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Why is the bedding so important? The quality of the bedding substantially affects the carrying capacity, serviceability, reliability, and the intended service life of the installed pipes, along with the settling behaviour of the soil. By the placement of bedding the following points should be considered:
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For concrete pipes, there are four installation types as per [[American Concrete Pipe Association Recommended Standard Installations]], which provide an optimum range of soil-pipe interaction characteristics. These four types of installations vary with the type of material (based on soil characteristics) and level of compaction, and the material utilized in constructing the four principal zones surrounding the lower half of the pipe (middle bedding, … |
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The image below presents the standard open cut installation of concrete pipes according to [[American Concrete Pipe Association Recommended Standard Installations]]. (Image: Standard trench installation according to ACPA) 1 - Clearance between pipe and trench wall shall be adequate to enable specific compaction, but not less than DO /6 2 - Outer bedding material and compaction each side, same requirements as haunch 3- Middle bedding loosely placed uncompacted … |
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Depending on the installation type for the concrete pipe, there are different bedding thicknesses and compaction requirements for the bedding area. The table below presents the [[American Concrete Pipe Association Recommended Standard Installations]]soil and minimum compaction requirements. (Table: Soil and minimum compaction requirement corresponding to installation type as per ACPA Standard Installation) |
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Bedding factors are needed to relate the in-place supportive strength to the more severe plant test strength in cases where the pipe strength used in the design has been determined by plant testing. By definition, the bedding factor is the ratio of the strength of the pipe under the installed condition of loading and bedding to the strength of the pipe in the plant test [[Yoo,Parker&Kang2005]] Bf=MTEST / MFIELD Where: Bf = bedding factor MTEST = maximum … |
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The bedding factors, as they relate to the standard installation types and pipe diameter, are presented below. (Table: Bedding factors, embankment conditions as per ACPA) |
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The following table presents the bedding types A, B, C and D as specified in the "Concrete and Box Culverts Installation" Guideline by [American Concrete Pipe Association (2017)]. (Table: Bedding types for concrete pipe installation using the open cut method as specified by ACPA) |
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The images below present embankment bedding class A for circular concrete pipe (both in inches and millimeters). (Image: Embankment bedding circular pipe (inches) according to [ACPA] [Image: visaplan GmbH] – Class A, concrete cradle) (Image: Embankment bedding circular pipe (millimeters) according to [ACPA] [Image: visaplan GmbH] – Class A, concrete cradle) |
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The images below present embankment bedding class B for circular concrete pipe (both in inches and millimeters). (Image: Embankment bedding circular pipe (inches) according to [ACPA] [Image: visaplan GmbH] – Class B, shaped subgrade with granular foundation and granular foundation) (Image: Embankment bedding circular pipe (millimeters) according to [ACPA] [Image: visaplan GmbH] – Class B, shaped subgrade with granular foundation and granular foundation) |
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The images below present embankment bedding class C for circular concrete pipe (both in inches and millimeters). (Image: Embankment bedding circular pipe (inches) according to [ACPA] [Image: visaplan GmbH] – Class C, granular foundation) (Image: Embankment bedding circular pipe (millimeters) according to [ACPA] [Image: visaplan GmbH] – Class C, granular foundation) |
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The images below present embankment bedding class D for circular concrete pipe (both in inches and millimeters). (Image: Embankment bedding circular pipe (inches) according to [ACPA] [Image: visaplan GmbH] – Class D, flat subgrade) (Image: Embankment bedding circular pipe (millimeters) according to [ACPA] [Image: visaplan GmbH] – Class D, flat subgrade) |
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The images below present trench beddings for non-circular concrete pipe. (Image: Trench beddings (inches) horizontal elliptical pipe according to [ACPA] [Image: visaplan GmbH]) (Image: Trench beddings (inches) vertical elliptical pipe according to [ACPA] [Image: visaplan GmbH]) (Image: Trench beddings (inches) arch pipe according to [ACPA] [Image: visaplan GmbH]) |
