SPECIFICATION FOR EXCAVATING AND FILLING SECTION D20

Transcription

1 SPECIFICATION FOR SECTION D20 A S.W. Revision Date Issue Authorised By Approved for Issue Date clarkebond Page 1 of 12

2 To be read with Preliminaries/ General Conditions. GENERALLY/ THE SITE 101 B GENERAL DESCRIPTION OF THE WORK: Site strip to remove all topsoil; fill material and existing foundations and structures and subterranean obstructions. A 102 B EXCAVATE: below site strip level for foundations, basements and the like. 103 B EXCAVATION: for Services as specified in the following sections: P30 Builders Work for Services R12 Drainage Below Ground R13 Land Drainage 110 SITE INVESTIGATION Report: Two reports by Terra Firma (Wales) Limited. Report No. 9476/2 dated August 2006 and Report No dated August A VARIATIONS IN GROUND WATER LEVEL Give notice: If levels encountered are significantly different from levels in the site investigation report, stated as assumed or previously measured. 150 EXISTING SERVICES/ FEATURES/ STRUCTURES Services: See section A12 for locations. Site features to be retained: See section A12 for details. Structures: See section A34 for details of protection. 151 B EXISTING SERVICES Services are anticipated under or close to the existing access road. Principle foul drainage routes from the existing school are to be established. 160 B EXISTING STRUCTURES The caretakers building to the East of the main entrance to the school has now been demolished. CLEARANCE/ EXCAVATING 164 TREE ROOTS Protected area: Do not cut roots within an area which is the larger of: - The branch spread of the tree. - An area with a radius of half the tree s height, measured from the trunk. Excavation in protected area: - Method: By Hand - Backfill as soon as possible or temporary line with polyethylene sheet to reduce evaporation. Outside protected area: Give notice of roots exceeding 25 mm and do not cut without approval. Cutting: - Make clean smooth cuts with no ragged edges. - Pare cut surfaces smooth with a sharp knife. - Treatment of cut roots: Seek specialist advice Backfill: As dug topsoil, loosely compacted 168 SITE CLEARANCE Timing: Before topsoil stripping, if any. General: Clear site of rubbish, debris and vegetation. Do not compact topsoil. Treatment: [ ] 170 REMOVING SMALL TREES, SHRUBS HEDGES AND ROOTS clarkebond Page 2 of 12

3 Identification: Clearly mark trees to be removed. Small trees, shrubs and hedges: Cut down. Roots: Grub up and dispose of without undue disturbance of soil and adjacent areas. Safety: Comply with HSE/ Arboriculture and Forestry Advisory Group Safety Guides. 175 FELLING LARGE TREES Definition: Girth over 600mm. Identification: Clearly mark trees to be removed. Safety: Comply with HSE/ Arboriculture and Forestry Advisory Group Safety Guides. Felling: As close to the ground as possible. Stumps: Remove mechanically to a minimum depth of 1.0m below ground level complete with all principle roots. Work near retained trees: Take down trees carefully in small sections to avoid damage to adjacent trees that are to be retained, where tree canopies overlap and in confined spaces generally. 180 CHIPPING AND SHREDDING General: Permitted 201 B PRIOR TO STARTING EXCAVATIONS: on site, a full method statement is to be agreed with the CA. 202 B ALL EXCAVATIONS: for foundations or pits are to be immediately protected with concrete blinding or mass concrete filling as appropriate before proceeding with adjoining excavations. See also clause E20/170A. 203 B LEVELS: to underside of concrete foundations shown on the drawings are estimated to be the final required levels. However, the actual levels shall be determined in accordance with the guidance given on the drawings and as agreed with the CA on site to achieve the necessary bearing capacity. If bases need to be taken deeper or shallower than the levels shown on the drawings then this must be agreed with the CA during excavations. 204 B THE BACKFILL: Filling up to final levels is to be carried out as soon as the bases and R.C. stub columns and ground beams are complete (and cured) in any area in order to allow as long as possible before casting of the ground floor slabs for consolidation settlements to occur in the underlying soil. 206 B THE STRIPPED FORMATION: level shall be inspected and agreed as adequate by the CA. The Subcontractor shall then place immediately a suitable depth and quality of crushed stone, hardcore and/or by other suitable means to fully protect the ground surface to prevent deterioration from site traffic and weathering. Any areas considered to be affected by lack of attention by the Subcontractor to suitable protection or undue trafficking shall be stripped down to undisturbed soil and made up in approved granular material or mass concrete as appropriate. A A 207B EXCAVATED MATERIAL CLASSIFIED AS CONTAMINATED FOR OFF SITE DISPOSAL All excavated material designated for off site disposal shall be suitably classified in accordance with WAC (Waste Acceptance Criteria) protocols. Materials shall be designated, following appropriate chemical testing, for deposition in the following types of landfill: Inert waste landfill Stable non-reactive hazardous waste in non-hazardous landfills Hazardous waste landfills Transportation of excavated materials shall be in accordance with: The Environmental Protection Act 1990 (Duty of Care) as laid down by the Environment Agency Planning conditions clarkebond Page 3 of 12

