Sonic Drilling and Teretek® Used to Address Rail Line Settlement at Wiggins Island Coal Export Terminal

The offshore wharf and loading facilities are situated north of Wiggins Island, adjacent to the Targinie Channel, with rail receival located north-west of Gladstone to reduce impact on the community. Rail unloading facilities are connected to the Golding Point stockyard via a 5.6km long overland conveyor. An elevated rail bund was built from natural materials, as well as general and engineered fill, with varying heights up to 6m above ground level. This bund supports the WICET coal stacker rail line.

Uniform residual settlement was anticipated in the design of the rail bund. However, four years after its construction, the bund displayed signs of differential settlement across its body, which threatened to move sections of the rail outside of working tolerance. WICET contracted Mainmark to undertake extensive and reliable soil testing, and identify a ground improvement and level correction solution to return rail levels to within working tolerance. The solution also needed to align with WICET health, safety, security and environmental policies.

The first objective was to identify weak soil layers beneath the rail bund by extracting samples for a soil profile to identify similarities, anomalies and variation of ground conditions at differing intervals along the rail beam. A series of Dynamic Cone Penetration (DCP) tests were then required to determine the soil strengths along the rail.

Geotechnical experts assessed the results and evaluated the soil conditions throughout the test areas. The information obtained identified the weak areas to be targeted in the subsequent treatment program.

Mainmark was required to supply all materials, equipment and trained personnel to complete both the soil analysis and remediation work quickly and cost effectively, while causing minimal disruption to the daily operation of the coal export terminal. Importantly, as works would be undertaken adjacent to the coal stock pipe, the chosen solution needed to avoid contamination of the stock.

During drilling, the resonant energy is transferred down the drill string to the bit face at a range of sonic frequencies. The relatively lightweight sonic drill rig is capable of an extremely fast penetration speed through most ground formations, and extracts quality, undisturbed samples. The technology is highly efficient, with lower noise levels compared to hammering, easily retrieving the drill string and casing using sonic vibrations, causing minimal impact to the samples and parent soil.

DCP tests were conducted using data collected at 25 locations along the edges of the rail beam. With results of both testing procedures assessed by geotechnical experts, the project team analysed an inferred soil profile to determine the best solution.

Mainmark used its proprietary Teretek® engineered resin injection solution to improve soil density and bearing capacity in weak layers beneath the rail system. Teretek® is a proven solution that is impervious to water and environmentally inert.

Mainmark Technicians Drilling Small Injection Points That Are Presicely Placed Along The Area To Be Treated

The resin was injected via tubes installed to various depths. A chemical reaction causes the resin to expand in the ground, filling voids and fissures, which increased the bearing capacity, and reduce water movement through the soil. A 5mm lift in the rail line was achieved as a confirmation of improvement to the targeted layers.

Injecting Teretek® Engineered Resin Injection Solution Through Small Tubes

Completed over 9 days and with no lost time to WICET’s operations, the project delivered a more cost-effective and time-efficient solution compared to the alternative, which would have required major shutdowns of the rail over several months to replace entire sections of the bund. It also provided the customer with a greater understanding of the condition of the rail bund and the ground conditions beneath the structure.