scholarly journals Theoretical Modeling of Rock Breakage by Hydraulic and Mechanical Tool

2014 ◽  
Vol 2014 ◽  
pp. 1-9 ◽  
Author(s):  
Hongxiang Jiang ◽  
Changlong Du ◽  
Songyong Liu ◽  
Liping Wang
Keyword(s):  
Theoretical Model ◽  
Water Pressure ◽  
Rock Fracture ◽  
Superposition Principle ◽  
Specific Energy Consumption ◽  
Critical Length ◽  
Rock Fragmentation ◽  
Rock Breakage ◽  
Hydraulic Impact ◽  
Mechanical Tool

Rock breakage by coupled mechanical and hydraulic action has been developed over the past several decades, but theoretical study on rock fragmentation by mechanical tool with water pressure assistance was still lacking. The theoretical model of rock breakage by mechanical tool was developed based on the rock fracture mechanics and the solution of Boussinesq’s problem, and it could explain the process of rock fragmentation as well as predicating the peak reacting force. The theoretical model of rock breakage by coupled mechanical and hydraulic action was developed according to the superposition principle of intensity factors at the crack tip, and the reacting force of mechanical tool assisted by hydraulic action could be reduced obviously if the crack with a critical length could be produced by mechanical or hydraulic impact. The experimental results indicated that the peak reacting force could be reduced about 15% assisted by medium water pressure, and quick reduction of reacting force after peak value decreased the specific energy consumption of rock fragmentation by mechanical tool. The crack formation by mechanical or hydraulic impact was the prerequisite to improvement of the ability of combined breakage.

scholarly journals An Experimental and Numerical Investigation on the Initiation and Interaction of Double Cracks in Rocks under Hydromechanical Coupling

2020 ◽  
Vol 2020 ◽  
pp. 1-13
Author(s):  
Jie Mei ◽  
Wanzhi Zhang
Keyword(s):  
Water Pressure ◽  
Critical Length ◽  
Maximum Energy ◽  
Enhancement Effect ◽  
Hydromechanical Coupling ◽  
Underground Engineering ◽  
Side Rock ◽  
Crack Tips ◽  
Dip Angle ◽  
Interaction Behaviors

The growth of double cracks is the main factor leading to progressive rock failure under hydromechanical coupling. The initiation modes and interaction behaviors of double cracks were investigated by using laboratory tests, and the influences of water pressure were analyzed. The maximum energy release rate criterion was modified to determine the crack growth characteristics. A numerical model was established and then verified by the test results. Based on the simulation, the distribution of stress fields and key fracture parameters of double cracks was investigated. Then, initiation characteristics and interaction behaviors of parallel and nonparallel cracks were quantitatively analyzed. The results indicate that the increase in water pressure leads to the crack initiation being inclined to the original surfaces and the growth length along the crack fronts tending to be uniform; the small tensile stress zones are formed close to the crack tips, and significant compressive stress zones are formed at both sides of the crack surfaces; stress superposition and interaction occur when crack spacing is less than 2.5a; the interactive weakening effect is mainly present in the inner side (rock bridge zone) of cracks, while a certain degree of interactive enhancement effect exhibits in the outer sides; the cracks are much easier to initiate at the outer wing cracks when the spacing is less than the critical length (0.5a); and cracks with a dip angle of 45° are much easier to initiate at the endpoints of long axis. The research results provide certain theoretical guidance for the safety assessment of underground engineering.

scholarly journals Experimental and Numerical Investigation of Hard Rock Breakage by Indenter Impact

2020 ◽  
Vol 2020 ◽  
pp. 1-12
Author(s):  
Hongxiang Jiang ◽  
Zhiyuan Cai ◽  
Ouguo Wang ◽  
Deguang Meng
Keyword(s):  
Energy Consumption ◽  
Impact Velocity ◽  
Impact Energy ◽  
Specific Energy ◽  
Specific Energy Consumption ◽  
Decisive Role ◽  
Rock Breakage ◽  
Radial Cracks ◽  
The Impact ◽  
Indenter Shape

To investigate the effect of indenter shape, impact energy, and impact velocity on the rock breakage performance, a test device for rock fragmentation by indenter impact was developed to obtain the rock breakage volume, depth, and area under different impact conditions. By comparing the rock breakage volume, depth, area, and specific energy consumption, the results show that indenter shape has a greater influence on the rock breakage performance than that of the impact velocity with the same impact energy, and impact energy plays a decisive role in rock breakage performance with an identical indenter shape and impact velocity. For the lowest to highest specific energy consumption, the order of indenter shape is cusp-conical, warhead, hemispherical, spherical-arc, and flat-top under the same impact energy and velocity, but the cusp-conical indenter is damaged after several impacts. The rock breakage volume, depth, and area all increase with the increase in impact energy, but the effect of the impact velocity could be ignored under the same impact energy. In addition, the rock breakage features of the numerical simulation and experiments are similar, which show that the crushing zone close to the indenter impact point is mainly caused by the high compressive stress, and then radial cracks are caused by the accumulative energy release. The findings of this study will contribute to progress in the performance and efficiency for percussive rock drilling.

