Geotechnical Investigation
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Transcript of Geotechnical Investigation
Importance of Proper Geotechnical Importance of Proper Geotechnical Investigation in Engineering Project: Investigation in Engineering Project:
Some case studySome case study
J.N.Jha*, K.S.Gill* & A.K.Chaudhary**J.N.Jha*, K.S.Gill* & A.K.Chaudhary**•*Department of Civil Engineering, Guru Nanak *Department of Civil Engineering, Guru Nanak
Dev Engineering College, LudhianaDev Engineering College, Ludhiana•** Department of Civil Engineering, NIT, ** Department of Civil Engineering, NIT,
JamshedpurJamshedpur
IntroductionIntroduction
Construction activities increased Construction activities increased manifold (development of economic manifold (development of economic activities)activities)
Different types of complex structures Different types of complex structures are coming up (to meet the growing are coming up (to meet the growing demand)demand)
Attempt being made to make soil Attempt being made to make soil suitable to project and not the suitable to project and not the project to soil.project to soil.
Geotechnical Engineer-Geotechnical Engineer-
very important role to play in this very important role to play in this challenging task.challenging task.
Geotechnical Engineering Practice-At Geotechnical Engineering Practice-At par with the best in the world.par with the best in the world.
Range of Geotechnical practice vary Range of Geotechnical practice vary widely in India.widely in India.
Field investigation-Most primitive Field investigation-Most primitive equipment are in useequipment are in use
Laboratory testing-Practice vary Laboratory testing-Practice vary widely with little standardization and widely with little standardization and accreditation. accreditation.
Quality of InvestigationQuality of InvestigationIndiaIndia World StandardWorld Standard
Generally Poor quality of the Generally Poor quality of the EquipmentEquipment
Highly sophisticated and Highly sophisticated and mechanized equipmentmechanized equipment
Calyx Drilling Technique Calyx Drilling Technique Continuous core sampling (in Continuous core sampling (in soils as well)soils as well)
SPT Equipment unchanged SPT Equipment unchanged over the years (unreliable)over the years (unreliable)
SPT Equipment with Blow SPT Equipment with Blow Energy Directly on top of the Energy Directly on top of the samplersampler
Conventional Static Cone Conventional Static Cone Penetration EquipmentPenetration Equipment
Static Cone Test with Electric Static Cone Test with Electric Cone Cone
Very recently few companies Very recently few companies have electric conehave electric cone
Result (Substandard practice)Result (Substandard practice)
Substantial difference between Substantial difference between actual soil profiles and available soil actual soil profiles and available soil profiles (at the time of design as part profiles (at the time of design as part of tender specifications)of tender specifications)
Variation can be minimized if Variation can be minimized if standard practices are followed standard practices are followed during the soil investigationduring the soil investigation
Unfortunately this is not the case quite Unfortunately this is not the case quite oftenoften
Who is responsible?Who is responsible?
Responsibility squarely rests on Responsibility squarely rests on Geotechnical community of the country Geotechnical community of the country and is a major failure on our part.and is a major failure on our part.
General and Standard Practice General and Standard Practice
Tender for a project (information Tender for a project (information supplied)supplied)
Subsoil profile and soil characteristics Subsoil profile and soil characteristics is of general information only is of general information only
Owner is not responsible for the Owner is not responsible for the correctness of this informationcorrectness of this information
Contractor if desired should satisfy Contractor if desired should satisfy the correctness of information before the correctness of information before submitting his offersubmitting his offer
To safeguard the owner to avoid any To safeguard the owner to avoid any disputedispute
Contractor (point of view)Contractor (point of view)
Time interval between issue of Time interval between issue of tender document and submission of tender document and submission of technical bid is very shorttechnical bid is very short
Soil investigation is expensiveSoil investigation is expensive Impossible to carry out soil Impossible to carry out soil
investigation investigation Bidder accepts the stipulation given Bidder accepts the stipulation given
in tender in tender
Case studyCase study
Road over Bridge (ROB)Road over Bridge (ROB) Bridge :Bridge :
5 span of 10.7 m with certain 5 span of 10.7 m with certain
embankment on either side embankment on either side
As per tender SPT value 12 to 16 for As per tender SPT value 12 to 16 for top two layer extending up to 7 m.top two layer extending up to 7 m.
Recommend allowable bearing Recommend allowable bearing pressure=150 kN/m2 at depth 2 m below pressure=150 kN/m2 at depth 2 m below GL for Pier foundation.GL for Pier foundation.
Accordingly Piers were constructed on Accordingly Piers were constructed on shallow foundationshallow foundation
4 Pier constructed and 54 Pier constructed and 5thth was under was under construction approach earth embankment construction approach earth embankment settled by 2 m and corresponding heaving settled by 2 m and corresponding heaving up of soil 1.5 mup of soil 1.5 m
EM BANKM ENT
9m 2m SET T LEM ENT BRIDGE
PIER
RAIL LINE
ABUT M ENT
SOIL HEAVE
SOF T CLAY
- 6m
SAND1 0 .7 m
ROT AT IONAL F AILURE
G.L.
