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(Image: Vitrified clay pipes, concrete cradle bedding according to [NCPI] [Image: visaplan GmbH] – Load factor = 3.4) When having a reinforced concrete cradle as bedding, the thickness of the bedding under the pipe barrel is at least 6 in or 1/4th of the pipe OD, whichever is greater. The initial backfill shall be either Class I, II, III, or IV, with a maximum particle size of 1½ in. Also, the cradle has to extend up the haunches to a height of minimum … |
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(Image: Vitrified clay pipes, concrete encasement according to [NCPI] [Image: visaplan GmbH]) Concrete encasement has to fully surround the pipe, and must have a minimum thickness of 1/4th the pipe OD or 4 in, whichever is greater, at any point [[VCP Engineering Manual]]. |
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Each bedding class offers a different load supporting capability for the pipe. Accordingly, load factors have been determined for each bedding class [[VCP Engineering Manual]]. The load factor is used to compute the field supporting strength (FSS) of VCP with any designated bedding class, which is obtained by multiplying the minimum three edge bearing strength [[ASTM C700]] by the appropriate load factor. FSS = Minimum Pipe Bearing Strenght x Load … |
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Use of native bedding material is the most cost effective method of installation. In addition, it provides suitable support for clay pipes. However, special care must be taken to remove rock particles that are larger than those indicated in the table on page 65, as they may be the cause of point loads [[VCP Engineering Manual]]. |
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Nov 23, 2019 AE-02 Open Cut Method: Embedment Zone and Pipe Installation Creation of the Bedding for Various Pipe Materials in the US The following table presents the compaction recommendations for foundation and bedding as per [[ASTM D2321–05]]. (Table: Recommendations for installation and use of soils and aggregates for foundation and bedding [ASTM D 2321-05]) |
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Nov 23, 2019 This following information is extremely useful for engineers and contractors who work internationally. The German standard [ATVA127] "Static Calculation of Drains and Sewers", categorizes the placement of the bedding in the following four conditions (B1 to B4). (Image: Bedding condition B1) Bedding conditions B1 (Image: Bedding condition B2) Bedding conditions B2 (Image: Bedding condition B3) Bedding conditions B3 (Image: Bedding condition B4) Bedding conditions … |
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Nov 23, 2019 (Image: Bedding condition B1) B1 - Placed lengthwise or in layers against the natural soil or embankment (without evidence of degree of compaction); also applies to soldier pile walls. |
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B2 - Vertical shoring within the embedment using piles or light sheet profiles, which are removed only after backfilling using equipment which ensures proper compaction of the embedment. (Image: Bedding condition B2) (Image: Bedding condition B2) |
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(Image: Bedding condition B3) B3 - Vertical shoring within the embedment using sheet piling and compaction against the shoring extending below the trench base. (Vertical sheeting using wooden piles, shoring panels or devices, which are removed only after the completion of the backfilling and compaction can result in the formation of voids which are not detectable by any computing model.) |
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(Image: Bedding condition B4) B4 - Placed lengthwise or in layers against the natural soil or embankment with compaction proof required by the StB ZTVE. The embedding condition B4 is not applicable to soils of the group G4 (In the future, named as B0). |
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Nov 23, 2019 (Image: Influence of the embedding condition on the pipe stress) The graphic shows the impact of the embedding conditions on the pipeline stress / strain. As an initial starting point, the embedding condition B1 is selected. In contrast, the pipe stress may be reduced by 20% as a result of compaction testing (B4). The stress on the pipe is increased by a factor of 2.5 if the shoring is removed abruptly rather than gradually during the backfilling … |
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Nov 23, 2019 In Europe, three basic bedding types are differentiated, with the difference being the thickness of the upper bedding layer which provides the necessary support angle (2α) :
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Nov 23, 2019 The bedding “Type 1” represents the standard. It is distinguished between a lower bedding layer “a” and an upper bedding layer “b”. As a rule, the bedding has to reach across the entire trench width. (Image: Bedding type 1 according to DIN EN 1610) (Image: Schematic representation of the type 1 bedding) |
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Nov 23, 2019 For a bedding “Type 2” there is no lower bedding layer. The pipes are directly laid on the accurately pre-profiled (pre-formed) trench bottom, thus reducing the thickness of the upper bedding layer at the same time. For that purpose it is required that the natural (in situ) soil is relatively fine and can be compacted well. (Image: Bedding “Type 2” DIN EN 1610) (Image: Bedding “Type 2”) (Image: Example bedding type 2 for a GRP pipe - Attention: Minimum … |
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The bedding “Type 3” is also only applicable in especially suitable soils. This method does not have a lower bedding layer or a pre-formed trench bottom. The pipes are laid directly on the trench bottom, hence increasing the risk of point load damage especially for pipes without a base. (Image: Bedding type 3 according to EN 1610) (Image: Schematic representation of the type 3 bedding) |
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When is a concrete bedding useful? Concrete bedding (concrete support) is a “special type of bedding construction” which is used in the following circumstances:
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The placement of pipes in concrete bedding includes:
(Image: Installation of a reinforced concrete … |
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In the case of concrete pipes with an integrated base, the base takes over the function of the upper bedding layer. Therefore, they can usually be placed directly on a prepared, horizontally levelled and compacted bedding of suitable soil material (lower bedding layer), directly on the prepared trench base or on a concrete support. Even with these type of pipes, it is necessary to compact the haunch areas by hand to ensure proper compaction. For placement … |
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(Image: Installation of a reinforced concrete pipe on a concrete base in accordance with) After the placement of the lower bedding (concrete slab), the pipe is first placed on wedges and then the upper bedding layer is cast. This "concreting in two phases" is practiced in order to ensure a uniform embedment. Direct “placement" of the pipe on a concrete slab followed by concreting of the pipe haunch can lead to a linear bearing! Important: The wedges … |
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In the structural calculation of the pipe, the pipe bedding is defined by the "placement method" and the "bedding angle" [ATVA127].
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The bedding type is determined as part of the planning process. The default bedding should be type 1. (Table: Bedding and Placement type allocation as per DIN EN 1610 and ATV-DVWK-A 127) |
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