Disaster Advances

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Disaster Advances

Vol. 6(11) November 2013

Debris Flow Monitoring – A Case Study of Shenmu Area in Taiwan

Huang Y.M.*, Chen W.C., Fang Y.M., Lee B.J., Chou T.Y. and Yin H.Y.

The debris flow had become a common natural hazard in Taiwan for past years. Shenmu, at the central part of Taiwan, was a “famous” location of frequent debris flows. A monitoring station was established in 2002 to observe and collect data of debris flow in Shenmu. The monitoring system has operated since then and had recorded several debris flow events. The direct and indirect methods used for debris flow warning were discussed in this study using a real case. The case history of debris flow in Shenmu was evaluated and findings about the rainfall parameters had been discussed. Criteria of maximum hourly rainfall of 8 mm and effective accumulated rainfall of 67 mm were noted for debris flow cases after 2009. Further case studies were suggested to revise the warning threshold of rainfall in Shenmu.

Numerical Simulations of Water-inrush induced by Fault Activation during Deep Coal Mining based on Fluid-Solid Coupling Interaction

Cheng Jiu-long1,*, Sun Xiao-Yun, Zheng Gong, Gao Feng, Kong Xiang-Ru and Zhou Jian

Under the condition of complicated geology mechanical environment with high underground stress, high water pressure, high temperature and strong mining disturbance and water-inrush through fault during deep coal mining, this study, by FLAC3D numerical simulation system based on mutual coupling between stress field and seepage field, analyzes systematically the coupling law between stress field and seepage field affected by fault dip angle, fault-fracture zone width and water-bearing bed pressure. The paper reveals dynamic processes between surrounding rock stress and rock fracture process, water-inrush mechanism, seepage properties caused by fault fracture extension under fluid-solid coupling interaction. The research results provide theoretical significance and engineering application value in predicting water-inrush through fault affected by deep coal mining.

Optimization of borehole spacing of gas extraction based on the method of structure curvature

Chen Wenxue, Ni Xiaoming* and Jia Bing

Reasonable borehole spacing is one of important measures to reduce gas content of coal seam and number of drilling holes. Based on the gas geological data in Sihe mine, combined with the method of structure curvature, of distinguishing coal body structure by well logging and of testing stress- strain- permeability in experiment and so on, the corresponding relationships among the permeability of the coal seam, coal body structure and the structure curvature were gained. Based on these studies, according to the motherboard contour line in 3304 working face, the permeability distribution law in working face was predicted. Based on the law of conservation of energy and Darcy's law, the mathematical model of influent radius under different extraction pressure, extraction time, permeability, gas pressure and aperture was established. According to the results of permeability prediction and the mathematical model of influent radius, the reasonable borehole spacing in different areas of the working face was determined. Field practice showed that this method determined the drilling holes spacing by size of the osmotic coefficient can reduce the amplitude of variation of the gas emission and reduce the number of drilling hole. It can be used as a theoretical guidance to determine borehole spacing in others similar geology tectonic regions.

Changes in Haucha Village in Taiwan due to Natural Calamity

Huang C. K. and Lu C.W.*

This paper is to describe a story of Taiwanese government trying to keep original culture and to provide a more convenient life circle for aboriginal villagers in Haucha village in south Taiwan and to introduce disasters that the Haucha villagers encountered by analyzing hydrological and geological conditions. This way one would learn the valuable experiences of Haucha villagers’ immigrations and the changes of the environment due to natural calamity. Moreover, the study could help the readers make a better decision on relocating people in the similar cases in the near future.

Experimental Study for Dynamic Mechanical Properties of Shale using Split Hopkinson Pressure Bar

Jianjun Liu* and Huijuan Zhang

The dynamic mechanical properties of shale are basic for shale gas reservoir reforming. In order to reveal the law of shale’s mechanical properties changing with the strain rate, the SHPB impact test has been done. Through the analysis of the experimental results, the relationship between shale’s mechanical parameters with strain rate is obtained. The experimental results can describe shale’s dynamic properties under the impact load. The results will provide the theoretical basis and calculation parameters for shale gas reservoir reforming and numerical simulation.

