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Excavation is an essential part of the construction process, particularly in relation to the construction of foundations and drainage work. In carrying out an excavation the soil conditions can vary widely, often within short distances. No soil whatever its nature can be relied upon to support its own weight for any length of time, let alone any additional loads which may be imposed by plant and material. It should never be forgotten that 1m3 of earth weighs approximately 1.3 tonnes. Therefore, unless the excavation can be terraced or battered to a safe angle (angle of repose), the sides must be supported to prevent the possibility of collapse and thus:
Provide a safe place of work for people in the excavation or near it;
Enable the work to be carried out without interruption;
Protect adjacent property and/or public services.
The Construction (Design and Management) Regulations 2015 require steps to be taken to prevent injury to persons due to the accidental collapse of an excavation or by fall of materials. Any excavation used as a place of work must be inspected before any work at the start of the shift and after any event likely to have affected the stability. A report of inspections should be made in the CDM Register HSF 804 at least every seven days or when conditions have altered.
The Project Management team is responsible for implementation of this procedure. The Operations Director is responsible for monitoring compliance with this procedure.
This is probably the safest method and almost all soils can be excavated to provide a safe batter if sufficient space is available and a safe angle of repose is known and adhered to. Where waterlogged ground is involved specialist advice should be sought. CIRIA report 97 on trenching can be used to identify angles of repose for different ground conditions. Where good conditions allow steps to be cut into the side of the excavations, there must be a step of 1m wide for every 1m of depth. So, a 3m deep excavation would have 2no 1m wide steps on both sides from the bottom of the excavation to ground level. This would create a 5m wide excavation at ground level.
Standard and designed solutions
Standard solutions should only be used in the following circumstances: double sided, narrow trench support, not exceeding 6 metres deep in non-water bearing ground or shallow pits not exceeding 6 metres deep. Designed solutions are required for any support system that does not come within the criteria described above; a competent person must carry out designed solutions.
Temporary works procedure AP 25 must be following for any excavation works, including standard solutions.
Care needs to be taken using the figures in the above table, as soils in their natural state are often a combination of those listed.
Safe means of access to and egress from an excavation must be provided, consideration must always be given to means of escape in an emergency e.g. ladders or steps. Access should only take place once adequate support is in place. Steps or shallow gradient ramps can be excavated, or proprietary steps installed to allow safe access.
Rigid barriers and toe boards must be provided where a person is liable to fall and be injured. However, if this is not achievable, then Netlon fencing can be used provided that it is place at least 1.5m back from any open edge (the minimum distance at which the Netlon fencing is effective), and it is regularly maintained. Non-penetrating pins or wooden pegs must be used to erect fencing. For shallow services or private drainage upto 1.5m deep half-height Hera panels can be used to secure the excavation. For excavations deeper than 1.5m full height Heras panels must be used. Barriers may be temporarily removed to allow access to persons, or for the movement of plant, equipment or materials. Where barriers are set back, all access to the excavation must be restricted to defined access routes.
Barriers or stop blocks are required to prevent vehicles and plant from moving too close to an excavation and endangering its stability. Suitable signage to warn of the danger must always be posted.
Manholes and road gullies must be protected immediately after construction to ensure they are safe and prevent falls. Steel manhole plate to be placed as soon as manhole cover slab is installed as this will allow vehicles to safely travel over the manhole without dislodging the cover. Manhole covers secured from accidental movement by haunching with concrete or mortar to be installed once brickwork/raising sections have been installed. Covering with ply/pallets or any other material is not acceptable and will be penalised heavily on future H&S inspection reports. Again, where not possible the manhole must be fenced off securely. All road gullies must have the grate installed immediately after installation. This applies even when the gulley has been filled with shingle (as per company procedures). Haunch the grate to protect from accidental movement.
Spoil heaps must be managed so as to prevent risk of heap collapse. Heaps when being moved or mucked away must be left with no sections undermined, tunnelled or bored, which could allow a section of the heap to collapse. Heaps must be kept at least 2m away from any designated pedestrian or traffic route. The entire perimeter of the heap must be graded to a safe angle, suitable for the material, which will prevent collapse or slippage. Heaps need to be sealed to prevent wet weather saturating the material.
Dumpers are prohibited from accessing a spoil heap. Any site where there will be a very large spoil heap must contact the H&S department for advice.
Excavators competing works on spoil heaps must ensure they create a level and compacted area for the excavator to work. This would include muck away operations so lorries can be safely loaded without the risk of the excavator overturning.
Excavations must be kept free from toxic or explosive gases, natural gases (methane, sulphur dioxide and hydrogen sulphide) and carbon monoxide emitted from exhaust fumes. Excavations can be a confined space, if there is any risk of a build-up of ‘gases’ in the excavation gas monitoring must be carried out by a trained and competent person who has had training in the use of a gas monitoring unit. It is essential that the gas monitor is treated with respect and calibrated at regular intervals as specified by the manufacturers. A calibration certificate and sticker confirming that it is within calibration period will be supplied.
Coinford’s H&S Management system on detecting and working around live services is written in line with industry best practice and HSE’s guidance HSG47: Avoiding danger from underground services. Our policy covers the four key areas.
Identifying and managing the dangers
Planning the work
Detecting, identifying and marking the underground services
Safe digging practices.
During our groundwork operations, we will encounter underground services the frequency of which is dictated by the site-specific conditions. It is common practice that clients and /or principal contractors terminate existing incoming services into a project at the site boundary, reducing the likelihood of having to excavate around a hazard. However, where this is not the case or when our works include 278 streetworks on public roads, new drainage connections or new road junctions to be constructed, etc. this may result in working around live existing services. All of our site supervisors are trained to identify where this is a risk and ensure controls are implemented and our procedures followed.
