From Ministry of Water DCOM Manual


1 Earthworks

1.1 General

1.1.1 Scope

This Specification covers the requirements for site clearance, demolition, excavation, shoring, backfilling, compaction, importation or exportation of materials, placing and compacting fill for embankments and other related earthworks required for structural works and installation of pipelines and appurtenances as specified. The work shall also include the placing of rip rap or stone pitching for bank protection.

1.1.2 Definitions

The following terms shall have the meanings assigned to them: “topsoil” means any surface material, including turf, suitable for use in soiling areas to be grassed or cultivated (class 1, DIN 18300).

“rock” is defined as material occurring in solid un-weathered banks or layers which, in the opinion of the Engineer, can only be removed by blasting, percussion drilling, wedging or splitting. Boulders exceeding one cubic metre in volume shall be classified as “rock” (class 7, DIN 18300).

“Subsoil” any material other than topsoil and rock shall be classified as (class 2-6, DIN 18300). means excavation in open cut (excluding trench excavation) down to levels specified on the drawings or otherwise as being the general levels after completion of excavation other than incidental excavation.

“trench excavation” means excavation, to levels and limits specified on the drawings or otherwise, of trenches into which pipes and the like are to be laid.

“incidental excavation” means excavation (generally in small quantities) below or outside the limits of normal excavation and trench excavation, but excluding excess excavation.

“excess excavation” means excavation outside the limits specified for normal, trench or incidental excavation. Excess excavation shall not qualify for any extra payment. If the Contractor encounters material other than that specified and which requires another performance procedure he shall be entitled for additional price negotiations.

1.1.3 Standards And Rules

The Contractor shall carry out works described in this Specification in accordance with the appropriate DIN standards or equivalent. The main standards for the execution are, but are not limited by, the following:
DIN 4124 Building pits and trenches
DIN 18300 General technical code for earthworks
DIN 18303 General technical code for excavation lining

1.2 General requirements

1.2.1 Levels To Be Recorded

Before the surface of any part of the site is disturbed or the works thereon are begun, the contractor shall take and record levels of any such part, in the manner specified or as agreed with the Engineer in his presence. Such levels, when agrees with the Engineer, are the basis for measurement. The Contractor shall also take and record such other levels and dimensions as are necessary during the progress of excavation.

1.2.2 Excess Excavation To Be Made Good

The Contractor at his own expense shall remove from the site all material resulting from excess excavation and shall make good the same with such kind of fill material or in such class of concrete as may be reasonably required by the Engineer having regard to the circumstances.

1.2.3 Explosives

Explosives, if needed, shall not be used without the prior consent of the Engineer. The Contractor shall ensure that all shots are adequately covered so that no damage can occur through flying rock fragments. He shall be responsible for any damage or claim arising through the use of explosive. The Contractor shall observe all laws, regulations and ordinances and make necessary applications for permits and give all necessary notices for the use, carrying and storage of explosives. The storage and handling of explosives is under control of the Tanzanian Army who normally set and place explosives.

1.2.4 Temporary Fencing And Protection

The Contractor shall have particular regard to the safety of persons and livestock and shall ensure that all open excavations, access routes and steep or loose slopes arising from the Contractor’s operations are adequately fenced and protected.

1.2.5 Safety Measures

The Contractor is responsible for all necessary safety measures. From the commencement of the work until final acceptance the Contractor shall strictly follow the safety regulations in order to prevent accidents. Proper strutting, sheeting and bracing, including pre-arrangement of the installations when necessary, protection of slopes, methods of excavation to reduce risks of slides, etc., shall be deemed to be included in the rates and prices entered for other items in the Schedule of Prices. In the event of soil slides occurring during earth and rock work all damage will be at the expense of the Contractor. The additional moving of soil resulting from such damage will not be paid for.

1.3 Preparation of Sites

1.3.1 Site Clearance

All areas of the site, marked on the drawings for clearance or from which material is to be excavated or upon which filling is to be deposited, shall be cleared of all buildings, walls, gates, fences and other structures and obstructions and of all bushes, hedges, trees, stumps, roots and other vegetation, except for trees marked for preservation. Material so cleared shall so far as suitable be reserved and stacked for further use but shall otherwise be disposed of at the site at locations to be found by the Contractor.

1.3.2 Trees And Stumps

Where directed by the Engineer trees shall be uprooted or cut down as near to subsoil level as possible. Branches and foliage shall be removed and disposed of off the site at locations to be found by the Contractor.

Stumps and roots whether existing or remaining after tree felling shall, where directed by the Engineer, be grubbed out and disposed of off the site at locations to be found by the Contractor. The resulting hole shall be filled with approved material and well compacted.

1.3.3 Stripping Topsoil

Topsoil shall be stripped from areas of excavation to such depths and over such areas as may be needed, as a separate operation prior to any further excavation which may be required. Topsoil shall be stored in tidy, stable and well-drained spoil tips until required for topsoiling. For further information refer to clause “Spoil tops on site”.

