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Compaction characteristics of towed wheels on clay loam in a soil bin
Soil & Tillage Research 65 (2002) 37±43
Compaction characteristics of towed wheels on clay loam in a soil bin K. CËarman Faculty of Agriculture, Department of Agricultural Machinery, University of SelcËuk, 42031 Konya, Turkey Received 16 November 2000; received in revised form 2 October 2001; accepted 9 October 2001
Abstract Wheel induced soil compaction is an ongoing concern in mechanized agriculture. This experimental study was performed with the aim to evaluate whether soil compaction is related to stresses induced by towed wheels. Soil bin studies were conducted and soil compaction variables were measured under two towed tires, with different tread patterns, commonly used in Turkey. Tests were carried out at three tire loads (3.5, 5.5 and 7.5 kN) and two forward velocities (0.8 and 1.4 m/s) on a clay loam. To determine soil compaction, surface sinkage, subsurface layer deformation, compaction index, penetration resistance and bulk density were measured. With increasing vertical load, average contact pressure of tires increased from 39.3 to 68.5 kPa. In different trials, surface sinkage, compaction index, penetration resistance and bulk density varied from 46 to 86 mm, 0.18 to 0.48, 1472 to 2530 kPa and 1.31 to 1.70 Mg m 3, respectively. The soil contact projected area of tire 2 was approximately 10% greater than tire 1. The greater contact surface reduced the compaction at the soil surface and subsurface, but the tire load was still the dominant factor in the 0±20 cm depth range used in this study. According to the experimental results, decreasing contact duration with increasing forward velocity decreased soil compaction. Tire load and type affected soil deformation characteristics stronger than forward velocity. # 2002 Elsevier Science B.V. All rights reserved. Keywords: Towed wheel; Rolling resistance; Sinkage; Compaction index
1. Introduction Soil compaction is a volumetric strain or the packing of soil particles to a dense state as a result of applied load. Previous research has shown that the compactive capability of a running device is a function of amount, rate, form and duration of applied compressive stress to the soil and the change in soil physical and mechanical properties (Barnes et al., 1984; Abebe et al., 1989). Agricultural ®eld operations employed in various levels of mechanization are heavily dependent on
E-mail address: [email protected] (K. CËarman).
wheel tractors as a source of traction power. It is common practice to use the same tractor for different operational requirements. Hence the soil with different load bearing capacity is exposed to repeated compressive stress of the same magnitude. This results in the formation of a dense layer within the soil mass which has low hydraulic conductivity and aeration (Rickman and Chanasyh, 1988; Barone, 1990). Thirty years ago, most of the soil compaction from wheel traf®c was in the plow layer and was removed by normal cultural practices. Today, increased machine size and the need for timely ®eld operations have led agricultural producers to express concern about the effects of excessive soil compaction induced
0167-1987/02/$ ± see front matter # 2002 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 7 - 1 9 8 7 ( 0 1 ) 0 0 2 8 1 - 1
38
K. CËarman / Soil & Tillage Research 65 (2002) 37±43
which towed tires included the determination of compacted characteristics. Therefore, the primary objective of this study was to examine effects of vertical load, forward velocity and tire type, which has two different tread patterns on rolling resistance, surface sinkage, subsurface layer deformation, compaction index, penetration resistance and bulk density in a soil bin.
by wheel traf®c. Wheel induced compaction may affect soil in all horizons, but this is especially true for topsoil where there is direct interaction between wheel and soil surface. The detrimental effects of soil compaction on crop growth include reduced seed emergence and root extension, limited water and nutrient uptake. Annual yield losses were estimated to be over a billion dollars ($ US) in Turkey (CËarman et al., 1992). Therefore, a better understanding of the mechanics of wheel induced soil compaction is needed to identify the cause and the effects of the compaction in order to improve management decisions for production agriculture (Barnes et al., 1984; Rusanov, 1991; CËarman, 1994). An increase in vehicle velocity on a soft soil with high porosity causes reduced soil compaction (Bolling, 1986). Therefore, seedbed preparation should be done at high velocities to reduce soil compaction (CËarman, 1992). The maximum wheel sinkage is the result of the balance between the wheel load and the vertical reaction force of the soil. The sinkage decreases with increasing velocity. The contact projected area of the wheel decreases with increasing velocity and therefore the maximum pressure increases (Grahn, 1991). Vehicular compaction can be minimized in a number of ways which include the following: a careful selection of the equipment on the basis of equipment weight and type of tires, optimizing the speed of operating the equipment, and a timely utilization of the equipment to take advantage of desirable ®eld conditions (Adebiyi et al., 1991). Approximately 50% of the soil in Turkey has a clay loam texture and is low in organic matter. Because of this situation, it tends to easily compact. An estimated 98% of ®elds for wheat (Triticum aestivum L.) production and 270% of ®eld for corn (Zea mays L.) production are traf®cked (CËarman et al., 1992). Hence the control of working depth in tillage needs to be studied. Very few published articles were found in
2. Materials and methods This study was conducted in a soil bin at the Department of Agricultural Machinery, Agricultural Faculty, SelcËuk University, Turkey using a single wheel tire test machine. The soil bin used in these tests was 20 m long, 2.25 m wide and 0.8 m deep. The soil bin facilities, constructed for testing of agricultural implement and tires, have been described in detail by Kural (1998). The towed wheel was suspended using slide bearings to give vertical freedom of motion. In order to load the pneumatic tire in the soil bin, impression spring and in®nite screw equipment were used. Both tires used in the study were 7.50±16, radial± ply tires. The lug height and total lug area of tire which two factors determined the pressure transmitted to the soil are different dimensions for both tires. The in¯ation pressure of both tires was 200 kPa. Some properties are given in Table 1. The single wheel tire test machine was operated at different vertical loads and forward velocities. Wheel slip was measured as 3.76±5.24%. Each of the test tires was operated at vertical loads of 3.5, 5.5 and 7.5 kN, and at a forward velocities of 0.8 and 1.4 m/s. The effect of velocity, load and type of tire on the depending variables were investigated. In the statistical analyses, three factors of design of ANOVA were used (Larsen and Marx, 1981).
