Thermal damage and energy evolution characteristics in process of impact failure of sandstone after high temperature treatment were studied by split Hopkinson pressure bar (SHPB) system. The ultrasonic P-wave velocity, density, porosity, peak stress, / 0 , thermal damage, fracture, and energy evolution characteristics of sandstone with temperature during the experimental process were explored. Results show that, with the increase of temperature, the ultrasonic P-wave velocity and density decrease, while the porosity increases. It is found that the peak stress and / 0 decrease with the increase of temperature, and the decreasing trend is fitted with the simple cubic equation. Above 600 ∘ C, dynamic peak stress and / 0 decrease rapidly. The thermal damage of rock increases with the increase of temperature, which is in accordance with the logistic curve model. The thresholds of damage strain energy release rate are 200 ∘ C and 800 ∘ C in this research. Its total input strain energy decreases with the increase of processing temperature and decreases sharply when the temperature is over 600 ∘ C. The variation of total input strain energy has small change at the range from 400 ∘ C to 600 ∘ C.

No abstract

No abstract

More and more attention has been paid to the supporting problem of deep soft rock roadway floor with long-term water immersion in recent years. However, the existing soft rock roadway support technology rarely takes into account the influence of the immersion softening phenomenon of the roadway floor and the self-supporting structure characteristics of the surrounding rock on the stability of the surrounding rock at the same time, and the influence of the creep characteristics of rock on the deformation zone of the surrounding rock requires further research on the nature and division of the self-supporting structure of the surrounding rock. In response to the issues mentioned, based on the loading and unloading properties of the surrounding rock of the soft rock roadway, a new concept of the internal and external self-bearing structure was proposed. The fact of water-immersed mudstone softening in the soft rock roadway floor was revealed through the field practice, and the shape of the internal and external bearing structure was determined based on the in situ monitoring results. Then, the instability mechanism of the internal and external self-bearing structure of the surrounding rock was analyzed, the position of the critical control point was calculated, and the key control technology based on the method of controlling floor heave by using double-row anchor cables to control the deformation of the roadway sides was put forward. Finally, the field industrial test showed that this support technology can effectively control the deformation and failure of soft rock roadway in the case of water immersion on the floor. This work can provide a technical reference for similar roadway support designs.

No abstract

No abstract

Abstract-The intention of this paper is to reveal the mechanical properties of steel fiber reinforced concrete (SFRC) at different volume fractions of steel fiber and demonstrate that it can be applied as support in underground coal-mine tunnels. With the similar simulation tests and FLAC finite-element numerical simulation, semicircular concrete specimens at the steel-fiber volume fractions of 0, 0.5% and 1.0 % were investigated. In the similar simulation test, a few of strain gages were distributed in the semicircular-arch specimens to analyze specimens' breaking process, the trend of crack development and the relation of stress versus strain at the measured points at different volume fractions of steel fiber; With the FLAC finite-element numerical simulation, the maximal principal stress distribution of the concrete specimens at three volume fractions of steel fiber was simulated. The results from the numerical simulation and from the simulation test were consistent. Both shed light on the rules that specimen's load-bearing capacity increases with the increase in steel fiber's volume fraction and that its neutral axis moves up with increase of the load. The result will play an important role in cutting down cost in support work, making support work more effective and efficient and developing a sound theory for support design in the coal mines.

By using the finite element software ABAQUS, the paper carries out numerical simulation analysis on influence of new coal lane tunneling along the groove disturbing the original high pumping Lane in a deep mine 1112 working face in Huainan. This article analyzes two tunnels in different distance with the new roadway excavation cause position change as well as an increase in the maximum stress and displacement of the original high pumping Lane in deep mine. In this essay, we explore the influence of new roadway excavation to original roadway stability, and study the deep adjacent tunnel excavation disturbance effect to the original roadway stress and strain change. The results show that: the reasonable distance between shallow tunnels is not applicable to deep condition. Meanwhile, the roadway excavation disturbance effect between adjacent tunnels is significantly in deep mine. In addition, the original roadway need to add new support measures on the basis of the existing supporting structure to ensure its normal use.