Proposed Changes to the Geotechnical Earthquake Engineering Provisions of the Bangladesh National Building Code
Tahmeed M. Al-Hussaini, Tahsin R. Hossain and M. Hayeem Al-Noman
ABSTRACT: The Bangladesh National Building Code (BNBC) has not been updated since its inception in 1993. Earthquake design
provisions are important, since Bangladesh is located in a seismically active region not far from the boundary of the Indian Plate and Eurasian Plate. Many advances in earthquake engineering research have taken place over the last two decades. In 2010, a project has been taken up for upgradation of the building code to incorporate current knowledge and developments. Significant changes have been proposed in the seismic design provisions of the updated version of the building code. This paper describes the salient features of the proposed changes to geotechnical earthquake engineering provisions affecting computation of the seismic loads. Major changes have taken place with regard to the seismic zoning map, soil classification system, site-dependent response spectrum, and in defining seismic design category.
Analysis of Soil Liquefaction during the Recent Canterbury (New Zealand) Earthquakes
RP Orense, MJ Pender and LM Wotherspoon
ABSTRACT: Four successive large-scale earthquakes, with moment magnitudes (M w) ranging from 5.9 to 7.1, struck the Canterbury region on the South Island of New Zealand within a period of 15 months in 2010-2011. These earthquakes caused extensive damage to lifelines and residential houses in Christchurch City and adjacent areas due to widespread liquefaction and re-liquefaction in areas close to major streams, rivers and wetlands. In this paper, various analyses were made considering the results of the reconnaissance work conducted immediately after the events, the acceleration records at strong motion sites and the available boring information. The liquefaction risk in the city was evaluated to explain the severity and extent of damage during the 2010 and 2011 events. Finally, simulation of recorded ground motions through 1D effective stress ground response analysis gave a better understanding of the dynamic properties of Christchurch soils.
Numerical Simulation of Seismic Slope Stability Analysis based on Tension-Shear Failure Mechanism
Yingbin Zhang, Guangqi Chen, Jian Wu, Lu Zheng, Xiaoying Zhuang
ABSTRACT: Most slope stability analysis approaches regard the failure mechanism of seismic slope as single shear failure while ignoring the influence of tension failure. However, many model testes and a large number of post-earthquake investigations provided supporting evidence of the significant influence of tension failure in seismic slope instability. To estimate the effects of tension failure on seismic slope stability, a numerical modeling considering both shear and tension failure is performed using FLAC3D. After discussions of failure mechanism, strength reduction techniques and the definition of slope failure, a homogeneity slope under a modified transverse earthquake load is analyzed. The results obtained from the simulation are presented in terms of permanent displacement, factor of safety and failure surface. Finally, the outcomes compared with those from various existing methods. The results show that the influence of tension failure is significant and consideration of it is necessary.
KEYWORDS: Seismic slope stability analysis, Numerical simulation, Failure mechanism, Tension failure, Factor of safety
A Real-time Prediction Method for Regional Rainfall-induced Geohazards in Post-earthquake Region of Wenchuan Earthquake
Z. Yang, J. Qiao, H. Tian, D. Huang, M. Wang and H. Meng
ABSTRACT: After years of the Wenchuan earthquake took place in 12 May, 2008, rainfall has been the most major triggering factor of geohazards in the earthquake stricken areas. As a random event, geohazards including landslides and debris flows occurrence are affected by environmental factors and triggering factors, as a result the hazard degree should be a variational value varying from the regional random precipitation triggering factor and regional geohazards susceptibility assessment environmental factors. According to geohazards mechanism, the probability based method of assessing the variational hazard degree of regional geohazards is proposed by the combination of probability of daily precipitation and susceptibility assessment. The prediction model is established by the analysis of geology and hydrology factors of the study area, which is incorporating with the analysis of geohazards occurrence data and the corresponding precipitation data. Then, the method is applied in earthquake region of Chengdu City, 8 km away from the epicenter of Wenchuan earthquake, Sichuan province. The validity of the prediction method is verified by evaluating the hazard degree of regional geohazards in Chengdu city on September, 24, 2008 and July, 17, 2009. It is found that the occurrence location and occurrence time of the two geohazards from prediction coincide with those from measurement. As a result, this variational hazard degree assessment model for regional geohazards demonstrates a useful application of a new predictive method and provides a basis for the prediction of time and space of regional Rainfall-induced geohazards.
Effects of Anisotropic Consolidation and Stress Reversal on the Liquefaction Resistance of Sands and Silty Sands
Abbas Galandarzadeh and Alireza Ahmadi
ABSTRACT: In this study, a total number of 83 undrained cyclic tests were carried out on Firoozkuh pure sand and sand-silt mixtures using cyclic triaxial apparatus. The tested specimens were subjected to both isotropic and anisotropic consolidation. The anisotropic consolidation was applied both in compression and in extension modes. The results indicate that the isotropic consolidated pure sandy samples when subjected to symmetric cyclic stresses exhibit asymmetric cyclic strains reversely, as extensional part of each cyclic strain curve is larger than compressional part. This behavior of sandy soils could be addressed to the anisotropic behavior of sands. The effect of adding silt on this deformational behavior of sandy specimens is studied too. The results indicated that this behavior disappears in silt mixed sand.
