spec for reinforced soil structures

7/30/2019 Spec for Reinforced Soil Structures

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SPECIFICATION FOR REINFORCED SOIL STRUCTURES

1.0 INTRODUCTION

2.0 DESIGN

2.1 Subsoil Investigation2.2 Design Standard2.3 Design Calculation2.4 ISO Certification

3.0 DEFINITIONS

4.0 MATERIAL REQUIREMENTS

4.1 Backfill material4.1.1 Physical Properties4.1.2 Resistivity4.1.3 pH value4.1.4 Chloride and sulphate content4.1.5 Sulphide Content4.1.6 Redox Potential4.1.7 Organic content4.1.8 Microbial Activity

4.2 Facing Element4.2.1 Precast Concrete Facing Panel

4.2.1.1 Casting of Panel4.2.1.2 Concrete Strength and Quality4.2.1.3 Facing Finish and Tolerance4.2.1.4 Anchorage Lugs4.2.1.5 Lifting Hooks4.2.1.6 Reinforcement Bars4.2.1.7 Marking4.2.1.8 Handling, Storage and Transportation

4.2.2. Alternative Facing Element

4.3 Concrete Anchor Blocks

4.4 Reinforcing Elements4.4.1 Galvanised Carbon Steel Bars4.4.2 Galvanised Carbon Steel Strips

4.5 Fabrication and Galvanisation

4.6 Connections

4.7 Joint Materials

4.8 Cushion Pad

5.0 CONSTRUCTION REQUIREMENTS



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The scope of this specification covers the design, supply, delivery and construction of reinforced soil structures with inextensible reinforcement.

2.0 DESIGN

2.1 Subsoil Investigation

Subsoil investigation shall be carried out prior to the commencement of thedesign and construction works to determine the adequacy of the subsoil tosupport the reinforced soil structure.

Scope of SI shall be performed by qualified P.Eng and according to therequirements specified in “Guideline for Planning Scope of SI for RoadWork”.

2.2 Design Standard

The following standard shall be adopted in the design of reinforced soilstructures:

BS 8006: 1995 Code of Practice for Strengthened/Reinforced Soils and otherfills.

The requirements of the above standard shall be deemed to form part of thisspecification.

2.3 Design Calculation

2.3.1 Design Report including design calculations shall be submitted by thespecialist contractor and indepently audited or to be reviewed bygeotechnical specialist registered with IEM / ACEM or checked by theconsultant.

2.3.2 Design Calculations and drawings shall be endorsed by a ProfessionalEngineer.

2.4 ISO Certification

The approved specialist contractor for the contruction of Reinforced SoilStructures shall have attained the certification of ISO 9001 unless otherwiseapproved by the client / owner.

3.0 DEFINITIONS



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“Anchored earth” shall mean a form of reinforced soil which uses anchors embeddedwithin the backfill soil mass to provide stability. Resistance to pull-out is provided bypassive action of the anchor and friction along the anchor shaft.

“Backfill material” shall mean fill material in the reinforced soil structure in contactwith the reinforcing elements, connections and facings including both selected fill andfilter material.

“Cohesive frictional fill” shall mean fill containing more than 15 % material passing a63 µm sieve in accordance with BS 410. See section 4.1.1

“Frictional fill” shall mean fill containing less than 15 % material passing a 63 µmtest sieve in accordance with BS 410. See section 4.1.1

“Reinforced earth” shall mean a form of reinforced soil which uses reinforcingelements embedded within the backfill soil mass to provide stability. Resistance topull out is provided solely by friction between the reinforcing element and the backfillmaterial.

“Reinforced soil structure” shall mean a structure with vertical or near-vertical facewhich comprises tensile reinforcements act through interface friction, bearing or othermeans to improve stability.

“Inextensible reinforcement” shall mean reinforcement that sustains the design loadsat strains less than or equal to 1%.

4.0 MATERIAL REQUIREMENTS

The component materials of a Reinforced Soil structure shall consist of the backfillmaterial, facing elements, reinforcing element with or without the anchor blocks andother accessories.

4.1 Backfill Material

The backfill material used in the Reinforced Soil structure shall be a frictionalfill material or cohesive frictional fill material free from organic or otherdeleterious material.

Cohesive frictional fill material may be allowable for Anchored Earth systemonly subject to the approval of the S.O. The use of cohesive frictional fillshall take proper consideration of the drainage requirements and the selectionof appropriate soil parameters.

