Raft foundation - Revision history

Designing Buildings at 09:07, 21 December 2022

2022-12-21T09:07:10Z

← Older revision		Revision as of 09:07, 21 December 2022
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		+	[[File:Raft_foundation.jpg\|link=File:Raft_foundation.jpg]]
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		+	= What are foundations? =
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	Foundations provide support for structures, transferring their load to layers of soil or rock that have sufficient bearing capacity and suitable settlement characteristics.		Foundations provide support for structures, transferring their load to layers of soil or rock that have sufficient bearing capacity and suitable settlement characteristics.

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	* Raft foundation.		* Raft foundation.

−	Raft foundations (sometimes referred to as raft footings or mat foundations) are formed by reinforced concrete slabs of uniform thickness (typically 150 mm to 300 mm) that cover a wide area, often the entire footprint of a building. They spread the load imposed by a number of columns or walls over the area of foundation, and can be considered to ‘float’ on the ground as a raft floats on water.	+	= What are raft foundations? =
		+
		+	Raft foundations (sometimes referred to as raft footings or mat foundations) are formed by reinforced concrete slabs of a uniform thickness (typically 150 mm to 300 mm) that cover a wide area, often the entire footprint of a building. They spread the load imposed by a number of columns or walls over the area of foundation, and can be considered to ‘float’ on the ground as a raft floats on water.
		+
		+	= Where are raft foundations appropriate? =

	They are suitable where:		They are suitable where:

−	* Floor areas are small and structural loadings are low, such as in one or two-storey domestic ~~construction~~.	+	* Floor areas are small and structural loadings are low, such as in one or two-storey domestic buildings.
	* A basement is required.		* A basement is required.
	* Ground conditions are poor and strip or pad foundations would require significant excavation, for example on soft clay, alluvial deposits, compressible fill, and so on.		* Ground conditions are poor and strip or pad foundations would require significant excavation, for example on soft clay, alluvial deposits, compressible fill, and so on.
	* Settlement, or differential settlement is likely.		* Settlement, or differential settlement is likely.
−	* Where it may be impractical to create ~~individual~~ strip or pad foundations for a large number of individual loads. In very general terms, if strip or pad foundations would cover 50% or more of the floor area, then a raft may be more appropriate.	+	* Where it may be impractical to create separate strip or pad foundations for a large number of individual loads. In very general terms, if strip or pad foundations would cover 50% or more of the floor area, then a raft may be more appropriate.

−	Raft foundations can be fast and inexpensive to construct, as they tend not to require deep excavations compared to strip or pad foundations and they may use less material as they combine the foundation with the ground slab. However, they tend to be less effective where structural loads are focussed on in a few concentrated areas, and they can be prone to erosion at their edges.	+	Raft foundations can be fast and inexpensive to construct, as they tend not to require deep excavations compared to strip or pad foundations and they may use less material as they combine the foundation with the ground slab. However, they tend to be less effective where structural loads are focussed on a few concentrated areas, and they can be prone to erosion at their edges.

−	~~They~~ are generally constructed on a compacted hardcore base (perhaps 100 mm thick). A layer of blinding concrete ~~may then be laid to allow formation of the raft~~ (typically 50 mm) with a waterproof membrane above.	+	= How are raft foundations constructed? =
		+
		+	The design of raft foundations involves a number of disciplines, as consideration must be given not only to the structure itself, but also to; integration of other constructions (such as external walls), insulation, damp proofing and complex ground conditions such as the presence of groundwater, trees or contamination.
		+
		+	Raft foundations are generally constructed on a compacted hardcore base (perhaps 100 mm thick). A layer of blinding concrete (typically 50 mm) may then be laid with a waterproof membrane above to create an even, dry surface to allow formation of the raft .

	The concrete raft tends to include steel reinforcement to prevent cracking, and may incorporate stiffening beams or thickened areas to provide additional support for specific loads, for example, below internal walls or columns (which may require punching shear reinforcement). Beams may stand proud of the raft, either above or below it, or may be 'hidden' beams, formed by reinforced areas within the depth of the raft itself. These thickened areas are particularly useful where there are poor ground conditions, as the required thickness of the raft itself might otherwise be uneconomic.		The concrete raft tends to include steel reinforcement to prevent cracking, and may incorporate stiffening beams or thickened areas to provide additional support for specific loads, for example, below internal walls or columns (which may require punching shear reinforcement). Beams may stand proud of the raft, either above or below it, or may be 'hidden' beams, formed by reinforced areas within the depth of the raft itself. These thickened areas are particularly useful where there are poor ground conditions, as the required thickness of the raft itself might otherwise be uneconomic.
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	Insulation will generally be laid on top of the raft, with a concrete floor, or raised floor above.		Insulation will generally be laid on top of the raft, with a concrete floor, or raised floor above.

