Alcorr Double Wall Corrugated (DWC) Polyethylene (PE) Piping System for Gravity Flow (Non-Pressure) Applications — Drainage, Sewerage & Cross-Drainage
This manual provides information on handling, jointing and installation of Alcorr Double Wall Corrugated (DWC) Polyethylene (PE) piping systems — henceforth referred to as DWC PE Piping System — for non-pressure applications in drainage, sewerage and cross-drainage (pipe culvert) applications.
The information contained in this manual is intended as a guide and should be used in adherence with national laws and standards, and other specifications dependent on site conditions. National safety regulations and guidelines must be followed during all phases of construction including foundation preparation, excavation, pipe transportation, handling, assembly and backfilling. These products are solely intended for the non-pressure (gravity) conveyance of water and waste water.
As part of the product marking system, the following information is generally marked on the body (outside) of the pipe:
The transportation of DWC PE pipes is considerably simpler compared to conventional rigid class pipes such as NP Concrete or Glazed Stone Ware (GSW), owing to their light weight and ease of handling. These pipes can be transported by road or rail, and can also be carried manually in situations where no other transportation means are available — for instance, in marshy lands or underdeveloped rural areas.
Loading pipes onto transport vehicles in a telescopic (nested) manner is advised where the consignment permits — smaller diameter pipes are inserted into the next higher size, each pipe having a conventional length of 6 metres. Stacking can be done to a height of 2.5 metres.
This nesting modality can carry up to 10 times more pipes compared to conventional rigid pipe transport, reducing logistic and handling costs and substantially lowering the carbon footprint through fewer transportation trips. While loading, spigot and coupler ends should be arranged alternately in corresponding layers to avoid damage.
A flat, debris-free area away from construction traffic should be set aside for stacking and storage. Pipes can be unloaded by carefully rolling and lowering from the delivery truck manually or with simple tools and tackles. The pipe can then be lifted and carried manually using a sling arrangement at mid-points or third points, as shown in the figure below.
| ID (mm) | Approx. Weight (kg/m) | Handling Method |
|---|---|---|
| 75 | 0.59 | Labour (manual carry) |
| 100 | 0.87 | Labour (manual carry) |
| 135 | 1.3 | Labour (manual carry) |
| 150 | 1.6 | Labour (manual carry) |
| 170 | 1.75 | Labour (manual carry) |
| 200 | 2.4 | Labour (manual carry) |
| 250 | 4.0 | Labour (manual carry) |
| 300 | 5.0 | Labour (manual carry) |
| 400 | 8.9 | Labour (manual carry) |
| 500 | 11.8 | Sling at mid-point |
| 600 | 22.0 | Sling at third points |
| 800 | 36.0 | Sling at third points |
| 1000 | 57.0 | Sling at third points |
Pipes can be stockpiled for temporary storage in a flat, debris-free area away from construction traffic. Begin the stockpile with secured timbers spaced at third-point intervals across the width. For pipes with on-line couplers, alternate the direction of pipe lengths so couplers are not confronted with each other — up to three pipes can be placed before alternating direction. Subsequent layers should follow the same pattern, with fewer pipes per layer, giving the stockpile a truncated pyramidal shape.
The trench width should be no wider than what is required to safely place, compact and construct the 'Backfill Envelope' on the lower, upper and either side of the Alcorr piping system. Trench width depends on the backfill material, compaction method and pipe diameter. International guidelines establish trench widths as the greater of: outside diameter plus 0.4 m, or 1.25 times the outside diameter plus 0.3 m.
In most installations, overly wide trenches are not only costly to excavate and refill — they can detract from the structural integrity of the PE Pipe / 'Backfill Envelope' / 'Native' Soil system. Undisturbed native soils contribute significantly to structural integrity when trenches are kept relatively narrow.
| Pipe Internal Dia (mm) | Trench Width (m) |
|---|---|
| 75 | 0.60 |
| 100 | 0.60 |
| 135 | 0.60 |
| 150 | 0.60 |
| 170 | 0.60 |
| 200 | 0.60 |
| 250 | 0.70 |
| 300 | 0.75 |
| 400 | 0.90 |
| 500 | 1.10 |
| 600 | 1.20 |
| 800 | 1.30 |
| 1000 | 1.80 |
Excavated spoils shall not be deposited in the near proximity of the trench to prevent collapse of sides. Trench sides shall be supported by shoring or MS sheet piling where necessary. DWC PE Pipes may be laid at very wide, smooth curvatures without transitional manholes, owing to their inherent flexible properties.
