406 - PIPE SEWERS - MTC FORM 406

Transcription

1 MTC FORM 406 INDEX GENERAL Types of Pipe Pipe Strength, Rigid Pipes Polyethylene Pipe Strength - Rigid or Flexible Pipe Strength and Treatment, Flexible Pipes Selection of Type, Strength and Treatment of Sewers Tender Items Specifications Special Provisions Standard Drawings COMPUTATION Source of Information Method of Calculation Components of Pipe Sewers A - Earth Excavation for Sewers B - Sewer Bedding (a) Bedding for Rigid Pipe Sewers (b) Bedding for Flexible Pipe Sewers C - Sewer Backfill Work Related to Sewers (a) (b) (c) (d) (e) (f) Manholes, Catch Basins and Ditch Inlets Connection to Existing Sewers, Drains and Service Connections Pipe Culverts Headwalls Grating and End Finish Protection Schemes B406-1

2 406.3 DOCUMENTATION A - Pipe Sewers and End Section Treatments (a) Contract Drawings (b) Contract Documents B - Class, Profile Number, Corrugation, Gauge and Treatment C - Bedding and Backfill D - Earth Excavation E - Connections to Existing Sewers F - Headwalls G - Grating and End Finish H - Unwatering I - Protection Schemes J - Trench Reinstatement GENERAL Where drainage of a roadway system cannot be accomplished by open ditches and culverts due to restricted property limits or susceptibility of a terrain to erosion, a storm sewer system is required. A storm sewer system is a series of rigid or flexible conduits, designed to carry storm water and are connected to catch basins which collect the surface water and direct it through the conduits to outlets into a natural watercourse. The general layout, size, types of pipe and capacity of a proposed sewer system are established, based on acceptable drainage theory, by the designer. Pipe Sewer Material Pipe sewers may be designed using either corrugated or smooth inside wall material with consideration of the design objectives of the storm sewer. The types of pipe are: 1) Concrete Pipe (all sizes) 2) Corrugated Steel Pipe (all sizes) 3) Polyethylene Pipe (for sizes 18" (450 mm) up to and including 48" (1200 mm)). 4) Polyvinyl Chloride (PVC) Pipe. When corrugated inside wall is specified the Contractor may choose one of the following types: Corrugated Steel - corrugated inside and outside wall Polyethylene - corrugated inside and outside wall B406-2

3 When smooth inside wall is specified, the following types qualify: Concrete Polyvinyl Chloride (PVC) - smooth inside wall Polyethylene - smooth inside wall Corrugated Steel - smooth inside wall When choosing concrete or smooth inside wall pipe, a smaller diameter may be used since the flow characteristics are different. The strength of the rigid pipe for a given installation is determined by the diameter of the pipe, the type of pipe, the type of bedding to be used under the pipe and the height of fill to be placed over the pipe. Tables giving the above information are found in the Ontario Provincial Standard Drawings (OPSD). Pipe Strength and Treatment, Flexible Pipes Polyethylene, Polyvinyl Chloride (PVC) and Corrugated Steel (CSP). The strength of polyethylene and polyvinyl chloride pipe is designated by the stiffness factor. The strength for any given installation is determined by the diameter of the pipe, the trench width and the height of fill to be placed over the pipe. Tables giving the above information are found in the 800 series of Ontario Provincial Standard Drawings. When the trench width exceeds the width indicated under "Trench Condition" on the above standard, the wall thickness of the pipe must be selected from the "Wide Trench Condition". The strength of corrugated steel pipe is designated by a combination of gauge number, wall thickness and type of corrugation. The types of corrugation are 68mm x 13mm, 76mm x 25mm and 152mm x 51mm. When designing for corrugated steel pipe sewer it is also important that the treatment of the pipe be specified. The possible treatments are as follows: Plain Galvanized (PG) - which is used for all installations except in the conditions listed below. Paved Invert (PI) - which is used for installations subject to heavy erosive forces such as gravel, high velocities, etc. In highly corrosive areas such as muskeg or industrial wastes consideration should be given to increase the gauge of the CSP or to use polyethylene or polyvinyl chloride or concrete pipe. The strength of pipe required for a given installation of corrugated steel pipe is determined by the diameter of pipe, the type of bedding to be used under the pipe and the height of fill to be placed over the pipe. Tables giving the above information are found in the Ontario Provincial Standard Drawings (OPSD) B406-3

