Soil compaction and over-winter changes to tracked-vehicle ruts, Yakima Training Center, Washington

We monitored two experimental areas at the Yakima Training Center (YTC) in central Washington to measure changes to M1A2 Abrams (M1) tank-rut surface geometry and in- and out-of-rut saturated hydraulic conductivity (K_fs), soil penetration resistance (SPR) and soil bulk density (BD). Profile-meter data show that rut cross-sectional profiles smoothed significantly and that turning ruts did so more than straight ruts. Rut edges were zones of erosion and sidewall bases were zones of deposition. K_fs values were similar in and out of ruts formed on soil with 0–5% moisture by volume, but were lower in ruts formed on soil with about 15% water. Mean SPR was similar in and out of ruts from 0- to 5-cm depth, increased to 2 MPa outside ruts and 4 MPa inside ruts at 10- to 15-cm depth, and decreased by 10–38% outside ruts and by 39–48% inside ruts at the 30-cm depth. Soil BD was similar in and out of ruts from 0- to 2.5-cm depth, and below 2.5 cm, it was generally higher in ruts formed on moist soil with highest values between 10- and 20-cm depth. Conversely, BD in ruts formed on dry soil was similar to out-of-rut BD at all depths. This information is important for determining impacts of tank ruts on water infiltration and soil erosion and for modifying the Revised Universal Soil Loss Equation (RUSLE) and the Water Erosion Prediction Project (WEPP) models to more accurately predict soil losses on army training lands.     

Agricultural traffic impacts on soil

Alternate configurations of tires and tracks vary in their ability to generate tractive forces. These tractive elements also vary in the way that they impact the soil with some causing more soil disturbance than others. This soil disturbance includes soil compaction and rut formation which negatively impacts rainfall infiltration, rooting, and crop production while potentially increasing soil erosion and runoff. This paper will review a portion of the agricultural research that has been conducted related to soil impacts caused by the use of vehicle traffic in agricultural fields. Recommendations will also be made for ways to minimize the effects of vehicle traffic on soils when trafficking is necessary. These include: reducing axle load; reducing tractive element–soil contact stress by using radial tires, duals, and tracks; increasing soil drying prior to traffic; using conservation tillage systems which minimize vehicle traffic; using controlled traffic systems which eliminate random vehicle traffic across fields; and subsoiling to eliminate compacted soil profiles in crop growth zones. Soil compaction resulting from vehicle traffic may not be able to be completely eliminated, but it can be controlled and reduced through intelligent management of vehicle traffic.     

Effects of two different forwarder steering and transmission drive systems on rut dimensions

Impact of two different forwarders, with similar carrying capacities but different transmission drive and steering systems, on rut formation was compared. El-forest F15 with three individual steerable axles without bogies, large wheels (?164 cm) and an electric hybrid transmission drive system, and a Valmet 860, with conventional transmission drive (?131 cm wheels, two bogies) were compared. The ruts from the El-forest with or without a load were generally deeper than those produced by the tracked Valmet when driving in a straight line on soft arable land. On an S-shaped or circular course the El-forest and Valmet produced the same rut depths after the first pass, but with an increasing number of passes, the Valmet made deeper ruts. On the intermediate forest land, after driving in a straight line, the El-forest generally produced shallower ruts than the non-tracked Valmet (tracks not used at this site). When driving on a circular course, this difference was also apparent when machines carried a load. The mean rut width created by the El-forest was significantly narrower than from the Valmet at both sites. A transmission drive system with axles and wheels that can be individually steered seems advantageous to reduce rut formation, especially if the wheels have reduced ground pressure on soft soils.     

An overview of methods to convert cone index to bevameter parameters

This paper reviews experimental methods for the conversion of cone index measurements to bevameter parameters in support of vehicle soil/tire/track interactions for two general soil types, sand and lean clay. The accurate prediction of traction, motion resistance, and sinkage of tire/tracks off-road requires estimates of soil strength. Equipment used in the measurement of soil strength to support predictions of off-road mobility include the bevameter and the cone penetrometer. The portability of the cone penetrometer and rapid estimates of spatial/temporal variability in all terrain conditions make it an invaluable tool. The bevameter, a less portable tool, is used for the mechanical analysis of soils. The bevameter measures parameters defining soil strength in terms of cohesive modulus of soil deformation (k_c), frictional modulus of soil deformation (k_φ), exponent of soil sinkage (n), cohesion (c), angle of internal friction (φ), and the plate pressure at 1 in. (2.54 cm) of penetration (K) (Bekker, 1969). The field of terramechanics would greatly benefit from having the ability to convert cone penetrometer data in areas where bevameter parameters are difficult to collect. That ability to convert from cone index to bevameter parameters could be used for the large sets of existing cone index data to support determination of traction and motion resistance. This paper examines those methods for converting cone index to bevameter plate penetration parameters k_c, k_φ, and n.     

