Case Study
on
Collapse of 16 Nos. Soldier Piles of Temporary works at A1- Bridge No. 19, Damanganga
❖ Preamble:
❖ On dated 23rd June 2019 at 8.00 am an incident of collapse of 16 Nos. soldier piles which were erected as part
of temporary works to facilitate construction of open foundation for Abutment A1 (Mumbai End) of Bridge No. 19
across Damanganga river was observed during the foundation excavation work. These 16 Nos. soldier piles
were fixed in the perpendicular direction of the proposed bridge alignment. Soon after the collapse of these
soldier piles, a speed restriction of 30 kmph was imposed by IR on 23-06-2019 from 8.30am for traffic on adjacent
IR track from Km 168/25 to 168/15. After carrying out the restoration works duly ensuring the safety of adjacent
IR track the SR of 30Kmph was restored to normal speed on 24-06-2019
Photograph after collapse of the Soldier piles Perpendicular to Alignment at Abutment-1 on 23-06-2019
❖ Details of Design Approvals of temporary works for A1:
1) Engineer vide Letter No. L/OCGC/DFCC/CMT/CTP-15A/1706/4757 dated 07.06.1017 has accorded the
approval of temporary works drawings for A1 & A2.
2) The method statement for construction of soldier piles at A1 & A2 for temporary works was approved by
Engineer vide Letter No. L/OCGC/DFCC/CMT/CTP-15A/1805/12003 dated 04.05.1018.
3) The design & drawings at A1 & A2 were submitted to IR for approval. DFCCIL vide their Letter No.
MUM/EN/BR/DAMANGANGA RIVER/15A/380 dated 6.11.2018 has communicated approval of CBE/WR
and the same has been communicated to contractor vide Engineer’s Letter No. L/OCGC/DFCC/ZMT2/CTP15A/1811/293 dated 10.11.2018.
4) The CRS sanction of temporary work at A1 & A2 has been communicated to the contractor vide Engineer’s
Letter No. L/OCGC/DFCC/ZMT2/CTP-15A/1812/328 dated 15.12.2018.
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❖ Design & Drawing Details of Temporary Works for A1
General Details:
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The proposed DFC Br. No. 19 is of span arrangement 6 x 45.5 m Steel Girder with open foundation
The proposed DFC Br. No. 19 is on East Side of the existing IR Br. No 275 having size 6 x 45.5 m Steel
Girder with Pile foundation
The centre to centre track distance between proposed DFC DN track and existing IR UP track is 22.130
Mts.
The existing IR embankment height on A1 side (Mumbai End) is 17.508 Mts (Approx)
Rail levels of proposed DFC & existing IR track are 21.476 and 20.025 respectively at this Bridge location
The designed founding level of proposed bridge of DFCC at A1 is RL 0.910
Purpose of Temporary Works for A1:
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To facilitate cutting for open foundation of A1 for the proposed DFC bridge, fouling within the proximity
of Wing Wall of adjacent IR track.
To retain existing high embankment of IR track in intact & safe position while excavation works for A1
foundation are done.
About the Temporary Design and Drawing for A1:
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L-Shape temporary protection works with soldier piles driven below poor rock strata was designed.
26 Nos. Soldiers Piles parallel to the track alignment, starting from North to South end of A1. These are
denoted as R1 to R26, referring “R” as “Rail side”
19 Nos. Soldiers Piles across to the track alignment, starting from East to West side. These are denoted
as E1 to R19, referring “E” as “Embankment side” (Perpendicular to Alignment)
ISMB 600 to be used in Soldier Piles.
The designed centre to centre spacing of soldier piles is 650mm
Wooden planks to be placed in between the soldier piles
As per the bore log in drawing the soldier piles are designed with grip length of 2.3m in poor rock
The designed top level of soft rock is RL 2.41. Thus, the designed pile bottom level is RL 0.11.
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The soldier piles were designed with benching of 1.5m between the soldier pile and the foundation
concrete.
Thus, it is concluded that the soldier piles were designed with 2.3m grip length in poor rock (0.80m below
designed founding level) with a benching of 1.5m in poor rock between soldier pile & A1
footing/foundation.
