Compressional waves velocity VP was measured during long-term experiments in a high-pressure vessel (in the range [10–75] MPa for confining and pore pressures). Experiments were carried out on a granite specimen prepared by a controlled heating treatment at 510 °C, which generated thermal cracks.
Data analysis is proposed by using an effective medium approach based on Kachanov's [Appl. Mech. Rev. 45 (1992)304] model. The elastic behaviour of the cracked rock is controlled by the crack density parameter which varies with confining and pore pressures due to crack closure. In order to model the progressive closure of cracks, we assume elliptical cracks with major axis 2c and aspect ratio . By using a conformal mapping technique, we derive the variation of the crack aspect ratio as a function of effective pressure, the effective pressure coefficient η depending on and Poisson's ratio ν0. As a result, we compute the crack density parameter and the elastic moduli of the cracked rock as a function of confining and pore pressures. To take into account the heterogeneity of the rock sample, a peak-like distribution of crack aspect ratios is introduced, which allows us to calculate the acoustic velocity VP for various effective pressures.
Comparison is made between theoretical and experimental values and shows that this simple model captures the essential features of the acoustic velocity variation: an increase of VP when pore pressure is decreased followed by a plateau for a threshold pore pressure. Best consistency between theoretical and experimental velocity values is obtained by introducing a second crack population with a higher mean aspect ratio and an irreversible closure mechanism as effective pressure is cycled. 相似文献
Introduction A great earthquake occurred on Sept. 25 of 1303 (Seventh of Dade, Yuan Dynasty) around Zhaocheng and Hongtong in Shanxi Province. The great earthquake is a very famous one, which is affirmed as the first earthquake with magnitude 8 in Chinese history. The catastrophes took place; meanwhile, huge archives of the disaster were recorded. According to these disaster recordings, the first isoseismal map in China was delineated, which provide us with abundant information of intensi… 相似文献
The response of underground structures subjected to subsurface blast is an important topic in protective engineering. Due to various constraints, pertinent experimental data are extremely scarce. Adequately detailed numerical simulation thus becomes a desirable alternative. However, the physical processes involved in the explosion and blast wave propagation are very complex, hence a realistic and detailed reproduction of the phenomena would require sophisticated numerical models for the loading and material responses. In this paper, a fully coupled numerical model is used to simulate the response of a buried concrete structure under subsurface blast, with emphasis on the comparative performance of 2D and 3D modeling schemes. The explosive charge, soil medium and the RC structure are all incorporated in a single model system. The SPH (smooth particle hydrodynamics) technique is employed to model the explosive charge and the close-in zones where large deformation takes place, while the normal FEM is used to model the remaining soil region and the buried structure. Results show that the 2D model can provide reasonably accurate results concerning the crater size, blast loading on the structure, and the critical response in the front wall. The response in the remaining part of the structure shows noticeable differences between the 2D and 3D models. Based on the simulation results, the characteristics of the in-structure shock environment are also discussed in terms of the shock response spectra. 相似文献
Based on a simplified media model of Gonghe area, the precursor characteristics of Gonghe M7.0 earthquake in 1990 are simulated in this paper by using the constitutive relationship of binary medium (solid and water).
The results show that the simulated state distribution and extension variation of media are identical with the spatial and
temporal distribution of reliable anomalies before Gonghe earthquake. The study also suggests that the development of the
Gonghe earthquake has experienced a series of processes such as elastic deformation of large scale, early nonelastic dilatation,
strain softening and elastic recovery in the neighbour region of Xining, nonelastic dilatation of high dense block near seismic
source and earthquake occurrence. Therefore, it can be concluded that this earthquake development is neither a simple process
for fissures developing and linking up with one another, nor a process of nonelastic volume expansion and water flowing into
medium around seismic source, contrary, it is a complicated medium state changing process, and the style of such changing
depends on geological structure environment of seismic source and its neighbour region. It is considered that different earthquakes
are accompanied by different geological conditions, the spatial and temporal behavior of their precursors are certainly different. 相似文献
The postseismic vertical deformation rates of the 1990 Gonghe MS=7.0 earthquake appears to have decreased exponentially. Based on Okada’s coseismic surface displacement solution caused by
a uniform fault slip in an elastic homogeneous half space, we derived its postseismic surface displacement by using a single-layer
standard linear solid model, and further derived a simplified formula for determining the effective relaxation time and viscosity
of the earth, which is independent of the dislocation parameters of the causative fault. From the postseismic vertical deformation
of the 1990 Gonghe earthquake, we inferred that the effective relaxation time defined by τ=η/μ is 2.6 years, and the effective viscosity η is about 1018 Pa · s.
This work was supported by Chinese Joint Seismological Science Foundation under the grants 92088 and 196098. 相似文献