Excavation Work Guidelines for Irrigation and Water Supply Projects

This excavation method statement serves as a guideline for the excavation works undertaken during the construction project.

The process will include methods to carry out the excavation and surface preparation, in compliance with the applicable environmental and safety measures.

Construction manager is responsible in ensuring the implementation of construction procedure and method statement, supervising the work and reporting the progress of work to the planning engineer.

QA / QC engineer is responsible in monitoring the execution and performance of the works in relation to this method of statement, approved drawings and technical specifications.

Site engineer is responsible for organizing all the works on site in a safe manner, ensuring it is in accordance with the schedule and the construction drawing. He must also assure the method statement procedure is followed and must notify the consultant for inspection.

Safety officer is responsible in ensuring that all activities are carried out safely at site, establishing the site safety plan, conducting continuous safety inspection and stopping any unsafe work.

Workers are responsible to properly wear the protective equipment provided and obey all the safety rules. He must also perform the work as described in the method statement.

The major equipment and machinery used for the excavation works include, but not limited to:

• Bulldozer
• Excavator
• Rock Breaker
• Wheel loader
• Tipper Trucks
• Wagon Drill
• Compressor (2 Jack Hammer)
• Bob Cat or JCB
• Water tank: 01
• Vibratory Steel Roller

Definitions & Abbreviations

Barricade: Any object or structure that creates a barrier obstacle to control, block  passage or force the flow of traffic in the desired direction.

Battering: To form the face, side or wall of an excavation to an angle to prevent earth slippage.

Benching: The horizontal stepping of the face, side or wall of an excavation.

Competent Person: A person who has acquired through training, qualification or experience the knowledge and skills to carry out the task.

Face: An exposed sloping or vertical surface resulting from the excavation of material.

Safe Slope: The steepest slope, at which an excavated face is stable against slips and slides, having regard to the qualities of the material in the face, the height of the face, the load above the face and the moisture conditions.

Sheet Piling: Vertical, close spaced or interlocking planks of steel, reinforced concrete or other structural material driven to form a continuous wall ahead of the excavation and supported either by tie backs into solid ground structural members from within the excavation as the work proceeds.

Shoring: The use of timber, steel or other structural material to support an excavation in order to prevent collapse so that construction can proceed.

Health and Safety Requirements

Safety precautions shall be of paramount importance in order to prevent danger to the public and ensure a safe working environment during the entire construction period.

A survey shall be carried out on areas on the site that may require specific Health and Safety attention to moderate and remove any hazards or risks.

The following safety measures shall be implemented on site during the execution works, along with the measures undertaken in the ‘Site Clearance’ and ‘Backfilling’ method statements and the approved project HSE plan:

Personnel and Equipment:

Prevent persons to enter a work area where there is a risk of injury.

Control all activities involving moving plant using nominated banks man.

Ensure that defective or suspect equipment, which has been withdrawn from service, does not get back into service without the inspection and approval of a competent person.

Existing Utilities:

Use cable detector to identify and locate the underground utilities and ensure it is protected.

Where overhead lines cannot be diverted or quarantined, ensure that plant is selected or modified so that it cannot reach the lines.

Protection of Excavated Face:

Considering soil condition and depth of excavation, batter sides of the excavation to a safe slope or provide shoring using steel sheeting, rails or props as directed by the Geotechnical Engineer.

Lower the underground water table if encountered to below the invert of the excavated area and always check the pumps to ensure its workability.

Fall into Excavation:

Establish a barricaded zone, 2m back from the left excavation face, in areas where there is a risk of falling and where the depth of excavation exceeds 2m.

Ensure that all barriers, cones and flagging warning tapes are in place prior to leaving the site.

Excavation by Blasting:

Hire licensed hot firer prior to commencing any blasting works.

Ensure that the use of explosives is limited to competent, licensed personnel who have experience in the work to be undertaken.

Check that all safety measures are being taken else blasting will be prohibited.

Secure all areas affected by blasting by flagmen to avoid any intrusions.

Relocate any vehicles and equipment parked within the blasting zone to safer locations.

Stop any influenced traffic prior to blasting.

Limit the use of blasting in built up areas.

Control ground vibration by limiting the blast size and the use of delays.

Take special care in order to avoid over breaks other than geological ones.

Quality Assurance and Quality Control Requirements

Quality assurance and quality control covers the records formed from site inspections, examinations and tests that serve as documentation of the conformance of site construction and erection to the drawings, specifications and regulations.

Develop Test and Inspection Plan in line with the work to be constructed showing ‘Hold and Inspection’ points.

Refer to the Project Quality Plan for all quality assurance issues.

