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………..