Colinwell Concrete

1

• Colinwell Concrete
• Segmental masonry retaining walls - advice and
  guidance
• RIBA-Approved CPD seminar

2
Masonry segmental retaining walls - advice and
guidance

• Contents
• Learning aims
• About us
• About retaining walls
• Segmental retaining wall introduction
• Benefits
• Technical innovations
• Advantages and disadvantages
• Appropriate and inappropriate applications
• Specification considerations
• How to avoid the pitfalls
• How to build a masonry segmental retaining wall
• Case studies

3
Masonry segmental retaining walls - advice and
guidance

• Learning aims
• In this seminar you will learn the basics of
  retaining walls and more in-depth knowledge of
  masonry segmental retaining walls. The objective
  is to enable you to design and specify with
  confidence by looking into the benefits, the
  pitfalls, technical innovations, design
  considerations and more.

4
Masonry segmental retaining walls - advice and
guidance

• About Colinwell Concrete
• Over 100 years ago, John McQuillan began
  quarrying limestone.
• On the slopes of Colin Mountain near Belfast.
• Our company remains family owned.
• Turnover is approximately 3 million
• We have developed into a walling product
  manufacturer.
• Today, Colinwell Concrete products include
• Architectural Masonry
• Martello Stone Walling
• Facing Bricks
• Allan Block Retaining Wall
• Landscape Walling Systems
• We operate throughout Ireland and Great Britain.

5
Masonry segmental retaining walls - advice and
guidance

• About Peter Gough
• With Colinwell since June 2008
• Technical Sales Representative
• Dealing with specifiers, contractors and end
  users
• Previous roles in field marketing and
  recruitment
• Previously Northern Ireland account manager with
  Hewlett Packard

6
Masonry segmental retaining walls - advice and
guidance

• Retaining wall overview
• A structure that holds back soil or rock.
  Usually moisture saturated earth.
• Usually made of masonry, stone, brick,
  concrete, steel, timber
• Remember the material behind the retaining wall
  is attempting to move.
• Pressure depends on
• The angle or friction.
• The strength of the retained material.
• Direction and magnitude of movement
• Pressure is greatest toward the base of the wall
  and causes movement.
• Your retaining wall must be designed to
  withstand these pressures.
• Incorrect design can cause overturning, sliding
  and water uplift.

7
Masonry segmental retaining walls - advice and
guidance

• Why specify a retaining wall
• Sloping sites reduce land use.
• By levelling you create additional spaces.
• This can be done on multiple levels through
  terracing.
• Additional spaces can be created above and below
  the wall.
• Alternatively the wall can simply make the site
  more visually appealing.

8
Masonry segmental retaining walls - advice and
guidance

• Types of retaining wall
• There are a many types of retaining wall
  including
• Gabions mesh cages hand filled with stones.
• Concrete crib retaining walls.
• Poured mass concrete.
• Concrete block retaining walls.
• Hollow block retaining walls.

9
Masonry segmental retaining walls - advice and
guidance

• Masonry segmental retaining wall introduction
• Hollow block
• Individual masonry blocks lock together
• Mortar-less
• This type of wall can be reinforced

10
Colinwell ConcreteSpecifying segmental retaining
walls - advice and guidance

• A segmental retaining wall block

11
Masonry segmental retaining walls - advice and
guidance

• Benefits of a masonry segmental retaining wall
  systems
• Less material.
• Less energy usage.
• Quick to construct.
• Construction in poor weather.
• Flexible once built to allow for movement and
  absorb pressure.
• Good drainage.
• Lets look at some of these benefits in more
  detail.

12
Masonry segmental retaining walls - advice and
guidance

• Focus on material and energy usage
• Less material that pour concrete retaining walls
  
• Or those built using traditional solid concrete
  blocks.
• Less energy used in production and less haulage
  movements.
• No mortar required so no cement mixer or
  deliveries of cement.
• Site won material can be used for the base
  material and for backfill.
• A traditional concrete block retaining wall may
  need to be faced.
• Masonry segmental retaining walls are
  ready-finished.

