Impact tests on soil material
Measurement of deceleration
Werner Gerber and Brian McArdell
Swiss Federal Research Institute WSL, Zürcherstr. 111, CH‐8903 Birmensdorf
([email protected])
Introduction
Tests carried out
Impacts of rockfall causes a lot of
damage to infrastructure facilities.
The ensuing forces during impact
are not known. They depend on the
mass and velocity of the block. But
mainly
the
impact
material
determines
the
deceleration
process and the forces. This poster
presents results from experiments
with various materials.
At the WSL test site Walenstadt over 220 drop
tests with cube‐shaped concrete bodies have
been carried out. During the experiments the
deceleration of the test bodies has been
measured using acceleration sensors attached to
the bock (Fig. 2B). With the measured values , the
dynamic penetration and the brake‐time is
determined. From the many experiments four
measurements from a block of 800 kg and a falling
height of 5.3 m were selected. The results of
experiments A, B, C and D were analyzed in more
detail and compared among themselves.
Fig. 1: Block of 9 m3 (24’000 kg) stopped before reaching the national freeway A2
Results of deceleration
Normalization of deceleration path
The maximum decelerations are in a range of 425‐1710 m/s2. The
results show a great difference between the material used. Also the
braking time varies over a wide range of 18‐39 milliseconds. The
deceleration affects the path of velocity and the depth of
penetration. These vary over a large range too, from 6.7‐26 cm
( Table 1 and Fig. 3).
To compare the different results of deceleration, braking time and
penetration depth we normalize the data with the braking time set
to 100% and the deceleration to 100% (Fig. 4). This diagram shows
the character of the deceleration process, especially the time of the
peak of deceleration. Experiments A and C have a peak near 17%
and the experiment B and D near 70‐80%.
A
Student
Institution
B
Student
Institution
C
Fig. 4: Normalization of braking time and deceleration
The second normalization is done with the penetration depth and
the deceleration set to 100% (Fig. 5). This diagram shows the
increase and the decrease of the deceleration during the
penetration. Experiments B and C have their peak near 90‐95% and
the experiment C and A between 30‐55%.
Fig. 5: Normalization of penetration depth and deceleration
Valuable formulas
(1)
_
(2)
_
Fig. 2: Experiments A, B, C and D: with a Block (800 kg) and a
falling hight of 5.3 m.
Comparison of measurements and model WSL
Fig. 3: Deceleration, velocity, penetration and braking time of the 4 Experiments
D
(3)
∙
(4)
The results of these 4 experiments are different, although the impact velocity and the mass of the
block were the same (Fig. 6). Nevertheless, the results can be summarized in a single formula (1).
With this formula the maximum deceleration can be calculated. In each result however, the
deceleration factor (3) and the penetration factor (4) are different. The deceleration factor
compares the maximum value with the mean value and the penetration factor compares the
penetration depth with the path without influencing by a braking force.
Table 1: Results of experiments with a concrete block of 800 kg and a falling height of 5.3 m (42 kJ).
Experiment
Material
Thickness
Structure
Deceleration a_max. (m/s^2)
A
Gravel
40 cm
Compacted
Concret slab
1710
B
Scree
50 cm
not comp.
Bedrock
795
C
Scree
130 cm
Compacted
Bedrock
710
D
Cellular glass
120 cm
‐
Concret slab
425
Braking time (ms)
32
18
27
39
Penetration depth (cm)
Deceleration a_mean
(m/s^2)
Deceleration factor (fd)
6.7
10.5
11.8
26
319
567
378
262
5.4
1.4
1.9
1.6
Penetrations factor (fp)
0.21
0.57
0.43
0.65
Fig. 6: Comparison of measured and calculated maximum deceleration