Humboldt 5000 BLU Light Weight Deflectometer - Manual (Page 27)

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4.3 Dynamic Plate Load Test
The dynamic plate load test with the Light Weight Deflectometer is a test method during which the ground
is subjected to an impact load. This impact load is caused by a weight dropping onto a load plate with a
diameter of 30 cm (radius r = 15 cm), which generates a maximum force (Fmax) of 7.070 kN. During
calibration of the device this force is adjusted so that the normal stress ( σmax) under the load plate
amounts to 0.1 MN/m 2 while tests are being performed. The parameter for the deformability of the soil
under this defined vertical impact load tmax is the so-called Evd value.
Evd = 1.5 r
smax = mean value of the settlements σ4max, σ5max, σ6max of 3 tests
(after 3 pre-consolidation tests)
r = radius of the load plate (15 cm)
σmax = normal stress under the load plate (0.1 MN/m 2 )
4.4 Area of Application
The dynamic plate load test with the Light Weight Deflectometer is suitable for testing the bearing
capacity and the compaction of subsoil / soil on the subbase of earthworks and road constructions. ‘Soil’
shall be understood as including backfill materials, base courses without binding agents, soil improvements,
cold recycling layers, mineral sealing layers, asphalt and cement, which has yet to set. The testing method
is especially suitable for coarse-grained and mixed soils with a maximum grain size of 63 mm.
The test can be performed in less than two minutes by a single operator, without a load testing vehicle.
Thus, it is possible to immediately evaluate the evenness of the bearing capacity within the inspection lot.
In Germany and Austria the dynamic plate load test may be performed as an alternative to the static plate
load test according to DIN 18134.
The use of the Light Weight Deflectometer always requires a prior determination of correlation values
with the degree of compaction or the deformation modulus. The evaluation of the measured Evd value
depends on the material and the subsoil being tested. It is always necessary to determine correlation
values of the static plate load test on a trial basis for the pre-existing ground or the ground intended for
backfilling. Homogeneous ground is a prerequisite for properly correlating the two measuring methods.
Accordingly, the water content of the soil must not vary widely at the different testing points.
ATTENTION (Quotation from ZTV E-StB 09)
‘The deformation modulus Ev2 is to be assessed by the static plate load test in accordance with DIN
18134 and the dynamic deflection module Evd with the dynamic plate load test in accordance with TP
BF-StB Part B 8.3.... The specifications of the building contract should state whether the static or dynamic
deflection modulus is to be established. If no such statement is to be found in the contract, the static
deformation modulus will need to be established.’
One advantage over the static plate load test according to DIN 18134 is the possibility to perform tests in
confined areas such as utility trenches or construction backfills.
In accordance with the German standard TP-BF StB Part B 8.3 the measuring range of a Light Weight
Deflectometer with 10kg drop weight must be specified as 15 MN/m
2 to 70 MN/m 2 , since it is only within
this measuring range that the device complies fully with the strict rules of the German Federal Road
Research Institute (Bundesanstalt für Straßenwesen).
σ
max
______
s
max