The Experts below are selected from a list of 1455 Experts worldwide ranked by ideXlab platform
Zhiye Zhao - One of the best experts on this subject based on the ideXlab platform.
-
Development of a new deformation-controlled rockbolt: numerical modelling and laboratory verification
Proceedings of the Ninth International Symposium on Ground Support in Mining and Underground Construction, 2019Co-Authors: Yasuhiro Yokota, Kensuke Date, Keita Iwano, Zhiye Zhao, Yu Koizumi, Yuko OkadaAbstract:To prevent large tunnel deformations caused by rock bursts or squeezing ground conditions, Rockbolts need to satisfy both strength capacity and the required deformability. Currently, energy-absorbing Rockbolts, such as the cone bolt and the D-bolt, have been successfully used in deep mining to avoid sudden tunnel collapses. This paper proposes a new energy-absorbing rockbolt, referred to as a deformation-controlled rockbolt (DC-bolt). The performance of the proposed DC-bolt was verified by numerical simulations using discontinuous deformation analysis (DDA) and by prototype laboratory tests. As a result, it is concluded that the DC-bolt possesses both high loading capacity and deformation capacity. Additionally, the DC-bolt can limit rock surface movement when it reaches a certain displacement. Thus, it can be a useful tunnel support for tunnels that are to be excavated in squeezing ground conditions.
-
Bond-slip modeling of a CMC rockbolt element using 2D-DDA method
Tunnelling and Underground Space Technology, 2019Co-Authors: Zhiye Zhao, Junlong Shang, Chuangzhou WuAbstract:Abstract The bonding condition at the rock and rockbolt interface is one of the most important factors to determine the load transfer mechanism of a CMC rockbolt element. The two-dimensional Discontinuous Deformation Analysis (2D-DDA) method is used in this paper to investigate the pullout performance of the CMC rockbolt element which is modeled as three components, i.e. the rock, the rockbolt and the mortar. The material properties used in the numerical models are calibrated against the experiments results. The simulated results show that a bond stress versus slip displacement curve of the CMC rockbolt element is exhibiting three stages which could be represented by a trilinear bond-slip model. Parametric studies have been carried out to investigate the effects of the confining pressure and those of the geometry configuration of the rockbolt ribs on the bond stress versus slip displacement curves and the crack propagations in the mortar. It is found that the maximum bond strength and the residual bond strength increase with the increase of confining pressure. Under lower confining pressure, the rib face angle controls the dilation of rock blocks. The obtained key parameters of the trilinear bond – slip models can be used to simulate the bond behavior between the rockbolt and rock interface in pullout test. The nodal axial forces and nodal bond force distributions along the rockbolt could be curve fitted using exponential models. The obtained parameters of the exponential models can be used for engineering practice under similar conditions.
-
analytical modeling of shear behaviors of Rockbolts perpendicular to joints
Construction and Building Materials, 2018Co-Authors: Zhiye Zhao, Jun PengAbstract:Rockbolts have been used to minimize the deformation of underground excavations where the surrounding rock masses contain weak planes such as fractures, joints or faults. Rockbolts installed across rock joints are able to resist the opening and shearing movements of rock joints. One of the rockbolt failure modes encountered in the field is caused by the excessive shear loads. A simple analytical model based on the Beam on Elastic Foundation (BEM) method is proposed in this study to predict the shear responses of a bolt installed perpendicularly to rock joint. The shear load-displacement curve of a double shear test can be divided into three stages: the elastic stage, the elasto-plastic stage and the plastic stage. The foundation stiffness for each respective stage are varied with the curvature influencing zone . The pretension effects are taken into account in the proposed analytical model. The model agrees well with the experimental shear tests, suggesting that the analytical model has the capability to predict the shear load-displacement curve of bolts crossing rock joints.
-
effects of joints on the reinforced rock units of fully grouted Rockbolts
Tunnelling and Underground Space Technology, 2018Co-Authors: Zhiye ZhaoAbstract:Abstract A rockbolt model has been implemented into the 2-dimensional discontinuous deformation analysis (DDA-2D) code to analyze the performance of the fully grouted Rockbolts installed in the jointed rock mass. Parametric studies are also conducted to investigate the effects of the rock properties, joint orientations, rockbolt lengths and in-plane spacings. The numerical study shows that the reinforcement area of the reinforcement rock unit (RRU) could be used to optimize the design of the rockbolt. The RRU induced by single rockbolt is normally in a cone shape and restrained by the orientation of the discontinuities. The RRU induced by grouped Rockbolts is heavily influenced by the joint orientations and the rockbolt spacing. The design of the in-plane rockbolt spacing has to consider the joints orientations.
