Urban slurry shield (Mixshield) · Ø 7.08 m

Analytical (browser)

Operator

Support pressure at the face (bar)

Filter cake

Slurry circuit

Alarms

Cycle

Advance with downtime

Thrust and torque

Segment lining

Ring forces by the elastic equation method (ITA WG2 2000) with Wood's joint reduction; jacking, bursting and grout checks after ITA (2000, 2019) and DAUB (2024). Ground stiffness, concrete modulus and the shoe pad are assumed.

Geological long section

15 Crossrail boreholes from the British Geological Survey, four over the river (Open Government Licence v3.0; contains British Geological Survey materials © UKRI 2026). Line © OpenStreetMap contributors (ODbL). River at mean high water from the Environment Agency Charlton gauge (estimate; © Environment Agency copyright and/or database right 2026, Open Government Licence v3.0). Unit parameters from open sources, some assumed, grain sizes assumed; the tunnel level is assumed within the published cover. Details: scenario format and sources.

Ground and surface

Model limits

  • Volume loss is a scenario input (default from measured Crossrail settlement, see the Ground panel); it does not yet respond to face pressure or grouting. One bore is modelled.
  • Buildings: OS OpenMap Local footprints (terraces merged into blocks), heights from Environment Agency LIDAR, listing from the National Heritage List for England, all under the Open Government Licence v3.0. Contains OS data © Crown copyright and database right 2026; © Environment Agency copyright and/or database right 2026; © Historic England 2026. Damage uses the greenfield trough under each footprint, without building stiffness.
  • Building categories come from the second-stage assessment of Mair, Taylor & Burland (1996, ISSMGE library): the building follows the greenfield trough, and each hogging or sagging span's bending or diagonal strain (from Δ/L, as a masonry deep beam, E/G 2.6) is combined with its average horizontal strain. That is conservative: real buildings are stiffer. Each building also shows its Δ/L and largest horizontal strain with an estimated stiffness (Potts & Addenbrooke 1997, as plotted by Mair 1997; 1996, Fig. 5), from floor slabs every 3.4 m acting together (an assumed upper estimate). These are shown only; they do not change the category.
  • The air-cushion dynamics (Boyle's law, level balance, first-order air regulator) are this project's own derivation; no open source with equations was found. Chamber area, air volume and regulator time are assumed.
  • Penetration uses DAUB's steady emax (conservative); the support transferred is approximated as 1 − e/L over the wedge length. Over-excavation when support falls short is illustrative.
  • The dry-mass balance assumes ideal density and flow meters; the separation plant is shown only as a load, not modelled.
  • Downtime uses distributions fitted on one 6.88 m metro EPB (Tabriz; Moosazadeh et al. 2018), applied to this slurry machine as an assumption. Separation-plant stops, pipe extensions and learning curve are not modelled.
  • Shield length, chamber sizes, friction coefficients and machine weights are illustrative assumptions.
Models: wedge-silo face support and DAUB window, filter cake and penetration (DAUB 2016; Broere & van Tol 2000), air cushion (own derivation), dry-mass balance (Shomee et al. 2022), deposit limit (Durand, after Miedema), thrust and torque components (Shi et al. 2011), Gaussian settlement (Peck; O'Reilly & New; Mair & Taylor), utilisation and downtime (Moosazadeh et al. 2018; record rates with sources). Machine class from published references.