4 Health and Safety Executive (HS(G)66) - Protection of workers and the general public during the development of contaminated land. All material must be removed for off site disposal by a licenced contractor. A copy of all consignment notes shall be available for inspection by the CA and incorporated into the Site File in accordance with the requirements of the Construction (Design and Management) Regulations B EXCAVATED MATERIAL CLASSIFIED FOR RE-USE ON SITE All excavated material designated for re-use on site, considered contaminated at a location remote from the original point of excavation must have approval from the Environment Agency for use as filling. Excavated materials must not be mixed or blended for re-use on site without the agreement of the Environment Agency Transportation of excavated materials shall be in accordance with: The Environmental Protection Act 1990 (Duty of Care) as laid down by the Environment Agency Planning conditions Health and Safety Executive (HS(G)66) - Protection of workers and the general public during the development of contaminated land. A copy of all records of agreements with the Environment Agency and others shall be available for inspection by the CA and incorporated into the Site File in accordance with the requirements of the Construction (Design and Management) Regulations B MATERIALS ARISING Ownership: Excavated material including topsoil, surplus to requirements for filling remain the property of the Employer unless the Contractor: - Is instructed to remove them from the site, or - Purchases them at a price to be agreed. 213 B TOPSOIL: means the top layer of soil that can support vegetation. 220 STRIPPING TOPSOIL General: Before beginning general excavation or filling, strip topsoil from areas where there will be regrading, buildings, pavings/ roads and other areas shown on drawings. Depth: - Remove to an average depth of 300mm - Give notice where the depth of topsoil is difficult to determine. Handling: Handle topsoil for reuse or sale in accordance with clause 225. Around trees: Do not remove topsoil from below the spread of trees to be retained. Site storage: Submit proposals. 221 TREATING TOPSOIL Treatment: Apply a suitable translocated nonresidual herbicide. Timing: Not less than two weeks before excavating topsoil. 225 HANDLING TOPSOIL Aggressive weeds: - Species: Included in the Weeds Act, section 2 or the Wildlife and Countryside Act, Schedule 9, part ll. - Give notice: Obtain instructions before moving topsoil. Earthmoving equipment: Select and use to minimize disturbance, trafficking and compaction. Contamination: Do not mix topsoil with: - Subsoil, stone, hardcore, rubbish or material from demolition work. - Oil, fuel, cement or other substances harmful to plant growth. - Other grades of topsoil. Multiple handling: Keep to a minimum. Use topsoil immediately after stripping. Wet conditions: Handle topsoil in the driest condition possible. Do not handle during or after heavy rainfall or when it is wetter than the plastic limit as defined by BS 3882, Annex N2. clarkebond Page 4 of 12

