N.N.Som Consulting Geotechnical Engineer Former Professor of Civil Engineering - PowerPoint PPT Presentation

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braced excavation in soft clay a case study of kolkata metro construction by cut and cover method n.
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N.N.Som Consulting Geotechnical Engineer Former Professor of Civil Engineering PowerPoint Presentation
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N.N.Som Consulting Geotechnical Engineer Former Professor of Civil Engineering

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  1. BRACED EXCAVATION IN SOFT CLAY A CASE STUDY OF KOLKATA METRO CONSTRUCTION BY CUT AND COVERMETHOD N.N.Som Consulting Geotechnical Engineer Former Professor of Civil Engineering Jadavpur University, Kolkata

  2. MAP OF WEST BENGAL SHOWING LOCATION OF CALCUTTA METROPOLITAN DISTRICT

  3. CALCUTTA METROPOLITAN DISTRICT

  4. RAPID TRANSIT SYSTEM FOR KOLKATA METRO - FIRST PHASE OF CONSTRUCTION BY CUT AND COVER METHOD

  5. CALCUTTA METRO ALIGNMENT

  6. GEOLOGICAL FEATURES OF CALCUTTA SOIL

  7. Soil Properties (average) Description of Strata N blows/30 cm W LL PL Cu mv (%) (%) (%) (t/m2) m2/t 0 • Light brown/brownish grey silty clay/clayey silt with occasional lenses of fine sand 5 – 8 30 54 24 4.0 0.002 4 2 – 4 II. Grey/dark grey silty clay, clayey silt with semi-decomposed timber pieces 50 55 28 2.5 0.007 14 III Bluish grey silty clay with calcareous modules 10 30 60 25 6.0 0.003 DEPTH (M) 20 IV. Brown/yellowish brown sandy silt/silty fine sand with occasional lenses of brown and grey silty clay 20 --- 25 V. Mottled brown/grey silty clay with laminations often with rusty brown spots 20 – 30 30 65 25 10.0 0.002 30 VI Brown /light brown silty fine to medium sand 40 / = 350 40 SUBSOIL OF KOLKATA : NORMAL CALCUTTA DEPOSIT

  8. 0 I. Light grey/brownish grey silty clay/clayey silt 3 IIA. Grey / light grey fine to medium sand DEPTH (M) N = 15 – 30 blows / 30 cm 25 • Mottled brown /grey silty clay with • laminations often with rusty brown silt 30 SUBSOIL OF KOLKATA : RIVER CHANNEL DEPOSIT

  9. LENGTH OF FIRST LINE OF KOLKATA METRO – 16. 633 Km • Elevated – 1. 228 Km. • Surface – 0. 270 Km. • Underground – 15. 135 Km • Sheet Piles : 0.356 Km. • H-Pile with Timber Lagging : 0.684 Km. • Diaphragm Wall : 12.687 Km. • Shield Tunnel : 1.090 Km.

  10. OPEN CUT IN MAIDAN AREA

  11. 0 (m) STRUT 1 Dessiccated Brownish grey silty clay - 1.5 - 2.0 Cu = 4 t/m2 - 3.8 2 - 6.0 Grey / dark grey silty clay with decomposed wood - 6.5 3 - 9.0 - 9.5 Cu = 2.5 t/m2 - 13.2 4 - 11.0 - 11.5 - 13.5 Bluish grey silty clay with kankar Cu = 6 t/m2 - 17.2 Yellowish Brown sandy silt with clayN = 21 - 37 TYPICAL EXCAVATION PROFILE OF CUT-AND-COVER CONSTRUCTION WITH DIAPHRAGM WALL AND STRUTS

  12. + 4.69m F I L L + 1.80 • = 1.9 t/m3 Cu = 3 t/m2 Brownish grey clayey silt - 0.12  = 1.9 t/m3 Grey silty clay / clayey silt - 2.00 Siltwith Decayed Wood LL = 58PL = 32 Cu = 2 t/m2 W = 50 T u n n e l s - 8.00 • = 1.9 t/m3 Cu = 3 t/m2 Bluish grey silty clay LL = 1.9 t/m3 PL = 3.6 t/m2 - 13.00 Brown silty fine sand - 19.50 SHIELD TUNNELLING BETWEEN BELGACHIA AND SHYAMBAZAR

  13. BRACED CUT WITH DIAPHRAGM WALL • Diaphragm Wall • Excavation & Strutting • Box Construction • Backfilling

  14. + + + å + + C N γ3D γ D C (H D D ) /D 2 u 4 c 4 f u 2 f 1 = F å + + γ (H D D ) 2 γ STABILITY AGAINST BOTTOM HEAVE IN STRATIFIED SOIL

