From Ministry of Water DCOM Manual

1 Siteworks

1.1 Scope

The works to be carried out under this chapter comprise various site works as roads and pavements, surface drainage, planting of lawn, shrubs and trees, erection of fences with gates, construction of septic tank with soak-away.

1.2 Mass Earthworks

Not used.

1.3 Roads, Pavements and Surface Drainage

1.3.1 Design of Roads

The structural design for pavements and roads shall correspond to the road category "D V" in accordance with Tanzania Road Design Manual or as directed by responsible authority. Roads and paved areas shall be laid out to plans prepared by the Contractor and approved by the Engineer. The plans shall make proper and adequate allowance for road curvatures, crossfalls, parking spaces and turning room both for passenger vehicles and, where appropriate, for goods vehicles. Upstanding kerbs shall be provided against footpaths and where it is essential to keep traffic from road verges which contain buried services, which are landscaped or which are close to buildings. Elsewhere kerbs shall be flush with the pavement surface.

1.3.2 Design of Drainage

Not used.

1.3.3 Precast Concrete Kerbs and Flags

Precast concrete kerbs shall comply with DIN 483.

1.3.4 Pipes and Fittings

Concrete cylindrical pipes and fittings shall be "standard" quality with approved flexible spigot and socket or ogee joints and shall comply with DIN 4032 or equivalent. Glazed vitrified clay pipes and fittings shall conform to DIN 1230 or their equivalent. These pipes shall not be used for diameters greater than 300 mm. Pipes for porous drainage shall be of PVC to DIN 4925.

1.3.5 Manholes Chambers and Gullies

Manholes, inspection chambers and gullies shall be constructed to details shown in the standards. Where precast they shall comply with DIN 4034 or DIN 4052 or equivalent. Cast iron covers or gully gratings shall comply with DIN 4290 or DIN 4052.

1.4 Roads and Pavements

1.4.1 General

Roads and pavements, as specified hereunder, shall include the construction of all roads and pavements to line and levels as shown on the approved drawings. In this work "earthworks" as specified under "General Specification - Earthworks", are not included. Materials shall be new and shall comply with standard quality and dimension provisions. For unstandardized materials and building components the Contractor shall, on demand, supply samples and name of manufacturer, and shall be subject to approval by the Engineer. Mineral materials shall be weatherproof, of adequate hardness, watertight and of sufficient adhesion to bind. They may not contain any swelling, weathering, loamy, clay or organic components in harmful quantities. Bituminous mixes must be blended so as to be suitable for the purpose of application. Special consideration shall be given to climatic and location conditions, volume and type of traffic.

1.4.2 Formation and Subgrade

Formation means the surface of the soil in cut or fill after completion of earthworks on which further roadwork construction is to be carried out. Sub grade means the soil immediately below the formation. The formation and sub grade shall be graded and compacted to the levels, falls, cambers and densities as required in RSTO 86 (Richtlinien für Standardisierten Oberbau). The sub-grade shall be compacted in accordance with the appropriate DIN standards or equivalent. As a minimum it shall be so compacted that the dry density of the upper 150 mm of the ground or fill is not less than 95 % of the maximum dry density determined by tests in accordance with DIN 18127. Where the sub-grade is in natural ground the compaction shall, whenever possible, be carried out at or near the natural moisture content of the ground. Any irregularities or depressions that develop in the formation during compaction of the sub-grade shall be corrected by loosening the surface of these places and adding, removing or replacing materials and re-compacting so that the surface is smooth and uniform. Any area of sub-grade that shall become muddy, broken up or loosened due to weather conditions or otherwise damaged shall be corrected or prepared again by the Contractor as specified above. Where existing ground conditions are such that direct compaction of the sub-grade cannot be carried out as specified, unsuitable material shall be removed and be replaced with granular sub-base. The formation shall be kept free of standing water at all times and drains shall be provided so that it will drain quickly and effectively during rain. On completion of compaction and before commencing the next operation, the surface of the sub-grade shall comply with the surface tolerances specified and to the satisfaction of the Engineer.

