One mistake we see repeatedly in San Bernardino is treating partially saturated soils like fully saturated ones. Builders assume that if the water table is deep — and in much of San Bernardino it sits well below foundation level — the ground is stable. That overlooks the suction-driven behavior of unsaturated soils, which can lead to unexpected heave in clay-rich alluvium or sudden collapse in loose sands when wetting occurs. In our experience, skipping the unsaturated soil analysis before designing slabs or shallow footings has caused costly repairs across the Inland Empire. A proper assessment starts with sampling that preserves in-situ moisture and then running consolidation tests to capture collapse potential, paired with suction measurements to quantify heave risk.
Unsaturated soil analysis is not optional in San Bernardino's alluvial environment — it separates a durable foundation from a costly heave or collapse failure.
Approach and scope
The equipment we use for unsaturated soil analysis in San Bernardino includes a Fredlund-type triaxial cell with independent suction control, plus tensiometers and filter-paper setups for matric suction. In our lab, we first classify the soil according to ASTM D2487 — many samples here fall into CL or CH groups from the old alluvial fans, or SM from the San Bernardino Mountains' granitic washes. Then we run a soil-water characteristic curve (SWCC) using a pressure plate extractor, which can take several weeks for low-permeability clays. The key parameters we extract are the air-entry value and the slope of the drying curve. That data feeds directly into Bishop's effective stress formulation for slope stability models and into Fredlund's shear-strength equation for foundation design. We also measure saturated hydraulic conductivity via flexible-wall permeameters to complete the picture.
Technical reference image — San Bernardino
Site-specific factors
ASCE 7-22 and the 2024 California Building Code require that foundation design account for soil volume change. In San Bernardino, where expansive clays from the San Timoteo formation and collapsible sands from the Santa Ana River wash coexist, ignoring unsaturated soil behavior is a liability. The code's Section 1803.5.3 specifically mandates evaluation of heave potential for slab-on-grade construction. Without suction-based analysis, you underestimate heave in dry months and risk collapse after the first wet season. We've seen retaining walls tilt and slabs crack within two years of construction because the original study assumed a saturated effective stress model that didn't apply.
Full SWCC using pressure plate extractors and dew-point hygrometers. We report air-entry value, residual suction, and fitting parameters for your geotechnical model.
02
Unsaturated Shear Strength Testing
Multistage triaxial tests with controlled matric suction. Provides cohesion and friction angle under partially saturated conditions for slope stability and foundation design.
03
Collapse Potential Assessment
Double-oedometer and single-oedometer collapse tests on undisturbed samples. Identifies the wetting-induced strain that can cause differential settlement in San Bernardino's sandy alluvium.
Relevant standards
ASTM D6836 (SWCC), ASTM D5298 (filter paper method for suction), ASTM D4767 (consolidated undrained triaxial with pore pressure)
Quick answers
What is unsaturated soil analysis and why does it matter in San Bernardino?
The reference range for this service in San Bernardino is US$1.060 - US$2.730. The final price depends on the project scope and volume.
Which ASTM standards apply to unsaturated soil testing?
ASTM D6836 covers SWCC measurement, ASTM D5298 covers filter-paper suction, and ASTM D4767 covers triaxial testing with pore-pressure control. For collapse potential we follow ASTM D5333.
How long does a typical unsaturated soil analysis take?
A full suite — SWCC, unsaturated triaxial, and collapse tests — typically takes 4 to 8 weeks. The SWCC alone requires 2 to 4 weeks due to the slow equilibration time in low-permeability clays.
What is the difference between saturated and unsaturated shear strength?
Unsaturated soils have additional apparent cohesion from matric suction. This can increase peak strength by 30% or more in dry conditions, but vanishes upon wetting — exactly the scenario that triggers failure in San Bernardino's alluvial slopes.
How much does unsaturated soil analysis cost in San Bernardino?
The typical range for a complete analysis including SWCC, triaxial, and collapse tests is between US$1,060 and US$2,730, depending on sample quantity and suction range required. Contact us for a quote tailored to your project scope.
