Falling weight deflectometer: Difference between revisions

Browse history interactively

← Previous edit

Content deleted Content added

VisualWikitext

Inline

Latest revision as of 09:48, 13 December 2024

The Fast FWD is 5 times faster per drop than the conventional FWD — Fast Falling Deflectometer

A falling weight deflectometer, towed by a truck

A falling weight deflectometer (FWD) is a testing device used by civil engineers to evaluate the physical properties of pavement in highways, local roads, airport pavements, harbor areas, railway tracks and elsewhere. The data acquired from FWDs is primarily used to estimate pavement structural capacity, to facilitate overlay design or determine if a pavement is being overloaded. Depending on its design, a FWD may be contained within a towable trailer or it may be built into a self-propelled vehicle such as a truck or van. Comprehensive road survey vehicles typically consist of a FWD mounted on a heavy truck together with a ground-penetrating radar and impact attenuator.

During testing, a FWD subjects the pavement surface to a load pulse which simulates the load produced by a rolling vehicle wheel. The load pulse is produced by dropping a large weight onto a "buffer" which shapes the pulse, and then transmitted to the pavement through a circular load plate. Data are acquired from various sensors for use in post-test analysis of pavement properties. Deflection sensors are used to measure the deformation of the pavement in response to the load pulse. In some FWDs the magnitude of the applied load pulse is an assumed constant value determined by system design; in others the force is measured by load cells.

The load plate may be solid or segmented. Segmented load plates adapt to the shape of the pavement to more evenly distribute the load on uneven surfaces. The load plate diameter is typically 300 mm diameter on roads and 450 mm on airports, and the load for road testing is about 40 kN, producing about 567 kPa pressure under the load plate (50 kN / 707 kPa according to European standard).

Load impact system

There are two different types of load impact systems; single-mass and double-mass.^[1]^[2]

In a single-mass system, a weight is dropped onto a single buffer^{[clarification needed]} connected to a load plate, which in turn rests on the surface being tested. Single-mass FWDs are typically smaller, faster and less expensive but, when used on soft soils, may overestimate the capacity of pavements due to the mass inertia of the pavement material.^[3]

In a double-mass system, the weight drops onto an assembly consisting of a first buffer, a second weight, and a second buffer.^{[note 1]} This produces a longer loading duration that more precisely simulates a wheel load, and yields higher reproducibility and gives a more accurate result on pavements built on soft soils.^[4]^[5]

There are also combined single/double mass systems where the falling weight and middle weight can be locked together giving 150 kN short pulse. In unlocked mode the FWD works as a double mass system giving 50 kN long pulse.

In all systems, the load pulse shape and rise time is important because it can affect the peak values of center deflection by as much as 10% to 20%.^[6]

Deflection sensors

Deflection sensors are used to measure the deformation of the pavement in response to the load pulse. The sensors are mounted radially from the center of the load plate at typical offsets of 0, 200, 300, 450, 600, 900, 1200 and 1500 mm (the deflections measured at these offsets are denoted D0, D200, D300, etc.).

Two types of deflection sensors are used: geophones and force-balance seismometers. Seismometers have built-in calibration devices and higher deflection measurement ranges (5 mm vs 2 mm). Geophones lack built-in calibration devices and are more sensitive to disturbances immediately before the impact since the initial error is integrated^{[clarification needed]}, but are much less expensive than seismometers.

Analysis

FWD data is most often used to calculate stiffness-related parameters of a pavement structure. The process of calculating the elastic moduli of individual layers in a multi-layer system (e.g. asphalt concrete on top of a base course on top of the subgrade) based on surface deflections is known as "backcalculation", as there is no closed-form solution. Instead, initial moduli are assumed, surface deflections calculated, and then the moduli are adjusted in an iterative fashion to converge on the measured deflections. This process is computationally intensive although quick on modern computers. It can give quite misleading results and requires an experienced analyst. Commonly used backcalculation software are:

BAKFAA (Federal Aviation Administration)
Clevercalc (University of Washington)
ELMOD (Dynatest)
Evercalc (WSDOT)
KGPBACK (Geotran)
MichBack (Michigan DOT)
Modulus (TxDOT)
PVD (KUAB)
PRIMAX DESIGN / RoSy Design (Sweco, former Carl Bro)

