Laboratory CBR Testing for Arkansas Pavement Design

For a single-point CBR test on a compacted specimen, including the four-day soak and load-penetration curve, our Little Rock lab charges between US$120 and US$210 per specimen. The exact number depends on whether we’re running a single point or a three-point curve, and whether the Proctor compaction curve is already available from previous testing. Most Arkansas DOT subgrade investigations need at least three CBR points per soil type, so we typically quote a package that bundles the Proctor and the CBR series together to keep the per-unit cost reasonable.

An unsoaked CBR test measures the soil’s bearing capacity at the moisture content it was compacted at, which is useful for understanding immediate construction trafficability. The soaked CBR test submerges the specimen in water for 96 hours to simulate the saturated condition the subgrade will experience over the pavement’s service life. In Little Rock, where seasonal groundwater can rise within a few feet of the surface in low-lying areas, the soaked value is almost always the one that governs pavement design—and it is frequently half or less of the unsoaked number.

The number depends on the site size and soil variability. For a typical commercial building pad with uniform geology, we recommend at least one CBR test per distinct soil type encountered in the borings, with a minimum of three specimens per soil unit to establish a reliable average. For linear projects like access roads or parking lots that cross the shale-to-alluvium transition common in western Little Rock, we sample at every major change in soil classification. The Arkansas DOT standard specifications provide guidance on sampling frequency, and we align our recommendations with those requirements.