Most pingos in the permafrost region of the high northern Tibetan Plateau form along active fault zones and many change position annually along the zones and thus appear to migrate. The fault zones conduct geothermal heat, which thins permafrost, and control cool to hot springs in the region. They maintain ground-water circulation through broken rock in an open system to supply water for pingo growth during the winter in overlying fluvial and lacustrian deposits. Springs remain after the pingos thaw in the summer. Fault movement, earthquakes and man's activities cause the water pathways supplying pingos to shift and consequently the pingos migrate.
The hazard posed to the new Golmud–Lhasa railway across the plateau by migrating pingos is restricted to active fault zones, but is serious, as these zones are common and generate large earthquakes. Pingos have damaged the highway and the oil pipeline adjacent to the railway since 2001. One caused tilting and breaking of a bridge pier and destroyed a highway bridge across the Chumaerhe fault. Another has already caused minor damage to a new railway bridge. Furthermore, the construction of a bridge pier in the North Wuli fault zone in July–August 2003 created a conduit for a new spring, which created a pingo during the following winter. Measures taken to drain the ground-water via a tunnel worked well and prevented damage before the railway tracks were laid. However, pier vibrations from subsequent train motion disrupted the drain and led to new springs, which may induce further pingo growth beneath the bridge.
The migrating pingos result from active fault movement promoting artesian ground-water circulation and changing water pathways under the seasonal temperature variations in the permafrost region. They pose a serious hazard to railway construction, which, in turn can further disturb the ground-water conduits and affect pingo migration. 相似文献
The Hope Slide, which occurred on January 9, 1965, involved an estimated 47-Mm3 of meta-volcanics and intrusive rocks. Previous workers reported the presence of tectonic structures (faults and shear zones) along the failure surface at the Hope Slide. These tectonic features were investigated in detail to assess their effects on rock-mass quality and the related implications for slope stability. This paper integrates basic field and laboratory concepts from structural and engineering geology. Subdividing the failure area into structural domains allowed distinct discontinuity sets to be associated with specific tectonic structures. The Geological Strength Index (GSI) was used to estimate the rock-mass damage related to the tectonic structures. Low GSI values were seen to outline tectonic damage zones. Point-load tests were used to characterise the compressive strength of rocks adjacent to the tectonic structures. Strength anisotropy, tentatively attributed to damage caused by a large shear zone, was observed in greenstone samples. Seepage zones along the failure surface were observed preferentially along shallow discontinuities that dipped downslope and in rock masses of good quality (GSI > 40). An alternative morphology of the slope failure is proposed by distinguishing between the extent of the surficial damage due to the rock-slope failure and the zone of failed material (depletion zone). For the first time, a kinematic mechanism for the Hope Slide is proposed, based on a preliminary 3-dimensional block model. A pre-1965 DEM was produced from estimates of material lost and gained as reported by previous workers. The pre-1965 DEM revealed that the tectonic structures recognised during fieldwork bounded the material that failed in the 1965 event. 相似文献
