Abu Dhabi, United Arab Emirates. STANDARD CONSTRUCTION SPECIFICATIONS (PART 1 - ROADS, Second Edition 2020)

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7.3.2.3

Construction Requirements

Excavation and backfill shall be in accordance with the requirements of Articles 2.4.2.11 and 2.5.2.4
of Chapter 2, Earthworks. If shafts are required, they shall be constructed in accordance with the
shaft installation plan, as approved by the Engineer and the requirements of Chapter 17, Drilled
Piles, and Chapter 18, Driven Piles.

a. Trench, Grade Beam, or Spread Footing Construction

Footing construction shall conform to the requirements of Table 7-10.

Table 7-10: Requirements for trench, grade beam, or spread footing construction

Boundary Wall Foundations

Description

Specifications Requirements

Below the existing ground line

Article 2.4.2.11 of Chapter 2, Earthworks, to the limits and
construction stages shown in the Contract plans;

Article 2.4.2.5 of Chapter 2, Earthworks, for removal of
unsuitable soils.

Above the existing ground line

Place and compact backfill material in accordance with
Article 2.5.3.2 of Chapter 2, Earthworks.

To retail their configuration during concrete placement, the steel reinforcing bar cage and the
boundary wall anchor bolts shall be installed and rigidly braced prior to grade beam and spread
footing concrete placement. Contractor shall not place individual or loose steel reinforcing bars and
anchor bolts and shall not install anchor bolts during or after concrete placement.

b. Cast-in-situ Concrete Panel Construction

Construction of cast-in-situ concrete panels for boundary walls shall conform to Chapter 4, Concrete
Works. Formwork shall comply with the requirements of Section 1.20.8 of Chapter 1, General
Requirements.

Cast-in-situ concrete panel tops shall conform to the top of the wall profile shown in the Contract
plans and the relevant tolerances included in Table 20-6 of Chapter 20, Earth Retaining Systems.
Where a vertical step is constructed to provide elevation change between adjacent panels, the
dimension of the step shall be 0.5 m. Each horizontal run between steps shall be a minimum of 15
m long.

c. Precast Concrete Panel Fabrication and Erection

Precast concrete panels shall be fabricated and erected by the Contractor in accordance with
Section 4.4.8 of Chapter 4, Concrete Works, and the additional requirements of this section.

An experienced supervisor shall be provided by the Contractor for panel construction and erection
having at least 2 years of successful experience in the proposed construction methods, similar to
the size and amount required for the project. Personnel may, at the Engineer

’s option, be required

to demonstrate technical competence by performing sample work or by displaying their qualifications
or certificates at no additional cost to the Owner.

Unless otherwise noted in the Contract plans and the particular specifications, concrete surfaces
shall receive a Class 2 finish in accordance with Section 4.4.3 of Chapter 4, Concrete Works.

Precast concrete panels shall be cast by the Contractor horizontally, with the traffic side surface cast
against the form liner on the bottom. These panels shall be fully supported to avoid bowing and
sagging surfaces. Formwork shall comply with Section 1.20.8 of Chapter 1, General Requirements.

After receiving the Engineer

’s approval of the shop drawings, the Contractor shall cast 1 precast

concrete panel to be used as the sample panel, which shall be constructed in accordance with the

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procedure and details specified in the shop drawings approved by the Engineer. These sample
panels shall be made available by the Contractor to the Engineer for approval.

Upon receiving the Engineer

’s approval of the sample panel, the Contractor shall continue production

of precast concrete panels for the boundary wall. All precast concrete panels will be evaluated
against the sample panel for the quality of workmanship exhibited. Sample panels shall be retained
at the fabrication site until all precast concrete panels have been fabricated and have received the
Engineer

’s approval. After completing precast concrete panel fabrication, the Contractor may utilise

the sample panel in production.

Precast concrete panels for boundary walls shall not exceed the scalar tolerances described in Table
7-11

Table 7-11: Construction tolerances for boundary walls

Parameter

Tolerance

Height of precast boundary wall panel

±3 mm per 1.5 m, not to exceed 6 mm total

Width of precast boundary wall panel

±3 mm per 1.5 m, not to exceed 6 mm total

Thickness of precast boundary wall panel

±6 mm

Difference between the measurement of the
diagonal of the faces of the panels

< 13 mm

Offset of precast concrete wall stem panels

(Deviation from a straight line extending 1.5 m
on each side of the panel joint)

Across panel face

Across top of wall

±10 mm

Joint space tolerances

As shown in the Contract plans

Position of wall

10 mm

Alignment of wall

2 minutes

Average levels of wall

+10 mm

Verticality of wall

±10 mm

Surface regularity of wall

3 mm

Precast concrete panels shall not be erected until the foundations for the panels have attained a
minimum compressive strength of 24 MPa. Wall panels shall be adequately supported to prevent
overturning and to prevent collapse until permanent connections are completed.

Bolts  connecting  the  precast  concrete  panels  to  their  foundation  shall  be  tightened  to  snug  tight,
which is defined as the tightness reached by either a few blows from an impact wrench or the full
effort  of  a  person  using  a  spud  wrench.  If  the  Contract  plans  call  for  welded  connections,  the
Contractor shall meet the structural welding requirements of ACI 551.1R.

Joints between precast concrete panels shall be sealed with a backer rod and sealant system as
specified on the Contract plans. Both

sides of the joint’s full length shall be sealed.

