Geotechnical Investigation


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

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Geotechnical Investigation

  1. 1. Importance of Proper Geotechnical Investigation in Engineering Project: Some case study <ul><li>J.N.Jha*, K.S.Gill* & A.K.Chaudhary** </li></ul><ul><li>*Department of Civil Engineering, Guru Nanak Dev Engineering College, Ludhiana </li></ul><ul><li>** Department of Civil Engineering, NIT, Jamshedpur </li></ul>
  2. 2. Introduction <ul><li>Construction activities increased manifold (development of economic activities) </li></ul><ul><li>Different types of complex structures are coming up (to meet the growing demand) </li></ul><ul><li>Attempt being made to make soil suitable to project and not the project to soil. </li></ul>
  3. 3. <ul><li>Geotechnical Engineer- </li></ul><ul><li>very important role to play in this challenging task. </li></ul><ul><li>Geotechnical Engineering Practice-At par with the best in the world. </li></ul><ul><li>Range of Geotechnical practice vary widely in India. </li></ul>
  4. 4. <ul><li>Field investigation-Most primitive equipment are in use </li></ul><ul><li>Laboratory testing-Practice vary widely with little standardization and accreditation. </li></ul>
  5. 5. 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
  6. 6. Result (Substandard practice) <ul><li>Substantial difference between actual soil profiles and available soil profiles (at the time of design as part of tender specifications) </li></ul><ul><li>Variation can be minimized if standard practices are followed during the soil investigation </li></ul>
  7. 7. <ul><li>Unfortunately this is not the case quite often </li></ul><ul><li>Who is responsible? </li></ul><ul><li>Responsibility squarely rests on Geotechnical community of the country and is a major failure on our part. </li></ul>
  8. 8. General and Standard Practice <ul><li>Tender for a project (information supplied) </li></ul><ul><li>Subsoil profile and soil characteristics is of general information only </li></ul><ul><li>Owner is not responsible for the correctness of this information </li></ul>
  9. 9. <ul><li>Contractor if desired should satisfy the correctness of information before submitting his offer </li></ul><ul><li>To safeguard the owner to avoid any dispute </li></ul>
  10. 10. Contractor (point of view) <ul><li>Time interval between issue of tender document and submission of technical bid is very short </li></ul><ul><li>Soil investigation is expensive </li></ul><ul><li>Impossible to carry out soil investigation </li></ul><ul><li>Bidder accepts the stipulation given in tender </li></ul>
  11. 11. Case study <ul><li>Road over Bridge (ROB) </li></ul><ul><li>Bridge : </li></ul><ul><li>5 span of 10.7 m with certain embankment on either side </li></ul><ul><li>As per tender SPT value 12 to 16 for top two layer extending up to 7 m. </li></ul>
  12. 12. <ul><li>Recommend allowable bearing pressure=150 kN/m2 at depth 2 m below GL for Pier foundation. </li></ul><ul><li>Accordingly Piers were constructed on shallow foundation </li></ul><ul><li>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 </li></ul>
  13. 14. <ul><li>Confirming soil investigation was carried out </li></ul><ul><li>Soil Profile: </li></ul><ul><li>Top 1-1.5 m : Sandy Clay </li></ul><ul><li>1.5-8 m : Soft marine clay </li></ul>
  14. 16. Rehabilitation Measure <ul><li>Piles installed around shallow foundation and integrated with foundation </li></ul><ul><li>Delay in completion of project, additional cost & dispute </li></ul>
  15. 17. Petro Chemical Complex <ul><li>As per Tender </li></ul><ul><li>Recommended depth of Pile = 25 m </li></ul><ul><li>Test pile –failed to take design load </li></ul><ul><li>Confirmatory (Bore hole) test </li></ul><ul><li>12 such confirmatory bone hole consistently showed that SPT value reported in original soil report are higher </li></ul><ul><li>Pile depth after confirmatory test =20m </li></ul><ul><li>Confirmatory soil investigation saved a major disaster. </li></ul>
  16. 19. Choice of Appropriate foundation and execution <ul><li>Optimum foundation design should ensure </li></ul><ul><li>Technical adequacy </li></ul><ul><li>Cost effectiveness </li></ul><ul><li>Ease of execution </li></ul>
