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Home › Seismic › Soil liquefaction analysis

Soil Liquefaction Analysis in Pomona: Mitigation Starts with Accurate Data

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The soil profile in Pomona shifts dramatically from the rocky alluvial fans near the San Jose Hills to the deeper sedimentary deposits around the Fairplex and downtown corridor. A foundation design that works on a compacted terrace might be dangerously inadequate just two miles south where the groundwater table sits higher and the fines content drops. This contrast is why a site-specific soil liquefaction analysis is not just a code requirement but a practical necessity. We run standardized penetration tests and collect undisturbed samples to calculate the factor of safety against liquefaction triggering, using the cyclic stress approach. When the IBC maps flag your parcel as a potential seismic hazard zone, you will need more than a desktop study to satisfy the building department and protect the structural investment.

In Pomona, liquefaction risk is not uniform—it concentrates in the alluvial corridors where groundwater and granular soils combine to create a critical condition during a design-level earthquake.

Our service areas

Investigation

Exploratory test pit ›CPT (Cone Penetration Test) ›SPT (Standard Penetration Test) ›
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In-Situ Testing

Field density test (sand cone method) ›Plate load test (PLT) ›Field permeability test (Lefranc/Lugeon) ›
VIEW ALL IN-SITU TESTING ›

Laboratory

Grain size analysis (sieve + hydrometer) ›Triaxial test ›Atterberg limits ›
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Our approach and scope

On a recent project near the 71 freeway expansion, the contractor hit saturated silty sand at just 16 feet and the standard penetration resistance dropped below 8 blows per foot. That single boring changed the entire foundation strategy. A reliable liquefaction assessment combines field testing like SPT with laboratory index tests to confirm the soil classification. The SPT drilling provides the N-values we need for simplified procedures, while sieve analysis quantifies the percentage of fines that influences cyclic resistance. We process samples through ASTM D2487 classification and apply corrections for overburden pressure, hammer energy, and borehole diameter. The output is a post-liquefaction settlement estimate and a residual strength profile that the structural engineer can use to design deep foundations or ground improvement. In Pomona, where the seismic hazard is driven by the San Jose Fault and the nearby San Andreas system, the difference between a generic report and a high-quality analysis is often the difference between a feasible project and an uninsurable one.
Soil Liquefaction Analysis in Pomona: Mitigation Starts with Accurate Data
Technical reference — Pomona

Local geotechnical context

A common pattern we see in older commercial strips of Pomona is the assumption that a one-story structure does not require a liquefaction study. The California Building Code triggers evaluation based on Seismic Design Category and soil profile, not building height. A light warehouse on liquefiable soil can experience differential settlement of 4 to 8 inches during a strong motion event, tearing apart slab-on-grade floors and severing utility connections. The cost to retrofit a settled structure is exponentially higher than the upfront analysis. In the southeastern part of the city, where the alluvial deposits from San Antonio Creek dominate, we have measured SPT N-values below 10 in the upper 30 feet and fines content under 15 percent. That combination produces a calculated factor of safety well below 1.0 for the MCE_R event. Ignoring these soil conditions is a business risk that no lender or insurer will overlook in today’s market.

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Relevant standards

ASCE 7-22: Minimum Design Loads and Associated Criteria for Buildings and Other Structures, IBC 2024 (California Building Code, Chapter 18: Soils and Foundations), ASTM D1586-18: Standard Test Method for Standard Penetration Test (SPT), ASTM D2487-17: Standard Practice for Classification of Soils for Engineering Purposes (USCS), ASTM D5778-20: Standard Test Method for Electronic Friction Cone and Piezocone Penetration Testing

Typical values

ParameterTypical value
Analysis MethodologySimplified Procedure (Seed & Idriss) per ASCE 7-22
Design EarthquakeMCE_R, 2,475-year return period (IBC 2024)
Field Test StandardASTM D1586-18 (SPT) / ASTM D5778-20 (CPT)
Laboratory ClassificationASTM D2487-17 (USCS) / ASTM D4318 (Atterberg Limits)
Output ParametersFS against liquefaction, LPI, post-liquefaction settlement
Groundwater CorrectionSeasonal monitoring + conservative design level per Pomona basin data
Reporting FormatGeotechnical report signed by CA-registered Professional Engineer

Common questions

What triggers a liquefaction study requirement in Pomona under the current building code?

The California Building Code (IBC 2024) requires a liquefaction evaluation when the site is in Seismic Design Category D, E, or F and the soil profile contains saturated, loose to medium-dense granular soils within 50 feet of the surface. In Pomona, the state’s Seismic Hazard Zone maps also mandate site-specific analysis for parcels within mapped liquefaction zones before permit approval.

How much does a soil liquefaction analysis cost for a typical commercial lot in Pomona?

For a standard commercial parcel requiring one or two borings with SPT sampling and a laboratory testing suite, the analysis typically ranges from US$2,230 to US$4,620. The final cost depends on the depth to refusal, the number of borings needed to characterize the site, and whether advanced testing like CPT or cyclic triaxial is required by the design team.

Can you use CPT data instead of SPT for the analysis?

Yes, CPT is accepted by ASCE 7 and the IBC as a valid method for liquefaction triggering analysis. We use the Robertson (2016) or Boulanger and Idriss (2014) correlations to compute the cyclic resistance ratio from cone tip resistance and sleeve friction. In Pomona’s mixed alluvial soils, we often combine SPT and CPT in the same investigation to cross-validate the results.

How long does the entire liquefaction analysis process take from start to final report?

Fieldwork including drilling, sampling, and groundwater monitoring typically takes 2 to 3 days on site. Laboratory testing for fines content and Atterberg limits requires an additional 5 to 7 business days. The engineering analysis and report preparation is usually completed within 10 to 14 business days from the completion of fieldwork, depending on the complexity of the soil profile.

Location and service area

We serve projects in Pomona and surrounding areas.

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