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    Grade Separator

    Challenges Faced

    in Planning, Design& Construction of

    Grade SeparatorNear Apsara Border,

    Delhi

    Alok Bhowmick,

    Managing Director, B&S

    Engineering Consultants Pvt. Ltd.,

    Noida

    The paper describes the salient features of design

    and construction of one of the most complex three

    level grade separators ever constructed in the city of

    Delhi. The Grade Separator comprises the following

    major structural components:

    A 6-lane flyover at Apsara Border along the GT

    Road

    2 Nos. 2 lane Underpasses along Road No. 56

    and Road No. 62

    2 Nos. RUBs constructed under extremelychallenging conditions by using box pushing

    technique

    2 Nos. of Foot Over Bridges across Road No. 56

    and Road No. 62

    Widening of existing bridge over Major Drain &

    Allied Works

    This is possibly the first project in India where

    contiguous piles in combination with prestressed

    horizontal anchors have been successfully used for

    supporting the existing ROB approach close to the

    proposed Underpass. This is also the grade separator

    with longest total length of Underpass constructed inDelhi (total length 1666m). The paper highlights the

    salient technical features of the project components

    including the design and construction issues.

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    IntroductionRapid development and urbanization

    of Delhi and surrounding areas

    coupled with the high average

    income of the populace (with large

    standard deviation) has largely

    eclipsed socio-cultural traits that

    used to represent Delhi until a few

    years after independence. Traffic

    congestion, longer travel times and

    high levels of air pollution are just

    some of the growing problems

    faced by the citys residents. Rising

    incomes and a burgeoning middle

    class has seen an increase in

    private vehicles in the past two

    decades, particularly because the

    public transport system has notkept pace. Delhi has nearly 4.5

    million vehicles, which is more than

    that in the three other major Indian

    cities of Mumbai, Calcutta and

    Chennai put together. The growth

    in the number of vehicles has had

    a knock on effect on the roads of

    the city. Traffic congestion, longer

    travel times and high levels of air

    pollution are just some of the

    problems faced by the citys

    residents. Coupled with the above,

    there was tremendous pressure to

    improve infrastructures in the urban

    areas in general for the

    Commonwealth Games of October

    2010, which led to the construction

    of this grade separator which was

    long overdue at this intersection in

    any case.

    Need for the ProjectThe need for a grade separator at

    the Seemapuri Border near Apsara

    Talkies was felt for more than two

    decades. Long queues at the

    Intersection, frequent jams with

    traffic stuck for hours were a

    common sight at this intersection.

    Public Works Department, Govt. of

    Delhi had initiated this ambitious

    project in the year 2006, with the

    objective to increase road

    connectivity between Delhi and U.P,

    between Anand Vihar to Shahdaraand between Ghaziabad to

    Maharana Pratap ISBT, Anand Vihar.

    Feasibility study for the project was

    carried out based on which, a six

    lane flyover is envisaged along the

    G T Road at this intersection

    connecting Delhi & U.P and two

    underpasses of 2 lane each are

    envisaged along Road No. 56 (one

    on either side of existing ROB) to

    connect Anand Vihar with Dilshad

    Garden.

    Fig. 01 shows the key plan

    showing alignment of Flyover,

    Underpasses and location of Foot

    Over Bridge. Part of the six lane

    flyover falls in U.P side, for which

    PWD got the working permission

    from UP government. Cost of the

    flyover however is borne by the Govt.

    of Delhi.

    Project Award dates

    Approval for this project from

    Technical Committee of DDA was

    obtained in September 2006. DUAC

    approval was obtained in July 2007.

    The administrative approval for the

    project was obtained on 9 th June

    2008 for an amount of 226.47

    crores.

    The construction contract for

    this project was awarded to M/S

    AFCONS Infrastructure Limited,

    Mumbai for an amount of `180.2crores. The construction period was

    allocated as 21 months. The salient

    dates for the project are as under :

    Date of Commencement of Work

    : 10th September 2008

    Stipulated Date of Completion

    : 9th June 2010

    Flyover opened to traffic on

    : 24th April 2010

    1st Underpass opened to traffic

    : 31st October 2010

    2nd Underpass opened to traffic

    : 5th January 2011

    Photo P1 shows the completed

    Grade Separator in Google Map.

    Photo 1: Completed Grade Separator in GOOGLE map

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    Salient Features &

    Components of the

    Grade SeparatorFlyover along G T RoadThe 6 lanes flyover with divided

    carriageways of 9m width (reduced

    3 lanes) is constructed along the G

    T Road. The total length of theflyover is 646m with length of the

    stilted portion of 340m and balance

    306m in solid fill with Reinforced

    Earth Walls. The overall width of

    the flyover including median is

    20.2m.

    The span arrangement for the

    stilted part of flyover comprises 3

    modules of continuous span units.

    The central module comprise 4

    spans of span lengths

    40m+50m+50m+40m, totaling a

    length of 180m, while the endmodules on either side of the

    central module comprise 2 span

    continuous structure of lengths

    40m+40m each. Expansion joints

    are provided at Abutments and at 2

    intermediate sections, 80m away

    from the abutments. Fig. 02 shows

    the General Arrangement of the

    Flyover.

