Formation Mechanism of Deep Cracks in the Left Bank Slope of Jinping-I Hydropower Station

Guan Rong 1,2*, Jun Peng1, Xiaojiang Wang1, Guang Liu1 and Di Hou1

The Jinping-I hydropower station sits in the west of Great River Bend of Yalongjiang River. Deep cracks are well developed in the slope of the hydropower station. This study is focused on formation mechanism of deep cracks in the left bank slope of Jinping-I hydropower station. Characteristics of in-situ stress in the dam site and the development law of deep cracks in the slope of Jinping-I hydropower station are analyzed. Finally, development of the river valley of Jinping-I hydropower station is simulated by adopting three dimensional distinct element code (3DEC) and variation of stress field as well as distribution of deformation and unloading in different stages of the river valley erosion are discussed. Based on the results and basic law of deformation and in-situ stress of the slope valley, it can be indicated that deep cracks developed in the left bank slope of Jinping-I hydropower station resulting from failure of rock masses which are controlled by the original dominated tectonic fractures. The failure is caused by the regional concentrated stress at the elevation of (EL.) 1700~1850 m in the slope during the process of valley erosion leaded by fast crust uplift and quick river erosion

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On the Spatial and Temporal Patterns of Flood and Drought Hazards of China

Jia Huicong1 and Pan Donghua2

The flood and drought hazards have been getting more serious attention since 1990’s. And they become the obstacle factors constraining China's agriculture and sustainable economic development. This paper selected 2,359 county units and with disasters frequency as flood-drought hazard assessment index, through hazard digital mapping, the spatial and temporal patterns were analyzed and hence understood the flood-drought high risk zone and the transfer causing factors, presented disaster prevention measures for the high-risk zones. In sum, the key areas of preventing and controlling flood and drought disaster should be Northeast Plain, central and eastern Inner Mongolia, North China Plain, the northern part of Shaanxi Province, the middle and lower reaches of Yangtze River Basin, Yunnan-Guizhou Plateau, the southeast coastal region and northern Xinjiang.

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Measuring System of Adverse Weather Phenomena

Radinović D. and Ćurić M.

A measuring system of adverse weather phenomena by unification of threshold scales and their units has been defined. All threshold scales of adverse weather phenomena have been reduced to three different types: standard frequency distribution, decile method and Beaufort scale. Their units are: standard deviation, decile of frequency and unit of the Beaufort scale. Four steps for each threshold scale are defined: normal, above normal, much above normal and extraordinary above normal or normal, below normal, much below normal and extraordinary below normal. The examples by observations of Meteorological Observatory in Belgrade are presented.

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Root Sum of Squares Cumulative Velocity: An Attribute for Earthquake Early Warning

Bhardwaj R.,* Kumar A. and Sharma M.L

A practical approach for mitigating earthquake risk may be the Earthquake Early Warning (EEW). An EEW system is capable of issuing a warning few seconds prior to arrival of approaching ground motion to the populated and other vulnerable area. In this study a simple and robust algorithm based on the exceedance of specified threshold time domain amplitude levels has been discussed for automatic primary wave onset (P-onset) detection and EEW analysis. The algorithm has been applied on combined strong motion database (KNET+PEER-NGA) and tested on Indian strong motion database which demonstrates satisfactory results. The databases are processed to compute two parameter, root sum of squares cumulative velocity (RSSCV) and cumulative absolute velocity (CAV) respectively and compared with specified threshold levels. In case of automatic P-onset detection, an accuracy of around 71% and 76% has been achieved for combined dataset and Indian dataset respectively, for a time difference of 0.1 sec. The estimated threshold levels for RSSCV and CAV attribute are 10 cm/sec and 41 cm/sec respectively. Percentage of correct P- onset pick as well as correct alarms estimation using RSSCV and CAV attributes has been discussed in details. Individual station vote for RSSCV and CAV values have been used to detect the occurrence of a major earthquake (M ≥ 6) and provide onsite warning within seconds after the arrival of the primary waves in the area around the station. When the array of stations is available, the approach can be applied to multistation data, a three stations vote method and average of event vote method have been used in this study.

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Wind induced Buffeting Reliability of Long-span Cable-stayed Bridge using Stochastic Finite Element Method

Lin Zhao and Yaojun G.E.*

Using the present wind-induced buffeting theories and the stochastic finite element methods (SFEM), failure probability about complex structures such as long-span cable-stayed bridges, is computed considering its more realistic behaviors by means of combining parameter sensitivity analysis technique with advanced first-order reliability method (AFORM) in the light of mode shape iteration method. In this process, several key stochastic factors i.e. aerodynamic loading, material properties and geometry characters, are analyzed quantitatively. Then the general methodology of buffeting probability assessment for long-span bridges cable-stayed is proposed. Finally, the buffeting assessment of the East Sea Bridge is selected as a numerical example and a series of steps, including mean wind prediction, stochastic wind field simulation, stochastic buffeting analysis are carried out with some important conclusions, in which the effects about aerodynamic admittance functions, returnperiods and several other stochastic factors on buffeting failure probability for long-span cable-stayed bridges are compared.

