Additions and replacements to existing superstructures, upgrading of structural loads and settlement or scour investigation all require the evaluation of existing foundations. Original pile installation records are often no longer available. GRL tackles the challenges of unknown foundations on a routine basis.
GRL assesses the depth and evaluates the integrity of piles supporting existing structures by one of several methods. The pulse echo, sonic echo or low strain integrity testing method (PIT), works well in certain soil-foundation conditions. In situations that require finding the length of existing steel piles (H-piles, Pipe piles, Cased Drilled Shafts, Steel Sheet Piles), GRL may perform an investigation by the Inductive Field Method using the LITE (Length Inductive Test Equipment). This test is performed by lowering a probe into a PVC lined hole drilled within 18 inches (450 mm) of the pile to be tested and observing the instrument readings. In still other cases GRL may attempt length determination by the Parallel Seismic Method. This method requires impacting the foundation with an instrumented hammer, and inserting a hydrophone receiver into a specially installed hole adjacent to the foundation. The hammer impact generates a stress wave that travels down the foundation and transmitted through the surrounding soil to the hydrophone. By examining the arrival times of these transmitted waves, it may be possible to detect the bottom of the foundation.
When capacity determination is the issue GRL Engineers perform a Wave Equation Analysis to select an adequate hammer to utilize for a Dynamic Load Test on a representative number of existing piles. The Dynamic Load Test gives sufficient information on pile capacity and integrity to aid the designer in the decision whether to reuse the piles.
A detailed job report, including theoretical discussions of the methods and techniques employed, is issued shortly after the conclusion of the field tests.