    The Superstructure comprises

    a steel concrete composite plate

    girder with in-situ RCC deck slab.

    The girders are supported on

    metallic bearings. The overall depth

    of the superstructure deck is kept

    at 1.925m. 4 plate girders are

    provided transversely at a spacing

    of 2.5m for supporting each of the

    3 lane carriageway. The depth of

    plate girders are kept as 1.7m. High

    strength steel of grade Fe540B

    conforming to IS:2062-2006 has

    been used. The deck slab of

    225mm thick is provided in M35

    concrete on top of plate girders.

    For the stilted portion, the two

    carriageways are structurally

    isolated and a longitudinal clear

    gap of 200mm is provided at the

    centerline of the median along the

    entire length.

    The bearing arrangement

    comprises series of Metallic Free

    POT cum PTFE bearings underouter girders, Guided Bearings

    under internal girders at Free /

    Expansion joint piers and Fixed

    Bearings under internal girders of

    fixed piers. The combination of

    these types of bearings ensure

    transfer of vertical loads and lateral

    loads from Superstructure to the

    foundation, through substructure.

    Fig. 03 shows the bearing

    arrangement for a typical

    carriageway of this project.

    RCC single circular pier of 2.0m

    diameter have been provided under

    each carriageway for all piers and

    abutments, except fixed piers P4, in

    which case pier diameter of 2.75m

    has been provided. Pier cap is

    cantilever type in all cases. Seismic

    stoppers / arrestors are provided in

    the transverse direction to arrest

    the possible dislodgement of

    Superstructure in the transverse

    direction under earthquake loads.

    Fig. 04 to Fig. 08 shows the typical

    details of various components of

    the Flyover.

    The foundation sub-strata as

    per the Geotechnical Report

    comprise road fill or loose filled up

    soil upto a depth of about 2.5m,

    followed by silty fine sand / fine

    sand layers upto 10-13m depthunderlain by very dense sandy

    strata upto the explored depth. Total

    of 10 number of bore holes have

    been taken at the project site to

    establish the geotechnical

    properties for foundation design.

    Bored cast-in-situ piles of

    diameter 1.2m have been used for

    supporting the stilted portion of

    flyover. Total of 108 numbers of

    piles have been provided for the

    flyover. Pile capacity considered is

    287 Tonnes for a length of 30m

    below pile cap bottom. The safe

    load capacity has been confirmed

    by conducting initial pile load tests

    as well as routine load tests on

    working piles. Number of piles

    provided under each foundation (for

    each carriageway) is as under :

    Abutments A1 & A2 : 4 nos.

    Piers P1, P3, P5 & P7 : 6 nos.

    Piers P2 & P6 : 5 nos.

    Pier P4 : 12 nos.

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    Photo P2 & P3 shows the

    completed Flyover in service.

    Underpasses along Road

    No. 56 & Road No. 62Two Vehicular Underpasses

    are provided alongside of

    Road No. 56 and Road No.

    62 connecting Dilshad Garden

    and Anand Vihar. The total

    length of the underpasses is 840m

    & 826m for Delhi side and U.P

    side respectively. Each underpass

    is provided with 2 lane carriageway

    of width 7.5m with 0.75m raised

    kerb/footpath on either side. Overallclear width between inner face of

    walls is kept at 9.0m. vertical

    clearance of 5m is provided in the

    covered portion of Underpass. Fibre

    Reinforced Concrete (FRC) wearing

    course of 125mm thickness has

    been provided over the base slab.

    The underpass has provision of four

    number of sumps of 40,000 litre

    capacity in each underpass with

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    two numbers of pumps of capacity

    10 to 15 HP including drainage

    arrangement. Fig. 09 & Fig. 10

    shows the General Arrangement of

    the Underpasses.

    Structural Scheme for Ramp

    Portion Open to Sky

    Total length of Ramp portion, open

    to sky is 328m for each Underpass.

    Where depth of excavation from road

    level is less than 3m, the proposed

    structural scheme comprise RCC

    cast-in-situ U-type RCC section,

    with variable height, constructed

    bottom-up with open cut.

    Prestressed vertical soil anchors

    are connected with the base slab

    which takes the buoyant forces due

    to rising of water table. For the

    vehicular traffic. Structural scheme

    adopted involves construction of

    Diaphragm Wall on either side withtop-down construction using RCC

    solid Slab on top. Fig. 13 shows

    typical cross section of Underpass

    & Fig. 14 shows various stages of

    construction in this portion.

    Construction of this covered portion

    had to be taken in phased manner

    to ensure uninterrupted traffic flow

    with minimal diversions.

