ABSTRACT INTRODUCTION MATERIALS AND METHODS

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1 INTENATIONAL JOUNAL OF AGICULTUE & BIOLOGY /6/ Multiplate Peetratio Tests to Predit Soil Pressure-siage Behaviour uder etagular egio M. ASHIDI 1, A. KEYHANI AND A. TABATABAEEFA Power & Mahiery Departmet, Faulty of Agriultural Biosystem Egieerig, Uiversity of Tehra, Tehra Ira 1 Correspodig author s [email protected] ABSTACT Soil ompatio may ause osiderable damage to the struture of the tilled soil ad the subsoil ad osequetly to rop produtio, ad the eviromet. The preditio of soil siage uder wheels ad tras is of great importae for determiig the off-road vehile performae ad the level of ompatio i the agriultural soils. Soil stiffess ostats gover the soil siage ad the behaviour of soil uder load. To determie the stiffess ostats of soil i the retagular regio, a sady-loam soil refletig geeral harater of a agriultural soil was seleted ad multiplate peetratio tests were oduted. Two low (135 g m -3 ) ad high (165 g m -3 ) apparet bul desities were osidered as treatmets i the sadyloam soil. For eah treatmet, from the pressure versus siage relatioship of soil uder differet loads, the average soil stiffess ostats, ad were determied from the sets of three siage tests usig three small retagular plates that differ i plate width ad havig aspet ratios lose to those of agriultural tires' footigs. Tests were repliated three times for eah of the three small retagular plates. Usig the alulated soil stiffess ostats for eah treatmet, the pressure-siage behaviour of a larger retagular plate was predited. For the apparet low bul desity the amouts of MSE ad MPD were 6 mm ad 8%, respetively. For the apparet high bul desity the amouts of MSE ad MPD were mm ad 11.5%, respetively. The results showed that the preditio was better for the lower desity soil. Key Words: Pressure-siage; Soil ompatio; Soil stiffess ostats INTODUCTION Soil ompatio is a proess through whih pore spaes are dereased. It alters the struture of ultivated soil, i.e., the spatial arragemet, size ad the shape of lods ad aggregates ad osequetly the pore spaes iside ad betwee these uits (Defossez & ihard, ). Soil ompatio a be aused by atural pheomea suh as raifall impat, soaig, iteral water tesio ad the lie. Artifiial soil ompatio ours uder the dowward fores of agriultural mahies (MKyes, 1985). I this paper we are oered with ompatio by the wheelig of agriultural mahies. Soil ompatio uder trators ad farm mahiery is of speial oer beause weights of these mahies have bee ireased dramatially i the last deades ad these implemets reate persistet subsoil ompatio (Abu- Hamdeh & eeder, 3). Agroomists are oered about the effets of heavy trators ad agriultural mahies o agriultural soils due to the possibility of exessive soil ompatio that impedes root growth leadig to yield redutio (Al-Adawi & eeder, 1996). Hee, the preditio of soil siage uder loads is a importat tas to determie the level of ompatio i the soil. For the last five deades, preditio of soil pressuresiage behaviour has bee of great iterest to researhers i both agriulture ad ross-outry mobility ad trasport (Beer, 1956; eee, 1964; Hegedus, 1965; Kogure, 1983; Upadhyaya, 1989; Upadhyaya et al., 1993; Çair et al., 1999; Defossez & ihard, ; ashidi et al., 5). Furthermore, the ability to predit soil siage a eable agriultural egieers to till or traffi the soil whe it is ot i a highly ompatible state or to estimate the damage beig doe to the soil struture due to their exessive loadig whe tillage or traffi is eessary. Models preseted i the literature are from a simple expoetial futio to a elastoplasti ompliated oe. Usually, i a more omplete (ad thus, a more ompliated) model, may parameters ad variety of properties are preset ad have to be ow prior to solvig the model. Therefore, the overall objetive of this study was to use a relatively simple model to predit the soil siage uder a retagular regio usig retagular plates havig aspet ratios lose to the agriultural trator tires' footig. The speifi objetives of the study were: a) to determie the soil stiffess ostats for siage of retagular regio with tests that use three small retagular plates i low ad high apparet bul desities, ad b) to predit the soil siage uder a larger retagular plate usig the soil stiffess ostats measured with three small retagular plates i the same soil oditios. MATEIALS AND METHODS Pressure-siage models. Ivestigatios ito the ature of suh pheomea ad the soil parameters ivolved have arrived at fidigs i two differet ategories: situatios i

