The Saint John area sits on a complex glacial legacy. The Wisconsinan ice sheet left behind dense lodgement till overlying Cambrian bedrock, but the real challenge lies in the post-glacial marine clays deposited by the former Goldthwait Sea. These sensitive silts and clays, often found in the lower Millidgeville area and along the Courtney Bay Causeway approaches, can lose significant strength when remolded. A standard penetration test alone won't capture this behavior. The triaxial test is the definitive method for measuring drained and undrained shear strength under controlled stress paths. For deep excavations near the Saint John River, understanding effective stress parameters matters. A deep excavations design without site-specific triaxial data on the Leda-type clays can either be overly conservative or dangerously optimistic. The laboratory program replicates field confining pressures, allowing the engineering team to model how the soil skeleton will actually respond when the shoring goes in and the water table, often just 2 to 3 meters below grade, begins to fluctuate.
Sensitive marine clay in Saint John can lose 80% of its undisturbed strength upon remolding, making the peak friction angle from a triaxial test a non-negotiable design input.
