**4. Off-road vehicle designs for soil compaction management**

Agricultural tractive power units are the largest source of unwanted soil compaction today. Significant research and financial investment have been made in

methodologies to reduce the compaction from these vehicles. Tracked systems and advanced tire systems are both designed to spread the loads imposed upon the soil below detrimental levels. This section will review these common undercarriage systems, along with advanced compaction reduction technologies for off-road vehicles.

### **4.1 Tracks**

Commercially successful track-type vehicles, which were recognized under the trademark name Caterpillar, began production in the early 1900s [27]. These early agricultural tractors, similar to the one shown in **Figure 8**, paved the way for future tracked vehicles and the continued use of the more complex metal grouser style tracks on construction equipment. Tracks did not remain popular in the agricultural sector, once pneumatic tires became available. They faded from use for many decades due to some specific issues that later rubber-belted machines were finally able to address.

While construction equipment is traditionally shipped to a worksite on a large trailer, tractors are generally driven from field to field on the road. Track-type machines with metal grousers are slower than pneumatic-tired machines during road transport under their own power. This slower transport speed, combined with a poorer ride for the operator and higher costs, eliminated most traditional track-type tractors from the agricultural market during the 1920s and 1930s. Two revolutionary designs, which are still produced by major manufacturers today, reintroduced the use of tracks on tractors. In 1986, Caterpillar launched the revolutionary rubber track Challenger 65® tractor, shown in **Figure 9** [3]. The Challenger used a two-track running gear system, similar to most construction equipment designs [28]. Shortly thereafter, Case IH introduced an articulated tractor with tracks at each corner of the machine. The Quadtrac®, shown in **Figure 10**, was configured like a traditional fourwheel drive tractor, with each of the contact points supported using a triangular track drive and bogie mechanism [29].

#### **Figure 8.**

*Benjamin Holt testing the first prototype gasoline-powered track-type tractor in 1908 (Caterpillar, Inc., 2021) – [27].*

*Reducing Soil Compaction from Equipment to Enhance Agricultural Sustainability DOI: http://dx.doi.org/10.5772/intechopen.104489*

**Figure 9.** *A 1986 Caterpillar challenger 65® rubber-tracked tractor (TractorData.com, 2016) – [3].*

#### **Figure 10.** *A 1997 Case IH Steiger Quadtrac® tractor (Case IH, 2022) – [28].*

Today, rubber-belted tracks have become so successful that a common argument in the agricultural world is the debate of tracks vs. tires. However, opting for a tracked configuration creates a sizable increase in both purchasing and operating costs for the tractor. The price jump from tires to tracks can often be in the neighborhood of 10–25% of the cost of the machine. The operating costs jump too. As can be seen in **Figure 11**, the specific operational cost difference between tracks and tires for a 358 *kW* tractor is approximately \$0.085/*kWh* [29]. Currently, available data and existing published studies seem to support both sides of the tracks versus tires debate.

**Figure 11.** *Costs of operating tractors on tires and tracks (Case IH, 2022) – [28].*

A 2018 European study involving a comparison of tracks and tires on two identical sugar beet harvesters revealed that the use of tracks does have a positive impact on reducing soil compaction [31]. Stress transducers were placed under the soil to analyze the compaction effects of the tractive devices. The mean ground pressure for the tire undercarriage system was measured to be 107 *kPa*, while the rubber tracks had a mean ground pressure of 84 *kPa*. As shown in **Figure 12**, ground pressure for the tires was also more concentrated, and it was more distributed under the tracks [31].

Because of their larger footprint, rubber tracks are often assumed to have a uniform weight distribution, but this is not true. Multiple design elements in a rubber track system, along with the integration of the track system onto the vehicle's frame, are critical to its effectiveness at reducing soil compaction. Common track systems, as shown in **Figure 13**, are traditionally composed of large driver and end wheels and smaller bogie wheels [29]. Bogie wheels, in theory, help to distribute the half the axle weight across the track's contact surface with the ground. However, in reality, the bogie wheels create ground pressure spikes beneath their relative positions. As can be seen in the right graph of **Figure 12**, the individual soil pressure peaks can be attributed to the bogies and wheels of the tracks evaluated in the study. The ideal

#### **Figure 12.**

*Soil compaction study findings for a beat harvesting machine on tires (left) and the same machine on tracks (right) (Lamandé et al., 2018) – [29].*

*Reducing Soil Compaction from Equipment to Enhance Agricultural Sustainability DOI: http://dx.doi.org/10.5772/intechopen.104489*

**Figure 13.** *Bogie wheel track design (Case IH, 2022) – [28].*

performance of a track can be identified by finding the theoretical applied ground pressure stress. This calculation is performed by dividing the load on the track by its contact area. In the sugar beet harvester study comparing tracks versus tires, the researchers discovered that the peak stress applied to the ground by the tracks was 5.7 times greater than the ideal ground pressure calculated value [31].