    Structural Scheme for Open to

    Sky portion adjacent to

    existing ROBFor the construction of Underpass

    close to the existing ROB with high

    embankment, vertical cuts had to

    be done upto a maximum height of

    about 14m close to the existing

    ROB approach road. The ROB had

    to be kept functional during the

    construction. This was achieved by

    providing 1.2m diameter contiguous

    piles, 20m length @ 1.5m c/c along

    the ROB on either side of the

    existing road . Total 484 numbers

    of piles (i,e 242 nos. on either side)

    have been used. The piles on eitherside of the ROB are connected to

    each other by using horizontal

    prestressed anchors of 50T capacity

    each. 151 numbers of horizontal

    soil anchors with 4 layers of waler

    beam have been used in this

    project to provide lateral support to

    the contiguous piles for retaining

    the embankment of ROB approach

    with vertical cut. By retaining the

    Photo 2: Completed Flyover along GT Road Photo 3: Underside of the Completed Flyover

    portion where the depth of

    excavation from road level is more

    than 3m, RCC diaphragm walls,

    800mm thick are provided with top-

    down construction. Fig. 11 & Fig.

    12 shows the typical cross section

    of Underpass open to sky with open

    excavation and with diaphragm

    walls respectively.

    Structural Scheme for Covered

    Portion under GT RoadFor the 150m and 164m long (UP

    side and Delhi side respectively)

    covered portion of Underpass below

    G T Road, the structural scheme

    had to be such that it involves

    minimum disturbance to the flow of

    traffic since this intersection caters

    to a significantly high volume of

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    erection of waler beam over

    contiguous pile.

    For the 98m long open

    to sky portion of

    Underpass, located

    adjacent to the existing

    ROB, the structural scheme

    proposed comprise

    providing 1.2m diameter

    RCC bored cast-in-situ

    contiguous piles @ 1.5m

    c/c towards the existing

    ROB side, 800mm thick

    RCC diaphragm walls onthe other side. Excavation

    is done in a phased

    manner with application of

    horizontal prestressed

    anchors connecting the

    earth with contiguous piles on ROB side,

    excavation for construction of underpass with

    vertical cut was possible, which helped in

    providing adequate working space as well in

    providing the thrust blocks for box pushing in

    the railway portion. Photo P4 shows the

    contiguous piles on either side of

    the existing ROB. Fig. 15 shows

    the typical cross section of

    Underpass open to sky adjacent to

    the existing ROB.

    Structural Scheme for Covered

    portion adjacent to existing

    Rail Line

    For the 200m long covered portion

    of Underpass, located adjacent to

    the existing rail line, on either side

    of the rail line, the height of ROB

    approach embankment ismaximum. The structural scheme

    proposed comprise providing 1.2m

    diameter RCC bored cast-in-situ

    contiguous piles, 20m long @ 1.5m

    c/c towards the existing ROB side,

    Photo 4: Erection of Waler Beam over Contiguous Pile

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    800mm thick RCC diaphragm

    walls on the other side of

    Underpass. Excavation is done

    in a phased manner withapplication of horizontal

    prestressed anchors connecting

    the contiguous piles on either

    side of the existing ROB, in 3 or

    4 layers. Fig. 16 shows the

    typical cross section of

    Underpass. Fig. 17 shows the

    sequence of application of

    horizontal prestressed anchors

    with contiguous piles in this

    zone.

    Two numbers RUB by Box

    Pushing TechniqueThe Underpasses crosses the

    Delhi-Howrah rail route, which is

    one of the busiest rail lines in

    Delhi. For the 50m length

    covered portion of Underpass

    below existing railway line, box

    pushing technique was therefore

    adopted, which ensured

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    un-interrupted flow of rail traffic

    throughout the construction period.

    In box pushing technique, entire

    length of reinforced concrete box is

    divided into segments (5 segmentsin this case). The segments are

    pre-cast over a horizontal RCC

    Thrust Bed. Thrust bed is

    constructed at a convenient location,

    in this case closer to the Rail line

    and close to the embankment. The

    Boxes are then pushed into the

    soil one after another one to the

    desired horizontal and vertical

    profile with the help of hydraulic

    force created by jacks. The force of

    the jacks is transmitted to the pre-

    cast segments and thus it moves

    forward. Equal and opposite

    reaction is absorbed by the thrust

    bed. Box pushing activity essentially

    involves following activities :

    a. Casting of thrust bed :

    b. Laying screed on the thrust bed

    c. Laying polythene sheets and

    grease over screed

    d. Casting of Boxes

    e. Installation of anti-drag system

    f. Pushing of the Boxes

    g. Soil Nailing

    h. Rail Track maintenance during

    box pushing & Quality ControlMeasures

    i. Control of alignment and levels

    during box pushing

    Rail track is continuously

    monitored & maintained during the

    construction process. Train

    movement at controlled speed

    during the construction phase. Anti-

    drag system provided to reduce

    friction during the box pushing.

    Details of the boxes pushed are as

    under :

    LHS Underpass (Ghaziabad Side)

    a. Length of the jacked box section

    : 50m cast in 5 segments of 10meach

    b. Dimension of clear opening

    : 9m wide x 5m height (Clear)

    c. Thickness of top and bottom

    slabs

    : 0.90m

    d. Thickness of Walls

    : 0.90m

    RHS Underpass (Delhi Side)

    a. Length of the jacked box section

    : 50m cast in 5 segments of 10m

    each

    b. Dimension of clear opening: 7.6m wide x 5m height

    c. Thickness of top and bottom

    slabs

    : 0.70m

    d. Thickness of Walls

    : 0.50m

    For the RHS underpass, the

    jacked box underpass section lies

    between existing ROB pile

    foundations on one side and

    abutment well foundation of Railway

    Bridge over nallah on the other side.

