“5.12”汶川地震后北川新县城选址地质安全研究

＂5.12＂汶川特大地震的发震断裂从北川县城穿过,地震时北川县城烈度大于等于10°;地震引发北川县城周围多处山体滑坡、崩塌次生灾害;对北川县城造成了毁灭性破坏,使其成为＂5.12＂地震中受损最为严重的县城。灾后重建必须把城市安全放在第一位,而城市安全主要取决于地质条件及其安全性。在搜集整理、分析研究大量资料和现场工程地质调查的基础上,首先研究北川县城原地重建的可能性,并提出备选场址比较方案;综合研究原县城驻地、备选场址的地形地貌、地质构造、新构造运动与地震、工程地质、水文地质、不良地质作用与地质灾害等地质安全要素,按照＂以人为本、安全第一＂的原则,最终推荐安昌东南作为北川新县城灾后重建场址。     

四川汉旺地震遗址保护地概念规划探讨

通过对四川汉旺震后破坏状况的介绍和与其他破坏严重地区的比较可以看出,设置汉旺5·12地震遗址保护地具有必要性。遗址保护地规划应从遗址保护地的定位、规划设计原则、主要构思、规划空间结构、保护措施、展示方式、重要场所意向性设计等方面进行。     

汶川地震断裂带科学钻探一号孔（WFSD-1）断层泥孔段泥浆体系的研究与应用

汶川地震断裂带科学钻探项目一号孔（WFSD-1）钻遇了30多米的断层泥。针对断层泥钻探的主要问题,对断层泥钻探泥浆体系进行了研究与应用,形成了具有高密度、低失水、低渗透、润滑减阻特点的泥浆体系,再加上重泥浆体系对地应力的平衡作用,成功地解决了断层泥的钻进取心问题,为顺利完成钻孔施工任务奠定了坚实的基础。     

Damage to sewage systems caused by the Great East Japan Earthquake,and governmental policy

The Great East Japan Earthquake and its accompanying liquefaction and tsunami severely damaged many sewage systems including sewage pipes, manholes, pumping stations and sewage treatment plants over a wide area from Tohoku to the Kanto region. We conducted a questionnaire survey, interview survey and on-site confirmation in order to summarize and categorize the damage factors that shut down facilities such as drainage systems and treatment systems. We also studied the effectiveness of countermeasures to prevent liquefaction of the sewage system. The results showed that 90% of sewage pipes and 70% of manholes were damaged by liquefaction and that 54% of wastewater treatment plants and 75% of pumping stations were damaged by tsunami. Nevertheless, no severe damage was found along sewage pipe sections where liquefaction countermeasures had been executed, suggesting that the countermeasures are effective.     

Mitigation of Liquefaction-Induced Lateral Deformation in a Sloping Stratum: Three-dimensional Numerical Simulation

Finite-element (FE) simulations are increasingly providing a versatile environment for conducting lateral ground deformation studies. In this environment, mitigation strategies may be assessed in order to achieve economical and effective solutions. On the basis of a systematic parametric study, three-dimensional FE simulations are conducted to evaluate mitigation by the stone column (SC) and the pile-pinning approaches. Mildly sloping saturated cohesionless strata are investigated under the action of an applied earthquake excitation. For that purpose, the open-source computational platform OpenSees is employed, through a robust user interface that simplifies the effort-intensive pre- and postprocessing phases. The extent of deployed remediation and effect of the installed SC permeability are investigated. The influence of mesh resolution is also addressed. Generally, SC remediation was found to be effective in reducing the sand stratum lateral deformation. For a similar stratum with permeability in the silt range, SC remediation was highly ineffective. In contrast, pile pinning appeared to be equally effective for the sand and silt strata permeability scenarios. Overall, the conducted study highlights the potential of computations for providing insights toward the process of defining a reliable remediation solution.     

