REHABILITATON OF LABUGAMA WATER

TREATMENT PLANT PROJECT

Contract No. P&P/WS/HUN/LABUGAMA/2010/01

BAILEY BRIDGE

PROGRESS REPORT AND

RISK ASSESMENT

7TH

JANUARY 2014

09.00 AM

ACCESS ENGINEERING PLC

COMPILED BY : H.T. SHAMEERA WIJESOORIYA

Table of Contents

1. Introduction ....................................................................................................................................... 4

2. Construction Progress ....................................................................................................................... 5

1. Mobilization ....................................................................................................................................... 5

1) DCC Site Office & Stores .......................................................................................................... 5

2) Access Stairway ........................................................................................................................ 6

2. Site Clearing and Excavation.............................................................................................................. 7

3. Problems Identified ........................................................................................................................... 9

1. Excavation .......................................................................................................................................... 9

1) Excavation Width ..................................................................................................................... 9

2) Bedrock Not Being Reached .................................................................................................... 9

3) Disposal of Excavated Materials ............................................................................................ 10

4) Excavation of the Sides of the Abutments ............................................................................. 11

2. Health and Safety ............................................................................................................................ 12

1) Vehicles Passing Over the Bridge ........................................................................................... 12

2) Landslides .............................................................................................................................. 12

3) Temporary Access Collapsing ................................................................................................ 12

4) Access Stairway ...................................................................................................................... 12

5) Unsafe Crossing across the Stream ....................................................................................... 13

3. Design .............................................................................................................................................. 14

1) Insufficient Rock Width in Abutment B ................................................................................. 14

2) Presence of Joints in the Bedrock .......................................................................................... 14

4. Miscellaneous .................................................................................................................................. 15

1) Water Pipe ............................................................................................................................. 15

4. Project Plan Comparison ................................................................................................................. 16

5. Recommendations ........................................................................................................................... 17

Table of Figures

Figure 2.1 - DCC Site Stores (left) and Office (right) ..................................................................................... 5

Figure 2.2 - DCC Site office ............................................................................................................................ 5

Figure 2.3 - Access Stairway .......................................................................................................................... 6

Figure 2.4 - Ground level of Abutment A ...................................................................................................... 7

Figure 2.5 - Excavation works of Abutment A ............................................................................................... 8

Figure 3.1 - Disposal of excavated .............................................................................................................. 10

Figure 3.2 - West face of Abutment A ........................................................................................................ 11

Figure 3.3 - Abutment B .............................................................................................................................. 13

Figure 3.4 - Southern face of Abutment B .................................................................................................. 14

1. Introduction

The existing Bailey bridge which is situated along the road to the Labugama Water Treatment Plant is

proposed to be upgraded. The Labugama Water Treatment Plant is over hundred years old. The Bailey

bridge has served as an essential access point into the site. Because of the time duration the bridge has

functioned, it has deteriorated over time. Even though it is still robust enough to carry light vehicles, it

cannot be guaranteed that it will be resilient enough to support heavy vehicles carrying loads.

The Bailey bridge is the only land route in and out of the Labugama site, therefore its importance is

elevated. Because of the scope of the construction to be conducted, the risk of the Bailey bridge failing

is too high to operate with the status quo.

As the Sub Contractor performing the civil works on the Labugama Site, Access Engineering has come

into an agreement with DCC to perform the construction of the proposed bridge. This report will

highlight the current progress, problems and concerns that Access Engineering has identified.

2. Construction Progress

1. Mobilization

1) DCC Site Office & Stores

Mobilization has begun in the construction site with some progress to show. Figure 2.1 and Figure 2.2

shows the completed DCC stores and site office. The storage area is located to the left hand side

partition and the site office to the right. It is adequate to perform the activities related to construction.

Security of the equipment and materials would become an issue in the near future, therefore it is

advisable to have a security officer present when the premise is unattended.