Many analysts use simplified methods to calculate related parameters that are empirical in nature. The most common is maximum deflection under the centre of the load plate (D0) which is related to empirical measures such as the Benkelman Beam deflection (after minor adjustment for differences in the two devices). Historically some used the radius of curvature (D0-D200) but this is out of favour now because it is clear that the steel loading plate of 300mm diameter affects the shape of the deflection bowl between the centre (D0) and the D200 sensor at 200mm. However this means that a lot of useful information about the shape of the deflected bowl is wasted. Horak and Emery have published indices that use this information: BLI=D0-D300 and gives an indication of the basecourse performance, MLI = D300-D600 and gives an indication of the subbase performance, and LLI=D600-D900 and gives an indication of subgrade performance. These and other similar indices are known as shape factors. The FWD data can also be very useful in helping the engineer divide the length of the pavement into homogeneous sections.

FWD data can also be used to calculate the degree of load transfer between adjacent concrete slabs, and to detect voids under slabs.

Other models

Dynatest was the first company to develop the Light Weight Deflectometer (LWD) The Light Weight Deflectometer is a portable falling weight deflectometer used primarily to test in situ base and subgrade moduli during construction. LWD measurement is faster than the isotope measuring method^{[clarification needed]} and requires no reference measurements. The equipment has no radioactive sources and can be operated by one person, allowing for on-site data analysis and report printing.^[7] Some LWDs have no load cell and assume a nominal load value, whereas others employ a load cell to measure the actual load. Depending on the system, a LWD may have a single geophone located in the centre or it may have two geophones, typically located at 300 and 600 mm positions.

A Fast Falling Weight Deflectometer (FFWD) is a FWD with pneumatic or electric actuators rather than hydraulic, making the mechanics several times faster.

A Heavy Weight Deflectometer (HWD) is a falling weight deflectometer that has higher loads (typically 300 kN to 600 kN), used primarily for testing airport pavements. A common misconception is that higher loads are needed to test an airport's capability to handle heavy aircraft, but in fact, the testing methods are not designed to test the strength of the construction but to find the material properties of the construction.

A Rolling Weight Deflectometer (RWD) is a deflectometer that can gather data at a much higher speed (as high as 55 mph) than the FWD, which allows the data to be collected without traffic control and lane closure.^[8] It is a implemented as a tractor-trailer with laser measuring devices mounted on a beam under the trailer. Unlike the FWD, which pauses to make measurements, a RWD gathers deflection data while it travels.^[9]

The test materials are described in ASTM D 4694, and the test method is defined in ASTM D 4695.140

Notes

^ In a double-mass system, the principle of operation is based on the law of conservation of momentum with an elastic collision of two unequal masses.

References

^ "KUAB two-mass FWD". Iowa State University. Retrieved 12 March 2014.
^ "KUAB two-mass FWD patent". Google patents. Retrieved 6 July 2015.
^ Crovetti, JA; Shahin, MY; Touma, BE (1989). "Comparison of Two Falling Weight Deflectometer Devices, Dynatest 8000 and KUAB 2M-FWD". Nondestructive Testing of Pavements and Backcalculation of Moduli. ASTM International. doi:10.1520/STP19799S. ISBN 978-0-8031-1260-5.
^ Meier, Roger W. "Backcalculation of Flexible Pavement Moduli from Falling Weight Deflectometer Data Using Artificial Neural Networks" (PDF). US Army Corps of Engineers. Retrieved 24 January 2017.
^ Shahin, M.Y. (2007). Pavement Management for Airports, Roads, and Parking Lots (2 ed.). US: Springer. ISBN 978-0387234656.
^ "Testing Different FWD Loading Times". Bulletin. 8. Stockholm, Sweden: Department of Highway Engineering, Royal Institute of Technology. 1980.
^ "Light Weight Deflectometer YouTube Video". Cooper Technology. Archived from the original on 2014-07-05. Retrieved 3 March 2014.
^ Elbagalati, Omar; Elseifi, Mostafa A.; Gaspard, Kevin; Zhang, Zhongjie (16 June 2017). "Development of an Artificial Neural Network Model to Predict Subgrade Resilient Modulus from Continuous Deflection Testing". Canadian Journal of Civil Engineering. 44 (9): 700–706. doi:10.1139/cjce-2017-0132.
^ "Megascale RWD patent". Google patents. Retrieved 29 October 2015.

