The Light Weight Deflectometer HMP LFG4 (HMP Magdeburger Prüfgerätebau GmbH, Germany) makes it possible to quickly determine, in an uncomplicated manner, the soil bearing capacity and compaction quality of soils, non-cohesive sub-bases, and pavement improvements.

The main advantages of this method are: 1) immediate obtaining of results and the possibility to make conclusions at the object on site, without special data processing in the office; 2) minimal test time per 1 point (2-4 minutes); 3) minor expenses; 4) there is no need for machinery to provide counterweight as in the case of a static plate test.

Tests with the HMP LFG4 equipment are performed in accordance with German standards TP BF-StB Part B 8.3 (Technische Prüfvorschriften für Boden und Fels im Straßenbau) and ZTV E-StB 09 (Zusätzliche Technische Vertragsbedingungen und Richtlinien für Erdarbeiten im Straßenbau), as well as the US standard ASTM E2835-11 (Standard Test Method for Measuring Deflections using a Portable Impulse Plate Load Test Device).

Execution of testing.

Once a testing place has been selected, it should be appropriately prepared for the test. If the test material is made of particles larger than 10 mm (coarse gravel, crushed stone, pebbles), it is recommended to create a fine sand „cushion” under the load plate. The main function of the sand „cushion” is the levelling of the surface for the plate to take horizontal position, as well as close contact with the surface to be tested. After its formation, the plate is placed, and the equipment and the electronic measuring device are connected. At the start of the testing, the falling weight device is lowered three times, creating a continuous, sequential impulse on the load plate. These three preliminary hits are not taken into account in the calculations; their main purpose is the pre-compaction of the soil for further testing. After completing the preliminary hits, the measurement device offers to commence testing, within the framework of which the falling weight device is also lowered three times, but the obtained results for each time are stored in the measurement device's memory and are used in calculations. After the third measurement, the performance measurement device will display the settlement amplitude s(m) and the dynamic deformation module Evd on the screen. Results can be printed at the object (the measurement device is equipped with a check printer) on site, or processed and properly executed in the original computer program at the office.

 Technical parameters of the LFG4 device: 

Load device

Total weight

15 kg

Falling weight device

10 kg

Maximum action force

7,07 kN

Action time

17.0 ± 1.5


Zinc coated steel.

Load plate (stamp)


300 mm

Plate thickness

20.0 mm

Total weight

15 kg


Zinc coated steel.

Electronic instrument for measurement of settlement




210х80х25 mm

Total weight

0.4 kg

Settlement measurement range

0,1- 2,00 mm ±0,02 mm

Evd measurement range

Evd <225 MN / m²

Temperature range

0 – 40ºС