Rut depth, soil compaction and rolling resistance when using bogie tracks

There are few studies of rolling resistance for bogie tracks on forestry machines. The aim of this study was to compare the effects of wheels and two types of bogie tracks on rut formation, cone index, and vehicle rolling resistance on some typical forest soils in Sweden. In an experiment, two types of tracks were put on a trailer with a bogie with hydraulic extension on the pulling bar giving the trailer repeatable travelling speed. Loads of 0 and 9.9 Mg were used on the trailer. The main results of this study are: Compared to rather wide and soft tires, tracks on the bogie reduced rut depth by up to 40% and cone index in the ruts by about 10%, although the tracks increased the mass on the trailer by 10–12%. The relative rolling resistance coefficient was not higher for tracks than for wheels. Further studies should be conducted to show the effect of track tension on rolling resistance and flotation and of the effects of tracks on heavy vehicles on subsoil compaction.     

Deficiency of Approximate Interblock Conductivities for Simulation of Horizontal Unsaturated Flow

Determination of appropriate horizontal interblock conductivities approximations (k _app) is a critical step for numerical solution of unsaturated flow by finite difference method. This study characterized the horizontal effective interblock conductivity (k _H) and the classical k _app by contour map. The deficiencies of the k _app were determined by both statistical method and wetting front prediction. Mathematical expressions of the k _H were redeveloped for three constitutive hydraulic functions. A large database including ten different k _app formulas, three hydraulic functions, and a large range of soil texture is used to determine the deficiencies of the k _app for simulation of horizontal unsaturated flow. Some k _app may be either higher or lower than the k _H since they depend on both the expression forms of the k _app and the specific hydraulic functions. For the soil described by the Gardner function, the horizontal wetting front generated from the k _H is almost equivalent to the analytical solution, but those predicted from the k _app with certain errors. For the soils described by the Brooks–Corey function and the van Genuchten function, the best k _app for approximating the k _H were also determined, but with conversions for the soils described by the van Genuchten function. For any two k _app that hold compatible medians, the k _app (>k _H) better tracks the wetting front and makes mass conservation than the k _app (<k _H) does. The ranking list of k _app with respect to the quality of approximation k _H is ultimately determined from the analysis of mass balance of the simulation based on the large database. Ten k _app can be divided into four clusters. The logarithm mean and the arithmetic mean calculated from saturation can produce the best simulation results with relative mass balance error averagely less than 2%. Simulations conducted with harmonic mean calculated from hydraulic conductivity are mostly associated with the largest mass balance errors. Such a mean can therefore not be used to simulate horizontal water front advance, whatever the soil type and whatever the model of hydrodynamic function. It is also suggested that use of the classical k _app in a numerical process may generate improper results, thus application of the k _H is convincingly recommended on the prediction of horizontal wetting front.     

Mechanical behaviour of the upper layers of a sandy loam soil under shear loading

The mechanical behaviour of the upper layers of a sandy loam soil was studied under standard triaxial compression and direct shear box tests. Variations of soil material properties were investigated at four different initial dry bulk densities of 1410, 1520, 1610 and 1670 kg/m³. Soil deformation and volume change under the triaxial compression loading were also studied at these bulk densities. Results from the two tests showed increases in the soil mechanical properties with the initial dry bulk density. The internal friction angle values measured with the triaxial compression apparatus exceeded those measured with the direct shear box. In contrast, the soil cohesion values measured with the direct shear box exceeded those measured with the triaxial compression apparatus. Under the triaxial compression test, the loose soil samples underwent contraction and volume reduction, whereas the dense samples swelled and failure cracks appeared clearly at various planes. The soil contraction for the former case characterizes the occurrence of soil compaction, whereas the cracks propagation and volume increase in the latter case characterizes the breaking up and loosening of soil during tillage operations. For the loose and moderately compacted states, the engineering Poisson's ratio increased with the axial strain until loading was completed. It also increased at the compacted and very compacted states until reaching given loading stages, after which its value started to decrease. This shifting in the engineering Poisson's ratio during loading may provide another identification of the moment of soil failure occurrence, in addition to that of the maximum shear stress.     

