bhagalpur bridge

vuql a/ k ku vfHkdYi vk Sj ekud laxBu RESEARCH DESIGNS AND STANDARDS ORGANISATION

Hk w&rduhdh b athfu;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.”

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

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

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 :

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

Abutment Latterally and Vertically Shifted

P2

Site PlanLocation: Km 291/11-12 (Bridge No. 144)

Cracks

A'

2. P1,P2,P3 & P4 Are Piers Of Bridge1. A1 & A2 Are Bridge AbutmentNOTES:

Direction of Slope Movement

Junction Box(Vertically Settled 2m)

2-2.5m Vertical Face of Slip Circle

A

Sahibganj

Research Designs & Standards Organisation

SETTLEMENT OF BANK ON THE APPROACHES OF BRIDGE NO.144 AT KM 291/11 - 12 BETWEEN LAILAKH MAMALKHA & SABOUR STATIONS ON MALDA TOWN DIVISION, EASTERN RAILWAY

NOT TO SCALE

D/S River

P3

U/S River

P4A2

A1 P1

RAIL

Bhagalpur

Left Bank

Right Bank

50.0m

Cracks

Cross section A-A at km : 291/11-12(A1 Approach Embankment of Bridge No. 144)

Vertical Faceof Slip Circle

G.L.

CL

14.9m

30.6m

4.9m


DRG. NO. GE/SK/ER/573/Rev.0/2007NOT TO SCALE

4.0m

25-30mRail Piling

7.1m8.9m

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

Re-profiling of Approach Embankment

Boulder filled Gabion Wall(Dimensions as per design)

HFL

LC

3H:1V

1m Minimum

Low Height Gabions (With Suitable Filter Material, as suggested by Dr. Venkatraman)


Suggested Re-profiling of Approach Embankment of

Bridge No. 144 At KM. 291/11-12 Between Lailakh

Mamalkha & Sabour Stations of Malda Division,

Eastern RailwayNot to scale

Boulder Pitching

Varying distance as per site condition

River channel

bhagalpur bridge

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