial selection of foundation possibilites.

5. DETAILED EXPLORATION: -
Additionaltestborings,
Undisturbedsamplingifcompressiblesoilsare
encounteredatcriticaldepth,
Laboratory/fieldtestsifdataonsoilstrengthand
deformationcharacteristicsareneeded.

7. Disturbed and Undisturbed Sample
Disturbed Sample: In Such sample natural soil structure is
modified or destroyed.
•If water content and mineral content are also modified
then it is a non-representative or remolded sample.
•If water content and mineral content are not modified
then it is representative sample.
Undisturbed Sample: Natural soil Structure, water content
and mineral content are preserved.

9. METHODS OF EXPLORATION
➢Direct methods
➢Pits (or) Trenches
➢Drifts and Shafts
➢Semi-Direct methods
➢Auger Boring
➢Wash boring
➢Rotary boring
➢Percussion drilling
➢Core boring
➢Indirect methods
➢Split spoon samplers
➢Scraper bucket sampler
➢Shelby tubes and thin-walled
samplers
➢Piston sampler
➢Denison sampler
➢Hand curved samples

10. AUGER BORING
✓Simplestmethodofexplorationandsampling.
✓Powerdrivenorhandoperated.
✓Max.depth10m,15to20cmindiameter
✓SuitableinallsoilsaboveGWTbutonlyin
cohesivesoilbelowGWT
✓Hollowstemaugersusedforsamplingor
conductingStandardPenetrationTests.

12. WASH BORING
✓Acasingisdrivenwithadrophammer.A
hollowdrillrodwithchoppingbitisinserted
insidethecasing.
✓Soilisloosenedandremovedfromthe
boreholeusingwateroradrillingmudjetted
underpressure.
✓Thewaterisjettedintheholethroughthe
bottomofawashpipeandleave’stheholealong
withtheloosesoil,fromtheannualspace
betweentheholeandwashpipe.
✓Thewaterreachesthegroundlevelwherethe
soilinsuspensionisallowedtosettleandmudis
re-circulated.

14. ROTARY BORING:-
✓Hollowdrillrodswithadrillbitisrotatedintothesoil.
Drillingmudiscontinuouslypumpedintothehole.
✓Itcanbeusedinclay,sandandrocks.
✓Boreholesofdiameter50mmto200mmcanbeeasily
madebythismethod.
COREDRILLING:-
✓Usedforobtainingrockcores.
✓Acorebarrelisfittedwithadrillbitisattachedtohollow
drillrods.
ROTARYBORING & COREDRILLING

16. PERCUSSION BORING
✓Grinding the soil by
repeated lifting and
dropping of heavy chisels
or drilling bits.
✓Water is added to form
slurry of cuttings.
✓Slurry removed by bailers
or pumps.

17. DESIGN FEATURES AFFECTING THE
SAMPLE DISTURBANCE

18. METHODS OF SAMPLINGS
✓It has an inside dia of 38 mm and an outside dia
of 50 mm.
✓ It has a split barrel which is held together using a
screw driving shoe at the bottom end a cap at the
upper end.
✓The thicker wall of the standard sampler permits
high driving stresses than the Shelby tube but
does so at the expense of higher levels of soil
disturbances.
✓Split spoon samples are disturbed.
✓They are used for visual examination and for
classification tests
SPLIT SPOON SAMPLER

20. SCRAPER BUCKET SAMPLER
✓When soil deposits are sand mixed with pebbles
obtaining samples by split spoon may not be
possible with a spring core catcher and scraper
bucket may be used.
✓It has a driving point and can be attached to a
drilling rod. The sampler is driven down into the
soil and rotated and the scrapings from the side fall
into the bucket.

22. SHELBY TUBES AND THIN WALLED
SAMPLER
✓It has a steel tube of dia 50 or 75 mm and length
of 600 – 900 mm.
✓The bottom end of the tube is sharpened.
✓The tubes can be attached to drilling rods.
✓The drilling rod with the sampler attached is
lowered to the bottom of the borehole and the
sampler is pushed into the soil.
✓The soil sample inside the tube is then pulled
out.
✓The two ends of the sampler are sealed and sent
to the lab.
✓The samples can be used for consolidation or
shear tests.

24. PISTON SAMPLER
✓When undisturbed soil samples are very soft or
larger than 76.2 mm in diameter, they tend to fall
out of the sampler. Then piston samplers are used.
✓They consists of a thin wall tube with a piston.
Initially the piston closes the end of the thin wall
tube. The sampler is lowered to the bottom of the
bore hole and the thin wall tube is pushed into the
soil.
✓Samples obtained in this manner are less
disturbed than those obtained by Shelby tubes.

26. FIELD STRENGTH TEST
The following are the major field tests for determining the
soil strength:
1. Vane shear test (VST).
2. Standard Penetration Test (SPT).
3. Cone Penetration Test (CPT).
4. The Borehole Shear Test (BST).
5. The Flat Dilatometer Test (DMT).
6. The Pressure-meter Test (PMT).
7. The Plate Load Test (PLT).

27. FIELD STRENGTH TEST

28. Standard penetration test (SPT) is the most commonly used in
situ test for sub- surface investigation. In SPT a split spoon
sampler is made to penetrate 15 cm by light blows of a 65 kgs
drop hammer on the top of the drill rod. The drill rod is
connected to the top of the split spoon sampler.

After initial penetration of 15 cm of the sampler, the drop
hammer is allowed to fall from a height of 75 cms and number
of blows required for 30 cms penetration of sampler is recorded.
This number of blows is called N-value or penetration number.
In this method the driving energy is supplied by the fail of the
drop weight. Hence it is essentially a dynamic sounding method.

29. STANDARD PENETRATION TEST

30. Corrections are normally applied to the SPT
blow count to account for differences in:
• Energy imparted during the test (60%
hammer efficiency).
• The stress level at the test depth
The following equation is used to
compensate for the testing factors (Skempton,
1986):

32. Cone Penetration Test (CPT).

34. PLATE LOAD TEST

35. PLATE LOADTEST

36. The following graphical presentations should
he attached to the report:
1. A site location map
2. A plan view of the location of the borings
with respect to the proposed structures and
those nearby
3. Boring logs
4. Laboratory test results
5. Other special graphical presentations
SUB-SOIL INVESTIGATION
REPORT

37. SUB-SOIL INVESTIGATION REPORT