2/20.5 Samples for Soil classification, laboratory moisture density relationship tests and CBR tests shall be taken prior to use, from any proposed source of material. Each sample shall represent not more than 1,500 Cu.m.
2/20.6 For every completed layer of subgrade, three field density tests shall be performed on every 1500 sq.m. of carriageway.
2/20.7 The frequency of field compaction tests on the shoulders shall be three every 1500 Sq.m. constructed or as directed by the Engineer.
ROCKFILL
2/20.8 Where embankments to be compacted are formed of material consisting predominantly of rock fragments of such size that the material cannot be placed in layers of the thickness prescribed without crushing, pulverizing or further breaking down the pieces resulting from normal excavation methods, the material may be placed in the embankment in layers not exceeding a thickness twice the average size of the larger rocks, except that no layer shall exceed 600 mm of loose measurement.
Materials shall be carefully placed so that all large stones will be well distributed and the voids completely filled with smaller earth, sand or gravel to form a solid embankment. Each layer shall be bladed or levelled with motor grader, bull dozer or similar equipment capable of shifting and forming the layer into a neat and orderly condition. No. rocks larger than eighty (80) mm in any dimension shall be placed in the top one hundred and fifty (150) mm of the embankment unless otherwise noted on the drawings. Conformance to these provisions and compaction in a manner and to a point of consolidation approved by the Engineer will be considered as fulfillment of the requirements for the type of compaction shown on the drawings. Normally, compaction tests will not be performed in these areas but the Engineer reserves the right to test compaction in some other manner if he deems a test necessary to ensure consolidation. Each layer must be approved by the Engineer before the next layer is placed.
Embankments, which are formed of materials that contain rock but also sufficient compatible material other than rock or other hard material to make rolling feasible, shall be placed and compacted in the manner and to the point of consolidation approved by the Engineer. Moisture shall be added as directed by the Engineer. Compaction tests will be made wherever the Engineer determines they are feasible and necessary. Each layer must be approved by the Engineer before the next layer is placed.
2/21 STABILISING CRUSHED MATERIAL
2/21.1 In the event the foundation on which the embankment or the subgrade materials will be laid is saturated by water and unstable, the Engineer may decide to lay crushed granular material to stabilise the foundation. Stabilising crushed material shall not be laid directly on ground soil but it shall always be laid on geotextile fabric covering the area to be stabilised as shown on the drawings or directed by the Engineer.
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2/21.2 Such stabilising crushed material when tested in accordance with ASTM C136 shall have the following gradation:-
BS SIEVE % PASSING 50 mm 100 25 mm 80 - 100 12.5 mm 60 - 85 4.75 mm 40 - 70 2.00 mm 20 - 50 850 microns 15 - 25 425 microns 0 - 10 180 microns 0 - 2
2/21.3 The stabilising crushed material shall have the following characteristics:-
- Los Angeles Abrasion (ASTM C131/C535) - Not more than 30% loss (after 500 revolutions)
- Bulk Specific Gravity (ASTM C127) - Not less than 2.65 - Absorption (ASTM C127) - Not more than 2.0%
2/21.4 The stabilising crushed material will be laid in layers of 15 cm and compacted until the foundation is fully stabilised such that the total thickness of the stabilising layer shall not be less than 30 cm. Only after inspection and approval by the Engineer the Contractor may be allowed to continue the construction of the embankment with other layers of embankment material and/or subgrade material. The Engineer may decide, after having taken the levels of the existing water table in the area, and keeping in consideration the finished road levels, to excavate portions of the foundation saturated by water, disposing of the excavated material, and replacing it with stabilising crushed material.
2/21.5 Before starting any stabilising of the foundation the Engineer will instruct the Contractor specifying the areas to be stabilised and the final levels to be reached with the stabilising crushed material.
2/22 GEOTEXTILE FABRIC
2/22.1 In areas where the Engineer deems the use of geotextile fabric necessary, the Contractor shall furnish and place geotextile fabric as specified and as directed by the Engineer.