The backfill material shall conform to the physical, electrochemical andchemical properties detailed below:-

4.1.1 Physical properties



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The grain size distribution and index properties shall comply with thefollowing table:

B. S. Sieve Size(mm)125 100 10075 85 - 100 85 - 10014 25 - 100 40 - 902 15 - 100 15 - 79

600 m icrons 9 - 100 15 - 7563 m icrons <15 15- 452 m icrons - 0 -20

Liquid Lim it % Not Applicable <45Plasticity Index % Not Applicable <25

Percentage by Mass Passing the Size Shown

F ric tional F ill C ohesiv e F rictional F ill

4.1.2 Resistivity

The resistivity of the backfill material shall be determined on a saturatedspecimen after one hour of soil water contact at 25 o Centigrade. Theresistivity of the material shall be greater than 1000 ohm-cm and 3000 ohm-cm for structures constructed outside water and in soft water respectively.

4.1.3 pH value

The pH value of the material shall be in the range of 5 to 10.

4.1.4 Chloride and Sulphate Content

Where the resistivity of the material is in the range of 1000 to 5000 ohm-cm orthe material is of industrial origin, the concentration of Chloride (Cl -) andsulphate (SO 4

2-) shall be checked and shall not exceed the following limits:-

Outside In softwater water

Cl- (mg/kg) 200 100SO4

2- (mg/kg) 1000 500

4.1.5 Sulphide Content

Where the origin of the material raises the possibility of the presence of sulphide, the concentration of the sulphide shall be checked and shall notexceed 300 and 100 mg/kg for structures constructed outside water and in softwater respectively.

4.1.6 Redox Potential



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The minimum redox potential shall be 0.43 volts based on laboratory test onsamples in accordance with BS 1377:Part 3

4.1.7 Organic Content

The maximum organic content shall be 0.2%. The test shall be carried out inaccordance with BS 1377:Part 3.

4.1.8 Microbial Activity

The Microbial Activity Index shall be less than 5. A method of calculating theMicrobial Activity Index may be obtained by reference to TRRL ContractorReport 54 ‘Soil Corrosivity Assessment’.

4.2 Facing Element

4.2.1 Precast Concrete Facing Panels

4.2.1.1 Casting of Panel

The panels shall be cast on a flat area with the mouldsproperly assembled such that the joints are grout tight. Theconcrete shall be placed and compacted to avoid honeycombsand blemishes. Care must be exercised so that the insertsshall not contact or be attached to the reinforcements. Thepanels shall only be demoulded after the concrete hasachieved a minimum compressive strength of 7 MPa.

4.2.1.2 Concrete Strength and Quality

Panels shall be made of vibrated concrete with the followingrequirements :

Characteristic compressive strength at 28 days : 30 MPaMaximum aggregate size : 20 mmMaximum free water/cement ratio : 0.55Minimum cement content 325 kg/m 3

The cover to reinforcement shall be in accordance to BS8110but not less than 40 mm.

For sea walls or structures facing very severe exposureconditions, thicker panels with higher cement content shall bespecifically designed for the intended purpose.



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4.2.1.3 Facing Finish and Tolerances

The finish of the exposed face of the panel shall be as shownin the drawings and shall be free of honeycombs, stains,irregularities or deep cracks. Surface deviation from smoothformed surfaces measured over a length of 1.5 m shall notexceed 5 mm.

Tolerance in dimensions are as follows :

a. the height of full panels shall be within +/- 5 mm whilethe height of half panels shall be within +/- 3 mm.

b. the width of all panels shall be within +/- 5mmc. the difference between the lengths of the diagonals shall

not exceed 10 mmd. twist or warp shall not exceed 5 mm

4.2.1.4 Anchorage Lugs

The anchorage lugs shall be pre-bent, holed and cast into thefacing panels in accordance to the dimensions shown in thedrawings. They shall be hot dipped galvanised to a minimumthickness of 85 µ m in accordance to BS 729. Care must betaken to ensure that the lugs do not come into contact withany surface of the internal reinforcements of the panels orblocks.

4.2.1.5 Lifting Hooks

The lifting hooks shall be pre-bent and cast into the facingpanels in positions in accordance to the dimensions shownson the drawings.

4.2.1.6 Reinforcement Bars

Where required the reinforcement bars shall be placed inaccordance with the drawings. They shall be high yielddeformed bars in conformity with MS 146:1973, BS4449:1969 and 1978.

4.2.1.7 Marking

The date of manufacture and type of each panel shall beclearly scribed on the unexposed surface of the panel.

4.2.1.8 Handling, Storage and Transportation

All the panels shall be handled, stored and transported in sucha manner as to eliminate the possibilities of chipping,



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discoloration, cracks, fractures, stains, and excessive bendingstress. The panels shall be stored in such a way that they arefirmly supported and the exposed finish surface protectedfrom staining. The concrete strength of the panels shallreach a minimum compressive strength of 23 MPa beforethey are allowed to be transported.

