Study on Dragline-Bulldozer Operation with Variations in Coal Seam Thickness

The dragline is one of the most promising surface mining machines in China. This paper studies the interac-tion between the working bench advancing speed and the stripping volume with variation in coal seam thickness. Ad-justing the bulldozing volume (depth) and/or changing the dragline bench height are proposed as means to ensure a smooth and economical mining operation. When the coal seam is getting thicker it is recommended to reduce the bull-dozing volume (depth) for a higher dragline efficiency. When the coal seam is getting thinner it is recommended to in-crease the bulldozing volume (depth) to ensure the dragline can work at the proper bench height.

EXPERIMENTAL AND NUMERICAL RESEARCH ON BULLDOZER WORKING PROCESS

A simulative analysis coupled with experiment on behaviors of a soil bed cut by a model bulldozer blade is carried out using the finite element/distinct element method（FE/DEM） facility built in the ELFEN package. Before simulation, tensile/compression, triaxial compression and the soil specimens are examined through uniaxial direct shear tests to obtain model characteristics and relevant parameters, then soil cutting experiments are carried out via a mini-soil bin system with a soil bed of 60/120 mm in width and 10 mm in depth cut by a 1/9 scale model bulldozer blade moving with the velocity of 10 mm/s. The soil constitutive model includes the tensile elastic model for tensile breakage and the compressive elastoplastic relationship with Mohr-Coulomb criterion. The cutting length in simulation is set as 1/4 of that in the experiment divided into 1 869 triangular elements. The comparison between the simulated results and experimental ones shows that the used model is capable of analyzing soil dynamic behaviors qualitatively, and the predicted fracturing profiles in general conform to the experiment. Hence the feasibility for analyzing soil fracturing behaviors in tillage or other similar processes is validated.

Sliding resistance of plates with bionic bumpy surface against soil

The non-smooth surface morphology of dung beetle, Copris ochus, was analyzed. The bulldozing plates with bionic geometric non-smooth or the chemical uneven surface were designed for the soil sliding test based on the simulation of the bumpy surface of the dung beetle. Special black metals— with different contents of alloys of manganese, silicon, chromium, copper and rare earth— were developed for making geometric non-smooth and chemical uneven surfaces by means of surface welding at the surfaces of a middle carbon steel plate. Four metals, with different surface properties including hardness and water contact angle were used to make the bulldozing plates for measuring the soil sliding resistance. Test results of soil sliding resistance indicate that all the geometric non-smooth plates and the chemical uneven plates reducing soil friction. Considering the materials and surface morphology, the bionic plate can reduce the soil sliding resistance from 18.1 % up to 42.2%, compared to the traditional smooth bulldozing plate made from middle carbon steel. The test results also show that the smaller the normal load, the greater effect on resistance reduction by the bionic non-smooth surface plates.

A Computational Model of Soil Adhesion and Resistance for a Non-smooth Bulldozing Plate

Adhesive forces exist between soil and the surfaces of soil-engaging components; they increase working resistance and energy consumption. This paper tries to find an approach to reduce the adhesion and resistance of bulldozing plate. A simplified mechanical model of adhesion and resistance between soil and a non-smooth bulldozing plate is proposed. The interaction force between moist soil and a non-smooth bulldozing plate is analyzed. The pressure and friction distribution on the bulldozing plate are computed, and the anti-adhesive effect of a corrugated bulldozing plate is simulated numerically. Numerical results show that the wavy bulldozing plate achieves an effective drag reduction in moist soil. The optimal wavy shape of the corrugated bulldozing plate with the minimal resistance is designed. The basic principle of reducing soil adhesion of the non-smooth surface is discovered.

Circular Disc Blade Considerations in Soil Force Prediction Modelling

Previous soil-disc force prediction models have considered spherical and concave blades, as used on disc ploughs and harrows, with many simplifying assumptions. This study proposes an approach applying the fundamental equation of earth moving mechanics for calculating the soil passive reaction acting on a rotating fiat disc blade as used on a zero-till single disc seeder. The study considers the effects of disc variable depth of cut, sweep and tilt angles, free rotation and a scrubbing reaction at the beveled edge. This paper outlines the modeling approach and prediction results for a fixed circular blade operating at 90° sweep angle over a range of speeds and at two tilt angles. To account for the varying depth across the circular disc shape width, elemental wide blade force reactions acting on wide blade segments of elemental width were integrated across the disc working width. By including inertia forces due to speed as well as additional bulldozing forces due to the loose soil accumulation in front of the blade the draught and upward vertical forces acting on the vertical disc blade were predicted with a deviation of 6%-19% and 1.5%-14% from measured data, respectively. The model was able to predict the effect of increasing the tilt angle from 0° to 20° on reducing both draught and upward vertical forces. Further development and validation of the model will be described in subsequent papers, reflecting a step by step approach of increasing complexity to model a disc blade as used on a zero-till single disc seeding system.

Spread of common native and invasive grasses and ruderal trees following anthropogenic disturbances in a tropical dry forest

Introduction:A fundamental challenge to the integrity of tropical dry forest ecosystems is the invasion of nonnative grass species.These grasses compete for resources and fuel anthropogenic wildfires.In 2012,a bulldozer from the Puerto Rico Electric Power Authority cleared a 570-m trail from a state road into a mature dry forest section of Guánica Forest to control a wildfire.We monitored colonization by a non-native invasive grass(Megathyrsus maximus),a highly invasive tree(Leucaena leucocephala),and a native grass(Uniola virgata),as well as natural regeneration,along the bulldozer trail.We determined whether bulldozing facilitated colonization by these species into the forest and the extent of spread.Results:Distance from propagule source and temporal variations strongly influenced colonization by our three focal species.Megathyrsus maximus invaded along the trail from source populations by the state road.The establishment of new colonies of M.maximus seedlings went as far as 570 m inside the forest(i.e.,at the end of the bulldozer trail),but we found most new colonies within 270 m of the road.Leucaena leucocephala exhibited a similar spreading pattern.Before disturbance,Uniola virgata was distributed widely across the forest,but the highest densities were found in areas near the latter portion(>401 m)of the bulldozer trail.Subsequently,the species formed new clumps along more than half of the trail(250 to 570 m),apparently colonizing from undisturbed patches nearby.Conclusions:Bulldozing facilitated the invasion of non-native vegetation.The projected community assemblage will be more fire-prone than before since M.maximus carries fire across the landscape better than U.virgata,emphasizing the capacity of invasive plant colonization to alter local ecological processes after only a single wildfire and bulldoze event.Our results provide a valuable baseline for short-term vegetation response to anthropogenic disturbances in tropical semi-deciduous dry forests.