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McIlwain was awarded the contract for the NDRRA restoration of Lamington National Park Road to treat slope failures following damage from ex-tropical cyclone Debbie.

 

PROJECT OVERVIEW

11,700m2 Hand Scaling off Ropes
270m3 Shotcreting Batters off Ropes 
1,300m of Soil Nails off Ropes
4,600m of Soil Nails with Excavator
600m of Micropiles
115 Steel Columns & 1100 Concrete Sleepers
244m of Bored & Reinforced Concrete Piles 120m of Capping Beam  1,011m3 of Reinforced Concrete Retaining Wall Footing  2,700m3 of Gabions
7,000m2 of Clearing and Grubbing
1,200m of Concrete Kerb
1,200m3 of Lightly Bound Pavement
20,500 Litres of Seal
6,000m2 revegetation

 

Reconstruction works comprised bored pier and capping beam, sleeper retaining wall with bored pier UC posts, shotcrete and soil nails, concrete footing and gabion basket retaining wall, rock scaling and revegetation sites, rock scaling only sites. Works initially included 32 civil sites and over 50 rock scaling / clearing / revegetation sites with an additional 28 sites as variations including D&C works with GHD and PCA.

TMR approached McIlwain to provide a design and construct solution for the slope stabilisation of two areas of work on the Lamington National Park Road designated as Site U & V. With a collaborative approach, an analysis of various options and weekly design focus meeting, the solution McIlwain supplied was a micropiled A-Frame arrangement with capping beam to address the global stability issue of the two sites and protect the TMR assets in the area.

The design and installation of the micropiles was completed by PCA Ground Engineering in collaboration with GHD. To save time and money, and to overcome logistical restraints, the 2700m3 of gabion baskets were pre-filed in a ‘gabion farm’ then trucked to site and craned into place. McIlwain provided micropile and capping solution for 4 sites (two of which were D&C and two site used to support the gabion wall foundation in place of defective original design). There was no micropiling in the original designed remediation proposals.

Using hollow bars to replace traditional soil nails avoided the latent conditions from collapsing holes. The original design treatment for Site 18 consisted of soil nails and reinforced shotcrete with heavy duty (SL81) mesh which was deemed to be unworkable due to the latent condition of undulating rock face post rock scaling. Reinforcing mesh was unable to follow the contours and sections of shotcrete would have been inordinately thick and costly.

McIlwain's innovation incorporated Fibrecrete with hollow bars and horizontal drains. The final surface was covered with a Geobrugg Tecco mesh for added slope stability and rock fall security.  Site 24 original design solution was to fracture the rock, temporarily secure than remove debris off the mountain. Because of the prohibitive cost McIlwain elected to remedy as a D&C, permanently securing the offending boulders using Geobrugg mesh and hollow bar soil nails. TMR accepted this solution and the ongoing maintenance.

Due to detailed logistical programming and comprehensive upfront planning the project was completed with budget savings on initial works and in original timeframe despite dramatic increase in scope. This project has won the 2019 CCF Earth Award Excellence in Civil Construction $10—$30 M category.