The procedures for trenching are based on sections of the Standard Specification for Civil Engineering. Construction, issued by the South African Bureau of Standards, Sections 1200DB, 1200L, 1200LB and 1200LD. Additional standards and recommendations are based on the Code of Practice SANS 0120, and Special Report No 35 'Pipe Laying Principles' published by HMSO to British Code of Practice and the National Building Regulations SANS 0400.

Specifications referred to below

No Reference No Reference No Reference
*1 1200DB C1.5.2 *2 1200DB C1.5.4 *3 1200DBC1.5.5
*4 1200DB C1.5.6.1 *5 1200DB C1.5.7.1 *6 1200DB CI.5.7.2
*7 1200LB C1.2.3 *8 1200LB C1.3.1 *9 1200LBC1.3
*10 1200LB C1.5.1.4 *11 1200LB C1.5.3 *12 DWG LB-2
*13 DWG LB-3 *14 1200 LD C1.3.2 *15 0120 CI.4
*16 0120 C1.5 *17 HMSO 35.6 18 SANS 0400
        19 SANS 0252 (2)


Pipe trenches shall be excavated to a depth suitable for the provision of adequate cover over the crown of the pipe, and to a specified or allowable width (*1).
The sides of trenches shall be as near vertical as possible for a height of at least the full diameter of the pipe, plus the specified depth of selected fill blanket over the pipe (*2).
Trench bottom: Material unsuitable for the bottom of the trench shall be excavated. The trench must be refilled with selected material and compacted (*3).
It is important that the trench is not opened too far in advance of the pipe laying operation. Pipes must be backfilled immediately after laying, with the joints left open for testing. It is recommended that the depth of cover, from the top of the pipe to the ground surface, be not less than 0.9m for sewers and 0.3m for drains.


Bedding and fill shall be selected granular material. The trench bed must be free of all stone or hard projections which are likely to cause damage to the pipe (*7 and *9).

Backfill Material

Selected fill material shall be used and shall be free of vegetation, lumps or stones or any other foreign particles of diameter exceeding 30mm.

Bedding Cradle

PVC-U pipe shall be supported on a continuous bed of selected granular material of compacted depth of at least 100 mm, and covering the full width of the trench (*11 and *12).

  • Selected granular material shall be material of a granular, non-cohesive nature, graded between 0.6 mm and 19 mm, free draining and the specified compactability (*8).
  • Compaction density for bedding cradle shall be 90% modified AASHTO (* 10).
  • Additional selected granular material shall be placed around the pipe in layers of approximately 100 mm (*13) and compacted to the specified density to a height of 100 mm above the crown of the pipe.

Fill Blanket

The fill blanket shall be the specified density (90% modified AASHTO) up to a depth of at least 300 mm above the crown of the pipe (*10 and *11). Particular care should be taken at all times to prevent damage, deflection or displacement of the pipeline.

Minimum cover over sewer and drains

Design the sewer invert level to provide a minimum crown depth cover over the top of the pipeline of 900mm for sewers and 300mm for drains. Calculate the expected traffic loads on sewers and drains where they run under roads or sidewalks, and, if necessary, increase the minimum cover in such areas. (See System Design)


Backfilling of pipe trenches shall commence after the pipe has been laid and firmly bedded in the bedding cradle, and the selected fill blanket placed and compacted as specified. (*4). Note: Pipe must be backfilled immediately after laying, leaving the joints exposed for testing. The pipeline must be laid directly on the prepared bedding in the trench, and any temporary supports, bricks or other foreign hard bodies must be removed.


Backfilling shall be in layers not exceeding 300 mm (after compaction) and the material compacted to 90% modified AASHTO density (*5). In areas of road traffic loads, trenches shall be backfilled in layers not exceeding 150 mm (after compaction) and the material compacted to 93% modified AASHTO density (cohesive soils) and to 98% in the case of non-cohesive soils (*6).

