Laying Drainage System Pipes

Laying Drainage System Pipes

Posted By: Nyumba Imara Blog on 17th of October 2013

Drainage systems are a common encounter our everyday world of building and construction. Most often people think of drainage as a piping systems of underground structures used to convey liquids of one sort or another. To a layman, the concept of drainage system installation sounds as easy and straight forward as digging  a trench, laying the pipe in the trench and filling covering the trench. Inasmuch as this simplified perspective of pipeline construction may be appealing, it does not to address the engineering concepts that must be observed in any drainage system and the underground installation of a pipeline. Generally there are two objectives that must be achieved in any drainage system installation. The first is to provide an envelope of embedment to protect the pipe from mechanical damage that may be caused by impact or hard objects like cobbles and boulders in the soil and is second is to cushion and support the pipe against earth and live load pressures. Some pipes are designed carry more loads and require less support from the soil but when support is needed to protect the pipe embedment should be applied around the drainage pipes. The embedment material used must be well compacted so as to provide sufficient resistance to the weight that earth and live loads may impose on the pipes. The trench back-fill placed on top of the embedment material should also be compacted as compaction of trench back-fill immediately above the pipe facilitates the redistribution of some of the load away from the pipe and into the side-fill soil. Let’s now take a look at what the laying of a drainage system involves; Foundation In some soil condition it may be found that the trench bottom cannot provide a firm working platform for placement of the pipe bedding material. In such conditions foundation is required to provide a solid base on which the drainage pipes may rest undisturbed so as to maintain a constant flow of the liquids being conveyed through it. The pipe’s ability to support loads and resist deflection is determined by the quality of the embedment material and the quality of its placement. Laying of drainage foundation in the initial back-fill zone includes bedding, haunching, primary, and secondary zones. Bedding Bedding plays a crucial role in leveling out any irregularities and ensures uniform support along the length of the pipe. It also helps bringing the trench bottom to required grade. Haunching Hauching refers to back-fill under the lower half of the pipe. It helps in the distribution of the superimposed loadings. The nature of the haunching material and the quality of its placement are one of the most important factors in limiting the deformation of the drainage pipes. Primary Initial Back-fill This zone of back-fill provides the primary support against lateral pipe deformation. To ensure such support is available, this zone should extend from trench grade up to at least 75 percent of the pipe diameter. Under some conditions, such as when the pipe will be permanently below the ground water table, the primary initial back-fill should extend to at least 6 inches over the pipe. Secondary Initial Back-fill Secondary initial back-filling helps in the distribution of overhead loads and isolate the pipe from any adverse effects of the placement of the final back-fill. Final Back-fill Since the final back-fill is not an embedment material, its nature and quality of compaction has a lesser effect on the flexible pipe. However, arching and thus a load reduction on the pipe is promoted by a stiff back-fill. To avoid the possibility of impact or concentrated loadings on the pipe both during and after back-filling, the final back-fill should be free of large rocks, organic material and debris. The material and compaction requirements for the final back-fill should reflect sound construction practices and satisfy local ordinances and sidewalk, road building, or other applicable regulations.