Numerical Simulation for Destroy Pattern of Surrounding Rock of Circle Tunnel with M-H Coupling Action

2011 ◽  
Vol 71-78 ◽  
pp. 3572-3576
Author(s):  
An Nan Jiang ◽  
Peng Li
Keyword(s):  
Numerical Simulation ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Rock Fracture ◽  
High Stress ◽  
Surrounding Rock ◽  
Zonal Disintegration ◽  
Affecting Factors ◽  
Tunnel Wall ◽  
Shear Belt

The uniform zonal disintegration of surrounding rock is the peculiar phenomena of deep and high stress field, researching the inner mechanism and affecting factors has important meaning for guaranteeing the safety of deep engineering. The paper adopted strain soft Mohr-Coulomb model and carried out numerical simulation of surrounding rock fracture and excavation. The simulation states that along with the unloading time accumulation, the shear belt produced from tunnel wall and developed to inner rock. The corresponding shear stress concentration zone also spread to inner rock and destroy zone increasing. The pore water pressure increasing will accelerate the shear belt developing and increase the destroy degree.

scholarly journals Potential effects of subglacial water-pressure fluctuations on quarrying

1991 ◽  
Vol 37 (125) ◽  
pp. 27-36 ◽  
Author(s):  
Neal R. Iverson
Keyword(s):  
Principal Stress ◽  
Water Pressure ◽  
Rock Fracture ◽  
Pressure Fluctuations ◽  
High Water ◽  
Potential Influence ◽  
Ice Flow ◽  
Rock Fragments ◽  
Influence Of Water ◽  
Bedrock Surface

AbstractWater-pressure fluctuations beneath glaciers may accelerate rock fracture by redistributing stresses on subglacial bedrock and changing the pressure of water in bedrock cracks. To study the potential influence of water-pressure fluctuations on the fracture of subglacial bedrock, ice flow over a small bedrock step with a water-filled cavity in its lee is numerically modeled, and stresses on the bedrock surface are calculated as a function of transient water pressures in the cavity. Stresses on the bed are then used to calculate principal stress differences within the step. Rapid reductions in cavity water pressure increase principal stress differences in the bed, increasing the likelihood of crack growth in the step and the formation of predominantly vertical fractures. Relatively impermeable bedrock may be most susceptible to fracturing during water-pressure reductions because high water pressure in cracks within the rock can be maintained, as water pressure decreases in cavities. These results, when considered in conjunction with the strong likelihood that increases in water pressure accelerate the removal of rock fragments loosened from the bed, suggest that in zones of ice-bed separation where water-pressure fluctuations typically are large, rates of quarrying may be higher than along other parts of glacier beds.

scholarly journals Investigation of Concrete Base-Roadbed Surface Contact Variation-Induced Vibration Characteristics of Vehicle-Slab Track-Subgrade System considering Fluid-Solid Interaction

2019 ◽  
Vol 2019 ◽  
pp. 1-14 ◽  
Author(s):  
Kai-Wen Liu ◽  
Fei Yue ◽  
Qian Su ◽  
Bao Liu ◽  
Pengfei Zhou
Keyword(s):  
Surface Layer ◽  
High Speed ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Critical Length ◽  
Bottom Layer ◽  
Dynamic Responses ◽  
Continuous Contact ◽  
Slab Track ◽  
Fluid Solid Interaction

The excessive pumping of fines in saturated roadbed surface layer, which is induced by the fluid-solid interaction under dynamic loads from high-speed train, is a special form of high-speed railway subgrade defect reported recently. This can deteriorate the interface between nonballasted track structure bottom layer and roadbed surface layer and therefore lead to associated contact variation with the moving of trains. According to the dynamic Biot’s equations known as u-p formulation and the vehicle-track coupling dynamics theory, a vertical vehicle-slab track-subgrade coupling vibration model is developed to investigate the aforementioned contact variation-induced dynamic behavior of the whole system considering the fluid-solid interaction. Dynamic measurements from a field case study are adopted to verify the computation model proposed. Based on the numerical model validated, the effects of three contact variation statuses (continuous contact, vibrating contact, and contact loss) on dynamic responses of track subsystem and subgrade subsystem, such as dynamic pore-water pressure, vertical accelerations, and dynamic displacements both in time and frequency domains, are investigated. Also, a sensitivity analysis involving rail speeds and lengths of contact loss zone is performed, and the critical length of contact loss zone is suggested.

