An Experimental Study of Single Bit-Tooth Penetration Into Dry Rock at Confining Pressures 0 to 5,000 psi

1965 ◽  
Vol 5 (02) ◽  
pp. 117-130 ◽  
Author(s):  
P.F. Gnirk ◽  
J.B. Cheatham
Keyword(s):  
Rock Sample ◽  
Drilling Fluid ◽  
Fluid Pressure ◽  
Confining Pressure ◽  
Small Scale ◽  
Rock Surface ◽  
Depth Of Penetration ◽  
Unit Energy ◽  
Experimental Apparatus ◽  
Confining Pressures

Abstract Single bit-tooth penetration experiments under static load were conducted on six rocks at confining pressures of 0 to 5,000 psi using sharp wedge-shaped teeth with included angles ranging from 30 to 120°. In general, the force-displacement curves for all rocks exhibit an increasingly nonlinear and discontinuous behavior with decreasing confining pressure. The confining pressure at which a rock exhibits a macroscopic transition from predominantly ductile to predominantly brittle behavior during penetration varies from about 500 to 1,000 psi for the limestones to greater than 5,000 psi for dolomite. The correlation between calculated values of force per unit penetration based on plasticity theory and experimental values is quite encouraging, even at confining pressures as low as 1,000 psi. A qualitative correlation between volume of fragmented rock per unit energy input for a single bit-tooth and drilling rate for microbits appears to exist over a confining pressure range of 0 to 5,000 psi. INTRODUCTION Laboratory experiments utilizing a small-scale drilling apparatus have demonstrated that penetration rates are reduced considerably as a result of increasing the confining pressure ham atmospheric to a few thousand psi.1–3 This undesirable situation can, in general, be attributed to a combination of decreased efficiency of chip removal at the bottom of the borehole, increased rock-failure strength, and a possible change in the mechanism of chip generation and rock fragmentation with increasing confining pressure. To more fully understand the principles underlying the last circumstance, it is the purpose of this investigation to experimentally study the mechanism of single bit-tooth penetration into dry rock at low confining pressures and, in particular, to establish the confining pressure at which the penetration mechanism may undergo a brittle to ductile transition for various rock types commonly encountered in drilling. Confining pressure as used here refers to the differential pressure between the borehole fluid pressure and the formation-pore fluid pressure. EXPERIMENTAL PROCEDURE Using an experimental apparatus previously described,4 a single, sharp wedge-shaped tool was forced under a "statically" applied load into an effectively semi-infinite dry rock sample subjected to a prescribed confining pressure. To prevent the invasion of the confining-pressure fluid into the pores of the rock sample during penetration, the exposed surface of the rock was jacketed with a layer of silicon putty.* Electrical instrumentation incorporated into the apparatus yielded a graphical plot of force on the tool as a function of penetration or displacement of the tool into the rock during an experiment. During the course of the experimentation the following conditions were maintained constant:pore pressure - atmospheric (i.e., the rock was dry);temperature - 75F;rate of loading - essentially static (approximately 0.002 in./sec);bit tooth - a sharp wedge-shaped tool loaded normal to the rock surface;rock surface smooth and flat;drilling fluid - hydraulic oil; andmaximum depth of penetration - approximately 0.1 in. In addition, each experiment was performed on a different rock sample so the rock surface is free of a layer of cuttings and of any previous indentation craters. The influence of the corners of a borehole was neglected, since each rock sample was cemented into a section of aluminum tubing to simulate a semi-infinite body.

