Things you need to know about falling weight deflectometer

The Falling Weight Deflectormeter (FWD) came into being in the early 1970s. It is a pulsed dynamic sinuometer. It simulates the instantaneous impact of automobile load on the road surface and obtains the instantaneous deformation of the road surface. Its measurement results are more accurate, and the information is large.

This article is mainly about three parts:

1、advantage of Falling weight deflectometer

2、the parameters of the Falling weight deflectometer

3、the future of falling weight deflectometer.

1、advantage of Falling weight deflectometer

Compared with the traditional measurement of bending and sinking of beckman beam, it is convenient, fast, safe, labor-saving, and suitable for long distance and continuous measurement. Through analysis and comparison, the federal highway administration of the United States confirmed that the Falling Weight Deflectormeter is a good equipment for evaluating the dynamic load carrying capacity of road surface, and selected the Falling Weight Deflectormeter as an important equipment for evaluating the road surface strength when implementing the SHRP program. Shell has officially included the Falling Weight Deflectormeter in its road design manual. 

 China introduced the Falling Weight Deflectormeter from abroad in the middle and late 1980s, and it has been more than ten years since then. During this period, the development and application of the Falling Weight Deflectormeter have made some important achievements in a large number of theoretical and experimental studies. In the roadbed and pavement field test regulations, the Falling Weight Deflectormeter has been listed as a bending and sinking test device.

2、the parameters of the Falling weight deflectometer

There are some technical indicators about falling weight deflectometer. The impact load can be up to 120KN (expandable) and is set to 50KN at the factory. Dynamic force measurements range from 0 to 120KN (expandable). The load measurement accuracy is 1%. The shape of the load pulse is a half sine wave. Displacement measurement range: ±5mm. The bending accuracy is 2%. Number of displacement sensors is one. The test speed per point is less than 20 seconds/point (with fast measurement software enabled, it can be narrowed down to 15 seconds/point). The way to lift the hammer is hydraulic. The lifting and lowering mode of bearing plate is hydraulic. Travel can speed up to 120km/h (depending on road conditions). DMI range sensor accuracy: 0.1%. The total Weight of The Falling Weight Deflectormeter is about 450kg. The external dimension is 1.3m high, and the other dimensions depend on the model provided by the user.

3、the future of falling weight deflectometer.

Due to the advantages of the falling weight deflectometer in simulating traffic load, speed measurement and accuracy, many countries have formulated the corresponding specification of the falling weight deflectometer. Due to the long-term neglect of pavement detection technology in China, the falling weight deflectometer and its related technologies were not systematically studied until the late 1990s. In particular, the urgent demand for testing technology in the construction of high-grade highways has prompted the new highway testing standards in China to include beckman beam, automatic sinuometer and drop hammer sinuometer in the roadbed and pavement field testing regulations. It can be predicted that the next period will be the development stage of coexistence of various bending and sinking instruments.