−	Drainage may be required ~~in some circumstances~~ under raft foundations, and geotextile barriers may be required to prevent free-draining materials from becoming clogged up by the surrounding soil.	+	Drainage may be required under raft foundations in some circumstances, and geotextile barriers may be required to prevent free-draining materials from becoming clogged up by the surrounding soil.
		+
		+	= What are the different types of raft foundation? =

	Types of raft foundation include:		Types of raft foundation include:
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	For more information, see Types of raft foundation.		For more information, see Types of raft foundation.
−
−	~~[[File:Raft_foundation.jpg\|link=File:Raft_foundation.jpg]]~~
−
−	The design of raft foundations involves a number of disciplines, as consideration must be given not only to the structure itself, but also to; integration other constructions (such as external walls), insulation, damp proofing and complex ground conditions such as the presence of groundwater, trees or contamination.

	Where soil is compressible, a raft foundation may be formed as a compensated foundation. In this case, the raft slab is provided to a depth that the weight of the excavated soil is equal to the raft slab weight plus that of the structure to be supported. This can be appropriate when constructing buildings on soft clay or loose sand, as settlement can be significantly reduced.		Where soil is compressible, a raft foundation may be formed as a compensated foundation. In this case, the raft slab is provided to a depth that the weight of the excavated soil is equal to the raft slab weight plus that of the structure to be supported. This can be appropriate when constructing buildings on soft clay or loose sand, as settlement can be significantly reduced.
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	For more information see: Compensated foundation.		For more information see: Compensated foundation.

−	= Related articles on Designing Buildings ~~Wiki~~ =	+	= Related articles on Designing Buildings =

−	* ~~Types of raft foundation~~	+	* Blinding.
−	* Strip foundation	+	* Building foundations.
−	* Pad foundation	+	* Cast-in-place concrete.
−	* Building foundations	+	* Cellular raft foundation.
−	* ~~Pile foundations~~	+	* Compensated foundation.
−	* ~~Piled~~ raft foundation	+
−	* ~~Cellular raft~~ foundation	+
	* Footings in foundations		* Footings in foundations
−	* ~~Raft system~~	+	* Pad foundation.
−	* ~~Trench fill foundation~~	+	* Pile foundations.
−	* ~~Types of pad~~ foundation	+	* Piled raft foundation.
−	* ~~How to design a pad~~ foundation	+	* Raft system.
−	* ~~Bearing capacity~~	+	* Strip foundation.
−	* Types of ~~beam~~	+	* Trench fill foundation.
−	* Types of ~~brick bonding~~	+	* Types of pad foundation.
−	* Blinding	+	* Types of raft foundation.
−	* Cast-in-place concrete	+
−	* Settlement	+
−	* Compensated foundation	+
−	* Driven piles	+
−	* Concrete	+

	[[Category:DCN_Definition]] [[Category:DCN_Guidance]] [[Category:DCN_Product_Knowledge]] [[Category:Products_/_components]]		[[Category:DCN_Definition]] [[Category:DCN_Guidance]] [[Category:DCN_Product_Knowledge]] [[Category:Products_/_components]]

Designing Buildings at 11:37, 10 February 2021

2021-02-10T11:37:57Z

← Older revision		Revision as of 11:37, 10 February 2021
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	* Cellular raft foundation		* Cellular raft foundation
	* Footings in foundations		* Footings in foundations
		+	* Raft system
	* Trench fill foundation		* Trench fill foundation
	* Types of pad foundation		* Types of pad foundation

Designing Buildings at 06:41, 27 August 2020

2020-08-27T06:41:55Z

← Older revision		Revision as of 06:41, 27 August 2020
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	* Concrete		* Concrete

−	[[Category:~~Products_/_components~~]] [[Category:DCN_Product_Knowledge]]	+	[[Category:DCN_Definition]] [[Category:DCN_Guidance]] [[Category:DCN_Product_Knowledge]] [[Category:Products_/_components]]

Designing Buildings at 16:54, 26 February 2020

2020-02-26T16:54:36Z

← Older revision		Revision as of 16:54, 26 February 2020
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	The design of raft foundations involves a number of disciplines, as consideration must be given not only to the structure itself, but also to; integration other constructions (such as external walls), insulation, damp proofing and complex ground conditions such as the presence of groundwater, trees or contamination.		The design of raft foundations involves a number of disciplines, as consideration must be given not only to the structure itself, but also to; integration other constructions (such as external walls), insulation, damp proofing and complex ground conditions such as the presence of groundwater, trees or contamination.

−	~~= Find out more =~~	+	Where soil is compressible, a raft foundation may be formed as a compensated foundation. In this case, the raft slab is provided to a depth that the weight of the excavated soil is equal to the raft slab weight plus that of the structure to be supported. This can be appropriate when constructing buildings on soft clay or loose sand, as settlement can be significantly reduced.

