Uniaxial compressive behaviour of a FRP standing support made of mine wastes

Twenty-seven specimens were tested to investigate the uniaxial compression behaviour of an innovative standing support for underground space applications.The innovative standing support consisted of an external fibre reinforced polymer(FRP)jacket and the infill column made of cementitious grout,tailings and coal wash rejects.Effects of the FRP layers number and water to the cementitious grout(w/g)ratio were evaluated.Test results indicated that lower w/g ratios produced stronger infill columns.With FRP confinement,the standing support demonstrated strain-hardening loading characteristics with a significant improvement in both strength and ductility.The highest strength and strain of the specimens achieved was 58.4 MPa and 11.8%respectively.Compared with the unconfined specimens,the confinement with four FRP layers increased the specimen strength and associated strain up to 3.6 and 27.0 times respectively.A correlation between the compressive strength of the infill material and the ultrasonic pulse velocity was also investigated.Furthermore,a simple design-oriented model was proposed to predict the peak strength and the corresponding strain of the innovative standing support.

A hybrid tubular standing support for underground mines:Compressive behaviour

This paper presents the development of an innovative standing support for underground mines.The main feature of this standing support is its exterior container,a combination of polyvinyl chloride(PVC)with large rupture strain and fibre-reinforced polymer(FRP)with high strength-to-weight ratio.To demonstrate the advantages of this cementitious grout filled PVC-FRP tubular(PFT)standing support,a series of compression tests were conducted.Test variables included the strength of cementitious grout infill material and the thickness of FRP jacket.Compression tests were also conducted on cementitious grout-filled PVC tubular(PT)support and cementitious grout-filled FRP tubular(FT)support.These tests showed that PFT support presents a typical strain-hardening behaviour together with an outstanding axial deformation ability(>20%of the overall height of the support).In addition,the maximum compressive strength of PFT support is much higher than that of the corresponding PT support and FT support.Furthermore,using thicker FRP jacket or high strength cementitious grout material can enhance the load carrying capacity of PFT support.These comparative results indicated that the high performance of PFT support is mainly attributed to the combination of confining constituents(i.e.PVC and FRP)and infill material.

Quantification of ventilation enhancement using the Eye CAN roof support

Convergence of roof and floor in underground mine openings is a common occurrence. This convergence not only adversely affects the ability of workers, equipment and supplies to travel through the mine, it also reduces the effectiveness of the mine ventilation system, which is essential for the dilution of methane gas and airborne respirable dust. While installing secondary standing supports to control floor and roof convergence, such supports, by nature, partially obstruct a portion of the airway. These added obstructions inhibit the ability of the ventilation system to operate as efficiently as it could by increasing the resistance in and reducing the cross-sectional area of the airway. This study introduces and demonstrates the benefits of The Eye CAN^(TM) standing roof support, which controls floor and roof convergence and is less obstructive to air flow than conventional wooden cribs. Laboratory findings show that the normal resistance of a supported lined airway is reduced by using this new product from Burrell Mining Products, Inc., while providing the same roof support characteristics of an established product—The CANò. Load vs. displacement curves generated from laboratory tests demonstrated that this new product behaves with the same roof support characteristics as others in The CAN product family. Ventilation data gathered from a simulated mine entry was then used for computational fluid dynamics(CFD) modeling.The CFD analysis showed an improvement with The Eye CAN vs. other accepted forms of standing roof support. This proof-of-concept study suggests that, when using this new product made by Burrell Mining Products, Inc., not only will the convergence from the roof and floor be controlled, but airway resistance will also be reduced.

Assessing support alternatives for longwall gateroads subject to changing stress

Longwall gateroad entries are subject to changing horizontal and vertical stress induced by redistribution of loads around the extracted panel.The stress changes can result in significant deformation of the entries that may include roof sag,rib dilation,and floor heave.Mine operators install different types of supports to control the ground response and maintain safe access and ventilation of the longwall face.This paper describes recent research aimed at quantifying the effect of longwall-induced stress changes on ground stability and using the information to assess support alternatives.The research included monitoring of ground and support interaction at several operating longwall mines in the U.S.,analysis and calibration of numerical models that adequately represent the bedded rock mass,and observation of the support systems and their response to changes in stress.The models were then used to investigate the impact of geology and stress conditions on ground deformation and support response for various depths of cover and geologic scenarios.The research results were summarized in two regression equations that can be used to estimate the likely roof deformation and height of roof yield due to longwall-induced stress changes.This information is then used to assess the ability of support systems to maintain the stability of the roof.The application of the method is demonstrated with a retrospective analysis of the support performance at an operating longwall mine that experienced a headgate roof fall.The method is shown to produce realistic estimates of gateroad entry stability and support performance,allowing alternative support systems to be assessed during the design and planning stage of longwall operations.