Table 1 Properties of the tires used in the study Tire's mark
Pirelli (tire 1) Lassa (tire 2)
Tread pattern
TD27 TR55
Lug height (mm)
Width (mm)
15 3
190.5 190.5
Ply rating
6 8
Total lug area (%) 23 100
Projected area on concrete (cm2) 3.5 kN
5.5 kN
7.5 kN
78 122
142 207
180 225
K. CËarman / Soil & Tillage Research 65 (2002) 37±43 Table 2 Initial condition of the clay loam used in the soil bin study Parameter
Mean value
Particle size distribution Sand (0.05±2.0 mm) Silt (0.002±0.05 mm) Clay (<0.002 mm) Moisture content Specific gravity Plastic limit Liquid limit Bulk density Cohesion Angle of internal friction Penetration resistance
360 g kg 1 240 g kg 1 400 g kg 1 124 g kg 1 2.63 Mg m 35.02% 28.5% 1.21 Mg m 6.50 kPa 31.858 1170 kPa
3
3
The soil bin was ®lled with a 0.5 m thick layer of clay loam. Physical and mechanical properties of the soil are as shown in Table 2. Before each trial, the soil with 12.4 g (100 g) 1 water content was loosened with a 30 cm deep working cultivator and afterwards processed with a rotary tiller in the top layer of 20 cm. The surface was leveled with a light roller. 2.1. Determination of contact area and pressure To determine the contact projected area of the tire in the soil bin, the wheel mounted on the test machine, was placed on the undisturbed ground during several seconds for three different loads. Then, the test tire was removed, and the observed projection of the line bordering the contact area was drawn on the transparent paper and measured by planimeter (Schwanghart, 1991; CËarman, 1996). The average contact pressure was calculated by the ratio of tire load to contact projected area. 2.2. Determination of rolling resistance of tire In order to determine the rolling resistance of the tires, a load cell was used to measure the tension force during working of a chain drive for the front and rear movements of test machine. 2.3. Determination of surface sinkage, layer deformation and compaction index The surface sinkage of test tires was measured using a pro®lemeter. This consisted of a set of vertical metal
39
rods, spaced at 2.5 cm intervals, sliding through a 100 cm long steel tube. The tube was placed across the wheel tracks perpendicular to the direction of travel and the rods were allowed to fall to conform to the shape of the depression (Davies et al., 1973; CËarman, 1994). Subsurface layer deformation of the soil was determined by an image processing technique. Plastic rods of different colors were buried in a horizontal plane to the right and left of the wheel track axis at three different soil depths (7, 14 and 21 cm) at 7 cm depth intervals. After passage of the wheel, a hole was dug and a photograph was taken of the rods. The coordinates of the rods were obtained using a Global Lab Image programme. For each range of depth, mean of displacement values in the vertical axis of rods was calculated (Kural, 1998). The intensity of soil compaction was expressed in terms of the compaction index which is an indicative coef®cient of soil under compactive stress. The degree of soil compaction was estimated by analyzing the displacement of rod planes below the center of the wheels. The area of the elemental rod planes at three different depth ranges was computed before and after the passage of the wheel in order to derive the area of compaction and the corresponding volumetric change. It was derived from the ratio of the volume absorbed after compaction of the soil to the initial volume (Abebe et al., 1989). 2.4. Determination of penetration resistance A soil penetrometer, with a cone angle of 308 and cone diameter of 12.83 mm, was used to determine soil penetration resistance. It was pushed by hand into the soil to a depth of 20 cm and penetrometer resistance for each 1 cm depth interval was drawn on paper. The values obtained at depth range of 20 cm were used as a mean of penetration resistance (CËarman, 1996; Yildiz and CËarman, 1998). 2.5. Determination of bulk density, cohesion and angle of internal friction In order to determine soil bulk density, soil cores were collected using stainless steel rings with a cutting edge (40 mm diameter, 40 mm length) at a depth range of 0±10 and 10±20 cm beneath the centerline of the
40
K. CËarman / Soil & Tillage Research 65 (2002) 37±43
wheel tracks. Each core was dried to constant weight at 105 8C and bulk density was calculated by the ratio of oven dry mass of soil to ring volume (50 cm3). The values obtained at the two different depth ranges were used as a mean of bulk density (Black, 1965). To determine the cohesion and the angle of internal friction of the soil, the direct shear box were used which composed of two metal rings, having circular opening (Mckyes, 1985). 3. Results and discussion
Fig. 2. Effect of vertical load on rolling resistance. (&) Tire 1, 0.8 m/s; (*) tire 2, 0.8 m/s; (&) tire 1, 1.4 m/s; (*) tire 2, 1.4 m/s.
