12.2.3 Bidirectional Lateral Load Test Bi-directional testing has been applied to the lateral load testing of drilled shafts (O’Neill et al., 1997; Brown et al. 2010). The method uses conventional bidirectional load cells (e.g., hydraulically activated load cells) embedded within the shaft instead of a load test frame at the top of the drilled shaft. Instead of the load cells installed horizontally at or near the bottom of a reinforcement cage, as in the case with an axial compression load tests, they are turned 90 degrees, and used to jack the two halves of a drilled shaft apart. The load in the cells is divided by the length of the test interval to derive the lateral load applied to the ground. Lateral displacements are measured during the test with linear displacement variable transducers (LDVTs) that are embedded in the shaft concrete. This bidirectional test does not apply load at the top of the foundation, and therefore cannot be used to determine the bending and deflection of the shaft, but it does provide a means to directly evaluate the lateral resistance of a zone of soil or rock at depth. This test may therefore find application in design of drilled shafts in water where the structural strength and deformation of the free length of the shaft may limit the displacement that can be achieved below the mudline during a conventional lateral load test. The test may also be useful for determining p-y curves in rock sockets. Two arrangements fora bidirectional test for drilled shafts are shown in Figure 12-4. The cell in the left photo was installed into aft diameter socket into sandstone at a depth of around ft below the surface. The pair of cells in the photo at the right were installed into a socket which was ft diameter and ft long into a chalk formation approximately ft below grade (Brown et al. 2010).
186 Figure 12-4: Bidirectional Lateral Testing Apparatus Using Embedded Load Cells (from Brown et
