Effects of tillage systems on compaction and crop yield of Albic Luvisol in Croatia

This four-year experiment was conducted in north-west Slavonia (agricultural area of Croatia) to evaluate the effects of different tillage systems on compaction of silty loam soil (Albic Luvisol). The compared tillage systems were: (1) conventional tillage (CT), (2) conservation tillage (CM), (3) no-tillage system (NT), and the crop rotation was corn (Zea mays L.) – winter wheat (Triticum aestivum L.) – corn – winter wheat. For detecting the soil compaction, bulk density and penetration resistance were measured during the growing seasons. In all seasons and tillage systems, the bulk density and penetration resistance increased with depth and the greatest increase from surface to the deepest layer in average was observed at CT system. The bulk density and penetration resistance increased at all tillage systems during the experiment, but the greatest increase was also observed at CT system. The greatest bulk density (1.66 Mg m⁻³) and the greatest increase of 6.4% were observed at CT system in the layer 30–35 cm. In the first season, the bulk density was the greatest at NT system, but during the experiment the lowest average increase of 1.9% was observed at this system. The greatest penetration resistance of all measurements (5.9 MPa) was observed in the last season at CT system in depth of 40 cm. The lowest average increase of penetration resistance 11.4% was also observed at NT system. The highest yield of corn in the first season was achieved with CT system while in other seasons the highest yield of winter wheat and corn was achieved with CM system.     

An in-situ determination of virgin compression line parameters for predicting soil displacement resulting from agricultural tire passes

This paper demonstrates the determination of the virgin compression line parameters from initial soil density, contact pressure and resulting rut depth in uniform soil conditions for which a constant soil density change to a depth of 500 mm was obtained in soil bin experiments (whereby total soil depth was 750 mm). The density change was determined with a “non-invasive” technique determining soil displacement (strain) by placing talcum powder lines into the soil during preparation of the soil bin and measuring the change in their relative position. The soil compaction model COMPSOIL with these parameters predicted wheel rut depth to within ±5%, from which in turn an absolute soil density increase can be determined to within ±3%. The model was successfully validated against data for uniform initial densities of 1.2 g/cm³ and 1.6 g/cm³ and a simulated layered field condition. The estimation of the virgin compression line was validated in the field as well. The parameters of the virgin compression line were estimated using soil density change data for the corresponding average contact pressures of different tires with loads of 4.5–10.5 t.     

Performance of an oscillating subsoiler in breaking a hardpan

A single shank tractor mounted oscillating subsoiler was developed to break hardpan, common in sugarcane (Saccharum officinarum) farms especially after harvest when heavy trucks transport the cut canes from the field to the sugar factory. Field experiments were conducted to determine the optimum combination of performance parameters of the subsoiler. Field tests were conducted at frequencies of oscillation of 3.7, 5.67, 7.85, 9.48 and 11.45 Hz; amplitudes of 18, 21, 23.5, 34 and 36.5 mm; and forward speeds of 1.85, 2.20 and 3.42 km h⁻¹ at moisture contents close to the lower plastic limit of the clay soil. A reduction in draft but an increase in total power requirement was found for oscillating compared to non-oscillating subsoiler. The draft and power ratios were significantly affected by the forward speed, frequency and amplitude. Their combined interaction, expressed in terms of the velocity ratio (the ratio of peak tool velocity to forward speed), however, had the strongest influence. At the same velocity ratio, the draft reduction and power increase were less at higher amplitude of oscillation. For the field conditions tested, the optimum operation for least energy expenditure was obtained at an amplitude of 36.5 mm, frequency of 9.48 Hz and speed of 2.20 km h⁻¹ with a draft ratio of 0.33 and power ratio of only 1.24. It could be concluded that the oscillating subsoiler reduces draft for breaking hardpan, reduces soil compaction and promotes the use of lighter tractors by utilizing tractor power-take-off (p.t.o.) power to achieve higher efficiency of power transmission. ©     

Modeling soil-bulldozer blade interaction using the discrete element method (DEM)

Limited studies have been conducted to establish scaling relationships of soil reaction forces and length scales of bulldozer blades using the Discrete Element Method (DEM) technique. With a DEM-based similitude scaling law, performance of industry-scale blades can be predicted at reduced simulation efforts provided a calibrated and validated DEM soil model is developed. DEM material properties were developed to match soil cone penetration testing. The objectives of the study were to develop a DEM soil model for Norfolk sandy loam soil, establish a scaled relationship of soil reaction forces to bulldozer blade length scales (n = 0.24, n = 0.14, n = 0.10, and n = 0.05), and validate the DEM-predicted soil reaction forces on the scaled bulldozer blades to the Norfolk sandy loam soil bin data. Using 3D-scanned and reconstructed DEM soil aggregate shapes, Design of Experiment (DOE) of soil cone penetration testing was used to develop a soil model and a soil-bulldozer blade simulation. A power fit best approximated the relationship between the DEM-predicted soil horizontal forces and the bulldozer blade length scale (n) (R² = 0.9976). DEM prediction of soil horizontal forces on the bulldozer blades explained the Norfolk sandy loam soil data with a linear regression fit (R² = 0.9965 and slope = 0.9634).     

