earth work in railway

EARTHWORKIN

RAILWAY PROJECTS

DEFINITIONS

DEFINITIONS • Track structure – consists of rail sleepers &

fastenings• Track foundation – constitutes the ballast, blanket

and subgrade, which placed / exist below track structure to transmit load to subsoil.

• Sub-grade – The part of embankment or of cutting above subsoil by borrowed soil of suitable quality upto bottom of blanket/ballast

• Ballast – crushed stone with desired specifications placed directly below sleepers.

• Sub ballast – The layer of coarse-grained material provided between blanket/subgrade and ballast & confined to width of ballast section.

• Blanket – The layer of specified coarse-grained material of designed thickness provided over full width of formation between subgrade and ballast.

• Formation top – the boundary between ballast and top of blanket or sub-grade

• Subsoil – the soil below natural ground level. • Formation – the general term referring to whole of

blanket, sub-grade and sub-soil.

• 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.

• Dispersive Soil – are those, which normally deflocculate when exposed to water of low salt content. Generally, dispersive soils are highly erosive & have high shrink & swell potential.

• Cess – Part of top of formation from toe of ballast to edge of formation

• Unstable Formation – Yielding formation with non terminating settlements including slope failure, which require excessive maintenance efforts.

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 and the settlements should be within limits.

Various Aspects of Designing

Subgrade/Subsoil

• Subgrade should be designed to be safe against shear failure & large deformation. – Deficient shear strength of sub-grade or bank-soil or sub-soil:

• Bearing cap, failure of subgrade 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.

RAILWAY FORMATION BEHAVIOUR

• Formation behaviour is not only dependant

on axle loads but also on traffic density &

pattern of traffic

• Therefore, simple bearing capacity formula

not applicatble.

STUDIES ON COHESIVE FORMATION • Studies carried by Office for Research & Experiments

(ORE) of the International Union of Railway (UIC)vide report No. D71/RP 12 – Findings are : – The prime factor influencing the distribution of stress within the

track foundation to a thickness of 60 cm is the packing condition under the sleeper

– Packing condition is subject to a high degree of random scatter which tends to mask the difference between the various packing methods

– The flexural rigidity of the sleeper is of secondary importance & for practical purposes similar stress distributions were obtained from both timer and concrete sleepers.

– In terms of stress distribution per unit load transmitted to the foundation, sleeper spacing over the range of 79-63 cm. has a negligible influence.

STUDIES ON COHESIVE FORMATION(cont.) • Main conslusion are:

– Under the action of repetitive loading some cohesive soils will fail at lower stresses than under a single application of load.

– For these soils a level of stress exists above which repeated application causes a terminating deformation, called “Threshold stress”

– Other cohesive soils,apparently those with a high silt or sand fraction do not exibit a distinct threshold stress.

– The threshold stress is not a unique material parameter but dependent on mean effective stresses & on loading wave shape, frequency & previous loading history.

– A value of threshold stress determined under standardised test conditions can be used for the design of the track foundation.

SUBGRADE

• The subgrade is the platform upon which the track structure is constructed. Its main function is to provide a stable foundation for the blanket & ballast layers

• The influence of the traffic induced stresses extends downward as much as five metres below the bottom of the sleepers

• Hence, the subgrade is a very important substructure components which has a significant influence on track performance & maintenance.

SUB GRADE (CONTD.)• To serve as a stable platform the following subgrade

failure modes must be avoided :• Excessive progressive settlement from repeated traffic

loading• Consolidation settlement & massive shear failure under

the combined weights of the train, track structure & earth• Progressive shear failure (Cess heave) from repeated

wheel loading. • Significant volume change (swelling & shrinking) from

moisture change• Subgrade attrition.

BLANKET • The layer between the ballast & the sub grade is the blanket• Functions :

1. Reduce stress to subgrade2. Keep subgrade & ballast separate3. Prevent upward subgrade fines migration4. Prevent subgrade attrition by ballast 5. shed water from above6. Drain water from below

• Ballast fulfills function (1) only• Blanket fulfills all functions and inclunding 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.

