Perspectives

6 things you need to know when working on constrained sites

All sites demand high volumes of traffic. After all, huge amounts of material and people pass through them and it’s not always as simple as A to B – sometimes they move from A to B, on to C and pass through D. It can be complicated. Sites are often located over a significant geographical area and extend to great vertical heights, they are very difficult to access and can be in very close proximity to the public.

So where do you start with constrained sites? The most critical factor to consider is safety. Safety, safety, safety, and safety. But you already know that, it’s true of any site. Specific to constrained sites, here are six things you need to know to make sure you get it right first time, every time:

1. Delivery routes, access points, egress points and how these will be segregated from the public

On constrained sites access and egress points are likely to be limited. The size of vehicles that can physically access the site safely may be compromised and this could lead to an increased number of smaller vehicle movements. The maximum amount of material that can physically be delivered or removed from site should be understood in detail so the programme accurately reflects the constraints. Delivery routes and how they can be separated from pedestrian access routes (both site based pedestrians and the general public) must also be one of those things you should just know of the top of your head.

2. Vertical transportation of both people and materials needs careful consideration

On all sites, but especially high rise projects, the efficient delivery of people and materials to the workface is paramount. Unless there is adequate provision for this then programme commitments will quickly come under pressure. The location of hoist and tower cranes must be robustly reviewed and comprehended. Constrained sites generally limit what is possible in this regard and getting this wrong will prove costly.

You’ve got to take into account vehicle delivery routes and vehicle and pedestrian segregation. Often hoists can be used to move materials or people and there less obvious lines of separation - compromising safety. The position of cranes and hoists and their interface with permanent works is vital. You’ve got to think where hoists or cranes may clash with permanent structures or services and pre-empt any delay in the removal of these items. Decide whether their location will postpone the completion of any permanent works and if so, determine what the impact will be from the outset.

3. Pick points relative to hooks

Even on a constrained site it may be possible to find a location for numerous cranes or hooks. What may be less obvious is that for a hook to be fully effective it needs a dedicated pick point that can ideally be accessed by delivery vehicles. Given the likely limitations identified in my first point above, this can often be challenging. If a project has six hooks but only three pick points then the operational effectiveness will at least be halved. Moreover, if one hook has to act as a “slave” hook to one of the others then you could be left with double or triple handling of materials - which is both slow and inefficient.

4. A robust and clearly communicated delivery and logistics plan is essential

… and it preferably will include detailed piece counts and material movements. This is a prerequisite to any site, but on a constrained site where space is limited it’s essential that deliveries spend the minimum amount of time possible on site. Unless the percentage of hook or hoist time allocated to each element of work has been reviewed, and aligned to the programme, then materials may arrive to site and be stockpiled because of insufficient means of vertically transporting them. On a site with limited space this can cause serious issues and lead to the necessity of moving materials multiple times. Again, not only is this inefficient, but increases the risk of safety incidents or damage.

5. Always just in time

With space at a premium, a well organised and well managed ‘just in time’ delivery protocol is essential. It requires everyone on site to be punctual while following set protocols. If absolutely necessary, consideration might be given to offsite holding areas or consolidation centres if the volume of deliveries is likely to put the ‘just in time’ delivery system under pressure. This allows you to take control of what is delivered to site and when.

6. Maximise offsite prefabrication and DfMA

Any site will benefit from more offsite production, but on a constrained site where movement of people and materials will always be a challenge, the benefits of offsite preassembly are exponentially beneficial. Offsite preassembly will lead to less deliveries to site, less operatives on site, less vertical and horizontal transportation, less public interface and generally a faster programme. On every site there should be a drive to maximise the amount of work that can be done off site. But on a constrained site the question should always be “what can’t be pre-assembled off site?”, rather than “what can?”

The initial site design should lend itself towards design for manufacture and assembly (DfMA) rather than the site team trying to reverse engineer DfMA solutions at a later date. Trying to shoehorn DfMA into a site that doesn’t naturally lend itself to an offsite solution is once again, inefficient. So, if you can, get it right from the beginning…

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  • Shaun Tate

    Director
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“On all sites, but especially high rise projects, the efficient delivery of people and materials to the workface is paramount. ”