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.     

Deformation processes below a plate sinkage test on sandy loam soil: theoretical approach

Mathematical models to predict the mode and extent of deformation occurring below sinkage plates are presented in the first part of this paper which encompasses the theoretical approach to the subject. These models are based on previous work by Earl (Earl R. Assessment of the behaviour of field soils during compression. Journal of Agricultural Engineering Research 1997;68:147–57)who developed a procedure to predict the likely mode of deformation using confined compression tests carried out alongside plate sinkage tests. This work suggested that soil behaviour, during increasing compression under a sinkage plate, is governed by three processes; (i) compaction below the plate with constant lateral stress, (ii) compaction with increasing lateral stress, and (iii) displacement and compaction of soil laterally. The aim of this second part to the paper is to observe soil deformation processes occurring below a circular sinkage plate to examine (i) whether the three phases of deformation referred to above occur in practice, and (ii) the accuracy of the models for predicting the soil deformation processes that occur. Tests were carried out on sandy loam soil under controlled conditions in a soil bin. Observations of deformation processes, recorded using long-exposure photography, revealed that during the initial stages of sinkage (a few millimetres), the corresponding disturbance of soil below the plate extended disproportionately further and was cylindrical in form. As sinkage progressed, the deformation process went through a transitional stage before reaching the more widely recognised form of the development of an inverted cone of compacted soil directly below the plate which moved with the plate causing lateral soil movement and compaction. Predictions for a medium density sandy loam were found to be in broad agreement with soil behaviour under a semi-circular sinkage plate observed behind a sheet of tempered glass under controlled conditions in a soil tank.     

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.     

Gas Condensate Relative Permeability for Well Calculations

This paper addresses several issues related to the modeling and experimental design of relative permeabilities used for simulating gas condensate well deliverability. Based on the properties of compositional flow equations, we make use of the fact that relative permeability ratio k _rg/k _ro is a purely thermodynamic variable, replacing saturation, when flow is steady-state. The key relation defining steady-state flow in gas condensate wells is relative permeability k _rg as a function of k _rg/k _ro. Consequently, determination of saturation and k _r as a function of saturation is not important for this specific calculation. Once the k _rg=f(k _rg/k _ro) relationship is experimentally established and correlated with capillary number (N _c), accurate modeling of condensate blockage is possible. A generalized model is developed for relative permeability as the function of k _rg/k _ro and capillary number. This model enables us to link the immiscible or rock curves with miscible or 'straight-line curves by a transition function dependent on the capillary number. This model is also extended to the case of high-rate, inertial gas flow within the steady-state condensate blockage regionand locally at the wellbore. We have paid particular attention to the effect of hysteresis on the relation k _rg=f(k _rg/k _ro), based on our observation that many repeated cycles of partial/complete imbibition and drainage occur in the near-well region during the life of a gas condensate well. Finally, the composite effect of condensate blockage is handled using a Muskat pseudopressure model, where relative permeabilities are corrected for the positive effect of capillary number dependence and the negative effect of inertial high velocity flow. Special steady-state experimental procedures have been developed to measure k _rg as a function of k _rg/k _ro and N _c. Saturations, though they can be measured, are not necessary. An approach for fitting steady-state gas condensate relative permeability data has been developed and used for modeling relative permeability curves.     

Changes in some mechanical properties of a loamy soil under the influence of mechanized forest exploitation in a beech forest of central Belgium

Modification of some soil mechanical properties (penetration resistance and consolidation pressure) induced by vehicle compaction during mechanized forest exploitation was studied in an acid and loamy leached forest soil of the loessic belt of central Belgium. In situ penetration tests and laboratory Bishop–Wesley cell tests were undertaken for the two main soil horizons of a beech high-forest, i.e. the eluvial E horizon (5–30 cm depth) and the underlying clay-enriched B_t horizon (30–60 cm depth). Both undisturbed and wheel-rutted soil areas were studied (E and B_t horizons vs. E_g and B_tg horizons).