Figure 2.1 - DCC Site Stores (left) and Office (right)

Figure 2.2 - DCC Site office

2) Access Stairway

As seen in Figure 2.3, the construction of the access stairway is completed. The materials utilized mainly

consist of galvanized iron pipes and clamps. It is fixed to the ground at the top and bottom as well as

obtaining lateral and vertical support from the existing temporary access bridge and stone dressing.

Figure 2.3 - Access Stairway

2. Site Clearing and Excavation

The Site Clearing works of both abutments has been completed. The extent of clearing is seen to be

sufficient. Soil and vegetation has been removed while some rock features are still present because of

the difficulty in removing them. The site level condition of abutment A can be identified form Figure 2.4.

Figure 2.4 - Ground level of Abutment A

Excavation works is still on-going. Excavation of the soil is only required in Abutment A as Abutment B is

located on a rock surface. The dimensions of excavation are approximated as follows:

Depth : 1.0 m Width : 1.8 m Length : 4.2 m

With the above approximation we can assume a total excavation of 7.5 m3. The bedrock on abutment A

has still not been reached. The excavation level is no coinciding with the level of the abutment

foundation.

Figure 2.5 - Excavation works of Abutment A

3. Problems Identified

This chapter will report any. It is important to note that that the issues identified is not confined to just

one party in this agreement but. Cooperation is required to build a quality end product while upholding

the ISO & OHSAS standards.

1. Excavation

1) Excavation Width

The current width of excavation is approximated to be 1.8 m. The dimensions for the jacket wall can be

obtained from the drawing provided (DRG. NO. LKWIP/L/A/Q-04). The horizontal width of the jacket wall

segments are as follows:

Min. jacket wall width : 500 mm

Base (horizontal) : 750 mm

Base (inclined) (approx.) : 1500 mm

Taking the above factors into consideration it is seen that a minimum width of 2250 mm must be

excavated. Taking the irregular texture of the stone abutment wall and allowances made to install

formwork and formwork supports it is advisable to further increase the excavation width.

2) Bedrock Not Being Reached

Excavation has been completed to an approximate depth of 1 m as mentioned above at Abutment A.

The excavated depth is in line with the foundation of the existing stone abutment dressing. It is unclear

how much additional excavation is required to reach the bedrock.

3) Disposal of Excavated Materials

Currently all the excavated materials are being disposed in the area under the temporary access bridge

which was constructed by Access Engineering as seen in Figure 3.1. The main issues with this

methodology is there being a risk of the scaffolding being damaged soil eroding into the waterway. As of

now a very basic method of preventing soil erosion is present. Several boulders have been placed along

the ridge. But because of the loose nature of the excavated soil this method is unsatisfactory to

maintain our guaranteed environmental standards.

Figure 3.1 - Disposal of excavated

4) Excavation of the Sides of the Abutments

Excavation of the sides of the abutments can be identified as a one of the more difficult stages of the

excavation process. As seen in Figure 3.2 numerous problems are present when excavating. The total

excavation length from the edge of the abutment wall is 1300 mm (ref. LAB-CW-BB-0105-B1). It is

evident that safety is a critical issue when excavating these areas. The western face of Abutment A has

large boulders which are held by loose soil. There is a very large risk for the soil to collapse during the

construction period. The eastern face of Abutment B is in close proximity to the stream and is also

covered by very loose soil. There is a very high risk for landslides to occur especially when the conditions

are wet.

Figure 3.2 - West face of Abutment A

2. Health and Safety

1) Vehicles Passing Over the Bridge

The existing Bailey bridge is in a very run down condition. Because of this, it has been noted by the

workers that debris is falling down from the deck area when vehicles are passing over it. This poses a

serious health risk to the workers as there is a possibility of the debris falling into the eyes of the

workers. It is also a general nuisance and creates an unpleasant working environment.

2) Landslides

The site is situated on an inclined terrain. As of now no measures have been taken to minimize the

possibility of a landslide from occurring. This could either affect the workers working in the vicinity or

pollute the stream below.

