Designing a path

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You have now surveyed the proposed routes on the ground and identified those that are feasible and needing work.  The next stage is the preparation of a 'design' for each route, based on information in the pre-construction information and the specification (red) survey. Whether it is replacing or upgrading an existing path or constructing a new path from scratch, the same design process will apply.  The aim should be to design a path, including any related features e.g. passing places, which is safe to construct, maintain, and use.

What is a design?

A design is a drawing, specification, bill of quantities that relate to a structure e.g. path, bridge, boardwalk or earthwork.  It can also include calculations prepared for the purpose of a design, or a product intended for a particular structure e.g. type of surfacing material, like tarmac or Toptrec, for a path.

When designing the path, including the drainage system or any related features, you will need to consider the following matters:

  • Fitting the path into the landscape over which it will cross

  • Who will be use the path afterwards

  • Least restrictive access (reasonable adjustments for people with disabilities)

  • Width of base and surface layers (to accommodate the different user groups and levels of use)

  • Depth of base and surface layers (based on ground conditions, different user groups and levels of use)

  • Type of separation and reinforcement layer if need (material type and strength grade based on ground conditions and different user groups and levels of use)

  • Site drainage conditions, e.g. work out where water is coming from and likely to go when it drains away)

  • Availability and suitability of materials to build the path (both on-site and off-site in the local area)

  • Reducing maintenance requirements

  • Site ground conditions, e.g. type of soil, wetness, vegetation, how hard the ground is along the route

  • Techniques and methods of constructing the path, including drainage system

  • Preparation of designs with adequate consideration to safety and ill health of everyone constructing, maintaining, and using the path or any other related structures, e.g. bridge

  • Foreseeable hazards on site or with the design harmful to health, likely to cause personal injury or lead to catastrophic events

  • Remaining risks with the design that cannot be removed but reduced and controlled on site by those carrying out the work

  • Site access, e.g. how easy or difficult will it be to get materials on site, where materials can be stored on site, can a one-way system be designed so vehicles do not need to reverse or turn

  • Any statutory requirements that will affect how and when the work is carried out, e.g. Water Environment (Controlled Activities) (Scotland) Regulations 2011.

When can a designer start 'detailed design work'?

The preparation of designs for a structure like a bridge, path is categorised as ‘detailed design work’.  Under the Construction (Design and Management) Regulations 2015, a designer must not start detailed design work without the appointment of a principal designer.  The principal designer needs to be involved in the design process to make sure other designers (if involved) perform their CDM duties properly, have considered and checked all health and safety matters when preparing or modifying the paths or any related structure designs.

A designer has a duty to advise the client of their responsibility to appoint a principal designer, before detailed design work commences - only ‘initial design work' should be permitted by the client without a principal designer appointed. If the client does not appoint a principal designer, they will then be principal designer for their project.

What is 'initial design work'?

Initial design work is 'feasibility work' that a designer could carry out for a client, to enable them to make important decisions on whether to or not to proceed with the project beyond the planning stage.  It could also include any work needed to identify the client's requirements in respect of their CDM responsibilities, or possible external constraints on the path's development.  The preparation of drawings, specifications or bill of quantities is not considered ‘initial design work’.  These design work activities are ‘detailed design work’ carried out at the design stage.

Hazard elimination and risk reduction

The main responsibility of a designer when preparing or modifying designs must be to remove foreseeable risks, if possible, and to reduce and control the remaining and unobvious risks.

A designer, when preparing or modifying their designs must take the following general principles of prevention into account - when considering materials, methods, and processes to be used by a contractor, who will build or install the structure designs:

