6.9.1 Inspection and Testing of Drainage Works
(1) Drainage works should be inspected and tested in two stages; a) As the work proceeds, and
b) Immediately before the work is handed over upon completion.
(2) The work should be protected during all stages of construction and the entry of foreign matter into any part of the systems prevented.
(3) Testing sequence shall constitute the following: a) First stage testing
(i) Tests should be carried out to locate and remedy any defects in soundness that may exist at the time of construction.
(ii) Such test should take place immediately before the work is covered up so as to facilitate replacement of any faulty pipes or pipe fittings or to rectify any joint defect.
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(iii) Inspection of the pipeline shall reveal any defects in the support and bedding. b) Final testing:
(i) Testing and inspection should take place immediately before handover when all relevant work been complete.
(4) Pre-test procedures are as follows:
(a) Before any tests are applied, attention should be given to the safety of the operatives and other persons involved in the testing operation.
(b) It is essential that proper means of access should be provided to the area of work and the sides of any trench or excavation in which work is to be tested adequately supported and free from hazards.
Figure 6-9 Cross-section of typical underdrain
(c) All obstruction, debris and superfluous matter should be removed from sections of pipeline, inspection chambers, manholes, or similar underground chambers and they should be flushed out before testing.
(d) Before any tests are applied, a disc or ball-type profile testing device should be passed through all drains and private sewers between inspection chambers, manholes or other suitable points of access and through all accessible branch drains.
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(e) Water tightness: After laying drains and combined drains, including any necessary concrete or other haunching or surrounding and backfilling, all pipes up to 300 mm diameter should be capable of withstanding a final water test to a pressure equal to 1.5 m head of water measured above the invert at the head of the drain, or an air test ensuring that head of water on a manometer does not fall by more than 25 mm in a period of five minutes for a 100 mm water gauge test pressure and 12 mm for a 50 mm water gauge test pressure.
Where the drain is water tested using a stand pipe of the same diameter as the drain, the section of the drain should be filled and left to stand for two hours and topped up.
The leakage over thirty minutes should then be measured and should not be more than 0.05 litres for each metre run of drain for a 100 mm drain - a drop in water level of 6.4 mm/m, and not more than 0.08 litres for a 150 mm drain - a drop in water level of 4.5 mm/m.
To prevent damage to the drain, the head of water at the lower end of the section should not be more than 4 m and it may be necessary to test a drain in several sections.
(5) Soundness tests for gravity drains constitute the following: (a) water test: Drains shall be tested as follows:
(i) A water test shall be applied to every drain and to any section of an existing drain that has been repaired
(ii) The head or water shall be at least 1.5m at the high end of the drainline and not more than 4.0m at the lower end.
(iii) The test shall be applied by Sealing all openings except the top of the section of the drain to be tested, filling the drain with water to the highest level in that section; and maintaining the water at this level for a period of 2.0hrs, topping up as necessary.
(iv) The test is considered to be successful if the quantity of make-up water (rate of water loss) measured after 2.0hrs does not exceed 1.0l/h per meter diameter linear meter run of pipe. For various pipe diameters, this rate of loss over a 30.omin period may be expressed as follows:
DN100 pipe- 0.05 litres per meter run DN150 “ - 0.08 “ “ DN225 “ - 0.12 “ “ DN300 “ - 0.15 “ “
(b) Interpretation of results: A change in water level in the test apparatus could be due to one or more of the following causes, which shall be rectified or appropriate allowances made for in the testing procedure:
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(ii) Exposure of pipes in direct sunlight, or changes of ambient temperature when pipes are laid.
(iii) Trapped air,
(iv) Leakage past expanding plugs or bag stoppers.
(c) Air test: an air test may be applied to the completed work, either in its entirety or in sections, in accordance with the following procedure:
(i) The air pressure test shall consist of applying a pressure of 3.0m water head to the drain and holding this pressure for 3.0min to allow the air temperature to stabilized.
(ii) The air supply shall then be shut off and the time taken for the pressure in the pipe to drop from 2.5m to 2.0m head of water shall be measured.
(iii) The drain is considered to have passed the test if the time taken is greater than 90.os for pipes of size DN225 or smaller, or 180.0s for pipes of sizes DN300 and DN375.
(6) Soundness tests for ancillary work:
(a) The design and construction of ancillary work such as inspection chambers, manholes, oil and grease separators, sumps, septic tanks, cesspools and similar underground structures should ensure a high level of resistance to water penetration, both inwards and outwards.
(b) Where construction work has been effectively carried out, visual inspection may be sufficient for acceptance without testing.
(c) Inspection should always be made to reveal any possible weaknesses in the structure and particular attention should be paid to the following:
(d) Water test
(i) All outlets, inlets and other connection points of the chambers or structures should be fitted with plugs and filled with clean water up to the underside of the covers.
(ii) The water is allowed to stand for up to 8.0hrs for absorption topping up the level as necessary.
(iii) The criterion for acceptance (at this stage) should be that no appreciable flow of water penetrate the structures.
(iv) Where water can be observed issuing from the outside face of the structures at an identifiable point or points, such leakage should be stopped.
(v) The external faces of a structure should not normally be backfilled or concrete surrounded before the test.
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6.9.2 Maintenance and Periodic Inspection
(1) Drainage systems should be inspected at regular intervals and, where necessary, thoroughly cleaned out at the same time. Any defects discovered should be made good. (2) The following operations should be carried out during the periodic cleaning of a drainage
system:
(a) Covers of inspection chambers and manholes should be removed and the sides, benching and channels cleaned.
(b) Main and branch drains should be cleaned and, afterwards, should be flushed with clean water. Any obstructions found should be removed and not flushed into system.
(c) Accumulated deposits in interceptors should be removed periodically.
(d) Covers of inspection chambers, manholes and interceptors should be replaced, bedded in suitable grease or other sealing material and/or bolted down as appropriate to the type. Missing bolts and broken items should be renewed.
(3) The drainage system should be cleaned, as appropriate, using one or more of the following methods:
(a) Rodding:
(i) Appropriate cleaning tools and techniques should be chosen to avoid damage to the pipework to be cleaned
(ii) It is important that correctly designed proprietary ends used on the rods.
(iii) Makeshift devices attached to the ends of rods should be avoided as they are not as effective as the correctly designed article and could become detached and create a blockage which would be difficult to remove. Furthermore, it is possible that such devices could cause damage to the pipeline.
(b) High pressure jetting techniques could be suitable for use with all currently available pipe materials and should also be considered.
(c) Shock waves could be induced and transmitted by water to the point of blockage, where the pipe is surcharged or can be filled with water from the blockage to a point where the shock wave is introduced.
6.9.3 Pipes, Fittings and Joints
Pipes, fittings and joints shall comply with the relevant Ethiopian Standards or equivalent and shall be acceptable upon the approval of the Building Official.
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