Cone resistance in sand by incremental method

A new method has been developed for the determination of cone resistance under drained conditions. Numerical methods are used for the solution of the differential equations of plasticity theory for soils and for the determination of the stress states in the soil produced by the penetration of the cone. It is assumed that the stresses produced by the penetration of the cone remain ‘locked in’ the soil and constitute boundary conditions for further penetration. The computation starts with the cone base at the surface and is continued by successively incrementing the depth by a small amount. Charts are given for the computation of cone resistance in sands for various friction angles. The importance of the effect of the shear stresses generated at the surface of the cone and characterized by the interface friction angle, δ, is discussed in detail.     

Determination of the soil pressure distribution around a cone penetrometer

The objective of this paper was to investigate the pressure distribution around a cone penetrometer using a pressure sensing mat under laboratory conditions. The investigation was conducted under (1) constrained conditions using cylindrical split pipe molds and (2) unconstrained conditions using a soil box. These tests were conducted in Capay clay and Yolo loam soil containing two different moisture conditions and two compaction levels.In the constrained tests, a maximum radial pressure of 111 kPa was observed in the Capay clay soil with 3.4–4.3% d.b. moisture content and three blows of compaction (cone index value of 2040 kPa) when using the 41 mm diameter split pipe mold. These pressure levels decreased to 82 and 22 kPa, respectively, when 65 and 88 mm diameter molds were used. In both the Capay clay and Yolo loam tests, the average radial pressure and average cone index values showed similar trends.In the unconstrained tests, a maximum pressure of 9.0 kPa was observed in the Capay clay with 4.5% d.b. moisture content and three blows of compaction (cone index value of 550 kPa) at a horizontal distance of 25.4 mm from the vertical axis of the cone penetrometer and minimum pressure levels in the range of 0.2–0.3 kPa when the horizontal distance of the penetrometer was in the range of 56.8–66 mm. The pressure levels are much smaller than the ones obtained in the constrained tests and may suggest that the pressure distribution under field conditions is small at a distance of 25.4 mm or higher from the tip of the cone.The experimental data were statistically analyzed to identify significant factors. The results of the analysis for the constrained test indicated that the mold diameter and number of blows significantly increased the pressure readings within the soil mass. Increasing the mold diameter led to a decrease in the average radial pressure and increasing the number of blows contributed to an increase in the average radial pressure. In the unconstrained test, the average radial pressure distribution at a given point were significantly influenced by the horizontal distance of the point from the vertical axis passing through the center of the penetrometer shaft, soil type, and soil moisture content. Higher pressure values were obtained in the Capay clay tests compared to the Yolo loam tests. In all cases, the pressure levels were greater for the drier soil than for the moist soil.     

Effect of multiple passes of tractor with varying normal load on subsoil compaction

A field experiment was conducted on alluvial soil with sandy loam texture, in a complete randomized design, to determine the compaction of sub-soil layers due to different passes of a test tractor with varying normal loads. The selected normal loads were 4.40, 6.40 and 8.40 kN and the number of passes 1, 6, 11 and 16. The bulk density and cone penetration resistance were measured to determine the compaction at 10 equal intervals of 5 cm down the surface. The observations were used to validate a simulation model on sub-soil compaction due to multiple passes of tractor in controlled conditions. The bulk density and penetration resistance in 0–15 cm depth zone continuously increased up to 16 passes of the test tractor, and more at higher normal loads. The compaction was less in different sub-soil layers at lower levels of loads. The impact of higher loads and larger number of passes on compaction was more effective in the soil depth less than 30 cm; for example the normal load of 8.40 kN caused the maximum bulk density of 1.53 Mg/m³ after 16 passes. In 30–45 cm depth layer also, the penetration resistance increased with the increase in loads and number of passes but to a lesser extent which further decreased in the subsoil layers below 45 cm. Overall, the study variables viz. normal load on tractor and number of passes influenced the bulk density and soil penetration resistance in soil depth in the range of 0–45 cm at 1% level of significance. However, beyond 45 cm soil depth, the influence was not significant. The R² calculated from observed and predicted values with respect to regression equations for bulk density and penetration resistance were 0.7038 and 0.76, respectively.     

