Light Weight Deflectometer (LWD) Zorn Overview
- Used for compaction control and bearing capacity estimation
- Unbound or partially bound layers (sub-grade, sub-base, base)
- Measures the deflection and stiffness (modulus)
- Immediate repeatable results so that on-site decisions can be made straight away
- Meets ASTM E2835-11 (2020) standard and Test Method Q258A Dynamic Modulus of Deformation – Light Falling Weight Device – Accelerometer Type – (DTMR QLD) March 2021
The Light Weight Deflectometer measures a deflection and calculates a modulus value based on the force required to generate a given deflection. 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).
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 sometimes partially bound material (e.g. stabilised) during construction or pavement rehabilitation.
The Zorn LWD’s measures the dynamic modulus of deformation Evd in the range from 15 up to 140 MN/m².
Using extensions to the Zorn LWD’s, dynamic CBR (California Bearing Ratio) can also be measured in-situ in the field and also laboratory CBR in a cylinder can be simulated.
The LWD is used for allowable bearing capacity Quality Assurance (QA) of prepared surfaces, prior to the installation of permanent structures (e.g. slabs, footings, pavements) or temporary works platforms (crane pads, piling rigs). The bearing capacity under the plate is from 30 – 400 kPA, achieved by changing plate diameters, drop weights and drop height.
Let’s take a crane lift. The insitu ground conditions have been identified in order for the temporary works platform to be designed. However, immediately prior to the crane lift, the insitu conditions are required to be verified to determine if the bearing capacity of a site has altered due to changing conditions, like rain. The LWD is used for this purpose.
Light Weight Deflectometers (LWD) from Zorn Instruments
The Light Weight Deflectometer (LWD) ZFG 3000 and ZFG 3.0 from Zorn Instruments are compaction control methods designed to ASTM E2835-11 (2020) Standard Test Method for Measuring Deflections using a Portable Impulse Plate Load Test Device, TPBF-STB Part B8.3 (2016) from the German Road and Transport Research Association (BaST) and Department of Transport and Main Roads Queensland (DTMR) Test Method Q258A Dynamic Modulus of Deformation – Light Falling Weight Device – Accelerometer Type
The LWD is well suited to in-situ testing of earthworks during construction, particularly where common techniques (e.g. nuclear gauge/sand replacement) are not appropriate or cost effective.
LWD’s are more accurate than the traditional DCP, especially in soft/loose materials or for estimating allowable bearing capacity.
Applications 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 (crane pads and piling rigs), building foundations (footings and slabs), wind farms, pipe laying, contaminated sites and tank farms.
ZFG Light Weight Deflectometers Advantages
The advantages of the Zorn ZFG Light Weight Deflectometers (LWD’s) include:
- Results immediately available so on-site decisions can be made straight away with no construction delay.
- Immediate wireless connection between LWD and iPhone/iPad and Android Smartphones/Tablets enabling you to send data from your phone to your PC / remote engineering support for further analysis, decision making and presentation using the ZORN Software.
- Approx 3 minutes per test
More accurate and repeatable
- Direct deflection readings: accelerometer directly connected to the base plate.
- High levels of repeatability
- As a surface based test, the LWD has no footprint that needs to be remediated
- The surface is not disturbed, which is very important for contaminated sites
- Granular and geo-reinforced materials can be tested
- Provides a more representative picture of a pavement’s ability to handle traffic loads than density or CBR measurements.
- By measuring the modulus value, the LWD provides the direct link between the pavement design specification (design modulus value) and the actual site condition (in-situ modulus value).
- Provides calibration of Intelligent Compaction (IC) rollers output in relation to the pavement design specification (modulus value) for a specific site.
- By pairing with the PANDA Instrumented DCP, you can increase the depth of the zone of assessment e.g. for deep lift compaction
- Equipment is instrumented (data is automatically and accurately recorded)
- Results are machine produced (overcoming manual data recording, transposition or calculation errors and fictitious results)
- Readings captured on SD-card for data memory (10,000 data sets) allowing immediate on-site results printing and data transfer for further analysis.
GPS located and time stamped – know where and when every test is done
- GPS-System for immediate determination of test position integrated with Google Maps.
Visually presented results
- Results including graphical outputs immediately available so integrity of results can be checked
- Data interpretation software allows data storage, analysis and manipulation and easy inclusion into reports.
- Less time testing near traffic at the construction site.
- Suitable for use in confined spaces and difficult to access locations, with no support equipment required.
More cost effective
- One person operation: portable, lightweight and easy to use.
- Cost-effective for completion at locations where equipment/plant has to be stopped whilst the test is completed.
- No additional counter weight vehicle or support is required.
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.
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