Dewatering Method Statement

Below is a complete and precise dewatering method statement that covers the installation of the dewatering system as designed and detailed by temporary works designer/ consultant.

Full time supervision shall be required to ensure the works are carried out in accordance to specifications, quality and approved drawings.

Pumping Duration: Pumps shall be kept running to maintain the water level in the work area to at least 250mm below the exposed ground level at all times.

Standby Pumps: Standby pumps shall be kept available on site in case any of the pumps fail.

Note: Quantity of manpower, materials and equipment’s shall be submitted on the daily progress report.

Necessary plant, tools and equipment shall be arranged as below:

  • Piling rig to auger in casings
  • 360 Excavator
  • 18 m³ Tippers
  • 6 inch Submersible Pumps, suction hoses and dewatering lay flat hoses
  • Drum Roller
  • Compacting Plates
  • Dewatering Settlement tank

List of Materials

  • Scaffolding
  • Formwork
  • Concrete
  • Steel Reinforcement

Roles & Responsibilities

Project Manager

Ensure the design is completed by Temporary Works designer, submitted and approved by project management and approved.

Make sure the the works are carried out according to the specifications and approved shop drawings.

Coordinate with the site managers for the provision of all the necessary information to be distributed among the construction team.

Ensure all the plant and equipment is available to progress the dewatering works.

Co-ordinate with safety officer to ensure that the works are carried out in a safe working practice.

Ensure full compliance of the works with the related quality procedure.

Site Manager

Ensure the works are carried out according to the specification and approved shop drawings.

Coordinate with the project manager the agreed sequence of works with respect to the construction program.

Make sure the proper distribution of the work force for the site teams.

Coordinate with the safety officer for ensuring safe working practices are implemented.

Ensure all necessary plant and equipment is available on site and ready to progress the works.

Safety Officer

Inspection of the access routes to the areas of work.

Ensure the areas of work are sectioned off to prevent unnecessary access.

To Provide / monitor a safe access and egress to the areas of work.

Ensure all operatives wearing full personal protective equipment i.e. PPE.

Ensure all Safety Signs are in place.

Ensure plant operators have a current certificate of competency.

Site Surveyor

To establish bench marks from agreed reference point.

Provide required setting out and level markings.

Coordinate with site manager for the sequence of work.

Site Engineer/ Forman

To coordinate with site manager for the distribution of the work force, plant and equipment on a daily basis.

Co-ordinate with the safety officer ensuring safe working practices is implemented.

To coordinate with the site manager if additional plant, equipment and operatives are required.

To ensure proper daily records are taken of the progress of works.

Sequence of Work for Dewatering Method Statement

Prior to commencement of the dewatering activities, the site surveyor will establish both vertical and horizontal control points using setting out stations.

Set out and excavate the site from the present level of  +2.3m down to +0.5m with the excavated materials taken off site using 18m3 tippers to be stock piled for future use as agreed / approved by the client.

Access will be clearly maintained across the site for both vehicles and pedestrians such that other areas of work are not affected.Cable Trench Dewatering Well Point System Method of Statement

When the +0.5m level is established, each end of the proposed filter drain will be set out and the correct fall established from one end to the other using profile boards.

Excavation for the filter drains will be commenced from the sump i.e. lowest end towards the highest end.

Side slopes shall be battered or stepped at 1V:2H for safety down to the bottom of the trench as per drawing and one 6 inch pump will discharge the water from the sump into the disposal area via a settlement tank.

The filter drain at the bottom of the trench will then be constructed 1.5m deep by 1.5m wide and filled with 2” to 4” natural gravel wrapped in a geotextile terram material.

Geotextile will be folded over at the top of the stone to prevent the filtration of fines and then the trench will be backfilled up to the existing ground level.

Where the permanent sumps cannot be installed, then temporary sumps will be placed at the lowest point where the excavation is commenced to ensure the water always runs away from the point of excavation and one 6 inch pump will discharge the water into the disposal area via a settlement tank.

If required, additional temporary sumps may have been installed at locations to help draw down the ground water.

The filter drains will be installed as shown on in the following sequence to match the excavation sequence from:

Permanent dewatering pumps will be located at sumps 1 and 2 and each shall contain one 6 inch pump with suction hose into the sump and flexible ‘lay flat’ hose discharging back into the creek via a settlement tank. Sumps will be constructed as per the site requirements.

Checks shall be carried out each week by visually inspecting the settlement tanks to monitor how much fines are being removed from the drain.

On completion of the works tidy the areas and compact ready for the main construction works.

HEALTHY, SAFETY AND ENVIRONMENTAL

During the excavation, ensure the area of work is protected by a demarcation barrier therefore isolating from all un-authorized personnel.

Side slopes must be checked to be cut to 1V:2H due to the nature of the soil.

All plant and equipment will be inspected by the site Safety Officer, Ensuring all the test certificates are provided and valid.

Ensure drip trays are placed under all static plant e.g. generators and pumps.

Make sure that the 6 inch pump discharges into a settlement tank and that the fines within the settlement tank are monitored and removed when necessary.

Ensure all operatives and Site management have full P.P.E available.

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