A TRICKY JOB: SIZE MATTERS UNTIL YOU CONSIDER THE SITE CONSTRAINTS (PART 1)
Our site team recently mobilized to a tricky site with 120 piles at 25m long taking loads between 200kN and 700kN… all spread out within a large existing structure. Critical to successful delivery of the projects were a number of factors, and this post will focus on design.
The capacity of a screw pile (kN) is highly dependent on the installation torque available and requires intricate planning and iteration of design considering the plant onsite. For example, if you wanted to achieve over 1,000kN compression you might want to install a screw pile with large diameter shaft and large diameter helix.
…. BUT! The large diameters require a lot of torque to install them – not only for the layers they have to get through – but the dense founding layer they have to embed into… So the site team will price the job assuming they can use the big excavators with big powerheads.
…. BUT!! When they get to the site they realise it is constrained by access limitations to enter, as well as the head height, and how much you can’t even slew around…. So the onsite operator/foreman goes back to the pile designer and says he can only get a 20T excavator into the site.
…. BUT!!! A 20T excavator can only drive a powerhead with (say) 100kNm of torque … not just the lifting of it, but hydraulic pressures to power it, and the slew brakes to hold the pile in position.
…. SO… the pile designer now has to collaborate with the installer to consider what pile capacity they might get with the smaller plant. They then have to collaborate with the structural engineer and reassess how this affects the superstructure design. And so begins the dance of balancing the pile capacity at each pile location the building’s overall requirements.
…AND…. This is why screw piling is best undertaken by designers who have intricate knowledge of the plant (and people) who will install it….
It's why we always recommend talking to a specialist screw pile company that can help guide you on this process - from start to finish.
Guiding our clients, consultants, and contractors.
REVEX PILING
Screw piling with space constraints.
Navigating tight accessways.
