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RESEARCH DESIGNS AND STANDARDS ORGANISATION
Hkw&rduhdh bathfu;jh funs’kky;
Geo-technical Engineering Directorate
Report Of Inspection On 4th December 2007
By Team Of Geo-Technical Engineering Directorate, RDSO
For Problematic Location At Bridge No. 144
Between Sabour & Lailakh Mamalkha Stations
Malda Division - Eastern Railway
RDSO’s team comprising of Sr. Executive Director/Civil, Executive Director/
Geo-technical Engineering with experts from Geo-technical Engineering and B&S
Directorates inspected the problematic site of Bridge No. 144 on Sadonia River
between Sabour and Lailakh Mamalkha stations near Bhagalpur in Malda Division of
Eastern Railway alongwith CBE, CTE/TP & Sr.DEN of Eastern Railway on 4.12.07.
At
this
location,
adjoining approach
embankment
of
Abutment No. A1 of
Bridge
No.
144
settled on 23.11.07
and it continues to
settle, leading to
disruption of traffic.
The
background,
observations
of
RDSO, causes of
problem and the
suggested remedial
measures
are
detailed herein.
1.
Background :
1.1
The Section was earlier referred to RDSO last year during the same period
vide Chief Bridge Engineer/Eastern Railway/Kolkata, letter no. W(7) 436/15/Pt.VI
/A, dated 22.12.06. Accordingly, RDSO team visited site on 24th & 25th December
2006 & advised following preliminary remedial measures there itself to ER officials :
i)
To prevent scouring of river, river training measures should be adopted.
ii)
Stone boulders crates alongwith two layers (zigzag) of rail piling at 1.0 m c/c
at toe of bank should be provided in the affected length of the bank. Cracks
should be filled up with gravel or sand.
iii)
Retaining wall should be provided upto suitable length of affected bridge
approach in downstream side.
iv)
Flattening of slope should be carried out and side slope of 2.5:1 should be
maintained in the first stage. Turfing shall be provided on slope of bank and
sub-bank.
v)
Proper boulder pitching on slope should be provided upto the HFL.
vi)
Earthwork shall be done as per RDSO’s “Guidelines for Earthwork in Railway
Project, GE: G-1, July–2003.”
Page 1
1.2
Also, three undisturbed and three disturbed soil samples & one sample of
stone dust were collected, as received in RDSO on 02.01.07. After testing the soil
samples in GE Laboratory at RDSO and analyzing the results thereof, final report
titled as “Consultancy Report On Rehabilitation of Bank On The Approach of Bridge
No. 144 between Sabour and Lailakh Mamalkha Stations - Malda Division, Eastern
Railway” - No. RDSO/2007/GE:CR-0099, April ’07 with following recommendations :
i)
To prevent scouring of problematic abutment, suitable river training
measures (one or combination of two as per site condition) as given in Para
808 of Indian Railway Bridge Manual-1998 should be adopted, especially
near abutment slopes.
ii)
Flattening of slope should be carried out. As per recommended profile, side
slope of 2.5H : 1V to be maintained at the cross section A-A and of 2.75H :
1V slope for the cross section B-B. Turfing shall be provided on slope of
bank.
iii)
Flattening of slope at cross section B-B’ upto 2.75H : 1V will result in
situation where the toe of flattened slope would fall into the river portion. To
avoid this situation, retaining wall would be required. The retaining wall to
contain the flattened slope be provided close to abutment A1
iv)
Retaining wall/boulder filled gabions should be provided upto suitable length
of affected bridge approach at downstream side as well as on upstream side.
Design of retaining wall should be ensured as per site condition.
v)
For CH type of soil, minimum 100 cm thick compacted blanket layer is
required at top of formation as per Para-4.3.2 and 4.3.4 of “Guidelines For
Earthwork In Railway Projects GE : G-1, July - 2003”, which shall be ensured
at site.
2.
Observations At Site On 04.12.07 By The Team Of RDSO :
i)
The suggested remedial measures by RDSO vide Consultancy Report no.
RDSO/2007/GE : CR-0099, April ’07 have not been implemented by the
Railways so far.
ii)
The same problem was faced last year at this location in the same period,
i.e. at the end of November ’06. Further, no problem was noticed during
peak season of monsoon with maximum floods. Settlement of approach
embankment took place during receding floods.
iii)
Restoration work was being carried out by dumping of stone dust on the
right approach bank of the bridge.
Lateral Shifting Of Abutment A1
Page 2
iv)
Longitudinal and transverse cracks were observed near the toe of
embankment and in the natural ground away from the embankment towards
the river. Abutment A1 itself also was shifted laterally and vertically
downwards by about 300 mm each.
Longitudinal & Transverse Cracks Near Toe Of Embankment And In Natural Ground
v)
It was observed that there was no wing wall existing at bridge abutments.
vi)
River training measures have not been adopted, as already suggested.
vii)
At right approach of bridge, a vertical slump of about 2m to 2.5m has
occurred on upstream side near track. This point seems to be top point of
slip circle. Even the Signal Junction Box, erected on cess on this approach,
settled down by about 2m.
Cracks In Bank And Vertical Slump Of 2m To 2.5m On Approach Of Abutment A1
viii)
About 7m to 8m
deep rails piling
in zig-zag form
has been done at
the toe of the
embankment on
downstream side.
This arrangement
is not effective in
preventing slip of
embankment as
failure
surface
may be deeper
than end of rail
piling.
Rails Piling At Toe In Zig-Zag Form
Page 3
3.