❖ Construction of Temporary Protection Works -A1
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Earth filling on the existing IR embankment was carried out upto a level of RL 14.5 to develop an even
working platform for the working of boring machine.
Boring of 650mm dia bore & Erection of Soldier piles parallel to track alignment was commenced from
24thDec’19 & completed on
Boring of 650mm dia & Erection of Soldier piles across/perpendicular to track alignment was
commenced from 06thJan’19 & completed on 22-03-2019
Wooden laggings between soldier piles was ensured up to rock level as encountered at site.
The soldier piles were grouted by M40 grade concrete up to poor rock level encountered at site.
The details of soldier piles depths are enclosed at Annexure-1
a) Soldier Piles Parallel to the track alignment (R1-R26)
• Soldier pile R2 to R5 could not be taken up at site due to infringement of wing wall
• Soldier pile R6 to R11, however, were terminated after PCC of wing wall encountered at varying level
from RL 8.40 to RL 3.70
• Soldier piles R12 to R26 were terminated into the rock with a minimum termination level of RL (-)0.05 to
a maximum level of RL (-)1.00
• The rock level encountered at site found varying from RL 4.00 to RL 2.60
• Embedment of soldier piles R12 to R26 into rock was ensured for a minimum of depth of 3.05m to 4.8m
as against designed embedment of 2.30m.
• Following additional support system were adopted at site in addition to the design recommendations:
➢ Waller support of ISMB 600 was provided at RL 10.5 connecting soldier piles from R6 to R26
➢ To ensure further safeguard of soldier piles R6 to R11 additional struts supports system as designed
by contractor is erected at site. As part of this system anchor support to R6 to R11 was ensured by
providing 2 Nos. ISMB 600 as struts anchored on 5 Nos. soldier piles casted at opposite of R6 to
R11. Detailed design & drawing of this arrangement was submitted by contractor vide letter No.
L/IISLT/ENGR/CTP-15A/DGN/TW/0519/2621 & L/IISLT/ENGR/CTP-15A/DGN/TW/ 0519/2622 on
dated 31.05.2019
b) Soldier Piles Across to the track alignment (A1-A19)
• Soldier piles A1 to A19 were terminated into the rock with a minimum termination level of RL 0.11 to a
maximum level of RL (-)0.52
• The rock level encountered at site found varying from RL 3.38 to RL 2.20
• Embedment of soldier piles A1 to A19 into rock was ensured for a minimum of depth of 2.50m to 3.99m
as against designed embedment of 2.30m.
❖ Monitoring of Deflection/ Tilt of Soldier Piles
• The permanent targets were fixed on the top of soldier pile.
• For soldier piles parallel to track alignment, targets were fixed on R15 to R25 (except for R19)
• For soldier piles across to track alignment, targets were fixed on E4, E5, E6, E7, E11, E,17, E18 & E19
• Monitoring of these targets through Total Station were recorded on daily basis during excavation work
for foundation.
• The limiting value for deflection indicated was 20 mm
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During the complete excavation process continuous & regular monitoring of deflection/ tilt of soldier piles
being recorded jointly at site.
The record of monitoring of deflection of soldier piles is at -Annexure-2
❖ Excavation for A1 Foundation
• After completing the temporary protection works on A1 side, the preliminary excavation work taken up
from start of 2nd week of April’19
• The excavation of earth below GL of (13.4 RL to 6.40) to poor rock level of RL 3.00 was carried out from
11-06-2019 to 19-06-2019.
• The excavation up to soft/poor rock top level was achieved for the complete foundation area from
19.06.2019 to 22.06.2019.
• As stated in above para, the wooden laggings were provided between soldier piles up to the soft rock
level as encountered at site.
• The deflection or tilt of all soldier piles was within limits of 20mm, during the above period.
• The excavation for foundation in soft/poor rock was started on19.06.2019 and designed founding level
of RL 0.91 was achieved for in majority of the foundation area.
• The excavation work for foundation in soft rock was carried out keeping benching of avg 1.5m from the
face of the soldier pile.
• The deflection of all soldier piles was observed within limits of 20mm, till 22.06.2019. The maximum
deflection of +16mm was observed for E6 on 22.06.2019(morning)
❖ Collapse of Soldier Piles E1 to E16
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At 07:30 Am on 23.06.2019, crack on soil behind was observed at a distance of 1.5m from the soldier
piles installed across to the track.