[principle-4] In a double-mass system, the principle of operation is based on the law of conservation of momentum with an elastic collision of two unequal masses.

[1] "KUAB two-mass FWD". Iowa State University. Retrieved 12 March 2014.

[2] "KUAB two-mass FWD patent". Google patents. Retrieved 6 July 2015.

[3] Crovetti, JA; Shahin, MY; Touma, BE (1989). "Comparison of Two Falling Weight Deflectometer Devices, Dynatest 8000 and KUAB 2M-FWD". Nondestructive Testing of Pavements and Backcalculation of Moduli. ASTM International. doi:10.1520/STP19799S. ISBN 978-0-8031-1260-5.

[5] Meier, Roger W. "Backcalculation of Flexible Pavement Moduli from Falling Weight Deflectometer Data Using Artificial Neural Networks" (PDF). US Army Corps of Engineers. Retrieved 24 January 2017.

[6] Shahin, M.Y. (2007). Pavement Management for Airports, Roads, and Parking Lots (2 ed.). US: Springer. ISBN 978-0387234656.

[7] "Testing Different FWD Loading Times". Bulletin. 8. Stockholm, Sweden: Department of Highway Engineering, Royal Institute of Technology. 1980.

[8] "Light Weight Deflectometer YouTube Video". Cooper Technology. Archived from the original on 2014-07-05. Retrieved 3 March 2014.

[9] Elbagalati, Omar; Elseifi, Mostafa A.; Gaspard, Kevin; Zhang, Zhongjie (16 June 2017). "Development of an Artificial Neural Network Model to Predict Subgrade Resilient Modulus from Continuous Deflection Testing". Canadian Journal of Civil Engineering. 44 (9): 700–706. doi:10.1139/cjce-2017-0132.

[10] "Megascale RWD patent". Google patents. Retrieved 29 October 2015.

[1]

[2]

[3]

[note 1]

[4]

[5]

[6]

[7]

[8]

[9]

