Effects of tine rake angle and aspect ratio on soil reactions in dry loam soil

Study was conducted in a laboratory glass-sided soil bin with dry compact loam soil with 5.2% (d.b.) moisture content. The specific objective of this study was to determine the effects of flat rigid tine rake angle (forward angle between tine face and horizontal soil surface) and aspect ratio (tine width/tine depth) on soil reactions. The tine was moved in the soil in a quasi-static condition and soil reactions were recorded using L-shaped force transducers. Corresponding soil failure patterns were observed through a glass window. Tine rake angles of 50°, 90° and 130° were used. The effects of aspect ratio were studied by varying both width and depth of the tines. Individual effects of width and depth were investigated by maintaining a constant aspect ratio of 2.0 but varying width and depth. Observations indicated that soil reactions are affected by tine design parameters. For all tine rake angles and aspect ratios, soil reactions were observed to be cyclic in nature and could be matched well with corresponding soil failure patterns. The horizontal and vertical soil reactions were in phase. Investigations into the individual effects of tine width and depth revealed that the aspect ratio alone cannot account for changes in soil reactions. The effects are mainly due to the individual changes in width and depth.     

The cutting of soil by narrow blades

The available models for predicting the forces acting on a narrow soil cutting blade have required separate measurements of the shape of the three-dimensional soil failure pattern ahead of the blade. It is proposed that a three-dimensional model consisting of straight line failure patterns in the soil can be used to predict both the draft forces and the volume of soil disturbed in front of a narrow blade. Limit equilibrium mechanics equations are written for the soil wedges in terms of an unknown angle of the failure zone and the theoretical draft force is minimized with respect to this angle. Force factors are thus found which are of the type to fit Reece's general earthmoving equation, but which vary with the width to depth ratio of the blade as well as with the rake angle of the blade and the friction angle of the soil. In addition the approximate geometry of the three-dimensional failure pattern in the soil is predicted for varying blade shapes and soil strengths. This allows the design of simple tools on the basis of their draft force requirements and their soil cutting efficiency. The draft force predictions and failure geometry calculations are shown to have considerable verification by experimental results.     

Dynamics of a powered disk in clay soil

Experiments were conducted with a single powered disk in a laboratory soil bin containing Bangkok clay soil with an average moisture content of 18% (db) and 1100 kPa cone index. The disk was 510 cm in diameter and 560 mm in radius of concavity. During the tests the disk angle was varied from 20° to 35°, ground speed from 1 to 3 km/h and rotational speed from 60 to 140 rpm. The working depth was kept constant at 12 cm. The vertical, horizontal and lateral reactions of the soil were measured by force transducers. The forward and rotational speeds were recorded. It was observed that disk angle, rotational speed and ground speed had significant effects on soil reactive forces and power requirement. With a small disk angle, low ground speed, and high rotational speed, the soil longitudinal reactive force was a pushing force and became a resistive one at larger disk angles and ground speeds. The soil transverse reactive force increased with an increase of rotational and ground speed but decreased with the increase of disk angle, whereas the vertical relative force increased only with the increase of ground speed but decreased with the increase of rotational speed and disk angle. It was found that the powered disk required the least power at a disk angle of 30° and rotational speed between 80 and 100 rpm. Increase in ground speed from 1 to 3 km/h increased the total power requirement by 31.8%. Upon driving the disk forward, the draft reduced considerably compared to that of the free-rolling disk. By driving the disk in the reverse direction, the draft reduced slightly. At a disk angle of 30°, rotational speed of 100 rpm, and ground speed of 3 km/h, the total power requirement of the forward-driven disk was 65% higher than that of the free-rolling disk. The predicted engine power of the forward-driven disk, however, was only 21% higher than that of the free-rolling one owing to the more efficient power transmission through the PTO, as opposed to the drawbar. The effects of reverse driving and free rolling of the disk were also studied.     

A dynamic model for soil cutting by blade and tine

A dynamic model for soil cutting resistance prediction by blade and tine was developed, taking account of shear rate effects both on soil shear strength and soil-metal friction, besides the conventional soil slice inertia, for both brittle and flow failure of soil. The model was verified with a series of tests in a soil bin with a blade and a tine, and the results were acceptable.     

