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Different Methods of FORMATION REHABILITATION

Different Methods of FORMATION REHABILITATION. DEFINITIONS. CESS. TRACK STR. B A L L A S T. TRACK-FOUNDATION. BLANKET. FORMATION. SUB - GRADE. SUB - SOIL. DESIGN OF RAILWAY FORMATION.

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Different Methods of FORMATION REHABILITATION

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  1. Different Methods of FORMATION REHABILITATION

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

  3. 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.

  4. SUB GRADE PARAMETERS Top width - 6.85(7.85) in filling & 6.25(7.85) in cutting Cess width > 900 mm + additional on curve Top slope 1 in 30 Adequate Erosion control measure Borrow Pit – away from toe Highly cohesive – special treatment Minimum height of bank - 1.00m Soil prone to Liquefaction Cu<2 not to be used but with proper design

  5. 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.

  6. Properties of Blanketing Material • It should be coarse granular and well graded. • Non plastic fines are limited to 12% where as plastic fines are limited to 5%. • Particle size distribution curve should be within the enveloping curve. • It should be impervious enough to intercept water coming from ballast away from subgrade and at the same time, pervious to permit drainage of water that is coming upwards from the subgrade.

  7. PROPERTIES OF BLANKET MATERIAL Reduce stress to subgrade : To serve as a structural material, it must have a High enough resilient modulus Should provide stable foundation under repeated wheel load To achieve these properties The material must be permeable enough to avoid significant positive pore pressure build up under repeated load Must consist of durable particles Must not be sensitive to changes in moisture content

  8. PROPERTIES OF BLANKET MATERIAL (CONTD.) SUBGRADE ATTRITION PREVENTION: High stresses at the ballast contact points on the subgrade surface are eliminated by the cushioning effect of the blanket DRAINAGE: PLAYS TWO ROLES SHED WATER ENTERING FROM SURFACE Its permeability should be smaller than that of ballast & have a surface sloped for lateral drainage Drain water seeping up from the subgrade To satisfy both roles, the sub-ballast must generally have a permeability between that of the subgrade & that of the ballast This requirement probably will be achieved just by satisfying the separation criteria. However, an addl. Criterion is used to ensure adequate permeability to drain an adjacent layer : D15(filter) > 4 to 5 D15 (soil being drained)

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

  10. 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

  11. 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.

  12. 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

  13. 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

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

  15. 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

  16. FORMATION REHABILITATION

  17. INTRODUCTION • Large length of weak formation exists on Indian Railways. • About 600 km of track is under PSR & nearly 2100km length is imposed with TSR during monsoon. (Action plan on formation rehabilitation) • This length has increased manifold after the introduction of higher axle load & increased GMT. RB vide letter No.2006/CE-I/Geo/235 dt19/10/2007 has issued comprehensive guidelines for review of weak formation. Hence Actual figures are much higher.

  18. Weak formations result in many direct losses such as ballast penetration, increased maintenance, imposition of speed restriction affecting punctuality etc. and indirect losses such as extra fuel consumption, passenger discomfort, extra maintenance cost and early renewal. • To minimize the losses it is necessary to rehabilitate the existing weak formation. • It is necessary to take up the formation rehabilitation works to reduce the direct and indirect losses. • Treatment to the formation with proper design is required for rehabilitation of the weak formation.

  19. Identification of weak formation • RB's letter no.2006/CE-I/Geo/235 dt19/10/2007 • Stretches with history of ballast penetration, excessive settlements, sign of distress, shear failure. • Stretches with track tamping cycles less than 1 year, low TGI value due to formation problem. • Locations where speed restriction of 75kmph or less due to weak formation.

  20. DATA COLLECTION • Earlier RDSO has issued Procedure Order for Classification of Formation Soil vide Circular No. GE-P1 in May 2003. As per this, Soil sample in every Block section at the rate of one sample per 2.5 Km are to be collected. • These samples should be tested for Atterburg limit test and grain size analysis to determine the Soil classification. • This soil classification is to be reflected in Track Diagrams (Para 211(v) of IRPWM).