@@ Line 1: / Line 1: @@
+[[File:Heavy Weight Deflectometer.jpg|thumb|alt=Heavy Weight Deflectometer|Heavy Weight Deflectometer]]
+[[File:Light Weight Deflectometer.jpg|thumb|alt=Light Weight Deflectometer|Light Weight Deflectometer]]
+[[File:Falling Weight Deflectometer (FWD).jpg|thumb|alt=Falling Weight Deflectometer (FWD) evaluates pavement conditions|Falling Weight Deflectometer (FWD) ]]
+[[File:FastFWD.jpg|thumb|alt=The Fast FWD is 5 times faster per drop than the conventional FWD|Fast Falling Deflectometer ]]
+{{Short description|Road testing device}}
+{{Refimprove|date=February 2013}}
+[[File:FallingWeightDeflectometer.jpg|thumb|A falling weight deflectometer, towed by a truck]]
+A '''falling weight deflectometer''' (FWD) is a testing device used by [[civil engineer]]s to evaluate the physical properties of [[pavement (roads)|pavement]] in highways, local roads, airport pavements, harbor areas, railway tracks and elsewhere. The data acquired from FWDs is primarily used to estimate pavement structural capacity, to facilitate overlay design or determine if a pavement is being overloaded. Depending on its design, a FWD may be contained within a towable trailer or it may be built into a self-propelled vehicle such as a truck or van. Comprehensive road survey vehicles typically consist of a FWD mounted on a heavy truck together with a [[ground-penetrating radar]] and [[impact attenuator]].
+During testing, a FWD subjects the pavement surface to a load pulse which simulates the load produced by a rolling vehicle wheel. The load pulse is produced by dropping a large weight onto a "buffer" which shapes the pulse, and then transmitted to the pavement through a circular load plate. Data are acquired from various sensors for use in post-test analysis of pavement properties. Deflection sensors are used to measure the deformation of the pavement in response to the load pulse. In some FWDs the magnitude of the applied load pulse is an assumed constant value determined by system design; in others the force is measured by load cells.
-[http://www.translinkinfra.com/]{{Refimprove|date=February 2013}}
-A '''falling weight deflectometer''' (FWD) is a testing device used by [[civil engineer]]s to evaluate the physical properties of [[pavement (roads)|pavement]]. FWD data is primarily used to estimate pavement structural capacity for 1) overlay design and 2) to determine if a pavement is being overloaded. Use includes (but is not limited to) highways, local roads, airport pavements, harbor areas and railway tracks.  The machine is usually contained within a trailer that can be towed to a location by another vehicle. It can also be built on a pickup truck, inside a mini van or on a heavy truck together with a TMA protection.
-[[File:Falling Weight Deflectometer .jpg|thumb|287x287px]]
-</gallery>
-|thumb]]
+The load plate may be solid or segmented. Segmented load plates adapt to the shape of the pavement to more evenly distribute the load on uneven surfaces. The load plate diameter is typically 300 mm diameter on roads and 450 mm on airports, and the load for road testing is about 40&nbsp;kN, producing about 567&nbsp;kPa pressure under the load plate (50&nbsp;kN&nbsp;/&nbsp;707&nbsp;kPa according to European standard).
-There are two different types of load impact systems; single-mass (e.g. Dynatest, Carl Bro, PaveTesting) and double-mass (KUAB).<ref>{{cite web|title=KUAB two-mass FWD|url=http://www.ceer.iastate.edu/facilities/fwd/|publisher=Iowa State University|accessdate=12 March 2014}}</ref><ref>{{cite web|title=KUAB two-mass FWD patent|url=http://www.google.com/patents/US4116041|publisher=Google patents|accessdate=6 July 2015}}</ref> In a single-mass system, a weight is dropped onto a single buffer connected to a load plate, which rests on the surface being tested. The load force is transferred through the plate, and the plate creates a deflection that simulates a wheel load. In the double-mass system, the weight drops onto a double-buffer system, which includes a first buffer, a second weight, and a second buffer. The double-mass system essentially produces a longer loading duration that more precisely represents
-a wheel load. The double-mass system has higher reproducibility and gives a more accurate result on pavements built on soft soils.<ref>{{cite web|last1=Meier|first1=Roger W|title=Backcalculation of Flexible Pavement Moduli from Falling Weight Deflectometer Data Using Artificial Neural Networks|url=http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA294717|publisher=US Army Corps of Engineers|accessdate=24 January 2017}}</ref> The single-mass system will seriously overestimate the capacity of pavements built on soft soils. However, single-mass FWDs are smaller, cheaper and faster. Low-cost FWD:s for the Indian market are currently (2015) being developed independently by Geotran, PaveTesting and KUAB.