PROPERTIES OF BLANKET

MATERIAL • Reduce stress to subgrade :• To serve as a structural material, it must have a

– High enough resilient modulus– Stable plastic strain accumulation characteristic 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

• Such a material is represented by mixtures of sand & gravel particles composed of crushing and abrasion resistant materials.

PROPERTIES OF BLANKET MATERIAL (CONTD.)

• PARTICLE SEPARATION: – MUST PREVENT

• intermixing of ballast & subgrade• Upward migration of subgrade particles into the ballast

– These properties can be achieved by proper gradation.– SEPARATION CRITERIA

• D15(filter)<5D85 (protected soil) ……. (i)• D50(filter)<25 D50 (protected soil) ……. (ii)

– The criterion in (i)Causes the particles at the coarsest end of the protected soil (D85)to be blocked by the particles at the finest end of the filter (D15).

– The criterion in (ii) helps to avoid gap graded filters and create a filter gradation that is somewhat parallel to that of the protected soil.

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)

•% 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

SPECIFICATION OF BLANKET MATERIAL

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.

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

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

DEPTH OF BLANKET LAYER CONTD.

• 100 cm thick blanket from soils– ML– ML-CL– CL– MI– CI– Rocks which are very susceptible to weathering

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

• Gco – 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 subgrade even 100 cycles of repeated load in

excess of threshold strength will cause failure of formation.

DEPTH OF BLANKET LAYER CONTD.

• In case more than one type of soil in top one of subgrade, 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 upto 25 t

• Add 30 cm thickness over & above as given for 22.5 t

– Above 25 t upto 30t • Add 45 cm thickness over & above the given for 22.5t

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.

• 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 as per frequency prescribed

– Use of material should be planned in such a way to use soil with higher % of coarse grain material in upper layers.

– 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 upto required level of

compaction before putting next layer.

FIELD COMPACTION TRIALS• WHY FIELD COMPACTION TRIAL IS REQUIRED?

- compaction process in lab & field is not comparable.- for deciding most appropriate compactor. - for determination of attainable dry density with type of compactor available under various combinations of field parameters

• PROCEDURE:- construct a ramp of about 30m long, 10m wide & 0.15m thick on one end and 0.55m on other end.

- divide the ramp equally into desired number say, 4 segments, each strip will be used for conducting trials

RAMP FOR FIELD COMPACTION TRIALS

• IN FIELD, IT IS GENERALLY NOT DONE

0.15m

0.55 m

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 : – Increas in shear strength– Reduction in deformation under traffic– Reduction in shrinkage & swelling– Reduction in permeablility– Reduction in construction time.

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.

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.

• 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.

• Pneumatic Rollers : – Compaction effort

depends on weight, tyre dia & inflation pressure.

– Both pressure & kneading action

– Suitable for cohesive soils at high natural m/c.

– Cohesionless sands and gravels.

• Vibratory Rollers : – Out-of-balance weight type or pulsating hydraulic type

– Frequency between 1000-3000 cpm.

– Suitable for grannular 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.

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

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

• 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.

SKETCH SHOWING BACKFILL DETAILS

IMPORTANCE OF BACKFILL• IMPORTANCE OF BACKFILL GENERALLY NOT UNDERSTOOD, IN SOME PROJECTS EVEN CE / CON. GIVEN WAIVAL FOR NON-PROVISION OF BACKFILL • 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.

Grain size Values of Ø in degree

Clay

Sand & Gravel

Blasted rock fragments

30 ( Generally 20)

32 – 41

40 - 50

• DIRECTION OF LATERAL EARTH PRESSURE - ACTS AT ANGLE OF WALL FRICTION FROM PERPENDICULAR TO BACK OF WALL ( Table below )

• THE MORE THE VALUE OF , LESSER WILL BE HORIZONTAL COMPONENT OF LATERAL EARTH PRESSURE • ANGLE OF WALL FRICTION MAINLY DEPENDS ON: - roughness of wall: the more rough is the back of wall,

the better it is.- ø of backfill: the more the value of Ø of backfill, the more is the value of .

WALL BACKFILL ANGLE OF WALL FRICTION -

-SMOOTH BACK FACE

-LESS ROUGH FACE

-ROUGH BACK FACE

0

1/3 * Ø

2/3 * Ø

W

F

• Drainage arrangement in banks & cutting

– Effective drainage of rainwater is 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 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.