Single-Blow Bit-Tooth Impact Tests on Saturated Rocks Under Confining Pressure: II. Elevated Pore Pressure

1967 ◽  
Vol 7 (04) ◽  
pp. 389-408 ◽  
Author(s):  
J.H. Yang ◽  
K.E. Gray
Keyword(s):  
Pore Pressure ◽  
Effective Stress ◽  
Confining Pressure ◽  
Rock Failure ◽  
Crater Formation ◽  
Depth Of Penetration ◽  
Impact Tests ◽  
Crater Volume ◽  
Confining Pressures ◽  
Stress States

Abstract Results of single-blow bit-tooth impact tests on saturated rocks under elevated confining pressures and zero pore pressure were reported in a previous publication. This paper presents an extension of the earlier work to include a study of crater formation during tooth impact on both gas- and liquid-saturated Berea and Bandera sandstones at elevated confining and pore pressures. The basic data obtained were force-time, displacement-time, velocity-time and force-displacement curves during crater formation. Crater volume was also measured and the mode of crater formation determined. Bit tooth geometry, depth of penetration and velocity of impact were held constant. Results indicate that, with pore fluid present in the rock, failure trends from brittle to ductile as pore pressure is increased at constant confining pressure (pore pressure and borehole pressure were equals For a given rock type, the mode of crater formation was dependent not only upon the nominal effective stress, but also upon the fluid which saturated the rock pore space. When confining pressure and pore pressure were equal (zero nominal effective stress), bit-tooth impact resulted in brittle failure for nitrogen-saturated Berea, and brittle to transitional failure for nitrogen-saturated Bandera; when saturated with liquid both rocks failed in a ductile manner at zero nominal effective stress. Introduction Dynamic wedge penetration tests have been conducted by investigators in several fields, but the failure mechanism of rock under dynamic stresses is not understood completely. The complex action of drilling bits, even considering the action of a single tooth, may be considered as a combination of drag bit and rolling cutter action. Thus, as a first step in understanding rock breakage in oil well drilling, single chisel impact and rock planing are of fundamental importance. For example, Gray and Crisp studied drag bit cutting action at brittle stress states. Simon and Hartman studied the reaction of rocks to vertical impact by means of drop tests. The depth of penetration, crater volume and force-vs-time curves during crater formation were observed. The significance of indexing single-bit impacts has been noted. Garner et al, reported impact tests on impermeable Leuders limestone at atmospheric and elevated confining pressures. In all cases the tests were accomplished on dry rock and pore pressure was considered to be zero. The importance of both confining pressure and pore pressure on the failure characteristics of rock was described. It was found that the yield strength and ductility of porous rock depend on the state of stress under which the sample is tested. The importance of pore pressure on drilling rate in microbit experiments was noted by Cunningham and Eenink, Robinson also pointed out that in drilling the most important parameter in rock failure is the effective stress, where effective stress is defined as confining pressure Pc minus pore pressure Pp. The effect of pore pressure and confining pressure on rock strength was also noted by Serdengecti and Boozer in strain rate tests, and by Gardner, Wyllie and Droschack in elastic wave studies. Until recently all reported wedge impact studies under simulated wellbore stress states have been conducted on dry rock. Maurer reported impact tests on samples saturated with deaerated water. Borehole and formation fluid pressures were equal in these tests except when mud was used in the borehole. With mud in the borehole and a high borehole-to-formation fluid pressure differential, Maurer observed "pseudoplastic" crater formation. Podio and Gray reported impact tests on Berea and Bandera sandstone saturated with pore fluids having wide ranges in viscosities. In Podio and Gray's tests, confining pressure was elevated, but pore pressure and borehole pressure were held fixed at atmospheric pressure. SPEJ P. 389ˆ

scholarly journals Experimental Study on the Permeability of Quartz Sandstone under Coupled Thermo-Hydromechanical Loading

Lithosphere ◽  
2021 ◽  
Vol 2021 (Special 5) ◽  
Author(s):  
Yu Zhang ◽  
Tingting Yu ◽  
Jianwei Li ◽  
Yun Jia ◽  
Dayong Li
Keyword(s):  
Experimental Study ◽  
Structural Stability ◽  
Fluid Pressure ◽  
Confining Pressure ◽  
Experimental Results ◽  
Petroleum Engineering ◽  
Different Temperatures ◽  
Confining Pressures ◽  
Fully Coupled

Abstract This paper focuses on the influence of coupled thermo-hydromechanical processes on the permeability of quartz sandstone. The permeability has been studied under five different confining pressures, three different temperatures, and three fluid pressures. The experimental results exhibit that the permeability of quartz sandstone decreases with the increase of confining pressure while it increases with temperature and fluid pressure. The identification of permeability under fully coupled thermo-hydromechanical conditions is also studied via the realization of four coupled tests. One observes that the temperature plays a more important role on the permeability with respect to the fluid pressure. Moreover, the influence of fluid pressure on the permeability of studied sandstone has been amplified by the temperature. The obtained experimental results allow us to get a good understanding of the permeability of quartz sandstone in petroleum engineering and can help us to guarantee the long-term structural stability.

