FE001P DD ST 001 Technical Report

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Mar. 2013

Project.: DOUBLING OF LINE BETWEEN

HOFUF AND RIYADH –

BRIDGE AT KM 426+617

Title: TECHNICAL REPORT

Page 1

TECHNICAL REPORT

INDEX

1. INTRODUCTION ....................................................................................................... 2

2. SCOPE OF WORK ..................................................................................................... 4

3. SURVEY ACTIVITIES .............................................................................................. 5

4. EXISTING UNDERGROUND UTILITIES ........................................................... 10

5. DESCRIPTION OF WORKS................................................................................... 12

6. CONCLUSIONS ........................................................................................................ 19



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1. INTRODUCTION

Doubling of line No.1 between Hofuf and Siding No. 5 and between Siding No. 9 and km

443+600 in Riyadh includes the doubling of the existing bridge located at km 426+617.

The existing bridge’s deck consist of a 3 span concrete post-tensioned box girders, with a

constant height of 3.00 m. Girders are simply supported over each span.

Bridge view.

Girder section.

Each pier consist of a circular column with 3.00 m diameter and a height of 10.25 m. On

the top of each column are placed 4 elastomeric bearings.

Pier’s foundation are made by a 15x10x2.70 m plinth, placed about 6.00 m beneath the

ground level. Each footing is already prepared for the doubling of the bridge and rebars for

the connections with the future column are provided and protected by a small concrete

column.



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Column for protection of rebars anchors.

Abutments consists of a single column per deck, with the same dimensions as the pier’s

one, and a earth-retaining wall 3.55 m high. Columns are sustained by the same

15x10x2.70 m footing as the pier: also abutment’s foundations are prepared for the

doubling of the bridge. On the top of each column are placed 2 elastomeric bearings.

Differently from the pier, on abutments columns for the new deck are already builded.

The bearings layout provides free restraints on each abutment, 2 fixed and 2 free bearing

on one pier and 4 fixed bearings on the other pier. Each bearing is fixed in the direction

transverse to the deck axis.



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2. SCOPE OF WORK

The targets of this project, as requested by Saudi Railway Organization, are:

1. doubling of the existing line located at km 426+617.

2. construction of a new bridge capable to 32.5 ton/axes loads, according to UIC

codes and Eurocodes;

An accurate diagnostic activity has been required to assess the actual conditions of the

structure.



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3. SURVEY ACTIVITIES

The examination of the existing structure has been carried out by mean of visual

inspections and laboratory test performed on specimens extracted from deck, columns and

footings. Also original drawings, structural calculation and geological report have been

found.

The visual inspection shown a structure in quiet good conditions, especially considering

that the structure dates back 30 years ago. Also the bearings, that usually are the first part

of the structure to need maintenance, seem to be in good conditions.

Deck external view.



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Deck internal view.

Pier’s column.



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Free bearing on abutment.

Fixed bearing on pier.



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Performed laboratory tests consist of:

• carbonation test by mean of phenolphthalein;

• uniaxial compression test for the determination of the compression strength of the

concrete;

• uniaxial compression test for the determination of the Young Modulus of the

concrete;

• ultrasonic test on concrete specimens;

• tensile test on steel bars.

A total number of 27 concrete specimens and 9 steel specimens have been collected.

Concrete specimens.

Steel specimen.



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Generally the tests shown concrete strength values lower than expected, while steelstrength abide the design value. No significant carbonation was detected on concrete

specimens.

Even if visual inspection gave a good impression of the structure, considering the low

strength values of the concrete and the fact that design loads are increased by 30% it was

decided to realize a new bridge with two spans (new abutments, new piers and new decks

with two spans: 28.45m and 34.45m).



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4. EXISTING UNDERGROUND UTILITIES

A sewage pipe with 2400mm diameter (RCP V pipe) is localized under the central span of

the existing bridge.

Existing sewage pipe

The footing of the new pier is realized near the sewage pipe.

A “Π” shaped concrete structure is realized between the pier and sewage pipe. That

structure will serve as a protection for the sewage pipe.



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New pier and existing sewage pipe



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5. DESCRIPTION OF WORKS

Considering the results of the survey activities work will consist in:

1. realization of “Π” shaped concrete structure for protection of sewage pipe;

2. realization of new abutments and piers;

3. realization of new deck adjacent to the existing one (on doubling line);

4. demolition of the existing piers;

5. removal of the existing deck and its demolition;

6. realization of new deck along the existing line.

The above activities will be scheduled in 16 phases.

Phase 1

In this phase is realized the “Π” shaped concrete structure for protection of sewage pipe.

After this is constructed the cofferdam for the new abutment on Riyadh side.

Phase 2

In this phase is realized the new abutment on Riyadh side.

Phase 2 – Part of longitudinal section

Phase 3-4-5

In these phases is realized the new pier.



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Phase 3-4-5- Part of longitudinal section

Phase 6-7-8

In these phases is realized the new abutment on Hofuf side.

Phases 6-7-8- Part of longitudinal section

Phase 9-10-11

In these phases is realized the new deck on doubling line. After phase 11 the rail traffic is

deviated on doubling line.

The new deck consist in a post-tensioned concrete box girder, with a constant height of

3.00 m.



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New girder section.

Phases 9-10-11-Plan and longitudinal section

Structural pot bearings are provided on piers and abutments. For each span longitudinally

fixed restraint on one end and free restraint on the other end are provided; each end is

restrained transversally.



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Bearing layout provides:

• free longitudinal restraints on both abutments;

• two pairs of longitudinally fixed restraints on pier;

Bearings layout.

Phase 12-13-14-15

In these phases is demolished the existing deck and realized the new deck on existing line.



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Phases 12-13-14-15-Plan and longitudinal section

Phase 12 involves the demolition of the existing deck. Considering the closeness of the

train traffic on new deck the demolition plan has been studied with the aims of avoid

dangerous situations and reduce annoyance to the train circulation.

The demolition of the existing bridge involves the following sub-phases:

1. removal of rails, ballast and sand;



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2. removal of parapets;

3. demolition of the external cantilever;

4. demotion of internal cantilever;

5. lift of residual box girder, deposit at ground level and demolition.



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Phase 16 In this phase is completed the rail line on existing line, is realized the definitive road in

front of new abutment on Hofuf side and rail traffic is deviated on both lines.

Phass 16-Plan and longitudinal section

For further details regarding to construction phases, refers to the specific drawings.



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6. CONCLUSIONS

The proposed design of the doubling of bridge at km. 426+617 has been carried out with

two targets:

• realize a new bridge adjacent to the existing one;

• ensure the structure’s safety under 32.5 ton/axis loads for both bridges.

Considering the increase of train loads and results of the laboratory tests on concrete

specimens, the existing structure was deemed not safe under new design loads and so it

was decided to realize a new bridge with two spans: 28.45 m and 34.45m: this solution

leads to an adequate safety level of the structure under new design loads.

In order to ensure safety conditions for the train traffic even during the works on the

bridge, the demolition of the existing bridge has been carefully planned, providing partial

demolition of the girder and then its removal and final demolition at ground level.

Also all phases of construction have been thought in order to minimize traffic

inconvenience.

FE001P DD ST 001 Technical Report

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