Causes Of Problem :
3.1
The factors involved in the settlement at the bridge approach include :
i)
Steep slope of the embankment (varying from 1.5H : 1V to 1.75H : 1V).
ii)
Steep longitudinal slope of the riverbed on downstream side.
iii)
Deep gorge formation due to non-availability of sufficiently wide waterway
due to scattered boulders.
iv)
Non-availability of guide bund on upstream side, specially near A1 where
river has meandered.
v)
Non-availability of wing walls.
vi)
Use of vulnerable soil, i.e. CH (highly plastic clay) in the construction of bank
alongwith damaging factors as mentioned in item 3(i) to 3(v) above.
vii)
Insufficient length of riverbed protection work on downstream side like
boulder dumping, caused heavy erosion of riverbed resulting into onset of
progressive slope failure.
3.2
Dr. M. Venkatraman, the Geo-technical Expert from Pune, as summoned by
EDCE (RC&F), Railway Board also visited the site with RDSO team and opined that
problem is more of hydraulic nature followed by geotechnical problem.
3.3
From the visual observation of site, it is found that bank slopes have failed
on both sides of river. It may be due to erosion of natural slope beyond toe by
running water of river stream.
3.4
Further, due to receding water after monsoon, sudden drawdown in the river
water level enhanced instability of side slope close to river stream. This caused the
progressive failure of slope on both sides of river.
Progressive Failure Of Slopes On Both Sides Of River
3.5
Toe of the right approach bank eroded due to high current of running water,
causing cracks in boulder pitching and slip of approach bank slope towards river.
The reasons for high current of running water are detailed at 3(iii) & 3(vii) above.
4.
Preliminary Suggestions As Discussed At Site :
4.1
The problematic site was also visited by Dr. M. Venkatraman, Geo-technical
expert from Pune. Detailed site investigation was already done as mentioned in
RDSO’s Consultancy Report no. RDSO/2007/GE : CR-0099, April ’07 and no further
geo-technical investigations are needed. The following remedial measures have
emerged during discussion by visiting expert and RDSO & Railway officials at site :
Page 4
i)
Railway bank should be flattened upto 3H : 1V on both sides. Flattening of
slope should be done after benching on existing slope and adequate
compaction of fill material.
ii)
Stone pitching 1.0 m above HFL should be provided.
iii)
Suitable river training measures should be adopted on downstream &
upstream sides.
iv)
Boulder filled Gabions or similar measures should be provided upto suitable
length of affected bridge approach at downstream side as well as on
upstream side
v)
At end of fattened slope, retaining wall preferably of non-rigid material
should be provided to protect erosion of toe.
vi)
Boulder pitching/low height Gabions beyond retaining wall should be
extended upto adequate distance towards river stream. A conceptual sketch
is enclosed showing various suggested remedial measures.
vii)
Complete topographic details should be plotted upto 500m upstream &
downstream.
viii)
River training work should be adequate to restrict meandering of river
towards abutment A1.
ix)
Longitudinal slope of river should be eased by providing step-falls on
downstream side, if needed as per topographic details.
x)
Since, river stream on upstream side appears shifted towards approach
embankment of Abutment A1 due to non availability of river training,
possibility of extending waterway by opening one or two more spans towards
Sahibganj end may be explored after detailed survey and study by the
Railway.
xi)
Other remedial measures, suggested in RDSO’s Consultancy Report no.
RDSO/2007/GE: CR-0099, April ’07 need to be implemented as mentioned
above in Para 1(i) to 1(v).
Shifted Alignment At Abutment A1
Cracks In Pier P4
Page 5
A
Right Bank
2-2.5m Vertical
Face of Slip Circle
Junction Box
(Vertically Settled 2m)
Abutment Latterally
and Vertically Shifted
U/S River
Bhagalpur
RAIL
Sahibganj
A1
P1
P2
P3
P4
A2
Cracks
D/S River
Left Bank
Site Plan
Location: Km 291/11-12 (Bridge No. 144)
Direction of Slope Movement
Research Designs & Standards Organisation
A'
SETTLEMENT OF BANK ON THE
APPROACHES OF BRIDGE NO.144
AT KM 291/11 - 12
BETWEEN
LAILAKH MAMALKHA & SABOUR
NOTES:
1. A1 & A2 Are Bridge Abutment
2. P1,P2,P3 & P4 Are Piers Of Bridge
STATIONS ON MALDA TOWN
NOT TO SCALE
DIVISION, EASTERN RAILWAY
Page 6
C
L
50.0m
30.6m
14.9m
4.9m
G.L.
Vertical Face
of Slip Circle
7.1m
8.9m
25-30m
Rail Piling
Cracks
4.0m
Cross section A-A at km : 291/11-12
(A1 Approach Embankment of Bridge No. 144)
Research Designs & Standards Organisation
CROSS SECTION PROFILE OF
BANK ON THE APPROACH OF
BRIDGE NO. 144 AT KM.
291/11-12 BETWEEN LAILAKH
MAMALKHA & SABOUR
STATIONS ON MALDA DIVISION,
EASTERN RAILWAY
NOT TO SCALE
DRG. NO. GE/SK/ER/573/Rev.0/2007
Page 7
C
L
Boulder Pitching
1m Minimum
3H
HFL
:1V
Varying distance as
per site condition
River channel
Boulder filled Gabion Wall
(Dimensions as per design)
Low Height Gabions
Re-profiling of Approach Embankment
(With Suitable Filter Material, as
suggested by Dr. Venkatraman)
Research Designs & Standards Organisation
Suggested Re-profiling of
Approach Embankment of
Bridge No. 144 At KM.
291/11-12 Between Lailakh
Mamalkha & Sabour
Stations of Malda Division,
Eastern Railway
Not to scale
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