Madison’s growth over the last century, expanding outward from the isthmus between Mendota and Monona, has pushed construction into the glacial terrain that defines the region. The downtown sits on a thin veneer of fill over lacustrine deposits, while projects near the Yahara River encounter compressible silts with high groundwater. This means excavation work here rarely follows a textbook profile. Our team deals with these local variations every day, installing inclinometers, settlement markers, and piezometers early in the dig so we catch movement before it becomes a problem. When a job on East Washington Avenue goes deeper than 15 feet, the loose saturated silt changes the risk profile completely—something we’ve learned from monitoring over a dozen basement excavations through the central isthmus. Because the soils shift noticeably between McKee Road and Lake Monona, we also recommend pairing monitoring data with a CPT test to correlate subsurface behavior with cone resistance in real time.
In Madison’s saturated lake plain silts, we’ve seen inclinometer deflections double in 48 hours when dewatering lagged behind excavation—early warning data keeps the crew safe.
