Slope Stability/Corrosion/Structural Pavement Sections:

Slope stability analysis can be used to evaluate the potential for plane or dip-slope failure, which is sliding along a bedrock discontinuity plane (such as bedding), and wedge failure, which is sliding along an intersection line of two intersecting discontinuity planes (such as bedding and a fault). The geometric relationship between the orientation of the discontinuity planes and the orientation of the overlying topography determine the kinematic stability of a slope.

Soil corrosivity represents the corrosion potential to concrete and ferrous metal directly contact to the soils. A major factor in determining soil corrosivity is electrical resistivity. The electrical resistivity of a soil is a measure of its resistance to the flow of electrical current. Corrosion of buried metal is an electrochemical process in which the amount of metal loss due to corrosion is directly proportional to the flow of electrical current (DC) from the metal into the soil. Corrosion currents, following Ohm's Law, are inversely proportional to soil resistivity. Lower electrical resistivities result from higher moisture and chemical contents and indicate corrosive soil. Field evaluation of corrosivity is generally limited to in-situ electrical resistivity testing either by electromagnetic or by the Wenner Four Pin Method.

Laboratory testing combines electrical characterization of the sample under controlled conditions with chemical analysis to characterize the soil corrosivity.

Laboratory chemical analysis is generally performed on soil/water extract solutions.

Once data are available general design recommendations can be developed. Recommendations vary with specific elements of soil corrosivity. The life of buried materials depends on thickness, strength, loads, construction details, soil moisture, etc., in addition to soil corrosivity, and is, therefore, difficult to predict. Of more practical value are corrosion control methods that will increase the life of materials that would be subject to significant corrosion.

• Chlorides can attack reinforcing steel
• Low pH soils consume concrete
• High sulfate soils attack concrete
• Low Electrical resistivity attack ferrous metals

Structural Pavement Sections (asphalt concrete (AC) or Portland cement concrete pavement (PCCP)) is determined based on the Traffic Index (TI) and the strength (R-value) of the sub-grade soils. Fine grained soils such as silt and clay exhibit low R-value, whereas granular soils such as sand and gravels exhibit high R-value. For the same TI, higher R-value will provide thinner pavement section.