Precast concrete panel tops shall conform to the top of wall profile shown in the Contract plans.
Where a vertical step is constructed to provide an elevation change between adjacent panels, the
dimension of the step shall be 0.5 m. Each horizontal run between steps shall be a minimum of 15
m long.

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d. Tilt-up Wall Construction

Tilt-up wall construction shall be done as shown on the Contract plans and approved shop drawings.
Precast concrete wall panels shall be cast-in-situ, in close proximity to their permanent locations.
Sequence for this type of precast construction shall be as follows:

1. Erect the wall panels in place by tilting them up to their permanent location

2. Temporarily brace the panels in place

3. Complete the permanent connections required to secure the precast tilt-up panel

4. Remove the temporary supports

A levelling pad shall be constructed for wall panels using high-strength mortar so that the panel in
place will have a level tolerance within 1 to 500. Levelling pads and foundations shall be inspected
and any errors, such as levelness or embedded article locations, shall be corrected prior to lifting the
wall panels into place.

Contractor may use spreader bars, chockers with equaliser sheaves, adjustable bracing, and other
erecting accessories, as required, to place panels in their permanent locations. Bracing equipment
must meet applicable codes.

Panels shall be tilted from the casting platform to slope within 1 horizontal to 6 vertical. Their initial
setting shall be plumb within 75 mm of true vertical with adjustable braces to vertical tolerance of 1
to 500. Contractor shall leave the braces in place until panels are secured in their final location.

Panel erection shall not commence until representative concrete test cubes have a minimum
compressive strength as specified on the Contract plans and Section 4.4.8 of Chapter 4, Concrete
Works.

Pickup points in concrete panels shall be located so that concrete tensile stresses during erection
do not exceed 10 % of the cylinder compressive strength at time of erection.

Panels may be connected to steel columns, precast concrete columns, or cast-in-situ concrete
columns. Details of connecting panels to supporting structures must be indicated on the Contract
plans or shop drawings. For cast-in-situ columns, horizontal reinforcing rods at the sides of panels
shall extend a minimum of 200 mm into column forms.

Panels shall be bolted to the supporting structure with high-strength bolts that meet the requirements
of ASTM A325, Type 1, and then panels shall be welded to the supporting structure.

Joints between wall panels and foundation and joints between wall panels and columns shall be
packed with mortar of the class shown in the Contract plans and meeting the requirements of Article
4.3.15.6 of Chapter 4, Concrete Works.

Holes in panels left after lifting rigging has been removed shall be packed with nonshrink mortar
meeting the requirements of Article 4.3.10.4 of Chapter 4, Concrete Works, and finished to match
adjacent surfaces.

e. Masonry Wall Construction

Construction requirements for masonry boundary walls shall be in accordance with Chapter 6,
Masonry.

f. Access Doors and Concrete Landing Pads

Access doors and door frames shall be installed by the Contractor as shown on the Contract plans,
with the access doors opening toward the roadway side. Door frames shall be set in place with grout
conforming to the requirements for grout for anchor bolts as defined in Article 4.3.10.4 of Chapter 4,
Concrete Works, with the grout completely filling the void between the door frame and the boundary
wall panel.

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Required coats of paint shall be applied by the Contractor, as specified in the Particular
Specifications and applicable requirements of Chapter 24, Painting, to all exposed metal surfaces of
access doors and frames, except for stainless steel surfaces.

Concrete landing pads shall be constructed on the roadway side of each access door location by the
Contractor, as shown in the Contract plans. Concrete shall be Class C25/20.

g. Finish Ground Line

Ground lines on both sides of the boundary wall shall be contoured and dressed by the Contractor
to the following specifications:

•

Provide the minimum cover over the foundation as shown in the Contract plans

•

Ensure good drainage away from the barrier

After the access roads are no longer needed for boundary wall construction activities, the Contractor
shall restore the area to the original condition. Access roads shall be recontoured to match the
surrounding ground levels, as approved by the Engineer.

7.3.3 Shotcrete Facing

7.3.3.1

Description

This work constructs shotcrete facing, also called pneumatically placed concrete, as shown in the
Contract plans.

Shotcrete facing consists of mortar or concrete conveyed through a hose and pneumatically applied
to prepared surfaces with reinforcing material in place, using either the dry- or wet-mix processes.

Dry-mix processes consist of thoroughly mixing a proportional combination of dry-fine aggregate and
cement and conveying the mixture through a delivery hose to a special nozzle where water is added
and mixed with the other materials immediately prior to its discharge from the nozzle.

Wet-mix processes consist of premixing, by mechanical methods, a proportional combination of
cement, aggregate, and water required to produce mortar or concrete; conveying the mortar or
concrete through the delivery hose to the special nozzle where additional compressed air is added
at the nozzle prior to its discharge.

7.3.3.2

Materials

Materials shall conform to the requirements of the Contract plans, these Specifications and as
approved by the Engineer, including those sections specifically noted in Table 7-12. Other materials
required shall be as specified in the Particular Specifications.

Table 7-12: Materials for shotcrete facing

Material

Specifications Requirements

Shotcrete and its constituent materials;

Steel reinforcing bar;

Preformed joint filler;

Waterstops.

Article 4.3.10.5 of Chapter 4, Concrete Works

Chapter 5, Reinforcing Steel

Article 4.3.15.2 of Chapter 4, Concrete Works

Section 4.3.16 of Chapter 4, Concrete Works

Gravel backfill

Section 2.5 of Chapter 2, Earthworks

Pipe underdrains

Section 12.1.3 of Chapter 12, Stormwater
Drainage

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Shotcrete shall be proportioned to produce a 30 MPa compressive strength at 28 days, in
accordance with Article 4.3.10.5 of Chapter 4, Concrete Works.

