Parallel Seismic Testing
When the top of a deep foundation is inaccessible—buried below a pile cap, abutment, or building—verifying its length presents a significant challenge. Parallel Seismic (PS) testing is a proven, non-destructive method for accurately determining the depth of foundations such as piles, drilled shafts, and caissons in these exact situations. By analyzing the travel time of seismic waves between the structure and an adjacent borehole, our experts can provide you with the reliable foundation length data necessary for structural analysis, load-rating calculations, and retrofit design, all with minimal disruption to the site.
When no information is known about the length of a foundation, ACER Associates, located in West Berlin, NJ, and serving NJ, PA, and Northeast and Mid-Atlantic regions, can employ a variety of methods to determine the size and condition of a buried foundation. Often the top of the foundation is not accessible or too small to be assessed via Sonic Echo/Impulse Response Methods, which can require alternate assessment methods. Parallel Seismic testing is conducted by drilling a water-filled or grouted & cased borehole next to the foundation in question and assessed by striking the top or side of the foundation and recording the velocity of the responses as the equipment is lowered into the borehole. Depth assessment accuracy can be determined within 5% of the size of the foundation, and additional details such as details about the soils beneath the foundation can also be obtained. This method is suitable for concrete, steel, wood, and masonry foundations.
Once the data is collected in the field, a seismic analysis and display program is then utilized to view the full range of the data in a stacked orientation. The data is then analyzed to identify a clear break in the data resulting from the change in velocity from the foundation member to the surrounding soils. When the wave must travel through more soil below the pile tip the wave arrives at the transducer at a later time. This generates a difference in the first wave arrival times that occur at the tip of the pile, indicative of the foundation depth.