-
an analytical model for fully grouted Rockbolts with consideration of the pre and post yielding behavior
Rock Mechanics and Rock Engineering, 2017Co-Authors: Zhiye ZhaoAbstract:For Rockbolts subjected to tensile loads, there exists a unique local slip–strain relationship as well as a unique bond–slip relationship between Rockbolts and rock mass. An analytical model is presented in this study for fully grouted Rockbolts under tension, based on the slip–strain relationship of Rockbolts. This analytical model takes into account the trilinear bond–slip relationship and the pre- and post-yielding characteristics of the rockbolt material. The reliability and accuracy of the proposed analytical model are verified by experimental pullout tests. Verification studies show that the proposed model is capable of representing the strain and stress distributions of the Rockbolts, and the overall load–displacement relationships of Rockbolts before and after yielding. Additionally, the model has successfully captured the decoupling mechanism at the bolt–rock interface.
Urs Sennhauser - One of the best experts on this subject based on the ideXlab platform.
-
Structurally embedded fiber Bragg gratings: civil engineering applications
Proceedings of SPIE, 1999Co-Authors: Philipp M. Nellen, Rolf Broennimann, Ph Mauron, Andreas Frank, Urs SennhauserAbstract:In civil engineering it is of interest to monitor long-term performance of structures made of new lightweight materials like glass or carbon fiber reinforced polymers (GFRP/CFRP). In contrast to surface applied optical fiber sensors, embedded sensors are expected to be better protected against rough handling and harsh environmental conditions. We report on two recently done fiber optical sensor applications in civil engineering. Both include structurally embedded fiber Bragg grating (BG) arrays but have different demands with respect to their operation. For the first application fiber BGs were embedded in GFRP Rockbolts of 3 - 5 m in length either of 3, 8, or 22 mm diameter. The sensor equipped Rockbolts are made for distributed measurements of boulder motion during tunnel construction and operation and should withstand strain up to 1.6%. Rockbolt sensors were field tested in a tunnel near Sargans in Switzerland. For a second application fiber BGs were embedded in CFRP wires of 5 mm diameter used for the pre- stressing cables of a 56 m long bridge near Lucerne in Switzerland. The permanent load on the cable corresponds to 0.8% strain. Due to the embedded sensors, strain decay inside the cable anchoring heads could be measured for the first time during loading and operation of the cables. For both applications mechanical and thermal loading tests were performed to assess the function of these new elements. Also, temperature and strain sensitivity were calibrated. Reliability studies with respect to stress transfer, fiber mechanical failure, and wavelength shift caused by thermal BG decay as well as monitoring results of both applications are presented.
-
fiber optic bragg grating sensors embedded in gfrp Rockbolts
Smart Structures and Materials 1999: Sensory Phenomena and Measurement Instrumentation for Smart Structures and Materials, 1999Co-Authors: Andreas Frank, Rolf Broennimann, Philipp M. Nellen, Urs SennhauserAbstract:Rockbolt anchors for tunnel or mine roofs are key elements during construction and operation. We report on the fabrication of glass fiber reinforced polymer (GFRP) Rockbolts with embedded fiber optical Bragg grating sensors and their first field application in a test tunnel. Optical fibers and in-fiber Bragg grating sensors were embedded in GFRP Rockbolts during a continuously ongoing pultrusion process on an industrial production machine. Depending on their outer diameter the rods equipped with fiber sensors serve as measuring Rockbolts or as extensometric sensors for the motion of boulders in the tunnel roof. The adhesion and force transfer of different fiber coatings were tested by push-out experiments. By temperature and strain cycle tests the performance of the rockbolt sensors was evaluated. We will present these results and the measurements made during a first installation of fiber optical rockbolt sensors in a tunnel.
-
Fiber optical Bragg grating sensors embedded in CFRP wires
Proc. SPIE 3670 Smart Structures and Materials 1999: Sensory Phenomena and Measurement Instrumentation for Smart Structures and Materials, 1999Co-Authors: Andreas Frank, Rolf Brönnimann, Philipp M. Nellen, Urs SennhauserAbstract:Rockbolt anchors for tunnel or mine roofs are key elements during construction and operation. We report on the fabrication of glass fiber reinforced polymer (GFRP) Rockbolts with embedded fiber optical Bragg grating sensors and their first field application in a test tunnel. Optical fibers and in-fiber Bragg grating sensors were embedded in GFRP Rockbolts during a continuously ongoing pultrusion process on a industrial production machine. Depending on their outer diameter the rods equipped with fiber sensors serve as measuring Rockbolts or as extensometric sensors for the motion of boulders in the tunnel roof. The adhesion and force transfer of different fiber coatings were tested by push-out experiments. By temperature and strain cycle tests the performance of the rockbolt sensors was evaluated. We will present these results and the measurements made during a first installation of fiber optical rockbolt sensors in a tunnel.
