Frank Georg Schulz | TERRATEST

Light Weight Deflectometer Determines Overall Compaction Quality of Soil

Dec 2nd 2015 at 12:45 AM

A light weight deflectometer is a specialized device that is used for measuring the degree of compaction, the bearing capacity (deflection), and the in-situ and lab dynamic CBR of different pavement surfaces. These include subgrades and subsoils, granular and unbound base lasers, soil stabilization with lime, backfilling materials, cycle tracks, cold recycling materials, footpaths, and other types of pavements.

Light weight deflectometer (LWD) devices may vary in design and features, but they work using the same basic principles. A typical LWD drops a 10-kilogram weight from a height of 72 centimeters. A 300-millimeter load plate catches this with a special arrangement of an acceleration sensor. This acceleration signal is the used to calculate the dynamic deformation modulus of the tested surface. Most light weight deflectometers feature acceleration sensors attached to their base plate. The first integration of acceleration indicates the velocity of the plate while the second indicates deflection. The degree of compaction is solely based on experience, providing examiners with a statement about the likely effectiveness or ineffectiveness of compaction. This enables users to make a decision about the need for soil improvement or replacement.

Hand-held testing devices like nuclear density gauges only measure limited amounts of space at a single time, thus covering a small percentage of the site's footprint. This makes light weight deflectometers more suitable for larger testing areas, as they can test the entire location or range of the project, with the added bonus of penetrating deeper into the pavement. In addition to determining the overall compaction quality of and density of soils, light weight deflectometers can also test stiffness, which can further be used as the basis for calculating other fundamental material properties for different applications. This includes the soil's modulus, which many experts agree, is the most precise, accurate, and independent means to judge deformation and compaction levels of materials.

Light weight deflectometers offer a world of benefits to on-the-field users including:

  • Immediate and on-site evaluation of measurements.
  • Direct deflection readings as accelerometers are directly connected to base plates.
  • Time-efficient testing, with a maximum of 2 to 3 minutes per measuring point.
  • Accurate and repeatable results.
  • Easy field testing and use (single-person operation).
  • No additional support/loading vehicle required.
  • Testing in locations with difficult accessibility.
  • Readings captured via powerful software and flexible storage/output options via modern devices, computers, and even in-built printers for on-site reports and data integration.

About The Author:
TERRATEST GmbH is world leader in development and manufacturing of Light Weight Deflectometers for dynamic load plate test. They offer the world’s first light weight deflectometer “TERRATEST 5000 BLU” with Bluetooth and voice navigation. For more information about their products visit their website!

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