ارزیابی اثر عبور متعدد چرخ بر تراکم و فشردگی خاک‌های کشاورزی در انباره خاک

Agricultural soil compaction is a destructive phenomenon, which is mostly attributed to the passage of agricultural machines during agricultural operations. In this research, the effect of wheel passage on the soil has been investigated in terms of density and stress in the soil. Tests have been designed and implemented using a single-wheel tester in the soil bin environment, which includes three independent variables of load on the wheel, forward velocity, and the number of wheel passages, in the number of levels 3, 3, and 25 levels, respectively. Stress measurement in the soil depth indicates the creation of a variable stress bell wave in the soil, which reaches its maximum value when the wheel travels on the stress transducer and then undergoes a sudden decrease. The stress changes in the first to fifth passes have caused the most changes, and in the upper passes, with the stabilization of the soil layer, the stress changes have decreased. Increasing the load on the wheel in any case leads to an increase in soil stress and density, and this change has appeared in the number of initial passes more than the passes above 10.
Nowadays, soil – tire interaction from the point of view of soil management and product production is of great interest, and efforts are being made to design and prepare tools and methods for dealing with soil in such a way that as much as possible, the destructive effects of soil and also the waste of energy that It includes economic and environmental limitations and should be prevented.
The research conducted by the researchers has shown that about 20-50% of the energy of the driving wheels is lost in the interaction between the wheel and the soil. Repeating wheel passes on the soil causes compaction in the soil, which, of course, has a non-linear relationship with the number of wheel passes. The speed of the machine on the soil is also considered to be involved in the amount of soil compaction by some researches.
Experiments have been designed and implemented to investigate the compaction effect of the wheel on the soil. This research was carried out using a single-wheel tester using the soil bin of the Terramechanics laboratory of the Department of Mechanical Engineering of Biosystems, Urmia University.
The research was conducted with the aim of investigating the effect of the number of wheel passes in three parameters of speed, load and number of passes on soil density and stress in wheel-soil interaction. Based on this, the test data were taken in two separate phases related to soft surface (soil) and rigid surface. In addition, the effect of these three variables on soil compaction was also investigated. The four-arm type single-wheel tester with the ability to apply vertical load and the tire used in this research is a standard tire with specifications Barez 8.25-16.
The experiments were performed with three levels of 2, 3 and 4 kN load on the wheel and three levels of forward speed of 0.5, 1 and 1.5 m/s. In order to separate the test plots and apply load and speed in separate traffic, indicator lines were implemented across the channel in the form of longitudinal and transverse division of the channel. By moving the wheel tester transversely, traffic was carried out on the indicated lines. 25 repeated passes of the wheel were made on each path and the amount of stress was measured at a depth of 10 cm from the soil surface by stress gauges buried in the soil.
After preparing the soil, the tests were performed at three levels of wheel speed, three levels of load on the wheel and in the number of 25 consecutive passes. By using stress gauges that were buried 20 cm from the soil depth, changes in soil stress were obtained according to changes in input parameters (load, speed and traffic).
Since the stress transducers displayed the amount of stress in the soil as a point, with the movement of the wheel on the soil surface, the stress changes were constant and when the wheel passed the place where the stress transducer was below was buried, the amount of stress in the soil at that point could be obtained through the data logger. In an overview, as the wheel approaches the stress transducer, the amount of stress in the soil starts to increase suddenly and decreases after passing. In the obtained results, the effect of traffic parameters, load and advancing speed on soil compaction and stress was investigated. Since the relative importance of wheel load and speed of progress during agricultural operations on the compression of the lower and upper layers of the soil has always been discussed, the investigation of soil stress through the factor of wheel traffic frequency was one of the goals of this research. During these tests, with the aim of determining the maximum amount of stress in the lower layers of the soil, soil pressure was measured at different load levels and speeds and the measured values were compared. Soil stress was measured at a depth of 20 cm from the soil using designed sensors. The amount of stress was the highest at low speed due to the maximum contact between the wheel and the soil, and with increasing load, it was much higher, which was consistent with the results of other researches.
Based on the results obtained in the first load level, the stress created in the soil has the highest value for the low speed and the lowest value for the third level speed. The reason for this can be explained by increasing the speed, the wheel does not have enough time to exert pressure on the soil. As in the lower speed, due to sufficient time and the maximum contact surface of the tire and the soil, the soil stress value has reached its maximum value. With the increase of one level of load, the value of the soil stress related to the first speed level has again the highest value, while the stress created for two levels of speed (1 and 1.5 m/s) has approximately been the same. By increasing the load to the third level (4 kN), this time the soil stress value related to the second speed level is the highest and the soil stress value related to the first speed is the lowest value. By increasing the speed to the third level again, due to the insufficient time in contact between the wheel and the soil, the amount of soil stress was reduced.