When we mobilise the jet grouting rig into a Cardiff site, the first thing we check is the access width—most of the city’s inner-urban plots were carved out in the 19th century, so tight gateways and narrow streets are the norm. The high-pressure monitor, typically running at 400 to 600 bar with a cement-bentonite slurry, cuts through the glacial tills and laminated clays that underlie much of Cardiff. We’ve found that the jet’s energy needs to be dialled back slightly in the softer Holocene deposits near the Taff and Ely rivers; otherwise, the return spoil becomes too fluid to manage. Before we design the column geometry, we always run a permeability field test to confirm the in-situ soil fabric won’t cause excessive washout.
Overconsolidated Cardiff tills with OCR > 6 demand a modified jet-grouting design to prevent column contraction and ensure full section development.