Before excavation commences our site management will check existing plans for details of services shown within the area relevant to our proposed works. These should be provided to Coinford by our client – the Main Contractor/Developer. If these plans have not been made available then Coinford need to request the information from the client, prior to commencement of excavations.
Any existing service drawings need to be interpreted carefully as the information may not be accurate. Problems relating to service plan drawings include:
Out of date information
Inaccurate positioning of marked services
Lack of detail – missing connections, pot ends, dead cables not shown.
Once existing service drawings have been obtained for the site, these would be used for all subsequent excavations within the relevant areas covered. Unless changes had been made to on site services during the contract, or other areas / phases are commenced for which information has not been obtained, we would not normally be provided with any further information by our client for subsequent or further excavations within these areas.
The area around the excavation needs to be inspected to look for signs of existing services, with the information provided by the service plans being taken into account. Signs to look out for are:
Manhole/stop valve chamber covers
Existing markings on surface showing service locations
Trench scares across tarmac, or a change of soil type
Pillar boxes or services coming out of the ground i.e. telegraph poles, streetlight etc.
Once the area has been visually surveyed and the service plans reviewed then the next step is to locate the services.
Coinford utilise the latest model CAT and Genny from C-Scope to improve detection and marking of the underground services. Our CAT detectors have the following advanced features.
Digital detection to avoid interference and calibration drift
Depth reading to identify service depth when used with a signal generator
Data logging- To record how the operator is using the CAT detector
Daily self- Test to ensure the CAT is working within its parameters.
All operatives using the CAT and Genny are trained and competent on how to correctly use the equipment and ensure all the modes are fully understood. Within this training, the operatives are taught the importance of clearly marking their findings by means of spray paint, to enable a clear visual marker of the presence of the underground service to others.
At this stage and before any hand or mechanical excavation commences a ‘Permit to break ground’ must be completed. This is completed by our site manager with the supervisor present who will be completing and supervising the works. If the Permit to break ground identifies that there is a buried service within 2m and we have ‘as built’ records of the exact laid location, then the engineer must plot and spray paint the ground the exact location. All of the above is checked through during the completion of the permit. The permit is then communicated to the operatives completing the task to ensure all parties understand the procedure and any remaining hazards.
Once the permit to break ground is issued the operatives will then begin to excavate the area. Our policy and industry best practice dictates that ‘there must be no mechanical excavation within 500mm of the service’. The operatives will hand dig a trial hole to confirm to location of the service, as detected by the CAT. Firstly, this confirms the information was correct, but also allows the operatives to check this is the only service detected, and that there is not another service below, to the side or above the detected service. If the existing service is believed to be a live electric main, then insulated hand tools MUST be used.
Throughout the trial hole excavation, it is important to repeat the use of the CAT detector to check if additional, deeper services are now detectable.
Where a service is exposed or additional unknown services are discovered, it is important to contact the utility providers to enable them to visit site and assist in identifying the service, and also check the status of the service i.e. live or redundant.
Many items of ground support equipment and drainage / pipework materials are beyond the lifting capabilities of workers. The use of mechanical plant reduces the risk of injury from manual handling, but lifting plant can create other hazards.
To ensure the lifting operations are managed the following steps must be taken;
Select suitable lifting plant, taking account of ground conditions and the load/radius anticipated;
Position the lifting equipment to avoid imposing undue additional loads on the ground immediately adjacent to the excavation;
Ensure that the weight of the items to be lifted is known;
Only attach lifting accessories to recognised lifting hooks not on the bucket teeth;
Lifting accessories such as chains, slings, shackles, nylon strops, are all subject to a weekly visual inspection, recorded in the LOLER Register HSF 801, and a six monthly thorough examination.
When excavators are used for lifting, refer to AP 21 Lifting Operations and Equipment
A high level of hygiene is required with all site work to ensure the heath of workers on site, excavation work can expose workers to micro-organisms such as Leptospirosis (Weil’s disease) and sewage related micro-organisms. If these hazards are identified it is essential that information should be provided to the workers and followed, this information may take the form of COSHH Assessments.
If there is a risk of exposure to potential forms of diseases and contaminated ground additional welfare facilities must be provided to ensure that PPE can be changed out of to eat meals .and proper washing facilities to wash arms up to the elbows, showers may also have to be provided. If in doubt please contact your H&S advisor.
The information on site hazards will be contained in the Health and Safety Information Pack and adequate facilities must be allowed for in the preliminaries for site set up.
Excavations that need to be supported or battered back to prevent danger must be inspected. The person in control of the excavation must arrange for a competent person to carry out these inspections:
At the start of the shift before work begins, after any event likely to affect stability and after accidental fall of rock, earth or other material. This also includes inclement weather heavy rainfall, freezing temperatures and snow.
A written report of the inspection is required prior to entry and recorded at a minimum of every 7 days, unless there has been a collapse/fall of material or other event likely to affect stability. In this case an inspection and report is required before work starts again. Refer to HSF 804
All plant and equipment must be inspected every 7 days and recorded in the PUWER Register HSF 310.
All plant (Excavator, Dumper, Roller, ADT, Dozer, Telehandler) operators will be required to complete a daily Pre-use checklist. This must be completed every day prior to putting the plant to work. Any faults identified during this inspection must be communicated immediately to the site manager who will arrange for the faults to be rectified.
All Company operatives are to be given briefing on the Method Statement and Risk Assessment and recorded on form HSF 204.
General Construction operatives should have a CSCS card and Plant Drivers a CPCS/NPORS card. For other types of plant training cards/certificates, please check with the safety department to see in they will be recognised by the company. In addition, check to make sure that training certificates are valid for cable avoidance tools and gas detection equipment. All copies of certification are provided for your H&S Records Folder.
See also: AP 18 Confined Space Entry