    Minimum clearances between the

    faces of the existing foundationsand the faces of the boxes to be

    pushed were specified by the

    Railways with the objective of

    reducing effects of lateral forces on

    the existing foundations generated

    during pushing of the boxes. This

    made the box pushing task

    extremely challenging and involved

    use of several alignment controlling

    measures like soil nailing,

    continuous supporting of track during

    pushing operation, etc. Added

    supervision by railway authorities

    24 hrs a day had to be taken to

    ensure safe construction.Fig. 18 shows the schematic

    cross section of Box being pushed

    on either side of ROB. Photo P5

    shows the construction of RHS side

    precast boxes for puhing below the

    rail lines.

    Foot Over Bridges

    Two numbers of Foot over bridges

    are presently under construction (i,e

    in July 2011). One FOB is being

    constructed at Road No. 62 towards

    Dilshad garden side with escalator,

    staircase and lift. The second Footover bridge is being constructed at

    Road no. 56, which is integrated

    with the Metro Station at Dilshad

    Garden and the petrol pump

    towards UP side. The FOBs are

    constructed with prefabricated steel

    girders for the deck with concrete

    deck slab, supported on steel

    columns and resting on open

    foundation. Roofing is not

    envisaged for the FOBs. Photo P6

    shows the erected FOB at Road

    No. 62.

    Bridge Over Drain & other

    Allied worksApart from the major work of

    construction of a Flyover and two

    Underpasses, the project also

    involved widening of the existing

    bridge over trunk nallah at the

    intersection of GT Road and Road

    No. 56. The bridge over nallah has

    been widened by 18m on both

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    sides by constructing RCC box type

    bridge for ease of traffic at surface

    level.

    Other allied works involved in

    the project includes:

    Construction of roadworks in slip

    roads, approaches of flyover,

    merging roads on the entry/exit of

    underpasses constructed with two

    layer (150mm thick each) of GSB,

    two layers (125mm thick each) of

    WMM, two layers (75mm each) ofDBM and 50mm thick BC as

    wearing coarse.

    Construction of Rotary at

    Intersection and Landscaping of

    the Rotary Island

    Shifting of sewer line, which was

    detected in the alignment of the

    Underpass on U.P side.

    Construction of Diversion roads &

    barricading duing the construction

    Horticulture, Landscaping, Traffic

    Signage & Electrical Street

    Lighting.

    Painting (Anti carbonation paint

    in exposed concrete surfaces of

    flyover, RE wall and crash barrier,

    synthetic enamel paint on

    surfaces of diaphragm walls,

    ceiling of deck slab of underpass,

    inner surface of crash barrier and

    outer surfaces of kerb stones)

    25mm thick cement tiles in

    pattern over 15mm thick cement

    plaster in 200m length of

    underpass, footpath tiles etc.

    Design &

    Construction Aspect

    of Flyover Along G T

    RoadFoundation & Substructure1200 mm diameter bored cast-in-

    situ piles have been chosen for thefoundation of the Flyover. 1.2m

    diameter was preferred as

    compared to 1.0m diameter due to

    following reasons:

    a) Span lengths are longer

    (minimum span 40m), thereby

    vertical loads per foundation is

    quite large.

    b) The design of foundation is

    governed by the

    horizontal forces caused

    by braking, seismic

    bearing restraint, wind

    etc. Larger diameter pileperforms better under

    lateral loads.

    The vertical load

    carrying capacity calculated

    based on static formula as

    per IRC:78-2000. Lateral

    load carrying capacity from

    geotechnical considerations

    is assessed based on

    provisions of Appendix-C of

    IS: 2911 (Part 1/Sec2) 1979. Initial

    and routine load tests were carried

    out at site to confirm the safe

    vertical as well as lateral load

    carrying capacity of piles. Integrity

    testing / low strain dynamic testing

    were also carried out on randomly

    selected piles to check the integrity

    of piling works. Hydraulic operated

    rotary type piling rig have been used

    for the piling works. Photo P7

    shows the piling work at LP1location.

    Pile caps of minimum thickness

    1.8m (i,e 1.5 times the pile

    diameter) has been provided. Pile

    caps are designed based on

    bending theory. Loads on piles are

    assessed by considering rigid body

    action of the pile cap.

    Photo 5: View of RHS Pusg Box Photo 6: Footover Bridge at Road No. 62

    Photo 7: Piling Work in progress at LP1 (U.P side)

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    Circular piers are provided with

    vertical grooves allround from

    aesthetic considerations. Base

    section of pier is designed for

    ductility with adequate confinement

    reinforcement. Cantilever type pier

    caps is provided supporting the

    superstructure on bearings. Pier cap

    is designed based on flexure theory

    for combined bending and torsion

    for the loads transferred from the

    deck. Photo P8 shows the

    concreting of Pier Cap at RP6.