Influence of water incursion on the pore characteristics of coal from Eastern China at different temperatures

Ni Guanhua, Lin Baiquan* and Zhaicheng

Influence of water intrusion on the pore characteristics of coal samples from China eastern coalfields which were prepared by water intrusion and water bath at different temperatures in advance, was investigated through mercury intrusion porosimetry (MIP), micro focus computerized tomography (µCT) and CO2 gas adsorption testing. The results show that at 20-70 °C, the coal porosity has a linear relationship with the increasing temperature but an indistinctive correlation between the coal pore connectivity and the temperature could be observed. Once the temperature reaches 80 °C, the porosity has a sharp increase and the pore connectivity also reflects a great change compared to before. For the pore size distribution, the micropore quantity increases with the temperature while its quantitative ratio keeps down. The macropore quantity and the macropore ratio present decreasing at beginning but increasing when the temperature is over 40 °C. However, the intruded water has not any evident impacts on the mesopore size distribution. For the pore volume and the surface area, the micropore volume and surface area show unobvious increasing trends with the temperature. The macropore volume has a decreasing-increasing trend while the macropore surface area has no significance by the temperature. The experimental results also show that the coal porosity and the average pore size share the same trends which are decreasing at first and then increase very soon. Moreover, the higher the coal rank is, the less influence caused by water intrusion on coal porosity and average pore sizes at various temperatures can be observed.

Research on Experiment and Mechanism of Foam Ceramics suppressing Gas Explosion

Baisheng Nie,* Hongqi Lu, Xiangchun Li, Fei Xue, Ruming Zhang and Yang Chen

Coal is the most important energy resource in China and accounts for 74% of China’s primary energy consumption. Gas explosion is one of the most severe accidents in coal mine. In order to analyze the effect of foam ceramics suppressing gas explosion, laws of two kinds of foam ceramics - Al2O3 and SiC affecting gas explosion are studied in the gas explosion experiment system. The structure of the foam ceramics is tested and the mechanism of their suppressing gas explosion is analyzed. The experimental results show that foam ceramics has a significant attenuation of overpressure and propagation speed of gas explosion. The foam ceramics can absorb the energy of gas explosion but the effect is varied as Al2O3 ceramics performs better. The meso-structure of foam ceramics is obtained by digital microscope. The results suggest that foam ceramics is a kind of cellular material and the pore canals have a good connectivity, so the explosion flame can be quenched and the heat can be consumed by reflecting and refracting and the propagation speed of the transverse wave can be weakened. The process of foam ceramics adsorbing heat has been analyzed. The foam ceramics can terminate the process of the transmission of heat so the energy of gas explosion can be absorbed. The findings provide a new method for suppressing gas explosion in coal mines, especially multiple and continuous gas explosion.

Large scale numerical investigation on methane explosion and propagation process in complicated laneway

Wang Cheng*, Han Wenhu, Ning Jianguo and Song Qingguan

In this paper a high-resolution, large-scale and parallel software is used to simulate methane explosion resulting from methane outburst in complicated laneway. Numerical results show that due to diffraction and reflection interaction in complicated laneway, the complicated wave structure can be formed. Explosion wave diffracts at the turning of laneway and strong rarefaction effect results in its strength weakness, leading to formation of the low pressure region at the location. This zone can be selected as a temporary place of refuge and setting place of an explosion-proof device. However, reflection of explosion wave on the wall and collision between explosion waves from the different lane way lead to the formation of high temperature and pressure region which causes second explosion. The explosion waves propagating in different laneway collide with each other at certain site and a high temperature region can be formed. The high temperature blocks the roadway and causes great difficulties of rescue in case of methane explosion. In the long and straight laneway, the explosion wave can propagate stably. So at this site, we can set an explosion-proof device which can play a better role in weakening the explosion wave. All the results above can provide important basis for the design and optimization of the mine laneway.

Interactive behaviors of anchor groups in sand

Hsu Shih-Tsung

Ground anchors are widely used in geotechnical engineering and are usually used in a group. This study adopted both numerical analyses and model tests to investigate the interactive behavior of anchor groups in sand. A constitutive model that considers both strain hardening and softening and volume dilatancy (SHASOVOD) and parameters needed for the model was used in conjunction with FLAC3D software to perform numerical analysis. This research also compared the results of the model anchor tests with those calculated numerically to enhance the applicability of the numerical method. Numerical results show that the load-displacement behaviors calculated numerically were consistent with those measured by anchor tests. The interference induced by the paired anchors was less than that induced by the triple anchors. When the spacing between neighboring anchors was small (e.g. the horizontal spacing (Sh) was 2D where D is the anchor diameter), the yielding zones of soil around the anchors were highly superposed, the average anchorage capacity of an anchor group was considerably smaller than that of a single anchor and the efficiency of an anchor group was 55%-70%. The superposition of yielding zones decreased as the horizontal spacing increased and the behavior of each anchor in the anchor group was similar to the behavior of a single anchor when the horizontal spacings exceeded 10D.