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Natural Disasters and Average Temperature in China

Chen Sha1 and Xiaoli Bi2*

As the global climate change intensifies, it has led to more frequent and intensified natural disasters in China. Here we employed a linear regression to analyze the relationship between the frequency of natural disasters and the average temperature of 194 national stations in China from 1951 to 2011. The results indicate that earthquake (seismic activity), flood and storm are strongly affected by the climate. If the average temperature in China increases by 1 oC, the occurrence of earthquake(seismic activity), flood and storm would increase by 2, 4 and 4 occurrences per year respectively.

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Lateral Resistance of a Single Vertical Pile installed near Geogrid-Reinforced Slope

Zomorodian Ali S.M.1* and Sadeghi H.2

The effect of reinforcing a sandy slope with geogrid on lateral resistance of a single pile located near a slope is studied by small scale model tests. Therefore, a broad series of conditions including unreinforced cases was tested by varying parameters such as: arrangement of geogrid reinforcements, pile distance from the slope crest, relative density of sand, angle of the slope, embedded length, shaft roughness and cross section of pile. The results indicate that improvement in lateral resistance of the pile intensively depends on the arrangement of geogrid reinforcements. The optimum length and width values of geogrid layers (i.e. the one leading maximum lateral resistance of a single pile) were 31d and 24.6d (d=pile diameter) and 2.82d, 1.64d for the depth of first layer and spacing between geogrid layers respectively.

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Inversion analysis of initial geostress in tunnel of DaPing mountain

You Z.M.* and Chen J.P

Based on the geological conditions and measured data of in-situ stress in DaPing mountain tunnel, the initial geostress field of tunnel area is analyzed by 3D multivariate FE regression. A 3D FE computational model is established to compute geostress in four cases, including gravity, tectonic stress field for horizontal extrusion and shear. And the regression coefficients are solved using the least square method and then the calculation value of the measured points, eventually the regression stress field of the whole area especially important engineering parts. Through comparison between the calculated and measured geostresses of measuring points, it is found that these two are similar which suggests that the geostress field obtained by regression is reasonable and conforms to the historical background of geological structure. The results of the geostress field have important reference value of the dynamic design and construction of projects.

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Assessment of Seismic Hazard Parameters for Guwahati Region in Northeast India

Maiti Soumya Kanti , Dasadhikari Manik and Nath Sankar Kumar*

Guwahati is fast emerging as a multi-ethnic cosmopolitan city with a burgeoning population and rapid unplanned urbanization. The city is located in the lower Brahmaputra Valley and underlain by thick alluvial deposits ranging from 25 to 600 m with granitic exposure at places. Large earthquakes in the past caused widespread damage to life and property in this terrain. Hence the study of seismicity of this area is mandatory for the purpose of seismic hazard analysis. This study attempts to evaluate probabilistic seismic hazard parameters ‘b’ value, the mean return period and the maximum regional magnitude. The seismic hazard parameters have been calculatedusing Gutenberg-Richer (G-R) recurrence relation and Kijko method for the study region. Higher ‘b’ value obtained in this study features the geological heterogeneity and increased seismcity of Guwahati region.

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Development of a guideline for thunderstorm reporting based on radar and lightning location data

Li P.W. and Chan P.W.*

Thunderstorm is a crucial weather phenomenon for reporting at synoptic stations (as SYNOP) and airports (as METAR/SPECI and location routine/special reports). Traditionally, it is reported based on hearing the thunder and/or seeing the lightning in association with the thunderstorm by the human observer. The use of data from weather radar and lightning location information system (LLIS) for the reporting of thunderstorm is considered in this paper. For this purpose, a method is described in determining the thresholds of radar reflectivity and the distance of cloud-to-ground lightning stroke from the prescribed reflectivity for reporting thunderstorm. It aims at achieving a balance between hit rate and false alarm for detecting thunderstorm. A comprehensive study has been conducted to identify the false alarm cases of LLIS by considering all the available meteorological data. The thresholds are determined to be 32 dBZ and 15 km respectively which are consistent with the results obtained by similar studies of another weather service, but the threshold values are not exactly the same. This points to the importance of establishing the local threshold values for the specific climatological condition of a weather station. Based on such threshold values, a set of guideline of reporting thunderstorm based on radar and LLIS data is proposed. Its impact on thunderstorm climatology is discussed using Hong Kong International Airport (HKIA) as an example.

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