13
Masonry segmental retaining walls - advice and
guidance

• Focus on flexibility and movement
• Retained material behind the wall is always
  attempting to move.
• This creates pressure.
• The amount of pressure is a function of
• The internal friction of the retained material.
• The cohesive strength of the retained material.
• The direction and magnitude of movement.
• Groundwater also adds more pressure.
• The interlocking blocks allow movement and
  absorb pressure.
• Retaining walls built using these block are
  unlikely to crack.

14
Colinwell ConcreteSpecifying segmental retaining
walls - advice and guidance

• Focus on drainage
• Free-draining granular material is inserted into
  the hollow block cores and just behind the wall

• Focus on drainage
• The material and disperses water. It can be the
  same material as used for base material.

15
Masonry segmental retaining walls - advice and
guidance

• Technical innovations Geogrids
• Geosynthetics polymer products used to solve
  civil engineering issues.
• Five main functions
• Reinforcement
• Separation
• Filtration
• Drainage
• Erosion control
• Geogrids are commonly used in segmental
  retaining walls.

16
Masonry segmental retaining walls - advice and
guidance

• Technical innovations in segmental retaining
  walls
• Geogrids

Machine or roll direction
Front of wall
Machine or roll direction
17
Masonry segmental retaining walls - advice and
guidance

• Advantages and disadvantages
• Advantages
• Reduction in material usage.
• Flexibility enabling the wall to tolerate
  natural movement.
• Water management.
• Ease and speed of construction.
• Technical innovations such as Geogrids.

18
Masonry segmental retaining walls - advice and
guidance

• Advantages and disadvantages
• Disadvantages
• There are limitations to the height of a gravity
  segmental wall.
• Beyond a height of 1.4m it is necessary to
  reinforce with Geogrids.
• This may require the services of a Geotechnical
  Engineer.
• Depth of back fill must be equivalent to 60-70
  of the wall height.
• You can use dry lean concrete but the
  environmental impact increases.

19
Masonry segmental retaining walls - advice and
guidance

• Appropriate applications
• Residential projects.
• Projects where aesthetics are important.
• If the use of concrete should be minimised.
• Where the re-use of site-won material is
  desirable.
• Inappropriate application
• Where there is not enough room to backfill the
  wall.
• If the wall needs reinforcement but the space is
  not available.

20
Masonry segmental retaining walls - advice and
guidance

• Design considerations
• Types of blocks
• Finishes
• Special blocks
• Colours
• Set back
• Anti-climb
• Fencing
• Green walls
• Tiered walls
• Detailed guidance is crucial

21
Masonry segmental retaining walls - advice and
guidance

• Design considerations
• Colours

22
Masonry segmental retaining walls - advice and
guidance

• Special blocks
• Standard blocks are 450w x 300d x 300h and weigh
  35kg
• Capping and corner blocks are available
• Specify a beveled edge block in secure locations
  to deter climbing.

23
Masonry segmental retaining walls - advice and
guidance

• Design considerations
• Fencing
• Design in fencing from the beginning.
• Installing it later may lead to disputes over
  who is responsible.
• Forming tubes can be including during
  construction.
• Green walls
• Plantable walls are usually built in the normal
  way.
• An irrigation tubing can run the length of the
  course.
• A drip-nozzle installed above each unit.
• The plantable cores are filled with soil after
  every other course is laid.
• The bottom of the cores allow for plant watering
  and drainage.

24
Masonry segmental retaining walls - advice and
guidance

• Environmental considerations
• Some or all of the back fill material can be
  from a recycled source.
• Reduction is necessary transport.
• Some material can be recycled.
• Flexibility leads to a long life.
• Green walls can be created by stepping back to
  create terraces.
• The terraces can be then planted using the
  hollow in the top course.

25
Masonry segmental retaining walls - advice and
guidance

• Cost considerations
• The average reinforced segmental retaining wall
  costs 150 - 200 / m2.
• Exact costs depend on individual site conditions
  costs.
• This is an average of 30 saving over a
  reinforced poured concrete wall.

