Underpass construction - Revision history

Designing Buildings at 08:01, 11 October 2020

2020-10-11T08:01:28Z

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	* Underpinning.		* Underpinning.

−	[[Category:Construction_techniques]]	+	[[Category:DCN_Definition]] [[Category:DCN_Guidance]] [[Category:Construction_techniques]]

Designing Buildings at 17:43, 27 September 2017

2017-09-27T17:43:16Z

← Older revision		Revision as of 17:43, 27 September 2017
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	= Introduction =		= Introduction =

−	An underpass, or subway, is a tunnel containing a road or pedestrian passageway running underneath a road or railway. Underpasses can also be constructed to allow wildlife to pass ~~through~~ safely.	+	An underpass, or subway, is a tunnel containing a road or pedestrian passageway running underneath a road or railway. Underpasses can also be constructed to allow wildlife to pass safely under a transport corridor.

	= Construction methods =		= Construction methods =
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	* Thrust-bored units.		* Thrust-bored units.

−	Precast concrete units are manufactured as standard units and can be provided to site as complete box-like open-ended sections, portal frame segments, or separate ~~units for walls~~ and roof.	+	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.

−	Box units are jointed ~~together~~ using a pre-formed sealant strip in a socket and spigot joint. Connection plates in the floor and roof are used to bolt together the units.	+	Box units are typically jointed using a pre-formed sealant strip in a socket and spigot joint. Connection plates in the floor and roof are used to bolt together the units.

	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. 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. The units are then placed in position, with lubrication applied to reduce stress-induced friction.

−	Wall and roof unit systems ~~are comprised of~~ precast units that are placed in position with the floor laid in situ using the units as shuttering. 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 roof units are then placed and the in situ loading slab poured, with loading requirements determining the thickness.

	Thrust-bored units require a suspension of bentonite as lubrication. As a means of transmitting the thrust load, the units must have direct edge contact rather than the pre-formed sealing strip. This jointing method should allow edge contact for jacking, but be capable of receiving a sealing compound from the inner face. This is possible by forming a rebated joint filled with mortar prior to applying the sealant.		Thrust-bored units require a suspension of bentonite as lubrication. As a means of transmitting the thrust load, the units must have direct edge contact rather than the pre-formed sealing strip. This jointing method should allow edge contact for jacking, but be capable of receiving a sealing compound from the inner face. This is possible by forming a rebated joint filled with mortar prior to applying the sealant.

Editor at 15:18, 10 July 2017

2017-07-10T15:18:39Z

← Older revision		Revision as of 15:18, 10 July 2017
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−	[[File:Underpass.jpg]]	+	[[File:Underpass.jpg\|link=File:Underpass.jpg]]

	= Introduction =		= Introduction =
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	In situ concrete underpasses are constructed using the same methods as any underground tunneling construction.		In situ concrete underpasses are constructed using the same methods as any underground tunneling construction.

−	[[File:Underpass.JPG]]	+	[[File:Underpass.JPG\|link=File:Underpass.JPG]]

	= Waterproofing =		= Waterproofing =
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	* Sewer construction.		* Sewer construction.
	* Substructure.		* Substructure.
		+	* Swimming pool construction.
	* Tunnelling.		* Tunnelling.
	* Tunnels of the world.		* Tunnels of the world.

Editor: Created page with "File:Underpass.jpg = Introduction = An underpass, or subway, is a tunnel containing a road or pedestrian passageway running underneath a road or railway. Underpasses can al..."

2017-07-10T15:18:06Z

Created page with "File:Underpass.jpg = Introduction = An underpass, or subway, is a tunnel containing a road or pedestrian passageway running underneath a road or railway. Underpasses can al..."

New page

[[File:Underpass.jpg]]

= Introduction =

An underpass, or subway, is a tunnel containing a road or pedestrian passageway running underneath a road or railway. Underpasses can also be constructed to allow wildlife to pass through safely.

= Construction methods =

There are three main methods for constructing underpasses:

* Precast concrete units.
* In situ concrete.
* Thrust-bored units.

Precast concrete units are manufactured as standard units and can be provided to site as complete box-like open-ended sections, portal frame segments, or separate units for walls and roof.

Box units are jointed together using a pre-formed sealant strip in a socket and spigot joint. Connection plates in the floor and roof are used to bolt together the units.

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. The units are then placed in position, with lubrication applied to reduce stress-induced friction.

Wall and roof unit systems are comprised of precast units that are placed in position with the floor laid in situ using the units as shuttering. The roof units are then placed and the in situ loading slab poured, with loading requirements determining the thickness.

Thrust-bored units require a suspension of bentonite as lubrication. As a means of transmitting the thrust load, the units must have direct edge contact rather than the pre-formed sealing strip. This jointing method should allow edge contact for jacking, but be capable of receiving a sealing compound from the inner face. This is possible by forming a rebated joint filled with mortar prior to applying the sealant.

In situ concrete underpasses are constructed using the same methods as any underground tunneling construction.

[[File:Underpass.JPG]]

= Waterproofing =

Waterproofing underpasses is commonly achieved by applying one of the following:

* Mastic asphalt.
* Bituminous or neoprene sheeting.
* Painted membrane.

Two coats of mastic asphalt should be laid, with joints staggered at least 150 mm. Bituminous sheeting should be applied in 2-3 layers, with hot bitumen fully bedding each layer. A self-adhesive bituminous polythene can be used and have the advantage of being easier and quicker to lie in place.

Once in place, the waterproof membrane must be protected by constructing a concrete-block skin against the membrane before backfilling with granular material. This helps to avoid the membrane being punctured.

= Lighting and drainage =

To try and avoid vandalism occurring, underpass lighting should be made using toughened glass and recessed into the walls or roof units.

The locality and use of the underpass will determine the finishes. Urban underpasses are often painted in bright colours or to suit the finish of its immediate surroundings, using mosaics, tiling and rendering. For underpasses where aesthetics are not as important, a plain concrete finish will often be chosen.

Drainage comprises normal falls, screeded floor and gullies or continuous side channels which will flow into a storm sewer as and when required.

= Find out more =

=== Related articles on Designing Buildings Wiki ===

* Basement excavation.
* Excavation.
* Groundworks.
* Road construction.
* Sewer construction.
* Substructure.
* Tunnelling.
* Tunnels of the world.
* Underpinning.

[[Category:Construction_techniques]]