Protective shoring works shall be strong enough to prevent caving of trench walls or subsidence of adjacent areas. Simple shoring shall comprise 38–50 mm thick and 30 cm wide timber planks set vertically at close intervals and firmly strutted at requisite horizontal layers. The topmost cross-strut layer shall extend beyond the shoring framework to rest on adjacent native soil for adequate protection.
In non-cohesive soils with high groundwater tables, continuous interlocking M.S. sheet piling may be necessary to prevent excessive soil movement due to groundwater percolation. Such sheet piling shall extend sufficiently below trench bottom unless the lower soil strata are adequately cohesive.
When M.S. Sheet Piling is used, the recommended construction sequence is:
Underground public and private utility services exposed during excavation shall be effectively supported under the guidance of the service owners.
Sewer installation trenches shall be adequately free from water during pipe placement at proper gradient until the pipe is integrated through joint assembly with the already-laid segment. Pumped water shall be continuously disposed of in a nearby drainage system or to the completed downstream portion of the sewer line.
A sound installation begins with a stable foundation. The trench bottom should be slightly over-excavated to allow for bedding material and should be free of large stones, soil lumps or debris. Over- or under-excavation may be required to remove rock outcroppings, muck or other unsuitable materials.
The light weight of DWC PE pipe makes it desirable for its structural integrity, hydraulic efficiency and ease of handling — but this same characteristic makes thermoplastic pipes prone to flotation. When the uplift on a pipe exceeds the downward force of self-weight and overburden load, the system will rise or heave. Where flotation is a possibility, proper installation and/or anchoring of the pipe are imperative.
| Nominal Diameter (mm) | Nominal OD (mm) | Weight Wpipe (kg/m) |
|---|---|---|
| 135 | 160 | 1.30 |
| 150 | 180 | 1.60 |
| 170 | 200 | 1.75 |
| 200 | 238 | 2.40 |
| 250 | 295 | 4.00 |
| 300 | 358 | 5.00 |
| 400 | 480 | 8.90 |
| 600 | 715 | 22.00 |
| 800 | 950 | 36.00 |
| 1000 | 1200 | 57.00 |
| Nominal Diameter (mm) | Minimum Cover 'H' (mm) |
|---|---|
| 135 | 105 |
| 150 | 119 |
| 170 | 132 |
| 200 | 158 |
| 250 | 194 |
| 300 | 239 |
| 400 | 322 |
| 600 | 476 |
| 800 | 636 |
| 1000 | 803 |
When adequate soil cover is unavailable to prevent flotation, one of two anchorage methods may be used:
Precast concrete weight placed over the pipe crown and connected with straps.
Commercially available screw anchors with transverse strap maintain pipe embedment grade and alignment.
Due to the light weight and user-friendly push-fit jointing procedure (no welding at site is necessary), assembly at ground level and subsequent lowering of the assembled pipe segment — preferably from manhole to manhole — by manual means with simple tools and tackle is recommended. If site conditions do not permit this methodology, individual pipes should be lowered into the trench manually or with simple equipment depending on pipe size and trench conditions.
For Shallow Trenches: Place the pipe manually on the bedding portion of the 'Backfill Envelope' at the proper slope, using a sight rail and fixed tee to maintain line and grade.
For Deep Trenches with Timber Shoring/MS Sheet Piling:
Various push-fit jointing methods are used, including the use of on-line or off-line regular couplers over spigots. The molded on-line coupler or separately manufactured off-line coupler has an internal surface with profiles/ribs for insertion onto the non-coupler end of the next pipe.
On the first valley segment of the corrugated pipe end (destined to receive the coupler end), one rubber sealing ring shall be fitted tightly, over which the coupler is rolled on manually with simple indigenous tools and tackles. This provides sufficient gripping lock and a leak-proof joint.
The same jointing system is used for fabricated accessories and moulded fittings such as Tees, Bends, Elbows and Reducer end-caps.