4 Selection of Type, Strength and Treatment of Sewers For all installations, whether rigid or flexible, the Contractor may select the class of concrete, the wall designation for polyethylene pipe or polyvinyl chloride (PVC) pipe and the gauge of corrugated steel pipe. The option of material selection by the contractor should only be allowed when the designer has ascertained that the functional requirements of the sewer design according to the Drainage Manual are met by all different material characteristics. If any material is found not to fulfil the requirements, the designers should delete that material from the list of options by modifying the appropriate special provision. In specific cases where the designer does not want to give the Contractor any options, he may do so by predetermining the type, class, wall designation and/or gauge on the appropriate Quantity Sheet. The Designer will always predetermine the treatment for corrugated steel pipe sewers and he will always indicate this treatment on the appropriate Quantity Sheet. The different design calculations should be retained as part of the design documentation. Tender Items "... mm Flexible Pipe Sewers" "...mm Rigid Pipe Sewers" Refer to the CPS Master Item list for actual items available. Separate tender items are required for individual pipe diameters. These tender items include the construction of the required storm sewer, excavation, granular bedding and the granular or native backfill required to backfill the sewer trench. Rock excavation for sewers combined with rock excavation for manholes is a separate tender item discussed in section B407-2 Specifications All information regarding the construction of pipe sewers is indicated in MTC Form 406. Special Provisions The Designer should refer to Chapter "E" of this manual to review the applicable special provisions. Standard Drawings The Designer should be familiar with the 800 Series of the Ontario Provincial Standard Drawings (OPSD) controlling the placing of pipe sewers. All excavation limits and B406-4

5 granular bedding and backfill limits shall be in accordance with the standards for the purpose of obtaining the estimated quantities COMPUTATION Pipe sewer items are Plan Quantity Payment items Source of Information The main sources of information for the computation of pipe sewer items are: (a) (b) (c) (d) Photogrammetric or survey plans to provide drainage areas, existing natural watercourses, soil types etc. Drainage Design Manual to provide drainage theory and practices, capacity, rainfall intensity, etc. Regional Geotechnical Office to determine the presence of rock on the contract and the soil types. Ontario Provincial Standards Drawings (OPSD) to provide trench widths, bedding types, treatment, strength, etc Method of Calculation The unit of measurement for pipe sewers is the metre. Measurement for the length of the sewer will be made along the invert of the sewer from centre to centre of the catch basins, and no deduction in length will be made for the catch basin. When designing a sewer system, the catch basins should be placed such that the length of sewer from centre to centre of the catch basins is in whole numbers. When the space is restricted, the metric design length of pipe sewers may be determined as the next larger 0.1 metre. If end sections per the Ontario Provincial Standard Drawings are to be installed on sewer outlets, they are to be added to the above design length without rounding. The Designer should keep in mind the following basic guidelines in laying out the sewer system: 1) Wherever possible, the invert elevation of a sewer pipe entering a catch basin should be slightly higher (30 mm) than the invert elevation of the pipe leaving the structure. 2) Culverts should never flow into a sewer system but the reverse is permitted. 3) The desirable depth of cover for sewers should be based on frost depth B406-5