    SuperstructureFabrication and Erection

    SchemeThe Plate Girders are fabricated

    in fabrication yard, located at

    Mundka and brought to site in

    pieces. Maximum length of

    individual piece is restricted to

    12m and maximum weight of a

    single plate Girder is restricted

    to 20 Tonnes. The prefabricated

    girders are first assembled on

    ground adjacent to the span in

    which it is to be erected. Girders

    were assembled in length as

    per the approved construction

    scheme. Erected girders are inlengths of about 45m (for 40m

    span) and 25m (for 50m span).

    Shear studs are fixed on top

    flange. Two cranes of 75 Tonnes

    capacity each are used to lift

    the assembled girder in

    position (Photo P9 & P10).

    Erected girders are supported

    on bearings over pier and on

    temporary cribs at the cantilever

    Photo 9: View of Girder Erection : LP4-LP5Photo 8: Concreting at RP6 Pier Cap

    Photo 11: Bottom Reinforcement in Deck Slab of Flyover

    Photo 10: Launching of Steel Girder for RP4 RP5

    overhang. After erection of all the

    girders in a module, the RCC deck

    slab is cast on top by taking support

    from the erected girders (Photo

    P11).

    Structural Modelling of

    Superstructure and Design

    IssuesSuperstructure is designed for

    following loads and their

    combinations

    a. Dead Loads & Superimposed

    Dead Loads

    b. Carriageway Live Loads

    c. Temperature Gradient Loads

    (Rise and Fall)

    d. Braking & Tractive Effort

    e. Bearing Friction

    f. Earthquake Loads or Wind Loads

    g. Stresses caused by Shrinkage of

    deck concrete

    h. Differential Settlement

    For the service stage

    analysis of Superstructure for

    superimposed dead loads and

    live loads, a grillage model is

    used and the analysis carriedout in software STAAD/Pro. The

    superstructure is modeled

    using discrete beam elements

    in orthogonal direction. Full

    composite action between the

    deck slab and the girder is

    assumed. Separate models

    have been used for live load

    analysis and superimposed

    dead load analysis since the

    modular ratio and section

    properties of longitudinal

    members for sustained loadsand for instant loads are

    different (to account for creep).

    Precamber has been provided

    in the girder (at splice locations)

    to account for deflection of

    permanent loads + 75% of the

    live load. Live load deflection is

    restricted to span / 800 as per

    the provisions of IRC:22. Deck

    slab is designed based on

    effective width method.

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    Design of the Superstructure

    takes into account the stage by

    stage construction process for dead

    load and dead load of deck slab,

    wherein the statical system keepschanging till all the girders in a

    module are erected. Design is

    based on provisions of IRC:22-1986

    and IRC:24-2001. Working Stress

    Approach has been adopted for the

    design of structural members.

    Bearings

    The bridge bearings are proprietary

    item, designed and manufactured

    by the manufacturer M/S Sanfield

    (India) Ltd., Bhopal. A warranty for

    trouble free performance for at least

    fifteen years and free rectification ofdefects / replacement, if any, during

    this period has been obtained from

    the manufacturer. Design of

    Bearings conforms to provisions of

    IRC:83 (Part 3). The types of

    Bearings used with design vertical

    and lateral loads are given below:

    a. Free POT cum PTFE Bearings

    : Vertical Load Capacity 230T

    (8 Nos.)

    : Vertical Load Capacity 100T

    (16 Nos.)

    : Vertical Load Capacity 95T

    (8 Nos.)

    b. Sliding Guided Bearings

    : Vertical Load Capacity 200T &

    Lateral load capacity 75T (8 Nos.)

    : Vertical Load Capacity

    100T & Lateral Load

    Capacity 30T (24 Nos.)

    : Vertical Load Capacity

    235T & Lateral Load

    Capacity 125T (8 Nos.)

    c. Fixed Bearings

    : Vertical Load Capacity

    230T & Lateral load

    capacity 125T (8Nos.)

    : Vertical Load Capacity

    205T & Lateral load

    capacity 85T (4 Nos.)

    Expansion Joints:Modular Expansion joints

    capable of accommodating

    the structures movement has

    been provided in the deck.

    Expansion joints are special

    type of joints, generally of the

    proprietary type. The Expansion

    joints are supplied with 15 years

    of replacement guarantee. The

    modular expansion joint system isdesigned for 40T bogie loading and

    impact in accordance with IRC:6-

    2000.

    The modular expansion joint

    system consist of a double layer,

    box type, preformed elastomeric

    joint seal mechanically held in place

    by steel edge and separation

    beams. Each elastomeric sealing

    elements are continuous

    transversely and has movement

    capacity limited to a maximum

    80mm of movement per seal. An

    independent support bar welded to

    the center beam individually

    supports each machined or

    extruded transverse center beam.

    These support bars are suspended

    over the joint opening by sliding

    elastomeric bearings. The modular

    expansion joint system provides

    equidistant control of the

    elastomeric seals.