1.4.3 Sub-Base and Road Base

The sub-base and road base shall be graded and compacted to the levels, falls, cambers and densities as required in RSTO-86 or as shown on the approved drawings. Material for the sub-base and road base shall be laid in one or more layers, each not exceeding 150 mm thick nor being less than 75 mm, and the total compacted thickness of sub-base and road base shall nowhere be less than the specified nominal thickness. The sub-base and road base materials shall be deposited in such a manner that there is no segregation and the material requires the minimum of blading or spreading. Each layer of material shall be compacted immediately after spreading in accordance to ZTVE-StB 78. If any of the subgrade material is worked into the sub-base material during the spreading, blading or compaction, all the sub-base material in the affected area shall be removed and replaced with fresh sub-base material. Upon completion of compaction and before commencing the next operation, the surface of the granular sub base and road base shall comply with the surface tolerances specified in ZTVT-StB 86 or ZTV bit-StB 84.

1.4.4 Sealing

Wherever possible, of final trimming of the formation, compaction of the subgrade, and placing and compaction of the granular sub-base and roadbase shall be carried out without intermediate delays. The Contractor shall be responsible for taking all necessary steps to prevent damage to the previously completed layer or layers by excessive wetting or drying due to weather conditions or by traffic or any other cause. If the Contractor considers it advisable or if so ordered by the Engineer, the completed layers shall be sealed using bitumen road emulsions in accordance with RSTO-86 and TV-bit. In any case, the completed surface of the road base shall be sealed as specified above immediately it has been completed and checked for compliance with the specified tolerances.

1.4.5 Surface Dressing

Where the Contractor proposes to use any completed layer of road construction for any significant amount of traffic, other than that required for the construction of succeeding layers, he shall first obtain the approval of the Engineer, who may direct which areas shall be surface dressed. In this case the layer shall be surface dressed in accordance with RSTO-86 and TV-bit using bitumen road emulsion and chippings. The Contractor shall in any case be responsible for making good any damage to the completed layers caused by his own construction traffic whether surface dressing as specified has been carried out in accordance with the Engineer's directions or not.

1.4.6 Flexible Road Surfacing

Unless otherwise specified or detailed, material for flexible road surfacing shall be coated macadam, in a quality corresponding to TV-bit. The surface on which each course of coated macadam is to be laid shall be free from standing water and any loose or deleterious material and shall be tested for accuracy. Before laying commences in any area, a tack coat of bitumen road emulsion shall be applied to the whole area of the preceding course, and also to kerbs and other concrete surfaces, manhole covers and gully grating frames, and any other surfaces with which the coated macadam will be in contact, including the edges of previously laid strips of coated macadam. The emulsion shall be allowed to break completely before the coated macadam is laid on it. The compacted thicknesses of individual layers shall be not less than the minimum compacted thicknesses specified or shown on the approved drawings.

1.4.7 Delivery of Coated Macadam

Coated macadam materials shall be delivered to site in clean vehicles and shall be protected to minimize loss of heat in transit and contamination by dust or other deleterious matter. The use of dust, oil or water on the interior of the vehicles to facilitate discharge is permissible, but the amount shall be kept to a minimum, and all necessary steps shall be taken to ensure that any excess is removed by tipping or brushing. The rate of delivery to the site shall be regulated so as to enable the material to be laid with the minimum of delay and so that the paver can operate continuously.

1.4.8 Concrete Paved Areas

Concrete paved areas shall be constructed in accordance with RStO-86 and ZTV Beton 78 and with the relevant requirements of the "General Specification for Concrete, Reinforcement and Formwork". Concrete for roads and pavements shall be of class B 25. The use of additives shall be subject to the approval of the Engineer. Concrete courses shall be never less than 100 mm thick. If reinforcement is required, it shall be achieved with reinforcement steel mesh of at least 2 kg/m2, unless otherwise approved. The reinforcement shall not influence the effectiveness of the joints. The concrete cover shall be at least 30 mm thick. Transport and placing of the concrete shall be coordinated so that the concrete can be completely placed prior to setting. The strength of the concrete and the properties of the concrete surface shall not be influenced by the execution of joints. The joints shall be made early enough so that no cracks appear. Expansion joints shall be executed at the required intervals and shall enable expansion of the plates and be fixed. The expansion joints shall be 20 mm wide. Dummy joints are to be executed by cutting a groove with a depth of at least 25 % of the concrete surface in the set concrete. In the case of butt joints, the set concrete side surface shall have a simple cold bituminous course. The upper part of expansion and dummy joints is to be poured to the edges with bituminous joint sealer. Prior to placement of the bituminous joint sealer the joint surfaces shall be dry and clean. If dowels are required for transmission of transverse forces and protection of the height of the plates, they shall be laid in the middle of the plate thick¬ness and in the inclination of the concrete surface so that they do not obstruct expansion of the plates. Dowels of reinforcement steel with the diameter of 25 mm and a length of 50 cm shall be used. The distance between dowels shall be uniform and not exceed 30 cm. In the case of the expansion joints a lead or PVC-sleeve shall be stuck on to the end of each painted dowel half, leaving an expansion facility of 15 mm. Dummy joints and butt joints do not require sleeves. The concrete shall be protected against harmful influences until correct setting, i.e. against permanent drying out, especially due to sun and wind, against washing out due to rain, against heating or quick cooling. The concrete surface shall be kept moist for 7 days or protected from drying out.