−	=== Related articles on Designing Buildings Wiki ===	+	For more information see: Compensated foundation.
		+
		+	= Related articles on Designing Buildings Wiki =

	* Types of raft foundation		* Types of raft foundation
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	* Concrete		* Concrete

−	[[Category:Products_/_components]]	+	[[Category:Products_/_components]] [[Category:DCN_Product_Knowledge]]

193.63.42.35 at 15:54, 7 November 2019

2019-11-07T15:54:56Z

← Older revision		Revision as of 15:54, 7 November 2019
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	Very broadly, foundations can be categorised as shallow foundations or deep foundations. Shallow foundations are typically used where the loads imposed by a structure are low relative to the bearing capacity of the surface soils.		Very broadly, foundations can be categorised as shallow foundations or deep foundations. Shallow foundations are typically used where the loads imposed by a structure are low relative to the bearing capacity of the surface soils.

−	Deep foundations are necessary where the bearing capacity of the surface soils is not adequate to support the loads imposed by a structure and so those loads need to be transferred to deeper layers with higher bearing capacity~~. Daniel Wickenden made this~~.	+	Deep foundations are necessary where the bearing capacity of the surface soils is not adequate to support the loads imposed by a structure and so those loads need to be transferred to deeper layers with higher bearing capacity.

	Shallow foundations include:		Shallow foundations include:

193.63.42.35 at 15:53, 7 November 2019

2019-11-07T15:53:03Z

← Older revision		Revision as of 15:53, 7 November 2019
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	Very broadly, foundations can be categorised as shallow foundations or deep foundations. Shallow foundations are typically used where the loads imposed by a structure are low relative to the bearing capacity of the surface soils.		Very broadly, foundations can be categorised as shallow foundations or deep foundations. Shallow foundations are typically used where the loads imposed by a structure are low relative to the bearing capacity of the surface soils.

−	Deep foundations are necessary where the bearing capacity of the surface soils is not adequate to support the loads imposed by a structure and so those loads need to be transferred to deeper layers with higher bearing capacity. ~~jack colvin~~ made this	+	Deep foundations are necessary where the bearing capacity of the surface soils is not adequate to support the loads imposed by a structure and so those loads need to be transferred to deeper layers with higher bearing capacity. Daniel Wickenden made this.

	Shallow foundations include:		Shallow foundations include:

193.63.42.35 at 15:49, 7 November 2019

2019-11-07T15:49:55Z

← Older revision		Revision as of 15:49, 7 November 2019
Line 3:		Line 3:
	Very broadly, foundations can be categorised as shallow foundations or deep foundations. Shallow foundations are typically used where the loads imposed by a structure are low relative to the bearing capacity of the surface soils.		Very broadly, foundations can be categorised as shallow foundations or deep foundations. Shallow foundations are typically used where the loads imposed by a structure are low relative to the bearing capacity of the surface soils.

−	Deep foundations are necessary where the bearing capacity of the surface soils is not adequate to support the loads imposed by a structure and so those loads need to be transferred to deeper layers with higher bearing capacity.	+	Deep foundations are necessary where the bearing capacity of the surface soils is not adequate to support the loads imposed by a structure and so those loads need to be transferred to deeper layers with higher bearing capacity. jack colvin made this

	Shallow foundations include:		Shallow foundations include:

Designing Buildings: Reverted edits by 193.63.61.226 (talk) to last revision by Designing Buildings

2019-01-31T15:01:24Z

Reverted edits by 193.63.61.226 (talk) to last revision by Designing Buildings

← Older revision		Revision as of 15:01, 31 January 2019
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−	~~SUBSCRIBE TO WILLNE~~
−
	Foundations provide support for structures, transferring their load to layers of soil or rock that have sufficient bearing capacity and suitable settlement characteristics.		Foundations provide support for structures, transferring their load to layers of soil or rock that have sufficient bearing capacity and suitable settlement characteristics.

193.63.61.226 at 13:18, 31 January 2019

2019-01-31T13:18:20Z

← Older revision		Revision as of 13:18, 31 January 2019
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		+	SUBSCRIBE TO WILLNE
		+
	Foundations provide support for structures, transferring their load to layers of soil or rock that have sufficient bearing capacity and suitable settlement characteristics.		Foundations provide support for structures, transferring their load to layers of soil or rock that have sufficient bearing capacity and suitable settlement characteristics.

Designing Buildings: Reverted edits by 160.9.42.77 (talk) to last revision by Designing Buildings

2018-11-14T22:46:23Z

Reverted edits by 160.9.42.77 (talk) to last revision by Designing Buildings

← Older revision		Revision as of 22:46, 14 November 2018
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	[[File:Raft_foundation.jpg\|link=File:Raft_foundation.jpg]]		[[File:Raft_foundation.jpg\|link=File:Raft_foundation.jpg]]

−	The design of raft foundations involves a number of disciplines, as consideration must be given not only to the structure itself, but also to; integration other constructions (such as external walls), insulation, damp proofing and complex ground conditions such as the presence of groundwater, trees or contamination~~.na fam.wunt dare~~.	+	The design of raft foundations involves a number of disciplines, as consideration must be given not only to the structure itself, but also to; integration other constructions (such as external walls), insulation, damp proofing and complex ground conditions such as the presence of groundwater, trees or contamination.

	= Find out more =		= Find out more =