Rate-of-Loading Effects in Chisel Impact

1962 ◽  
Vol 2 (02) ◽  
pp. 105-110
Author(s):  
F.C. Appl ◽  
W.S. Gatley
Keyword(s):  
Rock Specimen ◽  
Strain Gauges ◽  
Rock Surface ◽  
Drilling Process ◽  
Atmospheric Conditions ◽  
Depth Of Penetration ◽  
Experimental Apparatus ◽  
Drop Tests ◽  
Non Linear System ◽  
Rate Of Loading

Abstract This paper presents a combined analytical and experimental study of chisel penetration vs time during chisel impact on rock, a problem of fundamental importance in improving the performance of roller-cone bits or percussion drilling tools. For a given force-time relationship between chisel and rock, the problem of determining the penetration (displacement) vs time of the chisel is formidable. This is so because the rock is a non-linear system with distributed mass and distributed damping (friction, dissipation of energy due to rupture, etc.). Since the literature does not contain adaptable solutions, the rock behavior to impact was simulated approximately by an "equivalent" lumped system, that is, an "equivalent" mass, spring, dash pot system. With this assumption, an analytical solution was found for chisel penetration vs time due to a sinusoidal load between chisel and rock. From this solution were found curves, in terms of dimensionless variables, for the maximum depth of penetration vs the frequency of the sinusoidal loading and for the energy transfer vs frequency. The results of this analysis were used to predict the penetration rate of rotary rock bits vs rotary speed. The curve indicated that an optimum speed exists. To verify this analysis, an experimental apparatus was constructed and used to apply a sinusoidal pulse to a chisel penetrating a rock specimen under atmospheric conditions. Strain gauges were mounted on the chisel shank and a velocity transducer was mounted between the chisel and the rock surface. The velocity was integrated electrically and picked up simultaneously with the strain gauge signal on an oscilloscope. Permanent records were made photo graphically to provide simultaneous records of force vs time and penetration vs time. In comparing the experimental results for limestone and dolomite with the theoretical results, good agreement was found in the frequency range of the experiments. Unfortunately, the inertia effect (peak penetration) indicated by the theory occurs at a frequency much higher than could be obtained experimentally with the apparatus constructed. A "rate-of-loading" effect is indicated theoretically, but has not yet been verified experimentally. Introduction The process of drilling with percussion tools or rotary rock bits is basically related to the transient response of rock to surface impact. Each time a bit tooth contacts the rock, high stresses are developed which result in penetration and rock removal. As the tooth moves on, stresses are relieved and a new cycle begins as the next tooth contacts the rock. Thus the drilling process, which consists of an endless succession of these cycles, can be studied in terms of a single cycle. It is apparent, therefore, that the study of single-chisel impact on rock is fundamentally important in improving the performance of roller-cone and percussive-type drills. Previous studies in this area have been conducted by Simon and Hartman by means of drop tests. In these tests a chisel was attached to a weight and allowed to fall, due to the force of gravity, so that the chisel was driven into a rock specimen upon impact. Strain gauges were attached to the chisel shank and the resulting force-vs-time curves were recorded photographically from an oscilloscope screen. The depth of penetration and crater dimensions were also measured. These tests have provided much valuable information but, as mentioned by the investigators, have not provided complete information on the effect of "rate of loading". This is partly due to the fact that the chisel motion during drop tests is not a controlled motion which can be varied in form and frequency. Therefore, it seemed that additional information could be obtained by studying chisel impact under conditions where both the motion and the frequency of loading could be controlled. SPEJ P. 105^