The following steps shall be followed by the engineer in charge before proceeding with the next activities:

• Fill the inspection check list to ensure that all activates are being performed as per the expected quality.
• The inspection check list shall include the specific requirements, safety and environmental measures.
• Prepare inspection request, as per QA/QC Plan, and submit to the Engineer for approval.
• Follow up on the Engineer’s site inspection and comments, until the IR form is approved.
• Circulate the approved IR form for records keeping, and issue order to proceed with next activities.

Environmental Requirements during Excavation Works

Excavation and surface preparation works shall be carried out in accordance with requirements of the Contractor’s Environmental Management and Monitoring Plan as described in the ‘Site Clearance’ and ‘Backfilling’ method statement.

In addition, the following precautions are essential and must be considered:

• Undertake the suitable procedures to avoid the slit of soil during excavation activities in rainy seasons.
• Take appropriate measures to minimize the effect of oil/diesel spill in case of machine failure.
• Reduce noise from machineries to avoid disturbing the surrounding. Machines shall be turned off when not in use.
• Set up the lighting needed for night works in such a manner that neighboring residents are not disturbed. However, the light should be sufficient for the crew to undertake their works safely.

Excavation Prior Activities

Prepare, check and submit verified construction drawings of excavation areas including setting out, levels and service drawings for the approval of the Engineer.

Upon obtaining all the necessary survey data, carry out a survey to obtain original ground levels and submit for the approval of the Engineer.

Set out the coordinates of excavation using steel rods driven into the ground and indicate on these rods the required depth to be excavated, where the maximum distance between rods is 20 meters.

Prepare access to the working area and plan for the dump truck and plant movement avoiding any close approach to the edge of excavation. Access shall be approved by the Engineer taking into account the site traffic management plan and the storage area for materials.

Carry out a survey with the coordination with the relevant authorities to identify any existing services and use cable detection tools and hand digging measures to clearly mark these services on the ground.

It has been identified that the ground conditions will allow for the excavated faces to stand within a slope of 1/2 without the use of supports, however if this is not the case, obtain more information about ground conditions to determine the appropriate support system such as benching, battering or using steel sheets driven into the ground.

If ingress of water occurs during any time the excavation is open, install adequate dewatering system through suction pumps to dispose water in accordance with the method statement for dewatering excavations.

Excavation Works Procedure

Strip and store topsoil within the working width as indicated in the site clearance method statement.

Carry out the excavation works in accordance with the relevant approved drawings and cross sections, to the widths and slopes shown thereon.

Where the excavation is to be done starting from less than 1.2m from the top, carry out the excavation at two stages to achieve the required slopes.

Recheck the excavated elevations and locations at the end of stage one to ensure that the face of excavation is finished to the required slope.

Carry out excavation works using a bulldozer with ripper and / or a 360° excavator assisted at all times by a competent banks man.

As the excavation progresses, use a combination of 360° excavator fitted with a hydraulic breaker and a JCB or excavator with a small bucket attachment, to excavate the side ditch of dimensions in accordance to the drawings and a distance from the wall, to prevent the flow of water into the excavation or behind the wall during the construction period.

It is the intention to excavate rocky areas by mechanical methods, however should the occasion arise, carry out controlled blasting technique.

Execute drilling by hydraulic rock drill with the sides of the excavation to be smoothly blasted in order to form straight lines.

Saw cut all the edges of excavated areas on concrete or bituminous footways and roadways to form trimmed edges and minimize damages.

Stockpile the excavated materials that are justified by the Engineer as suitable backfilling material, at the lower side of the excavation far away from the area.

Transport the surplus of such materials using dump trucks to approved stockpile area for future use, or to a recycling area for crushing and screening into reusable course materials.

Dispose unsuitable excavated materials to spoil areas approved by the Engineer.

Upon completion of excavation, verify set out locations and check the edge slope and the bottom founding level of excavation.

Trench Surface Preparation

Trim the finished surface of formation to the required profiles and levels within the specified design.

If the surface is other than rock, apply water spray and compact using a vibratory roller, immediately prior to placing the 100 mm blinding concrete.

Where instructed by the Engineer, establish a site investigation to identify the properties of the ground on which the structure will be founded and provide details on bearing capacity.

Replace any removed loose soil encountered at formation level, or any excess depth excavated below the formation level, with soil-cement mix or with  approved imported fill material compacted in accordance to specification.

Wash the rocky foundation surface using water or air compressor and clean it from dust, mud, loose or fractured material and other debris, immediately prior to placing the 100mm blinding concrete.

Where rock surfaces reach high temperatures under the influence of the sun, carry out washing at night or in the early morning, to avoid fracturing due to thermal shock.