Upload
skumarsr
View
227
Download
0
Embed Size (px)
Citation preview
7/31/2019 Apsara Border
1/15
136 NBM&CW SEPTEMBER 2011
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.
7/31/2019 Apsara Border
2/15
140 NBM&CW SEPTEMBER 2011
Grade Separator
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
7/31/2019 Apsara Border
3/15
142 NBM&CW SEPTEMBER 2011
Grade Separator
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.
7/31/2019 Apsara Border
4/15
144 NBM&CW SEPTEMBER 2011
Grade Separator
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
7/31/2019 Apsara Border
5/15
146 NBM&CW SEPTEMBER 2011
Grade Separator
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
7/31/2019 Apsara Border
6/15
148 NBM&CW SEPTEMBER 2011
Grade Separator
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
7/31/2019 Apsara Border
7/15
150 NBM&CW SEPTEMBER 2011
Grade Separator
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
7/31/2019 Apsara Border
8/15
152 NBM&CW SEPTEMBER 2011
Grade Separator
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
7/31/2019 Apsara Border
9/15
154 NBM&CW SEPTEMBER 2011
Grade Separator
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)
7/31/2019 Apsara Border
10/15
156 NBM&CW SEPTEMBER 2011
Grade Separator
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.
7/31/2019 Apsara Border
11/15
160 NBM&CW SEPTEMBER 2011
Grade Separator
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
7/31/2019 Apsara Border
12/15
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
162 NBM&CW SEPTEMBER 2011
Grade Separator
7/31/2019 Apsara Border
13/15
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
7/31/2019 Apsara Border
14/15
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
7/31/2019 Apsara Border
15/15
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)