7.3.3.3

Construction Requirements

Prior to construction of any shotcrete facing, the Contractor shall do the following:

•

Submit and receive the Engineer

’s approval for shotcrete mix design, proposed methods and

equipment to finish and cure the shotcrete, and documentation of the nozzle operators’
experience in applying shotcrete per Sub-article a, of Article 7.3.1.1.

•

Finely grade, and thoroughly compact, all surfaces on which shotcrete is to be placed to the

lines and grades shown on the Contract plans or established by the Engineer

•

Uniformly water all surfaces on which shotcrete is to be placed so that water will not be drawn

from the freshly placed shotcrete.

•

Remove any curing compound on previously placed shotcrete surfaces by sandblasting.

•

Install reinforcement of the shotcrete as shown in the Contract plans

i. Wire reinforcement shall be securely fastened to the steel reinforcing bars so that it will be

25 mm to 38 mm from the face of the shotcrete at all locations, unless otherwise shown in
the Contract plans

ii. Wire reinforcement shall be lapped 1.5 squares in all directions, unless otherwise shown in

the Contract plans

•

Install noncorroding alignment wires and depth gauges every 2 m longitudinally and

transversely, with no less than 2 gauges per increment of surface area to receive the shotcrete,
to establish thickness, and plane surface of the completed facing.

•

Install alignment wires at corners and offsets not established by formwork. Contractor shall

ensure that the alignment wires are tight, true to line, and placed to allow further tightening.

•

Complete and receive the Engineer

’s approval for preconstruction testing.

If forms are used, they shall be plywood sheathing or other suitable material, true to line and grade,
and sufficiently rigid to resist deflection during shotcrete placement. They shall be constructed to
permit the escape of air and rebound during the gunning operation.

a. Equipment

Equipment to be used shall be approved by the Engineer prior to placement of slope protection.
Contractor shall furnish the Engineer

with 2 copies of the manufacturer’s specifications and operating

instructions for the equipment used.

Equipment shall deliver a continuous, smooth stream of uniformly mixed material accurately and at
the proper velocity, to produce a uniform shotcrete facing that meets the additional criteria of these
specifications. Equipment used with the wet-mix process shall be the pneumatic feed type, unless
the Engineer provides written approval of a positive displacement feed type.

For dry-mix shotcrete, the following is required:

1. Nozzle shall be equipped with a manually operated water ring for directing an even distribution

of water through the fine aggregate-cement mixture

2. Nozzle water ring shall provide ready adjustment to vary the quantity of water

For wet-mix shotcrete, the following is required:

1. Nozzle shall be fitted with an air ring for injecting additional compressed air into the premixed

material flow.

2. Size of delivery hose shall be 32 mm to 64 mm.

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3. Air compressors shall have ample capacity to furnish an adequate supply of clean dry air to

maintain required nozzle velocity for all phases of the work and simultaneously operate a blow
pipe for removing rebound.

4. Air hose shall be equipped with a filter to prevent oil or grease contamination of the shotcrete.

Constant air pressure shall be maintained in the placing machine when using the dry-mix process,
or at the nozzle when using the wet-mix process. Minimum required air pressure shall be at least
550 kPa for hoses shorter than 30 m and shall increase by 35 kPa for each additional 15 m of hose
or fraction thereof.

b. Testing

A 300-mm by 300-mm shotcrete test panel shall be prepared in accordance with AASHTO T 24M to
evaluate shotcrete quality, strength, and aesthetics. Both preproduction and production test panels
shall be prepared.

At least 3 cores shall be removed from the preconstruction panels and at least 3 cores from the
production panels. All cores obtained for the purpose of shotcrete strength testing shall comply with
the following:

1. Core diameter shall be at least 3 times the maximum aggregate size and a minimum of 50 mm

2. Core height shall be a minimum of 1.5 times the core diameter

3. Cores removed from the panels shall be immediately wrapped in wet burlap and sealed in a

plastic bag

4. Cores shall be clearly marked to identify from where they were taken and whether they are for

preproduction or production testing. For production testing, the section of the wall represented
by the cores shall be clearly marked on the cores

5. Cores shall be delivered to the Engineer within 2 hours of coring.

Remaining test panels shall be the property of the Contractor.

c. Preproduction Testing

At least one 300-mm by 300-mm test panel shall be prepared for each mix design for evaluation and
testing of the shotcrete quality and strength, and at least one 1.25 m by 1.25 m qualification panel
for evaluation and approval of the proposed method for shotcrete installation, finishing, and curing.

All test panels shall be constructed using the same methods and initial curing proposed to construct
the shotcrete facing, except that the 300-mm panel shall not include wire reinforcement and shall be
constructed to the minimum thickness necessary to obtain the required core samples. Nozzlemen
proposed for production shotcreting shall also apply the shotcrete for the preproduction panels.

Qualification panels, measuring 1.25 m in size, shall be constructed to the thickness of the production
facing.

Test data and a visual description shall be submitted by the Contractor of each core to the Engineer
for approval. Submittal shall include the following:

1. Details concerning presence of voids, sand pockets, lamination, and other inadequacies.

Visual quality of the cores shall not be lower than grade 2 according to shotcrete grading
requirements of ACI 506.2.

