Bi-Directional Static Load Testing (BDSLT)

BDSLT with the GRL-Cell

A bi-directional static load test (BDSLT) is a test in which a deep foundation element is internally loaded from a specific location along its embedded length.  Load is applied by hydraulically pressurizing one or more GRL-Cells, often affixed between upper and lower bearing plates.  The GRL-Cells, instrumentation spanning them, and upper and lower bearing plates (if present) are collectively referred to as the jack assembly which is cast into the foundation element. The jack assembly simultaneously pushes upward against the shaft resistance above the jack assembly location and downward against the sum of the shaft resistance below the jack assembly location as well as against the foundation elements toe or base resistance.


Shaft and toe movements as well as embedded strain gage instrumentation are monitored for each applied load. An estimated top load movement curve is constructed from the measured shaft resistance load-movement and base resistance load-movement responses.


Bi-Directional Static Load Test Benefits include:

  • High-capacity static load test method for drilled shafts, bored piles, ACIP/CFA piles, and barrettes.
  • Separates soil/rock resistance and movement data for shaft and toe.
  • Determines magnitude of the mobilized shaft and toe resistances.
  • Embedded strain gauges within the foundation determine the soil/rock resistance distribution along the foundation length for optimizing the foundation design.
  • Not restricted by structural or geotechnical limit of load frame, reaction beams, or reaction piles.
  • Multiple GRL-Cells can be used at a single jack assembly location or at multiple jack assembly locations to apply larger loads.

During a bi-directional static load test, the deep foundation element is instrumented to provide information about soil and foundation response to load. GRL cells can be installed in drilled shafts, augercast piles, drilled displacement piles and barrettes.

Bi-Directional Static Load Testing (BDSLT) is standardized by ASTM D8169 – Standard Test Methods for deep foundations under Bi-Directional Static Axial Compressive Load.


Standard GRL-Cell Details*
GRL-Cell Capacity (tons) Maximum Test Load (tons) Outside Diameter (inches) Maximum Stroke (inches)
350 700 12 9
500 1000 15 9
750 1500 18 9
1100 2200 21 9
1500 3000 24 9
2000 4000 28 9
2500 5000 31 9
3500 7000 36 9

*GRL-Cell sizes are subject to change.