1.3.4 Demolition Works

Existing structures on site which the Engineer may order to be demolished or may require to be removed for the construction of the permanent works shall be demolished to the extent necessary to construct the various units to a depth of 0.5 m below the finished subsoil level when not otherwise required in the particular specification. Before commencing demolition work on any unit the Contractor shall ensure that all services to that unit have been disconnected.

1.4 Excavation

1.4.1 General Excavation

General excavation means excavation, whether normal or incidental, required for structures, road works, trenches and borrow areas. Where nominal “payment” limits of excavation are not shown on the drawings or not otherwise specified they shall be deemed to be the minimum net limits which would allow the outline of the completed structures to be lowered vertically from subsoil level into its final position. The Contractor shall make his own allowance for any working space required, and any excavation outside the aforesaid limits which has not been ordered by the Engineer, whether it be excavated to suit the Contractor’s method of working or unavoidable over break or due to his carelessness or error, shall be held to be excess excavation.

1.4.2 Maintaining And Supporting Other Services And Structures

The Contractor shall be responsible for maintaining all watercourses, sewers, drains, gas pipes, water pipes, electricity and telecommunication cables, other services and structures encountered during the con¬struction of the works and for any remedial measures necessary to make good any damage arising out of the construction of the works. He shall temporarily support or divert and subsequently reinstate all such services and structures to the satisfaction of the Engineer and the appropriate authority.

As soon as an existing service is encountered in the excavation the Contractor shall forthwith call the attention of the Engineer and the appropriate utilities service authority thereto.

Where permanent diversion or support is rendered necessary as the unavoidable result of the construction of the works in accordance with the Contract or where in the opinion of the Engineer the position of existing services warrants temporary diversion or support the Engineer will instruct the Contractor accordingly. Notwithstanding any relevant information furnished by the Employer or the Engineer, the Contractor shall be responsible for ascertaining, from his own inspection of the site and from the respective supply authorities and other public bodies and by excavating trial pits, the position of all mains, pipes and cables whether underground or overhead, within or near the site.

1.4.3 High Water Table To Be Expected

It is expected that the high level of the water table may present problems during excavation. The Contractor shall satisfy himself as to the extent of this problem and make due allowance in his tender for draining and maintaining all works in a dry condition during construction. Water removed from excavations must not be allowed to cause nuisance or damage to traffic or any public or private property or service. Generally all dewatering arising shall be pumped to drains and under no circumstances shall they be discharged into any part of the sewerage system or an irrigation canal.

All proposed methods for dewatering excavations shall be submitted to the Engineer for his approval. The responsibility for dewatering rests with the Contractor for the duration of the Contract. Care shall be exercised during dewatering so that no material in or around the excavations is disturbed as a result of dewatering.

The Contractor shall include for the necessary diversion of all natural and artificial waterways encoun-tered in the work. Land drains may be used to lead away from the site any springs encountered during excavation. The Contractor shall seek the Engineer’s approval for the type and routing of any such drains.

The Contractor shall take care to avoid undermining any part of the works or other properties by pumping but should undermining occur he shall immediately make good the same to the satisfaction of the Engineer. In cases where the Contractor considers it desirable to place the construction on a layer of waterproof paper he shall obtain prior approval of the Engineer but all costs related to the provision and use of such paper shall be borne by the Contractor.

1.4.4 Excavation To Be Kept Free From Water

The Contractor shall keep all excavations free from water and sewage whether caused by tides, floods, storms or otherwise so that the works shall be constructed in dry conditions.

The Contractor shall keep the sub-soil or accumulated water at a level lower than the bottom of the perma¬nent work for such a period as required by the provisions of this Specification and the Contractor’s method of construction.

In the event of the Contractor requiring drainage grips channels or sub-drains the Engineer will permit these to be constructed below the level of and within the width limits of the permanent work provided he has approved the details of the Contractor’s proposals.

Any sub-drainage that the Contractor constructs below the permanent works shall if left in place be made to provide support at least equal to the permanent support. Ballast filled sub-drains underneath permanent in-situ concrete shall be covered with a water-proof membrane.

No sub-drainage pipes shall be left in place unless they are sealed with concrete or other approved material.

No water shall be discharged into any watercourse without the Contractor having first obtained all necessary consent and the permission in writing of the Engineer and such permission shall not be granted unless the Contractor shall have provided to the satisfaction of the Engineer an efficient settling basin or sand trap through which all such water shall pass before discharge into the said watercourse.

1.4.5 Trial Pits

The Engineer may direct that trial pits shall be excavated well ahead of excavation to such depths, as he shall order to determine the location of the works. Such excavation shall be held to be incidental excavation.

