The lateral earth pressure on retaining structures due to Piedmont residual soils is difficult to quantify by traditional methods and is often over predicted. Thus, large safety factors are used in retaining structure design that increase conservatism but not necessarily the engineer's confidence in the design. Much of this conservatism can be attributed to the divergence between the behavior of Piedmont residual soils and traditional cohesive and cohesionless soils.
The objective of this proposed project is to develop a simplified model for lateral earth pressure in Piedmont residual soil based on insitu soil tests. This model will be determined by measuring the lateral earth pressure behind sheet pile retaining walls in three of the geologic zones of North Carolina: the Carolina Slate Belt, the Charlotte Belt, and the Inner Piedmont.
A novel approach using instrumented sheet piles as ""moment-cells"" will be adapted from the analysis of piles under lateral loading. Sheets will be instrumented to measure bending moment and slope, and through differentiation, the shear stress in the wall due to earth pressure will be determined. To include the effect of joint orientation within the residual soils, an approach is proposed to bracket the two extreme conditions (joints dipping in and joints dipping out of the excavation) at each test wall site.
Based on the results of the research program, a simple lateral earth pressure model will be developed that will be a function of easily measured insitu soil properties and the joint fabric characteristics of the residuum.
