Poor Geological Conditions Research Articles

Guidelines for Selection of Appropriate Seismic Countermeasures for Existing Mountain Tunnels in Poor Geological Conditions

In this study, the authors performed model tests and numerical analyses to clarify the quantitative effect of seismic countermeasures for existing mountain tunnels in poor geological conditions. It has become apparent that inner reinforcement can control the initiation of cracks and prevent spalling; backfill grouting can improve deformation performance of the tunnel and control compressive failure in arch crowns; and rock bolts can control heaving of the roadbed. Even though there are many restrictions associated with construction of inverts, it has become apparent that inverts are a fundamental countermeasure to control tunnel deformation and heaving of the roadbed.

The Mechanism behind Seismic Damage to Railway Mountain Tunnels and Assessment of their Aseismic Performance

In this study, the authors performed case studies and model experiments to investigate the mechanism behind seismic damage to mountain tunnels and their aseismic performance, and the conditions under which such damage tended to be severe were clarified. Model experiments were performed with focus on damage to shallow tunnels or those in ground characterized by poor geological conditions, and the degree and extent of disasters caused by mountain seismicity were successfully reproduced. The experiments clarified the damage mechanism and seismic performance of tunnels in question. It was concluded that sound tunnels and those with inverts are less susceptible to seismic damage, and it was also confirmed that such damage tends to be greater when tunnels have voids above the lining and a lack of thickness, or when local displacement acts on them.

A catastrophic rockslide-debris flow in Wulong, Chongqing, China in 2009: background, characterization, and causes

On June 5, 2009, a catastrophic rockslide-debris flow occurred at the crest of the Jiweishan Mountain in Wulong, Chongqing, China. Approximately five million cubic meters of limestone blocks slid along a weak interlayer of bituminous and carbonaceous shale. The source mass descended from the upper part of the slope rapidly, crossing a 200-m wide and 50-m deep creek in front of it. Blocked by the opposite steep creek wall, the sliding mass changed its direction and traveled a further 2.2 km along the creek in debris-flow mode, finally forming a large accumulation zone with an average depth of 30 m. This is one of the most catastrophic rockslide events in recent years in China. It buried 12 houses and the entrance of an iron mining tunnel where some 27 miners were working inside. Ten people died, 64 missing, and eight wounded. Immediately after this disaster happened, the government organized an expert team to assist the rescue work. As one of the geological experts, the author did a lot of field investigations and collected first-hand information. Multi-methods including the remote sensing, 3D laser scanning, geophysical exploration, and numerical modeling were used for analyzing the characteristics and the triggering mechanism of the Wulong rockslide. The preliminary investigation results reveal that this rockslide with poor geological conditions was mainly induced by the gravitation and the karst effect and also affected by the previous mining activities. The research in this paper is meaningful and useful for further research on such kind of rockslides that are geologically similar to the Wulong rockslide.

Experimental Study of Marine Magnetotelluric in Southern Huanghai

AbstractIn the southern Huanghai (Yellow Sea), seismic exploration for oil and gas in pre‐Tertiary strata encounters some difficulties, such as poor geological conditions at depth, screened seismic waves, and serious attenuation of seismic energy, so that the reflective signals from the Mesozoic and Paleozoic systems cannot be recognized. To solve this issue by other approach, an experiment of seafloor magnetotelluric (MT) sounding was carried out in this region in May 2006. This work has deployed 3 measurement sites on the Wulian slope and Jiaozhou sag in the basin and obtained good data. In this article, we present the difference of data processing between the marine MT and routine MT soundings, and analyze the influence of marine electromagnetic noise on the MT observation on seafloor. We propose correction methods for the horizontal attitude and orientation of the instrument as well as removal of marine noise. Using these and other regular methods, we have performed data processing and inversion, and a comprehensive analysis of geology and physical properties. The result shows that there are residual Paleozoic strata below the seafloor in the southern Huanghai. This is of great significance for prospect assessment of oil and gas in the pre‐Tertiary system in this region. The experiment also demonstrates that the marine MT technology can play an important role in exploration of relict basins of Paleozoic time.