ASCE 7-22 and the California Building Code (CBC) Chapter 18 classify much of Fresno at Site Class D by default, but that default assumption can penalize a project with overly conservative foundation costs. In our experience across the Fresno-Clovis metropolitan area, the upper alluvial stratigraphy changes fast—a half-mile shift can mean the difference between clean coarse sands and a lens of fat clay. An exploratory test pit lets the geotechnical engineer observe these transitions directly in the sidewall, measure infiltration rates where stormwater disposal matters, and collect undisturbed block samples for laboratory strength testing. When the pit reaches four to fourteen feet in the San Joaquin Valley formations, we document the soil profile using the Unified Soil Classification System (USCS) per ASTM D2488, and we correlate our field logs with nearby SPT drilling data to build a defensible ground model for the structural engineer. The City of Fresno Public Works Department accepts test pit data for shallow foundation submittals, provided the exploration depth exceeds the zone of influence of the proposed footing.
A four-foot-deep test pit in Fresno's alluvium often delivers more actionable bearing-capacity information than a twenty-foot boring that missed the critical clay seam.
