Geotechnical Investigation

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Information about Geotechnical Investigation
Technology

Published on November 1, 2008

Author: jagadanand

Source: slideshare.net

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Importance of proper geotechnical investigation for engineering projects to avoid delay and any disastar.

Importance of Proper Geotechnical Investigation in Engineering Project: Some case study J.N.Jha*, K.S.Gill* & A.K.Chaudhary** *Department of Civil Engineering, Guru Nanak Dev Engineering College, Ludhiana ** Department of Civil Engineering, NIT, Jamshedpur

J.N.Jha*, K.S.Gill* & A.K.Chaudhary**

*Department of Civil Engineering, Guru Nanak Dev Engineering College, Ludhiana

** Department of Civil Engineering, NIT, Jamshedpur

Introduction Construction activities increased manifold (development of economic activities) Different types of complex structures are coming up (to meet the growing demand) Attempt being made to make soil suitable to project and not the project to soil.

Construction activities increased manifold (development of economic activities)

Different types of complex structures are coming up (to meet the growing demand)

Attempt being made to make soil suitable to project and not the project to soil.

Geotechnical Engineer- very important role to play in this challenging task. Geotechnical Engineering Practice-At par with the best in the world. Range of Geotechnical practice vary widely in India.

Geotechnical Engineer-

very important role to play in this challenging task.

Geotechnical Engineering Practice-At par with the best in the world.

Range of Geotechnical practice vary widely in India.

Field investigation-Most primitive equipment are in use Laboratory testing-Practice vary widely with little standardization and accreditation.

Field investigation-Most primitive equipment are in use

Laboratory testing-Practice vary widely with little standardization and accreditation.

Quality of Investigation Very recently few companies have electric cone Static Cone Test with Electric Cone Conventional Static Cone Penetration Equipment SPT Equipment with Blow Energy Directly on top of the sampler SPT Equipment unchanged over the years (unreliable) Continuous core sampling (in soils as well) Calyx Drilling Technique Highly sophisticated and mechanized equipment Generally Poor quality of the Equipment World Standard India

Result (Substandard practice) Substantial difference between actual soil profiles and available soil profiles (at the time of design as part of tender specifications) Variation can be minimized if standard practices are followed during the soil investigation

Substantial difference between actual soil profiles and available soil profiles (at the time of design as part of tender specifications)

Variation can be minimized if standard practices are followed during the soil investigation

Unfortunately this is not the case quite often Who is responsible? Responsibility squarely rests on Geotechnical community of the country and is a major failure on our part.

Unfortunately this is not the case quite often

Who is responsible?

Responsibility squarely rests on Geotechnical community of the country and is a major failure on our part.

General and Standard Practice Tender for a project (information supplied) Subsoil profile and soil characteristics is of general information only Owner is not responsible for the correctness of this information

Tender for a project (information supplied)

Subsoil profile and soil characteristics is of general information only

Owner is not responsible for the correctness of this information

Contractor if desired should satisfy the correctness of information before submitting his offer To safeguard the owner to avoid any dispute

Contractor if desired should satisfy the correctness of information before submitting his offer

To safeguard the owner to avoid any dispute

Contractor (point of view) Time interval between issue of tender document and submission of technical bid is very short Soil investigation is expensive Impossible to carry out soil investigation Bidder accepts the stipulation given in tender

Time interval between issue of tender document and submission of technical bid is very short

Soil investigation is expensive

Impossible to carry out soil investigation

Bidder accepts the stipulation given in tender

Case study Road over Bridge (ROB) Bridge : 5 span of 10.7 m with certain embankment on either side As per tender SPT value 12 to 16 for top two layer extending up to 7 m.

Road over Bridge (ROB)

Bridge :

5 span of 10.7 m with certain embankment on either side

As per tender SPT value 12 to 16 for top two layer extending up to 7 m.