• 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.

CATCH WATER DRAIN

LOWERING OF GROUND WATER IN A WET CUT

• Erosion control of slopes on bank/cutting– Exposed surface of bank/cutting experiences surfacial erosion due to action

of enogenous wind & water– Erosion control measures are commonly classified into

• Conventional non-astronomical system• Bio-technical System• Engineering system• Non conventional hydro-seeding system.

– Conventional non-agronomincal system• This system uses asphalting, cement stabilisation pitching etc.• System is best utilized against seepage, erosion by wave action etc.

– Biotecnical system• Vegetation is provided on exposed surface• Best suited for soils having some clay fraction, • Suitable grass used are doob grass, chloris gyne, Inponea gorneas, casuariva & goat foot

creepers, vetiver grass etc

– Engineering System• Geo-jute

– Used in areas having high erosion– Biodegradable & helps in growth of vegetation on degradation– Two types – fast/slow biodegradable.

– Polymer geogrids• Used under unfavourable soil & rainfall condition where

vegetative growth in difficult• Flexible, non biodegradable. Resistant to chemical effect,

ultravoilet degradation resistant & stable over a temperature of 60-1000C

– Hydro-seeding system • Non-conventional & innovative system of development of

vegetation• Verdyon mulch solution @ 100 to 150 gm/m2 is sprinkled on

surface from germination of vegetation as per local soil/climatic condition.

SHOTCRETING

PITCHING

RETAINING WALL

GABIONS

ROCK BOLTING

MICROPILING

SOIL NAILING

HSBN

MSBN

BOULDERNETS OF GEOSYNTHETICS

BOULDERNETS OF GEOSYNTHETICS

CATCH FENCING

GEOMAT/GEONET

GEOMAT/GEONET

• Other aspects– General points

• Suitable slope be provided during rolling to avoid ponding of water• Top slope 1 in 30 way from centre• Extra wide bank by 500 mm on either side & then cut & dressed to avoid loose earth

on shoulders• Minimum overlap of 200mm between each run of roller• At the end of working day, fill material should not be left uncompacted.• Rain cuts should not be allowed to developed deep and wide.• After finishing formation movement of vehicals should not be allowed on top.• In conversion/doubling/rehabilitation projects, suitable benching of existing slopes be

done before new earthwork is taken up.• 30cm granular base be provided where water table is high & fill material is fine

grained.• At places where embankment material are not conductive to plant growth, top soils

from site clearance/cutting/borrow pits be stored for covering slopes of embankment/cutting.

• WIDENING OF EMBANKMENT -

• Uprout vegetation, remove loose materials.

• Benching at every 30cm ht.

• E/w in layers. Each layer sloping out 1:30.

• Compaction by using vibrating rollers of around 900mm wide.• 6 to 8 passes normally sufficient

• 98% of MDD or equal to existing bank.

• Density to be checked at 200m length.

• Width of each layer in excess by 300mm.

• Excess width to be cut and dressed

• RAISING OF EXISTING FORMATION -

• Raising to be done after widening.• Raising <150mm, with ballast restricting overall thickness to 350mm.• Raising <150mm to 1000mm,

• existing ballast to be taken out• granular material to be provided• top 600mm of granular material shall satisfy the specifications of

blanket & compacted • thereafter clean ballast to be inserted.

• Raising >1000mm, desirable to lay a detour temporarily.

• EARTHWORK IN DETOURS• In accordance with RDSO’s guidelines.

• EMBANKMENT ON SOFT SOIL– Soil shall be improved using

• Preloading and stage construction as per the design.

• Installation of vertical sand drains.

• Installation of prefabricated vertical drains.

– Selection of perticular scheme depends on rate of construction & techno-economic consideration.

– This may be decided in consultation with RDSO.

• SANDWICH CONSTRUCTION OF BANK WITH COHESIVE SOILS– May be adopted with cohesive soils having very low

permeability (< 10-2 cm/sec) & bank height more than 3m. – A layer of coarse sand (Cu > 2) of about 20 to 30 cm be

provided at interval of 2 to 3 m. – Even upto 3 m bank height, a bottom layer of sand be

provided– Before adopting such construction a detail techno-

economic study be carried out if required, RDSO be consulted.

