Light Weight Deflectometer (LWD) Zorn ZFG 3000 Overview
Light Weight Deflectometer’s (LWD’s) are a light weight, portable tool used to determine the stiffness of unbound materials (subgrade/subsoils and base layers, granular layers & backfilling materials) or partially bound material (e.g. stabilised) during construction or pavement rehabilitation. For example, for a highway to perform well over the long term, its soil and aggregate layers need to provide a stiff, stable foundation. Inspections are required during construction to ensure that pavement foundation materials have been compacted enough to ensure this condition.
The device measures a deflection and estimates a modulus value based on the force required to generate a given deflection for that soil type. Modulus is the most accurate and independent means for judging deformation (stiffness) and, thus, a material’s level of compaction. By measuring the modulus value, the Light Weight Deflectometer provides the direct link between the design specification (design modulus value) and the actual site condition (in-situ modulus value).
The LWD provides immediate repeatable results so that on-site decisions can be made straight away and it can be used in confined spaces and difficult to access locations, with no support equipment required. An optional GPS-System allows the user to immediately determine and record the test position and this is integrated with Google Maps.
The Light Weight Deflectometer (LWD) ZFG 3000 from Zorn Instruments is a compaction control device, according to ASTM E2835-11 (2015) and Department of Transport and Main Roads Queensland (DTMR) Test Method Q726B: Deflections – Portable Impulse Plate Load Test Device.
The Zorn ZFG 3000 LWD measures the dynamic modulus of deformation Evd in the range from 15 up to 105 MN/m². Using extensions to the ZFG 3000, dynamic CBR (California Bearing Ratio) can also be measured in-situ in the field and also laboratory CBR in a cylinder can be simulated.
Key applications and advantages of LWD testing are:
- In-situ testing of earthworks during construction, particularly where common techniques (e.g. nuclear gauge/sand replacement) are not appropriate or cost effective
- Equipment of higher precision than a typical tests (e.g. traditional DCP) used for QA of allowable bearing capacity of prepared surfaces–prior to the installation of permanent structures (e.g. slabs, footings, pavements) or temporary works platforms (crane pads, piling rigs)
- As a surface based test, the LWD has no footprint that needs to be remediated, and is cost-effective for completion at locations where equipment/plant has to be stopped whilst the test is completed
- LWD’s are more accurate than the traditional DCP, especially in soft/loose materials. For example, in locations where existing bearing capacity is an issue, the LWD would be the preferred investigative tool.
The other advantages of the Zorn ZFG 3000 Light Weight Deflectometer (LWD) include:
- Providing a more representative picture of a pavement’s ability to handle traffic loads than density or CBR measurements
- Direct verification of the in-situ modulus values compared to pavement design parameters
- No manual recording of data – results date/time stamped and GPS located so data recording / transposition errors eliminated)
- GPS-System for immediate determination of test position integrated with Google Maps
- Readings captured on SD-card for data memory (10,000 data sets) allowing immediate on-site results printing and data transfer for further analysis
- Results immediately available so decisions can be made on-site with no construction delay
- Time saving in testing and getting results (a maximum of 3 minutes per measuring point)
- Allows the use of the equipment to support (and supersede the turnaround time) of traditional test results, such as soaked CBRs
- Immediate wireless connection between ZFG device and iPhone/iPad and Android Smartphones/Tablets
- Results Viewer App for data and graphs – compatible with iPhone/iPad and Android Smartphones/Tablets. Connect GPS data from your ZFG device with Google maps. Send data from your phone to your PC / remote engineering support for further analysis, decision making and presentation using the ZORN Software.
- Data interpretation software allows data storage, analysis and manipulation and easy inclusion into reports
- Provides calibration of Intelligent Compaction (IC) rollers output in relation to the pavement design specification (modulus value) for a specific site.
- Safer for field technicians: Less time testing near traffic at the construction site
- Direct deflection readings: accelerometer directly connected to the base plate
- Accurate repeatable results
- One-person use: being designed for field testing, the device is portable and lightweight
- Easy to use
- No additional loading vehicle or support is required
- Using extensions to the ZFG 3000, dynamic CBR (California Bearing Ratio) can be measured in-situ in the field and also laboratory CBR in a cylinder can be simulated.
Applications for this non destructive method for compaction control testing include flexible pavements, unsealed roads and mine access roads, tunnels, railway track beds, airport runway and taxiways, hard standing areas, dam construction, canal building, embankments, temporary works platforms (e.g. for mobile crane pads and piling rig foot standing pads (outriggers)), building foundations, wind farms, pipe laying and tank farms.
Clients include those involved in pavement construction, pavement rehabilitation, material testing, geotechnical testing, pavement investigation and site investigation and include road authorities, councils, asset managers, mines, mobile crane operations, engineering and construction groups, EPCM’s, subcontractors, geotechnical consultancies and research organisations.
The Light Weight Deflectometer (ZFG 3000) is a portable device designed for compaction control and has been approved by ASTM E2835-11 (2015) Standard Test Method for Measuring Deflections using a Portable Impulse Plate Load Test Device and the German Road and Transport Research Association under TPBF-STB Part B8.3_97.
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