2. Sample identification, including mix designs and test panel numbers and orientation.

3. Date and time of sample preparation, including curing conditions and sample dimensions

4. Date, time, and type of test

5. Complete test results, including load and deformation data during testing, sketch of sample

before and after testing, and any unusual occurrences observed

6. Name and signature of person performing the test

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7. Location of steel reinforcement, if used, covered by shotcrete

8. Name and experience qualifications of the nozzleman

Production shotcrete work shall not begin until satisfactory test results are obtained and the
preproduction panels are approved by the Engineer.

d. Production Testing

Testing of shotcrete shall meet the applicable requirements of Article 4.3.10.5 of Chapter 4, Concrete
Works, and as specified herein.

At least one 300 mm by 300 mm panel shall be made for each section of facing shotcrete, where a
section is defined as 1-

day’s placement. Panel thickness shall be as thick as the structure being

constructed but not less than 75 mm.

Panels shall be prepared by applying shotcrete mix to a piece of plywood that is true and not warped,
bowed,  or  deformed  in  any  way  using  the  same  methods  and  initial  curing  used  to  construct  the
shotcrete  wall;  except  that  production  panels  shall  not  have  wire  reinforcement.  Panels  shall  be
constructed to the minimum thickness necessary to obtain the required core samples.

Cores shall be obtained from the panels and tested in accordance with the requirements of AASHTO
T 24. Cores shall have a minimum diameter of 75 mm and a length to diameter ratio of at least 1.

Cut surfaces of the test specimens will be carefully examined for soundness and uniformity of the
material and shall be free from laminations and sand pockets.

If the production shotcrete is found unsuitable based on the results of the test panels, the sections
of the wall represented by the test panels shall be repaired or replaced to the satisfaction of the
Engineer at no additional cost to the Owner.

e. Qualifications of Contractor

’s Personnel

All nozzle operators shall have at least 1-

year’s experience in the application of shotcrete. Each

nozzle operator will be qualified, by the Engineer, to place shotcrete, after successfully completing
1 test panel for each shooting position and surface type expected to be encountered. Satisfactory
evidence of such experience shall be provided to the Engineer for approval when requested.

Qualification will be based on a visual inspection of the shotcrete density, void structure, and finished
appearance along with a minimum seven-day compressive strength of 17.5 MPa determined from
the average test results from two cores taken from each test panel.

Notification shall be provided by the Contractor to the Engineer not less than 2-days prior to the
shooting of a qualification panel. Mix design for the shotcrete shall be the same as that planned for
the wall being shot.

Shotcrete shall be placed only by personnel qualified by the Engineer. If shotcrete finish Alternative
B or C is specified, per Table 7-13, evidence shall be provided that all shotcrete crew members have
completed at least 3 projects in the last 3 years where such finishing, or sculpturing, and texturing of
shotcrete was performed.

f. Shotcrete Application

Nozzlemen who created acceptable test panels shall be used for production shotcrete application.

During  construction,  the  Contractor  shall  protect  all  retaining  walls,  columns  and  structures  from
concrete  splash  or  overspray.  Suitable  covering  shall  be  provided  if  such  protection  is  deemed
necessary by the Engineer.

Shotcrete shall be applied within 45 minutes of adding cement to the mixture. As shotcrete leaves
the nozzle, its velocity shall be maintained uniform and at a rate approved by the Engineer for the
given job conditions. Rebound or previously expended material in the shotcrete mix shall not be used
in any portion of the work. All rebound shall be removed prior to final set and before placement of
the shotcrete on adjacent surfaces.

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Shotcrete shall not be applied during any precipitation of sufficient intensity that can cause the in-
place shotcrete to run or during wind conditions that can cause separation of the nozzle flow.

A clean, dry supply of compressed air that is sufficient for maintaining adequate nozzle velocity for
all parts for the work and for simultaneous operation of a blow pipe for cleaning away rebound shall
be maintained at all times. Thickness, method of support, air pressure, and rate of placement of
shotcrete shall be controlled to prevent sagging or sloughing of freshly applied shotcrete. If the
shotcrete must be applied in 2 layers to achieve the required thickness without sagging or sloughing,
an initial layer of shotcrete may be placed, broomed, or scarified, and allowed to harden. Surfaces
may then be dampened and an additional layer applied.

Shotcrete  shall  be  applied  from  the  lower  part  of the  area  upwards.  Surfaces  to  be shot  shall  be
damp, but free of standing water. Nozzles shall be held at an angle approximately perpendicular to
the  working  face  and  at  a  distance  that  will  keep  rebound  at  a  minimum  and  compaction  will  be
maximised,  typically  600  mm  to  1,500  mm.  Shotcrete  shall  emerge  from  the  nozzle  in  a  steady,
uninterrupted flow.

If, for any reason, the flow becomes intermittent, the nozzle shall be diverted from the work until a
steady flow resumes. Surface defects shall be repaired as soon as possible after initial placement of
the shotcrete. All shotcrete that lacks uniformity, which exhibits segregation, honeycombing, or
lamination

— or which contains any dry patches, slugs, voids, or sand pockets — shall be removed

and replaced with fresh shotcrete by the Contractor, to the satisfaction of the Engineer and at no
cost to the Owner.

Premolded expansion joint material measuring 13 mm thick and conforming to the requirements of
Article 4.3.15.2 of Chapter 4, Concrete Works, shall be placed at 18 m intervals on all shotcrete or
concrete bank protection. Weakened plane joints, or scoring, shall be at 4.5 m intervals between
expansion joints. All expansion joint material shall extend the full depth of the concrete being placed
and shall be flush with the top of the finished surface; furthermore, expansion joint material shall be
supported, prior to the placement of the concrete, as to ensure tight joints. Reinforcing material shall
be cut at all expansion joints.

