A Critical Review of RDSO Guidelines BS 96

On

UNDERWATER INSPECTION OF BRIDGES

Under Guidance of

Shri Ajay Goel Sr. Prof. Bridge/IRICEN

Girish Kumar, Dy.CE/C/ECR

Background:

On 22 June 2001, The train no. 6602, M anglore-Chennai Mail met with an accident over Kadalundi bridge, in which 57 passenger died.

It was an 140 yr old bridge and another bridge. The Bridge was inspected by Division and no abnormality was found. It is at the tidal river in Palghat Division of Southern railway and during tide sea water used to rush in. It was a screw pile bridge built in around 1860s and the piles were perennially submerged.

Later one pile was dug out on CRS instruction and it was found that the Steel Shell of Screw Pile was rusted almost to the full thickness at places and cracks were found in the portion under water of screw piles.

Train No 6602 Mangalore Chennai Express on 22 June 2001 met with an accident at Kadalundi, Palghat Division

View of Rusted Screw piles after the accident

This accident would have been avoided had proper under water inspection of Piles been conducted. Here, it would be worth mentioning that In Indian Railway system only in Southern Railway there are departmental divers. But there had been no guideline existing on Under water Inspection of Bridges. Indian Railway Bridge M anual 1998 provides in para 1107 (2) (d) simply for M asonry substructure Under water Inspection. • This sparked a need for Under Water Inspection System of bridges in

Indian Railways and on 13th July 2001 Railway Board asked RDSO to prepare guidelines for underwater Inspection of Bridges and as a result BS-40 was issued by RDSO on Oct’2001

. 1. The Chronology of development (in this regard is as follows): • Railway Board asked RDSO to prepare guidelines for underwater Inspection of

Bridges vide 2001/CE-1/BE-III /9 dtd. 13th July 2001 • BS40 issued by RDSO on Oct’2001 • U/W Insp. of Bridges : IRICEN: June2005 • U/W Bridge Inspection M anual : Feb.’2006, by RAMBOLL Denmark for Central

Rly. • BS 96 issued by RDSO on July’2008

The Central Railway Under Water Bridge Inspection M anual issued in Feb.’2006, and prepared by RAMBOLL Denmark has been fairly exhaustive based on underwater inspection system adopted world over. This necessitated a need for revision of RDSO guideline. As a result BS-96 was issued.

Aim of the present report is to critically discuss the provisions and omissions of

the BS 96, July2008.

2. General Provisions of BS 96 Underwater Inspection is to be done by suitable method for bridges normally

(perennially) under water for that portion of bridge which is perennially submerged. It is a General Guideline: CBE can to modify/supplement bridge specific underwater Inspection method.

Master list of inventory records for all such bridges (individually) to be

maintained with following Details:

• Type/Location • Type & frequency of Inspection • Member location (for inspection) • Inspection procedures • Special Equipments Required

• Dates of previous inspection • Findings of last (earlier inspection) • Follow up inspection of last Inspection • Elevation of bottom of Foundation/Pile/well

3. Frequency & Level of Underwater Inspection:

In fact, BS-40 Suggested UWI to be conducted during Low water or during the period of Low Pollution level or Good Visibility also 20% of Underwater units for each Bridge selected Randomly should be inspected so that entire structure is covered in 5 years.

BS-96 provides for UWI to be conducted Post M onsoon (Immediately after M onsoon). It has been dealt in para 1.3 & 1.4 & 6.2 for type frequency and reporting being dealt at two places. BS 96 suggests 3 Types of UWI:-

(a)Routine Inspection: Level- I -To be done once in a year

b) Detail Inspection: Level –II -At least Once in 5 yrs for even bridges in sound Condition

c) Special Inspection: Level –III : -To be decided by Sectional Sr.DEN/DEN 4.0 S alient Features of Different Inspection Levels: 4.1 Routine Inspection: Level- I

• “Swim By Inspection” by Experienced Diver to detect obvious

damage for all submerged parts

• It is predominantly a visual Inspection

• In case of low Visibility : Clear box is to be used or Feel inspection by sweeping motions of hands is to be done.

