Midas is a great software for tunnel design. I highly recommend all.

The Thames Tideway project will create a super-sewer beneath London capable of providing the required overflow capacity to the existing sewage network. Deep intervention shafts are needed along the route to connect the existing network into the tunnel. This webinar describes the numerical modelling undertaken using MIDAS GTS NX to analyse one of these shafts; a 50m deep excavation in East London formed within diaphragm walls. The inputs and background to the analysis will be presented followed by a walkthrough of the model and discussion of the key results.

Key points

1. Modelling of deep excavations Primary: Provide structural forces (bending, shear and axial) for primary lining (D-Wall) to confirm adequacy of reinforcement proposed by the Contractor. Secondary: Provide structural forces for Secondary lining (cast insitu), Base slab, and Cover slab

2. Structural connections Tunnel to Shaft: Elements with high strength (but zero tensile) with 50MPa stiffness (1/30th of Chalk) assigned around opening to allow tunnel to distort without transferring significant loads into the primary lining. CSO to Shaft: High strength (but zero tensile) low stiffness elements to ‘disconnect’ diaphragm and secant pile walls.

3. Application of secondary lining Uncertain interface between the primary and secondary linings of the shaft. Therefore range of models undertaken to bound structural forces on primary lining.