Construction joints in the shotcrete shall be uniformly tapered over a minimum distance of twice the
thickness of the shotcrete layer. Surface of the joints shall be cleaned and thoroughly wetted before
adjacent shotcrete is placed. Shotcrete shall be placed in a manner that provides a finish with uniform
texture and colour across the construction joint. Square construction joints shall not be used.

When shotcrete is specified in the Contract plans as the final fascia finish, the curing requirements
specified  in  Section  4.4.2  of  Chapter  4,  Concrete  Works,  shall  apply.  For  intermediate  shotcrete
surfaces,  or  if  a  stained  or  finished  final  surface  is  required,  liquid  membrane-forming  curing
compound method of curing shall not be used. Shotcrete shall be cured by applying a clear liquid
membrane-forming  curing  compound  in  accordance  with  Article  4.4.2.3  of  Chapter  4,  Concrete
Works.  Curing  compounds  shall  be  applied  immediately  after  final  gunning.  Two  coats  of  curing
compound shall be applied to the shotcrete surface immediately after finishing.

If field inspection or testing, by the Engineer, indicates that any shotcrete produced fails to meet the
requirements, the Contractor shall immediately modify procedures, equipment, or system, as
necessary

— and as approved by the Engineer — to produce material that meets requirements. All

substandard shotcrete already placed shall be repaired by the Contractor, to the satisfaction of the
Engineer, at no additional cost to the Owner. Such repairs may include removal and replacement of
all affected materials.

Contractor shall remove alignment wires after facing construction is complete.

A written report shall be prepared and submitted by the Contractor to the Engineer within 24 hours
of shotcrete production and application for each shift. Report shall include the following:

1. Quantity and location of shotcrete applied, including sketches of the areas placed

2. Observations of success or problems of equipment operation, application, final product

condition, and any other relevant issues during production and application

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3. Batch numbers, if applicable

4. Name of nozzleman

5. Names and signature of person performing the observation

g. Shotcrete Finishing

After the shotcrete has been placed as nearly as practicable to the required thickness and shape
outlined by forms and ground wires, the surface shall be checked with a straightedge and any low
spots or depression shall be brought up to proper grade by placing additional shotcrete in such a
manner that the finished surface shall be smooth and uniform.

When the shotcrete facing is an interim coating to be covered by a subsequent shotcrete coating or
a cast-in-situ concrete fascia later under the same Contract, the Contractor shall strike-off the surface
of the shotcrete facing with a roughened surface as specified in Section 4.4.4 of Chapter 4, Concrete
Works. Grooves of the roughened surface shall be either vertical or horizontal.

When the shotcrete facing provides the finished exposed final surface, the shotcrete face shall be
finished using the alternative aesthetic treatment shown in the Contract plans. Alternatives are
described in Table 7-13. Shotcrete surfaces shall have a natural gun finish, unless otherwise shown
on the Contract plans or specified in the Particular Specifications, as approved by the Engineer.

Table 7-13: Aesthetic alternatives for shotcrete facing

Description

After the surface has taken its initial set (crumbling slightly when cut), the surface shall be
broom finished to secure a uniform surface texture.

Shotcrete shall be applied in a thickness a fraction beyond the alignment wires and forms.
Shotcrete shall stiffen to the point where the surface does not pull or crack when screeded
with a rod or trowel. Excess material shall be trimmed, sliced, or scraped to true lines and
grades. Alignment wires shall be removed and the surface shall receive a steel trowel finish,
leaving a smooth uniform texture and colour. Once the shotcrete has cured, pigmented
sealer shall be applied to the shotcrete face. Shotcrete surface shall be completed to within
a tolerance of 13 mm of true line and grade.

Shotcrete shall be hand-sculptured, coloured, and textured to simulate the relief, jointing,
and texture of the natural backdrop surrounding the facing. Ends and base of the facing shall
transition in appearance as appropriate to more nearly match the colour and texture of the
adjoining roadway fill slopes. This may be achieved by broadcasting fine and coarse
aggregates, rocks, and other native materials into the final surface of the shotcrete while it
is still wet, allowing sufficient embedment into the shotcrete to become a permanent part of
the surface.

7.3.4 Gravity Walls

7.3.4.1

Description

This work shall consist of furnishing and installing units for gravity walls in accordance with the details
shown on the Contract plans as required herein or as described in the Particular Specifications, as
approved by the Engineer. Gravity walls retain earth by virtue of their mass, without reinforcement
that extends into the retained earth. Types of gravity walls are described herein, as follows:

•

Rock wall, Article 7.3.4.2

•

Concrete block wall, Article 7.3.4.3

•

Gabion wall, Article 7.3.4.4

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7.3.4.2

Rock Wall

a. Materials

Rock for rock walls and chinking material shall consist of hard, sound, and durable material, free
from seams, cracks, and other defects that can destroy its resistance to weather, and shall meet the
minimum requirements of Table 7-14.

Table 7-14: Requirements for rock for rock walls and chinking material

Test

Test method

Requirements

Specific gravity

AASHTO T 85

2.55 minimum

LA wear

AASHTO T 96

50 % maximum

Absorption

AASHTO T 85

3 % maximum

Rock for rock wall sizes are approximately as described in Table 7-15. Minimum average dimension
of chinking material shall be 100 mm.

