Hydraulic Asphalt Engineering

Impermeable facing for dams.

Bituminous lining systems have been used for upstream facings for more than 100 years. Installation is undertaken by special slope pavers, secured by a winch at the crest. The final compaction is achieved by rollers secured by smaller winches. There are different combinations of equipment used, depending upon the project requirements and parameters. WALO’s specialist equipment is all designed, developed, manufactured and are unique to  WALO. A lining system normally consists of a binder course (a permeable bituminous layer), and the impermeable dense asphalt concrete. Slope lengths of up to 200 metres and a maximum gradient of up to 1:1.5 can be lined, with ease. The high resistance of the asphalt to mechanical influences (e.g. ice drift, debris, vandalism) means that no additional measures are needed to protect the sealing layer, once installed. At the same time the bituminous lining can accommodate settlements and deformation, up to 10 %. An asphalt liner is environmentally friendly and non-toxic, making it also ideal for dams containing drinking water and irrigation purposes.

Jointless lining for large structures.

Hydraulic asphalt is a perfect medium for creating an impermeable and durable barrier for large structures such as pump-storage or compensation reservoirs. The lining system remains uncovered and can be inspected whenever required. Asphalt production and installation is highly mechanised and as a consequence, construction times can be effectively optimized. The use of asphalt as the lining system, enables both the design of the structure, and the mix of the asphalt, to be the developed to maximise the project parameters, ensuring the structure is effectively “fit-for-purpose”. The removal of sediments from within reservoirs is possible due to the robust nature of the asphalt lining system (can be trafficked by waggons and loading shovels/dozers), and access to the reservoir by a ramp. The largest asphalt linings for pump storage plants can be found in the USA, China and Central / Western Europe.
Large reservoirs are constructed and lined in asphalt, high in the mountains, where the stored water (collected in the spring/summer times), is used for the production of artificial snow, using “snow cannons”, on the autumn and early winter times. Asphalt linings in these circumstances because they can easily accommodate the significant stresses and loads endured by these structures, due to the extream changes in temperature and water loads experienced during operation.

WALO provides an impermeable asphalt lining to new or existing channels.

Asphalt layers can be installed onto a stable subbase course or old existing linings (e.g. asphalt or concrete). Placing the asphalt layers can be installed by a specially developed “channel paver” along the channel, or in the conventional vertical method, depending on the cross-section of the channel bed. Gradients of up to 1:1.25 on the slopes are possible. Channels can be completely lined with the entire surfaced covered (slopes and bottom), or individual areas lined, depending on the project requirements. Modern, sophisticated machinery guarantees high quality and performance, significantly reducing construction times. 

Dense Asphalt Concrete cores for embankment dams.

Rockfill or earthen dams can be made impermeable by installing an asphalt concrete core inside the embankment body. This robust and flexible core is constructed simultaneously, layer by layer, as an iterative process, with the dam itself. The width of the asphalt core is less than 1 % of the dam height and modern machinery allows the dam to rise up to 750 mm per day. The asphalt material is placed by a “core finisher” which also installs the upstream and downstream transition, or filter zones. After the asphalt material is compacted, environmental factors (weather - extream heat or cold), will not affect the bituminous barrier in anyway. This makes the use of asphalt for embankment cores ideal for locations, where adverse weather conditions are common, or where other natural lining materials are unavailable. The Moglice dam in Albania is 157 high and the installed asphalt core with its inherent flexible behaviours, ensures the impermeability of the dam, as a consequence of deformation caused by settlements and seismic activity.

WALO has created a dense asphalt concrete (DAC) impermeable barrier system for landfills. It is impermeable to methane and leachate, which are found in most solid waste deposits and are a major concern for any waste deposit site operator due to their negative impact on the environment.

The application of dense asphalt concrete (DAC) means that landfill sites can now safely house toxic waste. Many potential sites, such as old quarries, are dismissed out of hand as unsuitable for waste treatment as they have very steep walls. However, landfill designers and engineers looking for practical solutions find that DAC is very stable on slopes, even those as steep as a 1:1.6 gradient, which means that even sites with very steep walls can now safely be used for landfill.

Very strong yet highly flexible, DAC provides an impermeable seal for the waste treatment industry that lasts for decades. A typical DAC system has a total thickness of approximately 340 millimetres. It comprises a sealing layer of dense asphalt concrete approximately 80 mm thick, a 60 mm asphalt binder layer and a 200 mm stabilising layer of crushed aggregate.

Maintenance, rehabilitation and modernisation.

Exposed asphalt facings will withstand the forces of weather, change of water load / temperature and other various stresses for decades without any additional special protection measures, and can be available for inspection at any time. It is common and good practice, to install a mastic coating after some 20 – 25 years, to renew the bitumen coat at the surface. Due to the thermo-plastic characteristics of asphalt concrete, even after many years of service, an existing lining can be increased by connecting new lining areas, to the existing asphalt (i.e. joining landfill cells together, or raise of the dam crest). There is also the option to transform a single lining system into a monitored multi-layer system. 

Enduring environmental protection.

WALO has played a leading role in the field of impervious asphalt lining systems of Landfills for over 50 years, mainly within Central Europe.  

In landfills in particular, it is absolutely essential that the lining is impermeable to liquids. In addition to water, landfills also contain liquids or dissolved materials (leachates), that are environmentally harmful and could pollute the groundwater and aquifers. The bituminous barriers from WALO are impervious, durable and suitable for highly hazardous materials. Consequently, no further measures are needed to protect the asphalt concrete layer, once installed. In addition, they are extremely resistant to ageing, increased temperature and flexible enough to absorb settlements and deformations of the subsurface.