6 4) The spacing of the catch basins is detailed in Section B407-1, "Manholes, Catch Basins and Ditch Inlets", such that the length of sewer may be calculated as described above Components of Pipe Sewers A. Earth Excavation for Sewers Earth excavation required to place pipe sewers is part of the cost for placing the pipe sewer. Excavated material may be used for embankment construction or used as native backfill to the excavated sewer trench as determined by the designer based on the recommendation of the Regional Geotechnical Section. Surplus or unsuitable excavation material should be incorporated in the design (refer to B206 of this manual). B. Sewer Bedding The selection of bedding will be the responsibility of the designer based on data and recommendations submitted by the Regional Materials and Testing Office at the request of Regional Planning and Design. The placing of the required bedding is part of the cost of placing the pipe sewers. When sewers are to be placed in areas of rock excavation or where an exceptionally large and complex system is to be constructed, the designer may request that soils borings be taken along the actual proposed sewer alignment for more precise data. The foregoing is also relevant to the selection of backfill materials and procedures. The types of bedding to be considered are outlined in the Ontario Provincial Standards Drawings (OPSD). (a) Bedding for Rigid Pipe Sewers The treatment of the foundation and the bedding requirements for rigid pipe sewers are outlined in the Ontario Provincial Standard Drawings and use of the various classifications is as follows: - A yielding foundation (such as earth subgrade) is to be treated as per Class A, B, C-1, or C-2. - An unyielding foundation (such as rock, hardpan or boulder subgrade) is to be treated as per Classes A, B, or C-2. Design should be based on the use of granular beddings, namely Class B in a yielding foundation and Class B or C-2 an unyielding foundation B406-6

7 The use of optional classes (i.e. B, C-1 for C-2) is at the discretion of the contractor, providing that bedding classes are not varied in individual runs of sewers. A general reference to the proposed type of bedding (i.e. Class 'C', not Class C-1 or C-2) is made in the description of contract items. (b) Bedding for Flexible Pipe Sewers C. Sewer Backfill Work Related to Sewers The treatment of the foundation and bedding requirements for flexible pipe sewers are outlined in the Ontario Provincial Standard Drawings as follows: - A foundation such as earth subgrade is to be treated as per Types 1, 2. - A foundation such as rock, hardpan or boulder subgrade is to be treated as per Types 2, 3, and 5. - Special Condition bedding such as Types 2, 3 and 5 are to be used on the recommendations of the Regional Materials and Testing Office and the dimensions must be indicated on the applicable Ontario Provincial Standard Drawings. There are two types of backfill to be considered; native backfill, which is the replacement of the excavated material after the pipe and bedding are placed and Granular Backfill, which is material "imported" to replace excavated material. Where native backfill is recommended the Regional Geotechnical Office may call for wrapping of C.S.P. pipe sewers to prevent seepage of fine sand at the pipe joints. Rock excavated from sewer trenches may be used as native backfill but the pipe must be protected by a layer of granular material. The selection of the type of backfill is the responsibility of the designer based on data and recommendations submitted by the Regional Geotechnical Office. (a) Manholes, Catch Basins and Ditch Inlets The above are dealt with in Section B407-1 of this chapter and should be read in conjunction with this section B406-7

8 (b) Connections to Existing Sewers, Drains and Service Connections These connections, if shown on the contract drawings, are considered part of the work of placing sewers. Where these connections are not shown on the contract drawings, the cost of connections must be negotiated with the Contractor. (c) Pipe Culverts Culverts are covered in Section B421 "Pipe Culverts" of this manual. Many of the principles contained in B421 can be applied to pipes used for the construction of sewers. (d) Headwalls As an aid in the prevention of erosion at an outlet, concrete headwalls may be constructed in accordance with the Ontario Provincial Standard Drawings. This is treated as a separate item of work, i.e. "Concrete Appurtenance" which includes the excavation necessary to construct the headwall. (See Section B ) (e) Grating and End Finish Grating may be installed over the ends of sewer outlets to prevent access by animals or children where the outlet is in a built-up area. The applicable drawing for such grating is shown in the Ontario Provincial Standard Drawings. A special provision is required to include this work as part of the work for placing the sewer. When corrugated steel pipe is used for a sewer outlet, the protruding end may be cut to more aesthetically blend with the surrounding slopes. The types of "cuts" or end finishes are listed on the "Pipe Culverts" sheet. The use of bevels or end sections is to be decided by the designer. If end sections are to be installed on sewer outlets a special provision is required to include the work as part of the work for placing the sewer. (f) Protection Schemes These will be applicable where the stability, safety or function of an existing roadway, railway etc. may be threatened or impaired due to the construction of a pipe sewer. Each site requires a separate tender item, however should protection be minimal such as sand bagging, a separate tender item for protection work may not be necessary and the protection would be covered by OPSS 539 which would be applied to the appropriate pipe sewer tender items DOCUMENTATION A. Pipe Sewers and End Section Treatment B406-8