    Expansion joints with Four and

    Two modules have been provided

    at intermediate expansion joint pier

    and at Abutment locationsrespectively. The expansion joints

    are installed after laying the wearing

    coat. Steps involved in installation

    of expansion joints are :

    a. Sae-cutting of the Wearing coat

    to the required width. Block-out to

    be clean, dry, free from loose

    particles with deck reinforcement

    fully exposed.b. Splicing of individual fabricated EJ

    segments by welding to achieve

    continuity and maintain alignment.

    c. Insertion of neoprene seal into

    the edge beam profiles to ensure

    locking using lubricant adhesive

    & adjustment of the gaps between

    edge beams.

    d. Levelling of the edge beam

    assembly and providing

    necessary formwork to ensure

    uniformity of expansion gap.

    e. Welding of studs anchorages with

    deck reinforcement & loosening

    of clamp plates & nuts as

    required.

    f. Covering of the gap between edge

    beam and central beam by

    masking tape and concreting of

    blockout ensuring proper

    compaction.

    Photo P12 shows a typical 4

    seal expansion joint being installed

    at P2 location.

    Reinforced Earth Wall for the

    Solid Fill portionThe solid fill ramp portion of theflyover on either side of the stilted

    portion is provided with reinforced

    soil wall panels (RSWP) using

    galvanized MS strips. The

    total length of RE wall

    portion is 306m. 146m

    length is provided on U.P

    side while the length

    towards Delhi side is 160m.

    Maximum height of wall

    above ground level is 5.5m.

    Walls are embedded in

    ground by 1.0m. TheReinforced Earth wall

    system is designed as per

    the provisions of BS:8006-

    1995 in absence of any

    specific guidelines in Indian

    Codes. For seismic design

    of RE Wall, provisions of

    AASHTO code (Mononobe-

    Okabe method) has beenPhoto 12: Fixing of 4-seal expansion joint at Pier P2, Flyover

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    followed since BS code is

    silent on seismic.

    The facia panels provided

    in RCC grade M35. Panels

    are of size 1.85m (width) x1.50m (height) with thickness

    of 180mm. Photo P13 shows

    the construction of RE wall in

    progress. The RSWP are

    anchored at 4 points with

    galvanized strips. Galvanized

    chequered steel strips,

    50mm x 5mm thick and

    conforming to IS:2062 have

    been provided on the backfill,

    connected to the facia panel. These

    specially manufactured strips are

    hot dip galvanized as per IS:4759

    having zinc coating of 1000 gm/

    sq.m as specified in BS:8006-1995.

    The coating thickness is based on

    100 year design life for the

    galvanizing, considering mild

    corrosive exposure in backfill. The

    long-term design strength of

    galvanized strips is taken as 40

    KN/m.

    Design &

    Construction Aspect

    Of UnderpassOpen to Sky Underpass Section

    RCC U-type Section proposed for

    the open to sky portion with depth

    of excavation less than 3m. This

    portion is constructed by open

    excavation method. For the portionwhere depth of excavation is more

    than 3m, adequate space is not

    available in the area for open cut

    excavation, hence diaphragm wall

    is provided. The construction

    scheme in this case involves

    strutted excavation after constructing

    the RCC diaphragm wall (800mm

    thick) on both sides of the

    underpass.

    Soil anchors are provided in

    the base raft in this zone to counter

    uplift forces due to buoyancy. The

    design water table is consideredas 1m below ground level for this

    purpose as per clients advice.

    Design of Shallow Depth

    PortionDesign of the shallow depth

    portion of Underpass is

    carried out by modeling thestructure in 3D-frame in

    STAAD/Pro. Due to presence

    of soil anchors, which

    imparts high concentrated

    load on the base raft, the

    simplified 2D method of

    analysis was not considered

    adequate in this case. The

    support springs at the base

    is given in the form of soil

    springs, at each nodes to

    represent the stiffness of the soil

    underneath. The design of open tosky portion caters for the following

    loads:

    a. Dead Loads & SIDL

    b. Lateral Earth Pressure (Active)

    c. Live Load Surcharge One side

    or both side

    d. Vehicular Live Load (Class A 2

    lane / Class 70R / Class AA )

    e. Buoyant forces

    Design of deeper open to sky

    portion with Diaphragm WallsDesign of the deeper portion of

    Underpass involving diaphragmwalls is carried out using the top

    down construction method. Different

    stages of Construction are as

    follows:

    a. Construction of Diaphragm Wall

    on both sides with M35 grade

    concrete (Photo P14).

    b. Excavation upto bottom of base

    slab in stages with intermediate

    strutting using waler beams

    (Photo P15).

    Photo 13: Reinforced Earth Wall work Delhi Side of Flyover

    Photo 14: Boring for Diaphragm Wall Construction

    Photo 15: Temporary Strut with

    Diaphragm Wall & Contiguous Pile

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    164 NBM&CW SEPTEMBER 2011

    Grade Separator

    c. Casting of Base Slab, intregated

    with diaphragm wall leaving

    pockets for the soil anchoring to

    be done later.

    d. Casting of road surface/wearingcoat, crash barriers over the

    walls, underside road kerbs etc.