  17. 20. <ul><li>Reasons </li></ul><ul><li>Insufficient and inaccurate information at the time of design variation in strata </li></ul><ul><li>Changes in project requirement during execution. </li></ul>
  18. 21. <ul><li>Achieving this is easily said than done-needs engineering judgement </li></ul><ul><li>Engineering Judgement – comes from experience. </li></ul><ul><li>Experience comes from bad engineering judgement </li></ul>
  19. 22. Case study <ul><li>Fertilizer plant in Gangetic belt-possibility of optimum design </li></ul><ul><li>Phase-I </li></ul><ul><li>Soil strata (Site) </li></ul><ul><li>N<10- For a depth upto 10 m </li></ul><ul><li>N-10-20-For a depth upto 10-20 m </li></ul><ul><li>>20 – For a depth upto 10-20m </li></ul>
  20. 23. <ul><li>Type of Soil </li></ul><ul><li>Silty sand with high water table </li></ul><ul><li>Threat of liquefaction during earthquake </li></ul>
  21. 24. Foundation Design (Recommended) <ul><li>Provide RCC cast in situ piles (diameter 400 mm) with pile capacity </li></ul><ul><li>Axial vertical load – 50 Tonnes </li></ul><ul><li>Uplift - 5 Tonnes </li></ul><ul><li>Horizontal capacity=2.5 Tonnes </li></ul>
  22. 25. <ul><li>To overcome the problem of liquefaction during earthquake </li></ul><ul><li>Provide sand compaction pile 2 to 3 rows around RCC piles </li></ul>
  23. 26. Total requirement <ul><li>As per design </li></ul><ul><li>No. of RCC piles 16000 </li></ul><ul><li>No. of sand compaction piles 32,000 </li></ul><ul><li>Time required for installation of RCC piles and sand compaction piles= </li></ul><ul><li>6 months more than what was originally planned </li></ul><ul><li>This prompted for the review of foundation design </li></ul>
  24. 27. Sand Compaction Pile <ul><li>Original design – </li></ul><ul><li>Spacing of compaction pile – 3D and 5D with triangular pattern </li></ul><ul><li>Spacing – 3D (desired improvement in N-values) </li></ul><ul><li>Spacing-5D (desired improvement in N values not adequates) </li></ul>
  25. 28. Additional Recommendation <ul><li>Spacing of sand compaction pile-4D </li></ul><ul><li>Result-Adequate to obtain required densification (N-values) </li></ul><ul><li>No. of piles (now required)=16000 instead of 32000 </li></ul>
  26. 29. <ul><li>Pile capacity (Revised) </li></ul><ul><li>Vertical downward-65 tonnes instead of 50 tonnes original </li></ul><ul><li>Uplift capacity=25 tonnes instead of 5 tonnes original </li></ul><ul><li>Lateral capacity-3.5 tonnes as against original 2.5 tonnes </li></ul>
  27. 30. <ul><li>Requirement of no. of RCC piles (based on revision)=9400 piles </li></ul><ul><li>Reduction in no. of piles =40% </li></ul><ul><li>Observation: </li></ul><ul><li>Performance of the foundation-fully adequate and satisfactory. </li></ul>
  28. 31. Phase-II (To double the capacity of the plant) <ul><li>Ground improvement – Vibro stone column in place of RCC piles and sand compaction piles </li></ul><ul><li>Vibro stone column diameter- 960 mm </li></ul><ul><li>Load test – carried on single column and group of columns </li></ul><ul><li>Footing test conducted for confirmation during execution. </li></ul>
  29. 32. Trial Test <ul><li>Test plot 10 m x 10 m </li></ul><ul><li>Vibro stone column – </li></ul><ul><li>11 m (length), </li></ul><ul><li>c/c spacing 15 m, 2.15m & 1.8 m (Triangular pattern </li></ul>
  30. 33. 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
  31. 34. Static Cone Penetration Test (SCPT) 130-300 kg/cm2 50-80 kg/cm2 2-8m Post-treatment (Cone Resistance) Pre-treatment (Cone Resistance) Depth
  32. 35. 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
  33. 37. <ul><li>Vibro Stone Column of 960mm with spacing 2D, 2.25D and 2.5D where adopted depending on loading intensity </li></ul><ul><li>Substantial saving in time and cost </li></ul><ul><li>Subsequently observation during the operation of Phase-II confirmed a satisfactory behaviour of foundation </li></ul>
  34. 38. Concluding remarks <ul><li>Commitment to excellence from Geotechnical Engineers </li></ul><ul><li>Positive attitude to continuously learn and to accept change for better </li></ul><ul><li>Partnership and team work among all concerned i.e owner, consultant and contractor </li></ul>
  35. 39. <ul><li>Thank you……….. </li></ul>