Serkan Saydam - One of the best experts on this subject based on the ideXlab platform.
-
mineralogically influenced stress corrosion cracking of Rockbolts and cable bolts in underground mines
International Journal of Rock Mechanics and Mining Sciences, 2019Co-Authors: Saisai Wu, P Hagan, Alan Crosky, Hamed Lamei Ramandi, Honghao Chen, Serkan SaydamAbstract:Abstract Stress corrosion cracking (SCC) of Rockbolts and cable bolts in underground mines has been identified as a serious international problem over the past two decades. The frequent occurrence of rockbolt and cable bolt SCC in strata containing clay and groundwater suggests the presence of certain mineral types may be an influencing factor. To identify the environmental factors leading to SCC and evaluate the effects of mineralogically influenced corrosion, a laboratory testing program capable of recreating the underground bolting environments was designed and conducted. A static load was applied to specimens of Rockbolts and cable bolts placed in “corrosion cells” containing groundwater, clay, coal or a combination of those materials for about 300 days. Results from these tests revealed that the mineralogical materials indirectly affected the rate of corrosion by significantly altering the local water chemistry. The mechanical load applied to the specimens was found to accelerate the rate of corrosion, and corrosion pits were observed to have formed on the steel surfaces. The generation of corrosion pits would likely result in local stress concentration and contribute to SCC. The results of this study provide further insights into the environmental factors leading to SCC and the proposed methodologies can be used for investigating this type of failure through in-situ experiments.
-
a laboratory study of shear behaviour of Rockbolts under dynamic loading based on the drop test using a double shear system
Rock Mechanics and Rock Engineering, 2019Co-Authors: L Li, P Hagan, Serkan Saydam, B Hebblewhite, Chengguo ZhangAbstract:Rockbolts are widely used as an underground support element to resist the convergence and maintain the stability of excavations. However, shear failure of Rockbolts is increasingly observed in jointed rock mass of underground tunnels, especially after being subjected to seismic events. At present, understanding of the mechanical response of Rockbolts subjected to seismic or dynamic loading in shear is still unclear. To investigate the shear performance of Rockbolts under dynamic loading condition, a series of tests were conducted using a drop mass of up to185 kg from a maximum height of 3 m based on a double shear test (DST) system. Three variables were examined in the laboratory test including rockbolt diameter (8 mm and 16 mm), installation angle (90° and 45°) and input energy (drop height). The duration of the impact was 10–12 ms from release of the drop mass to first contact. By evaluating the DST system’s displacement/velocity/acceleration–time characteristic and the amount of energy absorption, the shear performance of rockbolt was assessed. When sufficient energy is applied into the DST system, the deformation of the rockbolt is dominated by localized shear force. The transient force can rupture the rockbolt with little bending and without any obvious tensile elongation. It was found that the averaged dynamic shear load is less than the peak static shear load whether horizontally installed or installed at an angle. In conclusion, the effectiveness of Rockbolts in resisting shear stress can differ significantly under static loading and dynamic loading condition; the difference is reflected in the level of shear deformation and amount of energy absorption. The shear capacity of a rockbolt under 1 s−1 strain rate can be determined by the energy absorbed and average dynamic load. This approach can be applied to the support system design in rockburst-prone condition.
-
failure of the threaded region of Rockbolts in underground coal mines
Mining Technology, 2018Co-Authors: Honghao Chen, Hamed Lamei Ramandi, Alan Crosky, Julian Walker, Serkan SaydamAbstract:HSAC 840 steel Rockbolts were examined, all of which had failed in service through the threaded region exterior to the rock face by brittle fracture transverse to the bolt axis. The bolts had been ...
-
Parametric Study of Rockbolt Shear Behaviour by Double Shear Test
Rock Mechanics and Rock Engineering, 2016Co-Authors: L Li, Serkan Saydam, Paul C. Hagan, Bruce Hebblewhite, Yuan LiAbstract:Failure of Rockbolts as a result of shear or bending loads can often be found in underground excavations. The response of rock anchorage systems has been studied in shear, both by laboratory tests as well as numerical modelling in this study. A double shear test was developed to examine the shear behaviour of a bolt installed across two joints at different angles. To investigate the influence of various parameters in the double shear test, a numerical model of a fully grouted rockbolt installed in concrete was constructed and analysed using FLAC3D code. A number of parameters were considered including concrete strength, inclination between rockbolt and joints and rockbolt diameter. The numerical model considered three material types (steel, grout and concrete) and three interfaces (concrete–concrete, grout–concrete and grout–rockbolt). The main conclusions drawn from the study were that the level of bolt resistance to shear was influenced by rock strength, inclination angle, and diameter of the rockbolt. The numerical simulation of the bolt/grout interaction and deformational behaviour was found to be in close agreement with earlier experimental test results.