Measurement of soil reaction forces on a single movable lug

In order to clarify characteristics of a new mechanism called a movable lug, a model of a single movable lug equipped with an L-shaped force transducer has been developed. The soil reaction forces (normal and tangential) on a flat single movable lug, a curved single movable lug and a fixed lug were measured on wet sandy loam soil in the laboratory soil bin test. These measured forces then were converted to lug pull and lift forces. The pull and lift forces obtained by the flat movable lug with 45° lug inclination angle and the curved movable lug were higher than those of the fixed lug. It was observed that the lift force of the fixed lug achieved its peak and dropped earlier than those of the movable lugs. However, the peaks of pull and lift forces of the flat and curved movable lugs were almost the same. The flat movable lug with 45° lug inclination angle generated a slightly higher peak of pull force than those with 30° and 60° lug inclination angles. However, the higher lug inclination angle produced, the lower peak of lift force. It was observed that the pull and lift forces increased as the sinkage increased. In contrast to the flat movable lug with 45° lug inclination angle, the curved movable lug produced greater lift force especially at high sinkage. The increase in lug slip from 5% to 25 and 50% caused an increase in the peaks of pull and lift forces. The soil moisture content affected the lug forces significantly.     

Hysteresis in soil mechanical behavior

The performance of a vertical tine was investigated at various water contents during wetting and drying cycles in a clay-loam soil. Results showed that at a given water content the soil during the wetting cycle failed by fracture mode and offered relatively more draft. Soil during the drying cycle cracked, and when a tine was pushed through the soil, it failed along the cracks. This failure mode was referred to as preferential fracture. For a given water content, tine forces and soil shear strength properties were found to be greater during the wetting cycle than the drying cycle, which leads to the conclusion that there is a hysteresis effect in soil caused by drying stress induced by seasonal wetting and drying.     

地震波倾斜入射下两相饱和土层响应数值模拟

基于Biot两相饱和多孔介质理论建立了频域内饱和土层的刚度矩阵,对从基岩倾斜入射地震波下饱和土层的波动响应进行了数值研究,入射波采取修正的Kanai-Tajimi谱。通过土层地表面处的水平以及竖直放大系数研究了在不同工况条件下土层的波动响应,研究结果表明,土层的波动响应在入射角接近临界入射角时达到峰值;土层的波动响应随着基岩埋深基以及土层阻尼比的增大显著减小;而土层与基岩的波速比对土层的波动响应的影响存在临界波速比,使土层响应达到极值。对于含有夹层的地质环境,研究了波动响应沿深度的分布,通过与均质土层下响应对比,显示非均质夹层能显著减小土层地表处的波动响应,尤其软夹层能较好地阻止入射波向上的传播。     

Determination of yield stress fluid behaviour from inclined plane test

The aim of this paper is to determine precisely under which conditions an inclined plane can be used as a rheometer, which could represent a practical and rapid technique for various types of industrial or natural viscoplastic coarse suspensions. We first examine its efficiency and relevancy for determining fluid yield stress in a straight way by measuring the deepest fluid layer able to stay on the inclined plane. We have made experiments with different materials (clay-water suspensions) whose yield stress ranged from 35 to 90 Pa, using 1 m long open rectangular channels with a slope ranging from 10 to 30° and a width ranging from 5 to 25 cm. Our procedure involved measuring the final fluid depth far from edges a long time after the end of the slow gravity-induced emptying of a dam placed upstream. The fluid yield stress was also estimated independently by fitting a Herschel-Bulkley model to simple shear rheometry data obtained within a relatively wide shear rate range. A good agreement between inclined rectangular channel tests and independent usual rheometrical tests is obtained even for aspect ratios (flow depth to channel width ratio) as large as 1 when one assumes that, when the fluid has stopped, the side and bottom wall shear stresses are equal to the fluid yield stress. These results prove the efficiency of the inclined plane test for determining yield stress when appropriate experimental precautions are taken for both tests. In addition we examine the possibility of determining the simple shear flow curve of a mud suspension from fluid depth, velocity and discharge measurements of different steady flows in a wide open channel (8 m long; 60 cm wide) equipped with a recirculating system. The results obtained from inclined plane tests are in good agreement with independent rheometrical data (with torsional geometries). However it is technically difficult to cover a wide shear rate range from the inclined plane technique since this requires a rather wide channel flow rate range.     

Improvement of a power tiller cage wheel for use in swampy peat soils

This study was aimed at investigating traction performance of a cage wheel for use in swampy peat soils in Indonesia. The tests were conducted in a soil bin filled with peat soil taken from the swampy areas. A set up was developed to measure tractive performance of a single cage wheel. Deep sinkage and high wheel slip were identified as the major problems of using the existing cage wheel design in swampy peat soils. The results revealed that increasing the lug angle from 15 to 35° and the length of lug improved the tractive performance of the cage wheel significantly, while increasing the number of lugs from 14 to 18 and width of lug did not improve the tractive performance significantly. A cage wheel with lug size 325×80 mm, 35° lug angle, 14 lugs (26° lug spacing), with 2 circumferential flat rings installed on the inner side of the lugs, out performed the other settings for use with power tillers in swampy peat soils.     

