B405 - PIPE SUBDRAINS - OPSS 405

Transcription

1 B OPSS GENERAL Subdrains are small diameter pipes, perforated or non-perforated, which are placed for the purpose of collecting sub-surface water and conveying it to a proper outlet. Guidelines on the engineering principles and practices for the detail design of subdrainage are contained in MTO Drainage Management Manual 1997 Edition Types and Sizes of Subdrains Subdrain pipes are produced from corrugated steel (CSP) or plastic (polyethylene and polyvinyl chloride). Perforations are either small holes (CSP) or small slots (plastic pipes). Perforated plastic subdrain pipes may be factory-wrapped with geotextile of a specific type. Perforated plastic pipe subdrains are also available from the manufacturer without geotextile wrapping. Subdrains are produced in 100 and 150 mm diameters REFERENCES MTO Drainage Management Manual (1997) Geotechnical Design Report project specific TENDER ITEMS Pipe Subdrains Closed-Circuit Television Inspection (Variation, metre, PQP) (Normal, metre, Non-PQP) The Pipe Subdrains tender item may contain a number of components of highway subdrains and field subdrains with differing requirements, depending on the applicable variables. Closed-Circuit Television Inspection is not required for new construction less than 1000 metres. December 2017 Page 1 of 6 CDED B405

2 405.4 SPECIFICATIONS Details of the construction of pipe subdrains are contained in OPSS SPECIAL PROVISIONS The designer should refer to Standard Special Provisions of the CDED Manual to review the special provisions applicable to these tender items STANDARD DRAWINGS Details of subdrain installation are contained in the 200 series for grading, 800 series for sewers, and 3000 series for bridge structures of the OPSD manual DESIGN Pipe Selection Unless otherwise specified there is no restriction as to pipe material and type of installation to be used on a contract. The specification gives the Contractor the option of pipe material. When significant subdrainage flow is expected (e.g. high water table) 150 mm pipe plastic subdrains are recommended. Otherwise 100 mm pipe plastic subdrains are used. The minimum CSP subdrain size manufactured is 150 mm and these are placed only when recommended by the Regional Geotechnical Section. Subdrain trenches shall be designed to allow the pipe subdrain to sit on a minimum of 50 mm pipe bedding as specified in the specification. The recommended pipe size, geotextile type (class, Filtration Opening Size) wrap, and embedment material for subdrain trench shall be determined by the Regional Geotechnical Section. Clear stone (19mm) should be specified unless the pavement consists of Open Graded Drainage Layer, then open graded drainage layer aggregate shall be considered as subdrain and outlet embedment. Usually 19 mm clear stone should be specified for subdrain embedment, unless the construction of the road involves OGDL. Not all road structure consists of OGDL, but when the road structure has OGDL, then the designer can specify OGDL aggregate to replace 19 mm clear stone for the subdrain embedment (one less item for the contract). December 2017 Page 2 of 6 CDED B405

3 The subdrain trench and outlet shall be wrapped with geotextile unless otherwise specified by the Regional Geotechnical Section. Outlets Outlets are 2.5 m long, fitted with rodent gates, which are placed at the end of outlet pipes, regardless of the subdrain material Types of Installations Perforated subdrains are commonly installed at the following locations: as collector drains in the roadbed at the outer edges of the granular sub-base, or at the edges of pavement. as collector drains alongside edges of pavement in retrofit situations. as collector drains behind structures or retaining walls, in the lower part of the granular embedment. as collector drains in sewer trenches which are backfilled with granular material. This is usually accomplished by placing a 6 m section of perforated subdrain alongside the downstream end of a sewer pipe, which outlets into a drainage structure. This applies to the main sewer run. It may apply to branch sewers, if the main sewer is backfilled with native material. It however does not apply to short lateral sewer connections. as interceptor drains in the roadbed or in interceptor ditches. as drawdown drains in the roadbed or in side ditches. as field subdrains when restoring field drainage disturbed by highway construction. These drains may be ploughed-in. Non-perforated subdrains are used in conjunction with perforated subdrains in the following locations: generally, to carry water collected by perforated subdrain to an outlet. as outlets in continuous installations of roadbed subdrains or bridge structure subdrains. to connect perforated subdrain systems in roadbeds outletting into a drainage structure. as outlets with rodent gates at the termination of outlet pipes. in the vicinity of large trees, within 5 m of the trunk. December 2017 Page 3 of 6 CDED B405