  • Avoid risks - ask yourself, can you get rid of the problem (hazard) altogether?
    • A bridge could be designed so it can be assembled on the ground and then lifted into position across a watercourse with a crane or large execavator to remove the risk of workers falling off when working at height
    • A bridge could be designed with a high handrail to remove the risk of a horse rider falling off the bridge
    • The end of a path could be positioned away from a material storage area, so workers and moving plant are separated when the path is being built
    • Design the drainage feature using a piped culvert under the path to remove the risk of users tripping over a open cross drain installed in the path surface
  • Evaluating the risks you cannot remove
    • Work out whether the effort, time and expense of installing a high handrail on a bridge is appropriate, if the bridge is only occasionally used by horse riders and the distance to fall is not far, and the risk of a rider falling of the bridge can be reduced using a lower handrail
    • Work out whether the effort, time and expense of installing anti-slip surfacing materials on a new boardwalk is appropriate, if the risk of someone slipping over can be prevented by carrying out regular maintenance - brushing off any loose or built up debris on the decking to stop it becoming wet and slippery
  • Combating the risk at source
    • Arrange for overhead power line to be isolated (electricity switched off), if possible with the service provider
  • Adapting the work to the individual
    • This relates mostly to buildings used as workplaces
  • Adapting to technical progress - consider new techniques or technologies
    • Prefabricating parts of a bridge off site
    • Specifying bridge or boardwalk decking boards with suitable slip resistant surfacing to stop people slipping on constantly wet surface
  • Replacing the dangerous with the non-dangerous or the less dangerous
    • Use stone to pitch a path or install steps that is lighter in weight
    • Substitute solvent based products with water based ones
    • Use untreated instead of treated timber
    • Use recycled tyre kerbing instead of heavy concrete ones
    • Use recycled plastic instead of treated timber
  • Developing a coherent overall prevention policy which covers technology, organisation of work, working conditions, social relationships and the influence of factors relating to the working environment - set standards
    • Specify cutting of concrete kerbing carried out using block splitter techniques rather than mechanical cutting (cut-off saw) that produces clouds of harmful silica dust
  • Give collective protective measures priority over individual measures, and make provisions so that the work can be organised to reduce exposure to hazards
    • Make provision for segregated routes so that barriers can be provided between pedestrians and moving traffic
  • Give appropriate information and instructions to everyone carrying out the work
    • Use symbols and/ or written information on drawings, plans, or instructions such as intended sequencing of assembling prefabricated parts of a bridge that may be unknown to those tasked to put them together

A designer must not just consider the consequences of their design in relation to just building the path, they must also consider how the design could affect the safety of people who use the path and maintain it.

Health and safety considerations for Designers

The design can influence health and safety in the construction of the path and future maintenance and use in many aspects.

CDM does not expect a designer to design out all risks, but should consider the consequences of the design and remove foreseeable risks and reduce and control remaining risks.  The risks will vary depending on the extent and complexity of the work to carry out.  Here are four health and safety considerations for designers that will crop up on many path projects:

Access

Consider access during path construction work and for future maintenance, after the work is completed.  Your design should allow for safe access during construction for site vehicles, plant, delivery vehicles, and pedestrians - consider space for turning, segregated routes, one-way traffic routes, and site access/ egress points.

Material

Some construction materials may need to be handled on site.  Their size and weight can affect the manual handing risks to workers when carrying out the work.  This should be a consideration on all projects, but particularly where materials need moving around the site, and over long distances, where access is poor and mechanical aids may not be practical to use.  For example, if a bridge design can accommodate smaller decking components, movement of materials around site and on the bridge becomes easier for workers.  This will also be of benefit to those who will maintain the constructed structure, as replacement of damaged components will be easier and safer.

Prefabrication

Prefabrication of whole or part of a structure such as a bridge or boardwalk can help to eliminate some health and safety risks.  The use of hazardous treatments or substances to prepare structure parts is always safer done off-site in a controlled environment.  For example, precast concrete products can significantly reduce concrete mixing on site and the risks associated with cement burns, and silica dust amongst others.

Trip hazards

You may have seen drainage features like water bars and cross drains across a path to catch running water flowing down the surface or to get water to cross the path from a ditch.  Consider building the path with a sufficient camber or cross fall to remove trip hazards. Where gradients on a path are moderately steep or steeper, install closed cut-off drains rather than water bars.  Where water in a ditch needs to cross the path, install piped culverts under the path instead of cross drains.  Avoid shallow steps, surface breaks (gaps wider than 12mm) and other uneven surfaces that could cause trips and falls, resulting in minor accidents and broken bones.

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