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991.
P. V. Hareesh Kumar A. Raghunadha Rao K. Anilkumar M. Padmanabham K. G. Radhakrishnan 《Natural Hazards》2011,57(3):643-656
Analysis of the time series data collected from a stationary location in the continental shelf of the southeastern Arabian
Sea during different month indicated prominent internal wave (IW) activity. Time evolution of temperature, resolved using
Morlet wavelet technique, revealed that maximum energy was concentrated in the diurnal band at the density interface, whereas
within the interior of thermocline, the dominant energy concentration shifted to semi-diurnal band. Both these harmonics have
maximum amplitude (>15 m) during the pre-monsoon and monsoon season when the water column was highly stratified (>0.05 kg/m4), but they were not discernable in the temperature record when the stratification was weak (i.e., especially during winter).
An acoustic propagation model based on ray theory, Bellhop (http:/oalib.hlsresearch.com/modes/acoustictoolbox/at.zip) was
utilized to compute the transmission loss (TL) associated with the passage of low-frequency IWs. The TL was computed using
the model considering (1) range-dependent and range-independent environmental scenario and (2) for different source and receiver
depth configurations. Intermittent fading of acoustic signals was observed in the presence of IW. It was also observed that
fading of signals very much depends on the source–receiver configuration. 相似文献
992.
In the context of natural hazard-related risk analyses, different concepts and comprehensions of the term risk exist. These differences are mostly subjected to the perceptions and historical backgrounds of the different scientific disciplines and results in a multitude of methodological concepts to analyse risk. The target-oriented selection and application of these concepts depend on the specific research object which is generally closely connected to the stakeholders’ interests. An obvious characteristic of the different conceptualizations is the immanent various comprehensions of vulnerability. As risk analyses from a natural scientific-technical background aim at estimating potential expositions and consequences of natural hazard events, the results can provide an appropriate decision basis for risk management strategies. Thereby, beside the preferably addressed gravitative and hydrological hazards, seismo-tectonical and especially meteorological hazard processes have been rarely considered within multi-risk analyses in an Alpine context. Hence, their comparative grading in an overall context of natural hazard risks is not quantitatively possible. The present paper focuses on both (1) the different concepts of the natural hazard risk and especially their specific expressions in the context of vulnerability and (2) the exemplary application of the natural scientific-technical risk concepts to analyse potential extreme storm losses in the Austrian Province of Tyrol. Following the corresponding general risk concept, the case study first defines the hazard potential, second estimates the exposures and damage potentials on the basis of an existing database of the stock of elements and values, and third analyses the so-called Extreme Scenario Losses (ESL) considering the structural vulnerability of the potentially affected elements at risk. Thereby, it can be shown that extreme storm events can induce losses solely to buildings and inventory in the range of EUR 100–150 million in Tyrol. However, in an overall context of potential extreme natural hazard events, the storm risk can be classified with a moderate risk potential in this province. 相似文献
993.
On November 4th 2007, along the Grijalva River in the state of Chiapas, Mexico, has occurred one of the largest landslides
ever known. This landslide, known as Juan del Grijalva, destroyed the town of the same name, killing 20 people, and moved 55 million cubic meters of rock and debris down slope
to completely block the Grijalva River. In order to understand the characteristics and factors that triggered the Juan del
Grijalva landslide, geologic studies were conducted at the site. The results indicate that the landslide was composed of a
lithologic sequence of thin-bedded shales and thin to medium-thick-bedded sandstones. This was faulted into several blocks
dipping in the same sense as the mass movement. The main triggering factor was the increment of the pore pressure into the
lithologic unit due to water saturation after 5 days of heavy rain before the incident. According to records from the last
century, the Juan del Grijalva mass movement represents one of the largest mass movements recorded all over the world. The
risk conditions of the area after the landslide lead to the rapid construction of an artificial channel to drain the accumulating
mass of water upstream and therefore prevent a future catastrophic inundation down stream. 相似文献
994.