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The following image presents the terminology used in PE pipe installation using the open cut method according to the [[Plastic Pipe Institute]]. (Image: Pipe trench for PE piping according to [Plastic Pipe Institute] [Image: visaplan GmbH]) 1- Final backfill |
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The Plastic Pipe Institute recommends that [[ASTM D2321–05]], [[AASHTO Section 30]] and [[CAN/CSA B182.11]] should be followed for good practices for the installation of thermoplastic pipes. Accordingly, any organization or agency, such as federal, state, county and city, have the task to determine their own set of governing standards applicable to the installation of HDPE pipes. Bedding is required to establish line and grade and to provide firm, … |
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Class IA materials should not be used where groundwater flow is anticipated unless a geotextile trench wrap is used to prevent soil migration. Class III materials are suitable when moisture content is controlled [[Plastic Pipe Institute]]. To equalize load distributions along the invert of the pipe, 4 in (0.1 m) of bedding should be placed and compacted on the foundation [[Plastic Pipe Institute]]. Generally, the bedding equal to one-third the pipe … |
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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 According to [[ASTM D2321–05]], the soil types applied in foundation can be identically suitable in other processes of embedment. In pipe bedding process, soil IA, IB, II, and III are installed and compacted in 6 in maximum layers. Level final grade by hand. Minimum depth is 4 in (6 in in rock cuts). Soil IV is only suitable in dry trench conditions and other parameters are identical with the above. Please refer back to page 34 for an overview of suitable … |
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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 Pipe bedding must be level throughout the pipe’s foundation and the material shall be placed and consolidated under the pipe, avoiding both vertical and lateral displacement [[HOBAS CCFRPM Guide]]. In the case of saturated soil with groundwater, the bedding material mist be free of fines. The trench shall be refilled and backfilled in 12 in (30 cm) layers. Each layer must be compacted separately. The pipes must be stable and proper compaction achieved. … |
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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 For proper installation of Centrifugally Cast Fiberglass Reinforced Polymer Mortar (CCFRPM) pipe, bell holes have to be provided at each joint for proper joint assembly and alignment. If the trench bottom is excavated below grade, it should be backfilled to grade and compacted as required to provide firm pipe support [[HOBAS CCFRPM Guide]]. The image on the right presents the correct vs. incorrect installation of bell holes. Special care must be taken … |
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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 (Image: Glass fibre reinforced plastic pipe (GRP pipe)) The minimum bedding thickness for glassfiber reinforced pipes (GRP) is given by [[ATV-DVWK-A 127]] standard, and must be at least 0.1 x Pipe OD, or at least 6 in (15 cm). If the soil is soft or not load bearing, another 6 in (15 cm) of the bedding has to be replaced with soils in groups G1 or G2. Requirements for bedding material:
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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 (Image: Attention!) Bedding for ductile iron pipe depends on its laying condition, as per [[ANSI/AWWA C150/A21.50]] [[DIPRA Installation Guide]]. More information about DIP installation will be presented in later sections. All soil compaction must follow [[AASHTO T99]]. |
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According to an extensive laboratory and field research conducted by the National Clay Pipe Institute, documented in the [[VCP Engineering Manual]], an ideal bedding system prevents pipe movement, which was found to be the leading cause of structural problems. Not all bedding materials provide the same longitudinal and circumferential pipe support. The following table presents the allowable bedding material and initial backfill per bedding class for … |
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(Image: Vitrified clay pipes, class D bedding according to [NCPI] [Image: visaplan GmbH] – Load factor = 1.1) When using Class D bedding, the pipe is placed on a firm and unyielding trench bottom with bell holes provided. The bottom of the entire pipe barrel will have a continuous and unifrom bearing support. The initial backfill can be either Class I, II, III or IV soil. The maximum particle size of the initiall backfill material shall be 1 in [[VCP … |
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