1.4.9 Kerbs

Precast concrete kerbs shall be laid true to line and level and any kerb found to be more than 3 mm out of line or level at either end shall be lifted and re-laid. Kerbs shall be bedded on a layer of 3:1 sand:cement mortar minimum 10 cm thick on a grade B 10 concrete foundation and shall be backed with concrete shaped up to the required cross-section. Specially cast circular kerbs shall be used on curves of 15 m radius or less. Kerbs shall be jointed with cement mortar except at expansion joints, which shall be made with preformed joint filler 10 mm thick.

1.4.10 Gravel Roads

Normally the construction of gravel roads will not be permitted, except if the construction is approved by the Engineer. The material for gravel roads shall be a natural or crushed well-graded gravel with a maximum grading of stone size of 32 mm. Preparation of the subgrade shall be as specified previously. The thickness of the compacted gravel bed shall be not less than 150 mm for roads with vehicular traffic or in other cases 100 mm. The material for gravel roads shall be approved by the Engineer.

1.4.11 Footpaths

Footpaths shall be surfaced with either precast concrete flags minimum size 0.3 x 0.3 m or with coated macadam. The base for footpaths shall be formed from flexible surfacing, laid and compacted to a minimum thickness of 75 mm using a roller of at least 2.5 tonnes mass or other approved equipment giving equivalent compaction. Precast concrete flags shall be bedded on a layer of sand approximately 50 mm thick tamped into place. Where footpaths have coated macadam surfacing, the construction shall be as follows: precast concrete edging in accordance with DIN 482 shall be bedded and backed with in-situ concrete. The base for the footpath shall be constructed as specified above and shall then be sealed. Surfacing shall consist of a single course of coated macadam flexible surfacing laid and compacted to a minimum thickness of 25 mm. Concrete footpaths shall be made of concrete B 25 with a mortar topping, constructed on a prepared bed as specified above. Concrete footpaths shall be con¬structed in accordance to the “General Specification for Concrete, Reinforcement and Formwork".

1.4.12 Reinstatement of Existing Roads and Footpaths

Not used.

1.5 Surface Drainage

1.5.1 General

Surface water shall be discharged or disposed safely at position where it does not endanger any structures, roads, crop fields and private property. Trenching for drainage pipework and excavation for manholes, gullies and the like shall be as specified in the "General Specification - Earthworks".

1.5.2 Drainage Work

Pipework, manholes and gullies shall be built and backfilled as specified before drainage is tested for watertightness. Open channels shall be constructed either as earth channels, in stone work or with precast concrete units in half-round sections or trapezoidal section. Open channels adjacent to buildings, basins and other structures and channels with longitudinal slopes steeper than 1:100, depending on the soil conditions, shall be constructed with precast concrete or stone work. Channel sections, which are subject to scouring, shall be protected with stone pitching. Precast concrete channels shall be manufactured from concrete class B 25. Installation of precast concrete channels shall be to the method specified in the "General Specification of Pipelines”. All backfilling shall be with selected excavated material approved by the Engineer. If the soil is unsuitable for laying of channels, the Contractor shall place a bedding layer of approved granular material or concrete B 10 under the channel. All road crossings of channels shall be constructed such that vehicular traffic is not exposed to danger, installation of pipes or culverts, or shall provide gratings over the channel.