3.1. Contact area and contact pressure
3.2. Rolling resistance
Fig. 1 shows that the contact projected area of the tested agricultural tires on the soil in the soil bin increased with greater load. Although both tested tires were the same size, the contact projected areas were very different in constant load. The soil contact projected area of tire 2 was approximately 10% greater than tire 1. The contact projected area for all tests was in the range 813±1120 cm2. Approximately, to double the vertical load resulted in an area increase of 29± 35%. Fig. 1 showed the average contact pressure. It increased nearly linearly with increase in vertical load.
Fig. 2 indicates the motion resistance of the soil to the tested tires measured by applying vertical loads of 3.5, 5.5 and 7.5 kN. As shown by Bekker (1969) and Abebe et al. (1989), it was found that the rolling resistance of the pneumatic wheel had a relation to the compaction level of the soil. According to the test results, the greater load and the less forward velocity tests showed higher values of rolling resistance. For tire 1, resistance was found to be greater than tire 2. The effects of tire type and vertical load on the rolling resistance were signi®cant P < 0:01. The greatest rolling resistance occurred at vertical load of 7.5 kN and forward velocity of 0.8 m/s under tire 1. 3.3. Surface sinkage, layer deformation and compaction index The relation between surface sinkage and vertical load was affected by tire type and forward velocity (Fig. 3). The rut or surface sinkage formed by the
Fig. 1. Effect of vertical load on contact projected area and pressure. (&) Tire 1; (*) tire 2.
Fig. 3. Effect of vertical load on sinkage. (&) Tire 1, 0.8 m/s; (*) tire 2, 0.8 m/s; (&) tire 1, 1.4 m/s; (*) tire 2, 1.4 m/s.
K. CËarman / Soil & Tillage Research 65 (2002) 37±43
Fig. 4. The relation of layer deformation with depth at forward velocity of 0.8 m/s (a) and 1.4 m/s (b). (&) Tire 1, 7.5 kN; (^) tire 1, 5.5 kN; (*) tire 1, 3.5 kN; (&) tire 2, 7.5 kN; (^) tire 2, 5.5 kN; (*) tire 2, 3.5 kN.
pneumatic wheels indicated the apparent soil compaction or the volume lost during compression. Approximately, to double the vertical load resulted in an sinkage increase of 61%, whereas almost twice the velocity caused a 6% decrease of the sinkage. The effects of tire type and vertical load on surface deformation were signi®cant P < 0:01. Test results con®rmed that the sinkage for vertical load of 7.5 kN and forward velocity of 0.8 m/s under tire 1 was greater than the sinkage caused by the other trials. Fig. 4 shows subsurface layer deformation as related to vertical load at depths of 7, 14 and 21 cm. The compacted zone most signi®cantly affected by load was found to be about 70±140 mm below the wheel base and the effect of load on layer deformation decreased with depth. In Fig. 5, the compaction index was in the range 0.18±0.48. The greatest compaction index was found at a depth of 70 mm at a vertical load of 7.5 kN and forward velocity of 0.8 m/s under tire 1, which had less contact projected area. When the effect of depths of 14 and 21 cm on compaction index in trials were considered, a similar trend of intensity of compaction was observed.
41
Fig. 5. The effect of vertical load on compaction index at forward velocity of 0.8 m/s (a) and 1.4 m/s (b). (&) Tire 1, 7 cm; (^) tire 1, 14 cm; (*) tire 1, 21 cm; (&) tire 2, 7 cm; (^) tire 2, 14 cm; (*) tire 2, 21 cm.
3.4. Penetration resistance Penetration resistance of soil increased with increasing tire load but the penetration resistance decreased with increasing forward velocity (Fig. 6). The penetration resistance at depth of 20 cm of the soil at different trials varied from 1472 to 2530 kPa. The effects of tire type and vertical load on penetration resistance were signi®cant P < 0:01. The greatest changes in penetration resistance occurred at a vertical load of 7.5 kN and forward velocity of 0.8 m/s under
Fig. 6. Effect of vertical load on penetration resistance at depth of 20 cm. (&) Tire 1, 0.8 m/s; (*) tire 2, 0.8 m/s; (&) tire 1, 1.4 m/s; (*) tire 2, 1.4 m/s.