+==Load impact system==
-==Deflection sensors==
+There are two different types of load impact systems; single-mass and double-mass.<ref>{{cite web|title=KUAB two-mass FWD|url=http://www.ceer.iastate.edu/facilities/fwd/|publisher=Iowa State University|accessdate=12 March 2014}}</ref><ref>{{cite web|title=KUAB two-mass FWD patent|url=https://patents.google.com/patent/US4116041|publisher=Google patents|access-date=6 July 2015}}</ref>
+In a single-mass system, a weight is dropped onto a single buffer{{clarify|date=October 2020}} connected to a load plate, which in turn rests on the surface being tested. Single-mass FWDs are typically smaller, faster and less expensive but, when used on soft soils, may overestimate the capacity of pavements due to the mass inertia of the pavement material.<ref>{{cite book |last1=Crovetti |first1=JA |last2=Shahin |first2=MY |last3=Touma |first3=BE |title=Nondestructive Testing of Pavements and Backcalculation of Moduli |chapter=Comparison of Two Falling Weight Deflectometer Devices, Dynatest 8000 and KUAB 2M-FWD |year=1989 |doi=10.1520/STP19799S |publisher=ASTM International|isbn=978-0-8031-1260-5 }}</ref>
-[[Deflection (engineering)|Deflection]] sensors ([[geophone]]s; force-balance [[seismometer]]s) mounted radially from the center of the load plate measure the deformation of the pavement in response to the load. Some typical offsets are 0mm, 200mm, 300mm, 450mm, 600mm, 900mm, 1200mm 1500mm. The deflections measured at these sensors are termed D0, D200, D300 etc. The advantages of seismometers compared to geophones are built-in calibration devices and higher range (5 mm vs 2 mm). Geophones are more sensitive to disturbance immediately before the impact since the initial error is integrated. Geophones however are much cheaper than seismometers. Dynatest, Carl Bro, Jils and PaveTesting use geophones while KUAB have seismometers in their standard FWD's and geophones in their low-cost models.
+In a double-mass system, the weight drops onto an assembly consisting of a first buffer, a second weight, and a second buffer.{{refn|group=note|name=principle|In a double-mass system, the principle of operation is based on the law of conservation of momentum with an elastic collision of two unequal masses.}} This produces a longer loading duration that more precisely simulates a wheel load, and yields higher reproducibility and gives a more accurate result on pavements built on soft soils.<ref>{{cite web|last1=Meier|first1=Roger W|title=Backcalculation of Flexible Pavement Moduli from Falling Weight Deflectometer Data Using Artificial Neural Networks|url=https://apps.dtic.mil/sti/pdfs/ADA294717.pdf|publisher=US Army Corps of Engineers|accessdate=24 January 2017}}</ref><ref>{{cite book|last1=Shahin|first1=M.Y.|title=Pavement Management for Airports, Roads, and Parking Lots|date=2007|publisher=Springer|location=US|isbn=978-0387234656|edition=2}}</ref>
-== Falling Weight Deflectometer in India ==
-Structural evaluation of pavements involves application of a standard load to the pavement and measuring its response in terms of stress, strain or deflection. Benkelman beam was the equipment used for measuring deflection and structural evaluation of pavements in India until new guidelines were issued in form of IRC: 115 2014 - "GUIDELINES FOR STRUCTURAL EVALUATION AND STRENGTHENING OF FLEXIBLE ROAD PAVEMENTS USING FALLING WEIGHT DEFLECTOMETER (FWD) TECHNIQUE." With this guideline usage of Benkelman Beam got obsolete and usgae of Falling Weight Deflectometer got mandatory. This also started the usage of mechanistic design principles for design of pavement.
+There are also combined single/double mass systems where the falling weight and middle weight can be locked together giving 150 kN short pulse. In unlocked mode the FWD works as a double mass system giving 50 kN long pulse.
-Due to high capital cost of the equipment there are very few agencies in the India to deliver pavement evaluation by FWD. Translink Infrastructure Consultants Pvt. Ltd. is the only infrastructure consultancy firm in India to own Heavy Weight Deflectometer of Dynatest. It has possibly done the most number of structural evaluation of National Highways in India.
+In all systems, the load pulse shape and rise time is important because it can affect the peak values of center deflection by as much as 10% to 20%.<ref>{{cite journal |title=Testing Different FWD Loading Times |journal=Bulletin |volume=8 |date=1980 |publisher=Department of Highway Engineering, Royal Institute of Technology |location=Stockholm, Sweden}}</ref>
-Following is the list of key projects done by Translink Infrastructure Consultants Pvt. Ltd.in India.