-
laboratory based coupon testing for the understanding of scc in Rockbolts
Mining Technology, 2016Co-Authors: D Vandermaat, P Hagan, Serkan Saydam, Alan CroskyAbstract:Coupon testing has been used extensively to understand the effects of general corrosion on engineering materials within their operational environment. This study examined the use of various coupon specimens to examine stress corrosion cracking (SCC) of Rockbolts in the underground mining environment. The standard ASTM G39 bend beam SCC specimen, as well as a pin-loaded slotted specimen, was used in this investigation. It was identified that the critical stress threshold for HSAC 840 rockbolt steel is approximately 580 MPa, slightly lower than the material’s yield strength. It was shown that the higher toughness HSAC 840 grade rockbolt steel performed better than AISI 1355 grade rockbolt steel, emphasising the importance of steel chemistry. It was also found that galvanising improved SCC resistance but shot peening reduced SCC resistance.
Andreas Frank - One of the best experts on this subject based on the ideXlab platform.
-
Structurally embedded fiber Bragg gratings: civil engineering applications
Proceedings of SPIE, 1999Co-Authors: Philipp M. Nellen, Rolf Broennimann, Ph Mauron, Andreas Frank, Urs SennhauserAbstract:In civil engineering it is of interest to monitor long-term performance of structures made of new lightweight materials like glass or carbon fiber reinforced polymers (GFRP/CFRP). In contrast to surface applied optical fiber sensors, embedded sensors are expected to be better protected against rough handling and harsh environmental conditions. We report on two recently done fiber optical sensor applications in civil engineering. Both include structurally embedded fiber Bragg grating (BG) arrays but have different demands with respect to their operation. For the first application fiber BGs were embedded in GFRP Rockbolts of 3 - 5 m in length either of 3, 8, or 22 mm diameter. The sensor equipped Rockbolts are made for distributed measurements of boulder motion during tunnel construction and operation and should withstand strain up to 1.6%. Rockbolt sensors were field tested in a tunnel near Sargans in Switzerland. For a second application fiber BGs were embedded in CFRP wires of 5 mm diameter used for the pre- stressing cables of a 56 m long bridge near Lucerne in Switzerland. The permanent load on the cable corresponds to 0.8% strain. Due to the embedded sensors, strain decay inside the cable anchoring heads could be measured for the first time during loading and operation of the cables. For both applications mechanical and thermal loading tests were performed to assess the function of these new elements. Also, temperature and strain sensitivity were calibrated. Reliability studies with respect to stress transfer, fiber mechanical failure, and wavelength shift caused by thermal BG decay as well as monitoring results of both applications are presented.
-
fiber optic bragg grating sensors embedded in gfrp Rockbolts
Smart Structures and Materials 1999: Sensory Phenomena and Measurement Instrumentation for Smart Structures and Materials, 1999Co-Authors: Andreas Frank, Rolf Broennimann, Philipp M. Nellen, Urs SennhauserAbstract:Rockbolt anchors for tunnel or mine roofs are key elements during construction and operation. We report on the fabrication of glass fiber reinforced polymer (GFRP) Rockbolts with embedded fiber optical Bragg grating sensors and their first field application in a test tunnel. Optical fibers and in-fiber Bragg grating sensors were embedded in GFRP Rockbolts during a continuously ongoing pultrusion process on an industrial production machine. Depending on their outer diameter the rods equipped with fiber sensors serve as measuring Rockbolts or as extensometric sensors for the motion of boulders in the tunnel roof. The adhesion and force transfer of different fiber coatings were tested by push-out experiments. By temperature and strain cycle tests the performance of the rockbolt sensors was evaluated. We will present these results and the measurements made during a first installation of fiber optical rockbolt sensors in a tunnel.