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2/22.2 The geotextile fabric furnished by the Contractor shall be of an approved grade suitable for placement over fine sand. The geotextile fabric shall be a woven or non-woven fabric consisting only of long chain polymeric filaments or yarns formed into a stable network such that the filaments or yarns retain their relative position to each other. The fabric shall be stabilised against ultra violet light, inert to commonly uncounted chemicals and chemical properties of the in-situ soil and water, and it shall conform to the following minimum requirements:
Property Test
Method (metric) Unit Min.Average Roll Values (140N) Grab Tensile Strength ASTM D 4632 lbs (kN) 120 Grab Tensile Elongation ASTM D 4632 % 50 Mullen Burst
Strength ASTM D 3786 psi (kPa) 240 (1654) Puncture Resistance ASTM D 4833 lbs (kN) 70 (0.31) Trapezoid Tear Strength ASTM D 4533 lbs (kN) 50 (0.22) Permittivity ASTM D 4491 sec 1.5
Flow Rate ASTM D
4491 gal/min/ft
2
(1/min/m2)
120 (4903)
2/22.3 The surface to receive the geotextile fabric shall be prepared to a relatively smooth condition free of obtrusions, depressions, and debris. The geotextile fabric shall not be laid in a stretched condition, but shall be laid loosely with the long dimension parallel to the centreline of the roadway. In the event that the width of the proposed area for fabric requires more than one panel width of fabric, the panels shall be overlapped a minimum 15 percent of the panel width. Longitudinal joints in the fabric shall have an overlap of 50cm. To prevent slippage of the overlapping fabric, the areas of overlap shall be stabilized as approved by the Engineer with pins, anchor blocks, or aggregate piles. In the event construction machinery is used to place the fabric, the working platform for the machinery shall be the soil and not the previously laid fabric.
2/22.4 Prior to placement of the granular material (Stabilizing crushed material) the Contractor shall spread a layer of sand over the geotextile fabric as directed by the Engineer. The aggregate material shall not be dumped directly on the fabric, nor shall haul trucks be run on the fabric. The aggregate shall be spread by a wheeled front-end loader.
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The blade or bucket shall be kept sufficiently high so that the aggregate is not being pulled over the fabric, but being dropped at a minimum height to the satisfaction of the Engineer.
2/22.5 Fabric damaged or displaced before or during installation or during placement of overlaying aggregate material shall be replaced or repaired to the satisfaction of the Engineer at the Contractor's expense.
2/23 EXCAVATION FOR STRUCTURES
2/23.1 This work shall consist of all excavation for structures, culverts, headwalls, catch basins, manholes, inlets, and retaining walls and shall include all necessary clearing and grubbing, all necessary bailing, drainage, pumping, sheeting, strutting and the construction of coffer dams or cribs, if found necessary, and their subsequent removal; also the disposal of all material obtained from such excavation and backfilling to the level of the original ground; it shall include the removal of that portion of existing structures below the ground which is necessitated by the construction of the new structure.
2/23.2 Prior to commencing any structural excavation work 1.5 metres or more in depth, the Contractor shall design and submit to the Engineer for review and approval, within a minimum period of 1 week before the intended commencement date, detailed working drawings of the structural excavation support member materials, sizes, spacing and engineering calculations to validate their design, including the maximum theoretical deflections of the support members. The system shall be designed in such a manner that no raker struts or any other support members extend through surfaces exposed in the finished construction, and no shoring or bracing is placed under permanent structures. 2/23.3 The engineering calculations shall show lateral earth pressure for the full excavation
depths, forces at various stages of support during installation and removal and concrete placement, the anticipated equipment loads, surcharge loads of any description, the maximum design loads to be carried by various members of the support system and strut preload forces.
2/23.4 If the structure support system proposed includes tieback anchors, the Contractor's submittal drawings shall show the profile of the soil in which each anchor is to be installed, the design load for the full depth of the excavation, the maximum design and proof loads, surcharge loads of any description; equipment loads, forces at various stages, support during installation and removal, and the criteria proposed for deformations under proof loads. Where a proposed system of tieback anchors projects beyond the vertical projection of the Contract limit lines shown on the Drawings on to the adjoining property, the permission of the owner shall be obtained in writing and such permission submitted to the Engineer at the time the shop drawings of the support systems are submitted.