Influence of the axle load, tyre size and configuration on the compaction of a freshly tilled clayey soil

Enhancement of the potential root growth volume is the main objective of farmers when they establish a conventional tillage system. Therefore, the main function of primary tillage is to increase soil’s structural macroporosity. In spite of this, during secondary tillage operations on these freshly tilled soils, the traffic on seedbeds causes significant increases in soil compaction. The aim of this paper was to quantify soil compaction induced by tractor traffic on a recently tilled non consolidated soil, to match ballast and tyre size on the tractors used during secondary tillage. The work was performed in the South of the Rolling Pampa region, Argentina. Secondary tillage traffic was simulated by one pass of a conventional 2WD tractor, using four configurations of bias-ply rear tyres: 18.4×34, 23.1×30, 18.4×38 and 18.4×38 duals, two ballast conditions were used in each configuration. Soil bulk density and cone index in a 0 to 600 mm profile were measured before and after traffic. Topsoil compaction increased as did ground pressure. Subsoil compaction increased as total axle load increased and was independent from ground pressure. At heavy conditions, topsoil levels always showed higher cone index values. From 150 to 450 mm depth, the same tendency was found, but with smaller increases in the cone index parameter, 22 to 48%, averaging 35%. Finally, at the deepest layer considered, 600 mm, differential increases due to the axle load are great enough as to be considered similar to those found in the upper horizon, 36 to 64%, averaging 55%. On the other hand, bulk density tended to be less responsive than cone index to the traffic treatments. Topsoil compaction can be reduced by matching conventional bias-ply tyres with an optimized axle weight.     

A robust integration algorithm for implementing rate dependent crystal plasticity into explicit finite element method

Severe numerical instability in the integration of rate dependent crystal plasticity (RDCP) model is one of the main problems for implementing RDCP into finite element method (FEM), especially for simulating dynamic/transient forming process containing complicated contact conditions under large step length, large strain and high strain rate. In order to overcome the problem, an implicit model is deduced with the primary unknowns of shear strain increments of slip systems under the corotational coordinate system in the paper. The homotopy auto-changing continuation method combined with the Newton–Raphson (N–R) iteration is adopted. The subroutine VUMAT is developed for implementing RDCP model in ABAQUS/Explicit. Simulation results show that the algorithm is stable and accurate in 3D FE simulations on both dynamic simple loading and complicated loading process containing nonlinear contacts under the conditions of the maximal step length of 3.5 × 10⁻⁶ s, the maximal strain of 1.05, the maximal loading speed of 120 mm s⁻¹, and the minimal material rate sensitivity coefficient of 0.01. The predictions of the model on crystal behaviors of anisotropy, rate sensitivity and elasticity, as well as ear profiles in deep cup drawing are in agreement with experiments.     

高填方路堤强夯效果的现场检测及三维有限元模拟

针对河南某岩石碎渣高填方路堤,提出了夯击能1000kN·m、虚铺厚度1.5m的强夯施工工艺,对试验段进行了现场检测：地质雷达波形较好地反映强夯后虚铺层厚度的减小幅度,并可判断强夯水平有效加固范围为4m,瑞利波速沿深度变化比较均匀,平均值达到了310m·s-1,重型动力触探结果表明试验段达到中密程度,灌水法测得的固体体积率都达到了83%以上,上述检测结果说明强夯的加固效果比较理想。采用ABAQUS有限元分析软件,将夯锤简化为刚性体,通过施加竖向初速度的方式模拟了强夯作用,结合雷达测试结果,认为夯沉量20mm可作为强夯的有效加固范围,最后模拟了存在涵洞结构物的路堤的强夯作用,指出涵洞上方路堤厚度必须达到8m以上,才能保证强夯安全作业。     

Modeling compaction in agricultural soils

Research was conducted to quantify the effect of tire variables (section width, diameter, inflation pressure); soil variables (soil moisture content, initial cone index, initial bulk density); and external variables (travel speed, axle load, number of tire passes) on soil compaction and to develop models to assess compaction in agricultural soils. Experiments were conducted in a laboratory soil bin at the Asian Institute of Technology in three soils, namely: clay soil (CS), silty clay loam soil (SCLS), and silty loam soil (SLS). A dimensional analysis technique was used to develop the compaction models. The axle load and the number of tire passes proved to be the most dominant factors which influenced compaction. Up to 13% increase in bulk density and cone index were observed when working at 3 kN axle load in a single pass using a 8.0–16 tire. Most of the compaction occurred during the first three passes of the tire. It was also found that the aspect ratio, tire inflation pressure and soil moisture content have significant effect on soil compaction. The initial cone index did not show significant effect. The compaction models provided good predictions even when tested with actual field data from previous studies. Thus, using the models, a decision support system could be developed which may be able to provide useful recommendations for appropriate soil management practices and solutions to site-specific compaction problems.     