Recommend allowable bearing pressure=150 kN/m2 at depth 2 m below GL for Pier foundation. Accordingly Piers were constructed on shallow foundation 4 Pier constructed and 5 th was under construction approach earth embankment settled by 2 m and corresponding heaving up of soil 1.5 m

Recommend allowable bearing pressure=150 kN/m2 at depth 2 m below GL for Pier foundation.

Accordingly Piers were constructed on shallow foundation

4 Pier constructed and 5 th was under construction approach earth embankment settled by 2 m and corresponding heaving up of soil 1.5 m

 

Confirming soil investigation was carried out Soil Profile: Top 1-1.5 m : Sandy Clay 1.5-8 m : Soft marine clay

Confirming soil investigation was carried out

Soil Profile:

Top 1-1.5 m : Sandy Clay

1.5-8 m : Soft marine clay

 

Rehabilitation Measure Piles installed around shallow foundation and integrated with foundation Delay in completion of project, additional cost & dispute

Piles installed around shallow foundation and integrated with foundation

Delay in completion of project, additional cost & dispute

Petro Chemical Complex As per Tender Recommended depth of Pile = 25 m Test pile –failed to take design load Confirmatory (Bore hole) test 12 such confirmatory bone hole consistently showed that SPT value reported in original soil report are higher Pile depth after confirmatory test =20m Confirmatory soil investigation saved a major disaster.

As per Tender

Recommended depth of Pile = 25 m

Test pile –failed to take design load

Confirmatory (Bore hole) test

12 such confirmatory bone hole consistently showed that SPT value reported in original soil report are higher

Pile depth after confirmatory test =20m

Confirmatory soil investigation saved a major disaster.

 

Choice of Appropriate foundation and execution Optimum foundation design should ensure Technical adequacy Cost effectiveness Ease of execution

Optimum foundation design should ensure

Technical adequacy

Cost effectiveness

Ease of execution

Reasons Insufficient and inaccurate information at the time of design variation in strata Changes in project requirement during execution.

Reasons

Insufficient and inaccurate information at the time of design variation in strata

Changes in project requirement during execution.

Achieving this is easily said than done-needs engineering judgement Engineering Judgement – comes from experience. Experience comes from bad engineering judgement

Achieving this is easily said than done-needs engineering judgement

Engineering Judgement – comes from experience.

Experience comes from bad engineering judgement

Case study Fertilizer plant in Gangetic belt-possibility of optimum design Phase-I Soil strata (Site) N<10- For a depth upto 10 m N-10-20-For a depth upto 10-20 m >20 – For a depth upto 10-20m

Fertilizer plant in Gangetic belt-possibility of optimum design

Phase-I

Soil strata (Site)

N<10- For a depth upto 10 m

N-10-20-For a depth upto 10-20 m

>20 – For a depth upto 10-20m

Type of Soil Silty sand with high water table Threat of liquefaction during earthquake

Type of Soil

Silty sand with high water table

Threat of liquefaction during earthquake

Foundation Design (Recommended) Provide RCC cast in situ piles (diameter 400 mm) with pile capacity Axial vertical load – 50 Tonnes Uplift - 5 Tonnes Horizontal capacity=2.5 Tonnes

Provide RCC cast in situ piles (diameter 400 mm) with pile capacity

Axial vertical load – 50 Tonnes

Uplift - 5 Tonnes

Horizontal capacity=2.5 Tonnes

To overcome the problem of liquefaction during earthquake Provide sand compaction pile 2 to 3 rows around RCC piles

To overcome the problem of liquefaction during earthquake

Provide sand compaction pile 2 to 3 rows around RCC piles

Total requirement As per design No. of RCC piles 16000 No. of sand compaction piles 32,000 Time required for installation of RCC piles and sand compaction piles= 6 months more than what was originally planned This prompted for the review of foundation design