5 230 B BENCHING: Surfaces of excavations with a gradient greater than 1:5 (20%) and which are to receive filling: Provide horizontal benches cut to match the depths of compacted layers of filling. 240 ADJACENT EXCAVATIONS Proximity: Where an excavation encroaches below a line drawn at an angle from the nearest formation level of another higher excavation, the lower excavation, all work within it and backfilling thereto must be completed before the higher excavation is made. Angle of line from horizontal: 30 degrees. 250 PERMISSIBLE DEVIATIONS FROM FORMATION LEVELS Beneath mass concrete foundations: ± 25mm. Beneath ground bearing slabs and r.c. foundations: ± 15mm. Embankments and cuttings: ± 50mm. Ground abutting external walls: ± 50mm, but such as to ensure that finished level is not less than 150mm below dpc. 255 ACCURACY LINEAR DIMENSIONS Permissible deviations from linear dimensions generally: to CIRIA Special publication SP B FORMATIONS GENERALLY: 1. To be inspected by CA before new work is laid on them. Give CA not less than 24 hours notice of when formations will be ready for inspection. 2. Remove the last 50mm of excavations just before inspection. Trim excavations to required profiles and levels, and remove all loose material. Protect from elements until sealed. 3. Unless otherwise instructed seal formations within 4 hours of inspection with concrete or other specified fill. 270 FOUNDATIONS GENERALLY Give notice if: - A natural bearing formation of undisturbed subsoil is not obtained at the depth shown on the drawings. - The formation contains soft or hard spots or highly variable material. 280 TRENCH FILL FOUNDATIONS Excavation: Form trench down to formation in one operation. Safety: Prepare formation from ground level. Inspection of formations: Give notice before commencing excavation. - Period of notice: 3 working days Shoring: Where inspection of formation is required, provide localised shoring to suit ground conditions. Concrete fill: Place concrete immediately after inspection and no more than four hours after exposing the formation. 290 A FOUNDATIONS IN MADE UP GROUND Depth: Excavate down 200mm into a natural formation of undisturbed sub-soil. Discrepancy: Give notice and obtain instructions if this is at a lesser or greater depth than that shown on the drawings. 300 B EARTHWORK SUPPORT: Use as necessary to support sides of excavations and remove on completion unless otherwise instructed. Take measurements of any supports which are left in position and inform CA. 310 UNSTABLE GROUND Generally: Ensure that the excavation remains stable at all times. clarkebond Page 5 of 12

6 Give notice: Without delay if any newly excavated faces are too unstable to allow earthwork support to be inserted. Take action: If instability is likely to affect adjacent structures or roadways, take appropriate emergency action. 320 RECORDED FEATURES Recorded foundations, beds, drains, manholes, etc.: Break out and seal drain ends. Contaminated earth: Remove and disinfect as required by local authority. 330 UNRECORDED FEATURES Give notice: If unrecorded foundations, beds, voids, basements, filling, tanks, pipes, cables, drains, manholes, watercourses, ditches, etc. not shown on the drawings are encountered. 340 B WATERWAYS: Temporarily divert as necessary all field drains and other waterways not shown on the drawings and encountered during the excavations, and: 1. If possible, reinstate on completion. 2. If not possible to reinstate, obtain instructions. 350 EXISTING WATERCOURSES Diverted watercourses which are to be filled: Before filling, remove vegetable growths and soft deposits. 360 A EXCESS EXCAVATION Excavation taken wider than required: - Backfill: Approved granular material or mass/ plain concrete as instructed. Excavation taken deeper than required: - Backfill: Granular material of the type designed to be laid on the correct formation level, or mass/ plain concrete as directed by CA. 361 B EXCESS DEPTH UNDER FOUNDATIONS: All excavations under foundations taken deeper than required, to be backfilled with mass/ plain concrete. 370 UNDERGROUND STRUCTURES IN LANDSCAPE AREAS Generally: Remove walls, roads, foundations, disused services, drains, manholes and the like to a minimum depth. Minimum depth below finished levels: - Grass, ground cover and perennial planting: 500mm. - Shrub planting: 750mm. - Within 2m of tree planting: 1000mm. Walls and slabs remaining: In every 10m 2 of wall or slab, make a drainage hole at least 600mm diameter. DISPOSAL OF MATERIALS 410 A EXCAVATED TOPSOIL STORAGE Storage: Stockpile in temporary storage heaps in areas agreed with the CA. 411 B EXCAVATED TOPSOIL STORAGE Storage: Stockpile sufficient excavated topsoil to carry out subsequent topsoiling operations in temporary spoil heaps in areas agreed with CA. 420 TOPSOIL STORAGE HEAPS Location: Submit proposals. Height (maximum): 1m Protection: - Do not place any other material on top of storage heaps. - Do not allow construction plant to pass over storage heaps. clarkebond Page 6 of 12

