The differences in geomechanical properties and the uncertainty in the spatial distribution of Bimrock pose significant challenges to the construction and disaster prediction of geotechnical engineering. To clarify the geomechanical characteristics of Bimrock, this paper summarizes the basic concepts and classification methods of Bimrock at home and abroad. It discusses the methods and characteristics of determining the geometric features of Bimrock blocks and explores the influencing factors and laws of failure modes and strength under different stress states of Bimrock. The study finds that the failure mode of Bimrock is mainly influenced by factors such as block proportion, degree of welding between blocks and matrix, strength ratio between blocks and matrix, and geometric properties of blocks. Among these factors, block proportion is the most significant, and the degree of welding is a controlling factor. However, due to the complexity of Bimrock structures, there is a lack of applicable methods and mechanical models for the evaluation of geomechanical characteristics of Bimrock in engineering practice. This article also explores the influence and research methods of the geological characteristics of Bimrock in slope and tunnel engineering and, finally, provides prospects for the future research trends relating to Bimrock.
It has been recognized that the anisotropic structures dominate the deformation and strength properties of laminated rock masses. The resultant strength anisotropy is strongly affected by confining pressures beyond anisotropic structures. Nevertheless, the effects of confinement are inconsistent among existing experiments and not fully understood. This study focuses on the effects of confining pressure on strength anisotropy through theoretical derivation together with experimental results analysis. The variations in the possibility of anisotropic structural plane dominant failure and strength anisotropy degree under different confining pressures are discussed. The different types of anisotropic structural planes, i.e., the fresh contact discontinuity or soft, thick layer, are found as the key factor resulting in different confinement effects. The strength anisotropy weakens gradually and vanishes eventually as confining stress increases for the anisotropic rock mass with the structural plane of fresh contact discontinuity. On the other hand, the strength does not vanish at very high confining stress and the anisotropic strength difference even rises as confining stress increases for the anisotropic rock mass with the anisotropic structural plane of the soft layer. This study improves the understanding of anisotropic rock mass mechanical behavior, especially at high confining stress, and may promote the development of excavation and supporting techniques for underground projects.
Characterization of the tensile mechanical behaviors of rocks under dynamic loads is of great significance for the practical engineering. However, thus far, its micromechanics have rarely been studied. This paper micromechanically investigated the compression-induced tensile mechanical behaviors of the crystalline rock using the grain-based model (GBM) by universal distinct element code (UDEC). Results showed that the crystalline rock has the rate- and heterogeneity-dependency of tensile behaviors. Essentially, dynamic Brazilian tensile strength increased in a linear manner as the loading rate increased. With the size distribution and morphology of grain-scale heterogeneity weakened, it increased, and this trend was obviously enhanced as the loading rate increased. Additionally, the rate-dependent characteristic became strong with the grain heterogeneity weakened. The grain heterogeneity prominently affected the stress distribution inside the synthetic crystalline rock, especially in the mixed compression and tension zone. Due to heterogeneity, there were tensile stress concentrations (TSCs) in the sample which could favor microcracking and strength weakening of the sample. As the grain heterogeneity weakened or the loading rate increased, the magnitude of the TSC had a decreasing trend and there was a transition from the sharp TSC to the smooth tensile stress distribution zone. The progressive failure of the crystalline rock was notably influenced by the loading rate, which mainly represented the formation of the crushing zone adjacent to two loading points. Our results are meaningful for the practical engineering such as underground protection works from stress waves.
The shear strength characteristics of rock masses containing non-persistent discontinuities are strongly affected by discontinuities and rock bridges. The linear Jennings criterion cannot reflect the nonlinear mechanical behavior during progressive failure of rock masses with non-persistent discontinuities. In this study, a new nonlinear shear strength criterion was developed. First of all, a series of shear test data about artificial rock mass samples were collected on the basis of the published literatures, and five types of samples were differentiated according to the positions of discontinuities. After that, a new nonlinear shear strength criterion was proposed by introducing two correction coefficients A and B into the basic form of the Jennings criterion, which could correct the weight of the cohesion and the internal friction coefficient of rock bridges respectively. Then, the new criterion was determined by fitting the basic form of the Jennings criterion with the laboratory data. It was found that the parameters A and B had a nonlinear exponential and negative exponential relation with the connectivity rate respectively. It indicated that both the cohesion and the internal friction coefficient estimated by the new criterion were superior to those estimated by the Jennings criterion. Compared with the linear Jennings criterion, the new nonlinear shear strength criterion had a better applicability.
