An Affordable Dynamic Penetrometer for Soil Resistance and Compaction

ABSTRACT

Soil compaction plays a vital role in determining ecosystem health, influencing water absorption, root growth for plants, and is crucial for the construction of safe foundations. Soil compaction is often measured by penetrometers, devices that gauge soil resistance to penetration to access compaction levels. Professional devices are often expensive, making them inaccessible in many communities. This raises the question of how soil compaction can be measured at a cost-effective level. In this project, we designed a novel, low-cost dynamic soil penetrometer using a 3D printed cone and concrete weight to evaluate soil compaction. A geophone, was used to record the impact of each weight drop. Preliminary analysis shows that the geophone is able to capture consistent vibration patterns during soil penetration and disturbance. This suggests that a low-cost, geophone assisted device could provide accessible soil compaction measurement methods for educational or low-resource applications.

INTRODUCTION.

Soil compaction is a widespread problem that affects agricultural yield, water absorption, and overall ecosystem health. As soil becomes compacted, its structure changes [1]. Pore size shrinks, which limits root growth and restricts the movement of air and water to plants [2]. These changes can often lead to increased greenhouse gas emissions, poor long term soil quality, and reduced or minimized crop yields [1].

To monitor and measures soil compaction, researchers and land managers often use a device called a soil penetrometer. Penetrometers measure the soil’s resistance to penetration, providing data on soil strength and density [3]. They are widely used in agriculture as a guide for tillage, in environmental sciences to measure soil health, and in construction and engineering to evaluate ground stability. However, commercial penetrometers can often be expensive and require specialized training, which severely limits their accessibility to educators, students, and community scientists [4].

Recent studies have highlighted the importance of developing affordable, cost-effective alternatives to traditional soil measurement tools. These devices can provide access to environmental data and support hands on learning in classrooms as well as citizen science interests [5]. By combining affordable materials and readily available electronics, new devices can be developed to provide insight into soil compactions without financial or technical barriers of professional systems.

In addition to physical penetration measurements, ground vibration sensors such as geophones allow information about the ground response. A geophone measures the grounds velocity, often created by surface level disturbances such as pedestrian traffic, machinery, or seismic movements. While it does not drectly measure soil compaction, geophones can detect and help visualize the force applied to the ground during impact. While a penetrometer measures soil resistance through penetration depth after a set number of strikes or after each strike, a geophone records the vibrations of the ground itself. Combined, these tools provide corresponding data, the penetrometer provides physical resistance, while the geophone visualizes the impact.

Here, we aimed to design and test a low-cost soil penetrometer based on previously existing and commercial designs of penetrometers [6,7]. Our prototype uses several modifications including, a sliding drop weight to standardize the drop path, a reinforced 3D printed strike plate, and integration of a Raspberry Pi for data visualization and storage. A geophone sensor was used as a secondary verification tool to visualize impact and compare responses across different topographies. The goal of this study is to create a device that is accessible to the public while still maintaining meaningful and consistent measurements of soil compaction.

MATERIALS AND METHODS.

DIY Soil Penetrometer.

The design of the penetrometer was created using basic materials and was modeled after the dynamic penetrometer designs of Herrick and Jones [6] and Vanags et al. [7] (Figure 1).

The design used by Herrik and Jones [6] consisted of a singular rod/pipe with a pointed cone that penetrates the soil after repeated strikes. This design showed both the use of a hammer and strike plate as well as a sliding weight design. The hammer and strike plate measures how many strikes it takes to reach a certain depth or how far the penetrometer penetrates after a set number of strikes. One limitation of the hammer and strike plate design is the variability between strikes. Each strike is done by manually swinging a hammer at a focus point on the top of the rod. To avoid this variation and to keep the strikes as uniform as possible, we chose to use the slide and drop weight method for our penetrometer [8]. This method uses a fixed 1kg weight, which is then raised to a marked height and dropped down the rod.

Our design uses a 121cm long, 1-inch diameter PVC pipe. A circular bubble level was fixed to the top to ensure a vertical drop alignment during testing. The drop weight design has a “collar” that stops the weight from striking the ground. This ensures that the weight is forcing the penetrometer into the soil rather than just sliding down the shaft and resting on the ground. To accomplish the idea of a collar, we used multiple iterations of designs (Figure 2.2). Early versions used external screws and wall brackets secured 65 inches from the top (Figure 2.2A and 2.2B). These designs failed due to stripping or instability after repeated trials. A final collar design was modeled in Fusion 360, a 3D designing software. Here we designed a round platform with cylinders protruding from the center, which will then be used to secure the collar inside the PVC pipe with adhesive (Figure 2.2C). All models were printed using an Ulti Maker S5 3D printer and standard PLA filament (Figure 3.1A).

Previous research [9] has indicated that the ideal weight for the soil penetrometer ranges between 1-2 kg. Thus, we created a mold in Fusion360 that could hold and shape concrete with a final weight of 1kg (Figure 3.1A and 3.1B). A circular design with a 90mm diameter and a 30mm hole was created. We mixed Quikrete quick setting cement using a given ratio of 5 ½ parts powder to 1 part water. The concrete was poured into the mold, tapped to release air bubbles and dried for one week before being fitted to the PVC pipe.

