Active/Passive Anchor Design for Madison's Glacial Terrain

For most commercial and residential excavation projects in the Madison area, anchor design packages range from US$1,020 to US$4,300. The final figure depends on the number of anchor types, the extent of pull-out testing required, and whether corrosion protection qualifies as Class I or Class II. A small basement cut with a single row of passive anchors will fall on the lower end, while a multi-level tieback system for a deep parking structure—with proof testing and creep monitoring on every anchor—moves toward the upper range.

Active anchors are the right choice when you cannot tolerate any lateral movement—think of a shoring wall directly adjacent to an existing building on East Washington Avenue, where even half an inch of displacement could crack masonry. The pre-stressing locks the wall into the soil before excavation proceeds. Passive anchors work well for temporary cuts or sites with ample setback, because they engage only as the soil deforms; they are simpler to install and generally require less post-tensioning equipment, but you must account for the expected deflection in your shoring design and confirm the adjacent structures can accommodate it.

We follow the PTI DC35.1 recommendations, which align with the AASHTO LRFD and IBC requirements adopted by the City of Madison. A performance test cycles the anchor through incremental loading and unloading to verify the apparent free length matches the design; a proof test holds the anchor at 133% of the design load while monitoring for creep; and for anchors in fine-grained glacial soils, we run an extended creep test at lock-off load for a full 60 minutes. The acceptance criterion is typically less than 1 mm of creep during the final log cycle, adjusted for the specific soil type encountered in the bond zone.