هذه مشاركة لي من خلال التدريب الصيفيChapter (2)TECHNICAL SPECIFICATIONSFOR SANTARY SEWERS
This chapter comprises the technical specifications for the supply, construction erection, testing and handing over in perfect working condition the following.
(i) Sanitary Gravity Sewers :
- Gravity pipes .
- House connections .
- Inspection chambers .
Pipe sizes are given throughout I metric dimensions, but the Contractor will be permitted to supply pipes in corresponding English Dimensions in inches .(see fig. 1)
The contractor shall state in his tender the suppliers of the various pipes he proposed to use .
The works include all labour equipment and material necessary to complete the work as stipulated in this specification and other contract documents . The contractor shall remove so much of the pavements as may be necessary while excavating the tranches and pits to the required dimensions construct and maintain all bridges required for traffic control ,sheet , brace and support the adjoining ground or structures where necessary, handle all drainage or ground water guard the site unload haul distribute and test pipes and accessories replace all damaged drains sewers or other structures backfill the trench and pits restore the road surface remove surplus excavated materials clean the sited of work test the completed lines for pressure and leakage requirements maintain the streets or other surface over the trenhes . Material and workmanship shall conform with me following technical specification or any other equal specifications . The factory shall have internationally approved certificates.
Fig (1) Sanitary Gravity Sewers
The scope included all works , material and equipment required for flow diversion from existing piplelines that shall be replaced new piplines including pumping and modification in existing manholes and all required works for septic tmks emptying demolition and backfilling of part of it with plain concrete of sand .
All pipes fittings and valves shall be tested in factory before being delivered and test certificate shall be submitted together with any consignment. Testing methods and apparatus used for testing of pipes, valves and fittings at the manufactures works shall be subject to the inspection and approval of the Engineer .
The following standards are referred to and the abbreviations shown have been used.
Whenever Saudi Standards are available they must be considered and have the priority over other standards .Saudi Arabia Standares (S.A.S)
British Standards (B.S) and British Standard Codes of Practice (C.P) . Published By : British Standards Institution .
British Standards House
2, Park Street,
American Society for Testing and Materials ( A.S.T.M) standards:
Published by : American Society for Testing and materials
1916 Race Street
German Standard ( DIN)
Published by: DIN
Deutch Verlag GMBH
1 Berlin 30
International Standard (ISO)
Materials and workmanship shall comply with the relevant standard ( With up to date amendments ) current at the thirty - first day of December of the year preceding the Tender date , unless a more recent amendment is specified hereinafter , or with the requirements of any other authoritative standard approved by the Engineer which shall be not less exacting ; in the opinion of the Engineer than the corresponding standard quoted herein where the relevant standard provided for the furnishing of a certificate to the purchaser at his request , stating that the materials supply comply in all respects with the standard the contractor shall obtain the certificated and forward it to the Engineer .
If ( S.A.S) is not available , then one of the above mentioned standards shall be applied.
2.3.1 Trench Excavation (General)
Trench excavation means excavation of trenching into which pipes are to be laid and the term pipes shall mean all kinds and for whatever purposes . (see fig. 2)
Ordinary soil means all kinds of soil formed of clay ,silt sand gravel, volcanic aches, cobbles... etc which canbe excavated and removed by ordinary excavating machines and tools but rock means any naturally occurring solid mass of hard material of not less than one cubic meter ( measured with in the excavation ) which can not be easily shattered or broken - up and in the sole opinion of the Engineer requires the use of explosives or special rock breaking techniques such as wedges and hammers , or compressed air drilling.
Soil which suspended to be rock should be subjected to the breaking test at an approved laboratory . Samples with dimensions 15x15x15 cm or 10x10x10 cm should with stand a stress not less than 70 kg/cm2 for dry samples and 40 kg/cm2 for wet samples .
Fig (2) Trench Excavation (General)
The line and level of trenches are as shown on the drawing or as may be directed by the Engineer . Before commencing trench excavation the route of the trench shall be pegged out accurately and the natural ground levels shall be agreed with the engineer . Strong sight rails shall than be fixed and maintained at each change of gradient and at as many intermediate points as may be necessary . On these rails shall be marked the centeriine and the level to which the excavation is to be carried out such rails being not more than 30 m apart or the distance between to successively manholes .
Prior to the commencement of any trench excavation necessary official permits should be obtained with the adherence to the time schedule for completion of works also permits should be obtained for the occupation of any part of the road by excavation works.
Asphalt layers over trenches shall be cut by the sawing machine and all the cracked surface shall be removed a signboard containing the name of the contractor the name of the project and the telephone number which to be contacted in case of any trouble should occur .
The contractor shall fix day and night warning and lighting signals at the trench sides . He shall provide and alternative for the pedestrians and traffic routes in the areas of excavations . All the above mentioned shall be with the coordination of the traffic department and according to her instructions .