1.6 Fencing and Gates

1.6.1 General

The works comprise the supply and erection of fences and gates both around the perimeter of the site and internal fencing. Internal fencing shall be of the standard type and fencing around the perimeter of the site shall be of the security type. Security fences shall be anti-intruder type. All items of material for fences and gates shall be standard products of manufacturers regularly engaged in the production of the type of fence specified herein. Posts and struts shall be either reinforced concrete or galvanized steel sections. Timber posts shall not be used. All wire shall be galvanized wire with plastic coating. The length of the sides of the chain link mesh shall be 50 mm. All chain link fencing shall be barbed along the top edge. The work pertaining to fencing shall consist of providing all necessary materials and constructing the fencing including all requisite materials, unloading and storage on site as well as any intermediate handling required. All earth, backfilling and concrete work shall be included in the offer. All posts and struts shall be anchored in rigid concrete B 25 foundations of sufficient depth. In the vicinity of gates, structures and fence openings, adequate provision to fix the fences shall be provided. The distance of the bottom of the wire mesh to the levelled ground surface shall not exceed 2.5 m.

1.6.2 Standard Fencing

Standard fencing shall consist of a 1.0 m high mesh wire fencing with steep posts of circular tubing or other cross sections of high tensile steel as approved by the Engineer. Posts shall be galvanized inside and outside and plastic coated and closed at the top with plastic or cast zinc alloy caps. End, intermediate, corner and straining posts shall be 1.5 m long, the gate post 1.5 m long. The distance between posts shall be approximately 2.5 - 3.0 m. Posts are to be set in sufficient B 25 concrete foundations. Intermediate straining posts are to be installed to 50 m intervals. The intermediate post shall have two diagonal struts and shall be provided with 3 double ratchet winders for the strain line wires and one joint clamp to fix the struts to the post. Strut foundations shall be cast in concrete B 25 and in sufficient size. Corner and end posts shall either be supported by struts as for intermediate straining posts or by a horizontal bracing. Sufficient straining wires, winding ratchets, jointing clamps and other required fittings shall be provided for all end, corner and gate posts. Three rows of straining wires are to be installed for the 1 m high fence.

1.6.3 Security Fencing

Security fencing shall be constructed as described for standard fencing, but with posts provided with barbed wire holders inclined inwards. The total fence height shall be 2.5 m. Post length shall be 3.5 m minimum. Three rows of galvanized and plastic coated 2 strand, 4 point barbed wire shall be fixed to the cranked top section of the post. Sufficient ratches, winders and clips are to be provided to assemble and to secure the barbed wire.

1.6.4 Gates

The tops of the gate frames shall be levelled with the tops of adjacent fencing. Gates in fencing with barbed wire on extension arms shall also carry wire mounted on extension arms as specified. All gates shall be of welded steel construction, galvanized and painted and covered with plastic coated chain link mesh and surmounted with galvanized, plastic coated barbed wire to match the fencing. Sliding gates shall be provided with roller support tracks Gates shall be complete with all fittings such as drop bolts, back catches, locking bars, lock plates and locks, etc., including two keys per lock.

1.6.5 Installation

Fences shall be installed in accordance with the fence manufacturer’s drawings and written installation instructions, except as modified herein. Each line of fencing shall be erected so that it is plumb, taut, true to line and grade, and complete in all detail. The outside face of the fabric shall be on the property line where the fence runs along the property boundary. Straining posts shall be installed at points where the slope of the ground and fence change by 20 degrees or more. Straining posts shall also be installed at changes in line where the angle of deflection is 10 degrees or more. Posts shall be suitably braced during concreting to ensure that they remain in the correct line and level during placing of concrete and the concrete shall be cured for 3 days before any further work is done on the posts.

1.7 Tests and Inspection - Generally

The Contractor shall, prior to execution, ascertain and upon request of the Engineer, prove that the materials and components used are suitable for the intended application. The Contractor shall during execution ascertain and shall upon request of the Engineer, prove that the materials and components used correspond to the contractual requirements. The Contractor's responsibility will not be released even if control tests have been performed by the Engineer. Sealed joint drains shall be tested in sections by water under a head of not less than 1 m to the Engi-neer's approval. Drains shall not leak under this pressure Soakaways, where provided, shall be tested by subjecting them to an overflow equivalent in volume to the design rainfall intensity for a time of 15 minutes on the area draining to the soakaway. The soakaway shall not back up during the test.