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RAILWAY FORMATION RDSO GUIDELINES FOR EARTHWORK/ BLANKETING

RAILWAY FORMATION RDSO GUIDELINES FOR EARTHWORK/ BLANKETING. DEFINITIONS. CESS. TRACK STR. B A L L A S T. TRACK-FOUNDATION. BLANKET. FORMATION. SUB - GRADE. SUB - SOIL. HOW SHALL WE PROCEED. Knowledge of Soil Mechanics Soil Elements Common Tests on Soil

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RAILWAY FORMATION RDSO GUIDELINES FOR EARTHWORK/ BLANKETING

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  1. RAILWAY FORMATIONRDSO GUIDELINESFOREARTHWORK/ BLANKETING

  2. DEFINITIONS CESS TRACK STR. B A L L A S T TRACK-FOUNDATION BLANKET FORMATION SUB - GRADE SUB - SOIL

  3. HOW SHALL WE PROCEED Knowledge of Soil Mechanics Soil Elements Common Tests on Soil Soil Classification Soil Surveys Earthwork in Railway Projects Definitions Execution of Earthwork Blanket

  4. INDEX PROPERTIES • Mechanical (Sieve) Analysis • Coarse grained soil • Hydrometer analysis • Fine grained Soil • Consistency Limits • Liquid Limit LL - WL • Plastic Limit PL – WP • Shrinkage Limit • Plasticity Index PI - IP

  5. SOIL ELEMENTS Degree of Saturation in % S=Vw/Vv Voids Ratio e=Vv/Vs Porosity in % n=Vv/Vt Water Content in % w=Ww/Ws Bulk density gm/cc γ=W/Vt Dry density gm/cc γd=Ws/Vt

  6. PARTICLE SIZE DISTRIBUTION D10– Effective size Coefficient of uniformity - Cu Cu=D60/D10 Coefficient of Curvature Cc Cc=(D30)2/D60XD10 D10 D60 D30

  7. LIQUID LIMIT - ATTERBERG’S LIMITS Liquid Limit is the water content at which 25 blows cause the groove to close.

  8. PLASTIC & SHRINKAGE LIMIT Plastic Limit is water content at which 3 mm diameter roller of soil starts crumbling Shrinkage Limit is water content beyond reduction which does not cause volume decrease Plasticity Index PI or IP = Liquid Limit (LL or WL) – Plastic Limit (PL or WP)

  9. CLASSIFICATION IS:1498 - 1970 BOULDERS COARSE SILT & CLAY 75>PS>4.75mm 4.75>PS>75μ GRAVEL SAND Fines<5% Fines>12% Fines<5% Fines>12% SW SP SM SC GW GP GM GC GM-GC SM-SC Fines between 5% to 12% Fines between 5% to 12% GW-GM GP-GM GW-GC GP-GC SP-SM SW-SC SP-SC SW-SP GW-GP SW-SM

  10. COMPACTION – Primarily Expulsion of Air

  11. COMPATION OF SOILS ID - Relative density – cohesion less soils γd =γ/(1+w/100) ID = {(emax-e)/(emax-emin)}x100 4.54 Kg 18”

  12. PERMEABILITY OF SOIL V = ki V – Velocity of flow cm/sec k – coefficient of permeability Porosity of soil Shape and size of voids i - Hydraulic gradient

  13. Cohesive subgrade – Subgrade constructed with soil having cohesive behaviour i.e. shear strength is predominantly derived from cohesion of the soil. Normally soil having fines (< 75micron) exceeding 12% (As per IS Classification all fine grain soils, GM, GM-GC, GC, SM, SM-SC& SC ) Cohesionless subgrade – subgrade constructed with cohesionless, coarse-grain soil i.e. shear strength is predominantly derived from internal friction of the soil. Normally soils having fines less than 5% (As per IS Classification GW, GP, SW & SP types of soils) Other type of soils having fines between 5 to 12% needs detailed study.

  14. FORMATION IN BANK

  15. DESIGN OF RAILWAY FORMATION A stable formation should be able to sustain the track geometry under anticipated traffic densities and axle loads during service under most adverse conditions of weather & maintenance of track structure, which are likely to be encountered. The formation should be structurally sound – not to fail in shear strength –dead and live loads and the settlements of sub grade and sub soil should be within limits.

  16. CHARECTERISTICS OF SOIL Coarse grained soil • Particle shape and size cubical • Angle of internal friction high • Gradation – important • Well graded, Poorly graded • Cohesion less • Permeability high • Pore water pressure- generally not important 26

  17. CHARECTERISTICS OF SOIL Fine grained soil • Particle shape - generally flaky • Cohesion – generally cohesive • Angle of internal friction low • Permeability low • Arrangement of soil particles – important • Sensitive to in-situ condition • Water absorption – high • Results into development of Pore water pressure 27

  18. Various Aspects of Designing Subgrade/Subsoil Subgrade and Subsoil should be designed to be safe against shear failure & large deformation. Deficient shear strength of sub-grade and sub-soil: Bearing cap, failure of sub-grade causing cess & crib heave, ballast pockets Interpenetration failure or mud pumping failure Slips in bank slopes or creep deformations Large deformation without strength failure due to : In-service compaction & consolidation of bank-soil/sub soil Swelling & Shrinkage characteristics of bank soil/sub soil.