• Supplemented by Water Depth Sounding of Piers/Abutment

• Continuity Verification in full length

• Spalling/ Corrosion/crack 0.2mm & larger and other damages to be

registered.

4.1.1 Conditions warranting Level II Inspection

• Inconclusive Level I Inspection Report • Critical Structure, damage to which shall have Detrimental Impact on Structure • Unique structure – Uncertain Structural performance • Prior evidence of distress • Adverse environmental condition i.e. brackish/polluted water etc.

4.2 Detail Inspection: Level –II

• At least Once in 5 yrs for even bridges in sound condition. • Detailed Visual Inspection • Elements as decided during Level I inspection • Surface Inspection & limited measurement of Damage, after surface

cleaning in 30 cm bands (for marine growth) • Extent & Severity of the Damage to be Recorded • If any Damage detected Special Investigation: Level III inspection to be

done to be decided by Sectional Sr.DEN/DEN 4.2.1 Conditions warranting Level III Inspection

• If Sectional SR DEN/DEN decides for Level III inspection on basis of Level II under water inspection report

• After unusual Floods • After Vessel impact • If Debris built up near Pier/abutment • If Excessive settlement/ Scour • Evidence of Deterioration/ M ovement • After Significant Earthquake

4.3 Special Inspection: Level –III Purpose: To access Type, Extent Severity and Cause of damage, material

strength, material Homogeneity & hidden or interior damage must be detected. Need for load restriction, closure of bridge, level of repair of bridge necessary to

be assessed NDT Methods or Partial Destructive Testing such as ULTRASONIC, SAM PLE

CORING, IN-SITU HARDNESS TESTING Etc.

4.3.1 UNDERWATER NDT INS PECTION INS TRUMENTS : as per use NDT Methods are to be as per RDSO Guideline BS 42-2002

1. Ultrasonic Thickness Gauge -Steel 2. Ultrasonic Testing -Concrete and Steel 3. Cover-meter: - Concrete 4. Schmidt Hammer: - Concrete & Masonry 5. Chloride content: -Concrete 6. Coring Equipment: - Concrete & Masonry 7. Evaluation of Concrete cores: -Concrete 8. Crack measuring Gauge: -Concrete & Masonry 9. Impulse Response Equipment: -Concrete 10. Impact echo Equipment: - Concrete & masonry 11. Half Cell Potential: -Concrete

5.0 Reporting of UWI

5.1 LEVEL I Inspection Reporting:

• To be done in Sectional AEN’s Presence • Bridge wise report with remarks to be sent to CBE • Investigation Method & Extent • Back ground material, Water current, Visibility & other Details • Recording of deficiency/damage warranting attention. • Condition rating of UW component • Need for further inspection Level- II or III • Photo/Video recording (Not mandatory)

-CBE to ascertain Requirement N.B. Photographs/Video in electronic form will add to appreciation of health &

Condition of UW structure & will be valuable as record to access rate of damage/Change in Hydraulic condition etc. in future (Not In BS 96)

5.2 LEVEL II Inspection Reporting:

• To be done in Sectional AEN’s Presence • Bridge wise report with remarks to be sent to CBE • Method, Extent & Location of Damage • Back ground material, Water current, Visibility & other Details • Recording of deficiency/damage warranting attention. • Condition rating of UW component • Whether Need for further inspection :Level- III • Photo/Video recording

NB: 30 Cm Clear band to be inspected in (i) Splash Zone ( Low waterline) (ii) M ud line (River bed) (iii) Construction joints/ M id way (iv) Damaged areas N also Undamaged areas.

