Laboratory CBR Test in Fort Worth: Pavement Design for North Texas...

The loading press applies 0.05 inches per minute, and the proving ring starts reading resistance in pounds. That is the moment a laboratory CBR test in Fort Worth actually begins. Our team prepares remolded specimens at optimum moisture from your Proctor data, soaks them for 96 hours to simulate the worst saturation the subgrade will ever see, then runs the piston penetration. In Tarrant County, where the Eagle Ford Shale weathers into highly plastic clay and the Trinity Sands can lose strength fast when wet, the soaked CBR value is the single most powerful number you will hand to your pavement designer. A six-inch-thick flexible pavement section lives or dies by whether the subgrade tests at CBR 3 or CBR 8 under ASTM D1883. We have seen both within the same Fort Worth subdivision, sometimes less than 300 feet apart. Before finalizing pavement structural numbers, engineers often cross-check with in-situ CBR field testing to compare lab-soaked values against in-place conditions at the actual construction bench.

A single soaked CBR value can cut pavement thickness by 30 percent or double it. We test to make sure the number is real, not assumed.

Technical details of the service in Fort Worth

In Fort Worth, many times we see project specifications calling for a CBR of 5 or higher on the lime-treated subgrade, yet the raw native clay barely pushes past 2. That gap is exactly where our laboratory CBR test becomes a construction tool, not just a design checkbox. We run the penetration on a calibrated mechanical press, recording load values at 0.1-inch increments up to 0.5 inches, and we plot both the uncorrected and corrected curves on the same graph. When the curve needs a zero-point correction because the initial seating load causes a concave upward shape, we apply it per ASTM D1883-21 and annotate the report accordingly. The lab compacts specimens using the modified Proctor effort by default, but we can switch to standard effort if the project follows an older TxDOT spec. For expansive subgrades common east of I-35W, we sometimes run the CBR on specimens that have undergone multiple wet-dry cycles, giving a more realistic long-term modulus. If the formation includes gravel lenses from the older Pleistocene terraces, we pair the CBR with a grain-size analysis to verify less than 30 percent retained on the 3/4-inch sieve, keeping the test valid for fine-grained interpretation.

Laboratory CBR Test in Fort Worth: Pavement Design for North Texas Soils

Parameter	Typical value
Applicable standard	ASTM D1883-21
Specimen compaction	Modified Proctor (56,000 ft-lbf/ft³), standard available by request
Soaking period	96 hours, with swell measurement before penetration
Penetration rate	0.05 in/min (1.27 mm/min)
Surcharge weight	10 lb minimum, simulating base and pavement mass
Typical local native clay CBR	2 to 4 (soaked); 8 to 20 (unsoaked)
Lime-treated subgrade target	CBR ≥ 5 at 95% compaction (TxDOT Item 260)

Risks and considerations in Fort Worth

Fort Worth's post-war expansion pushed residential streets and commercial pads onto the Eagle Ford formation across vast swaths of the city. That shale-derived clay holds a plasticity index frequently above 30, and when it gets wet under a pavement section, the soaked CBR can drop below 3. A pavement designed on an assumed CBR of 6, without a soaked laboratory CBR test, will rut and crack within three to five years. We have pulled cores on arterials in south Fort Worth where the asphalt was laid over untreated high-PI subgrade, and the base course had pumped fines up into the aggregate layer. The repair cost exceeded the original pavement budget. For rigid pavement design, the modulus of subgrade reaction (k-value) correlates directly with the CBR, so an underestimated CBR means an undersized slab thickness and uncontrolled transverse cracking. In warehouse districts near the Alliance corridor, where truck traffic applies heavy repeated loads, the difference between a tested CBR of 4 and an assumed CBR of 7 represents a slab life reduction measured in decades. Our reports include the swell percentage during soaking, which tells the civil engineer whether moisture-induced heave will add to the distress beyond the bearing capacity loss.

Need a geotechnical assessment?

Reply within 24h.

Email: contact@geotechnical-engineering1.org

Applicable standards: ASTM D1883-21 – Standard Test Method for California Bearing Ratio (CBR) of Laboratory-Compacted Soils, ASTM D1557-12e1 – Standard Test Methods for Laboratory Compaction Characteristics of Soil Using Modified Effort, AASHTO T 193 – Standard Method of Test for The California Bearing Ratio

Our services

We run the laboratory CBR test as part of a broader pavement geotechnical package for projects across Tarrant County. Our lab compacts specimens within 24 hours of receiving the bulk sample to minimize moisture loss, and we report both the CBR at 0.1-inch and 0.2-inch penetration, using the higher value by default unless the corrected curve dictates otherwise.

Soaked CBR with Swell Measurement

Four-day soaking under surcharge, with daily swell readings. We provide the CBR at 0.1-inch and 0.2-inch penetration, the corrected stress-penetration curve, and the dry density-moisture relationship used for specimen preparation. This is the standard TxDOT and AASHTO subgrade evaluation for flexible pavement.

Unsoaked CBR for Granular Base

For crushed limestone base courses sourced from local quarries, we run the CBR immediately after compaction at optimum moisture, without soaking. Typical values exceed 80 for high-quality flex base, and we report the data to support layer coefficient selection in AASHTO 1993 pavement design.

Quick answers

What is the typical turnaround time for a laboratory CBR test in Fort Worth?

We can complete a standard soaked CBR test, including the 96-hour soaking period, in five to seven working days from the moment the specimen is compacted. If you need preliminary unsoaked results to keep the earthwork moving, we can run the penetration on a duplicate specimen within 48 hours and follow up with the final soaked report.

How much does a laboratory CBR test cost for a project in Tarrant County?

Can you run the CBR test on lime-stabilized soil specimens?

Yes. We compact the soil-lime mixture at the target mellowing period specified by your mix design, then cure the specimen in a humidity-controlled environment before soaking and penetration. This is standard practice for TxDOT Item 260 subgrade treatment verification, and we report the CBR alongside the pH and strength gain data.

What soil sample quantity do you need for a laboratory CBR test?

We require approximately 50 pounds of material passing the 3/4-inch sieve for a single-point CBR test with its corresponding Proctor curve. If the soil has significant gravel, we will need more. Bucket samples should be sealed to preserve field moisture, and we prefer you deliver them to our lab within 24 hours of sampling.