In addition, the effect of anisotropic consolidation on deformational behavior of pure sand and sand-silt mixtures was considered. The results indicate that the cyclic resistance of saturated sand to liquefaction is the function of compressional or extensional consolidation and besides, reversal of cyclic deviator stress. Anisotropic consolidation exerts an initial static deviator stress in triaxial tests. Effect of initial static shear stress on the cyclic liquefaction of sands is acknowledged in the literature and a correction factor of k is introduced to take this into account. However, shear stress reversal in the cases with presence of initial static shear stress is another factor that affects the liquefaction potential. A new coefficient called rc is introduced in this study to show degree of cyclic stress reversal. Combined effect of initial static shear stress and shear stress reversal is studied and it is shown that the correction factor for initial static shear stress k is not sufficient and stress reversal effect should also be considered for correction of cyclic resistance to liquefaction. Effect of initial shear stress and cyclic stress reversal on the silt mixed sands is also studied.
Characteristics of Slope Failures During Natural Disasters Considering Geographical Features and Groundwater Level: Case Study of the Chuetsu Region of Niigata, Japan
H. Toyota
ABSTRACT: Several natural disasters—earthquakes, heavy rainfall, and snow—struck the Chuetsu region of Niigata during the short period of 2004-2011. Recently it has been pointed out that damage by a certain natural disaster is exacerbated by other natural disasters occurring before and after the natural disaster. This phenomenon, designated as a compound disaster, is of widely acknowledged importance. Records of such uncommon disaster circumstances and effects are presumed to be valuable from the viewpoint of disaster prevention. Therefore, actual conditions of damaged areas were investigated in the Chuetsu area to assess the degree of damage, with consideration of geographical features including geology and groundwater level. Moreover, the results of follow-up monitoring related to the damaged slopes during the unprecedented Chuetsu Earthquake are briefly introduced in this paper.
KEYWORDS: ground water level, model test, monitoring on site, site investigation, slope stability
Overview of the Geotechnical Damages and the Technical Problems Posed after the 2011 off the Pacific Coast of Tohoku Earthquake
M. Kazama, T. Noda, T. Mori and J. Kim
ABSTRACT: The 2011 Off the Pacific Coast of Tohoku Earthquake which occurred on March 11, caused serious damage to the infrastructural facilities in Tohoku and Kanto districts due to the strong motion of the earthquake and the subsequent tsunami. This paper includes a brief outline of the earthquake, the earthquake damage to various facilities, and the main geotechnical engineering problems which have emerged after this disaster.
Development of Potentail Map for Landslides Induced by the Chi-Chi Earthquake Using Instability Index
Meei-Ling Lin and Yu-Hung Shu
ABSTRACT: In Taiwan, sloping lands cover more than 70% of the total area, and the geological condition of Taiwan is fairly fragile. The topography, geology, and tectonic setting make it highly prone to landslides induced by earthquake. In this research, data of the landslides triggered by the Chi-Chi Earthquake was analyzed for assessment of the potential and a predictive model was established for landslide occurrence of the area if similar earthquakes occur. Influence factors were selected and the instability index was used for assessing landslide potential. Through verification of an independent set of ground-based investigation data, results of the prediction model appeared to be satisfactory and can be used for mapping of landslide potential induced by similar earthquake in the future.
Geotechnical Hazards with Emphasis on Seismically-Combined Effects on Slopes
Ikuo Towhata
ABSTRACT: This paper first addresses several examples of complex or compound natural disasters with an emphasis of slope instabilities. In many of them, the first effect was produced by earthquakes and the second one was made by heavy rains. Weathering is another kind of the first event. Because the complex events are of stronger action, it is made more difficult to achieve safety. Hence discussion is often made of the importance of relocation of habitats to safer places and/or emergency evacuation. Technical visits to sites of such “soft” measures revealed that the success of those measures depends on education of people and the administrator’s reasonable respect of the people’s need for good jobs and reliable income.
Monitoring on Earthquake Induced Landslide – A Case Study in Northwest Chengdu, China
Hongling Tian, Jianping Qiao., Taro Uchimura and Lin Wang
ABSTRACT: Many after-shock slopes covered by loose deposits, when heavy rain comes, the slope easily slides and turns into debris flow. Thus, the slope movement and the moisture of slope are most important factors for landslide and debris flow. For these style landslides, real-time monitoring is a good way for local people. After analysed the system requirements, the authors proposed an easy-to-use and low power consumption monitoring system. This system consists of two parts, field part and data processing part. The field part includes a few sensors and a data transferring unit. The sensors are made up of tilt sensor, soil moisture meter and rain gauge. A demo system was setup on a sliding slope in Taziping, northwest of Chengdu city. After a field test with artificial rainfall, a criterion for warning was drawn. The demo system has proved it’s effective. It is an economy and simple solution for similar area.