42
K. CËarman / Soil & Tillage Research 65 (2002) 37±43
Fig. 7. Effect of vertical load on bulk density. (&) Tire 1, 0.8 m/s; (*) tire 2, 0.8 m/s; (&) tire 1, 1.4 m/s; (*) tire 2, 1.4 m/s.
tire 1. For this trial, the penetration resistance increased about 116% compared with the initial condition. 3.5. Bulk density The bulk density of the soil at a depth of 0±10 and 10± 20 cm below the tire track increased with increasing vertical load and decreased with increasing forward velocity (Fig. 7). The bulk density of the soil in different trials varied from 1.31 to 1.70 Mg m 3. The effects of tire type, vertical load and forward velocity on the bulk density were signi®cant P < 0:01. As expected, the greatest bulk density was observed at a vertical load of 7.5 kN and forward velocity of 0.8 m/s with tire 1. For this trial, the bulk density increased about 40% compared with the initial condition. For an increase of approximately 100% in tire load, bulk density increased about 23%. The effect of forward velocity on bulk density was signi®cant, and the difference between bulk density values as for different values of forward velocity was found to be about 3.9%. 4. Conclusions The following conclusions can be drawn from the soil bin experiments designed to study the interrelationships between an applied load, the forward velocity, tire type and the resulting soil deformation characteristics after the passage of a wheel: 1. Surface and subsurface soil deformation characteristics which were taken as indicative values of soil compactibility strongly indicated that the greatest compaction occurred at a vertical load of 7.5 kN and forward velocity of 0.8 m/s with tire 1.
2. Vertical load was the major contributory factor on soil compaction as compared to tire type and forward velocity. 3. The contact projected area for tire 2 was approximately 10% greater than for tire 1 and the compaction at the soil surface and subsurface was correspondingly less than that for tire 1. 4. Spreading the applied load over the larger contact projected area of tire 2 which has greater total lug area and less lug height, reduced soil unit pressure at the surface. 5. Soil was compacted more at the lower forward velocity because of increasing contact duration. 6. Subsurface layer deformation and compaction index decreased with increasing depth.
References Abebe, A.T., Tanaka, T., Yamazaki, M., 1989. Soil compaction by multiple passes of rigid wheel relevant for optimization of traf®c. J. Terramechanics 26, 139±148. Adebiyi, O.A., Koike, M., Konaka, T., Yuzawa, S., Kuroishi, I., 1991. Compaction characteristics for the towed and driven conditions of a wheel operating in an agricultural soil. J. Terramechanics 28, 371±382. Barnes, K.K., Taylor, H.M., Throckmorton, R.I., Vanderberg, G.E., Carleton, W.M., 1984. Compaction of Agricultural Soils. ASAE, St. Joseph, MI. Barone, L., 1990. Wheel traf®c effect on soil compaction. In: Proceedings of the International Symposium on Mechanisation and Energy in Agriculture, Adana, Turkey, pp. 159±165. Bekker, M.G., 1969. Introduction to TerrainÐVehicle Systems. The University of Michigan Press, Michigan. Black, C.A., 1965. Methods of Soil Analysis, Part I. American Society of Agronomy, Madison, WI. Bolling, I.H., 1986. How to predict soil compaction from agricultural tires. J. Terramechanics 22, 205±223. CËarman, K., 1992. The investigation of effect on compaction of contact time in tire±soil interface. J. Agric. Faculty, University of SelcËuk 2 (4), 49±58 (in Turkish). CËarman, K., 1994. Tractor forward velocity and tire load effects on soil compaction. J. Terramechanics 31, 11±20. CËarman, K., 1996. Prediction of penetration resistance, sinkage and bulk density in soil±tire interaction. In: Proceedings of the International Symposium on Mechanisation and Energy in Agriculture, Ankara, Turkey, pp. 417±423. CËarman, K., Ogut, H., Peker, A., 1992. The investigation of ®eld traf®c for some agricultural crops produced in Altinova Farm. J. Agric. Faculty, University of SelcËuk 2 (4), 79±85 (in Turkish). Davies, D.B., Finney, J.B., Richardson, S.J., 1973. Relative effects of tractor weight and wheel-slip in causing soil compaction. J. Soil Sci. 24, 399±409.
K. CËarman / Soil & Tillage Research 65 (2002) 37±43 Grahn, M., 1991. Prediction of sinkage and rolling resistance for off the road vehicles considering penetration velocity. J. Terramechanics 28, 339±347. Kural, H., 1998. The rolling resistance of 7.50±16 free-rolling tires used in agricultural machinery and their effects on soil compaction. D.Sc. Thesis. Graduate School of Natural and Applied Sciences of SelcËuk University, Konya, Turkey (in Turkish). Larsen, R.J., Marx, M.L., 1981. An Introduction to Mathematical Statistics and its Applications. Prentice-Hall, Englewood Cliffs, NJ. Mckyes, E., 1985. Soil Cutting and Tillage. Elsevier, Amsterdam, the Netherlands.
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Rickman, J.F., Chanasyh, D.S., 1988. Traction effects on soil compaction. In: Proceedings of the Conference on Agricultural Engineering, Hawkesbury Agricultural College, pp. 103± 108. Rusanov, V.A., 1991. Effects of wheel and track traf®c on the soil and on crop growth and yield. Soil Till. Res. 19, 131±143. Schwanghart, H., 1991. Measurement of contact area, contact pressure and compaction under tires in soft soil. J. Terramechanics 28, 309±318. Yildiz, U., CËarman, K., 1998. Effects of some working characteristics on soil compaction of 7.00±18 radial tire size. In: Proceedings of the National Symposium on Mechanisation in Agriculture, TekirdagÏ, Turkey, pp. 355±361 (in Turkish).
