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(Image: Pipe haunches for pipes with circular outer contour) Adequate compaction of the haunch area is decisive to achieve a long service life of the sewer pipe. Because of that, European Standards aim to ensure a working space for all pipes and types of installation, which allows sufficient compaction of the haunch and side fill. Therefore the calculation of the minimum trench width is independent of pipe material and installation type and just a … |
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Nov 23, 2019 What are the consequences of non-compliance? If the trench width is too narrow, proper compaction of the backfill material (bedding/pipe support) at the pipe haunch zone cannot be achieved. (Image: Pipe haunches for pipes with circular outer contour) (Image: Inadequate working space at the side of the pipe (no arrow)) (Image: Non-compliance with the minimum trench width - Compaction of the haunch zone and side fill not possible) (Image: Non-compliance … |
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Nov 23, 2019 (Image: Attention!) What are the consequences of non-compliance? A proper compaction of the side fill is impossible when the required minimum trench width is undercut. Static assumptions cannot be met in such a case. (Image: Inadequate working space at the side of the pipe – Proper compaction is impossible) |
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Nov 23, 2019 What are the consequences of non-compliance? Failure to comply with the minimum specified trench width leads to inadequate compaction of the bedding. This results in overloading of the pipe and cracking at the quarter points or in case of plastic pipes to deformation. (Image: Concrete pipe failure at the quarter points due to insufficient bedding compaction) (Image: Clay pipe failure due to insufficient bedding compaction) (Image: Clay pipe failure … |
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What has to be considered when selecting the trench width? The following details are to be taken into account in the selection of the trench width:
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Animation: Exercise Work safety - Minimum working distance [Animation: visaplan GmbH]. This interactive object is only visible in the online version of the module. |
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The base of the trench is the level onto which the sub base backfill material is placed. (Image: Trench base) (Image: Trench base) (Video: Loosening the trench base with an excavator bucket) Which excavator bucket is suitable for the trench base? Select the correct image by clicking on it. (Image: False excavator bucket) (Image: Correct excavator bucket) |
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The following rules and regulations are applicable in the United States of America (not an exhaustive list):
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The following rules and regulations are applicable in Europe:
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The embedment for standard trenches comprises of four zones: foundation, bedding, haunch, initial and final backfill [[ASTM D2774-12]]. The following image presents the terminology used in open cut installation of underground pipes. (Image: Installation terminology according to ASTM D 2774-12) 1 - Sloped wall (as required) 2 - Trench wall (native) 3 - Final backfill 4 - Initial backfill 5 - Pipe embedment 6 - Haunch zone 7 - Springline 8 - Bedding 9 - Bell … |
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Important: Drains and sewers must be leak-tight, operationally and structurally safe. If the structural stability is no longer given, the other requirements are usually not fulfilled either. As a matter of principle, structures, and thus also drains and sewers, must be designed and manufactured in such a way that they achieve their intended service life under the external and internal loads and stresses acting on them, with unrestricted serviceability. |
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Not all soils are suitable for use in the embedment zone. The following section presents in detail the types of soil that are plausible to use in embedment zones, according to both American and European standards. |
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The following materials are usually suitable for use in embedment:
If the excavated soil material meets … |
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What kind of soil is usually suitable for use in the embedment zone? Table 2 in [[ASTM D2321–05]] encompasses the recommendations for installation and use of soils for foundation, embedment and backfill. Generally speaking, materials in Class IVB and Class V are unsuitable as embedment materials. They may be used as final backfill as permitted by the engineer. (Table: Description of embedment material [ASTM D 2321-05]) |
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(Image: Cracks orginating at a point with reference to [Young84] [Image: S&P GmbH]) To prevent point loads, the maximum aggregate size of components in the embedment zone is defined as follows:
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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. The bedding layer must provide an even pressure distribution under the pipe, and support its entire length, in order to prevent damage due to point loading stresses. (Image: Crack formation in a clay pipe) (Image: Laser profile survey) (Image: Pipe cracking … |
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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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