Dense Asphaltic Concrete has been as a Landfill Lining membrane material for many years and although it is not commonly seen in the UK, it is used much more often in Europe, and particularly in Germany.

The Dense Asphaltic Concrete is formulated in a manner which ensures both very low permeability and possibly as low as 1 x 10^-11 m/s, and permeability to landfill gas is also lower than for clays.

This is an imporant point as the ability of clays to pass some methane gas is often overlooked for single clay liner designs. Let us not forget either that the primary motivation for the composite lining (clay/HDPE)systems which are the norm now throughout the British Isles, was originally the concerns about landfill gas movement through the clay membrane. It happens also to be far less likely that a pinhole in the HDPE will ever leak when in a composite arrangement that hole will be backed up by the clay geomembrane layer.

Asphaltic concrete is stable on steeper slopes than HDPE unless special measures are taken to support and/or reinforce the HDPE, and much less prone to the sort of slip plane development we often see between HDPE and clay and sand/HDPE on slopes and banking.

Another big assett when considering this alternative lining material is its robustness during the infilling of the first layer of waste. All CQA Engineers worth the name will have experienced HDPE lining damage which occurs when the top 300mm of leachate drianage stone is being emplaced, and then potentially can occur again when the compactor vehicle runs in with the first waste lift.

Resistivity checks completed once the leachate drainage stone over the membrane often identify small holes in the HDPE liner after the leachate stone has been spread and levelled. These tend to be caused by a moments lack of concentration which the driver may suffer. Unfortunaelty, one unfortunate jab downwords (as the backactor spreads the sand or gravel of the leachate drain over the HDPE geomembrane) can be all that it needs to created minor pin holes, and to see about a dozen occurring per hectare was not uncommon in CQA Reports, a few years ago.

A UK specialist contractor offering Dense Asphaltic Concrete in the UK is WALO UK. http://www.walo.co.uk/

The widely used definition of geophysics is that provided by Sheriff in the Encyclopedia of Exploration Geophysics.

For the purposes of this site, we refer more specifically to the following definitions - these focus on Environmental and Engineering Geophysics:

1. Geophysics is: The subsurface site characterization of the geology, geological structure, groundwater, contamination, and human artifacts beneath the Earth’s surface, based on the lateral and vertical mapping of physical property variations that are remotely sensed using non-invasive technologies. Many of these technologies are traditionally used for exploration of economic materials such as groundwater, metals, and hydrocarbons.
2. Geophysics is: The non-invasive investigation of subsurface conditions in the Earth through measuring, analyzing and interpreting physical fields at the surface. Some studies are used to determine what is directly below the surface (the upper meter or so); other investigations extend to depths of 10’s of meters or more.

Both of these definitions have a common component, namely that geophysics represents a class of subsurface investigations that are non-invasive (i.e. that do not require excavation or direct access to the sub-surface). The exceptions are borehole geophysical methods that expand the use of holes already drilled to access the subsurface on a very localized basis.