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Be On Your Guard

Safety enforcement campaigns are now focusing more on the provision of piling rig guards. Designers need to pay attention as well as well as contractors and site operators, explains Arup geotechnical engineer Alice Berry.

Practical ways for piling contractors to meet the new emphasis on the legal requirements for pile guards on rigs and drilling equipment have been examined in recent issues of Ground Engineering.

The use of guards on piling rigs is covered by the Provision and Use of Work Equipment Regulations 1998 amended 2002 (PUWER).But designers have a responsibility under the Construction (Design and Management) Regulations 2007 (CDM) to allow for guarded rigs to be used, which raises important questions for their work too.

The Health & Safety Executive (HSE) is clear that condoning the removal of guards from a rig could be treated as wilful negligence, and has indicated that in cases where rigs are found to be working without guards then one of the points of investigation will be whether the designer has breached the CDM regulations.

What does this mean for the responsible, and legally compliant, designer?

One of the requirements for the designer is to avoid foreseeable risks “so far as is reasonably practicable, taking due account of other relevant design considerations”.

The requirement in the CDM Approved Code of Practice acknowledges that during design many factors must be taken into account and that “health and safety considerations have to be weighed alongside other considerations, including cost, fitness for purpose, aesthetics, buildability, maintainability and environmental impact.”

Meanwhile, the PUWER regulations require the rotating parts of piling rigs to be guarded “where practicable”.

The absence of the word “reasonably” in front of the word “practicable” in the PUWER regulations adds stringency and means that if it is possible to guard a rig then guards should be fitted and used.

Pile rig guards tend to restrict how close a piling rig can get to an above-ground obstruction, such as a wall.

The interpretation of these words means that no other considerations, such as cost, are to be taken into account.

The use of “practicable” in the PUWER regulations is stronger than the “reasonably practicable” of the CDM regulations.

This means that the designer’s obligations under the CDM regulations change to mean that their designs must be constructible using an appropriately guarded rig.

“Where practicable” means that arguments against using a guarded rig on grounds of cost, complexity of construction or value to the client are not allowed.

Pile rig guards tend to restrict how close a piling rig can get to an above-ground obstruction, such as a wall.

Figure 1 illustrates an example where there is a requirement to construct a dry basement as close as possible to a building.

An inexperienced architect might expect to be able to use basement space right up to a 300mm thickness of a reinforced concrete wall from the existing building or property line.

In reality, space needs to be left for a guidewall, for a suitable offset from the existing building to accommodate the pile rig head and guards, space for sufficiently stiff retaining wall piles, and space for a drained cavity or similar to provide a dry basement environment.

The loss of basement space due to an increase in the required piling offset can have significant consequences.

Calculations for a typical London project on a medium-sized site show that a 200mm increase in the piling offset around the entire perimeter could result in a loss of capital value of perhaps £400,000 (see table).

However, the impact could actually be even greater.

Gloucester_piling06

There may be cases where the loss of 200mm available space, even along just one wall, could result in an inability to fit in a whole row of car parking spaces which could represent a loss of capital value of approximately £1.25M. In these instances, other types of wall may provide better value to the client.

The size and shape of a pile rig guard may also affect the locations of individual piles.

Difficulties might occur, particularly when working in an internal corner using a piling rig with a guard.

In such cases, when locating the pile the designer needs to take into account, amongst other things, suitable offset distances, space for the rig operator to work, space for the guard to be opened and access for an excavator to scrape away spoil and provide new sections of casing or auger.

Where piles are designed to carry vertical load that comes down from a wall, then the further they are located from the wall, the less direct the load path and thus the more reinforcement is required to transfer the load, resulting in increased cost to the client and increased embedded carbon.

These examples show that for economic design, the use of an appropriately guarded rig means that pile and piled wall positions will require early consideration before it becomes too costly to make changes.

Understanding the offset distances achievable by appropriately guarded piling rigs is key to getting the best out of a safe design.

It is also worth remembering that although the PUWER regulations that require rigs to be guarded are not new, the recent HSE campaign means that achievable pile edge to obstruction offset distances may be in a state of change and could have increased compared to distances previously advised by contractors.

But what if it is just not possible to position the piles so that they can be constructed using a guarded rig?

The aim in this case should always be to change the design and thus eliminate the risk. How can this be achieved?

  • Consider who is taking on the role of the designer under the CDM regulations. Is the architect pushing for a smaller offset distance, the quantity surveyor asking for less reinforcement, or is the client stipulating the number of parking spaces? If so, by constraining the design, they are taking on duties as a designer under the CDM regulations. Explain to them about their resulting responsibility to allow for the use of guarded piling rigs.
  • The CDM regulations place a duty on all involved parties to collaborate and coordinate with each other in order to eliminate and reduce risks. Arrange a meeting with the client, the CDM coordinator, designers, principal contractor and specialist piling contractor as appropriate, to discuss ways to work round the problem.
  • Consider moving the piles to a location where they can be constructed using a guarded rig. Or consider an alternative technique that may allow a closer offset distance, such as diaphragm walling or pressed-in sheet piles. Be aware that alternative techniques may have their own safety implications as well as affecting other things such as cost, environmental impact and programme.
  • As a last resort, there might, in theory, be a situation where using a piling rig is found not to be practicable for any conceivable design. In this theoretical case, then a rig with trip wires fitted in accordance with the stringent requirements of the HSE could be used. However, such a situation has not yet been satisfactorily demonstrated to the HSE, and arguing impracticality of using a guarded rig as a way out of a difficult design or commercial situation is not advocated as an approach that is likely to get a sympathetic response!

There are clear drivers to keep pile offset distances as small as possible, as shown in the examples above.

Designers need to ensure that their clients and architects understand the legislative requirements for rig guarding and the implications for the design in order that these requirements can be taken into account right from the earliest stages of a project.

Meanwhile, piling contractors who can devise appropriate guarding systems that allow smaller offset distances are likely to have a competitive advantage.

It should be added that a short article cannot cover all the issues raised.

For fuller details see the relevant Approved Code of Practice published by the HSE on the CDM regulations and the hierarchy of controls for risk.

Other piling design health and safety considerations are highlighted in CIRIA C662 and similar guidance on CDM.

References

Federation of Piling Specialists (FPS). Notes for guidance on PUWER (Regulations 11 and 12) in relation to guarding and cleaning of augers on piling operations.

March 2010.

British Drilling Association (BDA).

Guidance notes for the protection of persons from rotating parts and ejected or falling material involved in the drilling process.

CIRIA C662. CDM2007 — Construction works sector guidance for designers.

Health & Safety Executive. Managing health and safety in construction.

Construction (Design and Management) Regulations 2007 Approved Code of Practice.

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