An analysis of the soil types across Europe was conducted to evaluate the maximum load capacity of different tractive devices, without causing permanent soil deformation [31]. **Figures 14**–**16** convey this analysis, showing soil types and the respective loads that can be handled by tires, tracks, and ideal tracks having a uniform pressure distribution. It is worth noting that a substantial load bearing increase could be achieved through improved track design.

Regardless of which side of the track versus tires argument is seen as the correct economic option, tracks do serve utility for farmers beyond that of tires. Although farmers prefer to be in the field when conditions are good, the weather does pose challenges. Depending on the geographic location of a farm and its soil type, it is common to deal with wet field conditions. As a result of the need to beat seasonal weather patterns, farmers often push acceptable limits to finish critical tasks in the field. Saturated soils are easier to tackle with tracks, because of their improved tractive performance over tires. Tracks are also less prone to rutting the soil in wet conditions. As seen in **Figure 10**, a side-by-side comparison of a tracked and tired machine shows the improved performance of tracks at staying on top of the soil. As can be seen, the track's footprint barely marks the ground, where the trailing tire cuts a deep rut. Severe soil compaction, like that caused by the tires in **Figure 17**, negatively impacts the health and performance of a farm's soil for the long-term [32]. However, the

#### **Figure 14.**

*European soil load carrying capacity map, showing the maximum load (kN) that can be carried by a 1050/ 50R32 tire without inducing permanent soil deformation at 0.35 m depth (Lamandé et al., 2018) – [29].*

inability to harvest crops negatively impacts the economics and viability of a farm's business today. Although tracks are pricier than tires and may only provide limited benefits toward economically reducing soil compaction, tracks clearly outperform tires in adverse conditions.

#### **4.2 Low inflation tires**

Although the European study concluded that the use of tracks had a positive impact on soil compaction, differing studies have led to opposite conclusions [31]. The argument for tires is that correct maintenance needs to be performed to ensure that the tires are inflated correctly. A common issue is that farmers will over-inflate tires. Studies, like the one highlighted in **Figure 18**, reveal that incorrectly inflated tires create the most compaction [33]. In this specific experiment, correctly inflated dual tires were found to be impressively less compacting to the soil than tracks, while demonstrating that tracks could be superior to poorly maintained dual tires.

Tracks are undeniably an expensive, but great option for reducing soil compaction. However, low-pressure, properly-inflated tires are a potential option to match the benefits of tracks, at a fraction of the price. It is well documented that the depth of soil compaction is strongly correlated with tire pressure. Lower pressures cause less

*Reducing Soil Compaction from Equipment to Enhance Agricultural Sustainability DOI: http://dx.doi.org/10.5772/intechopen.104489*

#### **Figure 15.**

*European soil load carrying capacity map, showing the maximum load (kN) that can be carried by a rubber track without inducing permanent soil deformation at 0.35 m depth (Lamandé et al., 2018) – [29].*

compaction. The limit to this practical method of reducing compaction is that the bead of the driving tires must remain on the rim. This low-pressure tire strategy helps reduce soil compaction by increasing the tire surface contact area with the ground. The increased contact area reduces the pressure exerted on the ground. Due to the limitations of decreasing the air pressure in traditional radial tires, tire companies have developed new flexion technology to allow even lower tire pressures. Increased Flexion (IF) and Very Increased Flexion (VF) tires, first introduced by Michelin during the 2000s, use a mature technology that greatly decreases the soil compaction from today's heavy machinery. The VF and IF tires can support the same loads with 40% and 20% less air pressure than radial tires, respectively by using increased tire sidewall strength [34].

