Seismic provisions in ASCE 7-22 and Chapter 18 of the IBC put Glendale projects under a regulatory microscope that few other Southern California cities face. The Raymond Fault runs through the northern hills, the Verdugo Fault skirts the eastern boundary, and much of the basin sits on dense alluvium that masks variable liquefaction susceptibility below 15 feet. When structural plans cross a plan-check desk at Glendale City Hall, the first thing reviewers look for is a defensible SPT log—blow counts, recovery, and groundwater observations tied to ASTM D1586 procedures. Without that data, foundation recommendations are essentially guesswork, and the building department will send the package back. We run the split-spoon sampler through the full depth of influence, typically 30 to 50 feet in this market, and deliver N-value profiles that let the structural engineer size footings with confidence. For sites near the LA River channel or in the Chevy Chase Canyon area, we often pair SPT data with CPT soundings to develop a continuous stratigraphic picture where interbedded sands and silts require higher resolution than hammer-driven sampling alone can provide.
N-values alone don’t tell the full story—correlating blow counts with fines content and saturation is what separates a defensible SPT report from a drilling log.
Scope of work in Glendale California
Risks and considerations in Glendale California
The USGS Quaternary fault map places Glendale within a zone where shallow Holocene alluvium overlies the Verdugo and Raymond fault splays, producing a seismic hazard profile that ranks among the highest in Los Angeles County. SPT refusal at depths less than 15 feet is common along the Chevy Chase escarpment, where weathered crystalline bedrock lies beneath a thin veneer of residual soil. In the flatlands between Brand Boulevard and the LA River, liquefable layers of fine sand and low-plasticity silt appear between 12 and 25 feet—depths that coincide with the bearing stratum for many two- and three-story buildings. Missing those layers during a site investigation triggers a cascade of problems: undersized footings, differential settlement after the first moderate earthquake, and expensive underpinning work that could have been avoided with two extra boreholes. Our drilling crews log every change in penetration resistance, note the presence of saturated granular soils in real time, and flag intervals where the blow count drops below 15 in potentially liquefable material so the engineer can run a Seed-Idriss simplified procedure before the structural drawings are finalized.
Our services
A single SPT program answers the bearing capacity and settlement questions, but most Glendale projects need additional data layers to satisfy the building department and the structural engineer’s risk assessment. The services below are the ones we most frequently coordinate alongside SPT drilling in this market.
Liquefaction Potential Analysis
We process SPT N-values through Seed-Idriss and Boulanger-Idriss CPT-based procedures, correcting for fines content and overburden stress to produce site-specific liquefaction triggering curves. Reports include factor of safety contours and post-liquefaction settlement estimates, formatted for Glendale plan-check submittal.
Seismic Site Classification
Using the SPT N-value profile and shear wave velocity correlations, we assign the ASCE 7 Site Class (A through F) that determines the seismic design coefficients fed into the structural model. This classification is mandatory for any Glendale project over two stories or within a mapped fault setback zone.
Common questions
What does an SPT test cost for a typical single-family lot in Glendale?
For a standard single-family residential project requiring two boreholes to 30 feet with SPT sampling at 5-foot intervals, the cost in Glendale typically ranges from US$480 to US$790 per borehole, including mobilization within the city, field logging, and the signed geotechnical report. Sites with difficult access—steep canyon lots, narrow easements, or heavy vegetation—add mobilization time, and encountering shallow refusal that requires rock coring will increase the total. We provide a fixed-price proposal after reviewing the plot plan and any prior geotechnical data.
How many SPT boreholes does the Glendale building department require?
The City of Glendale generally follows IBC Section 1803, which requires a minimum of one borehole for every 1,600 square feet of building footprint, with at least two boreholes for any structure. For irregular lots, split-level designs, or sites within 500 feet of a mapped fault trace, the plan-check engineer often requests three or more boreholes to capture lateral variability. We coordinate the layout with the structural team before drilling to avoid having to remobilize later.
Can SPT data alone determine if my Glendale site needs deep foundations?
SPT N-values are the primary input for bearing capacity and settlement calculations, but the decision to use deep foundations depends on more than blow counts alone. In Glendale’s hillside zones, shallow refusal in weathered rock or colluvium may point toward drilled piers, while low N-values in saturated sands on the valley floor usually trigger a liquefaction analysis first. We interpret SPT data alongside CPT soundings, laboratory grain-size curves, and the structural loading demands to recommend whether spread footings, mat foundations, or piles are the appropriate solution.