Single-Blow Bit-Tooth Impact Tests on Saturated Rocks Under Confining Pressure: I. Zero Pore Pressure

1965 ◽  
Vol 5 (03) ◽  
pp. 211-224 ◽  
Author(s):  
A. Podio ◽  
K.E. Gray
Keyword(s):  
Experimental System ◽  
Confining Pressure ◽  
Mineral Oil ◽  
Pore Fluid ◽  
Single Tooth ◽  
Experimental Apparatus ◽  
Crater Volume ◽  
Confining Pressures ◽  
Stress States ◽  
Impact Data

Abstract Berea and Bandera sandstone samples were impacted with both 3/4-in. and 1/2-in. long wedges, each having a 60° included angle and a 0.05-in. flat, at various confining pressures, with borehole and pore pressures held fixed at atmospheric pressure. Samples were saturated with air, water, glycerine-water, soltrol, mineral oil and soltrol, mineral oil mixtures to obtain a wide range of pore fluid viscosity. Penetration depth was held constant at 0.1 in. Dry and soltrol-mineral oil-saturated Berea samples were impacted at depths of penetration from 0.01 to 0.04 in. under 1,000 psi confining pressure to study crater initiation. Results indicate that viscosity of the pore fluid is influential primarily during the early stages of crater formation. Differences in bit force, crater volume and blow energy for tests parallel and perpendicular to bedding were significant, but decreased as the stress state was elevated. Crater volume, blow energy and bit force were nonlinearly related with depth of penetration. Crater volume was nonlinear with energy of blow. Fixed-penetration tests on saturated Berea yielded greater crater volume than did similar tests on dry samples. Differences in the nature of deformation for low values of bit penetration were noted between saturated and unsaturated samples. INTRODUCTION Rock failure during bit-tooth impact and scouring action constitutes a vital part of the drilling process and a difficult problem for researchers. Much study has been devoted to various aspects of the problem, and much has been learned about mechanics of rock failure. However, analytical treatment of drilling at depth remains difficult, partly because there are so many factors involved and because valid simulation of downhole conditions is extremely difficult. Forming individual craters by a bit tooth or chisel impacting, or indenting, a rock mass has been studied by many investigators.1–18 Similarity between single-tooth chisel impact and the corresponding action of a rotary bit has been discussed by Appl and Gatley.9 Garner, Podio, and Gatlin18 compared the similarity in single-blow impact tests with microbit drilling data reported by Cunningham and Eenink.19 Maurer11 has used single-tooth impact data to develop a "perfect cleaning" theory of rotary drilling. Individual roller cutter-tooth impact data have been reported by Young.20 Single-tooth tests in all of the cited literature were carried out on dry rocks. Inasmuch as any subsurface rock of oilfield interest is saturated with some fluid, it seemed desirable to study crater formation in permeable rocks saturated with a viscous pore fluid as a step, however short, toward more realistic simulation of subsurface conditions. This paper presents results of single-blow chisel impact studies on Berea and Bandera sandstones, both dry and saturated with pore fluids of various viscosities at confining pressures to 10,000 psi. EXPERIMENTAL APPARATUS AND PROCEDURE EXPERIMENTAL APPARATUS The same basic apparatus for single-blow chisel impact at elevated stress states, described in earlier papers was used in this study.16,18 Fig. 1 shows the complete experimental system; Fig. 2 shows a cross section of the pressure cell, with a sample ready to be impacted. EXPERIMENTAL PROCEDURE Two different rocks, Berea and Bandera sandstones, were used in this study. Both rocks have been used extensively in research, and rock descriptions can be found in a paper by Gnirk and Cheatham.1 Permeability to air of Berea is about 300 md normal to bedding and 540 md parallel to bedding. Bandera had vertical and horizontal air permeabilities of 18 and 57 md, respectively. EXPERIMENTAL APPARATUS The same basic apparatus for single-blow chisel impact at elevated stress states, described in earlier papers was used in this study.16,18 Fig. 1 shows the complete experimental system; Fig. 2 shows a cross section of the pressure cell, with a sample ready to be impacted. EXPERIMENTAL PROCEDURE Two different rocks, Berea and Bandera sandstones, were used in this study. Both rocks have been used extensively in research, and rock descriptions can be found in a paper by Gnirk and Cheatham.1 Permeability to air of Berea is about 300 md normal to bedding and 540 md parallel to bedding. Bandera had vertical and horizontal air permeabilities of 18 and 57 md, respectively.