4.2.2 Alternative facing element shall be subjected to the approval of S.O.provided the structural strength of the alternative facing element isequivalent to the precast concrete facing panels.

4.3 Concrete Anchor Blocks

For Anchored Earth system that requires concrete anchor blocks, they shall becast with the same concrete strength and quality as stated in clause 4.2.1.2.The dimensions of the blocks shall not be less than those shown in thedrawings.

4.4 Reinforcing Elements

The reinforcing elements shall either be galvanised carbon steel barsconnected to concrete anchor blocks or galvanised carbon steel strips.

4.4.1 Galvanised Carbon Steel Bars

The reinforcing bars shall generally be in accordance with thecomposition and property requirements of MS 146 or BS 4449:1988.

4.4.2 Galvanised Carbon Steel Strips

The carbon steel strips shall comply with BS 1449: Part 1 (1972) eitherquality KHR 34/20P or KHR 54/35P.

4.5 Fabrication and Galvanisation

The reinforcing elements shall be cut to length and threaded or holed inspecified locations. They shall be inspected to ensure that they are free fromdefects that may impair their strength and durability.

They shall be hot dipped galvanised with zinc in accordance with BS 729 witha minimum thickness of 85 µm. The sacrificial thickness to be allowed for oneach surface exposed to corrosion shall be 0.75 mm.

4.6 Connections

Connections shall be as specified on the drawings and shall comprise one ormore of the following:-



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a) Precision hexagon bolts, screws and nuts shall comply with thedimensional requirements of BS 3692 and shall be made from steel alloyGrade 8.8 complying with BS 3692 hot dipped galvanised in accordancewith the requirements of BS 729.

b) Black hexagon bolts, screws and nuts shall comply with BS 4190 andshall be hot dipped galvanised in accordance with the requirements of BS 729. The strength grade designation of bolts and screws shall not beless than 4.6 and of nuts not less than 4.0.

c) Plain washers shall be of either Form A or Form E to BS 4320 and shallbe made from cold rolled carbon steel strip CS4 complying with BS1449:Part 1 hot dipped galvanised in accordance with BS 729.

d) Anchorage lugs shall be made from carbon steel strips complying withBS 149:Part 1 (1972) either of quality KHR 34/20/P or KHR 54/35P.

4.7 Joint Materials

The fillers for the vertical and horizontal joints where pads are used shall beflexible open cell polyurethane foam strips of 40 mm square cross section orapproved equivalent materials.

4.8 Cushion Pad

The cushion pads placed at the horizontal joint shall be made of rubber withshore hardness 85 or approved equivalent materials..

5.0 CONSTRUCTION REQUIREMENTS

5.1 Method Statement

The contractor shall submit to the engineer method statement prior to thecommencement of construction. The method statement shall contain specificworking details of manpower, machine and materials requested to execute theworks. Proposals shall also include the following:-

a. sequence of construction,b. programme of work,c. details of compaction methods including the thickness of compacted fill

layers and capacities of the earthmoving and compaction equipment,d. method of supporting the facing panels during construction,e. details of all necessary temporary works including temporary drainage for

the construction of the reinforced soil structures, andf. the names and records of experience of the supervisory staff to be used on

the works.



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5.2 Setting Out

The setting out shall be carried out as shown on the set out drawings.

5.3 Site Preparation

5.3.1 Excavation

Confirmatory tests such as Mackintosh probes or boreholes specifiedby designer shall be carried out to confirm the bearing capacity beforeexcavation.

Excavation for the base of the wall shall be carried out in accordancewith the site setting out in accordance with the drawing.

5.3.2 Base Preparation

The foundation base shall be graded level and well compacted for awidth equal to the length of the reinforcing elements. Any weak material or debri shall be removed and replaced with compactedgranular material .

5.3.3 Concrete levelling pad

The plain concrete levelling pad shall be cast accurately to line andlevel as detailed on the drawing 24 hours before the actual wallerection works commence. Grade 20 concrete shall be used and noreinforcement is required.

5.4 Wall Erection

5.4.1 Installation

The facing panels shall be hoisted with the aid of a lifting device.They are placed in sucessive courses. The spacing, level and alignmentof each panel shall be checked immediately after its placement andagain at the completion of each course.

