Flexible Pavement Design for Arlington’s Expansive Clay Soils

A few years back, we were called to look at a parking lot off Cooper Street that had turned into a washboard after just two summers. The asphalt was riddled with alligator cracking, and the owner couldn't understand why — the pavement section looked thick enough on paper. What the original design missed was Arlington's subgrade reality: highly plastic Eagle Ford clay that swells with winter moisture and shrinks dramatically during our 100-degree August afternoons. A flexible pavement here isn't just a structural section; it's a moisture management system. The subgrade support can drop by half between March and September, and if your CBR pavement design doesn't reflect that seasonal swing, you'll be repaving within three years. We've seen it too many times to count.

In Arlington, a pavement designed without accounting for seasonal subgrade moisture variation is a pavement designed to fail within five years.

Methodology and scope

The contrast between Arlington's dry summers and occasional intense rainstorms creates a punishing cycle for flexible pavements. When the expansive clay beneath an asphalt layer wets up, it loses stiffness rapidly, and the repeated traffic loads then pump fines up into the base course. That's why we lean heavily on chemical stabilization — lime treatment is practically standard here for new construction east of Cooper, where the clay fraction exceeds 60 percent. On the western edge of town, where you start seeing more sandy loam, cement-modified base can work better. The design process always starts with a thorough subgrade survey, combining grain size analysis to quantify the clay content and Atterberg limits to nail down the plasticity index. From there, we build the asphalt layer configuration using AASHTO 93 for structural number and AASHTOWare ME for rutting predictions over the 20-year design life. For arterial roads with heavy truck traffic, the difference between a 4-inch and 6-inch asphalt concrete layer often comes down to whether the subgrade resilient modulus was measured at the dry season low or the wet season low — and we always design for the worst case.

Local geotechnical context

The pavement design challenge varies noticeably between North and South Arlington. Up around River Legacy Park, the alluvial soils near the Trinity River bring a higher water table and more silt, so we worry about pumping and loss of base support during wet cycles. Down south near the Parks Mall area, the issue is almost purely expansive clay — the soil can swell enough to lift a poorly designed pavement section by over an inch, then shrink back and leave a void underneath the asphalt layer. The risk isn't just cracking; it's differential movement at joints with rigid pavement transitions and around drainage inlets. We've also seen cases where a flexible pavement design imported from a generic Texas manual didn't account for the thermal gradient specific to Arlington, where surface temperatures can hit 140°F. That kind of heat softens the asphalt binder and accelerates rutting in the wheel paths. A proper mix design with polymer-modified binder, tied to a subgrade that has been stabilized and proof-rolled, is the only way to avoid the maintenance headaches we keep seeing on older commercial properties.

Typical values

Parameter	Typical value
Design methodology	AASHTO 93 and AASHTOWare Pavement ME
Design traffic (ESALs)	500,000 to 15 million for municipal roads
Asphalt concrete thickness	4 to 8 inches on stabilized subgrade
Base course material	Crushed limestone, TxDOT Grade 2, 6 to 10 inches
Subgrade stabilization	Lime treatment at 4-6% by weight for PI > 25
Target subgrade CBR	Minimum 6 after stabilization
Design life	20 years for arterials, 10 years for residential
Drainage coefficient	1.0 to 1.2 depending on edge drain configuration

Complementary services

Subgrade Evaluation and CBR Testing

Field and laboratory California Bearing Ratio testing to establish the seasonal support value for the pavement section, including moisture-conditioned samples.

Lime and Cement Stabilization Design

Mix design and specification for chemical treatment of expansive subgrades, including pH testing and strength verification per TxDOT guidelines.

AASHTO Structural Section Design

Full structural number calculation and layer thickness optimization for asphalt concrete, base, and subbase courses under projected traffic loads.

Pavement Forensic Investigation

Post-construction distress surveys and coring to diagnose premature failures in existing flexible pavements, with recommendations for rehabilitation.

Quick answers

What does flexible pavement design cost for a commercial project in Arlington?

For a typical commercial parking lot or small access road in Arlington, the geotechnical investigation and pavement design package runs between US$1,680 and US$4,460, depending on the number of borings, the extent of laboratory testing required, and whether lime stabilization mix design is included.

Why does Arlington's soil require special consideration for asphalt pavement?

The Eagle Ford formation under much of Arlington is a high-plasticity clay with significant swell-shrink potential. When this soil gets wet, its bearing capacity drops sharply, and the volume change can lift or undermine an asphalt section. Without stabilization, the pavement life can be cut in half compared to designs on more forgiving soils.

How many soil borings are needed for a pavement design project?

We typically follow TxDOT guidelines, which call for borings every 200 to 300 feet along the alignment for roadways, with a minimum of three borings for a parking lot under one acre. The borings should extend at least five feet below the proposed subgrade elevation to capture any deeper moisture-sensitive layers that could affect long-term performance.