1.4.6 Supporting Excavations

The Contractor shall support the sides and ends of all excavations including trench excavations to prevent any fall or run from any portion of the ground outside the excavation and to prevent settlement or damage to structures adjacent to the excavation.

The Contractor shall provide, install and maintain all materials necessary to provide such support.

If, for any reason, any portion of the bottoms, sides or ends of any excavations shall give way the Contractor shall take all necessary remedial measures including the excavation and removal of all the subsoil thereby disturbed both inside and outside the nominal limits of excavations.

Where the Contractor proposes to perform excavations with sloping faces (other than sloping excavations shown on the drawings or required as permanent features of the works) and without shoring, the excavated faces shall be to stable slopes and heights. Full details shall be submitted to the Engineer for approval.

1.4.7 Shoring

When the material being excavated has bedding planes inclined towards the trench, adequate shoring must be carried out immediately after excavation. Particular care should be taken with earth, which, though firm when trenched, may be rendered unstable by rain or seepage of groundwater.

If the width of the trench is unavoidably increased by slipping or collapsing of the sides of the trench, work should be suspended and the Engineer informed of the occurrence, in order that the design of the pipeline may be reviewed in the light of the increased trench width and, if necessary, the class of bedding amended accordingly.

The method of shoring to be used is left to the discretion of the Contractor. He will be fully respon¬sible for the stability and the effectiveness of the shoring. Costs for shoring shall be included in rates and prices entered for other items in the Schedule of Prices.

1.4.8 Disposition Of Excavated Material

Subject to any specific requirements of the Contract the disposition of excavated material shall be at the Contractor’s discretion but shall be so arranged as to suit the overall requirements for the construction of the works.

The Contractor shall ensure that no excavated material which is suitable for and is required for re-use in the works is disposed of outside the site.

The term “excavation” shall be deemed to include for disposing of excavated material within the site in any of the following ways:
•Backfilling to excavations and completed structures (except where such backfilling is specified as special filling) using suitable excavated material and including placing in temporary spoil tips and any double handling required all as specified hereafter; or
•Transporting and placing (approved) excavated material in permanent spoil tips, including the shaping and drainage of such tips all as specified hereafter; or
•Transporting selected excavated material to locations within the site where embankments are to be constructed or where filling around structures is specified to be constructed as embankment including tipping ready for spreading and compacting; or
•Transporting excavated material off the site all as specified hereafter

1.4.9 Spoil Tips On Site

Only material which is approved by the Engineer shall be placed in the various spoil tips. No tree trunks, stumps, roots, branches or rubbish of any kind shall be placed in spoil tips.

Temporary spoil tips may be used to store excavated material as required and shall be arranged by the Contractor subject to the Engineer’s approval having regard to any particular requirements of the Contract.

Temporary spoil tips shall be so shaped as to maintain stability and good drainage at all times.Topsoil stripped from the site shall be stored in separate spoil tips for use in reinstatement or landscaping.

1.4.10 Disposal of Excavated Material (Off-Site)

Excavated material which is not required or is unsuitable for re-use in the works shall be disposed of off-site at locations to be found by the Contractor.

Material to be disposed shall become the property of the Contractor and he shall be entirely responsible for its removal from the site and ultimate disposal.

1.4.11 Disposal of Materials

The disposal by the Contractor of materials arising from site clearance or from excavations shall be undertaken as work progresses so that the site is kept free from unnecessary obstruction.

1.4.12 Trimming Excavations and Blinding

All foundation surfaces must be levelled, profiled and compacted, either by suitable materials or concrete in such a manner that further execution of works will not disturb the foundation surface. If not mentioned otherwise in this Specification, all foundation surfaces shall be protected by a minimum 10 cm thick concrete layer (blinding) immediately upon completion of the excavation.

1.4.13 Inspection by the Engineer

When the specified levels or limits of excavation are reached the Engineer will inspect the subsoil exposed, and if he considers that any part of the subsoil is by its nature unsuitable he may direct the Contractor to excavate further. Such further excavation shall be refilled to the specified levels or limits with class B 10 concrete, or with approved selected imported material.

Should the material forming the bottom of any excavation, whilst acceptable to the Engineer at the time of his inspection, subsequently become unacceptable to him due to exposure to weather conditions or due to flooding or have become puddled, soft or loose during the progress of the works, the Contractor shall remove such damaged, softened or loosened material and excavate further by hand. Such further excavation shall be held to be excess excavation.

The omission by the Engineer to give an instruction under this clause shall not relieve the Contractor from any responsibility for defects in the works due to the construction being placed upon an unsuitable formation if prior to the construction of the work the Contractor shall have failed to call the attention of the Engineer thereto in writing.

1.4.14 Excavation beneath Structures

Except where otherwise specified for a particular structure or ordered by the Engineer, excavation shall be carried out to the grade of the bottom of the footing, slab or drain rock layer. Where ordered, areas beneath structures shall be over-excavated. After the required excavation or over-excavation has been completed, the exposed surface shall be scarified to a depth of 15 cm, brought to optimum moisture content and compacted to 100 % of maximum density in accordance with the appropriate DIN standard.