Table 7-15: Sizes of rock for rock wall

Rock size

Rock Weight (kg)

Average Dimension (mm)

One man

20 to 90

300 to 450

Two man

90 to 300

450 to 700

Three man

300 to 900

700 to 925

Four man

900 to 1,800

925 to 1,225

Five man

1,800 to 2,700

1,225 to 1,375

Six man

2,700 to 3,600

1,375 to 1,525

Backfill for rock walls shall be crushed gravel measuring between 50 mm and 150 mm in size.
Acceptance shall be determined by visual inspection by the Engineer.

Gabion cribbing, wire mesh fabric, polyvinyl-chloride coating for welded-wire mesh fabric, gabion
basket fasteners, and stone shall be as described in Sub-article b, of Article 7.3.4.4. Construction
geotextile shall be as defined in Article 2.5.2.9 of Chapter 2, Earthworks.

b. Construction Requirements

Completed wall shall meet the tolerances of Table 7-16.

Table 7-16: Geometric tolerances for rock walls

Wall Dimension

Tolerance

Wall batter

6:1 or flatter as specified in the Contract plans

Exterior slope plane and
grade

±150 mm

Maximum

void

between

adjacent rocks

150 mm, as measured at the smallest dimensions of the void
within the thickness of the wall

Excavation shall conform to the requirements of Article 2.4.2.11 of Chapter 2, Earthworks, of these
standard specifications, and to the limits and construction stages shown on the Contract plans.
Excavation limits shall be restricted by the Contractor to the length of rock wall that can be
constructed in one day of work, except as otherwise noted. Excavation beyond these limits may be

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permitted by the Engineer provided the Contractor either demonstrates that the excavation will
remain stable until the rock wall is completed, or the Contractor shores the excavation in accordance
with Article 2.4.2.11 of Chapter 2, Earthworks.

Slope above the rock wall shall be established prior to excavating for the wall. For rock walls
constructed in fills, the fill shall be overbuilt and cut back to construct the wall.

An L-shaped sample section of wall shall be constructed at least 1.5 m high and 2.5 m long,
demonstrating construction of the following elements:

•

Face wall

•

Top wall

•

Method of turning corners

•

Method of forming joints

Prior to rock placement, the foundation, if not in rock, shall be compacted as approved by the
Engineer. Any foundation soils found to be unsuitable shall be removed and replaced in accordance
with Article 2.4.2.7 of Chapter 2, Earthworks.

Geotextile placement shall be as shown on the Contract plans.

Rocks shall be placed to conform to the following requirements:

1. Foundation masonry may be constructed at any time

2. Bottom course of rocks shall be in full contact with the foundation soils. If necessary, the

excavation shall be shaped to fit the rocks. Rocks may be dropped to shape the ground
provided the rocks do not crack. Cracked rocks shall be replaced and the foundation regraded
to fit the replacement rock

3. There shall be no continuous joint planes in either the vertical or lateral direction

4. Face stones shall be set in random bond to produce the effect shown on the Contract plans

and to correspond with the approved sample section

5. Each rock shall bear on at least 2 rocks below it, where possible

6. Each face stone shall bond with all contiguous face stones at least 150 mm longitudinally and

50 mm vertically

7. Rock orientation shall consist of the following:

i. Maximise flat surface contact points between adjacent rocks

ii. Minimise point-to-point contact between adjacent rocks

iii. Arrange natural irregularities in the rocks so as to key the rocks together and to key the

courses together

In constructing rock masonry walls, the Contractor shall not do the following:

•

Construct any masonry other than foundation masonry until the sample is approved

•

Extend beds in an unbroken line through more than 5 rocks

•

Extend joints through more than 2 rocks

•

Construct so that the corners of four stones are adjacent to each other

•

Group small rocks or rocks of the same size, colour, or texture

Rocks shall increase in size from the top of the wall to the bottom at a uniform rate. Minimum rock
sizes, as referenced from the top of the wall, shall be as in Table 7-17.

ONSTRUCTION

Table 7-17: Minimum rock sizes

Depth from Top of Wall (metres)

Minimum Rock Size at Depth from Top of Wall

Top of wall

Two man or larger

Three man

Four man

Five man

Where voids larger than 150 mm are present, chinking rock shall be keyed between the rocks to fill
the void. Backfill for the rock wall shall be placed behind each course and tamped to provide a stable
condition prior to placing rocks for the next successive course.

Where headers are required, the Contractor shall distribute headers uniformly throughout the walls
of structures to form at least 20 % of the faces.

Individual rocks composing the backing and heart shall be bonded with the rocks in the face wall and
with each other, where applicable, per the wall design shown on the Contract plans. All openings
and interstices in the backing shall be filled completely with mortar or with quarry spalls surrounded
completely by mortar.

Copings shall be constructed as shown on the Contract plans. Where coping is not required, the top
of the wall shall be finished with rocks measuring 0.5 m to 1.5 m long, at least 150 mm high, and
wide enough to cover the top of the wall. Rock heights shall be random for the top course, and rocks
shall be laid such that the top course is an integral part of the wall, pitched to line in both vertical and
horizontal planes.

Parapet walls shall be constructed with selected stones, squared, and pitched to line, with heads
dressed in the ends and in all exposed angles and corners. Headers shall be interlocked with as
many headers as possible, extending entirely through the wall. Both the headers and stretchers shall
be interlocked in the 2 faces of the wall. Headers and stretchers shall comprise nearly the whole
volume of the wall. All interstices and spalls shall be completely filled with mortar.

Weep holes shall be installed for all walls and abutments at the lowest points where free outlets can
be obtained. Weep holes shall be spaced no more than 3 m centre-to-centre.

