TenCate Mirafi® PET Mine services corridor, Cape Preston WA

The Sino Iron Project is a world class, Part of this services corridor consisted to soft replacement. large scale magnetite iron ore project of a 2 km long constructed The only solution that was economically located at Cape Preston, 100 km south through a river estuary. The and environmentally viable was to use west of Karratha, in Western Australia’s conditions within the river estuary basal reinforcement across the base of Pilbara region. This iron ore project is consisted of soft estuarine mud of the causeway to enhance the largest planned magnetite project approximately 4 m in depth overlying stability and achieve the required in Australia with an estimated 2 billion firm sandy soil. The estuarine mud factor of safety. A detailed analysis was tonnes of identified magnetite ore. Mine consisted of a slightly overconsolidated performed using the limit equilibrium development and infrastructure costs crust of 1 m in thickness with an method to determine what strength are estimated at USD 3.5 billion. undrained ranging from 7 properties the basal reinforcement kPa to 10 kPa. Below this the undrained should have to meet the stability The project has an extremely tight time shear strength increased with depth requirements. schedule, with construction beginning from around 6 kPa to around 20 kPa at 4 in mid-2008 and is due for completion m depth. Once the basal reinforcement design at the end of 2010. In addition to the loads were established, other factors large open pit mine, major infrastructure The causeway embankment ranged such as the effect of the placement and items consist of a 450 MW power in height from 1 m to 7 m, with a crest compaction of the coarse mine waste station, a 25 km long slurry pipeline, a width of 32 m, and consisted of mine rock fill on the basal reinforcement were 50 gigalitre desalination plant to supply waste rock fill. The side slopes of the also evaluated, as as the design life fresh water, and a new deep water causeway were maintained at 1V:2H. over which the basal reinforcement was port with stockpile facilities. The port At the centre of the causeway a 200 m handles the import of long reinforced concrete bridge was Shear strength (kPa) 0 10 20 30 for the mine site as well as the export of constructed to enable river flows during 0 magnetite pellets. both normal and flood periods. Mud crust 1 A crucial component of the overall In addition to the tight construction project was the construction of a 30 schedule, the causeway embankment km long services corridor connecting had to be designed to allow for heavy 2 Estuarine the port to the mine site. This services vehicle loadings from 240 tonne haul mud corridor had to be completed in trucks as well as the safe transport of Depth (m) 3 advance of other infrastructure items 1400 tonne giant grinding mills for the to enable the transportation of all heavy mining operations. equipment for the mine site, power 4 station, desalination plant and all other To construct the causeway a number of Firm sandy soil stratum related facilities. design and construction options were 5 evaluated. These ranged from stage Foundation undrained shear strength profile Causeway centreline 16 m 150 mm thick concrete protection 2 1 ® 3 layers Mirafi PET800-50 Max. 7 m Mine waste rockfill embankment geotextile reinforcement

4 m Estuarine mud layer

Firm sandy soil stratum Typical cross section through the basal reinforced causeway required. Taking all these factors into top. Finally, the third geotextile layer Client: CITIC Pacific Mining account, 3 layers of Mirafi® PET800-50 was placed and then the embankment Management Pty Ltd, Perth, WA, geotextile reinforcement was chosen was constructed to its completed Australia. as the basal reinforcement for its ability alignment. to meet all of the requirements. Mirafi® Consultant: Connell Wagner Pty Ltd, PET800-50 geotextile reinforcement Where the causeway embankments Perth, WA, Australia. is a woven geotextile with abutted the central bridge structure a tensile strength of 800 kN/m at 10% another three layers of Mirafi® PET800- Contractor: MCC Mining (Western strain in the longitudinal direction and a 50 geotextile reinforcement, placed Australia) Pty Ltd, Perth, Australia. tensile strength of 50 kN/m in the cross coincidentally with the cross-wise direction. The polyester yarns used are layers, was used at the base of the 7 Photographs courtesy of CITIC Pacific of high tensile modulus and have an m high abutments to ensure adequate Mining Pty Ltd. excellent resistance to creep. stability in the vicinity of the main river channel. These 3 layers were placed The Mirafi® PET800-50 geotextile 40 m into the causeway to ensure reinforcement was placed directly the bridge abutments had adequate on the surface of the soft estuarine stability. mud with the rolls of geotextile laid out 90 degrees to the direction of The use of basal reinforcement has the causeway embankment. No enabled the causeway embankment to geotextile joins were allowed in this be constructed quickly, directly on the direction across the width of the estuarine mud foundation, without soil Construction of basal reinforced causeway embankment. The first mine waste replacement. Consequently, the impact abutment rock fill lift was placed on top of the on the environment has been reduced geotextile reinforcement, spread out to a minimum. Further, the services and compacted to construct an initial corridor has been completed on fill platform of 0.5 m thickness. On top of schedule. No subsequent embankment this fill platform the second geotextile deformations have been observed. reinforcement layer was placed and then a 0.3 m thick fill layer placed on

Completed reinforced causeway and bridge structutre

Transport of giant grinding mill along services Layout of Mirafi® PET800-50 woven geotextile reinforcement on site corridor