Recreating Herrick and Jones design [6], Fusion 360 was used to model a circular cone with a 30-degree angle measured to fit within the end of the PVC pipe and printed using a 50% infill and standard PLA filament (Figure 3.1C and 3.2C). The cone was secured at the end of the PVC with adhesive.

Multiple trials were conducted with the 3D printed cone and collars. A final iteration was created with the 30-degree angle on the cone and a filleted/curved edge on the joining seams for the collar (Figure 3.1A). Without this curved edge, the pressure after a weight drop on the 90-degree angle overhang was too much and caused the collar to break at the connection to the PVC pipe.

Marks were placed 5cm and 10 cm from the tip and 2 cm from the top. The marks at the tip were used to measure penetration depth after each strike.

Geophone System.

An SM 24 Geophone was connected to a Raspberry Pi running the Bookworm OS to visualize and store the ground velocity data. The geophone continuously recorded signals corresponding to the grounds movements during each penetrometer strike. Data was then saved to a CSV file for post-analysis

The geophone was used as a secondary verification tool for visualizing responses. It did not measure soil compaction, instead it confirmed impact occurrence, visualized ground response, and allowed qualitative comparison of different topographies such as soil and mulch.

RESULTS.

The data collection phase for the prototype soil penetrometer was completed successfully. A total of five sample sites were assessed, with ten weight drops at each site. Penetration depth was recorded to evaluate relative soil resistance. Areas with compacted soil showed significantly lower penetration depth compared to mulch covered areas, indicating greater resistance.

Data from the geophone simultaneously shows clear responses corresponding to each penetrometer weight drop (Figure 4). Soil trials produced higher amplitude, sharper signal peaks immediately following impact. This indicates efficient transmission of energy through compacted soils. In contrast, the mulch trials showed lower amplitude peaks and more prolonged signal tails. This reflects more signal absorption.

The geophone recordings qualitatively support the penetration measurements. Surfaces that resisted penetration (soil) produced stronger and more distinct vibration response. While surfaces that allowed deeper penetration (mulch) displayed lower amplitude and more distributed signal patterns.

DISCUSSION.

The preliminary results demonstrate that the prototype soil penetrometer successfully differentiated between compacted soil and mulch surfaces. Despite being constructed from basic, low-cost materials, the prototype produced results that aligned with expectations and trends reported in existing literature [8].

The integration of the geophone system provides an additional layer of validation by confirming the impact consistency and visualizing the ground response. Although the geophone does not direct quantify the soil compaction or resistance, these recordings strengthen the penetrometer accuracy by illustrating the differences between energy transmission and compaction of the ground.

Limitations of this study include the small number of test sites and mechanical durability. Challenges were encountered during early design iterations. Future works should include further reinforcement for long-term durability, expanded testing across multiple soil types, and comparison with commercial penetrometers from calibration.

Overall, this research demonstrates an important step in environmental sensing technology and providing hands-on research opportunities for students and community scientists by creating a low-cost and accessible soil measurement device.

ACKNOWLEDGMENTS.

We would like to thank the School for Science and Math at Vanderbilt for the amazing opportunity to conduct this research. Dr. Vishesh Kumar for being the mentor throughout this project. Finally, Mr. Jacob Marina for letting us use his space.

REFERENCES.

1. B. D. Soane, C. van Ouwerkerk, Soil compaction problems in World Agriculture. Developments in Agricultural Engineering. 11, 1–21 (1994).
2. M. Pulido-Moncada, S. Katuwal, L. J. Munkholm, Characterisation of soil pore structure anisotropy caused by the growth of bio-subsoilers. Geoderma. 409, 115571 (2022).
3. T. Keller, P. Défossez, P. Weisskopf, J. Arvidsson, G. Richard, SoilFlex: A model for prediction of soil stresses and soil compaction due to agricultural field traffic including a synthesis of analytical approaches. Soil and Tillage Research. 93, 391–411 (2007).
4. S. W. Duiker, Diagnosing soil compaction using a penetrometer (soil compaction tester). Penn State Extension (2002), (available at https://extension.psu.edu/diagnosing-soil-compaction-using-a-penetrometer-soil-compaction-tester).
5. H. Vereecken et al., Modeling soil processes: Review, Key Challenges, and New Perspectives. Vadose Zone Journal. 15, 1–57 (2016).
6. J. E. Herrick, T. L. Jones, A dynamic cone penetrometer for measuring soil penetration resistance. Soil Science Society of America Journal. 66, 1320–1324 (2002).
7. C. Vanags, B. Minasny, A. B. Mcbratney, (PDF) the dynamic penetrometer for assessment of soil mechanical resistance. The dynamic penetrometer for assessment of soil mechanical resistance (2004), (available at https://www.researchgate.net/publication/237557382_The_dynamic_penetrometer_for_assessment_of_soil_mechanical_resistance).
8. P. Paige-Green, L. Du Plessis, The use and interpretation of the dynamic cone penetrometer (DCP) test (2009), (available at https://rtdcp.co.za/wp-content/uploads/2019/11/The_use_and_interpretation_of_the_Dynamic_Cone_Penetrometer_01.pdf).
9. 9. B. O. Benn, P. A. Smith, A guide for collecting seismic, acoustic, and magnetic data for multiple uses (1975), doi:10.21236/ada005148.

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Posted by buchanle on Thursday, May 14, 2026 in May 2026.

Tags: Geophone, Penetrometer, Soil Compaction, Soil Resistance