Results show that: The experimental overconsolidation pressure of the eluvial reference horizon (E) is about 50 kPa higher than the value calculated from soil overburden pressure; this probably results from suction action during dry periods. The clay-enriched reference horizon (B_t) shows the same trends. In wheel-rutted areas, seven years after logging operations, the E_g horizon memorizes only 14.5% of the wheel induced stress due to forest machinery.

In the compacted B_tg horizon, the experimental overconsolidation pressure represents 96% of the exerted theoretical stresses due to harvesting actions. The good recording of the exerted stresses, after seven years, can be explained by: (1) The B_tg depth which keeps it from seasonal variations i.e. from desiccation–moistening or freeze–thaw cycling; (2) amorphous and free iron accumulation inducing a “glue” effect of the B_tg soil matrix, which could stabilize the soil structure and prevent recovery to initial conditions. These results provide clear evidence that on loessic materials, soil compaction due to logging operations leads to modifications in both physical (bulk density, total porosity) and mechanical (penetration resistance and consolidation pressure) soil properties.     

Rolling resistance and rut formation by implement tyres on tilled clay soil

The rolling resistance and rutting incurred by towed flotation implement tyres were investigated on an arable clay soil in three different soil strength conditions. Three radial (600/55R26.5) and two bias ply (600/55–26.5) tyres were compared. Experimental wheel loads were in the 35.4–36.4 kN range. Tyre inflation pressures, representing typical field operation, and road transport applications were in 100–150 kPa and 150–200 kPa, respectively. Soil strength was determined from mean soil penetration resistance (CI_0–15, in the layer 0–15 cm) and mean cohesion (C_0–10, 0–10 cm). Wheel rolling resistance evaluated by the coefficient of rolling resistance (CRR), rut depth (RD), driving speed, and field gradient were measured with the tyres mounted on a test trailer hitched to a tractor. CI_0–15 and C_0–10 values predicted the sinkage and the resistance to travel motion on clay soil reasonably well. When the CI_0–15 was less than 1 MPa and C_0–10 was below 100 kPa, CRR and RD increased rapidly. On average, CRR was 20% lower for the radials than the bias plies. In soft conditions (CI_0–15 ? 0.48 MPa), the radials produced 15% shallower ruts than bias plies, and the CRR was lower and RD shallower with field inflation pressures than with road pressures used. According to our results, flotation tyres can be recommended to agricultural machines when the implement or trailer is used in soft soil conditions.     

Mineralogical characteristics of soil dust from source regions in northern China

Mineral compositions of aerosol particles were investigated at four sites （Aksu, Dunhuang, Zhenbeitai, and Tongliao） in desert regions of northern China from March to May in 2001 and 2002 during the intensive field campaign period of ACE-Asia （Aerosol Characterization Experiments-Asia）. The X-ray diffraction （XRD） results show the main minerals for Asian dust are illite, chlorite, kaolinite, quartz, feldspar, calcite, and dolomite. Gypsum, hornblende, and halite are also detected in several samples. Semi-quantitative mineralogical data of aerosol samples show that carbonate content decreases from western to eastern source areas; that is, soil dust collected at western source area sites of Dunhuang and Aksu are enriched with carbonate, while northeastern source area site of Tongliao is associated with low carbonate content. But the spatial distribution of feldspar exhibits a different pattern as compared to carbonate, increasing from the western to the eastern sources. The total clay content is significantly higher （73% in average） at the deposition site of Changwu than those at source areas. Air-mass back trajectory studies for the three dust storm events observed at Changwu, showed that soil dust transport pathways were as expected from carbonate content for the source identification, further demonstrating that carbonate was a useful tracer for eolian dust on regional scale in northern China.     

UPM indoor tyre traction testing facility

Universiti Putra Malaysia (UPM) tyre traction testing facility was designed and developed to spearhead fundamental research on traction mechanics with high-lug agricultural tyres on tropical soils. This available facility consists of a moving carriage with a cantilever-mounted tyre that moves in either forward or reverse directions on rails well above a soil tank. The present facility set-up was able to operate in either: (a) towing test mode for tyre motion resistance studies, or (b) driving test mode for tyre net traction and tractive efficiency studies. The test tyre on the moving carriage under the towing test mode was made to rotate and engage onto the soil surface in the tank through a chain drive system. Under the driving test mode, the test tyre on the moving carriage was powered to rotate by a motor and a gearbox system with an additional pull provided by a cable-pulley mechanism connected to a tower with hanging dead weights. All controls on the moving carriage were activated from the main control console. Respective transducers were positioned at various localities within and interfaced to a data acquisition system to measure tyre horizontal and vertical forces, tyre sinkage, tyre speed and motion carriage speed. The data acquisition system was able to receive the measured signals in real time, display on the monitor screen and record into its CPU storage memory. Static calibration tests on various associated transducers showed excellent linearity with coefficients of determination (r²) of close to 1. The developed facility was successfully tested to determine motion resistance and net traction ratios for high-lug agricultural tyre at the recommended inflation pressure on sandy clay loam soil.     

