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Dynamic Deflection Instrument™
The Dynamic Deflection Instrument™ measures tool movement resulting from ramming deflections in order to document lift by lift aggregate pier quality relative to engineering specifications, while allowing the contractor to optimize productivity.
Dynamic Deflection Instrument. The Dynamic Deflection Instrument measures stiffness, or the ability of a material to resist deformation under load, rather than density, or the weight of a material per unit volume. Course aggregate is rammed into a boring in layers. Ramming compacts horizontally and laterally. The lateral compaction builds up lateral stress in the surrounding soil. The influence of a high lateral stress is analogous to that which occurs during triaxial laboratory testing, strengthening the soil and postponing normal consolidation to a higher stress level (Handy 2001). There are two distinct stages which can be interpreted from the Dynamic Deflection Instrument, 1) compaction of the aggregate, and 2) lateral bulging. An intelligence package collects data from a patented accelerometer, which measures deflections from ramming events. The intelligence package graphs and measures the deflections relative to design deflections. The Dynamic Deflection Instrument notifies the operator when the proper level of compaction has been achieved. Compaction levels for every lift of the aggregate pier are predetermined by the engineer and are verified during construction. Electronic recording of the construction process is made for QA/QC analysis and long term design and construction liability control. |
Depth Measurement The Dynamic Deflection Instrument measures the ramming deflection results from the bottom of the pier to the top. This provides a more complete picture of pier/soil stiffness than other random sampling compaction measurement processes, such as plate load testing or penetration testing. The plate load test process typically only measures less than 18 feet deep*, and the penetration test measures only a few inches deep. Depth of measurement validates your compaction work and ensures that every lift of every pier meets stiffness requirements. * Boussinesq pressure bulb theory indicates the majority of added stresses are carried 6-7 times the width of the plate, deep. 18 feet assumes a typical 30 inch round diameter plate.
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