This paper microscopically investigated progressive failure characteristics of brittle rock under high-strain-rate compression using the bonded particle model (BPM). We considered the intact sample and the flawed sample loaded by split Hopkinson pressure bar respectively. Results showed that the progressive failure characteristics of the brittle rock highly depended on the strain rate. The intact sample first experienced in microcracking, then crack coalescing, and finally splitting into fragments. The total number of the micro cracks, the proportion of the shear cracks, the number of fragments and the strain at the peak stress all increased with the increasing strain rate. Also, a transition existed for the failure of the brittle rock from brittleness to ductility as the strain rate increased. For the flawed sample, the microcracking initiation position and the types of the formed macro cracks were influenced by the flaw angle in the initial stage. However, propagation of these early-formed macro cracks were prohibited in the later stages. New micro cracks were produced and then coalesced into diagonal macro cracks which could all form 'X'-shape failure configuration regardless of the incline angle of the flaw. We explored micromechanics on progressive failure characteristics of the brittle rock under dynamic loads.
The pore structure is one of the most important properties of soil, which can directly affect the other properties such as water content, permeability and strength. It is of great significance to study the soil pore structure for agricultural cultivation, water and soil conservation and engineering construction. This paper investigates the 3D pore characterization of intact loess and four kinds of compacted loess (with different dry density) in northwest China. Micro scale computed tomography and mercury intrusion porosimetry tests were performed to get the porosity, specific surface area, pore size distribution, connected pores content and isolated pores content of different samples. Results show that the intact loess has more connected pores than the compacted loess, and the compacted loess whose dry density appears to be modelled well still have different pore structure with the intact loess. In addition, as the compactness increasing, the large pores (>13 µm) were firstly broken into medium pores (8~13 µm) and some small pores (<8 µm) until the pore structure was close to the natural structure of the intact loess, after that medium pores began to be broken into small pores.
In rocks or rock-like materials, the constituents, e.g. quartz, calcite and biotite, as well as the microdefects have considerably different mechanical properties that make such materials heterogeneous at different degrees. The failure of materials subjected to external loads is a cracking process accompanied with stress redistribution due to material heterogeneity. However, the latter cannot be observed from the experiments in laboratory directly. In this study, the cracking and stress features during uniaxial compression process are numerically studied based on a presented approach. A plastic strain dependent strength model is implemented into the continuous numerical tool-Fast Lagrangian Analysis of Continua in three Dimensions (FLAC3D), and the Gaussian statistical function is adopted to depict the heterogeneity of mechanical parameters including elastic modulus, friction angle, cohesion and tensile strength. The mean parameter µ and the coefficient of variance (hcv, the ratio of mean parameter to standard deviation) in the function are used to define the mean value and heterogeneity degree of the parameters, respectively. The results show that this numerical approach can perfectly capture the general features of brittle materials including fracturing process, AE events as well as stress-strain curves. Furthermore, the local stress disturbance is analyzed and the crack initiation stress threshold is identified based on the AE events process and stress-strain curves. It is shown that the stress concentration always appears in the undamaged elements near the boundary of damaged sites. The peak stress and crack initiation stress are both heterogeneity dependent, i.e., a linear relation exists between the two stress thresholds and hcv. The range of hcv is suggested as 0.12 to 0.21 for most rocks. The stress concentration degree is represented by a stress concentration factor and found also heterogeneity dominant. Finally, it is found that there exists a consistent tendency between the local stress difference and the AE events process.
With about 2.2 million Americans currently using wheeled mobility devices, wheelchairs are frequently provided to people with impaired mobility to provide accessibility to the community. Individuals with spinal cord injuries, arthritis, balance disorders, and other conditions or diseases are typical users of wheelchairs. However, secondary injuries and wheelchair-related accidents are risks introduced by wheelchairs. Research is underway to advance wheelchair design to prevent or accommodate secondary injuries related to propulsion and transfer biomechanics, while improving safe, functional performance and accessibility to the community. This paper summarizes research and development underway aimed at enhancing safety and optimizing wheelchair design.
