大理石板中心受压至断裂时P波速度变化的实验研究c
AN EXPERIMENTAL STUDY OF THE VARIATION OF P-WAVE VELOCITY IN A MARBLE SLAB LOADED TO FAILURE AT THE CENTER
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摘要: 本文叙述无水注入情况下,中心受压的大理石板(60060020毫米)破裂前,P波走时变化的实验结果。 路径穿过未来裂缝、靠近受压中心时,走吋上升一回降;不靠近受压中心则走时只上升。路径近于平行且靠近未来裂缝,走时一般不变。路径不穿过未来裂缝和受压中心,发射点附近形变小时,走时不变;发射点附近形变大时,走时一般下降。路径穿过受压中心吋,有些走时先上升后恢复再下降。有些则下降后回升。 这说明在岩石破裂前,破裂孕育区附近同时存在P波速正负异常区和正常区。 同时还观测到,P波速度负异常区随中心压力增加逐步扩大。 由裂缝一侧波源所得的正常区正好是由另一侧波源所得的负异常区。Abstract: The P-wave travel time variation in a dry marble slab of size 60060020 mm loaded at its center to failure has been experimentally studied, the results of which are described in this paper.For the wave paths crossing the forthcoming fracture and the portion nearby the center of loading, the travel time increases first and then decreases as the loading increases, while for the portion farther away from the center, the travel time merely increases. For those wave paths nearby and parallel to the fracture, the travel time remains unchanged. However, for the wave paths not crossing the fracture and passing the center of loading, the travel time remains unchanged if the deformation is small in the vicinity of the wave emmitting source but generally decreases if the deformation there is large. For those paths passing through the center of loading, some of the travel times increase first and then decrease while others decrease first and then increase. These results may indicate that before fracturing there exist positive and negative anomalous and normal regions of P-wave velocity around the fracture during the process of its development.Meanwhile, it is also observed that the regions of negative anomalous P-wave velocity are enlarged by steps as the central loading is increased. The regions of normal P-wave velocity as observed from the wave emmitting source located on one side of the fracture is usually the same region of negative anomalous P-wave velocity as obtained from a wave emmitting source located on the other side.