  21. Data Collection for Suspected Weak Formation • Plotting cross sections of bank at every 20m, upto 10m beyond toe of bank. • Gang record of attention of track. • Recording of ballast penetration profile at every 20m. This can be done manually. In other Railways latest technique of Georadar is used which work on the principle of emitting and receiving electromagnetic waves.

  22. Analysis of data to decide type of failure • Failure of the base of subsoil strata. • Failure of fill material. • Failure of formation top.

  23. FIVE STEP TREATMENT • Railway Board vide letter no. 91/CE-II/SF/9 dated 04.07.1991 and 03.08.1995, issued Five steps action plan to be followed before undertaking rehabilitation measures as given below- • Make the formation width, cess level and side drains with standard profile. • Carry out shallow screening/deep screening of ballast section. • Ensure no loose or missing fittings. • Increase ballast cushion to 30 cm/35 cm. • If the problem still persists increase sleeper density to 60cm c/c.

  24. FORMATION TREATMENT FOLLOWING TREATMENTS TRIED IN PAST: To improve the shear strength of the formation soil • Lime pile. • Ballast piling • Cement grouting • Sall balli/ sleeper/ rail piling

  25. To improve the Drainage of Fill material • Vinyl drains/Band drains • Open cross drains filled with coarse grained material • Polyethylene and other similar impervious sheets However none of these methods could successfully improve the desired properties

  26. SUCCESSFUL METHOD OF TREATMENT • Full width blanket is the successful method. • This is the only method, which is universally acceptable to the World Railways with or without use of geotextile/geogrid. This is based on the philosophy of reducing incoming stresses on the top of subgrade and to avoid penetration of water in formation. • In order to perform the desirable functions, the blanket material has to pass through a strict qualifying criteria of grain size distribution etc. • Specification of blanket should be as per Guidelines of Earthwork in Railway Project, July-2003.

  27. Different methods of laying full width blanket material in existing formation • Aluminum alloy girder method • Track dismantling method • Manually operated portal method • C.C.Crib &rail cluster method • Rail cluster method • Mechanised formation rehabilitation method

  28. Al- ALLOY GIRDER METHOD - BLANKET DEPTH : 1 - 1.2M - PERMISSIBLE SPEED ON GIRDERS: 20 Kmph PROGRESS : 300 TO 350 M PER MONTH.

  29. ALUMINIMUM ALLOY GIRDER • Salient features • Girders designed by B&S directorate of RDSO in consultation with DRDO, Pune. • The material used for fabrication of girder is light weight silicon- manganese- aluminium. • Overall length – 6.6 m • C/c span – 6.0 m • Total depth – 600 mm • Depth from bottom of rail – 500 mm • Weight – 2.3 ton • In four main parts each weight 600 kg • Speed 20 kmph.

  30. LAYING BLANKET WITH ALUMINIMUM ALLOY GIRDER • Pre block operation : • Cutting of cess • Arranging Blanket & other material • Insertion of girder (Ist block – 3 ½ hrs) • Cutting crib space • Placing crib • Insertion of girder & linking track • Post block operation • Cutting earth under girder • Laying blanket • Shifting girder (2nd Block 3 ¼ Hrs) • Longitudinal shifting of girder • Blanket at crib location • Laying top layer of blanket • Linking track soil Ballast.

  31. CASE STUDY APPLICATION OF ALUMINIUM ALLOY GIRDER • Rehabilitation of the weak stretch between Wadi-Nalwar stations, GTL div., SCR has been carried out successfully with this method between year 1998-2001 ( 2.34 km length in UP line). As a result permanent speed restrictions due to weak formations has been removed. • Northern Railway also procured 5 set of Aluminium alloy girder & railway will use for rehabilitation work in Delhi division

  32. TRACK DISMANTLING METHOD

  33. TRACK DISMANTALING METHOD • Main operations involved are - Dismantling of track & removal of ballast. - Excavations of existing formation to required level with pocklain. - Spreading of blanket material & compaction with 10 t roller - Lifting of track & packing. • The above operations falls under three categories - before traffic block - during traffic block - after traffic block

  34. C.C.CRIB & RAIL CLUSTER METHOD

  35. DURING BLOCK

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