Within no time the crack got wider and the soil started collapsing towards the soldier piles
Due to excessive soil pressure exerted by the collapsing soil, by 08:00AM on 23.06.2019, soldier piles
E1 to E16 erected/installed across to the track alignment collapsed inside the excavated foundation.
❖ Root Cause of Collapse of Soldier Piles
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The reason for sudden development of crack on soil on Mumbai side and was basically responsible
initially for the collapse of the soldier piles.
The soldier pile design not suiting the site conditions was also a part to be analysed.
GT investigation details adopted for design of soldier pile are to be reviewed
The design for temporary works to be reviewed generally considering site photographs and also the site
visit by the design verification engineers
Some of the reasons could be as under: ➢ Insufficient grip length in rock in view of poor quality of rock
➢ Benching of 1.5m is shown in the design, however, it seems that working space required for casting
of foundation below rock level was not considered. Provision of working space will reduce the
designed bench width from 1.5m to 1.0m at site.
➢ Use of breaker for cutting of rock may have developed these cracks on soil/poor rock
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Photographs during Execution of works
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Image dated 18.06.2019
Image dated 19.06.2019
Image dated 20.06.2019
Image dated 21.06.2019
Image dated 22.06.2019
Image dated 22.06.2019 (evening)
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Photographs of Restoration works Post Collapse of soldier piles considering safety of IR side embankment
Other Photographs on different dates
Image dated 18.06.2019
Image dated 19.06.2019
Image dated 20.06.2019
Image dated 21.06.2019
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Image dated 22.06.2019
Image dated 23.06.2019
Image dated 23.06.2019
Image dated 23.06.2019 (night)
Image dated 24.06.2019
Image dated 24.06.2019
Image dated 27.06.2019
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❖ Observations of ZMT-2 on temporary soldier pile works and remedial action for review of alternate type
of foundations for Abutments:
1. Though all the design & drawings were cleared by Engineer and CBE/WR. The constructability of the soldier
piles design suiting the site conditions and protection to adjacent ground & high approach embankments of
existing IR bridge at Damanganga could have been sturdier to deal with actual construction parameters and
earth pressure.
2. SBC of bed-rock adopted for A1 foundation was 3029 kN/m2 at RL of +0.910 whereas the soldier pile embedment
was designed at RL of +0.11 in poor rock. The excavation in rock for actual foundation for abutment is at 0.91
m and there is only 0.8 mts embedment in poor rock is only available below the foundation bottom of Abutment.
The poor rock around the foundation i.e the bench between the soldier pile and foundation periphery (only 1.5
mts) got crumbled & collapsed at some locations being soft in nature & also the embedment of 2.3 mtr in poor
rock reduced.
3. Thus, the soldier piles couldn’t withstand the earth pressure behind and finally collapsed hardly giving any time
to take any additional support or remedial measures perhaps the soldier pile design is not suiting the site
condition.
4. It is also observed that no walers have been provided at different depths of soldier piles driven to act all soldier
piles together as a combined supporting wall to retain the earth. The additional protection measures taken for
R6 to R12 on IR side with waler & strut supporting for additional soldier piles on other side as instructed by
engineer at site has supported and protected the soldier pile parallel to IR embankment which did not collapse.
5. During the visit of the Engineer & CBE/WR, it was opined that the present temporary works to deal with such a
deep foundation adjacent to IR embankment & dismantling of part of IR return wall to accommodate the
foundation of DFC abutment is not suitable. It was suggested to go for pile foundation as done for existing IR
bridge.
6. It is to be noted that the excavated foundation pit for abutment is filled with the collapsed I-Sections & other steel
material etc. It will be difficult to remove the same by excavating again keeping in view of safety of adjacent IR
high embankment & wing wall/return wall. Therefore, larger span to avoid existing foundation pit/ difficulty of
boring for piles in the present condition in the location to be reviewed. Similar review of design on A2 side is also
required at same location as the excavation of foundation has not been done.
7. NCR-03 -WDFC-PMC2-ZMT2-NCR-CTP15A-QAQC-0003 was issued to IHI L&T to submit the corrective action
(Copy Enclosed)
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