Note: Concrete encasing of horizontal uPVC pipelines is not recommended, as it converts a flexible pipeline into a long, unreinforced concrete beam of negligible strength, likely to fracture with minor ground movement (*15).
Under concrete slabs or raft foundations, a minimum compacted cushion of 75 mm fill between the crown of the pipe and soffit of the slab should be provided. Where a pipe passes through a ground beam or footing, a lintel, relieving arch, or similar device, should be used to provide a minimum of 50 mm clearance (* 17).

Maximum gradients and anchor blocks

Grade the sewer to follow the slope of the ground as far as is practical. Where slopes greater than 1 in 10 are required, provide 20MPa concrete anchor blocks that are at least 300mm wide and that are embedded into the sides and bottom of the trench to a depth of 150mm. Avoid sharp transitions at the bottom of steep slopes.

Minimum gradients

The minimum permissible full bore velocity, normally 0.9m/s, determines the minimum gradient. In exceptional circumstances only, a minimum velocity of 0.6m/s may be used.

Rule of thumb test for suitability of soil as a backfill material.


Make a representave sample by quartering
Step 2
Take a 250mm length of 160mm diameter pipe. Fill it loosely with sample
Lift pipe off loose filling
Step 4
Tamp filling back into pipe about 60mm at a time using a metal rammer with 37 mm diameter head. Tamp until no further compaction can be obtained.


if X = 25mm or less - the soil is suitable
if X = 26mm to 75mm - the material can be used only with extra care in compacting backfill, but not in wet conditions.
if X = 76mm or over - the material is unsuitable.



Cut the pipe square with a cross cut saw or angle grinder depending on the pipe size. Clean away swarf. The pipe end must be chamfered again to 15° to ensure easy insertion when making a joint.

Cleaning the seal

It is important to ensure that the seal is free of grit and mud before making the joint. Pipe ends are often accidentally dipped into the sand.


DPI Plastics has a liquid lubricant and a jelly-like lubricant known as gel. Both products are designed for lubricating pipe seals. In order to make a leak-free joint effortlessly, use liberal amounts of lubricant, but avoid getting it into the seal housing. Ensure seal and pipe ends are free of dirt.

Depth of entry

Unlike a pressure pipe, no depth of entry mark is provided. Insert the pipe fully to avoid hang-up and possible blockages.


It is important that the pipe ends and sockets are aligned and free of burrs, otherwise insertion into the seal ring will be difficult. Insert the pipe into the socket fully. For protection of the pipe ends use a lever against a wooden block.


Flexible rubber ring joints are available for all types of pipe and should be used in preference to rigid joints, allowing the pipeline to flex in the event of soil movements and also allowing for thermal change.


The Kimberley Socket

The Kimberley Socket is used to make repairs to pipework or to insert new fittings in the line.


1. Cut and remove the portion of the pipe which is to be replaced.
  • Chamfer and remove burrs.
  • Prepare the replacement pipe or fitting.
2. Lubricate both seal rings of the Kimberley Socket and locate the fitting on the existing pipe.
3. Fit the replacement unit into position.

4. Slide the Kimberley Socket over the joint between the new and existing pipe.

To insert a socketed fitting, proceed as above, but first fit a length of pipe into each socket of the fitting and position it between two Kimberley Sockets as before.


Snap-off seal ring

Some Durodrain fittings have removable snap-off seal housings that hold the rubber seal in place in both 110 mm and 160 mm fittings. This allows the fitting to be dismantled by simply inserting a screwdriver at one of the three indicator triangles and prising the ring off.

Reasons for dismantling a fitting:
  • It allows the pipe and fitting to be separated with ease when working in narrow trenches.
  • Replacing a damaged seal ring or rubber seal.


If the drainage system is designed and laid correctly, rodding is seldom needed. (If incorrect procedures and / or equipment are used, rodding may cause damage — irrespective of what the drain is made of). It is strongly recommended that a drain cleaning expert is consulted for advice on the correct type of equipment to use.

