Soil Cutting Processes: The Cutting of Water Saturated Sand

2011 ◽  
Author(s):  
Sape A. Miedema
Keyword(s):  
Pore Water ◽  
Cutting Forces ◽  
Water Vapor Pressure ◽  
Cutting Process ◽  
Shear Stresses ◽  
Saturated Sand ◽  
Pore Water Pressures ◽  
Offshore Industry ◽  
Cutting Processes ◽  
Water Saturated

The cutting process in water saturated sand has been the subject of research in the dredging industry for decades already. The Dutch dredging industry started this research in the sixties, resulting in a number of models in the seventies and eighties (van Leussen & van Os (1987) and Miedema (1987 and later). The application of the theory in the offshore industry is rare, although Palmer (1999) used it. In the last decades trenching has been a practice where these theories can be applied and with the tendencies of working in deeper water and in arctic conditions it is useful to try to combine the knowledge from the dredging and the offshore industry regarding cutting processes. The cutting process in water saturated sand is dominated by the phenomenon of dilatancy. Due to shear stresses, the porosity of the sand increases, resulting in an absolute decrease of the pore water pressures. Since the soil stresses are a constant, and equal to the sum of the grain stresses and the pore water stresses, this implies that the grain stresses increase with decreasing pore water stresses. This results in much higher cutting forces. The decrease of the pore water stresses is limited by the water vapor pressure and so are the cutting forces. At shallow waters, the pore water may start to cavitate if the strain rates are high enough, but at very deep water this will probably not occur. In this paper the basics of the cutting theory are explained. This cutting theory however requires a lot of finite element calculations in order to determine the pore water pressures. The paper gives simplification that allows the user to apply the theory with the help of pre-calculated coefficients.

Laboratory investigations of cutting processes applied to coal-winning machines

1968 ◽  
Vol 3 (3) ◽  
pp. 232-243 ◽  
Author(s):  
C D Pomeroy ◽  
J H Brown
Keyword(s):  
Cutting Forces ◽  
Laboratory Experiments ◽  
Cutting Process ◽  
Laboratory Findings ◽  
Cutting Mechanics ◽  
Cutting Zone ◽  
Laboratory Investigations ◽  
Cutting Processes

Laboratory experiments on cutting mechanics in coal are described, and the conclusions reached are tested in underground trials on standard coal-winning machines. In general the laboratory findings are verified but such discrepancies as are observed are attributed to the fact that in the laboratory the cutting process is studied independently of the flow of broken coal from the cutting zone, whilst in some underground applications the forces and power needed to move and cause secondary degradation of the extracted coal can swamp the true cutting forces.

Base liquefaction: a mechanism for shear-induced failure of loose granular slopes

2014 ◽  
Vol 51 (5) ◽  
pp. 496-507 ◽  
Author(s):  
W. Andy Take ◽  
Ryley A. Beddoe
Keyword(s):  
Pore Water ◽  
Strain Softening ◽  
Back Analysis ◽  
Monotonic Loading ◽  
Saturated Sand ◽  
Centrifuge Modelling ◽  
Geotechnical Centrifuge ◽  
Groundwater Flux ◽  
Static Liquefaction ◽  
Pore Water Pressures

For the deviatoric strain-softening associated with static liquefaction to occur in a landslide, the soil must be contractile, be subjected to a monotonic loading trigger, and be sufficiently saturated to permit the generation of excess pore-water pressures upon loading. It is hypothesized in this paper that static liquefaction might preferentially occur in the saturated granular soil located at the base of the landslide in certain circumstances rather than the well-drained inclined portion of the slope. This hypothesis was tested using the technique of geotechnical centrifuge modelling with a loose granular slope, which was brought to failure under a step-wise increase in groundwater flux. The rising pore-water pressures eventually led to a small localized failure at the toe of the slope. This toe failure acted as the monotonic loading trigger to shear the loose contractile saturated sand at the base of the slope and cause liquefaction to occur in the base region. A back-analysis of the landslide indicates that these types of analyses should be viewed with great caution as the progressive nature of the event following triggering will be likely to lead to erroneous back-calculations of mobilized strength.

