STATEMENT OF METHODOLOGY FOR CONSTRUCTION OF DRAINAGE SYSTEM

 

TITLE: CONSTRUCTION OF DRAINAGE SYSTEM

1 SCOPE

This method statement deals with surveys and layout, excavation, pipe laying, pipe collaring and backfilling of drainage system in the preparation of drainage box to complete the drainage line.

2 REFERENCE DOCUMENTS

2.1 Project Specification

2.2 Approved Plans

2.3 ITP – Inspection Test Plan

3 WORK PROCEDURE

3.1 Survey and Layout

A. Preparation

• Orientation of Workers or toolbox meeting before start of work.

• Wear complete personal protective equipment always on the jobsite.

• Secure work permit based on the scope of work to be executed.

• Review plans for what and where the activity must be conducted.

• Clear the area and install barricades before execution of the activity.

• Ensure that all submittals are approved and signed.

B. Execution

• Ensure that the request for layout was submitted to survey group a day before the execution of activity.

• Provide work activity permit prior to start the activity.

• Coordinate with the survey team to determine the exact location of the drainage lines prior to excavation.

3.2 Excavation

• Provide work activity permit prior to start the activity.

• Ensure that the area is free from obstructions.

• Make reference line marking for proper elevation of trench to excavate prior to pipe laying.

• Trenches for drainage pipes may be excavated as soon as the subgrade is already prepared provided that there is sufficient cover over the pipes that will protect the pipes from crushing during rolling compaction activity. Otherwise, trenching shall be made only after sub-base is prepared and before laying off the base course.

• The trench shall be excavated to the required depth, given by the survey or line grade shown on the plan. The bottom of the trench shall be shaped to conform to the shape of pipe for at least ten percent of its outer diameter. The width of the trench shall not be greater than necessary to permit satisfactory jointing and thorough tamping of bedding material under and around pipe.

• Where rock and hard layer ae encountered, the rock shall be excavated to a minimum over depth rock excavation and all excess trench excavation shall be backfilled and thoroughly tamped with loose moist earth or gravel without big stones. This selected backfill shall be graded and prepared to provide a firm and uniform bearing throughout the entire length of the pipe.

Inspection

• Provide survey report.

Request for inspection shall be submitted (to inspect the depth and alignment of drainage) to operations and QA/QC in advance as per approved Project Specification and plan. 

Any comment or minor changes has to be fulfilled and re-inspection must be carried out to satisfy the design and the Consultant’s requirements.

3.3. Pipe Laying

A. Preparation

• Orientation of workers or toolbox meeting before start of work.

• Wear complete personal protective equipment always on the jobsite.

• Secure work permit based on the scope of work to be executed.

• Review plans for what and where the activity must be conducted.

• Clear the area and install barricades before execution of the activity.

• Ensure that all submittals are approved and signed.

• Check the condition of base where the pipes will be laid.

• Make sure that the pipes (RCP) are in good condition and passed the quality test/Three Edge Test.

• Prepare and make sure the good condition of “lifter” that will be used in laying large diameter pipes.

B. Execution

• Ensure that the area is free from obstructions

• Make reference line marketing for correct elevation needed in drainage system to avoid backflow and ponding of water.

• Installation of ladder is required for safe ingress and egress of workers works on excavation area.

• In laying of larger pipes, make sure that there are no workers under the excavation area while lifting operation are in progress.

• Pipes shall be layed carefully true to lines and grades shown on the drawings or as directed by the engineer with the groove update. The pipe section shall be layed and filled to form a smooth and uniform invert when completed. All joints shall be filled with mortar composed of one part portland cement and three parts of cleaned graded sand passing #8 sieve with enough water added to obtain proper consistency.

• A shallow excavation is made underneath the pipe of the groove end and is filled with mortar. The tongue and groove ends of the pipe also should be well cleaned and thoroughly soaked with water just before the joiint is made. Cement mortar is then applied to the lower portion of the groove end of the pipe being laid. The tongue end is then inserted to the groove end of the first pipe until mortar is squeezed out on the interior and exterior surface of the pipe is then cleaned of all extruding mortar and the remaining annular space is filled with mortar. Sufficient additional mortar shall be used to form a band round the outside of the joint.

• Water shall be kept out of the trench until the joint has set. Any pipe that has grade or joint disturbed after laying shall be out and relaid.

• Pipes and accessories shall be handled as such manner as to ensure placement in the trench in sound undamaged condition. Cutting shall be done only when necessary in neat and workmanlike manner without damaging the pipe. The contractor shall be responsible for and shall take all necesssary precaution to protect and preserve all existing surface and sub-surface structures. He shall provide permanent repairs for any structures damaged thru his negligence.

3.4 Pipe Collaring

• Make sure the proper ratio of 1:2.5 for cement and sand with water-cement ratio of 0.4 is followed.

• Follow the proper thickness of cement mortar base on the plan.

• The presence of the site QA/QC engineer is needed for adjustment of the mixture of the concrete if necessary.

3.5 Backfilling and Compaction

• Ensure that the area is free from obstructions.

• Ensure that there are no materials and workers on the excavated area before backfilling.

• Make reference line and markings for correct elevation needed for drainage system to avoid backflow and ponding of water.

• Compaction must be nade every 250mm layer of backfill of water by water compaction and use of walk-behind compactor.

• After the compaction, the area must undergo inn FDT to satisfy the specification of the project.

3.6 Construction of Drainage Manholes

• Ensure that all the area are free from all obstructions.

• Make reference line and markings for correct elevation and station of manholes.

• Trim to meet he proper dimensions of mahole flooring then pour with lean concrete / gravel bedding.

• Bend, fabricate and install rebars of manhole when pour with concrete for flooring.

• Proceed to formworks for walls, pour with concrete that meet the required design.

• Provide ladder rung to the manhole to the required depth and also the lot connections.

• Install CHB and plaster for finishing.

• Installation of scaffolding and and p;atform is required in construction of manholes 3 meters and above in height.

• Install the surface cover.

3.7 Flow Test

3.7.1 Materials

1. Floating device – Ping-pong/Styro Ball

3.7.2 Procedures

a. Prior to testing, inspect the drainage lines to be tested for possible clogged materials that may affect the flow test.

b. Manholes should be free from scrap materials and properly cleaned and should be supplied by sufficient ventilation.

c. Adequate source of clean water for continuous flushing shall be provided. Floating device or materials shall be used to determine the continuity and slope of the pipe line from one manhole to connecting manhole.

d. Choose the starting point/manhole and continuously pour water by using water truck to supply water.

e. The group shall move to the ending connection to verify if the floater reached its end point. If the ball is not seen on the endpoint, check the pipe for possible clogged pipes. Repeat the test otherwise.

f. After completing the above steps, record data on the report form.

g. After the testing, clean and organize the test area.

4 MAJOR PLANT AND EQUIPMENT

4.1 Backhoe

4.2 Concrete vibrator

4.3 Skidloader

4.4 Mixing Board

4.5 One Bagger

4.6 Water truck

5 QUALITY ASSURANCE/CONTROL

7.1 Tests

Refer to Project-WP-ITP–Inspection and Test Plan/Construction Specifications.

7.2 Measuring and Testing Equipment to be Calibrated

Survey Equipment

FDT Equipment (Sand cone/Nuclear Density Gauge)

7.3 Inspections

Refer to WP-ITP – Inspection Plans

Refer to WP-Forms – Inspection Checklists and Forms

7.4 Parties and Products Requiring Accreditation or Certification

N/A