Mechanical behavior of 2G NPR bolt anchored rock samples under static disturbance loading

The deep mining of coal resources is accompanied by severe environmental challenges and various potential engineering hazards.The implementation of NPR(negative Poisson's ratio)bolts are capable of controlling large deformations in the surrounding rock effectively.This paper focuses on studying the mechanical properties of the NPR bolt under static disturbance load.The deep nonlinear mechanical experimental system was used to study the mechanical behavior of rock samples with different anchored types(unanchored/PR anchored/2G NPR anchored)under static disturbance load.The whole process of rock samples was taken by high-speed camera to obtain the real-time failure characteristics under static disturbance load.At the same time,the acoustic emission signal was collected to obtain the key characteristic parameters of acoustic emission such as acoustic emission count,energy,and frequency.The deformation at the failure of the samples was calculated and analyzed by digital speckle software.The findings indicate that the failure mode of rock is influenced by different types of anchoring.The peak failure strength of 2G NPR bolt anchored rock samples exhibits an increase of 6.5%when compared to the unanchored rock samples.The cumulative count and cumulative energy of acoustic emission exhibit a decrease of 62.16%and 62.90%,respectively.The maximum deformation of bearing capacity exhibits an increase of 59.27%,while the failure time demonstrates a delay of 42.86%.The peak failure strength of the 2G NPR bolt anchored ones under static disturbance load exhibits an increase of 5.94%when compared to the rock anchored by PR(Poisson's ratio)bolt.The cumulative count and cumulative energy of acoustic emission exhibit a decrease of 47.16%and 43.86%,respectively.The maximum deformation of the bearing capacity exhibits an increase of 50.43%,and the failure time demonstrates a delay of 32%.After anchoring by 2G NPR bolt,anchoring support effectively reduces the risk of damage caused by static disturbance load.These results demonstrate that the support effect of 2G NPR bolt materials surpasses that of PR bolt.

Spatio-temporal characteristics of acoustic emission during the deformation of rock samples with compressional and extensional en-echelon faults

The spatio-temporal characteristics of acoustic emission (AE) during the deformation of rock samples with compressional and extensional en-echelon faults have been studied. The results show that the pre-existing structure can significantly influence the patterns of AE spatial distribution. With increasing of differential stress, AE events firstly cluster around the two ends of pre-existing faults inside the jog and then along the line joining the two ends. The biggish AE events often occur around one end repeatedly. The image of AE clusters indicates the direction and the area of the fracture propagation. The direction of the macroscopic fracture in extensional and compressional jogs is perpendicular and parallel to the direction of axial stress, respectively. The weakening process before the fracturing of jog area is remarkable, and one of the typical precursors for the instability is that the cumulative frequency of AE events increases exponentially. After the fracturing of the jog the frequency and releasing strain energy of AE events decrease gradually. During the friction period, there is no precursory increasing of AE activity before the big stick-slip events. The change of b value in jog shows a typical change of decreasing tendentiously returning quickly before the instability. The decrease of b value occurs in the process of stress increasing and sometime goes down to the weakening stage, and the quick increase b values appears in a short time just before the instability. The comparative analysis shows that the difference in b value due to the different structures is larger than b value variation caused by increase of the differential stress. For the same sample, the temporal sequence of AE is strongly affected by the mechanical state, and the high loading velocity corresponds to the high release rate of strain energy and low b value. Due to its lower failure strength, the broken area is sensitive to small changes in differential stress. Therefore, it offers a potential explanation for the phenomena of precursory window or sensitive point and separation of seismic source and precursors.

Some results of modeling D-D seismogenic pattern by the fracture model experiment of large-scale rock samples(I)

sing the natural limestone samples taken from the field with dimension of 500 mm×500 mm×1 000 mm, the D-D (dilatancy-diffusion) seismogeny pattern was modeled under the condition of water injection, which observes the time-space evolutionary features about the relative physics fields of the loaded samples from deformation, formation of microcracks to the occurrence of main rupture. The results of observed apparent resistivity show: ① The process of the deformation from microcrack to main rupture on the loaded rock sample could be characterized by the precursory spatial-temporal changes in the observation of apparent resistivity; ② The precursory temporal changes of observation in apparent resistivity could be divided into several stages, and its spatial distribution shows the difference in different parts of the rock sample; ③ Before the main rupture of the rock sample the obvious ″tendency anomaly′ and ′short-term anomaly″ were observed, and some of them could be likely considered as the ″impending earthquake ″anomaly precursor of apparent resistivity. The changes and distribution features of apparent resistivity show that they are intrinsically related to the dilatancy phenomenon of the loaded rock sample. Finally, this paper discusses the mechanism of resistivity change of loaded rock sample theoretically.

Fluorine Assessment of Igneous Rocks by Neutron Activation Analysis

The main goal of the current study was to determine the fluorine in the rock samples coal (SARM-18, SARM-19, and SARM-20), opal glass NBS91 and phosphate rock NBS694 using neutron activation analysis. Neutrons energy of 14 MeV used for irradiation was produced by bombardment of a water-cooled titanium tri-tide target with a beam of deuterons accelerated to a potential of 350 KV to develop a neutron flux (108 n⋅cm-2⋅s-1) on the sample at the neutron generator in the ECN (Netherlands Energy Research Foundation) Petten. This new approach contributes to the existing knowledge of fluorine measurement by the coincidence channels investigation of the positron energy with respect to decay time for each radionuclide element. The present study was designed to determine the fluorine by fast neutron through the reaction of F19 (n, 2n) F18. Interference was treated by irradiating the standard of these elements and reasonable selection of the decay time between the end of irradiation and beginning of counting time. The results of this method indicate that the concentration of fluorine is agreed fairly with literatures.

Study of native oil-bearing rocks of the Cuban basin by high resolution NMR spectroscopy

Application of high resolution^(13)C nuclear magnetic resonance(NMR)spectroscopy to characterize Cuba oil and oil-containing rock samples from Cuban basin was demonstrated.The chemical shifts of^(13)C NMR functional groups for later determination the composition of the oil and rock samples were determined.The different contribution of the studied samples in the aliphatic and aromatic areas was determined.Molar fractions of primary,secondary,quaternary,tertiary,aromatic groups,aromaticity factor and the mean length of hydrocarbon chain length of aliphatic hydrocarbons were estimated.Comparative analysis on the quantitative level for all major hydrocarbon components,the aromaticity factor and the mean length of the hydrocarbon chain were carried out.