It is imperative that one ensures that the rubber seal ring and pipe are well cleaned before making a connection. The major reason for rodding is caused by root ingress which can be avoided if rubber seal rings are not dislodged or damaged during installation:

  • ensure rubber seal ring and pipe are well cleaned before making a joint.
  • correct amount of lubrication must be used.


Water jetting is becoming increasingly popular as a method for cleaning a maintaining sewers and drains. This method is suitable for use on PVC-U pipe systems.
DPI Plastics successfully conducted a series of tests under the auspices of the Structured Wall Pipe Association of South Africa. The United Kingdom based Water Research Council's acceptance testing methods were adopted as a pipe materia1 selection criteria suited for installation where water jetting is to be carried out. DURODRAIN Solid Wall pipe systems meet the test criteria which is far more onerous than operating conditions. The equipment manufacturers provide instructions for correct cleaning methods that will prevent unnecessary accidents to the operations and the sewer system.


Air testing (Manometer test) in sewers and drains is the accepted method that has been adopted by the industry as the most effective means of establishing acceptance by the respective authorities. Water testing is an easier method of finding leaks, but water is not always available and generally is too costly an exercise.

SANS 1200 describes the "Test and Acceptance/Rejection Criteria".

Equipment required:

  • An approved Manometer in a leak free condition.
  • Testing plugs in a leak free condition (ensure that the rubber seals are not perished and that the end caps are sealed and not cracked).
  • Stopwatch for recording time.
  • Bottle of soapy water to check for air leaks.
  • Large bucket.
  • Small funnel for filling Manometer tube.

Useful tip:

Test line at short intervals to simplify the locating of possible leaks. Allocate responsibility of testing to a crew. Their familiarity with the equipment will save time and effort.


  • Check all equipment for leaks.
  • Ensure that the section of pipeline to be tested has been sealed off at all branches and that all access openings are secure.
  • Insert testing plugs and secure.
  • Adjust the water level in the Manometer to zero on the scale (by adding water slowly).
  • Open the valve on the Manometer and pump until a reading of 400mm is reached (this reading equals a pressure of 4.00kPa). 400mm has been selected as it is easier to read than 375mm (3.75kPa) referred to in the specification.
  • Close the valve and allow the water column to settle for two minutes. (There might be a marginal drop in pressure). Should it not stabilize, check the connections on the Manometer and plugs for leaks by pouring soapy water over them. Should there be any leaks, these must be repaired before proceeding with the test.
  • Open the valve and adjust the pressure to a reading of 250mm (2.50kPa) and start recording time. The pressure is permitted to drop to a reading of 125mm (1.25kPa) and the time taken to drop to this level should be no less than the time stated in the table below.

FROM 250mm (2.50kPa) TO 125 mm
(1.25kPa) IN MINUTES
110 2
160 3
200 4
250 4.5
315 6
355 7.5
400 8
450 9
500 10




Pipes and fittings manufactured in PVC-U are strong, durable, light weight and easy to handle. In common with most construction materials, they should nevertheless not be handled carelessly, as this may cause damage. Pipe should not be dropped or dragged along the ground.


Pipes should be stored on level, flat ground, free of stones or sharp protrusions.
Alternatively, they may be stored on timber supports of at least 75 mm width placed 1.5 metres apart with side supports.
The height of pipe stacks should not exceed 1.5 metres. All pipe stacks and stored fittings should be covered to avoid prolonged exposure to direct sunlight. Where the pipes are fitted with an integral socket, they should be stacked with sockets protruding at alternate ends.


A flat-bodied vehicle is ideal for transporting pipes. Pipes with integral sockets should be loaded and spaced so that sockets protrude at alternate ends. When a mixed load of pipes (i.e. varying diameters) is to be transported, the larger pipes should be placed at the bottom. Pipes should not overhang the vehicle by more than 1 metre.

Durodrain Sewer and Drain Codes of Practice

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