Compaction characteristics of towed wheels on clay loam in a soil bin K. CËarman Faculty of Agriculture, Department of Agricultural Machinery, University of SelcËuk, 42031 Konya, Turkey Received 16 November 2000; received in revised form 2 October 2001; accepted 9 October 2001
Abstract Wheel induced soil compaction is an ongoing concern in mechanized agriculture. This experimental study was performed with the aim to evaluate whether soil compaction is related to stresses induced by towed wheels. Soil bin studies were conducted and soil compaction variables were measured under two towed tires, with different tread patterns, commonly used in Turkey. Tests were carried out at three tire loads (3.5, 5.5 and 7.5 kN) and two forward velocities (0.8 and 1.4 m/s) on a clay loam. To determine soil compaction, surface sinkage, subsurface layer deformation, compaction index, penetration resistance and bulk density were measured. With increasing vertical load, average contact pressure of tires increased from 39.3 to 68.5 kPa. In different trials, surface sinkage, compaction index, penetration resistance and bulk density varied from 46 to 86 mm, 0.18 to 0.48, 1472 to 2530 kPa and 1.31 to 1.70 Mg m 3, respectively. The soil contact projected area of tire 2 was approximately 10% greater than tire 1. The greater contact surface reduced the compaction at the soil surface and subsurface, but the tire load was still the dominant factor in the 0±20 cm depth range used in this study. According to the experimental results, decreasing contact duration with increasing forward velocity decreased soil compaction. Tire load and type affected soil deformation characteristics stronger than forward velocity. # 2002 Elsevier Science B.V. All rights reserved. Keywords: Towed wheel; Rolling resistance; Sinkage; Compaction index
1. Introduction Soil compaction is a volumetric strain or the packing of soil particles to a dense state as a result of applied load. Previous research has shown that the compactive capability of a running device is a function of amount, rate, form and duration of applied compressive stress to the soil and the change in soil physical and mechanical properties (Barnes et al., 1984; Abebe et al., 1989). Agricultural ®eld operations employed in various levels of mechanization are heavily dependent on
E-mail address: [email protected] (K. CËarman).
wheel tractors as a source of traction power. It is common practice to use the same tractor for different operational requirements. Hence the soil with different load bearing capacity is exposed to repeated compressive stress of the same magnitude. This results in the formation of a dense layer within the soil mass which has low hydraulic conductivity and aeration (Rickman and Chanasyh, 1988; Barone, 1990). Thirty years ago, most of the soil compaction from wheel traf®c was in the plow layer and was removed by normal cultural practices. Today, increased machine size and the need for timely ®eld operations have led agricultural producers to express concern about the effects of excessive soil compaction induced
0167-1987/02/$ ± see front matter # 2002 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 7 - 1 9 8 7 ( 0 1 ) 0 0 2 8 1 - 1
38
K. CËarman / Soil & Tillage Research 65 (2002) 37±43
which towed tires included the determination of compacted characteristics. Therefore, the primary objective of this study was to examine effects of vertical load, forward velocity and tire type, which has two different tread patterns on rolling resistance, surface sinkage, subsurface layer deformation, compaction index, penetration resistance and bulk density in a soil bin.
by wheel traf®c. Wheel induced compaction may affect soil in all horizons, but this is especially true for topsoil where there is direct interaction between wheel and soil surface. The detrimental effects of soil compaction on crop growth include reduced seed emergence and root extension, limited water and nutrient uptake. Annual yield losses were estimated to be over a billion dollars ($ US) in Turkey (CËarman et al., 1992). Therefore, a better understanding of the mechanics of wheel induced soil compaction is needed to identify the cause and the effects of the compaction in order to improve management decisions for production agriculture (Barnes et al., 1984; Rusanov, 1991; CËarman, 1994). An increase in vehicle velocity on a soft soil with high porosity causes reduced soil compaction (Bolling, 1986). Therefore, seedbed preparation should be done at high velocities to reduce soil compaction (CËarman, 1992). The maximum wheel sinkage is the result of the balance between the wheel load and the vertical reaction force of the soil. The sinkage decreases with increasing velocity. The contact projected area of the wheel decreases with increasing velocity and therefore the maximum pressure increases (Grahn, 1991). Vehicular compaction can be minimized in a number of ways which include the following: a careful selection of the equipment on the basis of equipment weight and type of tires, optimizing the speed of operating the equipment, and a timely utilization of the equipment to take advantage of desirable ®eld conditions (Adebiyi et al., 1991). Approximately 50% of the soil in Turkey has a clay loam texture and is low in organic matter. Because of this situation, it tends to easily compact. An estimated 98% of ®elds for wheat (Triticum aestivum L.) production and 270% of ®eld for corn (Zea mays L.) production are traf®cked (CËarman et al., 1992). Hence the control of working depth in tillage needs to be studied. Very few published articles were found in
2. Materials and methods This study was conducted in a soil bin at the Department of Agricultural Machinery, Agricultural Faculty, SelcËuk University, Turkey using a single wheel tire test machine. The soil bin used in these tests was 20 m long, 2.25 m wide and 0.8 m deep. The soil bin facilities, constructed for testing of agricultural implement and tires, have been described in detail by Kural (1998). The towed wheel was suspended using slide bearings to give vertical freedom of motion. In order to load the pneumatic tire in the soil bin, impression spring and in®nite screw equipment were used. Both tires used in the study were 7.50±16, radial± ply tires. The lug height and total lug area of tire which two factors determined the pressure transmitted to the soil are different dimensions for both tires. The in¯ation pressure of both tires was 200 kPa. Some properties are given in Table 1. The single wheel tire test machine was operated at different vertical loads and forward velocities. Wheel slip was measured as 3.76±5.24%. Each of the test tires was operated at vertical loads of 3.5, 5.5 and 7.5 kN, and at a forward velocities of 0.8 and 1.4 m/s. The effect of velocity, load and type of tire on the depending variables were investigated. In the statistical analyses, three factors of design of ANOVA were used (Larsen and Marx, 1981).
