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Section 8 - DRAINAGE PIPES, OUTLET DRAINS AND CULVERTS

8.1 STANDARDS OF CONSTRUCTION

Refer to clause 1.1.1 of this specification, which applies to this section. Notify Engineer of discrepancies with normal Vietnam materials, methods and practice.

All materials used for the construction and workmanship for drain works shall generally comply with the existing requirement of the relevant authorities.

8.2 SETTING OUT

The Contractor shall employ a qualified for the setting out and submit a copy of the setting out plan duly endorsed to the Engineer for record. The Contractor shall ensure that the drains and drainage reserves are properly set out and correctly aligned within the drainage reserve as indicated on the Drawings.

Any work not correctly aligned may have to be demolished and reconstructed at the Contractor's own costs and expenses as directed. If it is not possible or practical to reconstructed the misaligned drain and provided that Local authorities has no objection, the Engineer may decide to allow for its retention subject to the Contractor paying all survey and checking fees. However, if the misalignment of the constructed drain resulted in the loss of land, the Contractor shall be required to compensate the Owner for the loss of land rental computed for 50 years which shall be determined based on rates Prevailing at the time of Computation for rental compensation.

8.3 EXCAVATION OF DRAINS

Excavation of drainage trenches Shall be to the lines slopes, limits, configuration and gradients required for the works. The trench bottom shall be of sufficient width to allow adequate space for workmen.

Unless otherwise specified, excavated materials shall not be de posited within 500mm of the edges of the excavation or as directed. The sides Of the excavation shall be supported by planking and strutting if necessary to ensure safely and the speedy and proper execution of the work.

Trenches deeper than 1.5m must be provided with planking and strutting. Method and materials for planking and strutting are to be approved by the Engineer. The excavation shall be kept free from water by pumping or other approved means.

In the event of excavation being made deeper than necessary, they shall be made up in grade 150 concrete at the Contractor's own expenses and costs.

8.4 EXISTING FENCES, WALLS ETC.

Where excavations are near to existing factory, building, boundary fencings or decorative walls, the Contractor shall take all necessary care and precaution to preserve such existing structures. If necessary, the contractor shall erect temporary fencing, remove existing fence or wall etc and on completion to re-erect such fencings or walls to quality equal to the original and made good all works disturbed all to the satisfaction of the Engineer and the factory owners. The Owner shall not entertain any claim for extras in this respect as the Contractor is deemed to have allowed for these in the Lump Sum Tender Price.

8.5 SHORING. SLIPS, FAILS AND UPHEAVAL ETC

Every precaution shall be taken by the Contractor against slips, falls and upheavals of earth etc in the excavation by proper shoring, timbering etc. If any slip, fall or upheaval etc shall occur, the Contractor must at once made good the same, including all surface restoration, all at the Contractor's own cost and expenses. If any such slip, fall or upheaval disturbs or affects any adjacent buildings or works, the Contractor shall be

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fully responsible for the reinstatement or prepare cost to the disturbance or damage caused by him and shall carry out such repairs or rectifications as directed by the Engineer.

8.6 TOPPING UP LOW LYING AREAS

Any suitable surplus earth resulting from the excavation of the proposed works shall be removed and used to top up the surrounding low lying areas approved by the Engineer, or in an area as specified. In topping up the low lying areas, the Contractor shall grade such areas In a systematic manner and in such a way that there shall be no stagnation of wafer.

However, if instructed by the Engineer, the Contractor shall cart away any surplus earth, suitable or otherwise to his own dumping ground (s).

The Contractor shall be deemed to have included for filling or carting of surplus earth the Lump Sum Tender Price.

8.7 CARTING AWAY OF EXCAVATED MATERIALS

If directed by the Engineer, the Contractor shall cart away the excavated materials immediately after excavations, and no surcharge earth shall be allowed on both sides of the excavation so as to prevent slips and fall of earth into the excavation. Carting away of earth to the Contractor's own dumping ground (s) and backfilling et adjacent low lying areas as directed by the Engineer shall be deemed to be included in the Lump Sum Tender Price.