2/23.5 At locations where the excavation extends below the ground water table, a dewatering system shall be provided which will effectively reduce the hydrostatic pressure and lower the ground water levels below excavation levels, as required for the safe and proper execution of the work and which will result in obtaining a stable, dry subgrade for the execution of subsequent operations. The Contractor shall design dewatering methods and settling basins so that no critical amounts of soil, sand or silt are removed during either the initial operations or the construction operations. Complete working drawings showing the type of dewatering and ground water control system proposed shall be submitted to the Engineer for his review.
2/23.6 The Contractor's submittal drawings shall show the arrangement, location and depths of the proposed dewatering system if required. A complete description of the equipment and materials to be used and the procedures to be followed shall be shown, together with the standby equipment, standby power supply and the proposed location or locations of
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points of discharge of water. Any required dewatering system design shall also include the measures taken to prevent damage due to settlement of pavement, utilities, sewers, buildings and other structures outside the excavation but within the area affected by the procedures.
2/23.7 The designs of the structure excavation support system and the dewatering systems specified above shall be prepared by and signed by a Professional Engineer approved by the Engineer specialising in this type of design work. Approval of the designs and shop drawings shall not relieve the Contractor of the adequacy and performance of these temporary works.
2/23.8 Pre-Construction Inspection-prior to the beginning of construction, the Contractor and the Engineer shall make a detailed inspection of all adjacent buildings, pavements, wells and other structures in order to determine its pre-construction condition and the Contractor shall prepare, for the Engineer's approval, a typed Inspection report of the findings.
2/23.9 The Report shall include photographs, drawings and sketches with levels and dimensions illustrating the structures condition, noting in particular any existing damage or structural inadequacy. Deficiencies and damage shall be suitably marked on the structure such that it is not permanently defaced.
2/23.10 Three copies of the Report shall be submitted for the approval of the Engineer. Once approved, five additional copies shall be supplied to the Engineer.
2/23.11 The Contractor shall notify the Engineer sufficiently in advance of the beginning of any excavation so that cross-sectional elevations and measurements may be taken of the undisturbed ground. The natural ground adjacent to the structure shall not be disturbed without the permission of the Engineer.
2/23.12 Trenches or foundation pits for structures or structure footings shall be excavated to the lines and grades or elevations shown on the drawings, or as ordered by the Engineer. They shall be of sufficient size to permit the placing of structures or structure footings of the full width and length shown. The elevations of the bottoms of footings, as shown on the Drawing shall be considered as approximate only and the Engineer may order, in writing, such changes in dimensions of elevations of footings as may be deemed necessary, to ensure a satisfactory foundation.
2/23.13 Unless otherwise provided for in the Drawings or Contract Documents or directed by the Engineer Structural excavation shall be carried out for a width of at least 500 mm beyond the horizontal outside limits of the foundation, footing, box culvert or structural member to which the excavation relates. Concrete blinding or sub- foundations are not to be considered as structure for the purpose of defining such excavation.
2/23.14 If during the progress of the work, loose or improperly compacted soil is encountered below the structural foundation levels, or adjacent thereof, which is the result of prior removal of utilities or structures, such material shall be completely removed within the limits as directed by the Engineer, backfilled with suitable material and compacted to 95% of the maximum dry density as determined by BS 1377 Part 4 (method 3.5 or 3.6) latest edition. Any previous excavations encountered which would in the opinion of the Engineer be detrimental to load distribution of new foundations to the underlaying soil, shall be excavated and backfilled with Class 25 concrete (clause 4/15).
2/23.15 After each excavation is completed, the Contractor shall notify the Engineer, for approval of the depth of excavation and the character of the material, prior to further structural works. Any over excavation shall be backfilled with Class 25 concrete (clause 4/15) at the Contractors expense.