The initial row of panels shall be braced externally. Each row of thepanels shall be followed immediately by the placement of fill and theconnection of the reinforcingelements before the next successive horizontal row of panels is beingerected. The subsequent rows of panels shall be held in place bytemporary clamps securing the present rows of panels to the previouslyerected rows which is already held firmly in place by the reinforcingelements buried in the backfill.

Except for the bottom course of panels, all others panels shall be tiltedtowards the fill material during placement to compensate for the



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outward movement expected during or subsequent to compaction of the fill material. The degree of inclination shall be adjusted wherenecessary as placement and compaction of fill material proceeds toensure that the verticality of the wall complies with the requirements.

5.4.2 Joint Materials and Cushion Pads

Joint materials shall be placed in all the joints between the panels.They shall be placed on the cleaned top edges of each facing panels

just prior to the placing of the mating facing panel. No joint material isrequired between the levelling pad and the bottom course of the facingpanels.

Cushion pads shall be placed at the slots on the top edge of each panelsbefore the installation of the subsequent row of panels.

5.4.3 Alignment and Verticality

The alignment and verticality is constantly checked with a plumb boband adjusted with the aid of temporary timber wedges inserted into the

joints between the panels. The timber wedges shall be removed assoon as their functions are fulfilled. The deviation from the designedalignment and verticality shall not exceed 50 mm. Ribs and otherfeatures on the face shall align exactly with corresponding features of adjacent panel.

5.5 Backfilling

5.5.1 Placement of Fill

Backfilling operation shall be carried out immediately following thecompletion of the installation of each row of panels. The fill materialshall be deposited, spread, levelled and compacted in layers of thickness of not exceeding 375 mm so that each reinforcing elementcan be fixed at the required level on top of the compacted fill materialwithout any voids forming directly underneath the reinforcing element.

The direction of travel of the construction vehicle for the placement,spreading and compaction of the fill shall be parallel to the alignmentof the wall at all time. Sharp turn of vehicle causing centrifugal forcesexerting toward the rear face of the panels shall be avoided.

No heavy vehicle weighing more than 1000 kg shall be allowed withinthe 1.5 m zone from the rear face of the panel.

The travelling of construction vehicles especially those with crawlertrack wheels directly onto the reinforcing element is prohibited.



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5.5.2 Compaction

The fill material shall be compacted to 95% of the maximum drydensity as determined in accordance with BS 1377:1990. Part 4 (4.5kgRammer)

During the backfilling operation and compaction, trucks and heavyconstruction vehicles shall be kept back at least 1.5 m away from theback face of the facing panel. The 1.5 m zone shall be compacted witha 1.0 ton vibratory plate compactor for at least three passess.

5.6 Drainage

5.6.1 Subsoil Drainage

The subsoil pipe, when indicated on drawing, shall be a 100 mmdiameter perforated PVC pipe or approved equivalent. The pipe shallbe perforated with 4 nos. 10 mm diameter concentric holes staggeredat 150 mm longitudinal spacing. Laying of the subsoil pipe shall be inaccordance with the levels designated on the drawings.

5.6.2 Temporary Surface Drainage

During the construction of the reinforced soil structure, temporarydrainage shall be constructed to divert any surface run-off away fromthe structure.

At the end of each day any surplus backfill behind the structure shallbe level-off at a gentle slope so that any surface run-off can flow into

the temporary drainage. Surface runoff water from adjacent area shallnot be allowed to enter the reinforced soil structure construction area.

5.7 Testing and Monitoring

5.7.1 Pull Out Test

Pull out test shall be carried out by the specialist contractor asspecified or as directed by the S.O.

5.7.2 Monitoring

Monitoring and instrumentation of the wall , where required, shall becarried out as shown in drawing.



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6.0 METHOD OF MEASUREMENT

6.1 Supply of System Components Materials

The unit of measurement for the supply of all system components materials forthe wall including the facing panels, reinforcing elements, anchor blocks, jointmaterials, fasteners and other accessories shall be in square metres of the wallsurface area.

6.2 Excavation

The unit of measurement for the volume of earth excavated shall be in cubicmeters.

6.3 Wall Erection

The unit of measurement for wall erection shall be in square metres of wallsurface area erected. The rate shall include compensation for all labour andmaterials required to install the facing elements, reinforcing elements, anchorblocks and other accessories to the lines and grade shown on the drawings.The embedded portion of the wall, joint gaps and drainage or service holes inthe wall shall be included in measurement of the wall surface area.

6.4 Concrete Levelling Pad

The unit of measurement for the concrete levelling pad shall be the length inlinear metre completed in place and accepted, measured along the line andgrade of the pad.

6.5 Backfill

The unit of measurement for backfill material shall be the compacted volumein cubic metre.

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