1.4.15 Excavation beneath Structure Paved Areas

Excavation under areas to be paced shall extend to the bottom of the aggregate base, if such base is called for; otherwise it shall extend to the paving thickness. After the required excavation has been completed, the exposed surface shall be scarified to a depth of 15 cm, brought to optimum moisture contents, and compacted to 98 % of maximum density in accordance with the appropriate DIN standard or equivalent.

1.4.16 Over-Excavation for Structures

Extreme care shall be taken in order to prevent over-excavation. If any part is over-excavated, it must be made up to the required level with class B 10 concrete. The Contractor shall bear all costs for such work in the event of over-excavation.

1.4.17 Trench Excavation

Trench excavation means excavation of trenches into which inter-connections to be laid and the term pipes shall means inter-connections of all kinds and for whatever purpose and shall include pipe and cable connection among the structures but shall not include trenches for long distance transport lines. Requirements for trenches for long distance transport pipelines are stated in the clause “Trenches for transport lines”.

1.4.18 Trenches For Inter-Connections

Unless otherwise shown or ordered, excavation for inter-connections shall be open-cut trenches. The bottom of the trench shall be excavated uniformly to the grade of the bottom of the pipe or cable, where necessary, to the bottom of the sand bedding.

Bedding shall be as required by the kind of pipes or cables (preparation of foundation surface accordingly). All trenches shall be in accordance to DIN 4124 and DIN 18303.

The depth of trench will always be measured from the final surface level.

1.4.19 Preparation of Trench for Inter-Connections

Where the pipeline is to be bedded on natural earth, a continuous trough should be excavated, trimmed to the required line and grade, and shaped to fit the pipe barrel over the appropriate width. Recesses should be provided in the trench bottom to accommodate couplings so that only the pipe barrel bears on the prepared bed.

Where the pipeline is to be laid on a bed of fine granular material, the trench bottom shall be trimmed to accommodate the required width and depth of fine granular material. The fine granular material shall then be placed, compacted, and trimmed, in accordance with clause “Compaction tests”.

All pipes shall be laid in trenches excavated in undisturbed soil. Under no circumstances may pipes be laid in non-compacted backfill. The Engineer reserves the right to change depth and grade indicated on the drawings, if necessary.

1.4.20 Trenches for Transport Lines

Trenches for transport pipelines means trenches for long distance transport pipelines and cables except where the context clearly renders this inapplicable. Trenches for inter-connections shall not be included. The line and level of trenches shall be as shown on the drawings or as may be directed by the Engineer.

Before commencing trench excavation, the routes of trenches shall be pegged out accurately and the natural subsoil levels shall be agreed with the Engineer. Strong sight rails shall then 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 centre line and the level to which the excavation is to be carried out, such rails being not more than 40 m apart.

1.4.21 Excavation For Transport Lines

Trench excavation shall be carried out in accordance to DIN 4124 and DIN 18303.

The sides of trench excavation shall be vertical unless the Engineer permits otherwise.

Any widening or deepening of trench excavations necessary to accommodate curves, joints or bends in the pipe or to provide extra working space for the construction thereof shall be held to be excess excavation. All excavation and other work carried out within the limits of any highway shall be completed as rapidly as possible and not more than half of the width of the carriageway shall be obstructed at one time.

The Engineer will normally direct that trench excava¬tion in highways shall be located in the verges rather than in the carriageway. In any event the Contractor shall take special precautions, which shall include the continuous support of the sides of the excavation, from the time when excavation is begun until the refilling of the trench is completed, to ensure that there is no disturbance of the adjacent road or road foundation.

Where excavated material has temporarily been depos¬ited on a grass margin, the margin shall on completion of refilling be restored entirely to its original condition and left free from loose stones. The term “fields” includes fields, grass verges and the like and all private lands, and no excavation located in fields shall be commenced until suitable temporary fencing has been erected around such length. Temporary fencing shall not be removed without the permission of the Engineer which will not normally be given until the excavation has been refilled and reinstated.

1.4.22 Preparation of Trench for Transport Lines

The following procedures shall be observed prior to laying any pipes. Where bedding material is required, all shattered and loose material shall be removed from the bottom of the trench excavation so that the bedding material rests on a solid and clean foundation.

1.4.23 Trenches not to be Left Open

Trench excavation both for inter-connections and transport lines shall be carried out expeditiously and, subject to any specific requirements of the Contract, the refilling and surface reinstatement of trench excavation shall be commenced and completed as soon as reasonably practicable after the pipes have been laid and jointed.