2 ASHIDI et al. / It. J. Agri. Biol., Vol. 8, No. 1, 6 whih time is osidered as a importat fator ad those where it is ot. For the ase where time is ot osidered to be a fator, oe of the earlier models was reported by Beer (1956), ad the followig equatio was proposed to desribe it (MKyes, 1985; Upadhyaya et al., 1993): Ρ = z (1) where: Ρ = vertial average otat pressure, Pa, = a soil stiffess ostat for siage, Pa / m, z = depth of siage, m, = a soil ostat related to the soil harateristis, odimesioal. The priipal defiiey of Eq. (1) for preditio of soil siage was foud to be the variability of the soil stiffess with the size of the objet o the soil. I ivil egieerig tehology, it was ow that the siage of the retagular plate, at a give average vertial pressure o a partiular soil, depeds also o the width of the retagle. Beer (1956) ombied the two oepts, amely the expoetial pressure-siage relatioship of Eq. (1), ad the plate size depedee of the soil stiffess ostat as follow (Upadhyaya et al., 1994; Çair et al., 1999): Ρ = / b + ) z ( where: b = plate width, m, ad = soil stiffess ostats for siage, whih are 1 presumed to be idepedet of plate width, Pa / m ad Pa / m, respetively. The two parameters ad separate the siage stiffess ostat ito two ompoets. Thus, three parameters are required to desribe the siage pheomeo. These parameters are determied usig surfae pressure-siage tests. I order to evaluate the soil ostat i Eq. (), it is eessary to odut at least two soil peetratio tests usig plates of differet widths. The measured sets of pressure ad siage values must the be aalyzed graphially or aalytially to fid the best fit. From the best fit expoetial urves, ostats ad a be determied for eah plate of the tests. The average value of is used together with the values from the two plates to ad obtai as show below (Upadhyaya et al., 1994): = b1b ( 1 ) /( b b1 ) (3) = ( b 1b1 ) /( b b1 ) (4) where subsripts 1 ad refer to the values measured for plates 1 ad. () However, it may be risy to attempt the measuremet of soil stiffess ostats with tests that use oly two plates, espeially if they are small plates. A large variability exists i soils, eve i arefully prepared laboratory samples, let aloe at differet loatios i a field. Large retagular plates, of the order 3 m or more i width, a redue the variatio i experimetal results, but they require large loads to approah pratial siage pressure level ad thus ioveiet ad ostly to perform, but smaller retagular plates i the rage of five to te m are hady for testig by oe perso. It has bee show that the variatio i ad a be osiderable whe oly two small plates are used. Whe several plates are used rather tha two, ad the observatios are pooled to fid average stiffess ostats, the the variatio i ad are redued dramatially. Whe more tha two siage plates are tested, a statistial method a be used to alulate the stiffess ostats. Costats ad are foud for eah plate. The a graph a be made of versus 1 / b, i order to solve for ad. A bestfit lie is foud by least square aalysis ad ad are the slope ad iterept of this lie (MKyes & Fa, 1985). Test uit developmet. A test uit was developed to determie soil stiffess ostats for siage. A selfexplaatory shemati piture of the test uit is preseted i Fig. 1. Three differet retagular plates were used i these tests. The plate dimesios are listed i Table I. Note that the three plates have the same otat area, but differ i width oly. The aspet ratio (legth/width) of these plates raged from 1.5 to.8, whih are similar to the oes expeted for peumati tires' footigs (for tras log arrow strips are reommeded). The aspet ratio of a tire or tra footig a be defied as the legth of the groud otat area divided by the width. Experimetal proedure. A sady-loam soil was hose for haraterizig the agriultural soil. The sady-loam soil was osisted of 16% lay, % silt ad 6% sad. To prepare soil samples, as a first step, soil was sieved usig a mesh size of 5 mm. The, the soil was watered ad overed with a sheet of plasti durig the ight i order to ahieve a uiform moisture distributio. The measured soil moisture otet was about % (d.b.), whih made the soil sample to be i a arable oditio as i the field. The soil was leveled ad the firmed i the ubi soil bi by a woode paer pisto with the aid of a hydrauli press. g / m Two low (135 ) ad high (165 ) apparet bul desities, represetig the field apparet bul desities, were osidered as treatmets. For eah test ru, eah of three small retagular plates was loaded slowly up to about 17 Pa ad pushed dowwards ito the soil ad at the same time the dowward displaemet (siage depth) 3 g / m 3 6