The effect of dynamic impact and water potential on some surface soil properties

A direct shear test with a superimposed impact was used to simulate the action of a track on the soil surface and to study the effect on soil surface properties. Results showed that impact increased bulk density, reduced saturated hydraulic conductivity and decreased cone penetrometer resistance. An impact plus shear treatment reduced the residual shear strength to approximately 60 kPa compared with 85 kPa for a shear only treatment. Water tension also greatly influenced the changes measured with the order of greatest change being −5>−10>−60>t-100>−300 kPa. The results are discussed with respect to soil trafficability and soil structural change with vehicle passage.     

The motion of a stone embedded in non-cohesive soil disturbed by a moving tine

As part of an investigation into impact damage on soil-working implements, a glass-sided model box has been used to study the motion of 10, 50 and 100 mm diameter hemispheres in sand as a 38 mm wide tine inclined at 45° approaches. The observations were made using high-speed photography. It was found that the sand did not always cause the hemisphere to move before contact with the tine, and that motion was determined by the position of the centre of the hemisphere relative to the boundary of soil disturbance ahead of the tine. This effect was independent of velocity. A minimum size of hemisphere was found below which motion always began before contact was made with the tine. In the particular arrangement used this was about 20 mm. Movement of the hemisphere before contact reduced the contact stresses and the practical implications of this are discussed.     

Effect of circumferential angle, lug spacing and slip on lug wheel forces

This study was conducted to investigate the effect of circumferential angle, lug spacing and wheel slip on forces produced by a cage wheel. Experiments were conducted in a laboratory soil bin having Bangkok Clay soil with 51% (d.b.) soil moisture content. Six ring-type loadcells were used to measure the soil horizontal, vertical and transverse reactions on the cage wheel lugs. The circumferential angle was varied from 0, 15, 30 to 45°. The lug spacing and wheel slip were varied from 20, 30 to 40° and 20, 35 to 50% respectively. All the force measurements were done at a constant 7 cm sinkage. The results showed that increasing circumferntial angle up to 45° can reduce variation in lug wheel forces, at the same time it had little effect on the mean pull and lift values. The side force was affected by the changes of circumferential angle. The 20° lug spacing not only gave the minimum variations but also maximum mean lug forces. The highest lug wheel forces occurred at 35% wheel slip.     

Power spectral density analysis of draft and torque fluctuations of a PTO powered disk tiller

Experiments were conducted in a typical Bangkok clay soil with a PTO driven disk tiller to collect the draft force and torque variation data. Tests were conducted at different forward speeds of 0.29, 0.59, 0.86, 1.08 and 1.37 m/s and at 28° and 33° disk gang angle settings. Average soil moisture content was 26% and average cone index of the test soil was 1870 kPa during all the tests. The draft force was measured by a three point linkage dynamometer. The PTO torque was measured by a slip ring type torque transducer. Tests were also conducted in the unpowered mode. Fast Fourier transform (FFT) and power spectral density (PSD) analysis techniques were used to analyse the draft force and torque variations in a time domain. The results indicated that the dominant frequencies of the draft force variations were within the range of 2.5–5.5 cycles/m of forward travel. The wave length was longer at a higher disk gang angle setting. The dominant frequency component of the torque variations varied from 3.3 to 4.3 cycles/revolution of the disk. In the unpowered mode the dominant frequencies of the draft signals had less magnitude than those of the powered mode for the same operating conditions at both disk gang angle settings of the powered disk.     

Mechanical properties in relation to vehicle mobility of Sepang peat terrain in Malaysia

An analytical framework for determining the mechanical properties of peat and predicting the tractive performance of tracked vehicle is presented. It takes into account the load-sinkage and shearing characteristics of peat as well as all major design parameters of tracked vehicle. An experimental study on the mechanical properties of peat soil was conducted at Sepang area, Selangor, Malaysia. The stiffness values of surface mat and underlying weak peat deposit from load-sinkage test were determined by specially made bearing capacity apparatus. The mean values of surface mat stiffness before and after drainage were found to be 31 and 45.62 kN/m³, respectively and the mean values of underlying peat stiffness before and after drainage were found to be 252 and 380.20 kN/m³, respectively. The mean value of the internal frictional angle, cohesiveness and shear deformation modulus of the peat soil sample were determined using a direct shear box apparatus in the laboratory. The mean values of internal friction angle, cohesiveness and shear deformation modulus before and after drainage were found to be 22.80° and 24.31°, 2.63 and 2.89 kN/m², and 1.21 and 1.37 cm, respectively.     

