Drained Residual Strength of Expansive Soils Causing Pavement Distress along Alabama Highway 5

Abstract

A segment of Alabama Highway 5 (AL-5) located in Perry County, Alabama has been experiencing severe pavement distress that is mostly caused by the behavior of soil beneath the roadway. AL-5 is a farm-to-market road that was built directly on the subgrade which consists of expansive clays with no compacted base. Previous laboratory tests confirmed shrink-swell behavior in the soil with swell pressures of up to 1500 psf. Five remediation techniques were investigated on sections of AL-5 in an attempt to identify a method that would increase the span between resurfacing. These remediation techniques included a sand blanket, vertical moisture barriers, lime columns, paved shoulders, and edge drains. Sensors were installed to remotely monitor the subgrade and asphalt conditions for the duration of the project. To further characterize the subgrade behavior, torsional ring shear tests were completed to determine the drained residual strength of the soil. Specimens from each remediation section were consolidated and then subjected to torsional shear in the ring shear device to determine the shear strength of the subgrade soils which may have contributed to pavement distress. Continuous monitoring of the pavement and subgrade instrumentation has shown improvement in the pavement distress over the past few years with the lime column test section as the most improved. The torsional ring shear tests resulted in very low angles of peak and residual resistance for the subgrade; therefore, the material was very weak and likely has contributed to the pavement distress. Slope stability analyses concluded the roadway embankments were stable at the end of construction, but quickly began to fail as the peak and residual shear strength values were reached.