5.3 LEVEL III Inspection Reporting:

• To be done in Sectional Sr DEN/DEN’s Presence • Bridge wise report with remarks to be sent to CBE for scrutiny • Method, Extent & Location of Damage & Deterioration • Back ground material, Water current, Visibility & other Details • Recording of deficiency/damage warranting attention. • Cause of Damage • Recommendation for maintenance & Repairs & precautions • Condition rating assessment of UW component • Whether Need for further inspection :Level- III • Photo/Video recording

N.B:-Para 1.4.1, 1.4.2 deals with reporting of Level I & II inspection and again

Para 6.2 deals with reporting for all 3 levels of inspection and gives a common format, which could have been avoided. Also following relevant detail for Level III inspection have escaped mention in BS 96 :

• Reason for the level III inspection • Background documents • Extent and Location of tests & Summary of the results • Evaluation of Damage registrations (i.e indication regarding cause) • Risk analysis of further deterioration & Precautions, Repairs • General considerations for future maintenance activities

(such as: further investigations, repair works, etc). 6.0 What Damages to look for in Under Water Inspection:

1. Structural damage: Permanent Deformation, Tilt/settlement, Abnormal Vibration. 2. Damage due to water: Scour, Deposition, Debris & Vegetation, Difference in

Level, Erosion, M aterial disintegration. 3. Damage on Concrete structure: Corrosion of concrete, wear/abrasion, Material

Deterioration, Impact, Fracture, weathering, honeycombing, (spalling of concrete, exposed Reinforcement etc. not mentioned in BS 96, however are common phenomena on substructures under water)

4. Damage on Steel structure: Corrosion, Cracks, Loose connections/ Bolts/rivets, eccentricity , Impact, Fracture.

5. Damage on M asonry: Deteriorated stone/brick/joints, Cavities, Cracks, spalling, unintended eccentricities, overloading, M oisture penetration, Impact damage, Fracture including reasons and remedy for them.

Some Photographs of Damage to Concrete Structure under water are shown below :

Scaling of concrete

Spalling of concrete

Disintegration of concrete

Deep Cavitation

7.0 What BS 96 does not Mention:

• Any specific numerical rating system on basis of UW inspection or investigation

for submerged structures, Central Railway Under Water Bridge Inspection Manual however provides the same.

• Rust staining, spalling, exposure of reinforcing steel & disintegration in concrete • Bulge in sub structure & remedial measures • STEEL WORKS- specific to --CI PIPES -- STEEL CAISSONS -- Screw Piles Other Structural Steel Works

• BS 96 mentions Location Charting for Inspection but not Identification Charting

of damages or any Numerical Rating system for it.

8.0 METHODS OF UNDER-WATER INSPECTION

1. SCUBADIVING -S ELF CONTAIN ED UNDERWATER BREATHING APPRATUS : WORK PERIOD AT A TIM E: 20 M IN AT 20M DEPTH 2. SURFACE SUPPLIED AIR DIVING OR MIXED GAS DIVING

8.1 SCUBA DIVING

• SCUBA Diver is provided with portable air supply & is connected to surface through an umbilical cable.

• Min. equipments are SCUBA, life preserver, weight belt, knife, face mask and swim fins depth gauge, wrist watch, wet suit ( t>10 c) or dry suit ( t<10 c)

• SCUBA dive duration can be more if mixed air is used. • SCUBA can be more effective if communication with surface engineer is

available.

8.1.1 ADVANTAGES OF S CUBA DIVING Boat may not be necessary. It has low operating cost and is low effort dive with increased mobility . It is suitable for short duration and low velocity currents. Rapid deployment, portability , minimum support from above is its characteristics.

8.1.2 DIS ADVANTAGES OF S CUBA DIVING Limited air supply Communication with surface difficult Depth limitation M any dives of short duration are needed

8.2. S URFAC E S UPPLIED AIR DIVING OR MIXED GAS DIVING • Min. equipment are life preserver, weight belt, Knife, face mask and swim fins

depth gauge, wet suit ( t>10 c) or dry suit ( t<10 c), communication cable, and fathometer.

• It is well suited to stream flow velocity upto 4 m/s, • It is suited to polluted water, long duration required • Dive time can be extended by NITROX in shallow water

TRIM IX or HELIOX REQUIRED for diver deeper to 36 m.