    The following analysis principal

    has been adopted for this portion

    of Underpass:

    a. Construction Stage Analysis

    b. Service Stage Analysis i.e.

    Wished in place structure

    analysis

    The construction stage analysis

    is carried out using standard

    software Wallap. The diaphragm

    wall is analyzed for earth pressure

    using Wallap for different stages

    of construction. The effect of

    temporary strut at intermediate level

    as well as effect of bottom slab is

    considered by adopting concrete

    strut and moment restraint at

    respective locations.

    Service stage analysis is

    carried out using software STAAD

    Pro. All the forces have been

    applied on the frame model. On

    the active side, net pressure

    applied while on the passive side,

    the supports are idealized assprings with stiffness taken based

    on the soil characteristics.

    Covered portion of

    Underpass800mm thick diaphragm wall

    with M40 grade concrete have

    been provided in covered

    portion of Underpass. Depth

    of diaphragm wall varies from

    8m to 14m in panels. Panel

    size is kept as 5m, interlinked

    with water stopper. The total

    length of diaphragm wall is2060m in this project and

    total number of panels are

    412 in both underpasses.

    The design of open to sky

    portion caters for the following

    loads:

    f. Dead Loads

    g. Earthfill on top

    h. Lateral Earth Pressure (At

    rest)

    i. Live Load Surcharge One side

    or both side

    j. Vehicular Live Loads as per IRC:6

    on top of slab as well as at base

    k. Buoyant forcesCovered portion of Underpass

    is constructed in following steps:

    a. Construction of Diaphragm Wall

    on both sides with M40 grade

    concrete.

    b. Excavation upto bottom of top slab.

    c. Casting of top slab, integrated

    with the diaphragm wall. Traffic is

    allowed over the top slab when

    the concrete gains strength.

    d. Excavate from below the top slab

    upto the bottom of base slab.

    e. Casting of Base Slab, intregated

    with diaphragm wall.

    f. Casting of road surface/wearing

    coat, crash barriers over the

    walls, underside road kerbs etc.

    The analysis principles are

    same as explained in case of open

    to sky portion.

    Horizontal & Vertical

    Prestressed Soil Anchors

    This is perhaps the only project in

    India where prestressed anchors

    have been used both in vertical as

    well as horizontal alignment. Forproviding vertical and horizontal

    anchors, PWD has engaged a

    specialist agency (M/S Tech9

    Engineering Solutions Pvt. Ltd.) for

    complete technical support in

    design and execution.

    Vertical Soil AnchorsVertical Soil anchors of safe tensile

    load capacity of 40 tonnes each

    have been provided on either side

    of the underpass raft in open to

    sky portion to cater for the upward

    water thrust, which can arise due

    to high water table in the area. A

    total of 776 numbers of vertical

    prestressed soil anchors, 17m in

    length (10m free length, 7m fixed

    length) have been used in this

    project. Longitudinal spacing of soil

    anchors varies from 4m to 1.4mdepending upon the depth of base

    raft of Underpass from GL.

    The various steps involved in

    the soil anchoring are:

    STEP 1 : Cutting of 15.2mm

    diameter 7-ply class II strands

    strands to required length.

    STEP 2 : Corrosion protection in

    free and fixed length

    STEP 3 : Applying Bond Breaker

    and internal grout vent fixing.

    STEP 4 : Drilling with TG 20 rig

    machine (Photo P16).

    STEP 5 : Homing of anchor and

    grouting simultaneously during

    extraction of casing pipe.

    STEP 6 : Allowing the grout

    to set.

    STEP 7 : Stressing of

    anchor to required load and

    locking - grouting of anchor

    pit.

    The anchors are

    installed in a drilled hole of

    diameter 200mm. The

    drilling of the hole is carried

    out using temporary casingfor the full depth, which is

    removed in stages after

    completion of grouting. For

    the design of soil anchors,

    the factor of safety for bond

    length between grout and

    soil is kept as 3.0 while the

    factor of safety for tensile

    stress in strand is kept as

    2.0. Each soil anchorPhoto 16: Vertical Soil Anchor Boring at RHS Underpass

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    166 NBM&CW SEPTEMBER 2011

    Grade Separator

    comprised of 3 Nos. of

    15.2mm diameter 7-ply

    class II strands

    conforming to IS:14268

    (LRPC).The free length of the

    anchors is encased in

    plain HDPE pipe of

    125mm OD. Fixed length

    of the anchor is

    encapsulated in

    corrugated HDPE pipe of

    125mm OD. The length

    of fixed portion is

    determined based on the

    requirement of bond

    length between grout and

    soil or between grout and

    strands, whichever is

    higher.

    The HT strands in the

    free length is covered by

    flexible HDPE tube of 20/

    22mm ID as a double

    protection measure. The

    thickness of the tube is

    kept as 2.5mm thick. The

    annular space between

    strands and the HDPE

    tube is filled with grease.