An empirical model to predict soil bulk density profiles in field conditions using penetration resistance, moisture content and soil depth

Cylindrical soil probes measuring 300 mm in diameter by 300 mm in height were prepared in the laboratory using samples extracted from a well drained loamy soil (FAO classification: Vertic Luvisol). These probes were compacted at different moisture contents [3, 6, 9, 12, 15 and 18 (% w/w)] and using different compaction energies (9.81, 49.05, 98.1 and 981 J). The soil penetration resistance was determined by means of the ASAE 129 mm² base area cone and seven other different cones with base sizes of 175, 144, 124, 98, 74, 39 and 26 mm². The variability of the penetration resistance measurements increased as the size of the cone decreased. Nevertheless, the penetration resistance values proved to be independent of the cone used, as long as the size of the latter was equal to or greater than 98 mm². This confirms the possibility of using cones with areas smaller than the ASAE standard when measurements are to be carried out in dry soils with high levels of mechanical resistance. The experimental data were used to develop an empirical model, a linear additive model on a log–log plane, capable of estimating soil bulk density depending on soil penetration resistance, soil moisture content and depth. This model has provided good results under field conditions and has allowed soil bulk density profiles and accumulated water profiles to be accurately estimated.     

Development and laboratory evaluation of a rheometer for soil visco-plastic parameters

A motorized rheometer was developed for determining soil visco-plastic parameters that works on the principle of torsional shear applied to a standard vane with controlled strain rate. Rheological measurements were carried at different soil moisture contents (10%, 13%, 17% and 20% dry basis (gravimetric)) and soil compaction levels (100, 150, 200, 300 and 400 kPa) to find their effects on soil viscosity and yield strength. The values of viscosity of the clay loam soil (29% clay, 24% silt and 47% sand) were found to spread in the range of 53–283 kPa s, and yield stress variation had a span of 4–28 kPa. Increase in soil compaction was accompanied by a sharp increase in soil viscosity, while moisture content affected soil viscosity negatively. Effect of both these parameters was statistically significant (95% confidence interval). Yield stress was positively related to soil compaction and the effect was statistically significant. However, it was negatively related to moisture content and the effect was not statistically significant for the levels of moisture content tested.     

Simulation on projectile with high rotating speed penetrating into the moving vehicular door

The numerical program LS-DYNA, is used to simulate the process of the projectile with high rotating speed penetrating into the moving vehicular door. Because of the moving of the vehicular door, the projectile will turn, and the ballistic trajectory will migrate. The paper provides a method to calculate the projectile’s angle of turning’s curve. In the process of the penetration, the projectile’s moving speed is 300 m/s, rotating speed is 0, 3600 n/s and 6370 n/s. The vehicular door’s moving speed is 0, 40 m/s and 80 m/s. The projectile is the semi-sphere nose projectile whose diameter is 7.62 mm; the vehicular door’s thickness is 2 mm. The material model is the JOHN-COOK material model that can characterize strain, strain rate hardening and thermal softening effects. Through comparing with the results by simulation to study the effects of the projectile’s final velocity, the angle of rotation and the ballistic trajectory’s migration with different projectile’s rotating speeds and the vehicular door’s moving speeds.     

Transient dynamic response of debonded sandwich plates predicted with finite element analysis

Dynamic transient response of a composite sandwich plate with a penny-shaped debonded zone has been studied by using the finite element analysis within the ABAQUS/Explicit code in this paper. In order to accurately predict the response of the debonded sandwich plate to impulsive loading, contact–impact and sliding conditions along the damaged skin-to-core interface were imposed in the model through a kinematic predictor/corrector contact algorithm. The accuracy of the finite element (FE) model used was verified by comparing between numerical predictions and experimental data known in literature for the frequency spectrum of a cracked polycarbonate laminated beam containing a delamination. By analyzing nonlinear aspects of the transient dynamics of the sandwich plate, it is shown that the presence of the debond significantly alters its short-term response. In this respect, a considerable influence of contact events within the debonded region on the plate’s global dynamic response was found out. These results were presented in both time and frequency domains. The predictions performed also showed that the FE model applied would be useful for nondestructive evaluation of defects in composite sandwich plates, and for studying dynamic response of such plates to impact.     

