Edition 14

News & project profiles from the team at Concrib

Phone 1800 021 800 Fax (07) 3375 1777Email admin@concrib.com.au Web www.concrib.com.au

Retaining Wall Design: Component Quality is Important

DUE DILIGENCE

When a designer issues a design certificate (a Form 15 in Queensland), the design is being certified against a specified criteria, for example AS 4678, Earth Retaining Structures code.

A core requirement of this code is design life; for residential retaining walls it is 60 years.

Often overlooked is the supporting criteria that references specific codes. These codes cover the quality and manufacture of the components that make up a particular retaining wall system.

An example is our Concrib Concrete Sleeper Wall System consisting of reinforced concrete sleeper beams and either hot-dipped galvanized steel posts or reinforced concrete posts.

For this system we must ensure that the components are compliant with the relevant codes:

• AS 3600 for Concrete Structures

• AS 4678 for Hot-Dipped Galvanizing

• AS 4100 for Fabricated Steel Structures, and

• AS 1554 for Structural Steel Welding.

The certifying engineer should always ensure that the structural design complies with the code, as well as the chain of supply used to fabricate or manufacture the wall components.

In this issueDue Diligence: Retaining Wall Design: Component Quality is Important

Project Profile: Varsity Heights Stage 2, Reedy Creek, Qld

Upcoming Events: Queensland Transport Infrastructure Conference

Here at Concrib, we operate a Quality Management System compliant with ISO9001:2008. This ensures we can supply all relevant documentation regarding certificates for structural steel, concrete, galvanizing, reinforcement etc.

We are also a Queensland Department of Transport & Main Roads-approved pre-caster of retaining wall products.

This provides peace of mind for both the designer and end user in regards to the retaining wall complying with Australian Standards.

Hybrid crib / geogrid reinforced soil wall designVarsity Heights is in an elevated, premium location at Reedy Creek on the southern Gold Coast. The land offers sweeping views to the ocean, yet offers a tranquil bushland setting.

To enable construction of the main 20m wide road reserve with a 20 kPa load, a retaining wall up to 7m was required to support the embankment.

A concrete crib wall was originally specified as a design and construct item which generally presents no problems, however, subsequent to a geotechnical investigation, the foundation profile revealed a 3.5m deep layer of soft clay, overlaying competent Argilite material.

This in-situ foundation condition initially lead to a foundation design incorporating 450dia bored piles at 2m centres along the length of the front and rear of the wall footing.

This pile design proved to be relatively expensive and presented some constructability issues with the soft clay and the presence of groundwater.

Concrib required a different approach and engaged Geoinventions Consulting Services to offer an alternative solution.

Having considered various possibilities, and with some innovative thinking, Geoinventions offered a hybrid-crib/geogrid reinforced soil wall design which

was to be constructed on some foundation improvement.

This design combines the excellent drainage characteristics of a crib wall face with the remaining structure consisting of reinforced soil using geosynthetics.

The foundation improvement was achieved by a geotextile wrapped rock mattress block beneath the crib section as well as a 750mm deep rock-mattress reinforced at the base with geogrid beneath the reinforced soil zone.

Miragrid 8XT was used in the reinforced soil zone and typically the grid length was 0.8H, where H = wall height.

This innovative design addresses the issues of a high 20kPa surcharge, offering a constructable design whilst delivering a cost effective solution to the client.

For more information contact www.concrib.com.au or www.geoinventions.com.au

Project: Varsity Heights Stage 2, Max wall height 7.4 metres, footing length 75 metres

Area: 380m2

Client: Civil Unlimited Pty Ltd

Contract: Design / Construct / Certify

PROJECT PROFILE

Varsity Heights Stage 2, Reedy Creek, Qld

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7350

200

2355 750

2000

3500

3200

7100

100mm Diameter AG Pipe Fall To Outlet

Miragrid 8XT 6.0m length Vertical Spacing 1.0m

200mm Thick Concrete Footingwith 150mm Embedment into Crushed Rock Base

Crushed Rock Base

Geotextile Layer Over Gravel

Macro 1300

Header

Front Stretcher

False Header

Geotextile Separation Layer (If Required)

Free Draining Granular Material

Back Stretcther or Spacer Block

Miragrid 8XT 6.0m length Vertical Spacing 1.0m

Miragrid 8XT 6.0m length Vertical Spacing 1.0m

Miragrid 8XT 6.0m length Vertical Spacing 1.0m

Miragrid 8XT 6.0m length Vertical Spacing 1.0m

Miragrid 8XT 6.0m length Vertical Spacing 1.0m

Miragrid 8XT 6.0m length Vertical Spacing 1.0m

Reinforced Fill As Per AS4678

Controlled Fill

S Clay

DW Agrilite

S Clay

20kPa Traffic Load

Varsity Heights Stage 2, Reedy Creek, QldTypical Cross Section of Crib Wall

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Call us today to plan your next project. Phone 1800 021 800 Fax (07) 3375 1777Email admin@concrib.com.au Web www.concrib.com.au

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