8.2.1 ADVANTAGES OF S URFACE S UPPLIED AIR DIVING

It accords Long duration/ deeper dive than 36 m,

unlimited air supply, backup system available, safe line attachment to surface, it is better for high velocity currents, suitable for polluted and turbid water, communication for audio video easy * Pneumatic fathometer are attached to the diver longer duration/detailed inspection (60 minutes at 18m depth) rapid deployment, portability , min. Support (“*” Not in BS 96)

8.2.2 DIS ADVANTAGES OF S CUBA DIVING It has large size of operation

9.0 Under Water Method S election, Procedure, Equipment, Diver Qualification and Safety aspect : 9.1 Factors influencing UWI method S election:

Water Depth Current Velocity Under Water Visibility Substructure Configuration Water bed Condition Debris Drift

9.2 UNDERWATER INS PECTION PROCEDURE:

• Initial inspection requires careful planning. • Prior site survey for selection of inspection methods, type and intensity level,

equipment required. • Review of available records and past history. • Availability of tools and plants. • Ability/qualification of diving team. • Scour investigation. • Inspection of sub structure.

9.3 Under water Photography & Video Equipment:

i. Still Photography- Digital still camera of Minimum 5.0 Mega pixel camera At low Visibility Clear Boxes to be used ii. Video photography- Submersible Camera connected to surface monitor & control/ Telemetry linked, capable taking images at zero LUX with LEDs on iii. Under water lighting- Turbid water limits viewing by Absorption( reduces light reaching Object & camera too), Refraction( Causes Dispersion) & Reflection (swamp the object Light kept away from the axis of camera) Tight beam spot ( beam angle < 10 D) Under water Torches/ Strobe torch light

9.4 QUALIFIC ATION OF DIVERS and DIVING S UPERVIS ORS :

• IS 10291-1982: Lays down safeguards for their working Safeguards for their working:

Diving team to have at least 3 Divers. Fitness of Diver must have been checked by doctor in last six months. (fitness tested for work at required depth or equivalent pressure in compression chamber) M ust have Knowledge of diving signals. Trained for work in no visibility conditions and 0.6m depth of mud and conduct search etc. Certification by Navy/Indian Register of Shipping (IRS) is mandatory. SCUBA Divers to be trained by SCUBA Diving PADI ( Professional Association of Diving Instructors).

9.5 S afety Precaution: Working agency to follow its Diving Safety M anual with following details: -Checklist for Diving operation & Safety Procedures -Assignment & responsibility of Dive Team members - Equipment, Procedures & Checklist -Emergency Procedures for -Equipment failures -Adverse Environmental Condition -Divers Injury/illness -Standard First Aid Kit -For Big works- have 2 teams + A Doctor -Before Dive Medical Examination Desirable

-Insurance cover -Dive Supervisor to Ensure that all equipment are in working Condition

10.0 REPAIR & TREATMENT TECHN IQUES : ( Not in BS -96)

M INOR DEFECTS– such as cracks – apply aqua resins for grouting by replacing water

– If Crack >6mm apply sand with grouting resins or use special grouting equipments

10.1 SPALLING OF CONCRETE

Preparation of surface by water jet at high pressure and applying thick coat of epoxy resin on the prepared surface for bonding of epoxy mortar.

10.2 DETERIORATION OF CONCRETE IN PILES : • Jacketing by Shotcrete/ gunite layer of approx.. 75mm thickness. • Shotcrete ring is prepared above low water level and lowered upto bottom. • Annular space is subsequently grouted with mortar displacing water

10.3 REPAIR BY UNDERWATER CONCRETING • Tremie concrete • Bottom opening skip box • Bagged concrete • Grout injection of pre-placed aggregate • Micro concreting by concrete mixed with anti-washable, anti-shrinkable (Fosroc)

chemical in 150mm layers. It has7 day crushing strength of 30 Mpa.

11.0 CONCLUS IONS: • Bs 96 provides the frame work and modus operandi for the under water inspection

of perennially submerged bridge substructure, some provisions have been repeated while some left out but are available in given references.

• Underwater bridge inspection specially on old bridges is necessary for increasing

the residual life of perennially submerged bridge foundations and avoid catastrophic failures atimes and the significant underwater damages can be repaired before it is too late.