For example, smoother select fill dirt would be used as back-fill and there are no above-ground applications for Direct Burial PVC Conduit. Vinidex Pty.DB Direct Burial PVC Utility Duct InstallationĪlthough the direct burial installation for DB PVC Utility Duct is very much the same as it is for Schedule 40 and Schedule 80 PVC Pipe, there are some differences in back-fill requirements and performance capabilities.Standards Australia AS/NZS 2033 “Installation of polyethyene pipe systems”. Standards Australia AS/NZS 2032 “Installation of PVC pipe systems”.Standards Australia AS/NZS 2566.1 “Buried Flexible Pipelines Part 1: Structural Design” and Supplement 1: Commentary.Minimum spacing for conduits in multi-duct banks – 100-150 mm conduit Guidance is given for maximum concrete pour depth for classes of pipes in our Technical Note VX-TN-4F. Note that deep pours can generate enough pressure and heat to collapse a PVC duct. It is noteworthy that complete concrete encasement is quite common in critical locations, and this technique allows a lower stiffness pipe and closer spacing, within the constraints of the concrete depth and flowability. If these minimum cover heights cannot be met, additional protection of some form should be provided, eg., concrete slab or concrete encasement. Subject to construction equipment loadings Subject to vehicle loading, not in roadways Minimum cover over the top ducts should be in accordance with AS/NZS 2032 and AS/NZS 2033 recommendations, repeated here for reference: Again, lower quality surround material may be used with increased spacing and higher stiffness ducts, but this play off is unlikely to offer a more economical solution. Low fines sand is the most commonly chosen material. Single sized crushed gravel offers the best support, but infiltration over time of soil from above may have longer term undesirable consequences. The material used for surround of multiple ducts must be readily compatible and free flowing. Compaction should be carried out layer by layer, and spacer jigs used to maintain alignment. Whilst alignment may not be functionally critical, displacement in one direction will detract from the ability to compact on the other side. This requires somewhat more care than for single duct installations. The other obvious difficulty with multiple ducts is maintaining alignment during the compacting process. Spacers should be used to control depth of sand, removed before compaction and placement of the next layer. The height between each layer must be sufficient to enable a uniform bed to be achieved. The requirement will vary somewhat with particular circumstances and size of pipe, but 40 mm could be considered a minimum convenient gap for a 100 – 150 mm duct to allow access with a hand compacting tool. There must be sufficient space between the ducts to allow placement of surround material and its compaction. A preferred method is to use sub-duct inside a larger duct. If this type of installation is necessary, part compensation is possible using a stiffer pipe. Conduits installed in this way will distort, possibly quite severely. Clearly, ducts cannot be installed in contact with each other with any expectation of support all round. The requirements for support are no different for multiple ducts, but the practicalities of achieving it are somewhat more tricky. General guidance for the installation of PVC and PE pipes are given in AS/NZS 2032 2 and AS/NZS 2033 3 respectively. Proper support is obtained by the use good surround material and compaction practice.įor single pipes or conduits, the relationships between surround material properties, compaction levels, and pipe stiffness are well established and design procedures are covered by Australian Standard AS/NZS 2566.1 1. All flexible pipes, regardless of material, require adequate support from the surround material to control vertical deformation due to soil loading. This property enables them to accommodate strains from soil movements, expansion and contraction, seismic and other loadings that would rupture rigid pipes. This note provides guidance on preferred installation practice. It has been common practice for many years with PVC and PE Telecommunications and Electrical conduits to install multiple duct banks in a single trench. Installation of conduits in multi-duct banks (VX-TN-12G) Introduction
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