The locality and use of the underpass will determine the finishes. To try and avoid vandalism occurring, underpass lighting should be made using toughened glass and recessed into the walls or roof units. This helps to avoid the membrane being punctured.
Once in place, the waterproof membrane must be protected by constructing a concrete- block skin against the membrane before backfilling with granular material. A self- adhesive bituminous polythene can be used and have the advantage of being easier and quicker to lie in place.
Bituminous sheeting should be applied in 2-3 layers, with hot bitumen fully bedding each layer. Two coats of mastic asphalt should be laid, with joints staggered at least 150 mm. Waterproofing underpasses is commonly achieved by applying one of the following: In situ concrete underpasses are constructed using the same methods as any underground tunneling construction. This is possible by forming a rebated joint filled with mortar prior to applying the sealant.
This jointing method should allow edge contact for jacking, but be capable of receiving a sealing compound from the inner face. As a means of transmitting the thrust load, the units must have direct edge contact rather than the pre-formed sealing strip. Thrust-bored units require a suspension of bentonite as lubrication. The roof units are then placed and the in situ loading slab poured, with loading requirements determining the thickness. Wall and roof unit systems comprise precast units that are placed in position with the floor laid in situ using the units as shuttering. The units are then placed in position, with lubrication applied to reduce stress-induced friction. Portal frame units, which are pre- stressed, require the lower waterproofing membrane to be placed on a concrete slab, with continuous concrete bearing pads (usually 300 mm wide x 25 mm deep) are laid on top. Connection plates in the floor and roof are used to bolt together the units. Precast concrete units are often manufactured as standard units and can be provided to site as complete box-like open-ended sections, portal frame segments, or as separate wall and roof units.īox units are typically jointed using a pre-formed sealant strip in a socket and spigot joint. There are three main methods for constructing underpasses: Underpasses can also be constructed to allow wildlife to pass safely under a transport corridor.