4 Trench Reinstatement Where existing driving lanes must be cut to allow the construction of subdrains, the affected roadbed must be rebuilt to acceptable standards to maintain the continuity of the pavement. This is particularly important where there is to be no resurfacing of the highway. Trench reinstatement is not often done. When done, it is to address a subgrade drainage problem, independently of other work. Most work involving pipe subdrains involves some grading COMPUTATION Pipe Subdrains is a Plan Quantity Payment item. Closed-Circuit Television Inspection is not a Plan Quantity Payment item Source of Information The main sources of information for the computation of the Pipe Subdrains tender item are field note books, plans, contour plans, profiles, standard cross-sections and the Pavement Design Report Method of Calculation For the Pipe Subdrains tender item, each combination of pipe diameter, pipe material, excavation and backfill requires individual length calculation. These lengths are calculated/measured from plans, horizontally, from end to end of the pipe, including outlets; or from end of pipe to the centre of the adjacent drainage structure to which the pipe is connected. The unit of measurement is the metre. The Closed-Circuit Television Inspection tender item is measured based on the linear metres of subdrains, outlet pipes and outlets that are inspected by Closed- Circuit Television (CCTV) Inspection. CCTV Inspection shall be based on random sampling to include 5% of the entire length of the subdrain system and 100% of all outlet pipes DOCUMENTATION Pipe Subdrains Drawings Subdrains, including the direction of flow, are to be symbolized on the contract drawings in accordance with the appropriate 100 series drawing of the OPSD Manual and MTO Drawings. Include grade and show alignment of the trench excavation. December 2017 Page 4 of 6 CDED B405

5 A typical section is usually provided due to the number of variables involved. Subdrains on a typical section shall be labelled "Pipe Subdrain" not CSP subdrain or plastic subdrain unless these are specifically required. Include the following details on the typical section, as applicable: Pipe diameter, metal thickness, corrugation profile, and coating requirements of corrugated steel pipe. Pipe diameter, type, and stiffness requirements of polyethylene and polyvinyl chloride pipe products. Wrapping of the subdrain pipe with a knitted sock geotextile The width (cross-section) of trench excavation. Bedding depth. Type, Class, Filtration Opening Size (FOS) and installation details of geotextile trench wrap, if required. Open graded drainage layer aggregate or clear stone type for embedment of subdrain and outlet pipes. Where Trench Reinstatement is used, a typical section, labelled as "trench reinstatement", must be shown on the contract plans. The drawing should show cross-section dimensions and refer to the applicable standard drawings for bedding and backfill up to subgrade. Above subgrade, the drawing should specify the types and depths of granular and pavement courses necessary to achieve roadbed integrity. Quantity Sheets Each length of pipe subdrain is entered in one line in the Quantities - Miscellaneous 1 sheet. Start and end chainages are provided. The offset, left or right, is stated in the location and position column. Pipe Subdrains is a variation tender item that has a number of variables, as shown in the bullet list above. Multiple combinations of variables apply to each pipe subdrain installation. Such variables may be addressed in the typical sections. Column headings in the Quantities - Miscellaneous 1 sheet will address these variables. Each column will include the title: pipe subdrains followed by the applicable variations. Each length of pipe subdrain is entered in the column with the appropriate column heading. If there are too many different combinations of variables to be accommodated within the typical section(s) or Quantities - Miscellaneous 1 sheet, a Non-standard Special Provision may be required to address one or more of the variables. December 2017 Page 5 of 6 CDED B405

6 Non-Standard Special Provisions A non-standard special provision is required if pipe bedding is not required. When trench reinstatement is provided, a non-standard special provision may be required to modify OPSS to clarify that payment of all excavation and granular backfill is included in the Pipe Subdrains tender item. Where pavement is removed and/or the excavation area is subsequently repaved, any pavement cutting, removal and paving should be done using appropriate tender items Closed Circuit Television Inspection Quantity Sheets The Quantities - Miscellaneous 1 sheet is used to document CCTV Inspection. One column has the title Closed Circuit Television Inspection. The estimated total quantity of Closed Circuit Television Inspection (m) is entered in one line of the Quantities - Miscellaneous 1 sheet. If there is a need to allocate where locations of CCTV Inspection are to occur, multiple lines in the Quantities - Miscellaneous 1 sheet may be used, each with the appropriate start and end chainage. Entry Accuracy Stations are recorded in whole number metres. Offsets are shown to 0.1 m accuracy, as required. December 2017 Page 6 of 6 CDED B405