Evaluation of Unknown As-Built Conditions for a Concrete Retaining Wall
Summary
NDT Corporation performed a comprehensive forensic evaluation of a deteriorating concrete retaining wall supporting a state highway in Hammondsport, NY.
With no original design drawings or as-built plans available, the owner required a full geometric and structural assessment to determine if the wall could be preserved.
NDT utilized a combination of Ground Penetrating Radar (GPR) and proprietary Impact Echo/Pulse Velocity (IE/PV) technology to map the wall's dimensions, internal reinforcement, and in-situ material strength.
Scope
Geometric Characterization: Employed GPR and IE/PV to determine the wall’s total height (including the portion extending below grade), thickness, and the degree of back batter.
Reinforcement Mapping: Conducted full-height GPR scans to identify the presence, spacing, and depth of any internal steel reinforcement.
In-Situ Strength Profiling: Collected surface wave velocities using IE/PV across the wall face to estimate concrete compressive strength at multiple locations.
Internal Integrity Scan: Evaluated the structure for subsurface cracking, honeycombing, and voids, particularly around visible spalling at pour joints.
Material Correlation: Extracted concrete cores using specialized large-diameter barrels to provide laboratory verification of the non-destructive strength estimates.
Solution
Dimensional Verification: Successfully confirmed the overall wall height, thickness, and batter by measuring thickness frequencies from the front face to the back of the wall across its entire vertical profile.
Reinforcement Findings: GPR data definitively indicated that the structure was unreinforced, a critical finding for the engineers' stability and load-rating calculations.
Strength Correlation: IE/PV strength estimates showed a strong correlation with laboratory compression testing, identifying several zones of weak concrete (less than 3,000 psi).
Forensic Material Insight: During core extraction, NDT identified that the poorly bonded 3-inch rounded river stone aggregate was a primary factor in the wall's deterioration. By adjusting to a larger core barrel, NDT secured intact samples for testing despite the compromised matrix.
Preservation Guidance: Delivered a complete "as-built" data package that allowed the owner to move forward with an informed decision regarding the repair, reinforcement, or replacement of this critical highway asset.