Understanding the physical vulnerability of buildings and infrastructure to natural hazards is an essential step in risk assessment for large cities. We have interpreted high spatial resolution images, conducted field surveys, and utilized numerical simulations, in order to assess vulnerability across Arequipa, south Peru, close to the active El Misti volcano. The emphasis of this study was on flash floods and volcanic or non-volcanic hyperconcentrated flows, which recur on average every 3.5 years across the city. We utilized a geographic information system to embed vulnerability and hazard maps as a step to calculate risk for buildings and bridges along the Río Chili valley and two tributaries. A survey of ~1,000 buildings from 46 city blocks, different in age, construction materials, and land usage, provided architectural and structural characteristics. A similar survey of twenty bridges across the three valleys was based on structural, hydraulic, and strategic parameters. Interpretation of high spatial resolution (HSR) satellite images, which allows for quick identification of approximately 69 % of the structural building types, effectively supplemented field data collection. Mapping vulnerability has led us to pinpoint strategic areas in case of future destructive floods or flows. Calculated vulnerability is high if we examine structural criteria alone. We further consider physical setting with the most vulnerable city blocks located on the lowermost terraces, perpendicular or oblique to the flow path. Statistical analysis conducted on 3,015 city blocks, considering nine criteria identified from HSR images, indicated that building-type heterogeneity and the shape of the city blocks, along with building and street network density, are the most discriminant parameters for assessing vulnerability. 相似文献
A series of undrained monotonic triaxial compression tests were performed on natural, medium-dense (relative density (RD) = 50%) Chlef sand containing 0.5% of non-plastic fines, under different confining pressures of 50 kPa, 100 kPa, and 200 kPa. This article focuses on distinctive states of the monotonic undrained response of sands, namely the critical state, the phase transformation state, the quasi-steady state, and the state of undrained instability (onset of flow liquefaction). Specimens were prepared using dry funnel pluviation and wet deposition to investigate the effect of the initial sand fabric on these states. The present data suggest that the initial fabric of the sand appears to have a significant effect on the undrained behavior in the early stages of shearing, with its influence vanishing at large strains. Wet deposition specimens demonstrate considerably larger undrained instability state strength than their dry funnel pluviation counterparts, and a unique critical state locus is reached by both dry funnel pluviation and wet deposition. 相似文献
Experimental observations have shown that the resilient modulus Mr of fine/coarse soil mixture can be significantly affected by the coarse grain content fv, deviator stress σd and suction \(\psi\). In this study, a constitutive model incorporating the soil–water retention curve (SWRC) was proposed to describe the effects of \(\psi\) and \(\sigma_{{\text{d}}}\) on Mr. This model was then extended to the effect of fv. The proposed model implied the resilient modulus at saturation condition (Mr-sat), the resilient modulus at optimum moisture content (OMC) condition (Mr-opt), the suction at OMC (\(\psi_{{{\text{opt}}}}\)) and the parameters related to SWRC. The model was validated using experimental data from five studies reported in the literature. Comparisons with three representative existing models showed that the proposed model was capable to well describe the suction-dependent effect of deviator stress in the full range of suction, while the existing models gave satisfactory simulation results only in the low suction range. Indeed, experimental studies revealed that there was a threshold suction \(\psi_{{{\text{th}}}}\), and with increasing \(\sigma_{{\text{d}}}\), the Mr decreased when \(\psi < \psi_{{{\text{th}}}}\), but increased when \(\psi > \psi_{{{\text{th}}}}\). When \(\psi < \psi_{{{\text{th}}}}\), all models gave good simulations. On the contrary, when \(\psi > \psi_{{{\text{th}}}}\), only the proposed model gave good simulations, in particular when \(\psi_{{{\text{th}}}} > \psi_{{{\text{opt}}}}\). This showed the performance of the proposed model in describing the variation in resilient modulus of unsaturated fine/coarse soil mixtures with changes in coarse grain content, deviator stress and suction.
