Papers by Keyword: Brittle Rock

Abstract: Due to the brittle rock deformation is not obvious, and the destruction process has the features of sudden and concealment, it is often neglected in the field during construction. In this paper, Brittle rock was selected as the research object. Using the vault subsidence as monitoring parameters, the excavation process was simulated in single line tunnel by the finite element analysis tool of ANSYS, we obtain the maximum displacement of brittle rock and stress variation with time. Then the subsidence effect of different buried condition were analyzed, to determine the stability period of IV Brittle surrounding rock. The research results can be used to guide the development of the monitoring standard, in underground engineering construction of the brittle rock.

Abstract: Due to the brittle rock deformation is not obvious, and the destruction process has the features of sudden and concealment, it is often neglected in the field during construction. In this paper, Brittle rock was selected as the research object. Using the vault subsidence as monitoring parameters, the excavation process was simulated in single line tunnel by the finite element analysis tool of ANSYS, we obtain the maximum displacement of brittle rock and stress variation with time. Then the subsidence effect of different buried were analyzed, to determine the stability period of III Brittle surrounding rock. The research results can be used to guide the development of the monitoring standard, in underground engineering construction of the brittle rock.

Abstract: Energy transformation in rock failure process is a complicate process, especially in the high geostress conditions. First from the point of energy, analysis and study on the rock deformation and failure process under uniaxial compression and triaxial compression condition. Based on the test results, the deformation failure characteristics and its energy in triaxial compression are analyzed. Reveal the energy dissipation and energy release characteristics in the process, and found the internal causes is stored elastic in rock mass unit can release suddenly and cause rock damaged. Especially in the high geo-stress condition, the compressed engineering rock mass are often faced with the risk of unloading damage. After add anchor, the mechanics performance of specimen after peak period is significantly improved, and can absorb more of the release of strain energy, which is helpful for maintaining the overall stability of surrounding rock.

Abstract: During the excavation by TBM of the Aicha Exploratory Tunnel along the Brenner Base Tunnel in Italy, in hard brittle granitic rocks, an instability phenomenon occurred at chainage 6+151. The left-hand sidewall lining partially collapsed for a length of approximately 60m. This led to a stoppage of the TBM lasting about 4 months. With the reconstruction of the geological model, a sub-vertical fault, not forecast at the design stage, was identified parallel to the direction of the excavation. In this paper, a three-dimensional (3D) model, which simulates the complex interaction between the rock mass, the TBM and its system components, and the tunnel support, is presented. The model accounts for the main machine components: shields, cutterhead, grippers, pea gravel and lining. The brittle failure of a thin granite diaphragm between the fault zone and the tunnel wall is reproduced and the results are discussed in terms of failure zone and horizontal displacements.

Abstract: The failure of rock materials in compression test suffers three characteristic stages: crack initiation, crack damage threshold, and macro-failure. There are some methods which can be adopt to identity the characteristic strengths in uniaxil or triaxial compression such as crack strain identifying method, AE activity and longitudinal wave velocity monitoring methods. In this paper, an creative experiment of recording stress-strain data, AE spectrums, and velocity of longitudinal wave is proposed and put into practice. Test results show that the mean initiation strength and damage strength by ratio of UCS are between 0.38 to 0.52 and 0.82 to 0.86 respectively with AE and longitudinal wave velocity methods synthetically. The AE monitoring method and the lateral P-wave or the axial S-wave test is an effective indicative of identifying the damage threshold when subject an axial compression failure.

Abstract: The stress-strain of triaxial rheological test for rock can be divided into three stages: initial attenuation rheological stabilization rheoligical and speedup rheological stages, the damage is rapid increased in the speedup stage. Damage mechanics is introduced into the Nishihara rheological model, a new rheological constitutive model is established which is combined with the concept of effective stress. The mechanical parameters are recognized by the experimental test data of greenschist. Computing result shows that, the presented model can described the mechanical characteristics in different rheological stage very well, and the error between simulated result and test data is small.

Abstract: In present，a series of uniaxial compressive experiments on sandstone samples have been conducted in the laboratory by using jointed devices of triaxial loading equipment and medical SOMTOM-plus CT scanner. Based on CT value, expression of density damage variables and density damage increments (DDI) of brittle rock and the method to determine the rock initial damage variables have been worked out. From real-time CT observations of sandstone sample under uniaxial compression condition and the analysis on CT digital images and the relation curve between sandstone density damage increment (DDI)and stress, the evolution process of fracturing in brittle rock sample can be divided into five stages, i.e. initial densification stage, crack occurrence-propagation, crack merging-bifurcation, crack rebifurcation-propagation, and crack cut-through-massive failure stage. Crack occurrence-propagation is a local phenomenon and the whole rock is still in the densification stage. Therefore, the rock failure process under compression is mainly including three stages, namely initial damage densification, local dilatation-bulk dilatation, and massive failure. The use of CT images and relation curve between density damage increment and stress in analyzing the meso-damage evolution processes of brittle rock sample is an important and effective method. As an important mechanics index in rock meso-mechanics, the density damage increment can be used to analyze the quantitative fracturing process in brittle rock under compressive condition, as well as being an important factor in a rock fracturing process model to be constructed.

Abstract: The dynamic impact loading has the destructive effect to the surrounding rock mass. Rock specimen such as rock plate was found to become invalid under dynamic impact loading. This paper presents brittle damage evolution law for dynamic impact damage of brittle rock based on low velocity (10m/s~40m/s) impact test, when a source of impact loading is applied to a rock plate specimen, damage cracks are developed from the source to the boundaries. This paper is concerned with the description and explanation of this phenomenon. The test results show that the cracks propagation length and break area are not arbitrary, but are influenced by the angle of dynamic impact loading. According to the test results, the study found that the scope of impact resistance optimization angle is about 30°~45°, and the cuspidal point of impact velocity is about 30m/s~35m/s; The crack length and the break area increase with the increase of the impact loading; When the break area decreases abruptly, the crack length increases suddenly, which shows that there was an obvious incubation period of crack forming, at first some pits appearing on the verge of the rock plate and the propagation rate of crack length and break area decreasing with the impact velocity increasing.

Abstract: This paper studies on the characteristics of strength and deformation of brittle rock under different compression condition by experimental tests. A lot of experimental tests for the Xiangjiaba sandstone are carried out under different compression condition, including uniaxial compression, triaxial compression, uniaxial monocyclic compression and uniaxial loading and unloading. Base on the experimental test results of the Xiangjiaba sandstone, the strength and deformation of brittle rock are analyzed, and some comparative analysis for the mechanics characteristics of brittle rock are carried out. The compute results show that, the peak strength of brittle rock is increased with the confining stress, and close to a linear relationship. Its also show that, the peak strength is not increased under the monocyclic compression, neither for the loading and unloading condition.

Abstract: A complete stress-strain experiment curve, gained through exerting low confining pressure on brittle rock, reflects the deformation and destruction process of rock under different confining pressure, and reveals that after the destruction of rock, not only slip deformation but also re-destruction process will take place, which would possibly lead to further reduction of the mechanical properties of the rock mass. Through the analysis of the relation between complex failure modes, load carrying capacity after rock destruction and the volumetric strain, the paper gives us a further explanation of the complex destructive process of rock. The basis for the rock’s load-carrying capacity after destruction is an effective restraint stress, which shows that effective supporting in underground engineering is the key factor for providing the cracked surrounding rock with load-carrying capacity and guaranteeing the stability of the structure.