.
Confirming soil investigation was Confirming soil investigation was carried outcarried out
Soil Profile:Soil Profile: Top 1-1.5 m : Sandy ClayTop 1-1.5 m : Sandy Clay 1.5-8 m : Soft marine clay1.5-8 m : Soft marine clay
1 0
8
6
4
2
0
1 2 S A N D
1 4
1 6
1 2
2 9
3 8
S IL T
C L A Y
B H -I S P T (N )
(a ) A s P e r te n d e r
10
8
6
4
2
0
0 .1
B H -I S P T (N )
(b ) A s P e r co n f irm a to ryb o re H o le
0 .0
0 .0
0 .0
15
1 1
0 .3
C = 4 0 K N /m2
C = 2 4 K N /m2
C = 3 1 K N /m2
C = 4 0 K N /m2
Rehabilitation MeasureRehabilitation Measure
Piles installed around shallow Piles installed around shallow foundation and integrated with foundation and integrated with foundationfoundation
Delay in completion of project, Delay in completion of project, additional cost & disputeadditional cost & dispute
Petro Chemical Complex Petro Chemical Complex
As per TenderAs per Tender Recommended depth of Pile = 25 mRecommended depth of Pile = 25 m Test pile –failed to take design loadTest pile –failed to take design load Confirmatory (Bore hole) test Confirmatory (Bore hole) test 12 such confirmatory bone hole 12 such confirmatory bone hole
consistently showed that SPT value consistently showed that SPT value reported in original soil report are higherreported in original soil report are higher
Pile depth after confirmatory test =20mPile depth after confirmatory test =20m Confirmatory soil investigation saved a Confirmatory soil investigation saved a
major disaster.major disaster.
3 2
2 4
1 6
8
0B H - 3 B H - F
T O P F I L L
S I L T
R O C K
C L A Y
S A N DB H - F ( c o n f ir m a t o r y )
B H - 3 ( t e n d e r )
4
1 2
2 0
2 8
8 1 6 2 4 3 2
S P T ( N ) V a lu e s
Depth( m )
Choice of Appropriate foundation Choice of Appropriate foundation and executionand execution
Optimum foundation design should Optimum foundation design should ensureensure
Technical adequacyTechnical adequacy Cost effectivenessCost effectiveness Ease of executionEase of execution
Reasons Reasons Insufficient and inaccurate Insufficient and inaccurate
information at the time of design information at the time of design variation in strata variation in strata
Changes in project requirement Changes in project requirement during execution.during execution.
Achieving this is easily said than Achieving this is easily said than done-needs engineering judgementdone-needs engineering judgement
Engineering Judgement – comes from Engineering Judgement – comes from experience.experience.
Experience comes from bad Experience comes from bad engineering judgementengineering judgement
Case studyCase study
Fertilizer plant in Gangetic belt-Fertilizer plant in Gangetic belt-possibility of optimum design possibility of optimum design
Phase-I Phase-I Soil strata (Site)Soil strata (Site) N<10- For a depth upto 10 mN<10- For a depth upto 10 m N-10-20-For a depth upto 10-20 mN-10-20-For a depth upto 10-20 m >20 – For a depth upto 10-20m >20 – For a depth upto 10-20m
Type of SoilType of Soil Silty sand with high water table Silty sand with high water table Threat of liquefaction during Threat of liquefaction during
earthquakeearthquake
Foundation Design Foundation Design (Recommended)(Recommended)
Provide RCC cast in situ piles Provide RCC cast in situ piles (diameter 400 mm) with pile capacity(diameter 400 mm) with pile capacity
Axial vertical load – 50 TonnesAxial vertical load – 50 Tonnes Uplift - 5 TonnesUplift - 5 Tonnes Horizontal capacity=2.5 TonnesHorizontal capacity=2.5 Tonnes
To overcome the problem of To overcome the problem of liquefaction during earthquake liquefaction during earthquake
Provide sand compaction pile 2 to 3 Provide sand compaction pile 2 to 3 rows around RCC piles rows around RCC piles
Total requirement Total requirement As per designAs per design No. of RCC piles 16000 No. of RCC piles 16000 No. of sand compaction piles 32,000No. of sand compaction piles 32,000 Time required for installation of RCC piles Time required for installation of RCC piles
and sand compaction piles=and sand compaction piles= 6 months more than what was originally 6 months more than what was originally
plannedplanned This prompted for the review of foundation This prompted for the review of foundation
designdesign
Sand Compaction Pile Sand Compaction Pile
Original design – Original design – Spacing of compaction pile – 3D and Spacing of compaction pile – 3D and
5D with triangular pattern5D with triangular pattern Spacing – 3D (desired improvement Spacing – 3D (desired improvement
in N-values)in N-values) Spacing-5D (desired improvement in Spacing-5D (desired improvement in
N values not adequates)N values not adequates)
Additional RecommendationAdditional Recommendation
Spacing of sand compaction pile-4DSpacing of sand compaction pile-4D Result-Adequate to obtain required Result-Adequate to obtain required
densification (N-values)densification (N-values) No. of piles (now required)=16000 No. of piles (now required)=16000
instead of 32000instead of 32000
Pile capacity (Revised)Pile capacity (Revised) Vertical downward-65 tonnes instead Vertical downward-65 tonnes instead
of 50 tonnes originalof 50 tonnes original Uplift capacity=25 tonnes instead of Uplift capacity=25 tonnes instead of
5 tonnes original5 tonnes original Lateral capacity-3.5 tonnes as Lateral capacity-3.5 tonnes as
against original 2.5 tonnesagainst original 2.5 tonnes
Requirement of no. of RCC piles Requirement of no. of RCC piles (based on revision)=9400 piles (based on revision)=9400 piles
Reduction in no. of piles =40% Reduction in no. of piles =40% Observation:Observation: Performance of the foundation-fully Performance of the foundation-fully
adequate and satisfactory.adequate and satisfactory.