8.8 DRAINAGE RESERVE AND ALIGNMENT

The Contractor shall ensure the alignment of drainage reserve and the outlet drain width are constructed to that as proposed. Care and constant checking should be carried out to enable the setting out line to be closed back by survey to the base line for each stretch of the drain construction.

8.9 DRAINAGE PROBLEMS

The Contractor shall include in his Lump Sum Tender Price all necessary works and costs incurred as a result of clearing, cleaning and pumping of water that discharges from roadside or other temporary drains into the excavation, to enable the works in the excavation to be constructed in the dry.

8.10 EARTH SCUPPER DRAINS

Where required or shown on the drawings, the Contractor shall excavate earth scupper drains to the correct sections, levels, slopes, lines, limits, gradients, and alignment and shall trim and tamp the sides and inverts properly to the. satisfaction of the Engineer.

Other drains shall be provided at outlets and points of water concentration to lead the water clear of the works to points of natural flow, into culverts or existing drainage system. As far as practicable, the drains shall follow existing water courses and depressions in the nature surface or as directed by the Engineer.

8.11 ROADSIDE DRAINS

The roadside drains shall be constructed section by section as directed by the Engineer and shall be generally completed before commencement of works on the carriageway and construction of kerbs.

8.12 PRECAST DRAINS

The pre-cast drain units and sections shall be true to shape and of correct dimensions, finish and strengthened with correct reinforcements whenever required. All pre-cast units shall first be approved for used by the engineer before they are incorporated in any part of the works.

8.13 LAYING PRECAST UNITS

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Pre-cast conduits shall be properly laid, bedded on a sand base of at least 75mm thick unless otherwise stated, and joins grouted and pointed in cement mortar

Side connections where required or shown on the drawings shall be formed and secured in concrete and/or cement mortar, as directed and shall finish to a smooth, uniform and regular appearance.

All pre-cast drains shall be laid to a fall as indicated on the Drawings or as directed by the Engineer.

8.14 GEOTEXTILES

Unless otherwise specified, geotextiles or geofabrics for use on roads or drains shall be non-woven and shall be made of polypropylene, polyethylene, polyester or a combination of the aforesaid approved materials.

Geotextiles shall not be susceptible to bacteria and fungus attack and shall be resistant to chemical action and not affected by exposure to ultra violet light.

Where the geotextiles serve a separation or reinforcement function, Class A geotextiles shall be used. Where the geotextiles serve a filtration function, Class B geotextiles shall be used. The Contractor shall submit samples and technical details of the geotextiles for the Engineer's approval method of laying and jointing to the engineer for approval prior to commencement of work.

8.15 BLOCK PITCHING TO DRAINS

Block pitching, where indicated, shall be granite blocks of size 200mm-300mm, selected, laid tightly and hand pitched to the required depth to the vertical or slope sides in such a manner that a strong retaining structure is obtained. The blocks shall be bedded in 1:3 cement mortar with the larger interstices wedged and filled with crushed stones. The joints shall be pointed where indicated and weep hole shall be provided at the appropriate intervals.

8.16 LAYING PRE-CAST BOX OR PIPE CULVERTS

Pre-cast culverts shall be laid on a sand base of at least 150mm thick compacted and screed off to the required levels or as shown on the Drawings and directed by the Engineer.

In poor ground condition, the Contractor shall excavate and remove the poor quality soil to the depth as required by the Engineer and replace the excavated materials with hardcore or other approved materials. The materials must be laid and compacted in layers of approved thickness by approved mechanical rammers.

8.17 TEST FOR PRE-CAST CONCRETE CULVERTS

The Engineer shall have access to the casting yards where the pre-cast concrete culverts-are being manufactured. A copy of the manufacturer's test certificate shall be provided to the engineer on demand.

8.18 FABRICATED STEELWORKS

Fabricated steelworks eg railings etc shall be made from standard steel sections with dimensions, tolerances and properties complying with the relevant standards and the section on Structural Steel Works in this specification.

The Engineer or his representative, shall have the right to enter the Contractor's premises at all reasonable times for the purpose of inspecting the fabrication works. Any works found defective or not in accordance with the Drawings shall be rejected.

