Ultraseismic (US) investigations are performed to determine the length and evaluate the integrity of shallow and deep foundation elements. This investigation technique is suitable for a variety of structures, from shallow wall-shaped substructures, to deep drilled shafts. US investigations are the ideal method when access to the top surface of a foundation element is not possible. Many structures can be analyzed provided that there is 1 – 1.8m of exposed structure for mounting the instrument.  This makes US particularly useful for testing abutments and wall piers of bridges due to the large exposed areas. US is a more sophisticated approach to the Sonic Echo/Impulse Response (SE/IR) method since multiple receivers are used. US promises greater clarity results at times were alternate investigation methods are inconclusive.  

The applications for Ultra-seismic are varied:

•    Structural investigations of structures where foundation depth is unknown
•    Assessing the condition of foundations
•    Investigation of damage to foundations
•    Investigation of bulbs in foundations

Ultraseismic works on similar principles as SE/IR. In an SE/IR test, the foundation top is struck by the hammer and the response of the foundation is monitored by a single receiver. The distinguising factor of US is that the reciever is repositioned between each impact, giving multiple perspectives. The reciver is typically moved along the exposed surface in increments of 150 – 300mm. The reciever can be moved either vetrically or horizontally depending on the geometry of the element. The reciever is triaxial which monitors movements in three dimensions allowing for both compressional and flexural wave analysis. The results can be used to determine the depth of elements or the presence of structrual abnormalities. An Olson Instruments Freedom Data PC system records the hammer input and the receiver output.

Vertical pro filing is suitable for deep foundation elements such as piers, without the need for excavation. The structure is struck near the top surface with the hammer and the response of the echo is recorded by the receiver. As figure 2 shows, the reciever is repositioned vertically along the longitudinal axis of the structure and the test is reperformed. After several tests the data is merged to provide a highly detailed response profile. A typical result is shown in figure 3.                                          .  

Incrementally moving the reciever horizontally along the foundation element means that less of the structure needs to be exposed. This is suitable for wide and shallow elements such as abutments.

 

Ultraseismic can be used when other tests such as the SE/IR method deliver inconslusive results. The US method can obtain functional results even when many reflecting boundaries are present. The ability to perform tests in either a vertical or horizontal manner increases the aplicability and affectiveness of this method. 

US  tests are accurate to within 5% in the  determination of the depth of the foundation.

Processing and analysis is performed by IX Foundation software on a complete data series rather than individual records. This stacking process allows for strong tracking ability of reflected waves. The slope of coherent events in the stacked records can be used to determine the velocity of the direct and reflected waves. These velocities are used to determine accurate depth calcualtions. Echoes can be enhanced with automatic gains and digital filters. Seperation of negative and positive polarised events enhances weak echoes caused by the reflection from the bottom of deep foundations. 

The SE and IR configurations are available seperatley or combined and are compatiable with both the Freedom DataPC and NDE360.