San Bernardino sits on a complex alluvial fan system with sandy gravels and silty sands extending over 300 feet in places, and the water table can rise to within 15 feet of the surface after heavy rains. For any deep excavation — say a basement for a new medical building or a parking structure — you need to account for the San Jacinto fault zone running through the eastern part of the city. We start every project with a site-specific subsurface investigation, combining SPT borings with cone penetration testing to map soil variability in the top 50 feet, then model the excavation using limit-equilibrium and finite-element methods per ASCE 7-22.
San Bernardino's shallow water table and proximity to active faults make deep excavation design a non-negotiable step for safe below-grade construction.
Approach and scope
At an elevation of roughly 1,050 feet, San Bernardino experiences a semi-arid climate with flash flood potential in the alluvial washes. The geotechnical design of deep excavations here must handle up to 24 feet of loose to medium dense sands underlain by stiff clay layers that can cause hydrostatic uplift if not dewatered properly. We follow IBC 2021 Chapter 18 for excavation support, and for each job we run sieve analysis, Atterberg limits, and direct shear tests to classify the soil. When we hit the old river channels, we often recommend soldier pile and lagging walls with tiebacks, and we always check the stability of slopes for the temporary cuts around the excavation perimeter.
Technical reference image — San Bernardino
Site-specific factors
I remember a job near the 215 freeway where a six-story apartment project needed a 35-foot-deep excavation for two parking levels. The contractor started digging without a proper shoring design, and within three days the sandy sidewall caved in, shearing off a water main. The geotechnical design of deep excavations in San Bernardino has to account for the loose granular soils that can run like dry sand, plus the occasional perched water table from leaky irrigation lines. We ended up redesigning with a secant pile wall and a deep well dewatering system, which saved the project but added four weeks to the schedule.
We design soldier pile and lagging walls, sheet pile cofferdams, and tieback anchor systems for excavations up to 50 feet deep. Our designs follow AASHTO LRFD and include global stability checks for the San Bernardino alluvium.
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Dewatering & Groundwater Control Plans
For excavations below the water table, we specify wellpoint systems, deep wells, or sump pumps with filtration to avoid soil piping. We model drawdown curves using local aquifer data and coordinate with San Bernardino County for discharge permits.
Relevant standards
IBC 2021 Chapter 18 – Soils and Foundations, ASCE 7-22 – Minimum Design Loads (including seismic), ASTM D1586-18 – Standard Penetration Test (SPT), OSHA 29 CFR 1926 Subpart P – Excavations
Quick answers
What codes govern deep excavation design in San Bernardino?
We follow the California Building Code (2022 edition), which adopts IBC 2021 with state amendments, plus ASCE 7-22 for seismic lateral pressures on shoring walls. OSHA Subpart P applies to all temporary excavations over 5 feet deep.
How does the San Jacinto fault affect deep excavation design?
The San Jacinto fault zone crosses eastern San Bernardino, and excavations within 50 feet of an active trace require a fault-rupture hazard analysis per Alquist-Priolo. We design shoring with additional ductility and avoid cantilever walls in those zones.
What is the typical cost range for a deep excavation design in San Bernardino?
For a standard commercial project with one to two levels of basement, the geotechnical design of deep excavations including analysis, shoring design, and dewatering plan typically runs between US$2,010 and US$7,300, depending on depth and site complexity.
Do you recommend soldier pile and lagging or sheet piles for San Bernardino soils?
Soldier piles with timber lagging work well in the granular soils above the water table because they are cost-effective and easy to install. Below the water table, we typically switch to interlocking sheet piles or secant pile walls to control groundwater inflow.
