1. Comparison of a Dynamic and Static Penetrometer for Reproducibility of Readings
Eric C. Brevik, Department of Physics, Astronomy, and Geosciences, Valdosta State University, Valdosta, GA.
Introduction
- Dynamic penetrometers have been promoted as instruments that give more reproducible readings over a wider resistance range than static penetrometers
- To test this, a dynamic Jornada Impact Penetrometer (JIP) was compared to a commercially available static pocket pentrometer
Results (Tables 1-6)
- Most of the readings taken in the sparesly vegetated area at Site 1 exceeded the upper measurement limit of the static penetrometer.
- Two of the readings in the pit bottom at Site 1 were below the lower limit of the static penetrometer (gave readings of 0)
- At Site 2, 18 of the 21 dynamic means compared were statistically equal, while 14 of the 21 static means were equal
- At Site 2, 14 of the 21 dynamic means had a standard deviation (SD) that was <20% of the mean, 19 had a SD that was <40% of the mean, and all 21 had SDs that were <60% of the mean. None of the 21 static penetrometer means had a SD <20% of the mean, only nine had a SD <40% of the mean, and 16 had a standard deviation<60% of the mean. Five of the static penetrometer means had SDs >60% of the mean.
Materials and Methods
- A soil science class was broken into groups.
- Each group was given two sets of locations (Sites 1 and 2) that they visited. Each member of each group determined penetration resistance at each location with both penetrometers
- Penetrometer readings from each group were averaged, and the averages compared using the statistical package embedded in Microsoft Excel.
The Model CL-700A pocket penetrometer set next to a ruler with cm (top) and inch (bottom) increments for scale.
A group of students uses the Jornada Impact Penetrometer.
Table 3. Summary statistics for the JIP analysis done at Site 2.
Station
Group 1
Group 2
Group 3
Mean (J/cm)
Std. Dev. (J/cm)
Min. (J/cm)
Max. (J/cm) 1 2 3 4 5 6 7
2.14a
2.55a
1.80a
2.32a
3.19a
2.51a
0.24
0.55
0.13
0.20
0.37
0.35
0.23
1.77
1.86
1.61
1.95
2.95
2.21
2.53
3.54
1.92
2.36
2.83
3.94
2.86
2.85b
2.23a
1.84a
2.81a
2.87a
3.71b
2.32ab
0.66
0.19
1.47
0.90
0.86
1.97
1.27
1.54
1.05
2.29
5.91
4.72
2.59ab
2.17a
1.90a
2.65a
5.40ab
2.02b
0.52
0.40
0.10
2.93
1.75
2.62
2.08
11.81
Same letter indicates means are equal
Table 5. Standard deviation as a percentage of the mean for the JIP readings done at Site 2.
Station
Group 1
Group 2
Group 3
Mean (J/cm)
Std. Dev. (J/cm)
% of mean 1 2 3 4 5 6 7
2.14
2.55
1.80
2.32
3.19
2.51
0.24
0.55
0.13
0.20
0.37
0.35
0.23
11.2
21.7
7.1
9.2
15.9
11.0
2.85
2.23
1.84
2.81
2.87
3.71
0.66
0.19
1.47
0.90
0.86
23.2
8.4
19.3
52.2
31.4
9.9
37.1
2.59
2.17
1.90
2.65
5.40
2.02
0.52
0.40
0.10
2.93
20.0
18.2
5.5
10.9
7.6
54.3
9.4
Conclusions
- The dynamic penetrometer had more reproducible readings and was able to take readings over a wider range of soil resistances when compared to the static penetrometer.
Table 1. Summary statistics for the JIP analysis done at Site 1.
Area
Group 1
Group 2
Mean (J/cm)
Std. Dev. (J/cm)
Min. (J/cm)
Max. (J/cm)
Natural
Pit bottom
Sparsely vegetated
Grassy
1.73
5.31a
34.25
7.53a
0.19
1.47
12.64
0.58
1.42
3.30
23.62
6.44
2.08
7.09
70.87
8.34
2.86
5.27a
10.44
7.93a
0.33
0.65
1.25
0.85
2.36
4.43
8.86
3.22
11.81
Same letter indicates means are equal
Table 4. Summary statistics for the CL-700A penetrometer analysis done at Site 2.
Station
Group 1
Group 2
Group 3
Mean (kg/cm2)
Std. Dev. (kg/cm2)
Min. (kg/
cm2)
Max. (kg/cm2)
Max. (kg/ 1 2 3 4 5 6 7
0.29
0.36a
0.01
0.67a
1.10a
1.44a
0.75a
0.25
0.27
0.04
0.31
0.47
0.60
0.33
0.00
0.30
0.75
0.80
0.50
0.10
1.25
2.00
2.60
1.30
0.82a
0.80ab
0.68a
0.59a
1.51a
1.61a
1.04a
0.19
0.46
0.62
0.28
0.54
0.35
0.77
1.00
1.50
2.10
0.69a
1.08b
0.41a
1.41
1.29a
1.71a
0.43
0.21
0.36
0.32
0.41
0.17
0.70
0.20
0.40
1.75
1.70
2.40
0.90
Same letter indicates means are equal
Acknowledgements and Disclaimer
This research was supported by a Valdosta State University faculty research grant. The author thanks the students of his Spring 2006 Environmental Soil Science class for participating in this study. Trade names or commercial products are given solely for the purpose of providing information on the exact equipment used in this study, and do not imply recommendation or endorsement by Valdosta State University.
Table 6. Standard deviation as a percentage of the mean for the CL-700A penetrometer readings done at Site 2.
Station
Group 1
Group 2
Group 3
Mean (kg/cm2)
Std. Dev. (kg/cm2)
% of mean 1 2 3 4 5 6 7
0.29
0.36
0.01
0.67
1.10
1.44
0.75
0.25
0.27
0.04
0.31
0.47
0.60
0.33
86.6
75.5
264.6
46.1
43.0
41.5
43.4
0.82
0.80
0.68
0.59
1.51
1.61
1.04
0.19
0.46
0.62
0.28
0.54
0.35
0.77
23.0
57.2
92.0
47.2
35.5
21.7
74.3
0.69
1.08
0.41
1.41
1.29
1.71
0.43
0.21
0.32
0.17
39.0
39.6
50.1
25.7
25.3
23.8
28.6
Table 2. Summary statistics for the CL-700A penetrometer analysis done at Site 1.
Area
Group 1
Group 2
Mean (kg/cm2)
Std. Dev. (kg/cm2)
Min.
(kg/cm2)
Max. (kg/cm2)
Min. (kg/cm2)
Natural
Pit bottom
Sparsely vegetated
Grassy
0.78a
0.97
4.43a
1.22
0.33
0.77
0.26
0.41
0.30
0.10
3.60
0.50
1.30
2.20
4.50
1.75
1.00a
0.40
3.84a
0.72
0.35
0.98
0.34
0.00
2.00
1.50
1.00
1.25
Same letter indicates means are equal