A New Statistical Model to estimate Eroded Caves behind a Concrete-faced Dyke along the Tsengwen River in South Taiwan

Lee Der-Her*, Lai Sin-Long, Lin Pin-Jun and Lin Hung-Ming

The increasing rainfall intensity and cumulative rainfall induced by climate change magnify the flow rate of a river and significantly erode a dyke. Securing the integrity of a dyke to protect the land is an essential topic in disaster prevention and water resource management. A concrete-faced river dyke increases erosion resistance and is usually used along the main river in south Taiwan. However, eroded caves behind the thick concrete face are difficult to detect. This study attempts to develop a new visual-based statistical model to estimate the degree of cavity erosion behind the concrete-faced river dyke. Because removing the in-situ concrete face of the dyke is usually forbidden, a non-destructive ground-penetrating radar (GPR) image is used to confirm the location and the size of the cavity. Therefore, an indoor test is conducted to identify the GPR signal of the cavity behind a concrete plate. The detection of in-situ caves associated with the removal of the concrete face during dyke repair is used to validate the statistical model. The degree of cavity erosion is classified based on the in-situ GPR detection results. The outlook factors of the concrete faces are collected by a visual survey to correlate the outlook factors of the concrete dyke to the internal cavity erosion degree by multiple linear regression analysis. The accuracy of the statistical model is verified by comparing the cavity erosion degree predicted by the statistical model and that defined by GPR.

Analyzing the slope stability of Jinping I hydropower station with the zone safety factor

Mengmeng Fu

Stability analysis of the left bank slope of Jinping I hydropower station is simulated with Fast Lagrangian Analysis of Continua in 3 Dimensions (FLAC3D). Variation in zone safety factor and distribution of fault deformation and slope stress field are discussed. The zone safety factor can be obtained as a quantitative indicator through the FLAC3D program with FISH language embedded to reflect the variable stability of the different parts of the slope. Results show that the zone safety factors of the shallow slope near the excavation surface are smaller than those of the other parts. Nearly all the zone safety factors of the slope with reinforced prestressed anchors exceed 1.0. By contrast, certain zones around the shallow slope near the excavation surface achieve safety factors below 1.0 in the case with inadequate prestressed anchor support. Variation in zone safety factor is therefore achieved. Results on the displacement of the faults and stress distribution of the slope under the two conditions examined indicate that prestressed anchors help reduce the displacement of faults and improve stress condition. Then prestress loss ratios that range from 5% to 20% are used in the analyses to evaluate the sensitivity of the prestress loss ratio to slope stability. The findings indicate that no significant effect is observed on the overall stability of the slope on the left bank although the average shear deformation of weak structural planes becomes obvious as the prestress loss ratio increases. The zone safety factor serves as a valuable quantitative reference as well as provides information on the distribution of fault deformation and the slope stress field to analyze the stability of complex slopes.

Trapping Effect of a Calm Zone by Lee Side-Internal Gravity Waves and Cyclonic Winds on Sudden High Concentrations of Particulate Matters combined with the Yellow Dusts from Gobi Desert in the Korean Eastern Coast

Choi Hyo

Sudden high particulate matter concentrations of PM10, PM2.5 and PM1 measured by a GRIMM-1107 aerosol sampler in the Korean eastern mountainous coast, Gangneung city were investigated on October 23 ~ 27, 2003. Until 18:00LST, October 24, before a Yellow Dust period under the transportation of dust particles to the city, PM10, PM2.5 and PM1 concentrations were lower than 40 μg/m3, 25 μg/m3 and 23 μg/m3 respectively. Backward trajectories of air by NOAA- HYSPLIT model and wind fields by numerical simulation by 3D-WRF-3.3 model indicated the transportation of dusts from Gobi Desert and the northern China toward the Korean coastal city from 1800 LST October 24 to 1900 LST October 25 (dust period). Under the combination of dust particles transported from China and local pollutants like gases and particulate matters emitted from vehicles and flying dusts on the road and additionally from heating boilers in the resident area, maximum concentrations of PM10 with 104.38 μg/m3 occurred at 07:00LST around the time to go to the office and maxima of PM2.5 and PM1 were at 09:00LST. Similarly, secondary maxima of PM10, PM2.5 and PM1 were detected at 17:00LST around the time to come from the office. After cold front passed by the Korean eastern mountainous coastal region, synoptic-scale north-westerly wind was more intensified which blew over the top of Mt. Taegulyang and moved down along its eastern slope toward the city, resulting in a strong downslope wind storm. The downslope wind storm caused the propagation of lee side-internal gravity waves along the eastern slope bounding up and down with a hydraulic jump motion of air and the gravity waves produced a cavity of calm or weak wind under wind shift by a cyclonic circulation in the coastal basin. Thus, as westerly downslope wind was prohibited from easterly wind from the sea toward the inland coast, the dusts transported from Gobi Desert combined with particulate matters or gases emitted from vehicles on the road of the city could be trapped and merged within a calm cavity in the coastal basin, resulting in maximum particulate matter concentrations in the city at 07:00LST, October 25.