Hydraulic Conductivity Tests for Evaluating Compatibility of Lateritic Soil—Fly Ash Mixtures with Municipal Waste Leachate 总被引:1,自引:1,他引:0
Agapitus Ahamefule Amadi 《Geotechnical and Geological Engineering》2011,29(3):259-265
Long term competent performance of liner systems is a critical issue in the design and construction of waste repositories
due to adverse interactions associated with leachate generated by wastes. This study was conducted to verify the efficacy
of fly ash stabilization in enhancing compatibility between lateritic soil and municipal waste leachate. Applications investigated
include soil mixtures containing 0, 5, 10, 15, and 20% fly ash compacted at approximately 2% wet of optimum moisture content
with modified proctor energy. Baseline hydraulic conductivity was first established at every level of fly ash content by permeating
soil mixtures with tap water before permeation with leachate in a compaction mould permeameter using the falling head test
method. Results show that the trend in hydraulic conductivity of specimen containing 0% fly ash was characterized by a gradual
but erratic decrease which may suggests partial entry of the leachate cations into the double layer. Conversely, specimens
containing fly ash showed a general trend consisting of an initial drop in k (up to an order of magnitude) that was followed
by slight decrease sustained until k stabilized and later terminated. Above 10% fly ash content, the relatively high values
of k observed was not connected with the reactivity of the soil mixtures with leachate, rather it may be attributed to excessive
fly ash content that altered their textural and hydraulic properties. The result of this study is potentially significant
in the assessment of fly ash as a compatibility enhancing agent which can be admixed in barrier materials that are susceptible
to adverse reactions with the liquid to be contained. 相似文献
995.
Myint Win Bo Victor Choa Kai Sin Wong Arul Arulrajah 《Geotechnical and Geological Engineering》2011,29(1):65-74
Ultra-soft soil with high moisture content will experience large strain deformation under one-dimensional compression with
little or no gain in effective stress. Such deformation behaviour does not comply with Terzaghi’s effective stress gain theory.
The e-log sv¢ \sigma_{v}^{\prime } relationship of ultra-soft soil is non-linear with large compression index in the first order of log cycle. This paper proposes
three compression indices (Cc1* C_{c1}^{*} , Cc2* C_{c2}^{*} and Cc3* C_{c3}^{*} ) for stresses covering three log cycles. Good prediction of settlement magnitude is possible with these newly proposed compression
parameters for ultra-soft soil. In addition, implicit finite difference model applying the large strain theory is also proposed
and validated with results from laboratory measurements. The time factor curves for ultra-soft soil with large strain compression
are also proposed and validated. 相似文献
996.
The cable shovel is widely used in surface mining. High operating and ownership costs necessitate efficient use of the cable
shovel. Operator practices have long been suspected to contribute towards the inefficient use of the shovel. Crowd arm and
hoist rope speeds are key measures of operator practices. The objective of this work is to find the crowd arm and hoist rope
speeds for optimal shovel performance for given initial conditions and material properties. Shovel kinematics and dynamic modeling, using shovel
geometry and the simultaneous constraint method, respectively, have been employed to build models of the excavation process.
Dynamic models of the shovel payload and the material cutting resistance have also been developed using geometric simulation
and passive soil pressures techniques, respectively. These models are solved numerically by combining Runge–Kutta and Gaussian
elimination algorithms to compute the work done and the resistive forces during shovel excavation. The algorithms have been
combined into a shovel simulator. The simulator has been used to simulate the P&H 2100BL shovel. The simulation results indicate
that input energy and digging time increase with increasing crowd arm and decreasing hoist rope speeds. The input energy per
unit loading rate is proposed as an appropriate measure of shovel performance. High energy per unit loading rate occurs for
high crowd speeds and low hoist rope speeds. For the simulated conditions and crowd arm and hoist rope speeds ranging from
0.25 to 0.5 ms−1 and 0.5 to 0.7 ms−1, respectively, the optimal crowd arm and hoist rope speeds were found to be 0.25 ms−1 and 0.7 ms−1, respectively, and the objective function value was 0.21 KJs/kg. This work establishes, theoretically, the fact that operator
practices have an effect on shovel performance and is useful in establishing optimum practices. The results are the initial
steps towards full automation of the excavation process. 相似文献
997.
