Benefits of the Rock Pressuremeter Test:
- Saves money for the project by accurately measuring the strength and deformation properties of rock
- Can be used for lateral load and deformation analyses of drilled shafts
Rock Pressuremeter Test: Engineers often have grossly underestimated the rock’s capacity (often by a factor of 10 or more) because of the difficulty of measuring the rock’s capacity. The rock modulus cannot be estimated or correlated from rock quality designation (RQD) as believed by many engineers (Figure 1). However, rock pressuremeter tests can be used for lateral load and deformation analyses of drilled shafts. (Failmezger, et al., 2005)
The conventional pressuremeter can only apply 100 bars of pressure, which is inadequate for testing rock. We use a rock pressuremeter that applies up to 300 bars of pressure (Figure 2). A hydraulic pump extends a piston inside the rock pressuremeter probe downward.
Figure 1: Shotgun Correlation between RQD and Rock PMT Modulus
Figure 2: Rock Pressuremeter Test Equipment
The fluid inside the membrane is pressurized which causes it to expand into the rock. The applied pressure is measured with an electronic transducer. The volume of the probe is measured with a linear variable displacement transducer (LVDT) located on top of the hydraulic piston. The volume equals the distance that the piston moves multiplied by the piston area.
The driller cores the rock with an NX-size core barrel. We examine the rock core with the inspecting engineer or geologist and determine the best locations to perform the tests. The rock pressuremeter probe is lowered to the test depths (Figure 3) and stress controlled pressuremeter tests are performed. The data are recorded on a field logger and downloaded to a computer for processing.
Figure 3: Lowering the Rock Pressuremeter into the Cored Hole