Table 1 Properties of the tires used in the study Tire's mark
Pirelli (tire 1) Lassa (tire 2)
Tread pattern
TD27 TR55
Lug height (mm)
Width (mm)
15 3
190.5 190.5
Ply rating
6 8
Total lug area (%) 23 100
Projected area on concrete (cm2) 3.5 kN
5.5 kN
7.5 kN
78 122
142 207
180 225
K. CËarman / Soil & Tillage Research 65 (2002) 37±43 Table 2 Initial condition of the clay loam used in the soil bin study Parameter
Mean value
Particle size distribution Sand (0.05±2.0 mm) Silt (0.002±0.05 mm) Clay (<0.002 mm) Moisture content Specific gravity Plastic limit Liquid limit Bulk density Cohesion Angle of internal friction Penetration resistance
360 g kg 1 240 g kg 1 400 g kg 1 124 g kg 1 2.63 Mg m 35.02% 28.5% 1.21 Mg m 6.50 kPa 31.858 1170 kPa
3
3
The soil bin was ®lled with a 0.5 m thick layer of clay loam. Physical and mechanical properties of the soil are as shown in Table 2. Before each trial, the soil with 12.4 g (100 g) 1 water content was loosened with a 30 cm deep working cultivator and afterwards processed with a rotary tiller in the top layer of 20 cm. The surface was leveled with a light roller. 2.1. Determination of contact area and pressure To determine the contact projected area of the tire in the soil bin, the wheel mounted on the test machine, was placed on the undisturbed ground during several seconds for three different loads. Then, the test tire was removed, and the observed projection of the line bordering the contact area was drawn on the transparent paper and measured by planimeter (Schwanghart, 1991; CËarman, 1996). The average contact pressure was calculated by the ratio of tire load to contact projected area. 2.2. Determination of rolling resistance of tire In order to determine the rolling resistance of the tires, a load cell was used to measure the tension force during working of a chain drive for the front and rear movements of test machine. 2.3. Determination of surface sinkage, layer deformation and compaction index The surface sinkage of test tires was measured using a pro®lemeter. This consisted of a set of vertical metal
39
rods, spaced at 2.5 cm intervals, sliding through a 100 cm long steel tube. The tube was placed across the wheel tracks perpendicular to the direction of travel and the rods were allowed to fall to conform to the shape of the depression (Davies et al., 1973; CËarman, 1994). Subsurface layer deformation of the soil was determined by an image processing technique. Plastic rods of different colors were buried in a horizontal plane to the right and left of the wheel track axis at three different soil depths (7, 14 and 21 cm) at 7 cm depth intervals. After passage of the wheel, a hole was dug and a photograph was taken of the rods. The coordinates of the rods were obtained using a Global Lab Image programme. For each range of depth, mean of displacement values in the vertical axis of rods was calculated (Kural, 1998). The intensity of soil compaction was expressed in terms of the compaction index which is an indicative coef®cient of soil under compactive stress. The degree of soil compaction was estimated by analyzing the displacement of rod planes below the center of the wheels. The area of the elemental rod planes at three different depth ranges was computed before and after the passage of the wheel in order to derive the area of compaction and the corresponding volumetric change. It was derived from the ratio of the volume absorbed after compaction of the soil to the initial volume (Abebe et al., 1989). 2.4. Determination of penetration resistance A soil penetrometer, with a cone angle of 308 and cone diameter of 12.83 mm, was used to determine soil penetration resistance. It was pushed by hand into the soil to a depth of 20 cm and penetrometer resistance for each 1 cm depth interval was drawn on paper. The values obtained at depth range of 20 cm were used as a mean of penetration resistance (CËarman, 1996; Yildiz and CËarman, 1998). 2.5. Determination of bulk density, cohesion and angle of internal friction In order to determine soil bulk density, soil cores were collected using stainless steel rings with a cutting edge (40 mm diameter, 40 mm length) at a depth range of 0±10 and 10±20 cm beneath the centerline of the
40
K. CËarman / Soil & Tillage Research 65 (2002) 37±43
wheel tracks. Each core was dried to constant weight at 105 8C and bulk density was calculated by the ratio of oven dry mass of soil to ring volume (50 cm3). The values obtained at the two different depth ranges were used as a mean of bulk density (Black, 1965). To determine the cohesion and the angle of internal friction of the soil, the direct shear box were used which composed of two metal rings, having circular opening (Mckyes, 1985). 3. Results and discussion
Fig. 2. Effect of vertical load on rolling resistance. (&) Tire 1, 0.8 m/s; (*) tire 2, 0.8 m/s; (&) tire 1, 1.4 m/s; (*) tire 2, 1.4 m/s.