Drained deformation and failure due to cyclic pore pressures in soft natural clay at low stresses

1987 ◽  
Vol 24 (2) ◽  
pp. 208-215 ◽  
Author(s):  
K. D. Eigenbrod ◽  
J.-P. Burak ◽  
J. Graham
Keyword(s):  
Pore Water ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Shear Stresses ◽  
Alternative Mechanism ◽  
Natural Clay ◽  
Deformation And Failure ◽  
First Approximation ◽  
Pore Water Pressures ◽  
Normal And Shear Stresses

Slow, recurring downslope movements in northern climates are frequently referred to as "creep movements," and are usually related to outwards freezing followed by vertical thawing movements. An alternative mechanism is examined in the reported test data.Undisturbed block samples of proglacial clay from a slope near yellowknife, N.W.T., have been tested by cyclically varying the pore-water pressure in triaxial specimens by an amount Δu, and measuring the resulting strains per cycle. The specimens were initially anisotropically consolidated with normal and shear stresses corresponding to those in the moving mantle. Drainage was permitted throughout the testing. This procedure represents changes that can occur in a natural slope from (a) seasonal groundwater level changes and (b) elevated pore-water pressures that accompany thawing. After 60–100 cycles, the pore-water pressure was systematically increased to the value Δuf at which the samples failed. This occurred on a steep, low-stress envelope, approximately c′ = 4 KPa, [Formula: see text]. The envelope is probably controlled by the nuggety macrostructure of the clay and appears to be slightly to the left of the [Formula: see text] locus.The strains per cycle were approximately linear in the range 30–100 cycles. As a first approximation they have been modelled as varying linearly with the ratio Δu/Δuf almost up to failure at Δu/Δuf = 1.0. Key words: downslope creep, solifluction, slope stability, clay, pore-water pressure, cyclic loading, low-stress failure.

Pore-water pressure response during undrained isotropic load changes in layered soils

1999 ◽  
Vol 36 (3) ◽  
pp. 544-555
Author(s):  
K D Eigenbrod ◽  
W H Wurmnest
Keyword(s):  
Pore Pressure ◽  
Pore Water ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Pressure Coefficient ◽  
Shear Stresses ◽  
Pressure Equalization ◽  
Pore Water Pressures ◽  
Internal Pore ◽  
Varved Clay

Low pore-water pressure responses observed during undrained isotropic loading of thinly interbedded varved clay specimens were related to internal pore-water pressure equalization and internal shearing between soft clay seams and stiff silt layers of the varved clay. Both processes were analyzed in two separate models: a finite element analysis of the layered soil specimen with different elastic properties for each layer showed that shear stresses can develop along the layer interfaces during undrained isotropic loading. However, because the shear stresses are small and restricted to a narrow zone close to the surface of the cylindrical specimen, it appeared that the effect of shearing on the overall pore-water responses is negligible. The analysis of the pore-water pressures during undrained, isotropic loading demonstrated that hydraulic gradients between the two layers will develop. As a result, pore water will drain from the clay into the silt, leading to consolidation of the clay and swelling of the silt seams. The stabilized pore-water pressures should be the same as the pore-water pressures measured for the overall specimen, if the effect of internal shearing is negligible. Comparison of the computed with the measured overall pore-water pressure responses during testing for Skempton's pore-pressure coefficient B indicated reasonable agreement.Key words: Skempton's pore-pressure coefficient B, pore-water pressure response, varved clays, internal shearing, internal pore-water pressure equalization.

Predicting the High Speed Cutting Process of Titanium Alloy by Finite Element Method

2011 ◽  
Author(s):  
Xiangqin Zhang ◽  
Xueping Zhang ◽  
A. K. Srivastava
Keyword(s):  
Finite Element ◽  
Cutting Forces ◽  
High Speed ◽  
Cutting Temperature ◽  
Chip Morphology ◽  
Cutting Process ◽  
Fe Model ◽  
Dry Cutting ◽  
Friction Coefficients ◽  
Machining Conditions