A Preliminary Study on the relationship between Cloud to Ground Lightning and Precipitation

Yang Yanrong

In-cloud particles in various phase states are the major part of thunderstorm disasters, by the aid of convection they would discharge and fall to ground as precipitation. This paper tried to give a preliminary study about cloud to ground (CG) lightning and precipitation providing technique support for thunderstorm disasters prevention. Data mainly obtained from Lightning Location System and Chinese Netrad were combined for a thunderstorm case in Jiangsu Province, China. The result showed that -CG numbers reached 92% of all. The macroscopic relationship between precipitation and lightning indicated that -CG locations were sometimes related with rainfall centers, when +CG was in majority, hail might occur. Rainfall centers had better one to one spatio-temporal relationship with -CG location centers, more –CG corresponded to less rainfall and vice versa. The microcosmic relationship between in-cloud precipitable particles and CG had been further studied to simply estimate CG positions and initial discharge time under the non-inductive electrification mechanism which combined with radar data assimilation and differential connection between in-cloud vertical electric field and precipitable intensity. The result showed that out of the 56 strokes observed in the first 30 minutes of this thunderstorm, 40 can be simulated; principal lightning falling locations were identical to observations.

Identification and classification of flood prone areas using AHP, GIS and GPS

Bhagat Madhuri, Ghare Aniruddha1* and Ralegaonkar Rahul

Flood is a disastrous event causing losses, damages and destruction to life, property and environment. Due to population growth and resulting industrial, commercial and agricultural activities, the devastations due to flood are making more severe impact on society. In order to assess, mitigate and manage the floods, the present paper elaborates a methodology for assessment of flood vulnerable areas using a multi-criteria decision making technique using the aforesaid parameters. The flood affecting parameters considered are rainfall, runoff, gauge, discharge and land use spatial data. Analytical Hierarchical Process (AHP) was used for estimating an index called as Flood Vulnerability Index (FVI). The estimated FVI represents an extent of vulnerability of the flood affected region. The vulnerability has been mapped using Arc GIS (Arc Map-10) and zoning map has been developed and further validated using a detailed survey of critical area using Global Positing System (GPS). The developed methodology has been illustrated for a study area which is a region in Wardha river basin situated in Chandrapur District, Maharashtra State, India. The developed methodology can be applied for any region by considering the predominant factors affecting the flood in that region and would help in prioritising planning prerequisites for flood emergency management.

A Study on Generation of Digital Terrain Model considering Elevated Road of Urban Environment from Airborne LiDAR Data

Yongmin Kim, Anjin Chang* and Yongil Kim

Modern urban environment is, unlike the past, composed of diverse features such as buildings, roads, vegetation and other structures and is fast changing day by day. Therefore, the study to comprehend and analyze such features in change has been carried out continuously in the field of remote sensing. In the past when the urban environment features were simple, the change of urban environment could be analyzed just through the satellite images of 2-dimensions. But, as the urban environment gets more complex and diverse, the necessity to analyze it with 3D information is growing more and more. The airborne light detection and ranging (LiDAR) is the best tool to analyze the urban environment and the studies related with it have been made actively in the remote sensing field. To extract diverse urban environment features through LiDAR, the prerequisite condition is the precise and correct generation of Digital Terrain Model (DTM). DTM can be generated through the extraction of ground points from the airborne LiDAR data and then the interpolation. The ground points are usually extracted in the leveling method. If there is an elevated road in the target area, the elevated road is also extracted as a ground point to cause an error in generating DTM. Therefore, this study proposes an algorithm to detect the elevated roads which become the problem in extracting the ground points from airborne LiDAR data. First, Digital Surface Model (DSM) is generated through the airborne LiDAR data; by applying mean planar filter, DSM is classified into planar surface and non-planar surface. Then, ground points are extracted by using the area-based filter. In the ground points extracted at this time, there are not only real ground points but also elevated road points. Therefore, to detect and eliminate the elevated road points among the extracted ground points, the regression plane is generated; the process is repeated to detect the elevated road points. In this process, diverse statistical figures are used to detect the points. Finally, DTM is generated with the ground points extracted through the above process. To verify the validity of proposed method in this study, the method was applied to the airborne LiDAR of San Francisco area, USA and the quantitative precision was evaluated on the extraction of elevated roads. And, to see the influence of proposed method on the precision of DTM generation, the visual analysis on DTM without removal of elevated road points was additionally carried out. As a result, the proposed method turned out to have better performance in extracting the elevated road points and DTM generated in this method was more accurate too. Therefore, the technique proposed in this study seems useful in urban environment management, feature extraction and urban planning through DTM of urban environment.