26
Masonry segmental retaining walls - advice and
guidance

• Cleaning, repair and maintenance considerations
• Cleaning is easy with no specialist materials or
  knowledge.
• Maintenance is minimal but drainage channels
  should be clear.
• Repairs can be carried out to the localised area
  not the entire wall.
• Health and safety considerations
• Your suppliers recommendations for stacking
  storage must be followed.
• Handling block weights two man lift 35kg

27
Masonry segmental retaining walls - advice and
guidance

• How to avoid the pitfalls
• Engage a Geotechnical Specialist for advice.
• A wall should be designed to withstand any
  current or future surcharges.
• What type of soil are you holding back?
• Is there a slope above or below the wall?
• Address water diversion and the potential for
  hydrostatic pressure build up.
• Drainage look at the water run off pattern on
  site.
• How much room do you have to work with?
• What is the base material?

28
Colinwell ConcreteSpecifying segmental retaining
walls - advice and guidance

• Building your segmental retaining wall
• Step 1 Site prep and Excavation
• Step 2 Install Base Material
•  

29
Colinwell ConcreteSpecifying segmental retaining
walls - advice and guidance

• Building your segmental retaining wall
• Step 3 Install Base Course

30
Colinwell ConcreteSpecifying segmental retaining
walls - advice and guidance

• Building your segmental retaining wall
• Step 4 Install Wall Rock and Backfill Materials
•  

31
Colinwell ConcreteSpecifying segmental retaining
walls - advice and guidance

• Building your segmental retaining wall
• Step 5 Install Geogrid
•  

32
Colinwell ConcreteSpecifying segmental retaining
walls - advice and guidance

• Building your segmental retaining wall
• Step 6 Install Additional Courses
•  

33
Masonry segmental retaining walls - advice and
guidance

• Case study Distribution Centre, Chepstow
• Client Winvic Construction
• Contractor J H Construction
• Project location Chepstow, Wales
• Date (year) 2008

34
Colinwell ConcreteSpecifying segmental retaining
walls - advice and guidance

• Case study
• Distribution Centre
• Chepstow

35
Masonry segmental retaining walls - advice and
guidance

• Case study La Mon Hotel
• Client Le Mon Hotel
• Contractor Dixons Contractors, Dunloy Ballymena
• Project location Castlereagh, Belfast
• Date (year) 2008

36
Colinwell ConcreteSpecifying segmental retaining
walls - advice and guidance

• Case study
• La Mon Hotel

37
Masonry segmental retaining walls - advice and
guidance

• Case study Dromara private house
• Client Private client
• Contractor Self build
• Project location Dromara, County Down
• Date (year) 2007

38
Colinwell ConcreteSpecifying segmental retaining
walls - advice and guidance

• Case study
• Dromara private house

39
Masonry segmental retaining walls - advice and
guidance

• Case study Hillhall private house
• Client Private client
• Contractor JA Smith, Dromore
• Project location Lisburn, County Down
• Date (year) 2008

40
Colinwell ConcreteSpecifying segmental retaining
walls - advice and guidance

• Case study
• Hillhall private house

41
Masonry segmental retaining walls - advice and
guidance

• Learning outcomes
• We have looked at retaining walls in general,
  their uses and types, in particular masonry
  segmental retaining walls.
• You should now be familiar with the benefits,
  technical innovations, the advantages and
  disadvantages. This should enable you when best
  to specify this type of wall.
• Other considerations, including design, special
  blocks, environmental impact, cost and
  maintenance, have been highlighted. The pitfalls
  of poor specification should also now be clear.
• Consider the type of material you need to retain
  and look at the site hydrology. Always use a
  Geotechnical Specialist if you need advice.

42
Masonry segmental retaining walls - advice and
guidance

• Contact details
• Peter Gough
• Colinwell Concrete Limited
• 37 Colinglen Road
• Dunmurry
• Belfast BT17 0LP
• T. 44 (0)28 9061 8145 from ROI 048 9061 8145
• info_at_colinwell.com
• www.colinwell.com

43
Masonry segmental retaining walls - advice and
guidance

• References
• Dept of Civil Transportation Engineering,
  Napier University, Edinburgh.
• www.sbe.napier.ac.uk/projects/retwall/help/index.
  htm
• External Works www.esi.info
• International Geosynthetics Society (IGS)
• www.geosynthetics-international.com
• Ground Engineering journal