_Applied_  
_sciences_  
_Article_  
Maximum Admissible Slip of Tractor Wheels without Disturbing the Soil Structure  
[PERSON] 1, [PERSON] 2,*\({}^{\copyright}\), [PERSON] 3\({}^{\copyright}\), [PERSON] 4, [PERSON] 4, [PERSON] 5 and [PERSON] 6  
1 Department of Mechanics, Faculty of Construction and Design, National University of Life and Environmental Sciences of Ukraine, 03041 Kyiv, Ukraine; [EMAIL_ADDRESS]  
2 Institute of Agricultural Machinery, Faculty of Engineering, Latvia University of Life Sciences and Technologies, Cakstes Blvd. 5, LV-3001 Jelgava, Latvia  
3 Department of Agricultural Machinery, -[PERSON]- University of Ruse, Studentska Str. 5, POB 7017 Ruse, Bulgaria; [EMAIL_ADDRESS]  
4 Department of Machine-Using in Agriculture, Dmytro Motornyi Tavira State Agrotechnological University, 18, Khmelnytskyi Ave, 72312 Mitelot, Ukraine; [EMAIL_ADDRESS] (V.N.);  
5 National Scientific Centre, Institute of Mechanization and Electrification of Agriculture, 11 Volkazlna Street, 08631 Kyiv, Ukraine; [EMAIL_ADDRESS]  
6  
Footnote 1: email: [EMAIL_ADDRESS]  
Footnote 2: email: [EMAIL_ADDRESS]  
Footnote 3: email: [EMAIL_ADDRESS]  
Footnote 4: email: [EMAIL_ADDRESS]  
Footnote 5: email: [EMAIL_ADDRESS]  
Footnote 6: email: [EMAIL_ADDRESS]  
Footnote 7: email:  
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creasing the rolling resistance coefficient (Figure 4) and the soil bulk deformation (Figure 5) requires less value of the slip \(\delta_{max}\).
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It should be noted that Figure 4 shows the dependence of the coefficient \(f_{k}\) not on the operating tractor wheels slip but the maximum allowable slip \(\delta_{max}\), which did not lead to a destroyed soil structure and was determined from Equation (1). Indeed, the larger the coefficient \(f_{k}\) was, the lower the strength of the soil was, and the less admissible the tractor wheels slip (\(\delta_{max}\)) could be realized on it.  
Simultaneously, if the first result (Figure 4) is, in principle, logical, then the second one (Figure 5) is not. The reason for this disagreement is the interrelationship between the coefficients \(k_{o}\) and \(f_{k}\). The analysis of the Equation (1) and the research results of other authors  
Experimental studies showed that, when the wheels of the HTZ-17021 tractor slipped 12.2% (plowing depth 0.26 m), the coefficient of soil structure \(k_{s}\) was equal to 0.51 (Figure 7). This was slightly less than the original value \(k_{sin}\) but more than the minimum acceptable \(k_{min}\).  
Simultaneously, when the tractor wheels slipped 19.6% (plowing depth 0.29 m), the soil structure coefficient decreased to 0.37. This meant that soil structure deteriorated and passed into the category of unsatisfactory.  
The soil quality became even worse when the tractor wheels slipped at 23.9% (plowing depth 0.32 m). In this case, agronomically valuable soil particles in the HTZ-17021 track were no more than 21% (see Figure 7).  
Hence, it follows that, to preserve the soil structure, the tractor wheels' slip should be strictly limited to the value determined from equation (1). For the soil conditions described in this work, the value of \(\delta_{max}\) should not exceed 15%.