7 - Prevent compaction and contamination. 441 SURPLUS SUBSOIL Excavated material: Stockpile in temporary storage heaps. Retained material: Spread and level surplus subsoil on site. - Locations: Submit proposals. - Protected areas: Do not raise soil level within root spread of trees that are to be retained. Remaining material: Remove from site. 450 WATER Generally: Keep all excavations free from water until: - Formations are covered. - Below ground constructions are completed. - Basement structures and retaining walls are able to resist leakage, water pressure and flotation. Drainage: Form surfaces of excavations and fill to provide adequate falls. Removal of water: Provide temporary drains, sumps and pumping as necessary. Do not pollute watercourses with silt laden water. 454 GROUND WATER LEVEL/ RUNNING WATER Give notice: If it is considered that the excavations are below the water table. Springs/ Running water: Give notice immediately if encountered. 457 PUMPING General: Do not disturb excavated faces or stability of adjacent ground or structures. Pumped water: Discharge without flooding the site, or adjoining property. Sumps: Construct clear of excavations. Fill on completion. - Locations: Submit proposals. 462B PERMANENT DRAINAGE SYSTEM Disposal of water from the excavations through system: May be used subject to: - Obtaining consent where necessary from the appropriate authority before discharging water. - Making good any damage or disturbance caused to drainage systems by discharging water. FILLING 500 A PROPOSED FILL MATERIALS Details: Submit full details of proposed fill materials to demonstrate compliance with specification, including: - Type and source of imported fill. - Proposals for processing and reuse of material excavated on site. - Test reports as required elsewhere. Approval: Obtain approval from CA of all filling materials whether site excavated or imported before use. Timing: Allow 21 days before starting filling minimum. 510A HAZARDOUS, AGGRESSIVE OR UNSTABLE MATERIALS General: Do not use fill materials which would, either in themselves or in combination with other material or ground water, give rise to a health hazard, damage to building structures or instability in the filling, including material that is: - Frozen or containing ice. - Organic. - Contaminated or noxious. - Susceptible to spontaneous combustion. - Likely to erode or decay and cause voids. - With excessive moisture content, slurry, mud or from marshes or bogs. - Clay of liquid limit exceeding 80 and/or plasticity index exceeding 55. clarkebond Page 7 of 12

8 - Unacceptable, class U2 as defined in the Highways Agency Specification for Highway Works, clause Chalk or Burnt colliery shale Testing: Submit test reports from a UKAS/ NAMAS accredited laboratory demonstrating compliance of the proposed material(s). 512 B SOLUBLE SULFATE CONTENT Soluble sulfate content (SO 3 ) of materials for filling under concrete slabs or within 1 m of substructures when tested to BS , clause 5 using a 2:1 water-soil extract (maximum): 1 g/litre 520 A FROST SUSCEPTIBILITY General: Fill must be non frost-susceptible as defined in Highways Agency Specification for Highway Works, clause Test reports: If the following materials are proposed, submit a report from a UKAS/ NAMAS accredited laboratory confirming the materials are non frost-susceptible: - Fine grained soil with a plasticity index less than 20%. - Coarse grained soil or crushed granite with more than 10% retained on a 0.063mm sieve. - Crushed limestone fill with average saturation moisture content in excess of 3%. 525 A TESTING OF SUITABILITY OF FILL MATERIALS BEFORE START OF FILLING Laboratory: UKAS/ NAMAS accredited laboratory. Submit report to: CA and Structural Engineer. - Approval: Obtain approval of all filling materials whether site excavated or imported before use. - Timing: Allow 21 days minimum. Samples: Deliver to laboratory as required. - Additional requirements: None Tests: Submit proposals in accordance with good practice. Frequency: Submit proposals in accordance with good practice. 530 PLACING FILL Excavations and areas to be filled: Free from loose soil, rubbish and standing water. Freezing conditions: Do not place fill on frozen surfaces. Remove material affected by frost. Replace and recompact if not damaged after thawing. Adjacent structures, membranes and buried services: - Do not overload, destabilise or damage. - Submit proposals for temporary support necessary to ensure stability during filling. - Allow 14 days (minimum) before backfilling against insitu concrete structures. Layers: Place so that only one type of material occurs in each layer. Earthmoving equipment: Vary route to avoid rutting. 535 COMPACTION General: Compact fill as soon as possible after placing. After compaction: Surface of each layer must be well closed, showing no movement under compaction plant, and without cracks, holes, ridges, loose material and the like. Defective areas: Remove and recompact to full thickness of layer using new material. 540 BENCHING IN FILL Adjacent areas: If, during filling the difference in level between adjacent areas of filling exceeds 600mm, cut into edge of higher filling to form benches 600mm minimum width and height equivalent to depth of a layer of compacted filling. New filling: Spread and compact to ensure maximum continuity with previous filling. 610 A COMPACTED FILLING FOR LANDSCAPE AREAS Fill: Material capable of compaction by light earthmoving plant and excluding the following: - Material from marshes or bogs. clarkebond Page 8 of 12