Pipe laying shall follow closely after trench excavation, and the Contractor shall not permit unreasonably excessive lengths of trench excavation to remain open while awaiting testing. The Contractor shall take precautions to prevent flotation of pipes in locations where open trench excavation may become flooded, and these precautions may include the partial refilling of trench leaving pipe joints exposed while awaiting tests of the joints.

1.5 Materials

1.5.1 Fill Materials

Fill material shall be, where not otherwise specified, selected and broken down after excavation so that no particle exceeds one half of the thickness of the layer for compaction. Fill material shall contain all sizes of material distributed through it from the largest permitted size to the smallest.

Fill material shall not contain gap graded materials except on the written authority of the Engineer for each case. Fill material shall not contain organic, soluble or other deleterious materials. Should the material selected as filling, while acceptable at the time of selection, become unacceptable to the Engineer for any reason including exposure to weather conditions, flooding, contamination by other materials or segregation during the progress of the works, the Contractor shall remove such damaged, softened or segregated material and replace it with fresh approved material at his own expense.

1.5.2 Free Draining Fill / Filters

Free drainage fill material and filters shall be formed of hard durable particles and shall be free from clay, silt, soluble or organic matter.

The particle size distribution of free draining fill materials and filters shall be calculated in accor¬dance with the filter rules set out in Terzaghi and Peck, 1967.

Material for free draining fill shall be provided by the Contractor from an approved source. The Contractor may use material from excavations having first pro¬cessed it so that it complies with the specification for free draining materials.

1.5.3 Rip Rap

Rip rap material shall be sound, un-weathered and with a low water absorption in order to avoid cracking, bursting and dripping as a result of weather influence. The rock shall mainly consist of large pieces with a lateral length of approximately 150 mm to 400 mm and smaller parts to secure the boulders against sliding and to form a mechanically interlocked uniform surface protection against the action of flowing water, waves, heavy rainfall, washouts, earthquakes, etc., and to provide stability to the fill structure. Each piece of rip rap shall have its greatest dimen¬sion not more than twice its least dimension. The density shall be not less than 22 kNim3 (solid volume without voids).

The material delivered shall be dumped and graded off to a uniform surface up to lines and grades shown on approved drawings.

No pockets of small rocks and clusters of large blocks will be permitted. The Contractor shall submit full details of the proposed source, certified test results and samples for the approval of the Engineer.

1.5.4 Stone Pitching

The materials used in stone pitching shall be obtained by the Contractor from sources approved by the Engineer.

The stone shall be sound durable and hard. It shall be free from laminations, weak cleavages, and undesirable weathering and shall be of such character that it will not disintegrate from the action of air, water or in handling and placing.

The maximum dimension of the stone shall be in the range of 300 mm to 400 mm and the minimum dimension shall be 200 mm. The minimum plane dimension shall be not less than two thirds the maximum plane dimension for each stone. The stones shall be rough hammered dressed so that they fit reasonably closed together. They shall be laid to a true and even surface, the spaces between the stones being clinked with rock-spalls and concrete.

The density shall be not less than 22 kN/m3 (solid volume without voids).

1.6 Backfilling

1.6.1 General

The approved materials shall be placed in layers, not exceeding 500 mm in depth before compaction and shall be well compacted as specified hereafter.

Where necessary the Contractor shall adjust the moisture content of the backfill to an optimum either by drying out or by adding water. After such drying out or adding of water the backfill shall be thoroughly mixed until the moisture content is uniform.

The Contractor shall, when placing the backfilling, make due allowance for any settlement that may occur before the end of the period of maintenance. Where necessary, the Contractor shall at the end of the period of maintenance remove any excess material or make up any deficiency of backfilling to specified levels.

1.6.2 Filling adjacent to Completed Structures.

The Contractor shall arrange the timing and rate of placing of fill material around or upon any completed or partially completed structure in such a way that no part of the works is overstressed, weakened, damaged or endangered. The layers of fill material shall be so placed as to maintain adequate drainage and to prevent accumulation of water.

In particular, the placing of fill material around the walls of basements and tanks shall commence only after the walls and floors have been completed and have attained their full-specified strength. Fill around the walls of reservoirs shall not commence until after satisfactory completion of testing. Fill material behind walls fixed at the top to the roof shall not be placed until the roof has been completed and, if made of concrete, has attained its full specified strength and had the temporary supports removed. The material shall be placed so as to exert a uniform pressure around the walls of a structure, and each layer shall be placed with a fall to prevent the accumulation of water.

Special measures shall be taken in compacting material laid immediately adjacent to a concrete wall to ensure that the material is well compacted. Hand operated vibrating plate compactors, vibro-tampers or power rammers shall be used. In other cases compaction shall carried out by vibrating compactors smooth wheel or pneumatic tyre rollers of types approved by the Engineer.

1.6.3 Refilling Trenches

Trench excavation shall normally be refilled using suitable material selected from excavation carried out within 200 m of the length to be refilled.

