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Automatic back-analysis to support the Observational Method in a railway tunnel portal

Updated: Apr 29

Railway tunnel portal

The purpose of using DAARWIN was to backanalysis the behavior of the ground and underground structure performance in a railway tunnel portal. The findings were used to gain design assurance to amend designs to implement the OMPM (Observational Method with Progressive Modification) and implement the findings to update the temporary works design to remove a level of temporary props.

By using its machine learning algorithms, DAARWIN provided a real time backanalysis to predict a range of likely geotechnical parameters. These findings were used to validate the design hypothesis and evaluate whether progressive modifications could be implemented to improve safety and provide cost and program savings.

The box excavated next to the tunnel portal was identified as the trial site to highlight the ability to remove temporary supports for similar retained excavations in similar ground conditions across nearby areas. The box was a 83m long, 33m wide by up to 25m deep retained excavation constructed in mudstone.

The portal comprised 4 sections to be supported by a permanent top prop and base slab, with temporary steel props. Measurements of wall deflection, prop load, groundwater levels and surface settlement were backanalyze using DAARWIN to compare against the predicted responses during the deeper works in the first box.

The backanalyze parameters of the mudstone highlighted that the ground parameters were better than indicated by the ground investigation and previous case studies.

The extension box, typically 20m deep, was to be supported by a permanent top prop and two levels of temporary props. The findings enabled the lower temporary prop (being 3 props) to be eliminated, whilst maintaining the permanent structural performance of the works and avoiding impact to adjacent third parties. The savings were estimated to be approximately 1 month and will reduce the critical path for the delivery of the tunnel boring machine.

The findings of the trial and successful implementation of the OMPM showed that by eliminating the need for a level of temporary props it can deliver major cost, time and carbon savings, improved safety by eliminating heavy and constricting temporary works (freer working space), highlighted the importance of teamwork and good communication. geotechnical, software engineer, geotechnical engineering software, construction AI, civil engineering software civil engineering, geotechnical, software engineer, geotechnical engineering, borehole

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