  19. SUB GRADE PARAMETERS Usually side slope 2:1 up to 6.0 m height Calculate Factor of safety of slopes High banks>6.0 m Poor sub soils including marshy soils Water table is high (submerged weight) Long term stability in cuttings

  20. SUB GRADE PARAMETERS Unsuitable soils for construction Organic clay, silts & peat; chalks, dispersive soils Poorly graded gravel and sand Cu<2 CH and MH in top 3 m bank Special Investigations and remedies if to be done including cutting through shales and soft rocks which disintegrate with water Mixed Soils and Boulders – Care to be taken

  21. SUB GRADE PARAMETERS Top width - 6.85 (7.85m) in filling & in cutting Ballast side slope will be 1.5H:1V For double line BG, width of formation in Bank & cutting will be 13.16m Cess width > 900 mm + additional on curve Top slope 1 in 30 Erosion control Borrow Pit – away from toe Highly cohesive – special treatment Minimum height of bank - 1.00m Soil prone to Liquefaction Cu<2 designed

  22. BLANKET The layer between the ballast & the sub grade is the blanket Functions : Reduce stress to subgrade Keep subgrade & ballast separate Prevent upward subgrade fines migration Prevent subgrade attrition by ballast shed water from above Drain water from below Ballast fulfills function (1) only Blanket fulfills all functions and including function (1), it reduces the otherwise required greater thickness of the ballast. In the absence of a blanket layer a high maintenance effort can be expected In addition, blanket dampens vibration.

  23. SPECIFICATION OF BLANKET MATERIAL • % FINES(PASSING 75µ) UPTO 5% PLASTIC FINES & UPTO 12% NON-PLASTIC FINES. • NO SKIP GRADING, COARSE GRAINULAR & WELL • GRADED & MORE OR LESS WITHIN ENVELOPING CURVE • THE MATERIAL –WELL GRADED WITH Cu & Cc AS BELOW: • - uniformity coefficient, Cu = D60 /D10 > 4(preferably >7) • - coefficient of curvature, Cc = (D30)²/D60 /D10 within 1& 3

  24. REQUIRED BALLAST/BLANKET DEPTH A min. ballast layer thickness is needed to provide for maintenance tamping & for void storage space A min. sub-ballast layer thickness is required for performing the functions of a separation/filter layer In addition, the combined ballast/blanket thickness must be sufficient to prevent progressive shear subgrade failure, and excessive rate of settlement through plastic strain accumulation in the sub-grade As per RDSO guide lines, thickness of blanket required is 0 to one meter as per soil used in top one meter of subgrade & Axle load.

  25. DEPTH OF BLANKET LAYER For axle load upto 22.5 t for different types of subgrade soils (in top one meter) No need of blanket for soils Rocky beds except shales & other soft rock, which are susceptible to weathering or becomes muddy on contact with water GW – well graded gravel SW – well graded sand Soil confirming to blanket material Soil having grain size distribution curve lying on right side of enveloping curve of blanket material in consultation with RDSO

  26. DEPTH OF BLANKET LAYER CONTD. 45 cm thick blanket for soils GP having Cu > 2 SP having Cu > 2 GM GM-GC 60 cm thick blanket for soils GC SM SC SM-SC Should increase to one meter if PI > 7

  27. DEPTH OF BLANKET LAYER CONTD. 100 cm thick blanket from soils ML ML-CL CL MI CI Rocks which are very susceptible to weathering

  28. DEPTH OF BLANKET LAYER CONTD. Soils having fines between 5 to 12% having dual symbol e.g. GP-GC, SW-SM etc. provide thickness as per second symbol Geo – synthetics can be used in consultation with RDSO as it reduced requirement of thickness of blanket. Blanket should be provided in new construction on all lines (even with light passenger traffic) In cohesive sub grade even 100 cycles of repeated load in excess of threshold strength will cause failure of formation.

  29. DEPTH OF BLANKET LAYER CONTD. In case more than one type of soil in top one of sub grade, soil requiring higher thickness of blanket will govern. For other types of soils not covered above, RDSO may be consulted for deciding thickness of blanket For higher axle loads Above 22.5t up to 25 t Add 30 cm thickness over & above as given for 22.5 t Above 25 t up to 30t Add 45 cm thickness over & above the given for 22.5t

  30. EXECUTION OF FORMATION EARTHWORK Before actual execution, details drawings to be prepared for entire length of the Project giving Alignment Formation levels Formation width at ground levels Cross-sections of catch water drain & side drains Cross section & levels of subgrade, blanket levels etc.