• Safety at work site– Necessary precaution towards safety at work

site including doubling & gauge conversion should be part of contract agreement

• Environmental aspect– Efforts should be made to ensure least

disturbance to surrounding environment– Rules & regulations of Govt. be followed in

this regard

QUALITY ASSURANCE OF EARTHWORK

• Adequate quality control/checks at all stages of construction be carried out– Selection of construction material– Adoption of Method– Use of suitable machinery– During execution of work.

• Setting up of GE lab field lab– No. of GE field labs be set up as per requirement of project/work site– Aspects to be looked after by GE lab

• Ensure quality of supplied soil and blanket material• Evaluate method of compaction by conducting test• Exercise moisture and density control

– Depending on requirement, field lab to be equipped with minimum equipment to ensure following minimum tests

• Gradation Analysis – Sieve and Hydrometer

• Atterhug’s limits – Liquid limit & plastic limit

• OMC, MDD & Relative density

• Placement moisture content & in-situe Density

• QUALITY CHECKS ON EARTHWORK– Quality control on construction Material

• To ascertain suitability of material• To decide OMC & MDD for quality control inputs for compaction

control• These tests to be done for both borrow material & blanket material

• Frequency of Testing of site– Borrow material

• One test at every change in strata• Minimum one test for every 5000 cum

– Blanket Material• Minimum one test for every 500 cum or part thereof

• Quality control checks on finished earthwork– Compacted earth

• Method of sampling• Acceptance criteria

– Coarse grained soil having fines upto 5%» By relative density Min. 70%

– All other types of soil & when compacted – » by dry density 98% of Max. Dry density.

– During widening/gauge conversion/rehabilitation work» 98% of MDD or» 70% of relative density

• Frequency of testing– For blanket/top one meter of subgrade

» One check for every 200 sqm– For other places

» One check for every 500 sqm– At special locations closer frequency may be adopted– Bank widening

» One check at every 200m

Method of sampling• DEGREE OF COMPACTION OF EACH LAYER ASCERTAINED BY MEASUREMENT OF DRY DENSITY / RELATIVE DENSITY OF SOIL AT LOCATIONS SELECTED IN SPECIFIED PATTERN SHOWN BELOW.

NOTE: x & y AS PER SAMPLING AREA RQUIREMENT

– Formation level• Subgrade 25mm• Blanket +25mm

– Cross slope• 1 in 28 to 1 in 30

– Side slope• Should not be steeper than design

– Formation width• Should not be less than specified

)(

MAINTENANCE OF RECORDS

• Quality control Records – Characteristics of borrow materials– Quality of blanket materials– Field compaction trials– Quality of compaction of earthwork including

blanket material

• Quality of material & its compaction of backfill behind bridge approach etc.

• Details of machineries engaged in execution of earthwork including output as per profoma decided by field engineers

• Permanent Records– Desirable to prepare completion drawing of embankments and

cutting including special features like• Toe walls• breast walls• Catch and side drains• Cross section of embankments/cutting• Type of soil in subgrade• Depth of blanketing material• Geological features.

Association of GE cells of Railways & RDSO

• New lines/Doubling/GC works to be executed in close association with GE cell on Railways

• Requirement of thickness of blanket & slope stability to be worked out in advance & approval of HOD in-charge of GE cell of Railways taken.

• Any special design problem be referred to RDSO for guidance and advice

• All formation rehabilitation scheme must be followed in consultation with GE Directorate of RDSO.

• RDSO will carryout stage inspections (mid-construction inspection) for quality assurance of work done.

SOIL CHARACTERISTICS CAUSING FORMATION PROBLEMS

• Grain Size : Fine grained, poorly graded• Liquid Limit > 50• Plasticity Index > 15• Natural Moisture Content :

– Stiff if NMC near Wp

– Soft if NMC Near Wl

• Activity of clay :

Activity = Plasticity index/ Clay Fraction >1.25, Active Clay

• Shrinkage Limit : < 12 Highly shrinkage• Degree of Compaction- Ratio of natural dry density and Max. dry

density >90% less settlement• Differential free swell > 60 highly swelling type.