  15. GUIDE WALL FOR DIAPHRAGM WALL TRENCH

  16. REINFORCEMENT CAGE OF DIAPHRAGM WALL

  17. DESIGN OF BRACED CUTS

  18. Adjacent building movement Buckled struts Wall position Movement of wall (a) (b) Water pressure Bottom heave (d) (c) Sand and/or gravel bottom BRACED CUT : MODES OF FAILURE (WINTERKORN & FANG 1972)

  19. GROUND SETTLEMENT FOR EXCAVATION BELOW 1ST STRUT

  20. WALL DEFLECTION IN SEQUENTIAL EXCAVATION AND STRUTTING (CONCEPTUAL)

  21. APPARENT EARTH PRESSURE DIAGRAM IN BRACED CUT (PECK 1969)

  22. GROUND SETTLEMENT IN BRACED CUT WITH SHEET PILE SUPPORT (PECK 1969)

  23. INSTRUMENTATION

  24. OBJECTIVE • To Study • Earth Pressure on Diaphragm Wall • Diaphragm Wall Movement • Strut Load • Ground Settlement

  25. CALCUTTA METRO CUT : LOCATION OF INSTRUMENTED TEST SECTIONS BETWEEN GIRISH PARK AND M. G. ROAD STATION

  26. LOCATION OF EARTH PRESSURE CELLS IN DIAPHRAGM WALL

  27. FLUID PRESSURE MEASURED BY EARTH PRESSURE CELLS IN DIAPHRAGM WALL TRENCH BEFORE CONCRETING

  28. Concrete Cover G.L Pit 600x600 600 50 mm Lean Concrete Settlement Stud GROUND SETTLEMENT MEASURING POINTS

  29. PORE PRESSURE DISTRIBUTION AS MEASURED BY VIBRATING WIRE PIEZOMETERS

  30. EARTH PRESSURE ON DIAPHRAGM WALL BEFORE COMMENCEMENT OF EXCAVATION

  31. VALUES OF IN – SITU KO Depth Location Location Location Average (m) 1 2 3 2 1.65 0.77* 0.55* 1.0 4 1.70 0.85 0.80 6 0.95 0.85 0.73 8 0.83 1.16 0.70 10 0.70 0.84 0.65 0.70 12 0.67 0.90 0.60 13.5 0.50 0.80 0.70 16 0.37 0.48 0.30 0.50 17.5 0.44 0.65 0.45 * Low values due to inadequate seating

  32. DIAPHRAGM WALL DEFLECTION AT DIRRERENT STAGES OF EXCAVATION

  33. MEASURED STRESSES ON DIAPHRAGM WALL AT DIFFERENT STAGES OF EXCAVATION

  34. SUMMARY OF MEASURED EARTH PRESSURE AT DIFFERENT STAGES OF EXCAVATION

  35. COMPARISTON OF EARTH PRESSURE BY PECK’S METHOD AND OBSERVED DATA Depth Method Maximum earth m Depth at which pressure linear variation changes to constant pressure m (t/m2) (m) 10.0 Peck 10.8 0.80 2.5 Observation 12.5 0.55 6.0 12.0 Peck 12.0 1.00 3.0 Observation 17.0 0.50 7.2 13.6 Peck 15.0 1.00 4.4 Observation 18.0 0.65 8.2

  36. FORCES ON DIAPHRAGM WALL

  37. FORCES ON DIAPHRAGM WALL

  38. DISTANCE FROM EXCAVATION MAX. DEPTH OF EXCAVATION VARIATION OF GROUND SETTLEMENT AT DIFFERENCE TEST SECTIONS

  39. CONSTRUCTION CONTROL

  40. CONTROL PARAMETERS PARAMETERS Effect on Adjoining Buildings Settlement at Different Stages of Excavation Angular Distortion of Buildings Placement of Strut Time Effect

  41. FIELD MEASUREMENTS Observations Settlement of Plinth / floor Tilt Cracks in Walls / Floors

  42. EFFECT ON ADJOINING BUILDINGS Observations Settlement of Plinth / floor Tilt Cracks in Walls / Floors

  43. GROUP A BUILDINGS : 60 Buildings Monitored Small and Minor Damages in the form of * Cracks & Minor Tilts * No Structural Distress * No Detailed Observation done except monitoring cracks & tilts

  44. GROUP B BUILDINGS 28 Buildings Required Detailed Study Moderate to severe damages Temporary Protective Measures Final Rectification after Construction

  45. MAXIMUM SETTLEMENT OF BUILDINGS

  46. Time of Construction

  47. Building Settlement at Different Stages of Excavation