    The greased HDPE

    pipes encasing the strands arefurther encased in 125mm dia plain

    HDPE pipe in the free length

    portion, which is cement grouted.

    The portion outside this HDPE pipe

    and 200mm diameter bore hole is

    also cement grouted, which gives

    3rd level of protection to the strands

    against corrosion.

    The treatment of the HT

    strands in free length includes

    cleaning followed by application of

    a coat of primer of minimum 40

    micron DFT. As soon as the primer

    coat dries up, three coats of epoxy

    based paint is applied sequentially.

    For the portion of strands in the

    fixed length portion, the HT strands

    are first pre-treated by thoroughly

    cleaning using thinner. First coat of

    epoxy formulation is uniformly

    applied on the strand and it is

    allowed to dry for a period of 2 to 3

    hours. The second coat is applied

    thereafter and is

    allowed to dry for

    24 hours. The

    surface is next

    made rough bymanually rubbing

    the top surface

    with sand paper

    and the third coat

    of epoxy based

    paint is applied

    uniformly. While

    third coat is still

    tacky, quartz sand

    is sprinkled over

    it to increase the

    bond.

    Fig. 19

    shows the

    s c h e m a t i c

    details of Vertical

    Soil Anchor

    adopted

    Horizontal Soil

    Anchors

    The horizontal

    soil anchor

    system has been

    adopted in the

    existing ROB to

    hold thecontiguous piles installed on either

    side of existing ROB together. Steps

    involved in the horizontal soil

    anchoring are :

    STEP 1 : Drilling horizontally from

    both sides.

    STEP 2 : Fabrication of horizontal

    anchors

    STEP 3 : Installation of

    anchors into drilled

    holes.

    STEP 4 : Waler beam

    erection on either side

    of the approachcarriageway.

    STEP 5 : Stressing of

    anchors simultaneously

    from both ends.

    STEP 6 : Grouting of

    anchors.

    Photo P17 shows the

    completed Underpass,

    RHS side.

    ConclusionConstruction of grade separator at

    Apsara Border was a daunting task,

    which was accomplished with

    exemplary quality of workmanship

    and team effort. The project not

    only involved constructing a 6 lane

    flyover in one of the busiest

    intersection in Delhi at Seemapuri

    Border, of NCR but it also involved

    conceptualization, planning and

    execution of 2 underpasses in an

    extremely challenging working

    conditions with restricted space

    between existing ROB with 10m

    high embankment on one side and

    a nallah on the other side. To add

    to the complexity of the problemwas the challenging task of railway

    box pushing between the two

    existing structures with very limited

    space in between. The challenge

    posed brought out number of

    innovative solutions, both in design

    as well as in execution, which had

    never been tried before. Credit for

    successful completion of this project

    goes to the excellent team work

    and understanding between the

    Client (PWD), Proof Consultant,

    Contractor & the Design Consultant.

    Quantities of Major Items in this

    project

    1. Cement : 35,034 MT

    2. Reinforcement : 9277 MT

    3. Structural Steel, Superstructure :

    1811 MT

    4. Structural Steel, Waler Beam :

    430 MT

    Photo 17: View of Completed Underpass LHS side

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    NBM&CW SEPTEMBER 2011 167

    Grade Separator

    5. Concrete : 92,500 cu.m

    6. Bitumen : 857 MT

    AcknowledgmentsThe author wish to place on records

    his appreciation for the cooperation

    received from the authorities of

    Delhi PWD (NCTD) during the

    entire duration of this project and

    also in writing this paper. The

    cooperation extended by Shri U C

    Mishra (Project Manager, PWD), Shri

    Mr Alok Bhowmick is the Managing Director of one of the reputed Structural Engineering

    firm, namely B&S Engineering Consultants Pvt. Ltd., Noida. The highlights of his carrier

    of 30 years include designing bridges, flyovers, Underpasses, Aqueducts, Industrial structures

    and other structural engineering works. His experience has been gained mostly working in

    various consultancy organizations. He is an active member of several technical committees

    of Indian Roads Congress (B-1 : General Features of Design Committee, B-2 : Loads &

    Stress Committee & B-4 : Reinforced, Prestressed and Composite Committee). He has

    been given the responsibility by IRC to draft the Explanatory Handbook and Commentary

    on Limit State code for Bridges. He is also a member of National Advisory Committee,

    National Information Centre for Earthquake Engineering (NICEE).

    Kailash Narain (EE,PWD) are

    noteworthy. Author is also grateful

    to the unsung heroes from the

    Proof Consultant, Contractors as

    well as from PWD, whose deepinvolvement and untiring efforts has

    helped to complete such a complex

    project in reasonable time.

    Credits Client: Public Works Department,

    NCT Delhi

    Proof Consultant: M/S B&S

    Engineering Consultants Pvt. Ltd.

    Contractor: M/S AFCONS

    Infrastructure Limited, Mumbai

    Design Consultant: M/S Crafts

    Consultants (I) Pvt. Ltd.

    Quality Assurance: Delhi

    Technological University (Formerly

    Delhi College of Engineering)


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