DESTRUCTION OF POROSITY THROUGH PRESSURE SOLUTION

Geophysics ◽  
1977 ◽  
Vol 42 (4) ◽  
pp. 726-741 ◽  
Author(s):  
Eve S. Sprunt ◽  
Amos Nur
Keyword(s):  
Pore Pressure ◽  
Effective Stress ◽  
Fluid Pressure ◽  
Confining Pressure ◽  
Pressure Solution ◽  
Porous System ◽  
Point Counts ◽  
Grain Crushing ◽  
Porosity Reduction ◽  
Confining Pressures

A stressed fluid‐filled porous system was modeled by hollow cylinders of St. Peter sandstone subjected to various combinations of pore and confining pressure at 270° to 280°C for up to four weeks. Large reductions in porosity, up to more than 50 percent, were produced purely by pressure solution without grain crushing. Most of the porosity reduction occurred early in the experiments and in samples with the finer of two grain sizes. Experiments with the same pore pressure, but different confining pressures, and experiments with the same effective stress, but different stress magnitudes showed that a simple effective stress law does not hold for pressure solution, and that the amount of porosity reduction depends on pore fluid pressure. However, nonhydrostatic stress appears to be necessary for rapid porosity reduction because experiments with hydrostatic pressure produced very little change in porosity. Also, experiments with the same confining pressure but different pore pressures showed that the amount of porosity loss is dependent on both pore pressure and effective stress. Pore pressure appears to place an upper limit on the rate of porosity reduction, while nonhydrostatic stress appears to be necessary for rapid porosity reduction. A dry control experiment showed that fluid must be present for porosity reduction at the temperatures and pressures in our study. The porosities of many of the samples in this study were determined both gravimetrically and by point counts on cathodoluminescent micrographs. Cathodoluminescence is useful in studying pressure solution because the intergranular relationships and pore spaces are very distinct. However, in examining natural samples caution is required when relying solely on the luminescence to determine pressure solution, because luminescent characteristics change with time.

Dependency of hydromechanical properties of monzonitic granite on confining pressure and fluid pressure under compression

2016 ◽  
Vol 30 (16) ◽  
pp. 1650086 ◽  
Author(s):  
Huanling Wang ◽  
Weiya Xu ◽  
Zaobao Lui ◽  
Zhiming Chao ◽  
Qingxiang Meng
Keyword(s):  
Failure Modes ◽  
Fluid Pressure ◽  
Confining Pressure ◽  
Triaxial Tests ◽  
Low Permeability ◽  
Failure Characteristics ◽  
Deformation Stages ◽  
Monzonitic Granite ◽  
Confining Pressures ◽  
Crack Damage Stress

Monzonitic granite is a low-permeability rock. Monzonitic granite formations are ideal for underground storage of oil due to their low permeability and high mechanical strength. In this study, a series of coupled hydromechanical triaxial tests are carried out using monzonitic granite specimens. The influence of confining and fluid pressures on stress, strain, and permeability is investigated. Failure characteristics under different confining and fluid pressures are discussed based on the analysis of macro fracture planes and micro scanning electron microscopy (SEM). The test results show that the change of permeability with stress and strain reflects the deformation stages of compaction, compression, crack propagation, coalesce, and failure of cracks. Due to the low porosity, the change of permeability is small in the initial phases of compaction and compression, whereas there is a significant increase in permeability when new cracks start to develop and coalesce. Confining pressures have a significant impact on the strength and permeability, particularly the crack damage stress of the rock. Compared with confining pressure, the effect of fluid pressure on rock strength and crack damage stress is small. For the monzonitic granite specimens tested, changing the confining pressure results in different failure modes, whereas the fluid pressure has a relatively small effect on the failure modes.

