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• Theoretical algorithms are proposed to determine the localization of multiple rock spheres. • One smart rock is a concrete sphere with a super-strong magnet embedding in the center. • Field tests with two smart rocks were conducted to validate the localization algorithm. • Numerical simulation is used to verify the theoretical algorithms. • Two smart rocks decays the magnetic intensity exponentially with an increase of the relative distance. In this study, algorithms are theoretically proposed to determine the locations of multiple smart rocks that are used to predict the topography in the vicinity of a bridge pier or abutment, with/without considering the effect of the ambient magnetic field (AMF). One smart rock is a concrete sphere with a super-strong magnet embedding in the center. The direction of the magnet cylinder is downward-pointing. To validate the localization algorithm, field tests at a bridge pier in the state of California, USA, were conducted in the case of two smart rocks. Numerical simulation is also performed to study the interaction between the two smart rocks as well as the influence of the interaction on the effective distance. The influence of the AMF on the effective distance is numerically simulated. Results show that the steel rebars in the bridge cause an inhomogeneous dispersion of the AMF, and the placement of double rocks changes the dispersion of the AMF in the vicinity of the bridge pier. The localization algorithms are successfully employed to determine the locations of the rock spheres, and the interaction between double rocks decays exponentially with an increase of the relative distance. [ABSTRACT FROM AUTHOR]