7.3.4.3

Concrete Block Wall

a. Description

Concrete block walls are defined as a wall of modular blocks acting as a gravity wall to retain soil or
act as a boundary wall. Modular blocks may have features designed to interlock the blocks together.
However concrete block walls shall not include reinforcement of the retained soil, nor any
reinforcement connection between the modular blocks and the retained soil. Concrete block walls
shall be constructed as shown in the Contract plans and as specified in the Particular Specifications.

b. Materials

Materials for concrete blocks and mortar shall conform to the requirements of Section 6.2.2 of
Chapter 6, Masonry.

c. Construction Requirements

Construction requirements shall conform to Section 6.2.3 of Chapter 6, Masonry.

ONSTRUCTION

7.3.4.4

Gabion Wall

a. Description

Gabion walls consist of flexible galvanised or aluminised steel-wire mesh baskets or mattresses,
called gabion cages, filled with stone. Gabion cages shall be constructed from wire of a specified
thickness with uniform openings and coated as the Contract plans and these Specifications require.
For gabion walls, earth is retained by virtue of the weight of the filled wire baskets.

b. Material

Materials shall conform to the specific requirements of this section, and additional materials shall be
as specified in these Specifications. Of particular note are the materials in Article 2.5.2.9 of Chapter
2, Earthworks, specifically: geotextile fabric, backfill, and base course.

1. Gabion Baskets and Mattresses

Gabion  cages  shall  be  either  baskets,  typically  used  for  wall  applications,  or  mattresses,
which  are  typically  used  as  single-layer  aprons  for  revetments  or  channel  lining  type
applications.  Dimensions  shall  be  as  shown  on  the  Contract  plans  or  as  approved  by  the
Engineer. Typical dimensions for each shall be as in Table 7-18. Gabions shall be furnished
in the required dimensions, ±5 %.

Table 7-18: Typical gabion basket and gabion mattress dimensions

Dimension

Basket

Mattress

Length

1 m, 2 m, 3 m, and 4 m

6 m

Width

1.0 m

2.0 m

Depth

0.3 m, 0.5 m, and 1 m

0.2 m, 0.3 m, and 0.5 m

Diaphragm spacing

1.0 m

0.6 m or 1.0 m

Wire for the construction of gabions shall be either galvanised steel wire conforming to ASTM
A 641M, Class 3, soft temper, or aluminised steel wire conforming to ASTM A809, soft
temper. Wire shall have a minimum tensile strength of 415 MPa when tested in accordance
with ASTM A370. Properties of gabion baskets shall conform to Table 7-19. Only one type of
mesh and protective coating shall be used throughout a structure. Tolerance on the specified
diameter of all wire shall be ±2.5 %.

Table 7-19: Requirements for gabion baskets

Property

Requirement for baskets

≥ 300 mm in the

vertical

dimension

< 300 mm in the

vertical dimension

Nominal dimensions of the mesh openings

≤ 115 mm

≤ 85 mm

Maximum area of any mesh opening

≤ 65 cm

< 39 cm

Hexagonal twisted wire mesh

Nominal wire size (galvanized or aluminized)

Minimum selvedge wire diameter

3 mm

3.8 mm

2.2 mm

2.7 mm

Welded wire mesh

Diameter of galvanized steel wire for fabricating
mesh

2.7 mm

2.0 mm

ONSTRUCTION

Property

Requirement for baskets

≥ 300 mm in the

vertical

dimension

< 300 mm in the

vertical dimension

Size of rectangular openings

PVC coating, if required

Nominal thickness

Minimum thickness

75 mm by 75 mm

0.55 mm

0.38 mm

38 mm by 75 mm

0.55 mm

0.38 mm

Gabion baskets shall be either hexagon-twisted wire mesh or welded wire mesh with the
following properties, as applicable:

Hexagon twisted wire mesh, per ASTM A 975:

a) Formed from galvanised or aluminised wire

b) Uniform hexagonal pattern with nonravelling double twist

c) Perimeter edges of the mesh for each panel tied to a selvedge wire that is the

same composition as the body mesh

ii.

Welded wire mesh, ASTM 974:

a) Fabricated from galvanised steel wire, galvanised before fabrication

b) Uniform rectangular pattern with a resistance weld at each connection in

accordance with ASTM A 185M

c) PVC coating, if required, fusion bonded to the welded wire mesh

A manufacturer’s certificate of compliance stating that wire baskets or mattresses, stiffeners,
lacing wire, and spiral connectors conform to the requirements established herein shall be
provided by the Contractor to the Engineer.

Wire mesh shall be fabricated in a manner to be nonravelling, meaning the wire mesh shall
resist pulling apart at any of the connections forming the mesh when a single strand in a
section of mesh is cut.

PVC  coating  shall  apply  to  welded  wire  mesh  only  and  PVC-coating  material  shall  be
accepted  by  certified  test  reports  of  an  independent  laboratory.  Initial  properties  of  PVC-
coating material shall have a demonstrated ability to conform to the requirements of  Table
7-20.

Table 7-20: Material requirements for PVC coating

Property

Test

Method

Requirement

Specific gravity

ASTM D792 1.2 to 1.4

Tensile strength

ASTM D638

≥ 15.75 MPa

Modulus of elasticity

ASTM D638

≥ 13.65 MPa at 100 Strain

Shore A-hardness

ASTM

D2240

≥ 75

Brittleness temperature

ASTM D746

≤-9.4

ONSTRUCTION

Property

Test

Method

Requirement

Salt spray exposure and
ultraviolet (UV) light
exposure

ASTM B117 PVC shall show no effect after the following:

3,000 hours of salt spray exposure; and,

3,000 hours of UV light exposure using apparatus
Type E, 63° C, and ASTM D1499.