-* Four/Two Lanning with paved shoulder of Gadu-Porabander section of NH-8E from Km 263.200 to Km 356.766 In the state of Gujarat through PPP on Hybrid (Annuity) mode.
-* Overlay design on the basis of FWD Survey for 3 Road Packages in Gujarat from Dhandhuka to Dholera, Dhandhuka to Pipali and Dhandhuka to Limdi having a total approximate length of 100 KMs.
-* Six Laning of Gulabpura – Chittorgarh Section of NH79 in the States of Rajasthan (Length 124.870 Km) on DBFOT (Toll) under NHDP Phase V Package-II
-* Six Laning of Kishangarh to Gulabpura Section of NH79A and NH79 in the States of Rajasthan (Length 90.000 Km) on DBFOT (Toll) under NHDP Phase V Package – I
-* 4 Laning of Chandigarh-Kharar Section in State of Punjab on EPC mode.
-* Development of 76 km long Kharar-Ludhiana section involves 6-laning of 54 km and 4-laning of 22 km of National Highways.
-* The 81 km long Phagwara - Rupnagar section passes through Banga Town and proposed Nawashahir bypass and terminates at Rupnagar.
-* Six Laning of Chittorgarh-Udaipur Section of NH 76 from Km 212+000 to Km 118+500 in the State of Rajasthan (Length 93.500 Km) on DBFOT (Toll) under NHDP Phase V.
-* The 111 km long Bar-Jodhpur section connecting western Rajasthan and border areas (Jodhpur-Jaisalmer-Barmer) to eastern part of Rajasthan i.e. Ajmer & Jaipur.
+==Deflection sensors==
-==Analysis==
+[[Deflection (engineering)|Deflection]] sensors are used to measure the deformation of the pavement in response to the load pulse. The sensors are mounted radially from the center of the load plate at typical offsets of 0, 200, 300, 450, 600, 900, 1200 and 1500 mm (the deflections measured at these offsets are denoted D0, D200, D300, etc.).
-FWD data is most often used to calculate stiffness-related parameters of a pavement structure.  The process of calculating the [[elastic modulus|elastic moduli]] of individual layers in a multi-layer system (e.g. [[asphalt concrete]] on top of a [[base course]] on top of the [[subgrade]]) based on surface deflections is known as "backcalculation", as there is no closed-form solution.  Instead, initial moduli are assumed, surface deflections calculated, and then the moduli are adjusted in an iterative fashion to converge on the measured deflections.  This process is computationally intensive although quick on modern computers. It can give quite misleading results and requires an experienced analyst. Commonly used backcalculation software are BAKFAA (Federal Aviation Administration), Elmod (Dynatest), PVD (KUAB), MichBack (Michigan DOT) and Modulus (TxDOT).
+Two types of deflection sensors are used: [[geophone]]s and force-balance [[seismometer]]s. Seismometers have built-in calibration devices and higher deflection measurement ranges (5&nbsp;mm vs 2&nbsp;mm). Geophones lack built-in calibration devices and are more sensitive to disturbances immediately before the impact since the initial error is integrated{{clarify|date=October 2020}}, but are much less expensive than seismometers.
+== Analysis ==
+FWD data is most often used to calculate stiffness-related parameters of a pavement structure.  The process of calculating the [[elastic modulus|elastic moduli]] of individual layers in a multi-layer system (e.g. [[asphalt concrete]] on top of a [[base course]] on top of the [[subgrade]]) based on surface deflections is known as "backcalculation", as there is no closed-form solution.  Instead, initial moduli are assumed, surface deflections calculated, and then the moduli are adjusted in an iterative fashion to converge on the measured deflections.  This process is computationally intensive although quick on modern computers. It can give quite misleading results and requires an experienced analyst. Commonly used backcalculation software are:
+* BAKFAA (Federal Aviation Administration)
+* Clevercalc (University of Washington)
+* [https://dynatest.com/elmod/ ELMOD (Dynatest)]
+* Evercalc (WSDOT)
+* KGPBACK (Geotran)
+* MichBack (Michigan DOT)
+* Modulus (TxDOT)
+* PVD (KUAB)
+* PRIMAX DESIGN / RoSy Design (Sweco, former Carl Bro)
 Many analysts use simplified methods to calculate related parameters that are empirical in nature. The most common is maximum deflection under the centre of the load plate (D0) which is related to empirical measures such as the Benkelman Beam deflection (after minor adjustment for differences in the two devices). Historically some used the radius of curvature (D0-D200) but this is out of favour now because it is clear that the steel loading plate of 300mm diameter affects the shape of the deflection bowl between the centre (D0) and the D200 sensor at 200mm. However this means that a lot of useful information about the shape of the deflected bowl is wasted. Horak and Emery have published indices that use this information: BLI=D0-D300 and gives an indication of the basecourse performance, MLI = D300-D600 and gives an indication of the subbase performance, and LLI=D600-D900 and gives an indication of subgrade performance. These and other similar indices are known as shape factors. The FWD data can also be very useful in helping the engineer divide the length of the pavement into homogeneous sections.