Phase-II (To double the capacity of Phase-II (To double the capacity of the plant)the plant)
Ground improvement – Vibro stone Ground improvement – Vibro stone column in place of RCC piles and sand column in place of RCC piles and sand compaction pilescompaction piles
Vibro stone column diameter- 960 mmVibro stone column diameter- 960 mm Load test – carried on single column and Load test – carried on single column and
group of columns group of columns Footing test conducted for confirmation Footing test conducted for confirmation
during execution. during execution.
Trial Test Trial Test
Test plot 10 m x 10 mTest plot 10 m x 10 m Vibro stone column – Vibro stone column – 11 m (length),11 m (length), c/c spacing 15 m, 2.15m & 1.8 m c/c spacing 15 m, 2.15m & 1.8 m
(Triangular pattern(Triangular pattern
Standard Penetration Test Standard Penetration Test AreaArea DepthDepth LayerLayer N After N After
treatmenttreatment % % increase in increase in N ValueN Value
Prill TowerPrill Tower 0-2.50-2.5
25-1125-11Silty ClaySilty Clay
Silty ClaySilty Clay1313
20-3620-363030
17-12017-120
Benefield Benefield AreaArea
0-2.30-2.3
2.3-112.3-11Silty ClaySilty Clay
Silty ClaySilty Clay2020
16-3416-348181
36-12336-123
Compressor Compressor HouseHouse
0-3.50-3.5
3.5-113.5-11Silty ClaySilty Clay
Silty ClaySilty Clay1111
24-4624-460101
60-40060-400
Static Cone Penetration Test Static Cone Penetration Test (SCPT)(SCPT)
DepthDepth Pre-treatmentPre-treatment
(Cone (Cone Resistance)Resistance)
Post-Post-treatmenttreatment
(Cone (Cone Resistance)Resistance)
2-8m2-8m 50-80 kg/cm250-80 kg/cm2 130-300 130-300 kg/cm2kg/cm2
Dynamic Cone Penetration Test Dynamic Cone Penetration Test (DCPT)(DCPT)
DepthDepth Pre-treatment Pre-treatment (No. of blows (No. of blows per ft.)per ft.)
Past-Past-treatment treatment (No. of blows (No. of blows per ft.)per ft.)
2-10 m2-10 m 10-40 10-40 22-9522-95
D E S C R P T IO N
1 .0
2 .0
3 .0
4 .0
5 .0
6 .0
7 .0
8 .0
9 .0
1 0 .0
1 1 .0
1 0 2 0 3 0 4 0 5 0 6 0
S O ILP R O F .
D E P T H (m )
S P T (N ) V A L U E
B R O W NC L A YS IL T
2 .5 0
5 .2 5
B R O W NS IL T F IN ES A N D
G R E YF IN E S A N D
G R E Y S IL T YM E D IU MT O F IN E S A N D
9 .5 5
X
P R E C O M P A C T IO N
P O S T C O M P A C T IO N
P O S T C O M P A C T IO N
P R E C O M P A C T IO N
Vibro Stone Column of 960mm with Vibro Stone Column of 960mm with spacing 2D, 2.25D and 2.5D where spacing 2D, 2.25D and 2.5D where adopted depending on loading adopted depending on loading intensityintensity
Substantial saving in time and cost Substantial saving in time and cost Subsequently observation during the Subsequently observation during the
operation of Phase-II confirmed a operation of Phase-II confirmed a satisfactory behaviour of foundation satisfactory behaviour of foundation
Concluding remarksConcluding remarks
Commitment to excellence from Commitment to excellence from Geotechnical Engineers Geotechnical Engineers
Positive attitude to continuously Positive attitude to continuously learn and to accept change for better learn and to accept change for better
Partnership and team work among all Partnership and team work among all concerned i.e owner, consultant and concerned i.e owner, consultant and contractorcontractor
Thank you………..Thank you………..