Except where concrete or granular bed, haunch or surround is specified, material Type “A” shall be deposited in 150 mm layers and thoroughly rammed under and around the pipe with suitably shaped rammers, working alternatively on either side of the pipe (particular care being taken to avoid damage to the pipe and any sheathing) until the trench has been refilled up to the swell of the pipe. Thereafter the filling shall be carried up to at least 300 mm above the top of the pipe, in 150 mm layers well compacted as specified hereafter.

Type “A” material shall be readily compatible material free from stones and lumps greater than the following sizes:
•20 mm (with occasional lumps up to 40 mm) for PVC pipes; additional requirements for Type “A” fill material for PVC pipes are specified in the following clause.
•50 mm for all other pipes.
The remainder of the refilling may consist of coarse material Type “B” free from boulders and clods of earth larger than 150 mm in size provided that the compacted backfill is, in the opinion of the Engineer, sufficiently dense to prevent material from the superimposed layers being washed into the voids in such backfill.

This coarse material shall be spread in layers of not greater depth than 250 mm and be thoroughly rammed by an approved mechanical rammer.

Type “B” filling is to be carried up to the level at which in roads surface reinstatement is to commence or (elsewhere) to such level as with the surface reinstatement of the whole of the topsoil will leave the finished work sufficiently “proud” to allow for future settlement to the original subsoil level. Hard material such as original road material shall normally be used only for the surface reinstatement or roads as specified but where it is suitable and available in sufficient quantity it may be used in place of or as well as the aforesaid coarse material.

Where necessary the Contractor shall adjust the moisture content of the refill material either by drying out or by adding water to assist the compaction of the material. Should the material being placed as refilling, while acceptable at the time when approved, become unacceptable to the Engineer due to exposure, weather conditions or flooding or have become puddled, soft or segregated during the progress of the works, the Contractor shall at his own expense remove such damaged, softened or segregated material and replace it with approved fresh material. Where directed by the Engineer, trench excavations shall be refilled with concrete, class B 10.

1.6.4 Refill Material - Special Measures

Where in the opinion of the Engineer sufficient supplies of measures the aforesaid material Type “A” for trench refilling cannot reasonably be obtained from trench excavations within 200 m of the length of the trench to be refilled without resorting to sieving or other special means, then the Engineer may order the Contractor:
•to carry out such work as may be necessary to sieve out stones, or
•to transport suitable material from trench excavation at distances greater than 200 m from the length to be refilled (“overhaul”), or
•to excavate material from suitable borrow areas and transport it to the length of trench to be refilled and the Contractor shall do any or all of these things as directed.

1.6.5 Field Drains

Should any existing subsoil or field drains be uncovered during general excavation, the Contractor shall either carefully replace them when backfilling, or, if this is un-practicable, he shall divert them to new drains or ditches, or otherwise re-lay them as the Engineer may direct.

1.7 Embankments and Fill

1.7.1 Embankments Generally

The term “embankment” includes the construction of embankments around structures, hard or other filling, embankments for road works and the like.

Backfilling to general excavations, the forming of spoil tips, and the re-filling of trenches are specified and included in clauses dealing with excavation.

1.7.2 Materials for Embankments

Excavated material (including material excavated from borrow pits) used as filling around structures shall be free from clods and lumps and shall be approved by the Engineer.

Should the material being placed as filling, while acceptable at the time of selection, become unacceptable to the Engineer due to exposure to weather conditions or due to flooding or have become puddled soft or segregated during the progress of the works, the Contractor shall at his own expense remove such damaged, softened or segregated material and replace it with fresh approved material.

When not otherwise specified, cohesive soil shall be placed in layers not exceeding 200 mm in compacted thickness, cohesion-less soil shall be placed in layers not exceeding 400 mm in compacted thickness. Material for hard filling shall be as specified below.

1.7.3 Filling with Hardcore

All filling under structures unless indicated other¬wise on the approved drawings or instructed by the Engineer shall be constructed with hardcore obtained from sources approved by the Engineer.

Hardcore shall be hard inert material passing a 75 mm sieve and free from clay silt soil and vegetable matter and shall not deteriorate in the presence of water.

Hardcore shall be placed in layers not exceeding 150 mm thick (measured after consolidation) and each layer shall be thoroughly compacted by mechanical means.

The final surface of hardcore shall be blinded with fine crushed stone and thoroughly compacted.

1.8 Reinstatement

1.8.1 Surface Reinstatement in the Field.

After the Contractor has refilled excavations in fields and grass verges in the manner and to the level specified he shall replace all topsoil previously removed and it shall be evenly distributed and levelled over the full extent of the stripped area.

Such of the working areas occupied by the Contractor as were originally down to grass shall be sown with grass seed of equivalent quality and maintained until the new grass is properly established. Other areas not originally down to grass shall be dressed with suitable fertilizers harrowed in so as to restore the original level of fertility.