Activities of Daily Living , Biomechanical Phenomena/methods , Biomedical Engineering/methods , Ergonomics/methods , Wheelchairs , Biomechanical Phenomena/trends , Biomedical Engineering/trends , Equipment Design , Equipment Failure Analysis , Humans , Man-Machine Systems
Increased physical activity is important for reducing the risk of cardiovascular disease. However, among people with disabilities, inactivity is prevalent. In order to encourage exercise among members of this group, an exercise system combining arm ergometry with video gaming, called the GAME(Cycle) was previously developed. User input was received through an arm crank ergometer on a swivel, with the angular velocity of the ergometer resistance wheel controlling one axis and rotation of ergometer about the swivel controlling the other. The purpose of this study was to detail the algorithms used in this device and present novel features included in a second generation of the GAME(Cycle). The features include a wheel on base, a steering return mechanism, and wireless fire buttons. A focus group of clinicians (n = 8), wheelchair users (n = 8), and clinician wheelchair users (n = 2) was conducted to evaluate the features of the GAME(Cycle). The focus group suggested improvements to the steering mechanism and to reduce vibration in the system. However, the focus group enjoyed the GAME(Cycle) and felt that it would encourage exercise among persons with disabilities.
Disabled Persons , Exercise/physiology , Physical Fitness/physiology , Video Games , Algorithms , Arm/physiology , Data Interpretation, Statistical , Equipment Design , Ergometry , Feedback , Humans , Surveys and Questionnaires
PURPOSE: Training of appropriate wheelchair propulsion methods may be beneficial to the individual who uses a wheelchair by reducing the incidence of pain and improving one's quality of life. This paper discusses the development and initial testing of a training device that was developed to aid in wheelchair propulsion techniques: GAME(Wheels) System. METHODS: Two separate models of GAME(Wheels) have been developed: a GAME(Wheels) Clinical and a GAME(Wheels) Trainer. Details of the development process and the refinement have been included in this manuscript. To verify and compare the practicality and functionality of the two GAME(Wheels) systems, several focus groups were conducted: first to determine whether the systems could be set-up with informational materials and second to determine if the systems could be taught to novice users. RESULTS: Results from the focus group indicate that the overall impressions of the systems were that they were 'fun' to play. Suggestions were raised to improve the design, which have been incorporated into further refinement of the GAME systems. CONCLUSIONS: This paper provides an overview of the development of a wheelchair-training device. Valuable information was gained to improve the design of the GAME(Wheels) systems.
Exercise/physiology , Video Games , Wheelchairs , Energy Metabolism/physiology , Equipment Design , Ergonomics , Focus Groups , Humans , Kinetics , Oxygen Consumption/physiology , Patient Satisfaction , User-Computer Interface
BACKGROUND: Almost 10% of all individuals who are legally blind also have a mobility impairment. The majority of these individuals are dependent on others for mobility. The Smart Power Assistance Module (SPAM) for manual wheelchairs is being developed to provide independent mobility for this population. METHODS: A prototype of the SPAM has been developed using Yamaha JWII power assist hubs, sonar and infrared rangefinders, and a microprocessor. The prototype limits the user to moving straight forward, straight backward, or turning in place, and increases the resistance of the wheels based on the proximity of obstacles. The result is haptic feedback to the user regarding the environment surrounding the wheelchair. RESULTS: The prototype has been evaluated with four blindfolded able-bodied users and one individual who is blind but not mobility impaired. For all individuals, the prototype reduced the number of collisions on a simple navigation task. CONCLUSION: The prototype demonstrates the feasibility of providing navigation assistance to manual wheelchair users, but several shortcomings of the system were identified to be addressed in a second generation prototype.
Some aspects of assistive technology can be enhanced by the application of virtual reality. Although virtual simulation offers a range of new possibilities, learning to navigate in a virtual environment is not equivalent to learning to navigate in the real world. Therefore, virtual reality simulation is advocated as a useful preparation for assessment and training within the physical environment. We are engaged in several efforts to develop virtual environments and devices for mobility skills assessment and training, exercise training, and environment assessment. Virtual reality offers wheelchair users a training tool in different risk-free environments without any indoor (e.g., walls, furniture, and stairs) and outdoor (e.g., curb cuts, uneven terrain, and street traffic) physical constraints. Virtual reality technology will probably become more common in the field of assistive technology, especially given the rapid expansion of gaming technology and the continued exponential growth of computing power.