3.1. Contact area and contact pressure
3.2. Rolling resistance
Fig. 1 shows that the contact projected area of the tested agricultural tires on the soil in the soil bin increased with greater load. Although both tested tires were the same size, the contact projected areas were very different in constant load. The soil contact projected area of tire 2 was approximately 10% greater than tire 1. The contact projected area for all tests was in the range 813±1120 cm2. Approximately, to double the vertical load resulted in an area increase of 29± 35%. Fig. 1 showed the average contact pressure. It increased nearly linearly with increase in vertical load.
Fig. 2 indicates the motion resistance of the soil to the tested tires measured by applying vertical loads of 3.5, 5.5 and 7.5 kN. As shown by Bekker (1969) and Abebe et al. (1989), it was found that the rolling resistance of the pneumatic wheel had a relation to the compaction level of the soil. According to the test results, the greater load and the less forward velocity tests showed higher values of rolling resistance. For tire 1, resistance was found to be greater than tire 2. The effects of tire type and vertical load on the rolling resistance were signi®cant P < 0:01. The greatest rolling resistance occurred at vertical load of 7.5 kN and forward velocity of 0.8 m/s under tire 1. 3.3. Surface sinkage, layer deformation and compaction index The relation between surface sinkage and vertical load was affected by tire type and forward velocity (Fig. 3). The rut or surface sinkage formed by the
Fig. 1. Effect of vertical load on contact projected area and pressure. (&) Tire 1; (*) tire 2.
Fig. 3. Effect of vertical load on sinkage. (&) Tire 1, 0.8 m/s; (*) tire 2, 0.8 m/s; (&) tire 1, 1.4 m/s; (*) tire 2, 1.4 m/s.
K. CËarman / Soil & Tillage Research 65 (2002) 37±43
Fig. 4. The relation of layer deformation with depth at forward velocity of 0.8 m/s (a) and 1.4 m/s (b). (&) Tire 1, 7.5 kN; (^) tire 1, 5.5 kN; (*) tire 1, 3.5 kN; (&) tire 2, 7.5 kN; (^) tire 2, 5.5 kN; (*) tire 2, 3.5 kN.
pneumatic wheels indicated the apparent soil compaction or the volume lost during compression. Approximately, to double the vertical load resulted in an sinkage increase of 61%, whereas almost twice the velocity caused a 6% decrease of the sinkage. The effects of tire type and vertical load on surface deformation were signi®cant P < 0:01. Test results con®rmed that the sinkage for vertical load of 7.5 kN and forward velocity of 0.8 m/s under tire 1 was greater than the sinkage caused by the other trials. Fig. 4 shows subsurface layer deformation as related to vertical load at depths of 7, 14 and 21 cm. The compacted zone most signi®cantly affected by load was found to be about 70±140 mm below the wheel base and the effect of load on layer deformation decreased with depth. In Fig. 5, the compaction index was in the range 0.18±0.48. The greatest compaction index was found at a depth of 70 mm at a vertical load of 7.5 kN and forward velocity of 0.8 m/s under tire 1, which had less contact projected area. When the effect of depths of 14 and 21 cm on compaction index in trials were considered, a similar trend of intensity of compaction was observed.
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Fig. 5. The effect of vertical load on compaction index at forward velocity of 0.8 m/s (a) and 1.4 m/s (b). (&) Tire 1, 7 cm; (^) tire 1, 14 cm; (*) tire 1, 21 cm; (&) tire 2, 7 cm; (^) tire 2, 14 cm; (*) tire 2, 21 cm.
3.4. Penetration resistance Penetration resistance of soil increased with increasing tire load but the penetration resistance decreased with increasing forward velocity (Fig. 6). The penetration resistance at depth of 20 cm of the soil at different trials varied from 1472 to 2530 kPa. The effects of tire type and vertical load on penetration resistance were signi®cant P < 0:01. The greatest changes in penetration resistance occurred at a vertical load of 7.5 kN and forward velocity of 0.8 m/s under
Fig. 6. Effect of vertical load on penetration resistance at depth of 20 cm. (&) Tire 1, 0.8 m/s; (*) tire 2, 0.8 m/s; (&) tire 1, 1.4 m/s; (*) tire 2, 1.4 m/s.
