Abstract: Evaluation of bridge substructures for vulnerability to scour or other potential sources of damage requires knowledge of foundation conditions beneath piers and abutments that are often unknown. This paper presents a potential method for determining unknown foundation conditions which is simple and inexpensive. The method is based on strain and rotation measurements which are used to compute a stiffness matrix for the unknown foundation. The stiffness coefficients in the matrix are then matched with values previously determined for known foundations. The objective of the reported work has been to demonstrate the feasibility of this method. Finite element models for representing pile and spread footing conditions have been used to characterize the difference in stiffness properties between the two foundation types. Field measurements of strains, displacements, and rotations have been taken on two bridges in Massachusetts: one with a spread footing and the other with a pile foundation. Parameter estimation models have been developed and used in conjunction with this field data to calculate the foundation stiffness properties. The paper describes the models, the numerical results, and the results of field testing. !14
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