1.8.2 Surface Reinstatement in Roads

Surface reinstatement of refilled excavations in metalled roads shall be in accordance with the re-quirements of the appropriate road authority.

The top layer of surface reinstatement to metalled roads shall be well rolled and finished level with existing surfaces and shall be so maintained (including topping up with additional material when necessary) until the end of the period of maintenance or until taken over for permanent reinstatement by the appropriate highway or other authority whichever shall be the sooner.

Gravel roads and unpaved roads shall be reinstated to their original condition. If the original road construction cannot clearly be applied, then 100 mm approved large gravel and 150 mm well graded gravel material compacted to 95 % of maximum density in correspondence to the tests in DIN 18127 shall be provided.

1.8.3 Existing Services

Where excavation is carried out close to or across the line of sewers, pipes, cables and other services whether underground or overhead, the Contractor shall where necessary provide at his own cost temporary supports or slings and where such sewer, pipe, cable or other service is temporarily disturbed it shall be replaced.

1.8.4 Hedges, Fences and Walls

Where excavation disturbs features, such as hedges, fences and walls, the Contractor, as a temporary measure, shall provide temporary fencing for any parts of such barriers as have had to be removed.

After excavation has been reinstated, the Contractor shall carry out such work as approved by the Engineer for permanent restoration of such barriers. In the case of a hedge the section removed shall be replaced by saplings of the appropriate variety and on both sides by providing an adequate post and barbed wire fence. During the period of maintenance all hedges replanted in the above manner shall be inspected and any dead saplings replaced by the Contractor.

1.9 Topsoiling and Landscaping

1.9.1 General

After most of the construction work is completed and after finalizing the mass earthworks, the area around structures and paved areas shall be planted with grass, shrubs and trees as specified by the Engineer.

1.9.2 Top Soiling

So far as is practicable topsoil shall be obtained from material emanating from excavations and separately stored in temporary spoil tips as specified. If, in the opinion of the Engineer, the Contractor cannot reasonably obtain sufficient topsoil in this way, the Engineer may order the Contractor to provide extra material from an approved source off the site.

Topsoil shall be evenly spread and trimmed over embankments and filled excavation to the slopes and levels as shown on the approved drawings. The depth after spreading and trimming shall be 250 mm measured perpendicularly to the surface. All clods and lumps shall be broken up and any rubbish, large stones, roots and weeds shall be removed.

Where the upper layer of natural soil is poor in organic matter, it shall be improved to a minimum depth of 25 cm by adding either clay or sand or silt to create a loamy soil texture consisting of:
•40 % sand (particle size 2.00 mm - 0.05 mm)
•30 % silt (particle size 0.05 mm - 0.002 mm)
•30 % clay (particle size below 0.002 mm).
A shallow ripping will be required before adding clay or sand or silt, which should be mixed under properly by using a disc harrow.

If it should be necessary for topographical reasons, levelling shall be carried out before adding sand, clay or silt. After planting of lawn, shrubs or trees, the topsoil shall receive a dressing of fertilizer. As minimum requirements dressing of topsoil shall be as follows:
• lime
• potash
• super-phosphate.
Dressing of topsoil shall only be carried out after watering or raining. The surface of the soil shall be kept wet until fertilizers have dissolved.

1.9.3 Landscaping and Grassing

Where the topsoil shall be sown with grass seed, the top 75 mm of the previously laid topsoil shall be brought to a fine tilth suitable for seeding, and sowing shall be carried out as soon as practicable after completion of top soiling having regard to the season and to weather conditions. If ordered by the Engineer, subsoil lime and fertilizer shall be applied in accordance with his directions.

After the seeds have been sown uniformly they shall be raked and lightly rolled into the surface. The young grass shall be kept free from weeds and any bare patches shall be re-seeded until an even close turf is established. The grass shall be watered mown and rolled as required and maintained in good condition until the expiry of the period of maintenance.

The Contractor shall replace, at his own cost, any damaged area where the grass has dried up, or has not adhered to the slope surface, which contains undesirable plants, or which has an irregular or unattractive appearance in the Engineer’s opinion.

Shrubs for borders and hedges shall have a minimum height of 600 mm. A minimum of 2 plants per m2 are to be planted to create an evenly dense area.

Trees to be supplied and planted shall have a minimum height of 1.5 m. For the plant holes, vegetable soil is to be used. Stabilization of freshly planted trees against wind shall be provided. Shrubs and trees shall be suitable for the site climatic conditions. The species the Contractor intends to plant shall be approved by the Engineer. Growth of shrubs and trees shall be guaranteed for one year from the day of planting. Any shrubs or trees which have died within the guarantee period must be substituted without extra payment.

1.10 Testing of Material

1.10.1 General

The Contractor shall furnish all equipment and materials necessary for collecting samples and carrying out field laboratory tests on materials for earthworks. Laboratory equipment shall be housed in a suitable laboratory building on the site, which shall also incorporate space for storage of field test equipment.

