UK Office: +44 (0) 203 488 7723
Hesselberg Hydro

Underwater Structures


The use of asphalt underwater has been developed for scour protection but there are many other applications.

Typical applications

  • Protection of tunnels, for example, under a busy port waterway
  • Protection of pipelines and cables under canals from dredging work or anchor drag
  • Outfall structures
  • Protection of sluice aprons

A choice of materials

  • A grouted stone layer
  • Prefabricated mattresses of Open Stone Asphalt
  • Prefabricated mattresses of Dense Stone Asphalt

The mastic / rock combination

A superior alternative to rock alone:

  • Reduces the amount of rock
  • Increases the security of the structure
  • Mastic’s thermoplastic properties give excellent performance under short-term high impact loads as well as under long-term settlement load

Tunnel Roof Protection


Where tunnels pass beneath navigable waterways there is a risk of damage to the tunnel structure from anchor drops.

Traditionally the tunnel has been positioned deeper to keep away from the anchors, or a relatively thick layer of rock armour has been used.  Reinforced concrete is an option but it is not flexible to withstand settlements/riverbed movements. Concrete is not an ideal material to withstand high impact loads.

Asphalt mattresses are another option which can give the following advantages :

  • Relatively thin mattresses – typically 0.25-0.30m thick.
  • Flexible material to withstand settlements at edges.
  • Excellent properties against high impact loads.

The thinner construction may give the following advantages :