With the rapid development of transportation in China, the number of tunnels is also increasing. However, tunnels may be affected by fire accidents during operation, and the surrounding rock will be irreparably damaged by high temperature. To investigate the influence of temperature on the physical and mechanical properties of red sandstone, physical properties were determined and the Brazilian splitting test was conducted on red sandstone after thermal treatment from 25 to 600°C. The results show that with increasing temperature, the apparent colour of the red sandstone gradually deepened. The P-wave velocity and Leeb hardness decreased with increasing temperature, and a typical temperature threshold (300°C) was identified. The tensile strength of red sandstone decreased quickly from 25 to 300°C and then decreased slowly from 300 to 600°C. The acoustic emission (AE) signal shows a high degree of consistency with the stress–time curve. As the temperature increased, the AE became more active, and when red sandstone was near failure, the AE signal increased sharply. The failure mode of sandstone mainly consists of a throughgoing main crack and a secondary crack, and the crack width also grows gradually. Moreover, we observe from polarized light microscopy images that the number of fractures in the sandstone also increases as the temperature rises. The variation of physical and mechanical properties of red sandstone is closely related to microstructure. These findings demonstrate that temperature has an obvious weakening effect on the physical and mechanical properties of sandstone, and provide theoretical guidance and significant engineering information for tunnel fire restoration. Thematic collection: This article is part of the Engineering Geology and Hydrogeology of the Anthropocene collection available at: https://www.lyellcollection.org/topic/collections/engineering-geology-and-hydrogeology-of-the-anthropocene
Abstract Based on GPS observation between 1991 and 1999 in Sichuan and Yunnan, we adopt the robust Baye's least squares estimation and multi‐fault dislocation models to analyze the quantitative kinematics models of the main boundaries of the rhombus block in Sichuan and Yunnan. The geodetic inversion suggests that the left‐lateral strike slip rates of the Xianshuihe fault zone and the Anninghe fault zone in Sichuan are about 30mm/a with overthrust faulting at rates of roughly 9 and 11mm/a respectively; in Yunnan, the right‐lateral strike slip rate of the Red River (Honghe) fault zone is 10mm/a with a normal faulting of 16 mm/a; and the left‐lateral strike slip rates of the Chenghai fault zone and the Heqing‐Eryuan fault zone are about 11 and 13 mm/a with normal faulting at rates of about 24 and 16mm/a separately. If all displacements along these faults were accommodated by elastic stress and strain, thus the accumulated seismic energy on each fault would be sufficient to produce a moderate earthquake with Ms ~6 each year. According to above results, the horizontal displacement and strain field caused by the main fault movement were simulated and showed the interaction among boundary faults.
: As an attempt, the Kalman filter was used to study the anomalous variations of ionospheric Total Electron Content (TEC) before and after Wenchuan Ms8.0 earthquake, these TEC data were calculated from the GPS data observed by the Crustal Movement Observation Network of China. The result indicates that this method is reasonable and reliable in detecting TEC anomalies associated with large earthquakes.
Abstract In many cases, 1D inversion is still an important step in transient electromagnetic data processing. Potential issues may arise in the calculation of apparent resistivity using induced electromotive force (EMF) due to overshoot and the presence of multi-valued functions. Obtaining reliable and consistent inversion results using a uniform half-space as the initial model is challenging, especially when aiming for efficient inversion. Focusing on these problems, we use the land-based transient electromagnetic (TEM) sounding data, which was acquired by using a large fixed-loop transmitter, and adopt a quasi-2D inversion scheme to generate improved images of the subsurface resistivity structure. First, we have considered directly using magnetic field data or converting induced EMF into magnetic field, and then calculating the apparent resistivity over the whole zone. Next, a resistivity profile that varies with depth is obtained through fast smoke ring imaging. This profile serves as the initial model for the subsequent optimal inversion. The inversion scheme uses a nonlinear least-squares method, incorporating lateral and vertical constraints, to produce a quasi-2D subsurface image. The potentiality of the proposed methodology has been exemplified through the interpretation of synthetic data derived from a 3D intricate resistivity model, as well as field data obtained from a TEM survey conducted in a coalmine field. In both cases, the inversion process yields quasi-2D subsurface images that exhibit a reasonable level of accuracy. These images appear to be less moulded by 3D effects and demonstrate a satisfactory level of agreement with the known target area.
Abstract Water and mud inrush caused by fault is a geological disaster characterized by high frequency and huge destructiveness. It is important to study the evolutionary laws of water inrush in fault fracture zones with various filling types. The effect of filling gradation on the mesoscopic structure and seepage characteristics of fault fracture zones was investigated. The law of water inrush evolution and water inrush characteristics of fault-fractured zones with different filling gradations and strong zoning filling characteristics were studied. The results showed that for the larger Talbot gradation indices, the mass of water inrush and the fractal dimension of the lost particles were larger, the peak water pressure and the mass of the lost particles were smaller, and the duration of the initial impermeability stage was shorter for the same loading water pressure. For the fault fracture zones with strong zoning filling characteristics, the peak water pressure, the mass of water surges, and the mass of lost particles were larger, the fractal dimension of the lost particles was smaller, and the duration of the initial impermeability stage was shorter for the fracture zones with larger filling gradation were used as the initial impermeability zones. Furthermore, with larger filling gradation, we observed a greater proportion of large pores, a larger equivalent throat radius, higher pore connectivity, and coordination numbers. Filling gradation and confining pressure greatly affected the permeability of the fault. The permeability decreased by 98.71% when the Talbot gradation indices decreased from 1.25 to 0.6, and decreased by 58.4% when the confining pressure increased from 5 MPa to 15 MPa.
'/%3e%3cuse xlink:href='%23a' transform='rotate(23.036 .093 25.536)'/%3e%3cuse xlink:href='%23a' transform='rotate(45.87 1.273 16.18)'/%3e%3cuse xlink:href='%23a' transform='rotate(69.945 .996 12.078)'/%3e%3cuse xlink:href='%23a' transform='rotate(20.66 -19.689 31.932)'/%3e%3c/svg%3e)