9 - Peat, logs, stumps, slurry, mud and perishable material. - Material susceptible to spontaneous combustion. - Material in a frozen condition. - Clay of liquid limit exceeding 80 and/or plasticity index exceeding Material having a moisture content greater than the maximum permitted in the specification. - Material containing scrap and rubbish. - Material likely to erode or decay and cause voids. - Unacceptable material class U2 as defined in clause 601 of the Highways Agency Specification for Highway Works. Filling: Layers not more than 200mm thick. Lightly compact each layer to produce a stable soil structure. 615 A LOOSE TIP FILLING FOR LANDSCAPE AREAS Fill: Materials excluding the following: - Material from marshes or bogs. - Peat, logs, stumps, slurry, mud and perishable material. - Material susceptible to spontaneous combustion. - Material in a frozen condition. - Clay of liquid limit exceeding 80 and/or plasticity index exceeding Material with excessive moisture content. - Material likely to erode or decay and cause voids. - Unacceptable material class U2 as defined in clause 601 of the Highways Agency Specification for Highway Works. Filling: Do not firm, consolidate or compact when laying. Tip and grade to approximate levels in one operation with minimum of trafficking by plant. 617A 618A HIGHWAYS AGENCY TYPE 1 GRANULAR FILLING Fill: To Highways Agency Specification for Highway Works, clause 803: - Crushed rock (other than argillaceous rock). - Crushed concrete. - Recycled aggregates. - Crushed non-expansive slag to clause Filling: To Highways Agency Specification for Highway Works, clauses and 802. HIGHWAYS AGENCY TYPE 2 GRANULAR FILLING Fill: To Highways Agency Specification for Highway Works clause 804: - Crushed rock (other than argillaceous rock). - Crushed concrete. - Crushed non-expansive slag to clause Natural gravel. - Natural sand. Filling: To Highways Agency Specification for Highway Works clauses and SUBGRADE IMPROVEMENT LAYER (CAPPING) Fill: To Highways Agency Specification for Highway Works, Table 6/1, Class 6F1 or 6F2. Filling: Place and compact to Highways Agency Specification for Highway Works, Table 6/1, clause 612 and clause 613.3, and B COMPACTED GENERAL FILLING: Fill: Materials arising from the excavations (or, where instructed imported) complying with Group 1 or Group 2 as defined below. If both suitable and unsuitable material is excavated, select and keep separate sufficient suitable material. If there is insufficient suitable excavated material provide CA with details and obtain instructions regarding the importation of material. Group 1: Cohesive materials: - Clays and marls containing up to 20% of gravel and having a moisture content not less than the value of the plastic limit minus 4 (determined in accordance with BS , clause 5). - Chalk having a saturation moisture content of 20% or greater. clarkebond Page 9 of 12

10 Group 2: Dry cohesive and well graded granular materials: - Clays and marls containing more than 20% of gravel and/or having a moisture content less than the value of the plastic limit minus 4 (determined in accordance with BS 1377 Part 2, clause 5) - Chalk having a saturation moisture content within the range 15-20%. - Well graded sands and gravels with a uniformity coefficient of more than Crushed hard rock or quarry waste (other than chalk). - Crushed concrete, crushed brick or tile, free from plaster, wood, organic material and rubbish. Filling: Lay and compact in layers using suitable plant as in the table below. The figures given alongside each type of plant and of each material group are the maximum depth of compacted layer in mm and (in parentheses) the minimum number of passes. Types of plant (alternatives) Group 1 Materials Group 2 Materials Smooth wheeled roller tonnes per m width of roll (8) 125(10) (6) 125(8) Over (4) 150(8) Vibrating roller: Static load in tonnes per m width of roller (12) 125(12) (8) 150(8) (4) 150(4) (4) 175(4) Over (4) 225(4) Vibrating plate compactor: Static load in tonnes per sq m of base plate (6) (6) 125(6) Over (6) 150(5) Vibro-tamper: Static load in kg (3) 100(3) Over (3) 150(3) Power rammer: Static load in kg Over (4) 150(6) 622B PROOF ROLLING STRIPPED FORMATION Ensure the formation is free of all loose soil, boulders, large stones, rubbish, ice or frozen material and standing water. Roll formation using compaction plant selected from the table below as most suited to the formation material. Group 1: Cohesive materials: - Clays and marls containing up to 20% of gravel and having a moisture content not less than the value of the plastic limit minus 4 (determined in accordance with BS , clause 5). - Chalk having a saturation moisture content of 20% or greater. Group 2: Dry cohesive and well graded granular materials: - Clays and marls containing more than 20% of gravel and/or having a moisture content less than the value of the plastic limit minus 4 (determined in accordance with BS 1377 Part 2, clause 5) - Chalk having a saturation moisture content within the range 15-20%. - Well graded sands and gravels with a uniformity coefficient of more than Crushed hard rock or quarry waste (other than chalk). - Crushed concrete, crushed brick or tile, free from plaster, wood, organic material and rubbish. The figures given alongside each type of plant and of each material group are the minimum number of passes. Types of plant (alternatives) Group 1 Materials Group 2 Materials Smooth wheeled roller tonnes per m width of roll clarkebond Page 10 of 12