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K. CËarman / Soil & Tillage Research 65 (2002) 37±43
Fig. 7. Effect of vertical load on bulk density. (&) Tire 1, 0.8 m/s; (*) tire 2, 0.8 m/s; (&) tire 1, 1.4 m/s; (*) tire 2, 1.4 m/s.
tire 1. For this trial, the penetration resistance increased about 116% compared with the initial condition. 3.5. Bulk density The bulk density of the soil at a depth of 0±10 and 10± 20 cm below the tire track increased with increasing vertical load and decreased with increasing forward velocity (Fig. 7). The bulk density of the soil in different trials varied from 1.31 to 1.70 Mg m 3. The effects of tire type, vertical load and forward velocity on the bulk density were signi®cant P < 0:01. As expected, the greatest bulk density was observed at a vertical load of 7.5 kN and forward velocity of 0.8 m/s with tire 1. For this trial, the bulk density increased about 40% compared with the initial condition. For an increase of approximately 100% in tire load, bulk density increased about 23%. The effect of forward velocity on bulk density was signi®cant, and the difference between bulk density values as for different values of forward velocity was found to be about 3.9%. 4. Conclusions The following conclusions can be drawn from the soil bin experiments designed to study the interrelationships between an applied load, the forward velocity, tire type and the resulting soil deformation characteristics after the passage of a wheel: 1. Surface and subsurface soil deformation characteristics which were taken as indicative values of soil compactibility strongly indicated that the greatest compaction occurred at a vertical load of 7.5 kN and forward velocity of 0.8 m/s with tire 1.
2. Vertical load was the major contributory factor on soil compaction as compared to tire type and forward velocity. 3. The contact projected area for tire 2 was approximately 10% greater than for tire 1 and the compaction at the soil surface and subsurface was correspondingly less than that for tire 1. 4. Spreading the applied load over the larger contact projected area of tire 2 which has greater total lug area and less lug height, reduced soil unit pressure at the surface. 5. Soil was compacted more at the lower forward velocity because of increasing contact duration. 6. Subsurface layer deformation and compaction index decreased with increasing depth.
References Abebe, A.T., Tanaka, T., Yamazaki, M., 1989. Soil compaction by multiple passes of rigid wheel relevant for optimization of traf®c. J. Terramechanics 26, 139±148. Adebiyi, O.A., Koike, M., Konaka, T., Yuzawa, S., Kuroishi, I., 1991. Compaction characteristics for the towed and driven conditions of a wheel operating in an agricultural soil. J. Terramechanics 28, 371±382. Barnes, K.K., Taylor, H.M., Throckmorton, R.I., Vanderberg, G.E., Carleton, W.M., 1984. Compaction of Agricultural Soils. ASAE, St. Joseph, MI. Barone, L., 1990. Wheel traf®c effect on soil compaction. In: Proceedings of the International Symposium on Mechanisation and Energy in Agriculture, Adana, Turkey, pp. 159±165. Bekker, M.G., 1969. Introduction to TerrainÐVehicle Systems. The University of Michigan Press, Michigan. Black, C.A., 1965. Methods of Soil Analysis, Part I. American Society of Agronomy, Madison, WI. Bolling, I.H., 1986. How to predict soil compaction from agricultural tires. J. Terramechanics 22, 205±223. CËarman, K., 1992. The investigation of effect on compaction of contact time in tire±soil interface. J. Agric. Faculty, University of SelcËuk 2 (4), 49±58 (in Turkish). CËarman, K., 1994. Tractor forward velocity and tire load effects on soil compaction. J. Terramechanics 31, 11±20. CËarman, K., 1996. Prediction of penetration resistance, sinkage and bulk density in soil±tire interaction. In: Proceedings of the International Symposium on Mechanisation and Energy in Agriculture, Ankara, Turkey, pp. 417±423. CËarman, K., Ogut, H., Peker, A., 1992. The investigation of ®eld traf®c for some agricultural crops produced in Altinova Farm. J. Agric. Faculty, University of SelcËuk 2 (4), 79±85 (in Turkish). Davies, D.B., Finney, J.B., Richardson, S.J., 1973. Relative effects of tractor weight and wheel-slip in causing soil compaction. J. Soil Sci. 24, 399±409.
K. CËarman / Soil & Tillage Research 65 (2002) 37±43 Grahn, M., 1991. Prediction of sinkage and rolling resistance for off the road vehicles considering penetration velocity. J. Terramechanics 28, 339±347. Kural, H., 1998. The rolling resistance of 7.50±16 free-rolling tires used in agricultural machinery and their effects on soil compaction. D.Sc. Thesis. Graduate School of Natural and Applied Sciences of SelcËuk University, Konya, Turkey (in Turkish). Larsen, R.J., Marx, M.L., 1981. An Introduction to Mathematical Statistics and its Applications. Prentice-Hall, Englewood Cliffs, NJ. Mckyes, E., 1985. Soil Cutting and Tillage. Elsevier, Amsterdam, the Netherlands.
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Rickman, J.F., Chanasyh, D.S., 1988. Traction effects on soil compaction. In: Proceedings of the Conference on Agricultural Engineering, Hawkesbury Agricultural College, pp. 103± 108. Rusanov, V.A., 1991. Effects of wheel and track traf®c on the soil and on crop growth and yield. Soil Till. Res. 19, 131±143. Schwanghart, H., 1991. Measurement of contact area, contact pressure and compaction under tires in soft soil. J. Terramechanics 28, 309±318. Yildiz, U., CËarman, K., 1998. Effects of some working characteristics on soil compaction of 7.00±18 radial tire size. In: Proceedings of the National Symposium on Mechanisation in Agriculture, TekirdagÏ, Turkey, pp. 355±361 (in Turkish).