Bolt is an important connection in underground construction and monitoring its stress characteristics is essential to evaluate the effectiveness of bolt. The strain information collected along a rock bolt reveals the long-term movement characteristics of rock mass, which greatly helps toward disaster prevention and risk warning.Grooving on the surface of a bolt and embedding an optical fiber is one of the main methods for monitoring the anchorage performance and stress distribution around the bolt in underground engineering. In this study, Pulse Pre-Pumped Brillouin Optical Time Domain Analysis (PPP-BOTDA) technology is used to evaluate the stress, axial force, and shear stress distribution of the bolt under tensile load for different types (grooved and nongrooved) of bolts embedded in concrete with resin as anchoring agent. The results show that the PPP-BOTDA sensor can be used to monitor the stress state of the bolt embedded in concrete with resin as anchoring agent when the bolt is subjected to a tensile force. However, the apparent stress value measured in this way is not the actual stress value of the bolt, but is an increased value caused due to the groove. The closer to the exposed end of the bolt, the greater is the deviation between the apparent stress value and the actual stress value of the bolt. Based on the monitoring results from this experimental study, a stress reduction calculation method is proposed, which can change the measured value into the actual stress of the bolt.
K E Y W O R D Saxial force, bolt, PPP-BOTDA technology, pullout test, shear stress 2012 |
The evolution of overburden deformation is crucial for safety and environmental efficiency and its monitoring is becoming a key scientific issue. The use of an optical fiber sensor (OFS) for mining engineering is now receiving praise by virtue of its distinct abilities of distribution, high accuracy, and anti-interference measurement. Nevertheless, the dynamic response of OFS monitoring on overburden deformation still needs to be characterized in detail. This paper analyzed the characterization pattern of overburden deformation based on distributed optical fiber sensing (DOFS) by means of an analogue model test. Then, we discuss the influence of rules of optical fiber embedding on a model test in a numerical simulation. The results show that the DOFS monitoring demonstrates the time-space evolution of overburden deformation and the development of three horizontal areas and three vertical zones. A standardization DOFS characterization model is proposed to expound the characterization mechanism of the overburden structure zoning process; the influence of optical fiber embedding on rock displacement in the model test is revealed, and it is found that the displacement error will increase sharply when the fiber diameter is larger than 2 mm. These findings could provide an effective solution for a monitoring method in intelligent mining from the perspective of a theoretical basis and technological system.
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