-
Fiber optical Bragg grating sensors embedded in CFRP wires
Proc. SPIE 3670 Smart Structures and Materials 1999: Sensory Phenomena and Measurement Instrumentation for Smart Structures and Materials, 1999Co-Authors: Andreas Frank, Rolf Brönnimann, Philipp M. Nellen, Urs SennhauserAbstract:Rockbolt anchors for tunnel or mine roofs are key elements during construction and operation. We report on the fabrication of glass fiber reinforced polymer (GFRP) Rockbolts with embedded fiber optical Bragg grating sensors and their first field application in a test tunnel. Optical fibers and in-fiber Bragg grating sensors were embedded in GFRP Rockbolts during a continuously ongoing pultrusion process on a industrial production machine. Depending on their outer diameter the rods equipped with fiber sensors serve as measuring Rockbolts or as extensometric sensors for the motion of boulders in the tunnel roof. The adhesion and force transfer of different fiber coatings were tested by push-out experiments. By temperature and strain cycle tests the performance of the rockbolt sensors was evaluated. We will present these results and the measurements made during a first installation of fiber optical rockbolt sensors in a tunnel.
Philipp M. Nellen - One of the best experts on this subject based on the ideXlab platform.
-
Structurally embedded fiber Bragg gratings: civil engineering applications
Proceedings of SPIE, 1999Co-Authors: Philipp M. Nellen, Rolf Broennimann, Ph Mauron, Andreas Frank, Urs SennhauserAbstract:In civil engineering it is of interest to monitor long-term performance of structures made of new lightweight materials like glass or carbon fiber reinforced polymers (GFRP/CFRP). In contrast to surface applied optical fiber sensors, embedded sensors are expected to be better protected against rough handling and harsh environmental conditions. We report on two recently done fiber optical sensor applications in civil engineering. Both include structurally embedded fiber Bragg grating (BG) arrays but have different demands with respect to their operation. For the first application fiber BGs were embedded in GFRP Rockbolts of 3 - 5 m in length either of 3, 8, or 22 mm diameter. The sensor equipped Rockbolts are made for distributed measurements of boulder motion during tunnel construction and operation and should withstand strain up to 1.6%. Rockbolt sensors were field tested in a tunnel near Sargans in Switzerland. For a second application fiber BGs were embedded in CFRP wires of 5 mm diameter used for the pre- stressing cables of a 56 m long bridge near Lucerne in Switzerland. The permanent load on the cable corresponds to 0.8% strain. Due to the embedded sensors, strain decay inside the cable anchoring heads could be measured for the first time during loading and operation of the cables. For both applications mechanical and thermal loading tests were performed to assess the function of these new elements. Also, temperature and strain sensitivity were calibrated. Reliability studies with respect to stress transfer, fiber mechanical failure, and wavelength shift caused by thermal BG decay as well as monitoring results of both applications are presented.
-
fiber optic bragg grating sensors embedded in gfrp Rockbolts
Smart Structures and Materials 1999: Sensory Phenomena and Measurement Instrumentation for Smart Structures and Materials, 1999Co-Authors: Andreas Frank, Rolf Broennimann, Philipp M. Nellen, Urs SennhauserAbstract:Rockbolt anchors for tunnel or mine roofs are key elements during construction and operation. We report on the fabrication of glass fiber reinforced polymer (GFRP) Rockbolts with embedded fiber optical Bragg grating sensors and their first field application in a test tunnel. Optical fibers and in-fiber Bragg grating sensors were embedded in GFRP Rockbolts during a continuously ongoing pultrusion process on an industrial production machine. Depending on their outer diameter the rods equipped with fiber sensors serve as measuring Rockbolts or as extensometric sensors for the motion of boulders in the tunnel roof. The adhesion and force transfer of different fiber coatings were tested by push-out experiments. By temperature and strain cycle tests the performance of the rockbolt sensors was evaluated. We will present these results and the measurements made during a first installation of fiber optical rockbolt sensors in a tunnel.
-
Fiber optical Bragg grating sensors embedded in CFRP wires
Proc. SPIE 3670 Smart Structures and Materials 1999: Sensory Phenomena and Measurement Instrumentation for Smart Structures and Materials, 1999Co-Authors: Andreas Frank, Rolf Brönnimann, Philipp M. Nellen, Urs SennhauserAbstract:Rockbolt anchors for tunnel or mine roofs are key elements during construction and operation. We report on the fabrication of glass fiber reinforced polymer (GFRP) Rockbolts with embedded fiber optical Bragg grating sensors and their first field application in a test tunnel. Optical fibers and in-fiber Bragg grating sensors were embedded in GFRP Rockbolts during a continuously ongoing pultrusion process on a industrial production machine. Depending on their outer diameter the rods equipped with fiber sensors serve as measuring Rockbolts or as extensometric sensors for the motion of boulders in the tunnel roof. The adhesion and force transfer of different fiber coatings were tested by push-out experiments. By temperature and strain cycle tests the performance of the rockbolt sensors was evaluated. We will present these results and the measurements made during a first installation of fiber optical rockbolt sensors in a tunnel.