3 MULTIPLATE PENETATION TEST TO PEDICT SOIL PESSUE-SINKAGE / It. J. Agri. Biol., Vol. 8, No. 1, 6 was measured with the siage measurig ruler. Differet loads were applied usig differet loadig weights ad tests were repliated three times for eah of the three small retagular plates i both apparet bul desities. ESULTS AND DISCUSSION Pressure-siage tests' results. The results of the pressuresiage tests were aalyzed usig the Berstei's siage formula. Table II shows the alulated ostats ad for eah of the plates ad treatmets. Very high values of oeffiiets of determiatio, ragig from.9 to.99 were obtaied for idividual siage tests. However, the aalysis idiated that the values of siage parameter varied osiderably betwee plates. O the other had, the expoet was less suseptible to this variatio betwee plates. Fig. 1. Test uit Table I. Sizes of siage plates used to determie soil stiffess ostats i this study Siage Plate Width, mm Legth, mm Aspet atio Table II. Values of ostats ad for eah of the plates ad treatmets Siage Plate Treatmet Low Apparet Bul Desity High Apparet Bul Desity ( Pa / m ) ( Pa / m ) Table III. esults of regressio aalysis of low ad high apparet bul desity soils usig three retagular siage plates Soil Low Apparet Bul Desity High Apparet Bul Desity Pa / m ) ( Pa / m ) 1 ( Table IV. Sizes of the large retagular plate Siage Plate Width, mm Legth, mm Aspet atio Large etagular Fig.. Determiatio of ad from values of idividual siage tests with plates of differet sizes i low apparet bul desity soil Pa/ m = (1/b) = /b ( 1 m ) As show i Figs. ad 3, to obtai ad by usig the data from Table I, regressioal aalysis was applied to the ostat ad the iverse of the plate width, 1 / b. From the liear regressio results, ad are the slope ad the iterept of the regressio lie, respetively. Our attempts to relate to 1 / b usig Eq. () resulted i very good agreemets. The alulated ostats ad for eah treatmet are give i Table III. Siage preditio of a larger retagular plate. Sie irular footigs have already bee used to test the validity of the Beer's model (MKyes & Fa, 1985; Çair et al., 1999), usig Eq. (), the soil stiffess ostats measured with three small retagular plates was used to predit the pressure-siage behaviour of a larger retagular plate, ad about three times the width. Besides, o results have bee 7

4 ASHIDI et al. / It. J. Agri. Biol., Vol. 8, No. 1, 6 Fig. 3. Determiatio of ad from values of idividual siage tests with plates of differet sizes i high apparet bul desity soil Pa/m = (1/b) = /b ( m ) Fig. 4. pressure-siage behaviour of the larger retagular plate ompared with that measured experimetally o low apparet bul desity soil Siage z (m) Measured Pressure - P (Pa) reported i the literature yet for verifiatio of the model for differet bul desities. Hee, a larger retagular plate with dimesios listed i Table IV was used to test the model i two apparet bul desities. a. Low apparet bul desity soil. Fig. 4 shows the predited pressure-siage behaviour of the larger retagular plate, usig the soil stiffess ostats derived from tests o three small retagular plates o the soil sample with a low apparet bul desity alog with the measured values. For measurig pressure-siage behaviour, the larger retagular plate was loaded slowly up to about 15 Pa ad at the same time the siage depth was measured with the siage measurig ruler. From ompariso of two urves, it ould be oluded that preditio is very reasoable over the measured siage rage. A liear regressio was performed to verify the validity of the preditio. Fig. 5 shows that the siage values predited usig the soil stiffess ostats derived from tests ad those measured experimetally were plotted agaist eah other ad fitted with a liear equatio with zero iterept. The slope of the lie of the best fit ad its oeffiiet of determiatio were.95 ad.99, respetively. oot of mea square errors (MSE) ad mea relative peretage deviatio (MPD) were used to he the disrepaies betwee the predited ad measured results. The amouts of MSE ad MPD were 6 mm ad 8%, respetively. egardig the statistial results, the validity of the preditio was ofirmed. b. High apparet bul desity soil. Fig. 6 shows the Fig. 5. ad measured siage values o low apparet bul desity soil Siage y (m) y =.95 x = Measured Siage - x (m) Fig. 6. pressure-siage behaviour of the larger retagular plate ompared with that measured experimetally o high apparet bul desity soil Siage z (m).3..1 Measured Pressure - P (Pa) 8

