Lab characterization of near-surface soils from Farm to Market Road 2

Distresses in pavements is a common issue in the state of Texas. Various research and mechanisms have been developed to study the performance of the pavements in the recent years. One of the major types of distress is longitudinal cracking caused by various environmental factors. These factors have been studied previously by many researchers, (Zornberg, Gupta, & Ferreira, Field performance of geosynthetic reinforced pavements over expansive clay subgardes, 2010), (Zornberg, Ferreira, & Roodi, GeosyntheticReinforced Unbound Base Courses: Quantification of the Reinforcement Benefits , 2013). One such factor is the expansive subgrade over which a pavement is constructed. The subgrade when wet, swells and shrinks when it gets dry. This swelling and shrinkage in different seasons causes significant cracking on the pavement surface as the subgrade moves. This affects especially the shoulders of the roadway as it is where the subgrade has the most chance to move. There are many ways for the characterization of the subgrade soil, for example in terms of strength, shear or swelling and shrinkage. For this research, the focus was on characterization in terms of swelling. For this, the process started with initial measurements (moisture content, density and suction), then index properties were calculated (Atterberg Limits) before running the centrifuge tests to get the stress-swell curves. One major common factor that affects the characterization is the initial conditions. If we start with wrong dry conditions, chances of getting over or underestimated results are high. This report reviews the co-relation used to get the dry initial conditions and further tests to characterize the soil. Sample borings were taken from 16 locations corresponding to the first 16 tests sections monitored in the previous research. (Zornberg, Ferreira, & Roodi, GeosyntheticReinforced Unbound Base Courses: Quantification of the Reinforcement Benefits , 2013) on the Farm to Market road 2 up to 10ft depth where each interval was 2ft. Initially the borings were weighed and measured to get an estimate of the volume and hence density and the initial moisture content was measured. Atterberg limits tests were conducted to get the dry conditions using the Tex-124-E correlation. Later, the borings were tested for their swelling potential using the centrifuge technique to match the in-situ stress and eventually get the stress-swell curves. Later on, the data collected in this reported will be used to calculate the Potential vertical Rise of these locations and eventually those PVR values will be used to correlate the subgrade soil behavior and performance of the pavements.