UNSUITABLE SOIL FOR CONSTRUCTION

• Soils normally to be avoided– Organic clays/silts

– Peat

– Chalk

– Dispersive soils

– GP & SP with Cu < 2

– CH & MH in top 3m of embankment

UNSUITABLE SOIL FOR CONSTRUCTION CONTD.

• Some typical unavoidable situation, may arise in construction of formation for economical or other reasons RDSO to be consulted for deciding special investigation & measures– Cutting passing through unsuitable types of soils, shales & soft

rocks which became muddy after coming in contact with water

– Construction of embankment on subsoil of unsuitable types of soils

– Use of CH & MH types of soils in top 3m of embankment

SN SYMPTOMS TYPE OF FAIL-URE

RECOMMENDED SCHEME FOR SOIL EXPLORATION & DATA COLLECTION

SOIL TESTING

1 I) Bank settlement – loss of longitudinal profile

II) Heaving of soil beyond toe

III) Leaning of telegraph posts, trees, etc. on the bank and at the toe

Base failure

i) Recording of bank profiles and ballast profile in x-section

ii) Undisturbed sampling

iii) Field tests-Vane shear DCP/SPT

i) Classification tests

ii) Consolidation tests

iii) Natural moisture content and Natural dry density tests.

iv) Peak and residual shear strength tests

SN SYMPTOMS TYPE OF FAIL-URE

RECOMMENDED SCHEME FOR SOIL EXPLORATION & DATA COLLECTION

SOIL TESTING

2 I) Flattening of Bank/slope

II) Bulging of slope surface

III) Longitudinal cracks on cess/slopes

IV) Leaning of OHE masts

Slope failure

i) Recording of Bank profile and x-section of ballast profile

ii) Survey and recording of surface cracks

iii) Undisturbed sampling

i) Classification and swell tests

ii) Peak and Residual Shear strength tests

iii) Natural moisture content and Natural dry density tests.

SN SYMPTOMS TYPE OF FAIL-URE

RECOMMENDED SCHEME FOR SOIL EXPLORATION & DATA COLLECTION

SOIL TESTING

3 I) Soil heaving on cess and on slopes

II) Ballast penetration exceeding 30 cm below formation

III) Excessive – cross level variations

Subgrade failure (by shear)

i) Recording of bank and ballast penetration profiles inside subgrade

ii) Collection of data

iii) Track geometry variations

iv) Excessive maintenance inputs

v) Quantum of ballast recoupment

vi) Speed restrictions imposed

vii) Undisturbed soil samples below the ballast penetration

i) Classification and swell tests

ii) Shear strength tests

iii) Natural Moisture content and Natural Dry Density tests.

SN SYMPTOMS TYPE OF FAIL-URE

RECOMMENDED SCHEME FOR SOIL EXPLORATION & DATA COLLECTION

SOIL TESTING

4 I) Fouling of ballast with subgrade fines

II) Ballast penetration below formation – 30 cm or less

III) Impaired drainage

IV) Excessive cross level variations in Monsoon

V) Hard running during summer

Subgrade failure (by mud pumping)

i) Recording of bank profile and ballast penetration inside subgrade

ii) Collection of data

a) Track geometry variations

b) Excessive maintenance inputs

c) Speed restrictions imposed

iii) Undisturbed soil samples from below the ballast penetration.

i) Classification and swell tests

ii) Shear tests

iii) Natural Moisture Content and Natural Dry Density tests.

SN SYMPTOMS TYPE OF FAIL-URE

RECOMMENDED SCHEME FOR SOIL EXPLORATION & DATA COLLECTION

SOIL TESTING

5 I) Reduced cess & Denuded slopes – loss of soil/absence of vegetation.

II) Formation of rills/gullies and pot holes on slopes & on cess

Erosion failure of slopes leading to ballast penetra-tion and slope failure

i) Recording of bank profile

ii) Disturbed soil samples

i) Classification tests

ii) Field crumb test for soil dispersivity

iii) Pin hole test

iv) Double hydrometer tests

v) Natural Moisture Content and Natural Dry density tests.