11 Over Vibrating roller: Static load in tonnes per m width of roller Over Inform and agree with the CA or Engineer on suitability of the formation and any identified soft spots. Excavate locally to remove soft material and backfill with graded granular fill in layers and compact as clause 633B. 626 A COMPACTED GENERAL FILLING Fill: Materials arising from the excavations or imported as defined below: - Well graded sands and gravels with a uniformity coefficient of more than Crushed hard rock or quarry waste (other than chalk). - Crushed concrete, crushed brick or tile, free from plaster, wood, organic material and rubbish. Excavated material: Select suitable material and keep separate. Filling: Spread and level material in layers. As soon as possible thoroughly compact each layer. Proposals: Well in advance of starting work submit details of proposed: - Materials to be used, including quantities of each type. - Type of plant. - Maximum depth of each compacted layer. - Minimum number of passes per layer. Timing: Obtain approval before proceeding. 628 B ROCK FILLING Fill: Hard material comprising rock, broken stone, hard brick, concrete or other comparable inert material graded from 400 mm to 150 mm and with not more than 10% less than 150 mm in size. Filling: Spread and level in layers not exceeding 450 mm loose depth using a crawler tractor weighing not less than 15 tonnes. Compact each layer with at least twelve passes of: - a towed vibratory roller with a static load of at least 50 kg per 25 mm width of roll, or - a grid roller with a load of at least 225 kg per 25 mm width of roll, or - other approved plant. Where rock filling contains suitable soft material, compact in accordance with Highways Agency Specification for Highways Works, as for well graded granular and dry cohesive soils in Table 6/ B GRADED GRANULAR FILLING Fill: To Highways Agency Specification for Highway Works, Clause 803 (Type 1) or other approved Filling: Lay and compact to Highways Agency Specification for Highway Works, Clause STARTER LAYER OF COMPACTED FILLING Fill: Suitable hard granular material. Compact thoroughly. Thickness: 100mm. 650 PROTECTION OF COMPACTED FILLING Temporary protective filling: Before allowing construction traffic, raise level of compacted cohesive soil filling at least 150mm above formation level using properly compacted temporary filling. Removal: Remove temporary protective filling from site before permanent construction. 700 BACKFILLING AROUND FOUNDATIONS clarkebond Page 11 of 12

12 Under oversite concrete and pavings: Hardcore. Under grassed or soil areas: Material excavated from the trench, laid and compacted in 300mm maximum layers. 710 A HARDCORE FILLING Fill: Granular material, free from harmful matter and excessive dust, well graded with a uniformity coefficient greater than 10, all pieces less than 75mm in any direction, minimum 10% fines value of 50kN when tested in a soaked condition to BS , and in any one layer only one of the following: - Crushed hard rock (other than argillaceous rock or chalk) or quarry waste with not more binding material than is required to help hold the stone together. - Crushed concrete, crushed brick or tile, free from plaster, timber and metal. - Gravel or hoggin with not more clay content than is required to bind the material together, and with no large lumps of clay. - Natural gravel. Filling: Spread and level in 150mm maximum layers. Thoroughly compact each layer. 720 B HARDCORE UNDER CONCRETE SLABS Fill: As clause 710 and not less than 150mm thick. Preparation: Excavate extra material as necessary. Increase thickness of hardcore as necessary to make up levels from stripped site levels to underside of slabs. Maximum total thickness of hardcore: 600mm. 730 A BLINDING Surfaces to receive reinforced concrete foundations, pile caps, ground beams: Lay 50mm blinding concrete. Surfaces to receive sheet overlays or concrete: Blind with: - Concrete where shown on the drawings or - Sand, fine gravel or other approved fine material applied to fill interstices. Moisten as necessary before final rolling to provide a flat, close smooth surface. Sand for blinding: To BS EN 12620, grade 0/4 or 0/2 (MP). Permissible deviations on surface level: mm. A clarkebond Page 12 of 12