In theory, there are 2 main kinds of modern landfills, the quarry-type below ground and the land raising-type. In the quarry or pit type the seeping groundwater and/or leachate must be piped to vertical shafts which are placed in the waste to keep the landfill dry.
Circular pre-cast concrete wells can be specified which are raised with the waste with each “cell lift” but they are stiff and unable to withstand the inevitable movement of the waste as it settles around it.
So, what very often happens is that the shaft “shears” and the rings are pushed off-centre. As soon as this happens the necessary occasional man access need to maintain such wells has to cease for safety reasons, sooner or later the a pump becomes stuck in the well or it becomes silted, and maybe due to concerns about landfill gas intrusion from damaged joints during maintenance – it cannot be cleaned.
The sad fact follows that damaging effects on the shafts, usually due to the settlement in the waste commonly of up to almost 40 percent by depth, destroy almost every other type of shaft construction.
Therefore the German company Bauku developed the supposed telescopic shaft about twenty years back. Here the individual shaft elements are stacked above each other flexibly and can move with the waste as it settles.
Generally the shafts have a diameter of 2000 mm or more as maintenance must be carried out in the shafts. This is done by lowering breathing apparatus equipped specialist access contractor’s operatives down the shafts on wire ropes.
At the base of the shaft there are pumps for the transport of the seeping water as well as the entrances to the leachate pipes laid on the landfill liner, which need to be cleaned at regular intervals.
The Bauku telescopic shafts permit construction heights of almost one hundred m in the waste mass.
The dump site Merchernich at Cologne is a reference case to exemplify a very tough installation project.
These days, as Bauku state in their web site, HDPE “PROFILEEN telescopic shafts are found in all pit-type disposals of the Federal Republic Germany and with the adoption of the European (EU) standards and Construction Quality Assurance guidances more neighbouring nations are also thinking about this cutting edge product when planning their waste disposal (landfill) sites.
Telescopic shafts may also be integrated into the existing landfills later so that the standard of the many old rubbish heap sites can be improved significantly. Bauku also inform us at their web site, that such projects were carried out by us on a large scale in Britain in the last few years.