All steelworks shall be prepared or primed against corrosion in the workshop before delivery. All paints, unless otherwise described shall comply with the relevant TCVN wherein applicable.

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All steelworks delivered to site shall be kept clear of the ground and shall be laid out or stacked so as to reduce to a minimum the amount of water or dirt that can accumulate on or against any of the surfaces. Suitable packing shall be placed between layers of stacked steelworks.

All drain gratings shall be fabricated in heavy section steel to sizes and dimensions indicated on the Drawings. The fabricated member shall then be galvanized for heavy duty purposes for incorporating into the drain structure.

8.19 PAINTING OF STEELWORKS ETC

All painting works necessary for steelworks, railings, etc shall be subject to the approval of the Engineer and the relevant Authorities. Painting works shall be made on clean and dry surfaces. The surface to be painted shall be scraped and wire-brushed. All paints shall be delivered to Site in manufacturer's sealed containers and are to be opened in the presence of the Engineer or his representatives.

The various coats of the painting shall be of a different shade. The final finishing coats snail be of the color and shade approved by Engineer

On completion of the works the Contractor shall touch up, or repaint the whole railings and steelwork after de-rusting before the inspection and taking over by the relevant Authorities.

8.20 CASTING BEDS. MOULDS AND FORMWORK

8.20.1 Casting Beds

Casting beds shall be properly leveled and aligned, and so disposed that no process being carried out on any unit will interfere with or adversely affect adjacent castings or operations. Adequate weather protection shall be provided where necessary in order to achieve the specified quality of product.

8.20.2 Moulds and Formwork

Construction of moulds and formwork shall be designed and constructed by skilled craftsman such that the same set of moulds can be used repetitively for other pre-cast cantilever sections of varying heights.

The moulds and form shall be sufficiently rigid not to deform and sufficiently tight to prevent loss of grout or mortar from the concrete, at all stages and for all methods of placing and compacting.

Metal moulds shall be used in order to achieve a good finishing surface.

8.20.3 Cleaning and Treatment of Forms.

All rubbish shall be removed from the interior of the forms before the concrete is placed. The faces of the moulds or formwork in contact with the concrete shall be clean and treated with suitable release agent, where applicable. Care shall be taken such that agents are uniformly applied without excess which might mar the surface, and kept out of contact with any reinforcement.

8.20.4 Holding Members

Provision shall be made to hold firmly and maintain in position all projecting reinforcement or other interconnecting devices together with bolts, fixing blocks etc so that they are within the specified tolerances.

8.20.5 Mould Oil

Mould oil or release agent shall be of the approved type. The Contractor shall be required i0 submit details of type and proprietary brand and obtain the approval of the Engineer before using the product.

8.21 BOX OUT IN REINFORCED CONCRETE DRAINS

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As depicted in the Drawings, box out in reinforced concrete drains are to be made to enable future connection of scupper pipes into the reinforced concrete drains. The Contractor shall include in his Lump Sum Tender Price for such works and ensure that these box-outs are properly located lengthwise as well as giving the correct invests.

8.22 REINFORCEMENT FOR CAST-IN-SITU DRAINS

For cast-in-situ drains, the Contractor may be allowed to use either steel bar, reinforcement to any drain depth or steel fabric reinforcement to drain depth not exceeding 1.6m all at the same Lump Sum Tender Price. Prior written approval must be obtained from the Engineer. Where steel fabric reinforcement is used, the main reinforcement bar diameter shall be the same as that for the steel bar reinforcement indicated specified.

8.23 HARDCORE/GRAVEL PACKING

All hardcore/gravel packing to be placed along the length of drains shall be crushed granite stone, broken bricks or other approved materials of uniformly graded dimension varying from 50mm to 100mm. The packing shall have a section of 300x300mm or as shown on the Drawings.

8.24 CONSTRUCTION OF OUTFALL STRUCTURES

Where outfall structures are provided for outlet drains, the Contractor shall be required to construct cofferdam or other structure water from the works. A joint pre-construction hydrographic sounding survey shall be carrying out by the Contractor's and Owner's Surveyors and shall serve as a record of the existing levels around the outfall structure area. The Contractor shall request for the survey when he is ready to carry out the Works.