Numerical and experimental study on dynamic characteristics of cavitation bubbles

2018 ◽  
Vol 70 (6) ◽  
pp. 1119-1126
Author(s):  
Feng Cheng ◽  
Weixi Ji
Keyword(s):  
Theoretical Model ◽  
Dynamic Characteristics ◽  
Water Pressure ◽  
Bubble Radius ◽  
Bubble Wall ◽  
Content Type ◽  
Cavitation Bubbles ◽  
Perturbation Frequency ◽  
Bubble Evolution ◽  
Evolution With Time

Purpose Cavitation bubbles cannot be avoided in the hydraulic system. Because of instability of flow and variation of water pressure, the jet often occurs in a bubble collapse. This study aims to accurately predict the shape, velocity and time of the resulting jet, so as to inhibit cavitation erosion. Design/methodology/approach In the study, a theoretical model of cavitation bubbles in the water has been developed by applying a periodic water film pressure into the Rayleigh–Plesset equation. A fourth-order in time Runge–Kutta scheme is used to obtain an accurate computation of the bubble dynamic characteristics. The behavior of the proposed theory is further simulated in a high-speed photography experiment by using a cavitation bubble test rig. The evolution with time of cavitation bubbles is further obtained. Findings A comparison with the available experimental results reveals that the bubble evolution with time has a duration of about 0.3T0, that well predicts the expanding and compressing process of cavitation bubbles. The results also show that the initial bubble radius in the water influences the moving velocity of the bubble wall, whereas the perturbation frequency of the water pressure has less effect on the velocity of the bubble wall. Originality/value A theoretical model well predicts dynamic characteristics of cavitation bubbles. The bubble evolution with time has a duration of about 0.3T0, Initial bubble radius influences the velocity of bubble wall. Perturbation frequency has less effect on the velocity of bubble wall.

Heat Induced Fracturing of Rock in an Existing Uniaxial Stress Field

1985 ◽  
Vol 50 ◽  
Author(s):  
J. I. Mathis ◽  
O. Stehpansson ◽  
B. Bjarnason ◽  
H. Hakami ◽  
A. Herdocia ◽  
...  
Keyword(s):  
Large Scale ◽  
Failure Time ◽  
Rock Fracture ◽  
Failure Process ◽  
Uniaxial Stress ◽  
Time To Failure ◽  
Rock Breakage ◽  
Rock Fracturing ◽  
Thermal Failure ◽  
Thermal Fracturing

AbstractThe thermal fracturing of rock has been the object of several research projects, notably for initial rock breakage in mining [4] as well as crushing [6] In addition, the process has been studied carefully in regards to the storage of radioactive waste underground where rock fracturing could lead to a loss of radioactivity confinement. The Stripa Project, a project concerning large scale testing of procedures for underground storage of nuclear waste, probably has dealt most thoroughly with this subject by theoretical studies and in-situ heater testing in an attempt to describe the thermal failure process in rock [13]This project was designed to test the agreement between theoretical and actual rock fracture times of a rock block, loaded with a physical as well as a thermal load. Laboratory testing consisted of physically loading center-drilled cubes of rock, 0.3 m on a side, uniaxially from 0 to 25 MPa. These were then thermally loaded with a nominal 3.7 kW (factory rating) cylindrical heater until failure occurred. This time to failure was recorded for comparison with a direct mathematical and a finite element solution. For both cases, calculations were performed at specific time-steps and an estimated failure time calculated from the compiled results.

scholarly journals Evaluation of the deformation shape of a balloon-type dielectric elastomer actuator prestretched with water pressure

2021 ◽  
Vol 8 (1) ◽  
Author(s):  
Natsumi Koike ◽  
Takeshi Hayakawa
Keyword(s):  
Theoretical Model ◽  
Theoretical Analysis ◽  
Good Accuracy ◽  
Water Pressure ◽  
Dielectric Elastomer ◽  
Experimental Results ◽  
Dielectric Elastomer Actuator ◽  
Elastomeric Material ◽  
Mechanical Models ◽  
Applicable Range

AbstractIn this study, we evaluated the deformation shape of a balloon-type dielectric elastomer actuator (DEA) that has been prestretched with water pressure. We fabricated the DEA with poly(dimethylsiloxane) (PDMS) as the elastomeric material and carbon grease as the electrode. We derived analytical solutions for the deformation of the DEA based on structural mechanical models. Additionally, we compared the deformation shapes obtained by theoretical analysis and experimental results. Our model can partially predict the deformation shape of the DEA with good accuracy. In addition, we discuss the applicable range of the theoretical model and error relative to the experimental results.

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