1.10.2 Main Tests And Standards

The Contractor shall carry out all tests in correspondence with the appropriate DIN standard or equivalent . For the various tests DIN standards given below are valid but not limited:
DIN 18121 Moisture test
DIN 18122 Consistency test
DIN 18123 Grading test
DIN 18124 Density test (solid volume without voids)
DIN 18125 Density test for the soil (including voids)
DIN 18127 Proctor Test, DIN 18134 Loading test

1.10.3 Compaction Test

The Engineer will conduct regular compaction tests in accordance with the appropriate DIN standards on the various layers of material during construction. If the results of such tests do not meet the specified requirements, the Engineer may instruct the Contractor to remove certain sections of the work and reconstruct them according to the specifications at the Contractor’s own expense.

All holes made by the Engineer for the purpose of tests shall be restored by the Contractor to conform to the characteristics of the adjacent layers. This work shall be conducted at the Contractor’s expense. Costs for compaction tests shall be to the Employer’s account, except where test results fail to comply with the specified standards. In this case, the cost of such test shall be to the Contractor’s account. All tests conducted on materials (sieve analysis, etc.) will be debited to the Contractor.

The compaction (as partially specified) required for various fills shall be as follows:
Item Material Prescribed for Fill Required Compaction (% of the Maximum Density
Mass fill and spoiled material No special requirements
Backfill for over- excavation (for pipe trenches only) Fine granular material 100 %
Initial backfill and bedding layer Fine granular material 100 %
Crushed stone supporting bedding layer Crusher run 95%
Final backfill of pipe trenches under roads Fine granular material 100%
Final backfill of trenches in general Fine granular material 98%
Sandy material 95%
Clayey material 93%
Backfill to structures Fine granular material 98%

Specification of materials Material Plasticity Index Material
Fine granular material 0 - 2
Sandy material 2 - 6
Clayey material 6 - 10
Gravel 10

1.11 Gabions

Not used.

1.12 Auxiliary works

1.12.1 General

Unless otherwise specified, all and any kind of works, materials, services, safety measures, etc., as well as, and if so requested by the Engineer, all tests and samples required for the completion of the work shall be included in the other items and prices entered in the Schedule of Prices. Hence, the auxiliary works comprise, but are not necessarily limited to, the following:
•Removing and storing of boundary stones, bench marks, etc., protection of surveying points and designation by means of boards, survey and protection of all secondary survey points, profiles etc.;
•Difficulties to be overcome where excavation may have to be carried out in layers or by hand;
•Keeping off or diversion of water, any pumping required, difficult work caused by water, etc.,
•Removal or any groynes, buried pipes1 wattle-work, fascines and the like that might interfere with excavation profiles, irrespective of whether or not such structures are specified in the Bill of Quantities;
•Difficulties resulting from the specifications relating to fills, compaction tests, eliminating unsuitable material from fills, and, if necessary, mixing of different soil materials;
•Transport of excavated material to fill or deposit, placing and spreading in layers according to conditions and drawings, and careful compaction;
•Difficulties in transport due to existing subsoil conditions;
•Grading of intermediate and top fill surfaces and slopes to lines and levels required;
•Sorting of excavated material, which, if necessary, is to be used for special purposes;
•Any expenditure for providing1 maintaining and later removal of drive-ways, maintaining existing ways and roads; providing, placing, maintaining and later removal of conveying and dumping equipment that might be required.

1.13 Measurement

See clause 1.2.

1.14 Special measures

1.14.1 Refill Material – PVC-Pipes

PVC pipes shall be bedded and backfilled in accordance with the particular requirements indicated below, and the special backfill material shall extend 100 mm above and below the pipe to the full trench width. The compaction fraction of the special backfill material shall be between 0.1 and 0.3.

Should the compaction fraction exceed 0.3 the Engineer may order the Contractor to supply suitable bedding material which meets the above requirements to provide a 100 mm layer above and below the pipe to the full trench width.

The compaction fraction is determined by the following method:
•Obtain a representative sample more than sufficient to fill an open-ended cylinder 250 mm long and 150 mm internal diameter. It is important that the moisture content of the sample should not differ materially from that of the main body of the material at the time of its use in the trench.
•Place the cylinder on a firm surface and gently pour the sample into it, loosely and without tamping. Strike of f the top surface level with the top of the cylinder and remove all surplus spilled material. Lift the cylinder up clear of its con¬tents and place on a fresh area of flat surface. Place about one quarter of the material back in the cylinder and tamp vigorously until no further compaction can be obtained. Repeat with the second quarter, tamping as before and so on for the third and fourth quarters, tamping the final surface as level as possible.
•Measure down from the top of the cylinder to the surface of the compacted material. This distance divided by the height of the cylinder gives the compaction fraction.