Two sites five miles apart in Ipswich can behave completely differently. A cutting in the London Clay near the town centre might stand almost vertical for a week in dry weather, then unravel in a single wet weekend. Over on the Orwell estuary side, a shallow slope in soft alluvium can creep for years before anyone notices the cracks in the brickwork. That contrast is exactly why we never apply a generic factor of safety to any job here. The geology under Ipswich shifts from stiff boulder clay and Red Crag in the north to compressible estuarine deposits in the south, and the groundwater table follows the River Gipping's seasonal rhythm. Before a retaining structure or an excavation goes in, we run a slope stability analysis that models the actual stratigraphy we've logged on the borehole. When the ground gets tricky, we often pair it with a CPT test to pick up thin silt seams that a standard sampler can miss.
Relict shear surfaces in Ipswich's London Clay don't announce themselves. You find them in the trial pit, or you find them after the slope moves.
