The training of wrist arthroscopy

The wrist is a complex joint that bridges the hand to the forearm. Patients with wrist disorders increasingly prefer minimally invasive procedures for wrist joint diagnosis and treatment. Wrist arthroscopy offers direct visualization of the structures of the joint anatomy and existing disease processes while causing minimal damage to surrounding soft tissue. However, it requires a high level of technical ability for wrist arthroscopy practitioners. Therefore, an improved focus on wrist arthroscopy training combining new educational media and traditional practice should aid in the development of novel wrist arthroscopy training mode. This article aims to describe the status of wrist training and evaluation systems and introduce a new progressive wrist training system

Experimental and numerical investigation of injection of coal washery waste into longwall goaf

Mining, preparation and consumption of coal produce large amounts of waste, of which the coal washery rejects account for a major part. Currently emplacement of coal washery waste not only requires large land, but also pollutes the air, soils and underground water. A number of methods have been developed to make use of coal wastes to fill the voids and strata gaps formed from coal extraction, including dry material backfill, paste backfill and overburden slurry injection. Without the need of underground transport system and interference with coal production, the overburden injection technology is considered a cost-effective method in which the coal washery slurry is injected from the surface down to the caved zone of the longwall goaf and fill the voids. In order to understand the mechanism and behaviour of the grout flowing in the caved zone, laboratory experimental and numerical studies were conducted. The laboratory experiment visually simulated the process of coal washery flowing in the caved zone. The process was also numerically simulated by developing a Computational Fluid Dynamics (CFD) model. These studies provide better understanding of the injection and flow mechanism of the grout in the broken medium. The agreement between the experimental and numerical models indicates that the CFD model is able to simulate the complicated flow and can be used to optimise the injection system design and operation parameters

Monitoring longwall weighting at Austar Mine using microseismic systems and stressmeters

Cyclic weighting is a major hazard for longwall operations in many deep mines with strong roof strata. Significant cyclic weighting events had been experienced at Austar Mine, resulting in production delays. Early warning of imminent weighting events by means of geotechnical monitoring will help to minimise the risk associated and to develop preventative solutions. This paper describes a study undertaken by CSIRO and Austar Mine in which an integrated stress and microseismic monitoring system was trialled to detect strata responses to the mining processes. The main objectives of this study were to understand the caving mechanics and develop an effective early warning system for roof weighting management. The field monitoring results clearly demonstrated the effectiveness of using both stress and seismic signatures to infer longwall caving and weighting events. Stress changes recorded by stressmeters in shallow surface strata and underground roadway roofs showed a strong correlation with the chock pressure increase at the longwall face. The same phenomenon had also been observed from the recorded microseismic events. In order to develop an automated early warning system for longwall weighting, a trigger index method, which integrates the warning signs from different sensors, was developed and tested against the mine weighting observations and chock pressure data. A remarkably good agreement was achieved. For a limited number of cases examined, the warning signs from the monitoring system mostly occurred at least several hours before the roof weighting events and the major increase in chock pressure. This has demonstrated that the integrated stress and microseismic monitoring system, together with the analysis method developed, is capable of providing sufficient early warning for imminent underground weighting events

Risk of shear failure and extensional failure around over-stressed excavations in brittle rock