9 (a) Contract Drawings All Pipe sewers either with or without end sections are to be indicated on the new construction plans of the contract drawings with the appropriate symbol. The pipe size and direction of flow arrow are to be indicated. Sewer profiles are also to form part of the contract drawings and are to be drawn as follows: i) A single, heavy vertical line plotted from the top of grate to the sump elevation is to be used to represent inlet structures. ii) iii) iv) A single, heavy line is to be used to represent the invert of the proposed sewer run between inlet structures or from structures to outlets. The catch basin number, rock line, subgrade and original ground must be indicated where applicable. All other information will be listed on the Quantity Sheets only. (b) Contract Documents Pipe sewers are shown on the "Quantities - Sewers" sheet using a separate column for each tender item. When sewer end treatments or prefabricated end sections are to be used, they should be noted and if aprons are required for the end sections, they should also be noted. Wherever possible, tee and wye connections and the degree of elbows used for sewer construction, should be indicated on the quantity sheets. B. Class, Wall Designation, Corrugation, Gauge & Treatment The class of rigid pipes, Wall Designation of polyethylene pipe, and Polyvinyl Chloride (PVC) Pipe and the corrugation and gauge for corrugated steel pipe are to be determined by the Contractor and it is not necessary to indicate this information on the quantity sheet. However, when in specific cases, the Designer wants to predetermine any of these selections, he must indicate this information on the quantity sheets. C. Bedding and Backfill The class of bedding for all rigid and flexible pipe sewers is to be determined by the Designer and indicated under the appropriate column of the Sewer and B406-9

10 Subdrain Quantity Sheet. Bedding for rigid pipe sewers are to be indicated class B, C-1, C-2, C-3 and flexible pipe sewers are to be indicated as type 1, 2, 3, etc. Alternate bedding for rigid pipe sewers must also be indicated by one or more of the following notes on the bottom of the quantity sheet. The type of backfill, either native or granular, for all rigid or flexible pipe sewers is to be indicated under the appropriate column on the Sewers Quantity Sheets. D. Earth Excavation On contracts where it is necessary to use the excavated material for the construction of earth embankments, the quantity for sewer excavation is to be calculated and the appropriate quantity indicated on the "Quantities - Grading & Granular" sheet under the "Material Available" column. E. Connection to Existing Sewers Locations where connections to existing sewers, drains and service connections are required are to be indicated on the new construction plans of the contract drawings. These locations are listed under an appropriately labelled column on the "Quantities - Sewer" sheet. When information on existing sewers or drains is not well defined, funds should be set up under Force Account and Contingencies on the Acquisition/ Construction of Physical Assets form. F. Headwalls When headwalls are to be placed on sewer pipes, they shall be calculated and indicated on the contract drawings and documents as described in Section B421 "Concrete Appurtenance". G. Grating and End Finish Grates to be installed over the ends of sewer outlets are to be indicated on the new construction plan sheets of the contract drawings using the appropriate OPSD number. These locations are indicated on the "Quantities - Sewers" sheets. All pipe sewers with end sections or bevelled ends are to be indicated on the new construction plans and profiles of the contract drawings with the appropriate symbol. They are also to be noted on the "Quantity - Sewers" Sheet. H. Dewatering There is no provision in MTC Form 406 for payment of dewatering for sewer construction by means of a separate tender item. Should a rare situation occur B406-10

11 where it would be unfair to the Contractor to include an expensive dewatering operation in his pipe bid price, then consideration could be given to using a separate tender item. "Disposal of Water" and the work done in accordance with OPSS 517. I. Protection Schemes When protection is required, a line diagram showing the line of protection or a protection scheme shall be shown on the contract drawings depending on the magnitude of the protection required. Elaborate protection schemes require separate tender items. If the sewer placement item is to include the work required to place the protection scheme, then a non standard special provision is required. J. Trench Reinstatement Where existing driving lanes must be excavated to allow the construction of sewer crossings, 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. To ensure that the contractor knows what is expected, a typical section, traditionally known as "trench reinstatement," must be shown on the contract 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. If no pavement resurfacing is to take place in the area of the reinstatement, a tender item for "Cutting Existing Pavement" is needed B406-11