SN SYMPTOMS TYPE OF FAIL-URE

RECOMMENDED SCHEME FOR SOIL EXPLORATION & DATA COLLECTION

SOIL TESTING

6 I) Cut slope failures

II) Choked side drains

III) Seepage of water

IV) Saturated subgrade

Failure of Cuttings

i) Recording of profile side slope, longitudinal drain sections, HFL and Ground water table

i) Classification of soils

ii) Cross section and Ballast penetration

iii) Natural Moisture Content and Natural Dry Density tests

iv) Lab. Shear tests.

TYPES OF TROUBLE / REMEDIAL MEASURES TROUBLE OF

FORMATION Track level variation due to & Treatment • Inadequate drainage due to High Cess –

– Lowering of Cess & Screening of Ballast– Adequacy of longitudinal & cross drains

• Weakening of soil at formation Top on contact with water resulting in Mud Pumping

– Provision of blanket– Cationic emulsion treatment– Geotextile

• Strength failure below ballast causing heaving up of cess or crib– Provision of blanket– Sand/Boulder drain.

FORMATION TREATMENT METHODS

CONTD. • Seasonal variation of Moisture in Expansive soil

causing alternate heaving & shrinkage – Blanket– Lime slurry pressure Injection – Geotextile with blanket

• Gradual subsidence of bank due to inadequate initial compaction/consolidation – Vertical sand drain for highly compressible soil– Cement pressure grouting of ballast pockets– Blanket– Sand/boulder drain for drainage.

FORMATION TREATMENT METHODS

CONTD. • Gradual consolidation of earth below embankment

– Vertical sand drain into ground and blanket at top of formation

• Ash pockets – Removal of ash pockets and replacement with blanket

– Sand drains extending upto ash pockets

– Cements grouting of deep ballast pockets.

FORMATION TREATMENT METHODS

CONTD. Problems of Side Slopes• Instability of bank cutting slopes due to

– Inadequate side slopes • Flattening of slopes• Provision of berms

– Consolidation/settlements of subsoils• Provision of vertical sand drains to expedite consolidation

– Hydrostatic pressure built in ballast pocket • Draining out ballast pockets by sand/boulders drain• Cement grouting of Pockets.

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.

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.

- BLANKET DEPTH : 1 - 1.2M

- PERMISSIBLE SPEED ON GIRDERS: 20 Kmph

PROGRESS : 300 TO 350 M PER MONTH.

Al- ALLOY GIRDER METHOD

CASE STUDY

• Blanketing work between Wadi-Nalwar stations, WD-RC section, Guntakal division, S.C.R with the help of Aluminum Alloy Girder.

• Blanketing ( 1m thick) was carried out in Up line from dec’1998 to may’1999.

• Blanketing material is available near by quarry.

• Compaction is done by vibrating earth rammer & screed board vibrator.

• Behavior of track improved a lot but not up to the expectations.

• Longitudinal & transverse cracks noticed at toe of ballast & cess.

• Subsidence noticed at crib locations.

FORMATION REHABILITATION TRAIN

(MODEL AHM 800R)

Block requirement - 8- 10 hrs

Subgrade depth - 50 cm

Progress - 4-5 km per month

FORMATION REHABILITATION TRAIN

(MODEL AHM 800R)

Salient Features: Method of Work

• Removal of the upper layer of ballast

• Crushing this ballast and return

• Producing the finished sand-gravel mixture while checking the moisture content

• Excavation of the remaining ballast material and the upper layer of subsoil

• Smoothing the new earth formation

• Installation of protective materials such as geo-textile, styrofoam, plastic sheeting or geo-meshing

• Installation of formation protective layer

Salient Features: Progress

• AHM 800 gives an average progress of 40 m per hour in a double shift .

• A progress of 500m in a day has been achieved in a double shift operation.

• Maximum annual progress of 60 Kms has been achieved i. e. average progress of 5 km in a month.

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

TRACK DISMANTLING METHOD

CASE STUDY

•Blanketing work between Chittapur-Malkhaid road stations, SC-WD section, Secunderabad division, S.C.R with mega block method.

• Blanketing ( 1m thick) was carried out in Up line during 1999-2000 in 50 traffic blocks of 2.35km long stretch.

• Natural blanketing material is used.

• Excavation was done with pocklain.