The capability to install pipe in a slightly curved line may allow a sewerage or drainage system to follow bends along roads or avoid existing utility lines without fittings or manholes. Curvature, if imperative, shall be established only at the joint location. Depending on the jointing system, a few degrees of angular misalignment can be obtained while maintaining joint integrity. If the required misalignment is insufficient, the pipe can be cut into shorter sections and rejoined, or a fitting can be used.
DWC PE pipe is easy to cut with a hand saw or similar tool. For pipe to be connected to a manhole or catch basin, the cut should be made in the corrugation valley. If pipe is cut to rejoin to another length, an off-line coupler and rubber sealing ring must be used to ensure optimal joint performance.
The 'Backfill Envelope' encompasses the bedding, haunching and remaining backfill zones surrounding the pipe. It is the critical structural element that distributes loads and maintains pipe geometry throughout the service life of the installation.
Bedding is the lower portion of the 'Backfill Envelope', placed directly on the foundation. It should provide uniform, firm support for the pipe and maintain pipe grade. Minimum bedding depth: 100 mm for pipes DN 400 and below; 150 mm for pipes above DN 400. Coupler holes (depressions in the bedding) are required to accommodate coupler connections without creating stress points.
The haunching area provides the majority of resistance against soil overburden and live (traffic) loadings. Backfill should be shovelled and knifed under the pipe, taking care to fill all voids. Compaction should be conducted uniformly on each side of the pipe in layers or lifts without disturbing pipe alignment. 'Backfill Envelope' construction continues from bedding level up to the pipe springline.
This area extends from the pipe springline to a minimum of 0.15 m above the pipe crown. It should be placed and compacted in layers. Mechanical compactors must not be applied directly on the pipe.
Final backfill extends from the top of the 'Backfill Envelope' to the bottom of the proposed road crust. Total minimum cover in trafficked installations: 0.45 m for pipe sizes 450 mm and below; one pipe ID for sizes above 450 mm. For heavily trafficked roads requiring immediate restoration, a high-strength material and compaction level is necessary to prevent settlement. Screened native soils are often suitable for final backfill in non-critical installations.
Compaction must not alter pipe alignment. Two standard methods:
Heavy construction vehicles can impose unanticipated loads on pipe with less than 1 m of cover. The preferred solution is to route construction traffic around the pipe. If this is not possible, additional compacted soil should be mounded over the pipe to achieve at least 1 m of cover at the pipe crown.
Pipe installation, like any other engineered system, benefits from frequent inspections to ensure it is installed according to specification. Improperly installed flexible pipe can often be detected by simple visual inspection made soon after installation, before the pipe is put into service. Closed-circuit television (CCTV) can be used for pipes inaccessible due to small diameter or safety hazards.
The internationally adopted Structural Design Method for Corrugated Polyethylene Pipe limits the initial deflection (at conclusion of 'Backfill Envelope' construction and subsequent backfilling) to 8.0% of the base diameter. A visual or CCTV inspection is generally all that is required to confirm installation quality.
Even though the system is designed for non-pressure conditions, pipe joints may need to be watertight — particularly for sanitary sewers and storm sewers in environmentally sensitive areas. Testing is carried out at 2.5 m water head for a period based on the length and size of the conduit system.
Each section of DWC PE pipe sewer shall be tested for water tightness preferably between manholes.
Pipes can usually be handled manually. For very large sizes, padded straps and hoisting equipment are required. Never drop, drag or climb on stockpiled pipes. Maximum stack height: 2.0 m.
Place and compact in uniform layers on either side of the pipe. Extend at least 0.15 m above pipe crown. Never apply mechanical compaction equipment directly on the pipe.
Total minimum cover in trafficked installations: 0.45 m for DN ≤ 450 mm; one pipe ID for DN > 450 mm. Shoring or MS sheet piling required where specified.
Pipe is easily cut with ordinary tools. Cut in the corrugation valley for manhole connections. Contact the manufacturer for rejoining recommendations to ensure optimum joint performance.
Visual inspection or CCTV for inaccessible pipes. Maximum initial deflection: 8% of base diameter. Watertight systems require 2.5 m head pressure testing after installation.
Water level must remain constant for 72 hours after initial 30-minute stabilisation. Water make-up during any 10-minute window must not exceed 10% of the test section volume.