5 MULTIPLATE PENETATION TEST TO PEDICT SOIL PESSUE-SINKAGE / It. J. Agri. Biol., Vol. 8, No. 1, 6 Fig.7. ad measured siage values o high apparet bul desity soil Siage y (m).3..1 y =.88 x = Measured Siage - x (m) predited pressure-siage behaviour of the larger retagular plate, usig the soil stiffess ostats derived from tests o three small retagular plates o the soil sample with a high apparet bul desity alog with the measured values. Agai, for measurig pressure-siage behaviour, the larger retagular plate was loaded slowly up to about 15 Pa ad at the same time the siage depth was measured with the siage measurig ruler. From ompariso of two urves, it ould be oluded that preditio is very reasoable over the measured siage rage. As before, a liear regressio was performed to verify the validity of the preditio. Fig. 6 shows that the siage values predited usig the soil stiffess ostats derived from tests ad those measured experimetally were plotted agaist eah other ad fitted with a liear equatio with zero iterept. The slope of the lie of best fit ad its oeffiiet of determiatio were.88 ad.99, respetively. Agai, root of mea square errors (MSE) ad mea relative peretage deviatio (MPD) were used to he the disrepaies betwee the predited ad measured results. The amouts of MSE ad MPD were mm ad 11.5%, respetively. egardig the statistial results, the validity of the preditio was ofirmed agai. More liely, reaso for suh egligible disrepaies betwee the predited ad measured results usig the soil stiffess ostats stem out primarily from usig three plates to ehae the level of ofidee of the alulated soil stiffess ostats. Had it bee four or eve five plates, the results would have bee improved further (MKyes & Fa, 1985). The model, to some extet, showed better results for the lower bul desity soil. Although the results for the higher bul desity soil are reasoable, it appears that due to a probable ueveess of bul desity, a more paed soil seems to build higher stress oetratios udereath some parts of the plate from the very first momet of the appliatio of the load. Therefore, ourree of a small variatio i the bul desity durig the soil sample preparatio, ould adversely affet the result. CONCLUSIONS The ad ostats were alulated usig three differet retagular plates with differet aspet ratios similar to those of peumati agriultural tires. I this study, the best-fitted regressio model was obtaied whe the data from three retagular plates were used i two soil oditios of low ad high apparet bul desities. The soil stiffess ostats measured with three small retagular plates were used to predit the pressure-siage behaviour of a larger retagular plate. The statistial results ofirmed the validity of the preditio, espeially i the low bul desity soil, ad demostrated that uder some oditios, it ould be very useful to determie the siage behaviour of tires ad tras of trators ad agriultural mahies i the laboratory oditio without goig to the field. EFEENCES Abu-Hamdeh, N.H. ad.c. eeder, 3. Measurig ad preditig stress distributio uder trative devies i udisturbed soil. Biosys. Eg., 85: Al-Adawi, S.S. ad.c. eeder, Compatio ad subsoilig effets o or ad soybea yields ad soil physial properties. Tras. ASAE, 39: Beer, M.G, Theory of lad loomotio-the mehais of vehile mobility. Uiversity of Mihiga Press, A Arbor, MI: 5pp Çair, E., E. Gülsoylu ad G. Keçeioğlu, Multiplate peetratio tests to determie soil stiffess moduli of ege regio. I: Proeedigs of Iteratioal Cogress o Agriultural Mehaizatio ad Eergy, pp May 1999, Adaa-Turey Defossez, P. ad G. ihard,. Models of soil ompatio due to traffi ad their evaluatio. Soil Till. es., 67: Hegedus, E, Plate siage study by meas of dimesioal aalysis. J. Terrameh., : 5-3 Kogure, K., Y. Ohira ad H. Yamaguhi, Preditio of siage ad motio resistae of a traed vehile usig plate peetratio test. J. Terrameh., : 11-8 MKyes, E, Soil Cuttig ad Tillage. Elsevier Siee Publishers. New Yor MKyes. E. ad T. Fa, Multiplate peetratio tests to determie soil stiffess moduli. J. Terrameh., : ashidi, M.,. Attarejad, A. Tabatabaeefar ad A. Keyhai, 5. Preditio of soil pressure-siage behavior usig the fiite elemet method. It. J. Agri. Biol., 7: 46-6 eee, A., Problems of soil-vehile mehais. Lad Loomotio Laboratory eport No. 847 (LL97). Warre, Mih.: U.S. Army Ta-Automotive Ceter Upadhyaya, S.K, Developmet of a portable istrumet to measure soil properties relevat to tratio. esearh report. Davis, Calif.: Agriultural Egieerig Departmet, Uiversity of Califoria Upadhyaya, S.K., D. Wulfsoh ad J. Mehlshau, A istrumeted devie to obtai tratio related parameters. J. Terrameh., 3: 1- Upadhyaya, S.K., W.J. Chaellor, J.V. Perumpral,.L. Shafer, W.. Gill ad G.E. Vade Berg, Advaes i soil dyami. Vol. 1. ASAE, USA (eeived Otober 5; Aepted 1 Deember 5) 9