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2/23.16 All rock or other hard foundation material shall be cleaned of all loose material and cut to a firm surface, either level, stepped, or serrated as directed by the Engineer. All seams or crevices shall be cleaned and grouted. All loose and disintegrated rock and thin strata shall be removed.
When the footing is to rest on material other than rock, excavation to final grade shall not be made until just before the footing is to be placed and special care shall be taken not to disturb the excavation. When the foundation material is soft or otherwise unsuitable as determined by the Engineer, the Contractor shall remove the unsuitable material and backfill with approved granular material. This foundation fill shall be placed and compacted in 150mm layers up to the foundation elevation and compacted to 95% of the maximum dry density as determined by BS 1377 Part 4 (method 3.5 or 3.6) latest edition. The placing of concrete shall follow as closely as practicable the structural excavation. 2/23.17 Control of Ground Water - Prior to the commencement of construction at any particular
location, the Contractor shall install and maintain a system of standpipes and other devices to monitor ground water level in any area which in the opinion of the Engineer is likely to be affected by the dewatering. The number, location and depth of all standpipes shall be to the satisfaction of the Engineer.
- The Contractor shall check ground water levels at weekly or where instructed by the Engineer, more frequent intervals and submit within 24 hours written reports to the Engineer in a form to be agreed.
- In the case of uncontrolled flow of water into any excavation, the Engineer reserves the right to order an immediate cessation of work and to order the Contractor to take immediate action to control the inflow of water. Such actions and remedial works shall be to the Engineer's approval.
2/23.18 Notification of Damage- The Contractor shall notify the Engineer immediately of any movement or any damage not noted in the pre-construction report, to any structure. The Contractor shall immediately cease his construction operations in the vicinity and shall take immediate action to prevent further movement or damage. The Contractor shall keep the Engineer fully informed of all such action.
2/23.19 Remedial and Preventive Works- Should remedial works be necessary due to damage caused to the structure or should the Engineer direct the contractor to carry out any works necessary to prevent damage to the structure due to the Contractor's construction works, the Contractor will present, without delay, detailed drawings and specifications, as necessary, showing his proposed remedial or preventive works for the Engineer's approval.
In either case the Contractor will suspend all construction activities in the vicinity of the structure until such time as the remedial or preventive works are carried out to the Engineer's satisfaction at the Contractor's expense.
2/23.20 Post Construction Inspection- On completion of, but prior to final acceptance of the works, the Contractor and the Engineer shall re-examine the structure to determine any change from the original conditions. The Contractor shall supply to the Engineer for approval five copies of a report describing measures he proposes to take to correct any damage which resulted from the construction of the works. The approved corrective measures shall be carried out by the Contractor at his expense, to the Engineer's satisfaction before final acceptance of the works.
2/23.21 Utilisation of Excavated Materials- All excavated material determined as suitable by the Engineer, shall be utilised as backfill or roadway fill. The surplus material, shall be disposed of as specified in sub-section 2/8 para 2. Excavated material shall not be
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deposited, at any time, so as to endanger the partly finished structure or cause an obstruction of any kind. All unsuitable material shall be disposed of to approved tips.
2/23.22 Backfill- Excavated areas around structures shall be backfilled with excavated materials or imported granular material approved by the Engineer. Backfill materials shall be placed in horizontal layers not exceeding 150mm in depth after compaction to 95% of the maximum dry density as determined by BS 1377 Part 4 latest edition (Method 3.5 or 3.6). The field density shall be determined by BS 1377 Part 9 latest edition (Method 2.1 or 2.2). Each layer of material shall be moistened or dried as required to enable thorough compaction as specified. Backfill shall be placed to the original ground level or as indicated on the drawings.
2/23.23 Backfill or embankment shall not be placed behind the walls of concrete structures or rigid frame structures until the top slab is placed and cured. Backfill and embankment behind abutments when held at the top of the superstructure shall be carried up simultaneously behind opposite abutments. Backfill shall be carried up equally on either sides of box culverts.
SECTION 3