Mechanical behaviour of powders using a medium pressure flexible boundary cubical triaxial tester

2003 ◽  
Vol 217 (3) ◽  
pp. 233-241 ◽  
Author(s):  
F Li ◽  
V M Puri
Keyword(s):  
Shear Modulus ◽  
Mechanical Behaviour ◽  
Triaxial Compression ◽  
Three Dimensional ◽  
Volumetric Strain ◽  
Confining Pressure ◽  
Alumina Powder ◽  
Medium Pressure ◽  
Mean Pressure ◽  
Confining Pressures

A medium pressure (<21 MPa) flexible boundary cubical triaxial tester was designed to measure the true three-dimensional response of powders. In this study, compression behaviour and strength of a microcrystalline cellulose powder (Avicel® PH102), a spray-dried alumina powder (A16SG), and a fluid-bed-granulated silicon nitride based powder (KY3500) were measured. To characterize the mechanical behaviour, three types of triaxial stress paths, that is, the hydrostatic triaxial compression (HTC), the conventional triaxial compression (CTC), and the constant mean pressure triaxial compression (CMPTC) tests were performed. The HTC test measured the volumetric response of the test powders under isostatic pressure from 0 to 13.79MPa, during which the three powders underwent a maximum volumetric strain of 40.8 per cent for Avicel® PH102, 30.5 per cent for A16SG, and 33.0 per cent for KY3500. The bulk modulus values increased 6.4-fold from 57 to 367MPa for Avicel® PH102, 3.7-fold from 174 to 637 MPa for A16SG, and 8.1-fold from 74 to 597MPa for KY3500, when the isotropic stress increased from 0.69 to 13.79 MPa. The CTC and CMPTC tests measured the shear response of the three powders. From 0.035 to 3.45MPa confining pressure, the shear modulus increased 28.7-fold from 1.6 to 45.9MPa for Avicel® PH102, 35-fold from 1.7 to 60.5MPa for A16SG, and 28.5-fold from 1.5 to 42.8MPa for KY3500. In addition, the failure stresses of the three powders increased from 0.129 to 4.41 MPa for Avicel® PH102, 0.082 to 3.62 MPa for A16SG, and 0.090 to 4.66MPa for KY3500, respectively, when consolidation pressure increased from 0.035 to 3.45MPa. In addition, the shear modulus and failure stress values determined from the CTC test at 2.07, 2.76, and 3.45MPa confining pressures are consistently greater than those from the CMPTC test at the same constant mean pressures. This observation demonstrates the influence of stress paths on material properties. The CTT is a useful tool for characterizing the three-dimensional response of powders and powder mixtures.

Effective rheology of a two-phase subduction shear zone: insights from numerical simple shear experiments and implications for subduction zone interfaces

2021 ◽  
Author(s):  
Paraskevi Io Ioannidi ◽  
Laetitia Le Pourhiet ◽  
Philippe Agard ◽  
Samuel Angiboust ◽  
Onno Oncken
Keyword(s):  
Simple Shear ◽  
Large Scale ◽  
Confining Pressure ◽  
Shear Zones ◽  
Dislocation Creep ◽  
Small Scale ◽  
Two Phase ◽  
Weak Phase ◽  
Pure Phases ◽  
Geodynamic Models

&lt;p&gt;Exhumed subduction shear zones often exhibit block-in-matrix structures comprising strong clasts within a weak matrix (m&amp;#233;langes). Inspired by such observations, we create synthetic models with different proportions of strong clasts and compare them to natural m&amp;#233;lange outcrops. We use 2D Finite Element visco-plastic numerical simulations in simple shear kinematic conditions and we determine the effective rheology of a m&amp;#233;lange with basaltic blocks embedded within a wet quartzitic matrix. Our models and their structures are scale-independent; this allows for upscaling published field geometries to km-scale models, compatible with large-scale far-field observations. By varying confining pressure, temperature and strain rate we evaluate effective rheological estimates for a natural subduction interface. Deformation and strain localization are affected by the block-in-matrix ratio. In models where both materials deform viscously, the effective dislocation creep parameters (A, n, and Q) vary between the values of the strong and the weak phase. Approaching the frictional-viscous transition, the m&amp;#233;lange bulk rheology is effectively viscous creep but in the small scale parts of the blocks are frictional, leading to higher stresses. This results in an effective value of the stress exponent, n, greater than that of both pure phases, as well as an effective viscosity lower than the weak phase. Our effective rheology parameters may be used in large scale geodynamic models, as a proxy for a heterogeneous subduction interface, if an appropriate evolution law for the block concentration of a m&amp;#233;lange is given.&lt;/p&gt;