While tires do not have as extensive of a surface area as most track designs, low pressure and Flexion-style tires make-up for some of the ground pressure shortcomings on tired vehicles, and in some applications, they can be a more viable option. Tracked vehicles experience pressure spikes at each bogie, whereas tires can be more consistent in the application of load to the soil [35]. Modern row crop tractors are commonly seen with dual rear tires and even dual front tires. As new equipment becomes larger and larger, single tires are no longer viable. As the demand for Modified Front Wheel Drive (MFWD) tractors has increased, additional weight has been

#### **Figure 16.**

*European soil load carrying capacity map, showing the maximum load (kN) that can be carried by a rubber track with perfectly even stress distribution without inducing permanent soil deformation at 0.35 m depth (Lamandé et al., 2018) – [29].*

added to the machines, requiring further soil compaction reduction methodologies to be undertaken. The most common MFWD tractors variants today have both dual front and rear tires. As would be expected with the addition of a second set of tires, soil compaction is reduced. This is achieved by essentially doubling the contact surface area [36]. The addition of a second set of tires allows for tire pressure to be reduced even further, also decreasing the potential for soil compaction [36]. These strategies can be combined for reasonably additive results. Using Flexion-type dual tires at low tire pressures can achieve even lower soil compaction. Under certain circumstances, properly inflated duals have been shown to be more effective at reducing soil compaction than tracks. Triple tires can be seen in certain high-power applications. However, they are not commonly seen in modern agriculture. The increased width of the tractor would be a benefit in the field, but transport on the road becomes infinitely more challenging. Axle stresses multiply significantly as well.

A recent innovation in agricultural tractor tires involves changing the overall design of the tires and the rim. New Low Side Wall (LSW) tires feature a significantly reduced tire aspect ratio, which results in a wider tire with reduced side walls. These LSW tires are intended to completely replace duals on modern farm equipment. While *Reducing Soil Compaction from Equipment to Enhance Agricultural Sustainability DOI: http://dx.doi.org/10.5772/intechopen.104489*

**Figure 17.** *Rut comparison of tracks vs. tires in muddy conditions (Elmers manufacturing Inc., 2019) – [30].*

#### **Figure 18.**

*Soil compaction comparison study findings (NTS Tire supply team, 2019) – [31].*

these new tires are a more expensive initial investment, including a completely different rim and new tires, they are still cheaper than modern tracked systems. LSW tires could be a viable option for reducing soil compaction, as well as providing other benefits to the operator [37]. Tractors with a high center of gravity and LSW tires can experience reduced sway in motion, as well as better resistance to power hop [37]. LSW tires have a larger width allowing for more surface contact with the soil, as well as retaining the reduced inflation pressures similar to the Flexion-style tires [37].

Tires are typically the more attractive option for most farms, due to lower purchase and operational costs. Since the potential benefit of tracks is only for the reduction of soil compaction, tire systems, which can effectively compete with tracks in this metric, have a competitive advantage. With LSW tires closing the marginal difference in performance between tracks and tires, tires in many standard applications may be the smarter option. However, any option to reduce soil compaction will pay-out in the long run for farmers and growers. Conservation of the world's natural resources is imperative for the continued survival of humanity, especially with the extreme population growth projected for the next fifty years. Producing more food with less resource inputs is the goal of all of agriculture. Conserving the land is the first step toward a better tomorrow that will continue to be able to feed its people from the soil.

#### **4.3 Two versus four wheel drives**

Four-wheel drive vehicles can produce less soil compaction than their two-wheel drive counterparts, assuming all other factors are equal. Four-wheel drive systems also encounter less slip in motion and have a more optimal weight distribution, which likewise helps reduce the soil compaction. Slip can be thought of as a horizontal component of soil compaction. Slip occurs as the soil behind the tire compacts to support the drawbar load. There is a shrinkage in the matrix of the soil [38]. When traveling off-road, all vehicles have some amount of slip. This slip is determined by the interface between the wheels and the ground. The larger the ground contact area, the less slip occurs. Four-wheel drive vehicles have less slip than two-wheel drive vehicles. While two-wheel drive vehicles may have the same number of wheels on the ground, the non-driving wheels do not provide any traction. Tracked vehicles have an advantage as the entire length of the tracks are driven, and therefore, they have reduced slip when compared to tires. Nonetheless, slip sufficient to support the forward travel and drawbar loads on the machine still occurs. The reduction in soil compaction behind four-wheel drive vehicles has been demonstrated experimentally. **Figure 19** shows that the bulk density of soil was found to be 5.6% less than in rear wheel drive and 7.3% less than in front wheel drive vehicles [39].

