In 2013, Power System Services were awarded a contract to manufacture and deliver numerous temporary propping systems, which once installed provided support to previously driven east and west bound tunnel walls whilst interlinking cross passages were constructed.
Power System Services provided technical and logistical support to this project. We provided advice on layout, feasibility, anchorage and visibility to ensure that the installation was easy and safe to install plus did not introduce a risk whilst in place.
The main design characteristic of all propping frames was a large heavy section fabricated channel located above and below the cross passage location, fixed to the tunnel pre-cast segments using large grouted bolts. In turn these large channels were supported by propping systems designed specifically with access considerations. For example some propping was achieved using heavy rolled section (see illustration) which was also bolted to tunnel segments. This allowed better access though the main tunnels. However the majority of the propping systems (over 20 in total) were propped by a simpler series of cross beams between the two fabricated channels.
The systems were 100% manufactured in our large factory and trial assembled to ensure there were no installation delays. It was, of course, critical that the manufactured quality and, in particular, the welds were of the highest standard and tested for design compliance. The fabricated channels which were from 40mm and 50mm plate needed to be flat, straight and structurally sound. To achieve all of this we adopted a welding procedure using Submerged Arc Welding which is an automatic consistent method which achieved 100% pass rate during non destructive testing. It is also worthwhile noting that for manually welded items such as the cross props the aspiration of 100% pass rate was also achieved.
"The propping systems were delivered on time, to a high quality of manufacture and has provided the client with a high level of confidence that our products and services are suitable for what currently is the largest construction project in Europe."