As per design

No. of RCC piles 16000

No. of sand compaction piles 32,000

Time required for installation of RCC piles and sand compaction piles=

6 months more than what was originally planned

This prompted for the review of foundation design

Sand Compaction Pile Original design – Spacing of compaction pile – 3D and 5D with triangular pattern Spacing – 3D (desired improvement in N-values) Spacing-5D (desired improvement in N values not adequates)

Original design –

Spacing of compaction pile – 3D and 5D with triangular pattern

Spacing – 3D (desired improvement in N-values)

Spacing-5D (desired improvement in N values not adequates)

Additional Recommendation Spacing of sand compaction pile-4D Result-Adequate to obtain required densification (N-values) No. of piles (now required)=16000 instead of 32000

Spacing of sand compaction pile-4D

Result-Adequate to obtain required densification (N-values)

No. of piles (now required)=16000 instead of 32000

Pile capacity (Revised) Vertical downward-65 tonnes instead of 50 tonnes original Uplift capacity=25 tonnes instead of 5 tonnes original Lateral capacity-3.5 tonnes as against original 2.5 tonnes

Pile capacity (Revised)

Vertical downward-65 tonnes instead of 50 tonnes original

Uplift capacity=25 tonnes instead of 5 tonnes original

Lateral capacity-3.5 tonnes as against original 2.5 tonnes

Requirement of no. of RCC piles (based on revision)=9400 piles Reduction in no. of piles =40% Observation: Performance of the foundation-fully adequate and satisfactory.

Requirement of no. of RCC piles (based on revision)=9400 piles

Reduction in no. of piles =40%

Observation:

Performance of the foundation-fully adequate and satisfactory.

Phase-II (To double the capacity of the plant) Ground improvement – Vibro stone column in place of RCC piles and sand compaction piles Vibro stone column diameter- 960 mm Load test – carried on single column and group of columns Footing test conducted for confirmation during execution.

Ground improvement – Vibro stone column in place of RCC piles and sand compaction piles

Vibro stone column diameter- 960 mm

Load test – carried on single column and group of columns

Footing test conducted for confirmation during execution.

Trial Test Test plot 10 m x 10 m Vibro stone column – 11 m (length), c/c spacing 15 m, 2.15m & 1.8 m (Triangular pattern

Test plot 10 m x 10 m

Vibro stone column –

11 m (length),

c/c spacing 15 m, 2.15m & 1.8 m (Triangular pattern

Standard Penetration Test 01 60-400 11 24-46 Silty Clay Silty Clay 0-3.5 3.5-11 Compressor House 81 36-123 20 16-34 Silty Clay Silty Clay 0-2.3 2.3-11 Benefield Area 30 17-120 13 20-36 Silty Clay Silty Clay 0-2.5 25-11 Prill Tower % increase in N Value N After treatment Layer Depth Area

Static Cone Penetration Test (SCPT) 130-300 kg/cm2 50-80 kg/cm2 2-8m Post-treatment (Cone Resistance) Pre-treatment (Cone Resistance) Depth

Dynamic Cone Penetration Test (DCPT) 22-95 10-40 2-10 m Past-treatment (No. of blows per ft.) Pre-treatment (No. of blows per ft.) Depth

 

Vibro Stone Column of 960mm with spacing 2D, 2.25D and 2.5D where adopted depending on loading intensity Substantial saving in time and cost Subsequently observation during the operation of Phase-II confirmed a satisfactory behaviour of foundation

Vibro Stone Column of 960mm with spacing 2D, 2.25D and 2.5D where adopted depending on loading intensity

Substantial saving in time and cost

Subsequently observation during the operation of Phase-II confirmed a satisfactory behaviour of foundation

Concluding remarks Commitment to excellence from Geotechnical Engineers Positive attitude to continuously learn and to accept change for better Partnership and team work among all concerned i.e owner, consultant and contractor

Commitment to excellence from Geotechnical Engineers

Positive attitude to continuously learn and to accept change for better

Partnership and team work among all concerned i.e owner, consultant and contractor

Thank you………..

Thank you………..

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