Geotechnical aspects of the design and construction of temporary works for support of Rail Receival Pit 3 at DBCT

Temporary works were required to support a near vertical excavation of approximately 50 m by 20 m in plan and up to 22 m depth, to allow the construction of a rail inloading pit. Significant constraints were placed on the construction by existing industrial infrastructure and site operations.

The temporary works construction comprised an upper anchored contiguous bored pile wall supporting fill, surficial soils and weathered rock and a lower passive rockbolt support system in the rock beneath the base of the piles. The design of the anchored pile wall and preliminary design of the passive rockbolt system were undertaken on the basis of information gathered during site investigations. The passive rockbolt system was amended and optimised as in situ rock data was obtained and further laboratory testing undertaken. In response to the high risk to the existing infrastructure of collapse the performance of the excavation was monitored by an array of survey monuments, inclinometers and extensometers and compared with modelled behaviour.

Data obtained from monitoring and site readings are presented.

Constructional constraints and the methods used to deal with them are discussed. Logic processes in the probabilistic design of rockbolt support in deep excavations and the interpretation of data obtained are also discussed.