Analyzing the dynamic pile load test measurement with an aid of stress wave theory

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Abstract:

A traditional static pile load test is considered to be a reliable, but time consuming and expensive way to determine the pile load-settlement behavior/bearing capacity. The imminent risks of personal injuries/site damage increases when heavy kentledge structures are used as counterweight and then collapse or when support elements fail. Static Load Testing (SLT) is nowadays often replaced by less time consuming and more economic methods, such as the High Strain Dynamic Testing (HSDT, commonly known as Dynamic Load Testing or DLT) and Rapid Load Testing (RLT). But these quick methods also have their own limitations and disadvantages. This paper focusses on the advantages/disadvantages of DLT, which is performed by dropping a reaction mass on the pile head. This introduces an impact load on the pile top and as a result stress waves will propagate in the pile from the pile top to the pile toe, where they will reflect. The stress waves also generate reflections when changes in pile cross section (necking’s, bulbs, pile toe), changes in pile material properties and friction along the pile shaft are encountered. The waves travelling from the top (downward waves) and waves travelling to the top (upward waves) contain information, and these waves can be separated to derive this information by performing measurements of strain and acceleration near the pile head. The mobilized pile capacity can be established by performing signal matching on the upward wave information, using wave equation software like AllWave-DLT or Capwap. This paper discusses the importance of understanding the principles of stress wave theory in combination with DLT and for the proper elaboration, interpretation and understanding of test results. Most important factors for setting up and performing a good field test, as well as for establishing mobilized capacity from the test results are also discussed in the paper.

MARCEL; MARCEL BIELEFELD

International Conference Proceedings