• Compaction was done with 9.5 t smooth wheeled roller.• Average progress achieved was 52m per day. •Performance of track was found satisfactory.• Speed relaxed to normal speed.

LIMITATIONS OF TRACK DISMANTALING METHOD

• Track to be dismantled completely.

• Entire work to be done in traffic block.

• Uniform cutting of formation, provision of proper cross- slope & drainage are difficult.

• Heavy machines are used which may infringe adjacent line in case of double line section.

• Difficult to achieve proper moisture content and compaction ( Degree of compaction achieved on SC-WD section was 89% - 92% as against minimum 98% stipulated).

BLANKETTING OF WEAK FORMATION BY USING C.C.CRIBS & RAIL CLUSTERS

COMPONENTS OF THE PROPOSED METHOD

C.C.CRIBS - 2

RAIL CLUSTERS – 2

A FEW WOODEN SLEEPERS

STEEL PLATES,SHEETS,BEARING PLATESRAIL SCREWS ETC,ETC.

ADVANTAGES

• EQPT. READILY AVAILABLE WITH PWI• EQPT.COST IS MINIMUM.• MULTIPLE EQPT SETS CAN BE DEPLOYED

TOGETHER AT ONE WORK SITE• MORE MANPOWER GIVES MORE PROGRESS• GOOD QUALITY CONTROL• EXECUTION UNDER TRAFFIC• BETTER SAFETY• ASSURED BLANKET DEPTH OF 60 CM.

DISADVANTAGES

• SHORT LENGTH (1 FOOT) BLANKET AT A TIME

• TRAFFIC BLOCK REQUIRED FOR CRIB INSERTION AND EXTRACTION

• CANNOT BE DONE ON METAL SLEEPERED TRACK

• MOVING OF HEAVY CRIB AND RAIL CLUSTER IS VERY DIFFICULT

• OUTPUT OF WORK IS VERY LOW – 1.5 M TO 2 M PER DAY

BLANKETTING BY CC CUBES• This is improvement over CC Crib method.• Work is in progress near Balasore, SE Rly.• About 3 km blanketing has been done.• Shifting of cubes is easier than crib as being light wieght.• 12 m long rail cluster is used for supporting sleepers and

rails.• Initially 1 hr block is required for insertion of 2 rail

clusters supported over 6 to 8 cubes.• Progress is about 10 to 12 m per day with 80 to 100

manpower.• 30 to 40 min. block may be required for shifting of cubes

on busy routes.

SIGNIFICANCE OF ADEQUATE BANK WIDTH

• MIN. 90 cm CESS , AS PER EXISTING PROVISION.

• IDEALLY, CESS SHOULD BE 160-200 cm FOR ALL

FUTURE WORKS TO CATER FOR MAINTENANCE

TOLERANCES , SPREADING OF SHOULDER

BALLAST AND STABILITY OF FORMATION.

• FORMATION PROBLEM OF A ( MIDDLE ) LINE

ALMOST DISAPPEARS WHEN 3rd LINE IS

CONSTRUCTED. EXAMPLE: HOWRAH BURDWAN

CHORD LINE , HWH DIVN., E. RLY.;

PANSKURA - TIKIAPARA, KGP DIVN. , S. E. RLY.

APPLICATIONS OF SOIL MECHANICS

TO TRACK FORMATION PROBLEMS

• Mechanics of formation• Analysis of track formation failures• Evolving suitable remedial measures• Choice of suitable materials for formation • Design of profiles of banks and cuttings• Deciding methods of execution of formation work

and exercising quality control.• Items 1 to 3 concern study of existing formations• Items 4 to 6 concern construction of new formations.

CONSISTENCY LIMITS • The limiting water contents, expressed as %age of the dry

weight, when a soil mass passes from liquid to plastic, plastic to semi-solid and semi-solid to solid states of consistency are respectively termed as Liquid Limit (WL), Plastic Limit (WP) and Shrinkeae Limit (WS)

• Plasticity Index , Ip= Wl-Wp

• Consistency Index, Ic= Wl=W--------------

Ip

• Liquidity Index, Il = W=Wp

----------

Ip

SOIL CONSISTENCY • Relative ease with which a soil can be deformed• Fine grained soils, particularly clayey soils, the

consistency is related to a large extent to water content. • Depending upon the water content, following four states,

– Liquid state– Plastic state– Semi-solid stae– Solid state

• The water contents at which the soild passes from one state to the next are known as consistency limits or Atterberg Limits.

