Summary In order to design roof bolting systems safely and economically, it is essential to understand the flexural behaviour of the immediate roof. Based on the strata sequence, the strata in the immediate roof are divided into three types. The flexural behaviour of the three strata types are investigated in terms of the following effects: roof span, horizontal stress, thickness and Young's modulus of the lowest strata.The suspension reinforcement mechanism is analysed using beam-column theory. The equations for the maximum bending stress, deflection and transferred bolt load for the bolted strata are derived. In the analysis, the bolt load is assumed to be a point load and a horizontal stress is uniformly applied to each stratum. The friction reinforcement mechanism is also investigated. The major function of roof bolting in this case is to create frictional resistance by tensioning the roof bolts so that the individual layers are combined into one single thick layer.A computer program and nomographs are developed for the determination of proper bolting pattern and bolt tension. It is hoped that this development can lead to maximum safety with minimum cost for the design of roof bolting systems in underground coal mines. 相似文献
A method of estimating in-situ hydraulic diffusivity of rock masses by means of well-injection history and frequency of induced seismicity is presented. The method is based on the diffusion of injected fluid from a spherical cavity in a poroelastic half-space and the effective stress theory, as proposed byTerzaghi (1925, 1936) andHubbert andRubey (1959). Application of the method to two different regions, one in western New York and the other in Japan, resulted in estimated diffusivities of the order 103 and 104 cm2/sec, respectively. These values lie within the range of published estimates of in-situ diffusivity by other means, a summary of which is presented in tabular form. The calculated diffusivities suggest that the characteristic time of fluid diffusion is close to 0.1, rather than unity, as is sometimes assumed in the literature. 相似文献
Conclusion The inference is that work produced by an explosive tends to be a result of explosive generated gas pressure rather than the more constant shock energy.The breakage and adiabatic work respond to calculated borehole pressure relationships with a very high correlation. This indicates that the primary mechanism for rock breakage is explosive generated gas pressure. 相似文献
Static and dynamic rock slope stability analyses were performed using a numerical discontinuum modelling technique for a 700-m high rock slope in western Norway. The rock slope has been investigated by the Geological Survey of Norway (NGU), which has been carrying out rock slide studies for the county Møre and Romsdal in western Norway. The purpose of numerical modelling was to estimate the volume of the rock mass that could potentially slide under static and dynamic forces. This estimation was required to assess the run-up heights (tsunami) in a fjord that could potentially be caused by the rockslide. Three cases have been simulated for predicting the behaviour of the rock slope. First, an initial static loading is applied in the numerical model to simulate the prevailing rock mass conditions at the site. Second, saturated and weathered joint conditions are modelled by reducing the residual friction angle along the discontinuities of the rock mass. In doing so, the model simulates the effect of degradation of discontinuities in the rock slope. Third, a dynamic loading, based on peak ground accelerations expected in the area, is applied to simulate dynamic earthquake conditions.
These numerical studies have provided some useful insights into the deformation mechanisms in the rock slope. Both sliding and rotation of blocks start to occur once the residual friction angle along the discontinuities is reduced and when the region is shaken by a strong earthquake. The results indicate that, due to variations in the inclination of discontinuities, the entire slope does not become unstable and that down-slope sliding and rotation of blocks occur mainly on the top layers of the slope. Within the range of parameter values considered for this study, it is unlikely that the whole rock slope can be destabilised. The study provides an illustration of how the geo-mechanical properties of a rock mass can be integrated in a discontinuum rock slope model, which is used for predicting the behaviour of the slope under existing environmental and earthquake conditions. This model has helped not only to better understand the dynamics of the rockslide but also to estimate the potential rock volume that can become unstable when subjected to static and dynamic loads. 相似文献
The Late Permian Emeishan Large Igneous Province (ELIP) is commonly regarded as being located in the western part of the Yangtze craton, SW China, with an asymmetrical shape and a small area. This area, however, is just a maximum estimation because some parts of the ELIP were not recognized or dismembered and destroyed during the Triassic to Cenozoic tectonism. In this paper, the chemostratigraphical data of the Zongza block, the Garze-Litang belt and the Songpan-Garze block suggest that the Late Permian basalts in these areas have remarkable similarities to the ELIP basalts in petrography and geochemistry. Flood basalts in the Sanjiangkou area are composed of the lower part of the low-Ti (LT) tholeiite and the upper part of the high-Ti (HT) tholeiite, which is the same as the flood basalts on the western margin of the Yangtze craton. Flood basalts in the Zongza and Songpan-Garze areas, which are far from the Yangtze craton, consist of HT tholeiite only. This is the same as the flood basalts within the Y 相似文献
The relationship between temporal-spatial evolution of gravity and earthquake activity during 1992–2001 has been analyzed
systematically by integrally adjusting the gravity observation data of the northeastern edge of Qinghai-Xizang (Qingzang)
block. The result shows that the gravity observation data of the northeastern edge of Qingzang block obtained by using the
uniform starting datum can completely reflect the precursory gravity information appearing during the seismogenic process.
In the genesis stage of an earthquake, regional gravity anomaly appears in a large area, resulting in related local gravity
anomaly. The dynamic image of gravity field can clearly reflect the orderly evolution and earthquake activity.
Foundation item: Key Project of China Earthquake Administration during the tenth Five-year Plan (100501-05-05). 相似文献