  31. Good Practices for execution of earthwork Preliminary work Preparation of Natural ground Site should be cleared properly for full formation width at Ground level plus one metre Benching should be provided on ground having steep slope Setting out of construction Limits Centre line of alignment (@200 m c/c or so) and full construction width be demarcated with reference pegs about 90 cm away from proposed toe of bank. Selection of Borrow area Sufficiently away from alignment Normally not less than 3 m plus height of embankment Selected having soil reliable for construction OMC & MDD should be checked in Lab

  32. General aspects Field trial for compaction test be done to access Optimum thickness Optimum number passes for type of roller planned Soil should be wet/dried out to get required OMC Clods or hard lumps to be broken to 75 mm lesser size Each layer to be compacted with specified roller commencing from sides up to required level of compaction before putting next layer.

  33. COMPACTION Compaction – Process of packing soil particles by mechanical means increasing the dry density, decrease of voids Consolidation : Gradual process of vol. Reduction under sustained loading Compaction : Rapid reduction mainly in air voids under a loading of short duration viz. blow of a hammer, passing of a roller, vibration. Advantages of compaction : Increase in shear strength Reduction in deformation under traffic Reduction in shrinkage & swelling Reduction in permeability Reduction in construction time.

  34. FACTORS AFFECTING COMPACTION Compacting effort – Higher the effort greater the compaction. Water content : Lubrication action increase in dry density till OMC. Type of soil : Fine grained soils give lower dry density than coarse grained soils Well graded soils have higher dry density than poorly graded soils Plastics fines have marked effect on compactibility Other factors : Thickness of lift Contact pressure Speed of rolling.

  35. FIELD COMPACTION EQUIPMENTS Three classes : Rollers, rammers & vibrators Smooth wheel rollers : 3 wheel or 2 wheel type best suited for gravel, sands, crushed rocks and any material requiring crushing action. More no. of passes, more compaction.

  36. Sheep’s foot Rollers : Numerous projections known as feet. Kneading action from bottom upwards When fully compacted no foot penetration Suitable for cohesive soils at low OMC. Unsuitable for gravels, sands More no. of passes more compaction.

  37. Pneumatic Rollers : Compaction effort depends on weight, tyre dia & inflation pressure. Both pressure & kneading action Suitable for cohesive soils at high natural m/c. Cohesion less sands and gravels.

  38. Vibratory Rollers : Out-of-balance weight type or pulsating hydraulic type Frequency between 1000-3000 rpm. Suitable for granular soils Allow compaction to a higher depth. Not suitable for cohesive soils. Rammers : Pneumatic or internal Combustion type. Suitable in area with restriction working space.

  39. ADVANTAGES OF COMPACTED BANK Higher speed of opening. Opening to goods & pass. Traffic simultaneously Max. sectional speed can be achieved in shortest time Ballast can be laid directly LWR can be laid

  40. MEASUREMENT OF FIELD COMPACTION determining dry density of soil in-situ methods : Sand replacement Any type of soils slow method Core cutter Fine grained cohesive soil convenient method Water displacement only cohesive soils Nuclear In-situ density & w/c

  41. Placement of Back-fills on Bridge approach Back fills resting on natural ground may cause differential settlement, vis-a-vis abutment, which rest on comparitively much stiffer base Back fill should be designed carefully to keep Settlement within tolerable limits Coefficient of subgrade reaction should have gradual change from approach to bridge. Backfills on bridge approaches shall be placed in accordance to para 605 of Indian Railways Bridge Manual 1998. Fill material being granular and sandy type soil be placed 150 mm on lesser thick layers & compacted with vibratory plate compactors. Benching should be made in approach embankment to provided proper bonding.

  42. SKETCH SHOWINGBACKFILL DETAILS

  43. IMPORTANCE OF BACKFILL • IMPORTANCE OF BACKFILL GENERALLY NOT • UNDERSTOOD. • MAGNITUDE OF LATERAL EARTH PRESSURE DEPENDS • ON: • - angle of internal friction – the more the value of ø, the lesser is the magnitude ( table below ) • - density • - presence of water may increase earth pressure upto • 250% • COHESIONLESS MATERIAL: - provide effective drainage. • - value of ø is more.

  44. Drainage arrangement in banks & cutting Effective drainage of rainwater in monsoon is very important to safe guard subgrade from failure Drainage of embankment Cross slope is provided from centre towards end. No side drains required except in case blanket layer goes below natural ground level On double line, central drain should be avoided as far as possible. Drainage in Cuttings Side drains Required water carrying capacity side drains and catch water drains be provided on both sides except where height of cutting is less than say upto 4 m. In deep cuttings, catch water drains of adequate capacity are required along with side drains.

  45. Catch Water Drains Required to control huge quantity of water coming from hill slope in cutting from safety consideration Catch water drains should be made pucca/lined with impervious flexible material locally available Catch water drains should be designed properly with Adequate slope No weep hole Sealing of expansion joint Regular inspection & maintenance Proper protection against tail end erosion.

  46. CATCH WATER DRAIN

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