2.3.2 Trench Excavation Width.
The Contractor shall excavate reasonable length of trenches in advance of pipe laying No length of trench excavation shall be started until the pipes to be laid in that length are available on site All excavations shall be made as nearly as possible to the required dimensions so that the minimum filling will afterwards be necessary.
The Contractor shall keep the sides of the trench true by stuts, wallings sheeting or otherwise if necessary. If excavation is below ground water level, water shall be removed by pumping to Engineers approval to permit concreting and laying of pipes to be carried out in the dry. All works required for dealing with water shall be soley the contractors liability.
Excavation shall be careied down to the depth required for laying the pipe bedding the bottome of the excavation shall whenever required by the Engineer be water and rammed before laying the concrete foundation.
The above mentioned requirements are applicable in case of excavation for manholes and any other sewerage and drainage works.
No excavation in materials which can be excavated by the use of pick and shovel will be considered or paid for as rock excavation Boulders less than one cubic meter in size will not be considered or paid for as rock excavation if the contractor wish to use explosive in connection with the works he shall comply with the government regulation . Blasting shall only be carried out in those sections of the works foe which permission in writing shall be given by the engineer and shall be restricted to such hours and conditions as he may prescribe such permission shall not be withheld nor such hours and conditions be imposed unreasonably.
The Engineer may require the contractor at any time during the period of the validity of the contract to make any opening or cuttings in any part of the worke or validity of the contract to make any opening or cuttings in any part of the work or to open out any part which may have been filled in buried or covered and the to open out any part which may have been filled in buried or covered and the contractor shall abide by such requisition to such extent as the Engineer may direct and shall reinstate the work and make it good again to the satisfaction of the Engineer.
2.3.3 Setting out of Axis and Levels:
The Contractor shall be solely responsible for setting out accurately the axis of lines of sewers and drains and fixing the levels for sight rails .
(i) Setting out of pipes Axis:
Before the ground is broken at the site of any manhole the center thereof shall be marked by a pag fixed in the ground and marks shall befixed at sutiable distance from the peg to enable the position of the pipe to be recognized when laid after excavation . Sufficient number of signs along the pipe axis shall be similary fixed before ground is broken in any section (see fig. 3)
(ii) Posts for sight Rails:
As soon as the work of excavation is sufficiently progressed arrangements shall be made for fixing the sight rails to each manhole and at intermediate points along the section such points shall be as near as possible form each other and at equal me section such points shall be as near as possible from each other and at equal distances in no case exceeding 30 meters. Wherever a sight rail should be fixed two opposite posts at nearly equal destnces from the center of the manhole or the axis of the pipeline shall be so arranged as to enable the sight rails fixed thereon to cross the center of the pag or the determined point on the axis . The two posts must not be placed at a point of an excavation intended to be carried out but at the manholes the post shall be placed as distant as possible from each of the manhole branches .
Fig. (3) 3 Setting out of Axis and Levels
(iii) Fixing of Sight Rails:
The sight rails shall be fixed agginst posts with the upper edge higher than the bed level of the pipe at this point by a suitable number of meters which shall be fixed for each of pipes diverging from manholes at different levels .
(iv) Bonding staves:
For the purpose of fixing and testing the levels of the pipes at any point, staves shall be supplied by the contractor in adequate quantities and of all required lengths .
2.3.4 Bedding for Pipes
The drawings give details of laying bedding and compaction for various pipes three types of beddings shall be used named type A, B and C type ( A) involves bedding with seclected granular material and shall be used in all normal cases while types (B) and (C) involve concrete surroundings of the pipes and shall be used where the cover to the pipes is little or great.
Bedding Type (A)
When using bedding type (A) the trench bottome shall be prepared I by excavating a minimum of 100 mm below the bottom of the coupling and a minimum of 150 mm below the barrel of the pipe A pipe bed of 150 mm thickness consisting of granular material conforming to ASTM C-33 gradation 67 shall then be laid and be thoroughly compacted to a minimum density of 90% modified AASHO.
A hole shall be dug out below each coupling to ensure that the full body of the pipe and not only the coupling rests continuously on the pipe bed.
After the pipe bed is prepared as described above the level ad slope shall be carefully cehecked and any adjustment necessary shall be executed . Thereafter the pipe shall be installed and jointed as previously described .
After the pipe with all fittings has been placed in its final position the backfill under and around the pipe up to center line of the pipe shall proceed the joints being left open until the leakge test has been satisfactorily completed.
The material for this backfill for the portion up to the centerline of the pipe consists of granular material conforming to ASTM C-33 gradation 67 above this level back-filling material for this part shall be sand or gravel containing negligible amounts of stones with a maximum particle size of 20 mm for plastic pipes and 50 mm for other pipes all bedding material shall be compacted by hand with hammers in layers not exceeding 300 mm to a minimum density of 90% modified AASHO Particular attention shall be drawn to the backfill under the lowed half of the pipe barrel the compaction of which is of vital importance for the ability of the pipe to withstand external loads the Contractor shall use suitable hammers to ensure that this part of the backfill is properly compacted.