The authors investigate the failure modes surrounding over-stressed tunnels in rock. Three lines of investigation are employed: failure in over-stressed three-dimensional (3D) models of tunnels bored under 3D stress, failure modes in two-dimensional (2D) numerical simulations of 1000 m and 2000 m deep tunnels using FRACOD, both in intact rock and in rock masses with one or two joint sets, and finally, observations in TBM (tunnel boring machine) tunnels in hard and medium hard massive rocks. The reason for ‘stress-induced’ failure to initiate, when the assumed maximum tangential stress is approximately (0.4–0.5)σc (UCS, uniaxial compressive strength) in massive rock, is now known to be due to exceedance of a critical extensional strain which is generated by a Poisson's ratio effect. However, because similar ‘stress/strength’ failure limits are found in mining, nuclear waste research excavations, and deep road tunnels in Norway, one is easily misled into thinking of compressive stress induced failure. Because of this, the empirical SRF (stress reduction factor in the Q-system) is set to accelerate as the estimated ratio σθmax/σc >> 0.4. In mining, similar ‘stress/strength’ ratios are used to suggest depth of break-out. The reality behind the fracture initiation stress/strength ratio of ‘0.4’ is actually because of combinations of familiar tensile and compressive strength ratios (such as 10) with Poisson's ratio (say 0.25). We exceed the extensional strain limits and start to see acoustic emission (AE) when tangential stress σθ ≈ 0.4σc, due to simple arithmetic. The combination of 2D theoretical FRACOD models and actual tunnelling suggests frequent initiation of failure by ‘stable’ extensional strain fracturing, but propagation in ‘unstable’ and therefore dynamic shearing. In the case of very deep tunnels (and 3D physical simulations), compressive stresses may be too high for extensional strain fracturing, and shearing will dominate, both ahead of the face and following the face. When shallower, the concept of ‘extensional strain initiation but propagation’ in shear is suggested. The various failure modes are richly illustrated, and the inability of conventional continuum modelling is emphasized, unless cohesion weakening and friction mobilization at different strain levels are used to reach a pseudo state of yield, but still considering a continuum

Stress change near a major geological structure during longwall mining

ABSTRACT: Stress state and geotechnical conditions often change significantly near major geological structures (e.g. faults, shear zones, dykes) in underground coal mines, which is the cause of most major mine instability and/or safety hazards including coal burst, roof falls, water inrush and gas outburst. In order to understand and quantify the stress state near major geological structures, an integrated study had been conducted in the vicinity of a dyke in an Australian underground coal mine. The field monitoring program included installing microseismic geophones, stressmeters and extensometers in the roadway roofs and coal pillars, aiming to obtain seismic and stress change data during longwall mining. The monitoring results indicate that the stress regime was clearly different on the inbye and outbye sides of the dyke. The inbye side had a much higher stress than the outbye side before and during the longwall mining. This study provided quantified field evidence that the stress concentration occurs near major geological structures. This stress concentration could lead to high strain energy concentration in the rib of a roadway, and hence increase the risk of coal burst

Hydraulically fractured hard rock aquifer for seasonal storage of solar thermal energy

The intermittent nature of solar thermal energy derives from its oversupply during the low season and undersupply during the peak season. The solution is to accumulate and store the surplus energy that can be used in times of high demand and low supply. The HYDROCK concept is a method developed for seasonal heat storage in artificially fractured bedrock. This study aims to investigate the rock fracturing process in the construction of hydraulically fractured hard rock aquifer for seasonal storage of thermal energy. The primary objective of this study is to perform a sensitivity analysis of numerical simulations of rock fracturing processes that are taking place during the development of artificially fractured heat storage in hard rocks. Coupled hydro-mechanical numerical models are generated using rock fracture mechanics code FRACOD2D. The sensitivity of critical parameters is presented, and all relevant influencing factors are investigated. Suggestions for practical applications of HYDROCK are given.Peer reviewe

Simulation of the interactions between hydraulic and natural fractures using a fracture mechanics approach

HYDROCK method aims to store thermal energy in the rock mass using hydraulically propagated fracture planes. The hydraulic fractures can interact with the pre-existing natural fractures resulting in a complex fracture network, which can influence the storage performance. This study investigates the interactions between hydraulic and natural fractures using a fracture mechanics approach. The new functionality of the fracture mechanics modelling code FRACOD that enables crossing of hydraulically driven fracture by a pre-existing fracture is presented. A series of two-dimensional numerical models is prepared to simulate the interaction at different approach angles in granitic rock of low permeability. It is demonstrated that multiple interaction mechanisms can be simulated using the fracture mechanics approach. The numerical results are in agreement with the modified Renshaw and Pollard analytical criterion for fracture crossing. The results show that for large approach angles, the hydraulic fracture crosses thenatural fracture, whereas for small approach angles, the hydraulic fracture activates the natural fracture and the wing-shaped tensile fractures are propagated from its tips. Thus, the presence of fractures with low dip angles can lead to the growth of more complex fracture network that could impair the thermal performance of the HYDROCK method.Peer reviewe