After  the  salt  spray  test  and  UV  light  exposure
specified  above,  the  PVC  coating  shall  not  crack,
blister, split, nor exhibit visible change in colour, and
material properties shall be within the following:

±6 % of original specific gravity.

±25 % of original tensile strength.

±25 % of original modulus of elasticity.

±10 % of original resistance to abrasion.

Where selvedge is not woven integrally with the mesh but has to be tied to the cut ends of
the mesh, it shall be attached by tying the cut ends of the mesh to the selvedge, so that a
force of not less than 8.5 kN applied in the same plane as the mesh at a point on the selvedge
of a mesh sample of 1m in length will be required to separate it from the mesh.

Diaphragms and end panels require selvedge on the top and vertical sides only. End panels
shall be attached by the cut ends of the mesh wires at the bottom of the panel being twisted
around the selvedge on the base of the gabion. Similarly, diaphragms shall be attached by
the cut ends of the mesh being twisted to the joints of the mesh in the base of the gabion. In
all cases, at least 6 kN/m of force shall be required to separate panels from the base.

2. Fasteners for Basket Assembly

Fasteners shall consist of one or more of the following materials:

•

Lacing wire, nominal sized 2.2 mm galvanised steel wire or aluminised steel wire, with the

same coating as the basket mesh

•

Spiral binders, for welded wire panels, nominal diameter 2.7 mm steel wire with a 75mm

pitch having the same specifications and coating as the wire mesh

•

Alternate fasteners must remain closed when subjected to a 2.67 kN tensile force when

confining the maximum number of wires to be confined. Installation procedures and test
results for alternate fasteners shall be submitted for approval. Alternate fasteners shall be
approved by the Engineer prior to use

Internal connecting wires shall be the same as required for lacing wire. Alternate stiffeners
may be used with the gabion manufacturer’s approval.

3. Fabrication of Baskets

Gabions shall be made so that the sides, ends, lid, and diaphragms can be assembled into
rectangular baskets of the required sizes at the work site. Common wall construction may be
used in gabion structures up to 4 m high. Common wall construction includes any basket that
uses its top to serve as the bottom of the one above it, or where one wall also serves as a
wall to an adjacent basket. When gabion structures are more than 4 m high, the baskets shall
have independent sides, ends, top, and bottom.

Each gabion shall be divided by diaphragms into cells the same length as horizontal basket
width. Diaphragms shall be made of the same mesh and gage as the basket body. All
perimeter and diaphragm edges shall be laced or clipped together so that joints are at least

ONSTRUCTION

as strong as the body of the mesh itself. Ends of the lacing shall be anchored by three tight
turns around the selvage wire.

Strength and flexibility at a point of connection shall be at least equal to that of the mesh.

4. Stone

Gabions shall be filled with clean, hard, durable stone as approved by the Engineer. Stone
shall be free of shale, caliche, or other soft particles and shall be dense enough to pass the
unit weight test described in the construction requirements of this section while meeting the
requirements for gradation in Table 7-21.

Table 7-21: Gradation and fracture requirements of stone for filling gabions

Sieve size

Percent passing

200 mm square

100

150 mm square

75 to 90

100 mm square

0 to 10

Percent fracture

75 minimum

c. Construction Requirements

1. Foundations

Before placing any gabion cribbing, the Contractor shall excavate the foundation or bed to
the specified width, line, and grade in accordance with Article 2.4.2.11of Chapter 2,
Earthworks. Foundation soils found to be unsuitable shall be removed and replaced in
accordance with Article 2.4.2.7 of Chapter 2, Earthworks. Excavation for toe or cut-off walls
shall be made to the neat lines of the wall.

For rocky foundations, 200 mm of aggregate material meeting the requirements of Table 2-
4 of Chapter 2, Earthworks, shall be placed under the wall base elements.

Where required, a foundation trench along the toe of the revetment or wall shall be excavated
to the dimensions shown on the Contract plans or indicated by the Engineer.

Where geotextile filter fabric is required, it shall be placed as shown on the  Contract plans
with minimum overlaps of  300 mm by 1,000 mm. Its movement shall be prevented during
filling of the gabion cages by a method acceptable to the Engineer.

2. Baskets

Gabion baskets and mattresses may be fabricated from either woven or welded steel wire,
but, a gabion structure shall not include both. Baskets may be assembled with fasteners that
meet the requirements of Sub-article b, of Article 7.3.4.4, but a perimeter or diaphragm edge
shall not include both lacing wire and clip fasteners.

During basket assembly, structure erection, cell filling, or backfilling, the Contractor shall take
care not to damage wire coatings. Any damage shall be repaired to the satisfaction of the
Engineer, or the damaged portion removed and replaced at no additional cost to the Owner.
Basket panels shall be rotated into position and the vertical edges joined with fasteners.
Temporary fasteners may be used for basket assembly, if they are supplemented during
structure erection with permanent fasteners. Diaphragms shall be rotated into position and
joined along the vertical edges.

All perimeter edges of gabions are to be securely selvaged or bound so that the joints formed
by tying the selvages have at least the same strength as the body of the mesh.

Abu Dhabi, United Arab Emirates. STANDARD CONSTRUCTION SPECIFICATIONS (PART 1 - ROADS, Second Edition 2020) - page 45