Uncertainty quantification and seismic fragility of base-isolated liquid storage tanks using response surface models

Seismic response of base-isolated liquid storage tank is represented using response surface model (RSM) to consider the uncertainty in the isolator parameters. The effectiveness of RSM to represent the probability distributions of the peak seismic response quantities of the base-isolated liquid storage tank is studied in the framework of Monte Carlo (MC) simulation. Broad and slender configurations of the tanks isolated by lead–rubber bearing (New Zealand – NZ system) characterized with non-linear force-deformation behavior is considered in the present study. The influence of the uncertain isolator parameters on the seismic response of the base-isolated liquid storage tanks is investigated. Subsequently, seismic fragility of the base-isolated liquid storage tanks is evaluated using the RSM based MC simulation. The RSM estimates the non-linear seismic response of the base-isolated liquid storage tanks with sufficient accuracy. It is observed that the uncertainties in the isolator parameters significantly influence the peak response quantities of the base-isolated liquid storage tanks. The effectiveness of the base isolation technique, in terms of the reduced probability of failure, is observed by comparing the fragility curves for the fixed-base and base-isolated liquid storage tanks. It is also observed that increase in the isolation time period decreases the probability of failure for the base-isolated liquid storage tanks. It is concluded that the peak ground acceleration (PGA) of the earthquake ground motion can be included in the RSM to reduce the computational efforts for seismic fragility analysis.     

云南城市抗震防灾能力现状分析及抗震对策措施建议

本文根据澜沧—耿马地震震害的调查和东川、丽江等八市(县)城市综合抗震防灾能力的研究结果为主要依据,对云南省城市抗震防灾能力的现状进行了初步的分析与估计,并就减轻城市地震灾害的对策、措施提出了若干建议。     

Joint First-Passage Probability and Reliability of Systems under Stochastic Excitation

The first-passage probability, describing the probability that a scalar process exceeds a prescribed threshold during an interval of time, is of great engineering interest. This probability is essential for estimating the reliability of a structural component whose response is a stochastic process. When considering the reliability of an engineering system composed of several interdependent components, the probability that two or more response processes exceed their respective safe thresholds during the operation time of the system is an equally essential quantity. This paper proposes simple and accurate formulas for approximating this joint first-passage probability of a vector process. The nth order joint first-passage probability is obtained from a recursive formula involving lower order joint first-passage probabilities and the out-crossing probability of the vector process over a safe domain. Interdependence between the crossings is approximately accounted for by considering the clumping of these events. The accuracy of the proposed formulas is examined by comparing analytical estimates with those obtained from Monte Carlo simulations for stationary Gaussian processes. As an example application, the reliability of a system of interconnected equipment items subjected to a stochastic earthquake excitation is estimated by linear programming bounds employing marginal and joint component fragilities obtained by the proposed formulas.     

Three-Degree-of-Freedom Rigid Model for Seismic Analysis of Cracked Concrete Gravity Dams

A rigid model with three-degrees-of-freedom is proposed for the purpose of seismic analysis of cracked concrete gravity dams. The model considers the geometry of the dam and all its possible modes of motion: sliding, rocking, rock-sliding, and drifting. The governing equations for all the modes are derived with the Mohr-Coulomb friction assumption at the crack, and corresponding conditions to initiate and maintain the modes are also given. For impact that follows rocking and drifting modes, postimpact velocities of the model are explicitly determined according to the momentum principle and the concept of restitution from classical point collision. Studies with the proposed model on rectangular blocks demonstrate two different types of rocking according to the slenderness. Applications to dams indicate that a large coefficient of friction does not necessarily prevent sliding, and rocking and drifting modes should not be neglected in estimating the stability of concrete gravity dams cracked at the base or at a height.     

The liquefaction cycle and the role of drainage in liquefaction

In this work the liquefaction cycle is introduced as a framework to describe the coupled processes that take place in fluid-saturated granular media that lead to liquefaction. The modular formulation of liquefaction makes it possible to test the various processes that contribute to liquefaction separately, and to assemble different formulations of the relevant physics into a numerical model for liquefaction. This view on liquefaction is used here to assess the role of drainage in liquefaction. We present a simple scale analysis of the role of drainage. A numerical implementation of the liquefaction cycle shows, however, that the scale analysis is deceptive for the case when strong spatial variations in the permeability inhibit fluid migration. As an illustration the numerical model is used to quantify the imprint of a low-permeability layer on the liquefaction behavior.We greatly appreciate our conversations with Masami Nakagawa and Vaughan Griffiths about this work. The critical and constructive comments of two anonymous reviewers are very much appreciated. The visit of Annemieke van den Beukel to Golden was supported by the Molengraaff fonds, the Schuurman Schimmel van Outeren Stichting, the Stichting Dr. Hendrik Mullers Vaderlandsch Fonds, and the Trajectum Fonds.