Nondestructive Evaluation and Repair of Concrete Retaining Walls at New Subway Station

Nondestructive testing is often used in conjunction with traditional methods to assess construction, material, or structural deficiencies in new construction. This presentation describes evaluation of unique delamination failures within below-grade, exterior walls of a new subway station. The walls were conventionally reinforced mass concrete cast against a soldier pile and lagging retention system. Shortly after construction, leakage at cracks and joints was observed and injection processes led to delamination of the interior surfaces. The assessment objectives were to determine the extent and cause of near-surface discontinuities and evaluate the structural integrity of the walls. Nondestructive testing included flaw detection using Impulse Response [structural mobility testing] and reinforcement locating using ground-penetrating radar. Sampling and petrographic examinations were conducted to correlate test results with distress conditions and evaluate the in-situ concrete. Analysis of construction records, mix designs, and thermal performance records enabled determination of the cause of the discontinuities. Partial depth repairs were implemented to restore structural capacity.

Presentation Learning Objectives:

1. Understand the use of NDE methods for assessment of internal concrete distress
2. Understand effective data presentation and reporting of NDE results
3. Understand how construction records can be helpful in determining the cause of observed distresses
4. Understand the fusion of field assessment, laboratory testing and structural analysis to develop a solution for distress in existing structures