Bedding type (B) and (c)
Concrete for bedding type ( B) and © shall be sulphate resistance concrete where bedding type (B) or (C) is specified the trench shall be excavated to the required depth as shown on the drawings minmum 250 mm and 300 mm below the pipe barrel for type ( B) and ( C) respectively .
In al cases where concrete protection is adopted a layer of blinding concrete at least 50 mm thick shall first be laid in the bottom of the trench and shall be allowed to set before pipe- laying is commenced individual pipes shall be firmly supported on concrete wedges as shown on drawing in such a manner that each pipe is accurately positoned in both line and level and the underside of the barrel is not less than 200 mm above the tope of the blinding layer for type ( B) and 250 mm for type ( C ).
Before the concreting proceeds the pipline thus installed and positioned on the wedges shall be tested after the pipeline has bee satisfactorily tested any reinforcement and formwork shall be fixed before the bedding concrete is cast the blinding concrete shall be placed and consolidated under the around the pipeline in such a manner so as not to cause any damage or disturbance to the pipe or Joints . The Contractor shall note that his method of placing this concrete shall be designed to ensure that the full length of each pipe is fully and adequately supported .The concrete protection shall be thoroughly worked around the undersides of the pipes and into the joint holes if any and shall be thoroughly compacted during the operation of placing.
Expansion and contraction joints shall be formed in he concrete protection at intervals not exceeding 25 meters . The expansion and contraction joints shall be coincident with the flexible joints in the piple lines the joints shall effect a complete discontinuity in the concrete protection and reinforcement ( if any)and shall comprise a layer of 10 mm (3/m in ) thick " Cellotex" or other approved joints filler cut to the appropritate shape .The costs of providing the materials for and forming the expansion and contraction joints shall be included in the Contractors rates of the concrete protection .
In addition to the expansion and contraction joints described above longitudinal reinforcement where specified (normally only for bedding type C) shall be cut off at a joint at bout 5 m intervals as shown on drawing .
The beginning and end of all concrete bedding shall be provided with one flexible joint where the pipe enters the concrete and another flexible joint about 500 mm outside the end of the concrete as shown on drawing .
The concrete used shall have a concrete used shall have a crushing strength not less than 25 N/mm2 after 28 days .
2.3.5 Trench Backfilling :
Trench shall not be backfilled without prior approval of the Engineer and pipe testing the Engineer should have the opportunity of examining the laid pipe before any backfilling start. Soft filling shall be used over the top of the pipe bedding in layers sutiable compacted to the satisfaction of the Engineer. Rocky bulk , debris and wooden pieces should not be used in backfilling . Backfilling shall be in layers not exceeding 300 mm to a minimum density of 90% modified AASHO (see fig. 4)
A warning tape shall be installed 50 cm above pipelines crwon .
Fig. (4) Trench Backfilling
2.3.6 Clean up an Reconstruction of Road Surface :
After completion of all works for construction of the pipeline the trench shall be restored to its original levels and state . The restoration of road surface curb-stones and sidewalks shall comply with road construction standards and the specification for excavation and re-asphalting works . The following shall be considered as a guide .
1- The asphalt layer shall be cut and removed from the two sides of the trench with not less than 40 cm distance . Base layer shall be cut removed form the tranch's end with not less than 20 cm accordingly an overlap shall be provided between the different layers . (see fig. 5)
2- Mechancial finisher shall be used for asphalt layers in case of big excavation with width of 1.50 m and length avove 10 m in case of small excavation the contractor shall used small rollers for rolling fill base and asphalt layers .
Fig. (5) Clean up an Reconstruction of Road Surface
The newly applied asphalt layer shall from a good bond with the old one and its level after good compaction shall not be higher than the old layer level by 1 .0cm
3- All backfill base and asphalt layers shall be similare to the old one and according to M.O.M.R.A standards .
2.4 Types of pipes and fitting for Gravity sewers :
2.4.1 Extra Strength Vitrified Clay pipes and fittings.
Gravity sewers of diameter up to and including 500 mm shall be of the vitrified clay pipes unless otherwise mentioned.
Vitrified clay pipes up to and including 300 mm diameter shall be in accordance with B.S 65 and 540 for British standard extra strength pipes and fittings pipes greater than 300 mm diameter shall comply with German DIN extra strength or with ASTM C-200 .
The pipes and fittings shall be provided with flwxible joints for either the spigot and socket or the sleeve type sealed with approved rubber gaskets . (see fig. 6)
Fittings shall be of the same class as specified for the straight pipes . If fittings are not available in the correct class the contractor shall include in rates for such concrete surrounding or other protection as is required to obtain a crushing strength equal to that of the pipes .
Fig. (6) Types of pipes and fitting for Gravity sewers