The economical solution for preventing damage to conduit shaft heads

In underground construction, there is often damage to manhole covers and adjacent areas. Fixing this damage through reconstruction or new construction is very expensive and annually brings costs amounting to millions. The most common damage involves level differences between the manhole covers and the road surface, which can then lead to damage to the road itself. This is why Cabka, together with the Civil Engineering and Pipeline Construction Research Institute in Weimar (FITR), has developed a new type of process for stabilizing the ground in the area around manhole covers in traffic surfaces.

The problem and the solution

Three million conduit shafts in Germany need renovation.*

Of the approximately 515,000 km of conduit in the Federal Republic of Germany, about 13 million shafts are in operation, and about 30 percent need renovation. Level differences between the manhole cover and the road surface, the consequential damage, are among the most common problems in road construction.

Of course, there are many self-leveling manhole covers that align the settling of the shaft cover to that of the street. However, these do not compensate for or eliminate the cause – weak compaction in the ground around the shaft due to technical factors. They also cannot really keep the shaft cover from sinking.

*) Dipl.-Ing. Robert Stein, Dipl.-Ing. Hasan Cakmak, S & P Consult GmbH, Bochum: “Zustand und Sanierungsbedarf von Schächten” (Condition and need for rehabilitation of shafts) “tis - Tiefbau Ingenieurbau Straßenbau,” 4/2007 edition

Fixcover increases subsoil stability, thereby reducing damage to manhole covers

The system consists of 20 individual elements that, at 18-degree angles from one another, form a circle around the shaft and lock together by force or shape. This system spreads loads over a wider surface.

The bending load of the stabilization elements also enhances load transfer over the horizontal components. The resulting horizontal tractive forces are absorbed through friction between the components and the surrounding material. As with a cushioned foundation, the subsoil’s load capacity is increased, while settling is minimized at the same time.

Without FIXCOVER, traffic loads are continuously transferred to the layers below.

Maximum economy

FIXCOVER is made of recycled plastic. The stabilization elements’ basic material is a mixed polyolefin from the dual system. That not only takes a long-term load off the environment. It also saves money on maintenance and repair work. Low manufacturing costs and excellent manageability make FIXCOVER extremely economical.

Maximum flexibility

Because the system allows variable arrangement of the components in the shaft collar, its internal diameter can be 900 mm to 1000 mm, depending on the installation depth.

Maximum reliability

The project-relevant material parameters for the polyolefin-sand mixture used in FIXCOVER have been investigated by the East Thuringian Materials Testing Company for Textiles and Plastics in Rudolstadt-Schwarza. During measurement, tensile testing was carried out according to DIN EN ISO 527-1 on type 1A tension bars sprayed according to ISO 294.

All important factors, such as asphalt, subsoil, settling, laying depth and molded part were considered during development.

Proven stability and security

  • For securing the subsoil, a recycled plastic stabilization component has been developed and tested: FIXCOVER
  • For the first time, subsoil can be stabilized and compression-related settling minimized by installing components made of a recycled polyolefin plastic mixture.
  • The system has been developed by CABKA in collaboration with the Civil Engineering and Pipeline Construction Research Institute in Weimar (FITR) and optimized in consideration of all important factors, such as asphalt, subsoil, settling, installation depth and the molded part.
  • Practical testing has been carried out during wastewater plant construction in Weimar and on CABKA’s company premises in Weira.