NEW CONSTRUCTION

• Soil Explorations & Surveys : – Paras E-409, 425 & 528 of Engg. Code– Preliminary & Final location surveys– Soil samples along alignment & from borrow pits– Where sub-soild problems, samples from concerned

depths

• Design Aspects– Choice of suitable materials– Design of profiles– Methods of Execution & Quality Control.

FORMATION PRESSURE • Depends on : • Strength of Rail – Higher the section, lesser the pressure.

Uneconomical method• Type of sleeper – Does not influence appreciably• Spacing of sleepers – Marginal relief by closer spacing• Depth of Ballast – Less pressure by increased depth economical

method• Type of Maintenance – Well packed, better distribution of

pressure• Speed of the wheel – No direct effect• Soil in Formation and Its condition – Good soil and Good

condition better bearing capacity.

FINANCIAL IMPLICATION

COST OF LAYING OF 1.0 m BLANKET ON NEW FORMATION

•NET COST : Rs. 6.2 LAKH PER km. RATE OF BLANKETTING: Rs. 50 TO 200 PER m³. IN FEW CASES Rs. 200-300 ALSO. RATE OF EARTHWORK : Rs. 30-75 PER m³ .

COST OF LAYING OF 1.0 m BLANKET PER km ON EXISTING UNSTABLE FORMATION

•AL. ALLOY GIRDER : Rs. 30 LAKH ( 5 SETS ) • MANUALLY (8-10 hr BLOCK) :Rs. 23 LAKH(SINGLE SITE)

•FORMATION REHABILITATION M/C (10 hr MEGA

BLOCK) :Rs. 45 LAKH (PROJECTED).

RECURRING EXPENDITURE FOR TRACK

MAINTENANCE PER YEAR /KM

• COST OF ADDITIONAL MAINTENANCE : RS.4.00 LAKH

• COST OF PREMATURE TRACK RENEWAL: RS.1.50 LAKH

• COST OF DEEP SCREENING : RS.0.11LAKH

TOTAL : RS.5.61 LAKH

• COST OF ONE TIME LOSS OF BALLAST IN

PENETRATION

= 0.7X1.0X3.5X500 : RS. 12.25 LAKH

JUSTIFICATION FOR LAYING BLANKET ON WHOLE

STRETCH

FOR PRESENT AXLE LOAD AND GMT.

• TOTAL TRACK km = 70,000 km (approx.)

• U/S FORMATION WITH PERMANENT S.R. = 750 km. (app.)

• U/S FORMATION WITH TEMPORARY S.R.

= 2500 km (app.)

• TOTAL LENGTH OF U/S FORMATION

= 5% (app.) OF TRACK km.

• RECURRING EXPENDITURE FOR 10 YEARS = 5.6x10

= Rs. 56 lakh

• REHABILITATION COST = Rs.25 lakh

• COST OF BALLAST LOST = Rs. 12 lakh

• TOTAL = 93 lakh ,SAY, Rs. 1 crore / km

•EXPENDITURE ON 5 km OF U/S FORMATION = Rs 5 crore

•COST OF BLANKETING OF 100 km STRETCH = Rs. 6-7crore

LENGTH OF U/S FORMATION WILL FURTHER

INCREASE WITH INCREASE IN AXLE LOAD AND GMT.

THEREFORE, WHOLE STRETCH OF NEW CONSTRUCTION

HAS TO BE PROVIDED WITH BLANKET

RECURRING INDIRECT LOSSES

• EXCESS FUEL CONSUMPTION

• SAFETY HAZARD

• REDUCTION IN LINE CAPACITY

• EXTRA SUPERVISION

• WEAR AND TEAR OF ROLLING STOCK

• MISC. LOSSES SUCH AS TILTING OF OHE MAST etc

• SOCIAL COST: TRAVEL TIME, PASSENGER

DISCOMFORT, RAILWAY’S IMAGE , POLLUTION etc.