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.

Bauku telescopic well schematic

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.

The often proposed alternative landfill liner system to Low Permeability Clay Layer or HDPE Lining Membrane consists of replacing the default design of compacted clay liner (CCL) with a Geosynthetic Clay Liner (GCL).

There are currently two major types of commercially available GCLs. One type consists of bentonite encased between two geotextile fabrics and the second type consists of bentonite glued to a HDPE geomembrane.

The type of clay typically used in GCLs is sodium bentonite. Sodium bentonite is the name given to the highly plastic clay mineral montmorillonite, with sodium as the primary exchangeable cation.

Bentonites used to fabricate GCLs are processed in an unhydrated state such that they appear to have a granular consistency. However, upon hydration with water, the bentonite swells to form a continuous clay layer.

GCLs are shipped in rolls typically 3.7 to 5.3 meters wide and 25 to 60 meters long. They are installed by unrolling to form panels. Adjacent panels are overlapped, and for some products, powdered bentonite is placed between the panels at overlaps.

Large-scale laboratory testing has shown that, when installed in accordance with the manufacturer’s specifications, GCL overlaps are self-sealing and do not create a preferential pathway for liquid flow.

GCLs have been used in liner systems and cover systems for landfills, surface impoundments, and tank farms, as well as in other structures. When used in landfills, GCLs are often substituted for the compacted low-permeability soil component of a composite liner. The function of the GCL in the composite liner is identical to that of a compacted soil liner, which is to provide a low-permeability barrier to liquid flow through any defect in the overlying geomembrane.

The GCL material is manufactured under strict quality control (QC) guidelines. The QC requirements include conducting index and performance testing on both the supplied materials and finished product at specified frequencies. After the material is approved at the manufacturing plant, care is taken to keep the rolls dry, not stack them too high, and keep them from damage during handling.

Prior to acceptance in the field, information concerning the manufacturer’s name, product name, lot and roll number, and length, width, and weight must be submitted to the on-site CQA representative, who will verify all records.

To analyze the leakage through a composite liner utilizing a GCL instead of a CCL, D’Arcy’s equation is utilized based upon an assumed design hydraulic head over the liner.

The leakage through a membrane liner has been found to be closely correlated with the hole defects. In a recent paper a defect size per acre of 1 cm2 was assumed, however assessments of defects and their likely frequency and size vary widely.