Presentation of the creep curves of solid biological materials by a simplified mathematical version of the generalized Kelvin-Voigt model

Published creep equations, derived from the Kelvin-Voigt model with a discrete retardation time spectrum were used to generate data for linear presentation of the creep function. It is shown that 2–3 term creep functions, containing 4–6 constants, could be reduced to an algebraic expression having two constants only. Consequently, entire creep curves of a variety of biological and food materials could be described by a single type of equation in the form of:P (t) = k ₀ + k₁ t + t/(k₂ + k₃t) whereP (t) is the creep parameter (compliance, strain or deformation),k ₀ a constant representing the instantaneous compliance,k ₁ a constant representing the steady-state flow, andk ₂ andk ₃ the characteristic constants of the creep function (t) obtained by regression from the linear relationship oft/ (t) vst.     

Prediction of trafficability for tracked vehicle on broken soil: real size tests

Full-scale tests were carried out within the broader framework of a study of an operational mechanical mine clearance system. This system is made up of a tracked machine pushing a mine clearance plow that scarifies the soil to approximately 30 cm depth. This study examines the capacity of the tractor to move on a disturbed soil. This paper presents motion resistance tests and drawbar pull tests on four types of soil. The soils have been chosen to be scientifically representative of the broad distribution on our planet: a sand (frictional soil), a silt (cohesive soil), a silty gravel (coarse-grained soil), and a silty sand (cohesive soil). The tests are performed in two configurations: on compacted soils and on soils scarified with an experimental plow. The results of each test condition are described. The effects of the soil type, its state, and the speed of the tested vehicle are presented. Using these results and, in addition, full-scale tests of scarification, we present an operational analysis determining the mobility of a tracked vehicle on broken soil. This method makes it possible to calculate the maximum speed of a mechanical mine clearance system for the whole range of soils tested.     

Using an Ensemble Kalman Filter Method to Calibrate Parameters and Update Soluble Chemical Transfer From Soil to Surface Runoff

A data assimilation method, an ensemble Kalman filter (EnKF), is applied to simultaneously calibrate parameters and update prediction for soluble chemical transfer from soil into surface runoff. The soluble chemical transfer is calculated using a two-layer analytical model with constant parameters, h _mix (water depth of the soil-mixing layer), α and γ (surface runoff and infiltration-related incomplete mixing parameters). The model is presented as the forward model. Based on laboratory experimental results, the measured chemical concentrations in the surface runoff are assimilated into the calculation through the developed EnKF method to calibrate the parameters and update chemical concentration in the runoff. In comparison with the calculation without data assimilation method, the updated solute concentration results are much closer to the experimental observed data and the calibrated parameters, h _mix, α and γ, are no longer constants, but time dependent, which are physically reasonable. The study results indicate that the EnKF method significantly improves the prediction for solute chemical transfer from soil into surface runoff, whereas the extended Kalman filter will not, and the ensemble size of 100 will be suitable for the chemical concentration calculation based on our trial.     

CMSC型固化剂改良土的新型CBR试验研究

针对苏北某高速公路沿线特殊软土的特点,采用两种方案按全粉料配料的方法配制CMSC型固化剂,并按一定剂量掺入土中。同时,考虑当地的水文气候因素,针对传统钢制击实筒的饱水条件偏保守的特点,研制了新型击实筒,在新型击实筒内制备试件并养护至规定龄期,采用新型浸水装置饱水,进行贯入试验。结果表明,试件的各向饱水条件更接近实际工况,增强了CBR值的可信度。CMSC型固化剂改良土的改良效果优于石灰改良土,且固化剂掺入剂量存在最佳掺量,同时分析了CMSC型固化剂的加固机理,为进一步研究和工程应用提供了参考。     

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.