To predict the cutting forces and cutting temperatures accurately in high speed dry cutting Ti-6Al-4V alloy, a Finite Element (FE) model is established based on ABAQUS. The tool-chip-work friction coefficients are calculated analytically using the measured cutting forces and chip morphology parameter obtained by conducting the orthogonal (2-D) machining tests. It reveals that the friction coefficients between tool-work are 3∼7 times larger than that between tool-chip, and the friction coefficients of tool-chip-work vary with feed rates. The analysis provides a better reference for the tool-work-chip friction coefficients than that given by literature empirically regardless of machining conditions. The FE model is capable of effectively simulating the high speed dry cutting process of Ti-6Al-4V alloy based on the modified Johnson-Cook model and tool-work-chip friction coefficients obtained analytically. The FE model is further validated in terms of predicted forces and the chip morphology. The predicted cutting force, thrust force and resultant force by the FE model agree well with the experimentally measured forces. The errors in terms of the predicted average value of chip pitch and the distance between chip valley and chip peak are smaller. The FE model further predicts the cutting temperature and residual stresses during high speed dry cutting of Ti-6Al-4V alloy. The maximum tool temperatures exist along the round tool edge, and the residual stress profiles along the machined surface are hook-shaped regardless of machining conditions.

A new approach to the stability analysis of thawing slopes

1980 ◽  
Vol 17 (4) ◽  
pp. 607-612 ◽  
Author(s):  
Luis E. Vallejo
Keyword(s):  
Stability Analysis ◽  
Water Content ◽  
Pore Water ◽  
Active Layer ◽  
Necessary Conditions ◽  
Mass Movements ◽  
New Approach ◽  
Pore Water Pressures ◽  
The Stability ◽  
Excess Pore

A new approach to the stability analysis of thawing slopes at shallow depths, taking into consideration their structure (this being a mixture of hard crumbs of soil and a fluid matrix), is presented. The new approach explains shallow mass movements such as skin flows and tongues of bimodal flows, which usually take place on very low slope inclinations independently of excess pore water pressures or increased water content in the active layer, which are necessary conditions in the methods available to date to explain these movements.

Stresses in Ultrasonically Assisted Turning

2006 ◽  
Vol 5-6 ◽  
pp. 351-358 ◽  
Author(s):  
N. Ahmed ◽  
A.V. Mitrofanov ◽  
Vladimir I. Babitsky ◽  
Vadim V. Silberschmidt
Keyword(s):  
Ultrasonic Vibration ◽  
Vibration Frequency ◽  
Cutting Forces ◽  
Plastic Material ◽  
Process Zone ◽  
Three Dimensional ◽  
Rate Sensitivity ◽  
High Strength ◽  
Material Model ◽  
Shear Stresses

Ultrasonically assisted turning (UAT) is a novel material-processing technology, where high frequency vibration (frequency f ≈ 20kHz, amplitude a ≈15μm) is superimposed on the movement of the cutting tool. Advantages of UAT have been demonstrated for a broad spectrum of applications. Compared to conventional turning (CT), this technique allows significant improvements in processing intractable materials, such as high-strength aerospace alloys, composites and ceramics. Superimposed ultrasonic vibration yields a noticeable decrease in cutting forces, as well as a superior surface finish. A vibro-impact interaction between the tool and workpiece in UAT in the process of continuous chip formation leads to a dynamically changing stress distribution in the process zone as compared to the quasistatic one in CT. The paper presents a three-dimensional, fully thermomechanically coupled computational model of UAT incorporating a non-linear elasto-plastic material model with strain-rate sensitivity and contact interaction with friction at the chip–tool interface. 3D stress distributions in the cutting region are analysed for a representative cycle of ultrasonic vibration. The dependence of various process parameters, such as shear stresses and cutting forces on vibration frequency and amplitude is also studied.

Modelling of the Deburring Process

2006 ◽  
Vol 5-6 ◽  
pp. 367-374
Author(s):  
C. G. Dumitraş
Keyword(s):  
Central Composite Design ◽  
Cutting Force ◽  
Cutting Forces ◽  
Cutting Process ◽  
Central Composite ◽  
The Way

Due to robotic deburring development, the research gains a new orientation and focused on the cutting forces and the chip control. The present paper will emphasize the main difference which occurs between the normal cutting process and the deburring process, the way it develops and the parameters which characterize this process. Also the dynamics of the process are considered. Based on a central composite design one determine a relation between the geometry of the tool, workpiece hardness and cutting force.

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