Identification of Cracking Mechanisms in Scaled FRP Reinforced Concrete Beams using Acoustic Emission

Acoustic emission was used to monitor the cracking mechanisms leading to the failure of scaled concrete beams having Glass Fiber Reinforced Polymer (GFRP) longitudinal reinforcement and no shear reinforcement. Dimensional scaling included that of the effective depth of the cross section, which is a key parameter associated with the scaling of shear strength; and maximum aggregate size, which affects the shear-resisting mechanism of aggregate interlock along shear (inclined) cracks. Five GFRP reinforced concrete (RC) beams with effective depth up to 290 mm and constant shear span-to-effective depth ratio of 3.1 were load tested under four-point bending. Two types of failures were observed: flexural, due to rupture of the GFRP reinforcement in the constant moment region; and shear, due to inclined cracking in either constant shear region through the entire section depth. Acoustic emission (AE) analyses were performed to classify crack types occurring at different points in the load history. The results of this study indicate that appropriate AE parameters can be used to discriminate between developing flexural and shear cracks irrespective of scale, and provide warning of impending failure irrespective of the failure mode (flexural and shear). In addition, AE source location enabled to accurately map crack growth and identify areas of significant damage activity. These outcomes attest to the potential of AE as a viable technique for structural health monitoring and prognosis systems and techniques.     

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.     

An inclined wall jet: Mean flow characteristics and effects of acoustic excitation

 The mean velocity field of a 30° inclined wall jet has been investigated using both hot-wire and laser Doppler anemometry (LDA). Provided that the nozzle aspect ratio is greater than 30 and the inclined wall angle (β) is less than 50°, LDA measurements for various β show that the reattachment length is independent of the nozzle aspect ratio and the nozzle exit Reynolds number (in the range 6670–13,340). There is general agreement between the reattachment lengths determined by LDA and those determined using wall surface oil film visualisation technique. The role of coherent structures arising from initial instabilities of a 30° wall jet has been explored by hot-wire spectra measurements. Results indicate that the fundamental vortex roll-up frequency in both the inner and outer shear layer corresponds to a Strouhal number (based on nozzle exit momentum thickness and velocity) of 0.012. The spatial development of instabilities in the jet has been studied by introducing acoustic excitation at a frequency corresponding to the shear layer mode. The formation of the fundamental and its first subharmonic has been identified in the outer shear layer. However, the development of the first subharmonic in the inner shear layer has been severely suppressed. Distributions of mean velocities, turbulence intensities and Reynolds shear stress indicate that controlled acoustic excitation enhances the development of instabilities and promotes jet reattachment to the wall, resulting in a substantially reduced recirculation flow region. Received: 24 November 1998/Accepted: 24 August 1999     

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.     

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 soil parameters useful in predicting tractive ability of off-road vehicles using an instrumented portable device

An instrumented portable device that measures soil sinkage, shear, and frictional parameters in situ was developed to investigate the complexity of soil-traction device interaction process. The device was tested to determine its ability to measure soil frictional and shear characteristics. Extensive laboratory tests were conducted using dry and moist Capay clay and Yolo loam soils. In addition, field tests were also conducted in a Yolo loam field located at the UC Davis Agricultural Experiment Station. The Cohron sheargraph was also tested under the same laboratory experimental conditions to determine adhesion, soil-metal friction, cohesion, and angle of internal friction of soil. The analysis of experimental data indicated that soil adhesion and soil-metal friction were found to be functions of the intercept and slope values of cone torque versus cone index plot (r² = 0.94 and 0.95, respectively). Moreover, soil cohesion was found to be related to adhesion by the constrained adhesion relationship, and soil angle of internal friction was proportional to soil-metal friction as reported by Hettiaratchi [7] and [8]. These results imply that a simpler device consisting of a rotating cone can be developed to measure soil frictional and shear characteristics. Preliminary results showed that the soil parameters determined using this device predicted the maximum net traction developed by four different radial ply tires tested by Upadhyaya et al. [18] under similar soil conditions quite well. These results indicate that the parameters obtained from the device could be useful in obtaining traction related parameters of a soil-tractive device interaction process.