By using pseudo-dynamic approach, a method has been proposed in this paper to compute the seismic passive earth pressure behind
a rigid cantilever retaining wall with bilinear backface. The wall has sudden change in inclination along its depth and a
planar failure surface has been considered behind the retaining wall. The effects of a wide range of parameters like soil
friction angle, wall inclination, wall friction angle, amplification of vibration, variation of shear modulus and horizontal
and vertical seismic accelerations on the passive earth pressure have been explored in the present study. For the sake of
illustration, the computations have been exclusively carried out for constant wall friction through out the depth. Unlike
the Mononobe-Okabe method, which incorporates pseudo-static analysis, the present analysis predicts a nonlinear variation
of passive earth pressure along the wall. 相似文献
998.
In dam safety assessment, it is customary to focus on stability analysis, and the safety factor is regarded as an assessment
index that cannot correctly reflect the effect of multi-factors and variable uncertainty. The factors that induce dam breaks
are complex and uncertain; however, three primary ones can be identified: hydrological factors, seepage and bank slope instability.
In this paper, the risk probability and the dam break threshold value for each factor individually, as well as coupled factors,
are studied. The threshold value is acquired using the relationship formula between risk probability and dam type. The Dongwushi
reservoir located in the Hebei province of China is taken as a case study. The results show that the dam break threshold values
for hydrological factors, seepage and bank slope instability are 2.53, 2.02 and 2.69, respectively. The integrated dam break
threshold value for the coupled factors is 1.25, which indicates that the dam is under serious stress according to the established
risk assessment standard. The safety factor is calculated as 1.15 using the Bishop method, which indicates that the dam is
under serious stress. The results obtained by the proposed method are consistent with those of the Bishop method. Finally,
the proposed theory and method are introduced into a dam safety evaluation system (DSES) for convenient and efficient dam
safety management. 相似文献
999.
Quantitative multi-risk analysis for natural hazards: a framework for multi-risk modelling 总被引:2,自引:1,他引:1
Jochen Schmidt Iain Matcham Stefan Reese Andrew King Rob Bell Roddy Henderson Graeme Smart Jim Cousins Warwick Smith Dave Heron 《Natural Hazards》2011,58(3):1169-1192
This paper introduces a generic framework for multi-risk modelling developed in the project ‘Regional RiskScape’ by the Research Organizations GNS Science and the National Institute of Water and Atmospheric Research Ltd. (NIWA) in New Zealand. Our goal was to develop a generic technology for modelling risks from different natural hazards and for various elements at risk. The technical framework is not dependent on the specific nature of the individual hazard nor the vulnerability and the type of the individual assets. Based on this generic framework, a software prototype has been developed, which is capable of ‘plugging in’ various natural hazards and assets without reconfiguring or adapting the generic software framework. To achieve that, we developed a set of standards for treating the fundamental components of a risk model: hazards, assets (elements at risk) and vulnerability models (or fragility functions). Thus, the developed prototype system is able to accommodate any hazard, asset or fragility model, which is provided to the system according to that standard. The software prototype was tested by modelling earthquake, volcanic ashfall, flood, wind, and tsunami risks for several urban centres and small communities in New Zealand. 相似文献
1000.
Martin Fahey Matthew Helinski Andy Fourie 《Geotechnical and Geological Engineering》2011,29(5):709-723
Paste backfill used to provide ground support in underground mining is generated from full-stream tailings and is almost always
placed underground with cement. For the backfill, both the rate of strength development and the final strength are important
considerations for design, particularly when the backfill is subsequently exposed in the stope-mining sequence. There is strong
evidence that strengths measured on specimens obtained from coring the in situ cemented backfill are much greater than laboratory-cured
specimens with the same cement content. The paper reviews some of the experimental evidence showing that one of the major
reasons for the different strength is the difference in effective stress acting on the backfill during curing. Laboratory
specimens are (almost) always cured under zero total stress, so no effective stress develops. In contrast, backfill in a stope
may cure under high effective stress, which develops due to either “conventional” consolidation in free-draining backfills,
or to the so-called “self-desiccation” mechanism in fine-grained fills. Evidence is presented showing how the final strength
is affected by applying stress to specimens at different stages of curing and at different rates. It is shown that a fully-coupled
analysis of the filling behaviour is required to determine the appropriate effective stress regime to apply in curing laboratory
specimens, where “fully-coupled” in this context means taking account of the interaction of consolidation/drainage rate, filling
rate and cement hydration rate. Curing protocols for laboratory specimens are proposed, which would ensure that the strengths
obtained are representative of in situ conditions. 相似文献