Based on borings at the site, GZA provided a geotechnical report for solar canopy foundation design by a design-build contractor. Their design assumed 36- to 42-inch-diameter drilled shafts installed with temporary casing. Drilled shaft installation went according to expectations, except for one area where multiple drilled shaft installations encountered “running sands”, which is caused by loose sands and shallow groundwater. The Owner and Contractor reached out to GZA to help find a construction solution while drilled shaft installation was halted.


Working promptly with the contractor and the project team, GZA suggested several alternative drilling methods, none of which was deemed practical by the contractor. GZA recommended extending the canopy drilled shafts to derive support from deeper, denser soils. Therefore, GZA conducted an additional boring program to further evaluate subsurface conditions. The borings identified a deep, very dense sand and gravel layer suitable for end bearing of the drilled shafts. GZA recommended the designer redesign assuming end bearing conditions with a permanent casing extending through the loose sands.


GZA was responsive to our client and their contractor to expedite the project schedule and find a construction solution to the difficult drilled shaft installation conditions; the solution did add cost but was definitive and worked to everyone’s benefit.