Cone penetration resistance equation as a function of the clay ratio, soil moisture content and specific weight

The cone penetrometer is a simple versatile device which is widely used to monitor the strength of a soil in terms of its resistance to the penetration of a standard cone. The soil penetration resistance is a function of soil moisture content, soil specific weight and soil type. The soil type is characterised by means of a clay ratio which is the ratio of the clay content of the soil to the content of silt and sand.Based on the classical bearing capacity theories for strip foundations, a general cone penetration resistance equation is developed to represent the variability of cohesion and friction angle by means of soil type and moisture content. The empirical relationship is shown to give an accurate prediction of the cone penetration resistance for a wide range of soils from a loamy sand to a heavy clay (clay ratios 0.10–1.60) and over a wide spectrum of soil moisture contents from 10 to 65% w/w.     

Measurement of compacted soil density in a compaction of thick finishing layer

The compaction of a soil is one of the important construction operations that influences the durability of soil structure. Therefore, the measurement of soil density, used to judge the degree of compaction, has to be performed exactly. Since a compaction of a thick finishing layer could be executed with the enlargement of compaction machinery and the improvement of productivity, new equipment which can measure the soil density in a deep stratum has to be developed. In this paper, we propose a method of accurately estimating compacted soil density based on the three dimensional stresses measured in the ground during compaction by a stress state transducer (SST). A tracked vehicle mounted with a vertical oscillator was used to compact a decomposed granite soil of 45 cm depth. A model experiment was executed at a frequency that was varied from 16 to 25 Hz, setting the load ratio of maximum oscillating force to the vehicle weight (4.9 kN) to be 1.2, 1.6 and 2.0. The three dimensional stresses in the ground were measured by use of the SST. Comparing the dry density converted from cone penetrometer test results and the dry density estimated from Baily’s formula, the compacted soil density at the lowest soil stratum could be estimated by measuring earth pressure using SST.     

Mechanical competence of bone-implant systems can accurately be determined by image-based micro-finite element analyses

The precise failure mechanisms of bone implants are still incompletely understood. Micro-computed tomography in combination with finite element analysis appears to be a potent methodology to determine the mechanical stability of bone-implant constructs. To assess this microstructural finite element (μFE) analysis approach, pull-out tests were designed and conducted on ten sheep vertebral bodies into which orthopedic screws were inserted. μFE models of the same bone-implant constructs were then built and solved, using a large-scale linear FE-solver. μFE calculated pull-out strength correlated highly with the experimentally measured pull-out strength (r ² = 0.87) thereby statistically supporting the μFE approach. These results suggest that bone-implant constructs can be analyzed using μFE in a detailed and unprecedented way. This could potentially facilitate the development of future implant designs leading to novel and improved fracture fixation methods.     

Progress in tire rating based on soil compaction potential

The general trend in soil protection is to reduce the detrimental soil compaction by loaded wheels of power and transport equipment. This paper reports on the progress in research of soil compaction risk assessment by means of Compaction Capacity (CC) tire rating originally introduced as compaction number (CN) rating [Grečenko A. Tire load rating to reduce soil compaction. J Terramech 2003;40:97–115]. The CC rating evaluates soil dry density along a vertical column 20–50 cm below the ground surface. The unique feature of the CC approach is that it converts laboratory compaction measurements directly to soil compaction profiles under evaluated tires without touching the stresses in the ground. The laboratory soil compaction is done with round pressure plate and similarly the tire contact area is represented by a virtual plate loaded by the same mean contact pressure. This paper describes laboratory testing procedures with fundamentals of data conversion and gives examples of CC rating application.     

Strength components in the forest floor restricting maximum tolerable machine forces

In forestry operations, machines used should have a high practicability, yet damage the stand as little as possible. Machine forces are undoubtedly too high in many cases, causing deep ruts, soil compaction and cutting off the tree roots. The knowledge of what forces a forest stand can withstand is still quite limited. One of the aims of our project is to supply information about the strength of the forest floor. Since the forest floor of podzol-type is a complex layered structure, we have started by studying the components in the system. A sand sediment can bear high pressures, whereas a moist fine sandy till soil should not be loaded to more than 30 kPa if severe soil compaction is to be avoided. However, the effect of shear forces and slippage is poorly studied. The humus layer above the mineral soil is armoured by tree roots, shrub roots, grass roots, etc. Intact bark is the best guarantee for healthy trees. During the sap period the shear strength of tree root bark is at least 40 N cm⁻². The armouring effect of roots and rhizomes on the humus layer is considerable, as the total length of roots may be 200–500 m m⁻². The strength of the humus layer is being measured.