Computer Simulation , Disabled Persons/education , Mobility Limitation , User-Computer Interface , Wheelchairs , Disabled Persons/psychology , Disabled Persons/rehabilitation , Humans , Microcomputers , Needs Assessment , Pennsylvania , Psychomotor Performance
Although wheelchair users are frequently subjected to oscillatory and shock vibrations, little research has been conducted to assess the whole-body vibration exposure of wheelchair users. The purpose of this study was to determine if selected wheelchair cushions alter potentially harmful whole-body vibrations transferred to wheelchair users. Thirty-two participants, who use wheelchairs as their primary mode of mobility, contributed to this study. Four of the most commonly prescribed wheelchair cushions were selected. Participants were asked to propel their wheelchair over a simulated activities of daily living (ADL) course while acceleration and force data were recorded. A repeated measures ANOVA showed no significant differences between the different cushions for the total averaged absorbed power (p = 0.190), the 50 mm curb drop (p = 0.234), or the rumble strip (p = 0.143). A repeated measure ANOVA for the peak curb drop absorbed power revealed a significant difference in the cushions (p = 0.043). The cushions that were most effective in this testing appear to be the Invacare Pindot and the Varilite Solo. Not only did those cushions appear to have the lowest values much of the time but also they did not display the highest values. When comparing results from a similar study, absorbed power appears to be as effective in determining vibration effects in the time domain as the methods in the ISO 2631 Standard.
Algorithms , Energy Transfer , Equipment Failure Analysis/methods , Ergonomics/methods , Physical Stimulation/methods , Wheelchairs , Adult , Female , Humans , Male , Vibration
OBJECTIVES: To compare the performance characteristics of different electric-powered wheelchairs (EPWs) and to evaluate the effectiveness of the American National Standards Institute/Rehabilitation Engineering and Assistive Technology Society of North America (ANSI/RESNA) wheelchair standards. DESIGN: Five types of EPWs were selected. Three wheelchairs of each type were tested according to the ANSI/RESNA wheelchair standards. SETTING: Rehabilitation engineering center. SPECIMENS: Fifteen wheelchairs. INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: Static tipping angle; dynamic tipping score; braking distance; energy consumption; static, impact, and fatigue strength; and climatic conditioning. RESULTS: There were significant differences (P<.05) among the 5 types of EPWs for static stability when facing both uphill and downhill in the most-stable and least-stable configurations. There were significant differences (P<.05) among the EPWs on most of the dynamic stability tests. There were also significant differences (P<.05) among EPWs for all the effectiveness of brakes conditions, as well as between 2 wheelchairs for the energy consumption testing. There were several failures among the wheelchairs during the static, impact, and fatigue strength testing and during the climatic testing. CONCLUSIONS: The results show that EPWs can vary greatly with respect to static and dynamic stability, braking distance, range, strength testing, and climatic conditioning. All these factors have a substantial effect on safety and performance.
Wheelchairs/standards , Equipment Design , Humans , Materials Testing
BACKGROUND: It is well established that physical activity is beneficial to health. For the individual in a wheelchair, a regular exercise program might not be available or may be too difficult to participate in physically and/or psychologically. Many exercise devices and regimes are boring. The goal, therefore, is to develop a device that makes exercise more exciting and, thus, motivates a person to exercise more or for a longer period of time, yielding increased energy expenditure. Our laboratory developed an interface between an arm ergometer and a computer game that allows the user to control game play on the screen as if using a joystick. The purpose of this study was to determine (a) whether the GAME(Cycle) system would elicit an exercise effect similar to arm ergometry, (b) whether perceived exertion would be different between the 2 devices, and (c) individuals' impressions regarding the GAME(Cycle) system. METHODS: Thirteen individuals who used wheelchairs participated in the study. Participants were asked to exercise for 2 separate, 19-minute sessions. For 1 session, a GAME(Cycle) system was used and for the other session, the same arm ergometer was used, but without the computer game being played. Physiologic data and perceived exertion were collected for each session. RESULTS: There were significant differences between playing the game and not playing the game for VO2 (P = 0.03) and VCO2 (P = 0.02), with higher values being found when the game was played. Perceived exertion was not significantly different between the 2 trials. CONCLUSION: GAME(Cycle) appears to be similar in nature with respect to energy expenditure to arm ergometry. Because this study was conducted on athletes, further research is needed with sedentary individuals to determine exercise effects and perceived exertion.
