Field Evaluation of Load Bearing Capacity and Embedment Depth of Existing Ballastless Plate Girder Bridge Foundations

The ballastless plate girder bridge, classified as a structure type that requires an emergent replacement among domestic railway bridges, generally tends to upgrade to a ballasted track along with continuous welded rail (CWR). The axial forces of the CWR due to the temperature change need to be distributed to the bridge foundations. Because most of the existing ballastless plate girder bridges of over 50 years of age do not provide any design information, such bridge foundations are regarded as unknown foundations, and therefore, it is crucial to identify the structural adequacy and dimension. In this study, an effort was made to establish a correlation between the standard penetration test (SPT) and mid-size pneumatic cone penetration test (MPCP) to estimate the load bearing capacity of an unknown foundation. A field test was conducted to estimate the depth of the unknown foundation by employing SPT and MPCP as the source wave part. The magnitude of the shear wave was mitigated by the presence of PVC and steel pipes, such that it might be possible to identify the embedment depth of unknown foundations.

Evaluation of Unknown Bridge Foundations Using Borehole-based Nondestructive Testing Methods: A Case Study in Urban Settings

There are a significant number of bridges for which information regarding the foundation is missing or incomplete. It is extremely challenging to evaluate the performance of such unknown foundation bridges (UFB), particularly against scour or when their foundations are reused. For critical UFB, it is often necessary to estimate performance by developing an appropriate working model of subsurface foundation conditions. Typically, nondestructive testing (NDT) has served as the most viable alternative due to the costs and risk associated with excavation, coring, and probing. NDT can be quite difficult to perform and their results can contain significant uncertainty in highly urban settings. The primary objective of this study was therefore to compare performance of borehole NDT methods when evaluating the depth of two in-service unknown foundations (concrete-filled steel pipe piles and H-piles) in highly urban settings. The borehole magnetic, parallel seismic, borehole sonic, and borehole radar methods were implemented to determine the foundation bottom locations. Though uncertainty was present in all measurements, the borehole magnetometer and radar results proved the most conclusive. Parallel seismic testing did not yield any evidence of foundations due to issues with background noise and lack of direct access to the foundation. Likewise, borehole sonic testing was generally inconclusive due to issues with sensor directivity and attenuation. Borehole magnetometer estimated the depth to the foundation bottom as 8.6 m and 9.2 m at the two sites. Borehole radar estimates for the depth to foundation bottom compared favorably at 9.8 m and 8.0 m for the two sites. Given the borehole construction and depth to competent rock at the sites, these results for borehole magnetometer and radar were likely a minimum estimate for the location of the foundation bottoms. Such information can help evaluate long-term performance of this system as part of rehabilitation and reuse efforts.