@@ Line 39: / Line 47: @@
 ==Other models==
-A Light Weight Deflectometer (LWD) is a portable falling weight deflectometer. It is used primarily to test insitu base and subgrade moduli during construction. Light Weight Deflectometer (LWD) is quicker than the isotope measuring method and requires no reference measurements. The equipment has no radioactive sources requiring safety courses and can be operated by one operator, allowing for the analysis of collected data and printing out of data files on site.<ref>{{cite web|title=Light Weight Deflectometer YouTube Video|url=https://www.youtube.com/watch?v=X6DUxSOj3WU|publisher=Cooper Technology|accessdate=3 March 2014}}</ref>
+[https://dynatest.com/ Dynatest] was the first company to develop the Light Weight Deflectometer (LWD) The Light Weight Deflectometer is a portable falling weight deflectometer used primarily to test in situ base and subgrade moduli during construction. LWD measurement is faster than the isotope measuring method{{clarify|date=December 2024}} and requires no reference measurements. The equipment has no radioactive sources and can be operated by one person, allowing for on-site data analysis and report printing.<ref>{{cite web|title=Light Weight Deflectometer YouTube Video|url=https://www.youtube.com/watch?v=X6DUxSOj3WU |archive-url=https://web.archive.org/web/20140705210351/http://www.youtube.com/watch?v=X6DUxSOj3WU |archive-date=2014-07-05 |url-status=dead|publisher=Cooper Technology|accessdate=3 March 2014}}</ref> Some LWDs have no load cell and assume a nominal load value, whereas others employ a load cell to measure the actual load. Depending on the system, a LWD may have a single geophone located in the centre or it may have two geophones, typically located at 300 and 600 mm positions.
+A Fast Falling Weight Deflectometer (FFWD) is a FWD with pneumatic or electric actuators rather than hydraulic, making the mechanics several times faster.
-A Heavy Weight Deflectometer (HWD) is a falling weight deflectometer that uses higher loads, used primarily for testing airport pavements. Maximum load for HWD:s are typically around 300&nbsp;kN (Dynatest, Carl Bro and PaveTesting) and 600&nbsp;kN (KUAB).
+A Heavy Weight Deflectometer (HWD) is a falling weight deflectometer that has higher loads (typically 300&nbsp;kN to 600&nbsp;kN), used primarily for testing airport pavements. A common misconception is that higher loads are needed to test an airport's capability to handle heavy aircraft, but in fact, the testing methods are not designed to test the strength of the construction but to find the material properties of the construction.
-A Rolling Weight Deflectometer (RWD) is a deflectometer that can gather data at a much higher speed (as high as 55&nbsp;mph) than the FWD. It is a specially designed tractor-trailer with laser measuring devices mounted on a beam under the trailer. Another advantage of the RWD over the FWD is that it can gather continuous deflection data as opposed to discrete deflection data collected by the FWD. RWD development has been carried out independently by Applied Research Associates (ARA) since 2005 and KUAB Sweden since 1991.<ref>{{cite web|title=Megascale RWD patent|url=https://www.google.com/patents/US6499339|publisher=Google patents|accessdate=29 October 2015}}</ref>
+A Rolling Weight Deflectometer (RWD) is a deflectometer that can gather data at a much higher speed (as high as 55&nbsp;mph) than the FWD, which allows the data to be collected without traffic control and lane closure.<ref>{{cite journal|last1=Elbagalati|first1=Omar|last2=Elseifi|first2=Mostafa A.|last3=Gaspard|first3=Kevin|last4=Zhang|first4=Zhongjie|title=Development of an Artificial Neural Network Model to Predict Subgrade Resilient Modulus from Continuous Deflection Testing|journal=Canadian Journal of Civil Engineering|date=16 June 2017|volume=44 |issue=9 |pages=700–706 |doi=10.1139/cjce-2017-0132|doi-access=free}}</ref> It is a implemented as a tractor-trailer with laser measuring devices mounted on a beam under the trailer. Unlike the FWD, which pauses to make measurements, a RWD gathers deflection data while it travels.<ref>{{cite web|title=Megascale RWD patent|url=https://patents.google.com/patent/US6499339|publisher=Google patents|access-date=29 October 2015}}</ref>
 The test materials are described in ASTM D 4694, and the test method is defined in ASTM D 4695.140
+==Notes==
+{{reflist|group=note}}
 ==References==