From a practical perspective, four-wheel drive and two-wheel drive vehicles are built differently. Four-wheel drive vehicles are designed to have a different weight distribution. A rear-wheel drive vehicle has the center of mass at roughly one-third of the wheel base forward of the rear axle. A four-wheel drive vehicle has the center of mass located slightly more forward. This is advantageous, because the tractive force from the wheel depends on the normal force with the ground. Under drawbar load, the front and rear ends of the tractor are supported more equally, and the peak pressure on the ground is lower. Larger wheels have a higher area of contact with the ground, which results in lowered soil compaction. Many four-wheel drive vehicles have an articulated chassis used for steering. An articulated vehicle's axles follow only a single pathway when turning, which also reduces the area of compaction.

Just as certain soils are more prone to soil compaction, some soil types benefit more from four-wheel drive tractors. It is more difficult to gain traction in loose soil. As **Figure 20** shows, the moisture content in the soil plays a significant role in the compaction tendency of the soil [39]. Soils with a greater moisture content typically generate more slip [41]. As discussed earlier, slip is correlated with soil compaction. "Tire travel" will be significantly more in wet soil to cover the same distance.

*Reducing Soil Compaction from Equipment to Enhance Agricultural Sustainability DOI: http://dx.doi.org/10.5772/intechopen.104489*

**Figure 19.**

*Bulk density of soil following a tractor pass with different drive systems (Abu-Hamdeh et al., 1995) – [37].*

**Figure 20.** *Effects of moisture on soil compaction between multiple vehicles (Abu-Hamdeh et al., 1995) – [37].*

#### **4.4 Sensors, actuators, and special applications**

Mechatronic agricultural systems are the future of agricultural machinery. One proposed means to reduce soil compaction is to utilize numerous smaller robotic machines, instead of progressively larger machines, to tend the fields. One limitation to further development along these lines is the price of a fleet of machines, while another is the human management factor. The price will likely come down as the technologies develop, but the human factor will remain stagnant until a "critical mass" of the new equipment enters the agricultural equipment market and demonstrates viability. These modern agricultural mechatronic systems will contain numerous sensors and actuators as their essential elements. Actuators perform the specific tasks directed by the vehicle's controller. Sensors facilitate the feedback from the actuators to the tractor's control system. The feedback data works as a performance measure for the actuators and the control system as whole. Specifically, the control system receives data on the success of the actuators' actions, the vehicle' position and motion, and the vehicle's immediate environment. Driveline control systems with the feedback

mechanisms can successfully address soil compaction problems in many special applications. These automatic control systems have potential for use in the envisioned swarm systems for everyday agricultural operations. A swarm of smaller automated machines could become a disruptive technology, which would shift the paradigm in the current soil compaction reduction practices for crop production systems. The utilization of real-time feedback from soil conditions has multiple previous implementations for experience to be drawn from.

One example is a unique tractor for special climates. The Gidrokhod 49,061 ("Gidro" – hydro "khod" – traveler), shown in **Figure 21**, is "a three-axle all-wheel drive machine with a hydrostatic driveline with an automatic control system" [42], p. 147], which combines an individually driven axle design with a feedback-based approach to vehicle control. The Gidrokhod's driveline operates as follows: "[The] driveline is a full-flow mechanism that includes three axial-plunger controllable reversible and invertible hydraulic pumps and six axial-piston controllable and invertible hydraulic motors. Each pump is associated with two tandem hydraulic motors that set into motion the wheels of one hypothetical axle. The torques and rotational speed of the hydraulic motors are controlled individually by varying the displacements of the pumps and motors by means of an automatic control system" [42], p. 147]. The Gidrokhod's automatic control system supplies the required power to each wheel "as a function of the current conditions of interaction with the soil" [42], p. 147]. Gidrokhod was originally designed to reduce soil compaction from human activity in tundra, where the plants and soil are particularly vulnerable to any soil loading, such as the pressure from tracks or tires. The Gidrokhod's hydrostatic driveline also improves the vehicle's off-road drivability by dampening returned ground shocks into the driveline. The Gidrokhod's hydrostatic driveline is a computercontrollable, tested technology that could be transferred to off-road vehicle applications in agriculture to address the soil compaction problem.

Another example of a special off-road vehicle is a small off-world exploratory rover. These machines closely resemble hypothetical swarm agricultural vehicles and are essentially miniature space tractors. The pace of modern technology suggests that humanity will start colonizing the Moon and Mars by the mid-21st century. The

**Figure 21.** *Gidrokhod 49,061 (Vantsevich & Blundell, 2015) – [39].*
