INVENTIONSC O N S U L T I N G S E R V I C E S

G E O I N V E N T I O N S C A S E S T U D Y

B u r n e t t H i g h w a y , M t M o r g a n R a n g e R o a d F l o o d R e s t o r a t i o n Wo r k s

Project: Burnett Highway, Mt Morgan Range Road Flood Restoration Works

PROJECT DETAILS

Client: Department of Transport and Main Roads

Contractor: RoadTek

Location: Queensland, Australia

Design of Reinforced Earth Embankments

Design Completion Date: January/February 2014

Construction Commencement Date: February 2014

Construction Completion Date: May 2014

The Burnett Highway (Road 41F) is located approximately

20km south west of Rockhampton. The flood restoration

area is situated in the Mount Morgan Range and is

characterised by intervening ridges and valleys and the

highway winds through these with numerous hairpin bends.

The original Mt Morgan Range Road was constructed in

1934/35 to engineering standards current at the time. The

road was later widened to its current width using won

materials from the up-slope cut and placed on the down-

slope batters. Due to steep batters, the degree of

compaction of the placed fill was questionable.

There was a major bush fire on the range in December

2012, and vegetation had not re-established prior to the

heavy rains during Cyclone Oswald in late January 2013

where 810mm of rain fell within 3 days.

Following intense rainfall associated with Cyclone Oswald

which was assessed to be in the order of 200 to 300 ARI

event, numerous failures occurred on both the up-slope

and down-slope batters as well as on the carriageway. Of

the documented failures, eight (8) were significant and

were classified as major failures. As a means of managing

the risks associated with the observed failures and potential

further failures the range was closed to traffic to ensure

safety of road users and to enable repairs. Steep batters,

poor compaction and saturation of the questionable fill

were considered the major factors that contributed to the

failures. The observations during the removal of the failed

materials supported the unengineered (to current standards)

status of the materials on the down-slope shoulder/verge

and on parts of the carriageway.

Photo 1: Failure of Major Fill Area

Photo 2: Removal of Failed Materials

Photo 3: Site Investigations

Based on options analysis carried out by the Department of

Transport and Main Roads (DTMR) engineers, the reinforced

embankment remedial option was adopted as the optimal

solution for remediating the eight (8) major failed sites. Several

geosynthetic suppliers were requested by DTMR to submit

conforming designs using 60kN/m uniaxial strength geogrid

that would meet functional and long-term performance

criteria in line with the Departmental Geotechnical Design

Standard (GDS) as well as provide facing capable of

withstanding bushfires characteristic of the range.

Global Synthetics provided a preliminary design for the

supply of their proprietary Terralink® reinforced embankment

system and provided fire resistance testing of their product for

evaluation by Roadtek and DTMR. Based on the information

provided, this system was selected as the preferred solution.

Global Synthetics engaged Geoinventions Consulting Services

(GCS) to provide a full design report, drawings and RPEQ

certification for the eight reinforced earth embankments.

GCS was requested to design the Terralink® reinforced earth

embankments in line with the DTMR Geotechnical Design

Standard which refers to BS8006. Several sections had to be

analyzed using SLOPE/W. All structures were analyzed for

external, internal and global stability. A design load of 20kPa

was provided as the surcharge loading for the highway.

Furthermore, it was requested by Roadtek that locally sourced

crusher dust be adopted as the reinforced fill (see photo 5).

GCS requested samples of the crusher dust material which

were sent for shear box testing. The shear box test results

indicated friction angles in excess of 45 degrees.

Terralink® Panels are 540mm in height and come with

preformed brackets which allow a 65 degree face. Acegrid

GG80 and GG100 polyester geogrids were adopted in

the GCS design to provide embankment stability. Geogrid

reinforcement lengths were approximately the same length

as the height of the embankment. To prevent future bushfire

damage, the welded mesh facing was shotcreted as shown

in photo.

Photo 4: Placing Terralink® Panels & Geogrid

Photo 5: Placing Facing Rock & Crusher Dust

Photo 6: Completed Terralink® Facing

Minimal field investigations were carried out however

these investigations revealed that the failed materials

consisted of fill of variable consistency and thickness

overlying residual soil and variably weathered rock

which is predominantly basaltic. GCS requested that

further investigations be conducted on site in the form of

Dynamic Cone Penetrometer (DCP) tests and Test Pits (TP)

as a means of confirming the parameters adopted in the

foundation design.

GCS completed all the designs, reports and drawings within

the desired time frame and provided an experienced RPEQ

engineer onsite to witness the construction and sign off the

completed works.

The completed works have experienced one cycle of

intense rainfall associated with Cyclone Marcia. No adverse

performance concerns have been raised and the reinforced

embankments have been performing satisfactorily.

O F F I C E 0 7 3 1 8 8 9 0 3 8 | W W W . G E O I N V E N T I O N S . C O M . A U

d y n a m i c e n g i n e e r i n g t h r o u g h i n n o v a t i o n

Photo 7: Completed structure

Photo 8: Application of Shotcrete