3) Temporary Access Collapsing

As seen in Figure 2.3 the excavation works have been conducted adjacent to the temporary access

bridge. Because of this there is a major possibility that the soil will erode and expose the foundations of

the temporary access bridge. If the scaffolding is not supported sufficiently, the risk of the temporary

access bridge failing will become critical.

4) Access Stairway

Even though the access bridge has been constructed, it is evident that it was a makeshift task. The steps

have been made by locking two G.I. pipes together using clamps. There is a concern that this will be

unsuitable for use when the environment is wet or when transporting goods down to the bottom of the

abutments.

5) Unsafe Crossing across the Stream

As seen in Figure 3.3 there is no proper way of crossing the stream. Workers are compared to hurdle

over the stream and climb up from the other side. This is acceptable at the present workload associated

with the construction, but it will be very difficult to employ the same strategy when items such as

reinforcement, formwork, tools etc. need to be transported across the stream.

Figure 3.3 - Abutment B

3. Design

1) Insufficient Rock Width in Abutment B

The width of the jacket wall base without the inclined portion amounts to 1250 mm. According to the

design, if the inclined portion is included the total width required will come up to 2250 mm. It is not

practical to carry out construction as detailed in the design as the distance of the rock from the

abutment wall is approximately 500 mm.

2) Presence of Joints in the Bedrock

As seen in Figure 3.4 it is obvious that the rock has undergone weathering over time. Therefore it is

questionable as to how stable this portion of the bedrock is. As seen in the segment of rock to the left in

Figure 3.4, it has already started to fragment. Because of the presence of a stream nearby it has

accelerated the weathering process. If the construction proceeds according to the submitted drawings,

there is a risk of the joints slipping in the rock and the bridge failing.

Figure 3.4 - Southern face of Abutment B

4. Miscellaneous

1) Water Pipe

As seen in Figure 3.4 there is a poorly built PVC water pipe along in the vicinity of Abutment B. The

owner of the pipe has granted permission to handle it in a way that construction will not be an

obstruction to construction and to inform him if it is eventually damaged. The probability of it being

damaged is very high especially when moving reinforcement and formwork. If the pipe is damaged at a

critical stage such as concreting, it would pose a severe risk to the quality of the construction. Moreover

additional time will have to be invested in order to repair the pipe to resume construction. As of now

the pipe has been elevated with a rope which hangs from the existing bridge truss with the aid of the

scaffolding and has been slightly shifted away from the working area. This might not be a sustainable

solution as the construction intensity increases and also when the bridge truss is under deconstruction.

4. Project Plan Comparison

According to the project plan which was submitted by the DCC the 30th December 2013, the

construction progress should have come to the stage where the total excavation works are completed

and the setting out for the bases should commence. It is not practical to commence the setting out

works as excavation has not been completed. Abutment B has been cleared and is ready for setting out.

But however, Abutment A is no position to begin the setting out process for the bases.

There is still a significant proportion of excavation to be conducted and it can be estimated that an

additional minimum of 2 days will be required at the current rate of progress.

Total duration : 57 days

Total working days : 08 days

Actual work completed : 05 days

Delay : 03 days

Project Completion (Time) : 14%

Work Completed : 09%

(As a % of planned duration)

5. Recommendations

1. Increase the excavation width to 2500 mm for the specified area which will undergo construction.

2. Construct a barrier using the excavated boulders around the excavated material dumping location to

minimise soil erosion.

3. Install a temporary sheet piles or another mean of soil collapsing to the side of the abutments

especially in Abutment A.

4. Install speed bump on either side of the bridge and install a sign mentioning that work is on-going

below the bridge.

5. Safeguard the foundations of the temporary access bridge.

6. Install a robust bridge across the stream which will be safe enough for the workers to transport

materials across the stream.

7. Coordinate with the design office in order to converge to a more site specific solution.

8. Revaluate whether the strength of the bedrock is acceptable.

9. Conduct meetings to discuss possible solutions for the issues where resolutions have not been

identified.