Exercise Test/instrumentation , Exercise Therapy/instrumentation , Spinal Cord Injuries/rehabilitation , User-Computer Interface , Video Games , Adult , Energy Metabolism/physiology , Equipment Design , Female , Humans , Male , Microcomputers , Middle Aged , Motivation , Physical Fitness/physiology , Software , Spinal Cord Injuries/physiopathology , Wheelchairs
Although the exposure to whole-body vibrations (WBV) has been shown to be detrimental to seated humans, the effects of wheelchairs and seating systems on the transmission of vibration to an individual have not been thoroughly examined. The purpose of this study was to determine if the selected wheelchair seat cushions and back supports minimize the transmission of vibrations. Thirty-two wheelchair users traversed an activities of daily living course three times using 16 randomly selected seating systems as well as their own. Vibrations were measured using triaxial accelerometers at the seat and participant's head. The weighted fore-to-aft (Tx), vertical (Tz), and resultant (Tr) transmissibility based on the vibrational-dose-value (VDV) were used to determine if differences existed among the four seat cushions and back supports. The obstacles that seem to have the largest effect on the transmission of WBV are the single event shocks and the repeated event shocks. Comparisons between the individuals own seating system and the tested seating systems suggest that the individuals are not using the most appropriate seating system in terms of the reduction of vibration transmission.
Equipment Failure Analysis/methods , Gait Disorders, Neurologic/physiopathology , Head/physiopathology , Nervous System Diseases/physiopathology , Posture , Wheelchairs , Acceleration , Activities of Daily Living , Adult , Equipment Failure Analysis/instrumentation , Female , Gait Disorders, Neurologic/etiology , Gait Disorders, Neurologic/rehabilitation , Humans , Male , Motion , Nervous System Diseases/complications , Nervous System Diseases/rehabilitation , Stress, Mechanical , Tooth/physiopathology , Transducers , Vibration
The purpose of this research was to study directional stability during reversing of rear-wheel drive, electric powered wheelchairs (EPW) under different initial front caster orientations. Specifically, the weight distribution differences caused by certain initial caster orientations were examined as a possible mechanism for causing directional instability that could lead to accidents. Directional stability was quantified by measuring the drive direction error of the EPW by a motion analysis system. The ground reaction forces were collected to determine the load on the front casters, as well as back-emf data to attain the speed of the motors. The drive direction error was found to be different for various initial caster orientations. Drive direction error was greatest when both casters were oriented 90 degrees to the left or right, and least when both casters were oriented forward. The results show that drive direction error corresponds to the loading difference on the casters. The data indicates that loading differences may cause asymmetric drag on the casters, which in turn causes unbalanced torque load on the motors. This leads to a difference in motor speed and drive direction error.
Electronics/instrumentation , Equipment Design , Rotation , Wheelchairs , Computer Simulation , Equipment Safety , Humans , Materials Testing , Motion , Motor Vehicles , Shear Strength
There are limited interface options for electric powered wheelchairs, which results in the inability of some individuals to drive independently. In addition, the development of new interface technologies will necessitate the development of alternative training methods. This study compares a conventional position sensing joystick to a novel isometric joystick during a driving task in a virtual environment and a real environment. The results revealed that there were few differences in task completion time and root-mean-square error (RMSE) between the two types of joysticks. There were significant correlations between the RMSE in the virtual environment and the real environment for both types of joysticks. The data indicate that performance in the virtual environment was representative of driving ability in the real environment, and the isometric joystick performed comparably to the position sensing joystick.
Central Nervous System Diseases/rehabilitation , Equipment Failure Analysis/methods , Psychomotor Performance , User-Computer Interface , Wheelchairs , Algorithms , Computer Simulation , Ergonomics/methods , Feedback , Female , Humans , Isometric Contraction , Male , Middle Aged , Movement , Task Performance and Analysis