Advanced Treatment of Domestic Wastewater Using Sequencing Batch Reactor Activated Sludge Process

1993 ◽  
Vol 28 (10) ◽  
pp. 267-274 ◽  
Author(s):  
M. Imura ◽  
E. Suzuki ◽  
T. Kitao ◽  
S. Iwai
Keyword(s):  
Activated Sludge ◽  
Sequencing Batch Reactor ◽  
Batch Reactor ◽  
Domestic Wastewater ◽  
Experimental Period ◽  
Small Scale ◽  
Experimental Plant ◽  
Activated Sludge Process ◽  
Nitrogen And Phosphorus ◽  
Experimental Apparatus

In order to apply a sequencing batch reactor activated sludge process to small scale treatment facilities, various experiments were conducted by manufacturing an experimental apparatus made of a factory-produced FRP cylinder transverse tank (Ø 2,500mm). Results of the verification test conducted for one year by leading the wastewater discharged from apartment houses into the experimental apparatus were as follows. Excellent performance was achieved without any addition of carbon source, irrespective of the organic compound concentration and the temperature of raw wastewater. Organic substances, nitrogen and phosphorus were removed simultaneously. Due to the automated operation format, stable performance was obtained with only periodic maintenance. Though water depth of the experimental plant was shallow, effective sedimentation of activated sludge was continued during the experimental period. Regarding the aerobic and anaerobic process, nitrification and denitrification occurred smoothly.

scholarly journals Research on Microscopic Evolution Laws of Sandstone Deformation and Failure Based on the Particle Discrete Element Method

2021 ◽  
Vol 2021 ◽  
pp. 1-12
Author(s):  
Zhiwei Cai ◽  
Tongqing Wu ◽  
Jian Lu ◽  
Yue Wu ◽  
Nianchun Xu
Keyword(s):  
Shear Crack ◽  
Rock Fracture ◽  
Confining Pressure ◽  
Particle Flow Code ◽  
Shear Cracks ◽  
Deformation And Failure ◽  
Fracture Development ◽  
Confining Pressures ◽  
The Law ◽  
Microcrack Growth

The fracture of sandstone is closely related to the condition of internal microcracks and the fabric of micrograin. The macroscopic mechanical property depends on its microscopic structures. However, it is difficult to obtain the law of the microcrack growth under loading by experiments. A series of microscopic sandstone models were established with particle flow code 3D (PFC3D) and based on the triaxial experiment results on sandstones. The experimental and numerical simulations of natural and saturated sandstones under different confining pressures were implemented. We analyzed the evolution of rock deformation and the rock fracture development from a microscopic view. Results show that although the sandstones are under different confining pressures, the law of microcrack growth is the same. That is, the number of the microcracks increases slowly in the initial stage and then increases exponentially. The number of shear cracks is more than the tensile cracks, and the proportion of the shear cracks increases with the increase of confining pressure. The cracking strength of natural and saturated sandstones is 26% and 27% of the peak strength, respectively. Under low confining pressure, the total number of cracks in the saturated sample is 20% more than that of the natural sample and the strongly scattered chain is barely seen. With the increase of the confining pressure, the effect of water on the total number of cracks is reduced and the distribution of the strong chain is even more uniform. In other words, it is the confining pressure that mainly affects the distribution of the force chain, irrespective of the state of the rock, natural or saturated. The research results reveal that the control mechanism of shear crack friction under the different stress states of a rock slope in the reservoir area provides a basis for evaluating the stability of rock mass and predicting the occurrence of geological disasters.

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