A commercial development on E Street near the 210 freeway required a deep soil mechanics study to address the variable fill and alluvial deposits common across San Bernardino. Our crew drilled borings to 80 feet, extracting undisturbed samples for laboratory testing. The site's proximity to the San Andreas fault zone demanded a detailed seismic site class assessment per ASCE 7. We combined Standard Penetration Tests with a respuesta sísmica profile to evaluate ground motion amplification, while cross-referencing the data against the city's historic liquefaction records near the Santa Ana River.
The alluvial fan deposits in San Bernardino vary from dense gravels to loose silts within a single site, demanding a phased SPT and laboratory testing strategy.
Approach and scope
San Bernardino expanded rapidly during the post-war boom, pushing construction onto steeper alluvial fans along the San Bernardino Mountains. These deposits vary from dense gravels near the mountain front to loose sands and silts closer to the valley floor, creating a wide range of bearing capacities within a single parcel. Our soil mechanics study process follows ASTM D1586 for the SPT and ASTM D4318 for Atterberg limits, ensuring consistent classification of these heterogeneous soils. When we encounter the collapsible soils common near Hospitality Lane, we run a double-ring infiltrometer test and recommend a suelos colapsibles assessment to quantify wetting-induced settlement risk. The combination of these tests gives the structural engineer a complete picture of the ground's behavior under load.
Technical reference image — San Bernardino
Site-specific factors
Our drill rig on a 3rd Street site encountered a buried debris flow channel at 22 feet, which we only identified through continuous sampling rather than standard split-spoon intervals. This is a recurring risk in San Bernardino—historic alluvial fan channels filled with loose sand and boulders can remain hidden beneath a uniform surface. A soil mechanics study that relies solely on shallow hand augers or limited borings will miss these features, leading to differential settlement or bearing failure. We recommend borings spaced at a maximum of 50 feet in alluvial fan areas, with at least one boring reaching competent bedrock or dense gravel.
Continuous SPT borings to 100 feet using a CME 75 rig, with Shelby tube sampling in clay layers. We log soil types, measure blow counts, and classify per USCS on-site.
ASTM D1586-18 (Standard Penetration Test), ASTM D4318-17 (Atterberg Limits), ASCE 7-22 (Seismic Site Class per NEHRP), IBC 2021 (Chapter 18, Soils and Foundations)
Quick answers
How many borings are needed for a soil mechanics study in San Bernardino?
For a typical commercial building on an alluvial fan site, we recommend 4 to 6 borings spaced 40 to 60 feet apart. One boring should reach competent material (dense gravel or bedrock) at 60 to 80 feet. Residential sites often need 2 to 3 borings to 30 feet.
What is the typical cost range for a soil mechanics study in San Bernardino?
A standard soil mechanics study for a single-family home or small commercial pad runs between US$3.130 and US$5.640. This includes drilling, SPT testing, laboratory work, and a written report with foundation recommendations. Larger sites or deeper borings increase the cost.
Does San Bernardino require a seismic site class analysis for new buildings?
Yes, per the 2021 IBC and ASCE 7-22, any new structure in San Bernardino must have a site class determined from a soil mechanics study. The city sits on Site Class C (very dense soil) to D (stiff soil) near the Santa Ana River, but deeper deposits can shift the class. We measure shear wave velocity using the SPT N-value correlation (Seed & Idriss) to confirm.
How long does it take to complete a soil mechanics study in San Bernardino?
Drilling and field testing usually take 2 to 3 days. Laboratory testing adds 5 to 7 business days. The final report with engineering analysis and foundation recommendations is delivered within 10 to 12 business days from the start of drilling.
What kind of foundation issues are common in San Bernardino soils?
Collapsible soils on the alluvial fans can settle 2 to 4 inches when wetted, especially near the mountain front. Expansive clay layers in the valley floor cause heave in slab-on-grade foundations. Our study identifies both risks and recommends mitigation such as deep foundations, soil replacement, or moisture control measures.
