徐州市建南地区的地陷及成因分析

１９９２年４月１２日，徐州市建南地区发生地面塌陷灾害。本文介绍了地陷的概况及其基本特征。从地质构造、地层岩性、地下水等因素进行了成因分析。     

地震引发的“多米诺”

以地震为诱因而引发的地质灾害叫做“次生地质灾害”,主要包括山体崩塌、滑坡、泥石流,堰塞湖、地面塌陷、地裂缝和海啸等,灾害间的关联形成灾害链,对人类的生命财产安全构成极大危害,是可怕的“多米诺”效应。如2004年印度洋地震海啸造成20多万人死亡。     

鲁豫交界区地质灾害研究

分析了发生在鲁豫交界区的地面塌陷、地裂缝等地质灾害现象的时空分布特征，对其成因类型进行了研究，认为灾害的发生主要取决于当地的水文地质条件及人为活动，此外还就灾害防御问题提出几点建议。     

南四湖地区煤炭开发地面塌陷影响分析

南四湖流域具有丰富的煤炭资源,是山东省主要的后备煤炭资源基地之一。近年来已相继开发矿井40余对。由于采煤活动的进行,对南四湖环境影响日益加大。主要表现为：地面塌陷、矸石堆放、交通运输、地表水污染和矿井废水。本文主要讨论因煤炭资源的开发引起的地面塌陷对南四湖的环境影响,在分析研究的基础上总结其影响规律。为湖区煤炭规划、开发和建设提供技术依据。     

土壤氡浓度测量在广州市岩溶地面塌陷、地面沉降地质灾害调查中的应用

由于受大型地下工程施工大量抽排地下水的影响,广州市大坦沙和金沙洲先后发生了大规模岩溶地面塌陷、地面沉降地质灾害,为查明区内岩溶发育和断裂带的分布情况,综合运用土壤氡浓度测量、高密度电法、浅层地震反射波、弹性波CT和地质雷达进行探则.由于受各种管线、电磁和震动的干扰,在城市开展电法、磁法、浅层地震等受到限制,而土壤氡浓度测量具有不受地电、地磁和震动干扰的优点.本文以土壤氡浓度测量在广州市金沙洲和大坦沙岩溶地面塌陷、地面沉降地质灾害应用为例,说明了土壤氡浓度测量机理、方法技术和影响因素,结果表明土壤氡浓度测量在广州市金沙洲和大坦沙岩溶地面塌陷、地面沉降地质灾害调查中取得了显著的效果,为广州市金沙洲和大坦沙地质灾害防治提供了基础资料.     

科学解读地面塌陷现象 “天坑”不足惧

地面塌陷往往会导致地面上出现一个大坑,人们称这些大坑为“天坑”。其实,从地质学的角度来讲,近期出现的大部分坑都是地陷洞,而非真正地质学意义上的天坑。     

城市岩溶塌陷灾害风险评估方法：以贵州六盘水市为例

岩溶塌陷是我国岩溶区主要地质灾害,它和崩塌、滑坡、泥石流以及地面沉降、地裂缝等构成我国六大地质灾害类型。随着我国“地质灾害防治管理办法”颁布和实施,不同灾种的风险评估已成为地质灾害防治管理的重要内容。针对城市岩溶塌陷风险评估问题,中国地质科学院岩溶地质研究所塌陷项目组结合多年岩溶塌陷研究的经验,研制开发了基于ＧＩＳ技术的岩溶塌陷灾害管理与风险评估系统（ＧＭＲＳ）。本文以水城盆地为例,全面介绍运用Ｇ     

地震危险性概率分析方法:存在的问题和纠正

地震危险性概率分析(PSHA)是目前最广泛应用于地震灾害与风险性评估的方法。然而它在计算中却存在着一个错误:把强地面运动衰减关系(一个函数)的条件超越概率等同于强地面运动误差(一个变量)的超越概率。这个错误导致了运用强地面运动误差(空间分布特征)去外推强地面运动的发生(时间分布特征)或称之为遍历性假设,同时也造成了对PSHA理解和应用上的困难。本文推导出新的灾害计算方法(称之为KY-PSHA)来纠正这种错误。     

我国地质灾害频繁发生

我国是一个地域辽阔、人口众多、地质灾害多发的国家。地质灾害种类多、分布广、影响大、制约着国民经济的发展 ,威胁着人民的生命和财产的安全。近年来我国地质灾害频繁发生 ,已成为世界上受地质灾害威胁最为严重的国家之一。据统计 ,全国崩塌、滑坡、泥石流灾害点 41万处 ,各类塌陷面积 1 50 0多 km2 ,水土流失面积超过 1 80万 km2 。仅崩塌、滑坡、泥石流灾害每年就造成 90 0多人死亡 ,全国有 40 0多个县 (市 ) ,1万多个村庄受到威胁 ,2 3个省 (区、市 )存在较为严重的地面塌陷 ,1 2个省 (区、市 )存在较为严重的地裂缝 ,1 6个 (区、市 )…     

湖北及邻区的斜坡类型及变形、破坏机理

针对湖北省及邻区地质灾害频发,山体滑坡、地裂缝、地面塌陷较多的事实,根据多年灾害防御工作实践经验,提出了不同地貌条件下的斜坡类型及其变形破坏机理,为国土规划和防灾减灾提供一定的科学依据。     

An efficient method for estimating the collapse risk of structures in seismic regions

Assessing the probability of collapse is a computationally demanding component of performance‐based earthquake engineering. This paper examines various aspects involved in the computation of the mean annual frequency of collapse (λ_c) and proposes an efficient method for estimating the sidesway collapse risk of structures in seismic regions. By deaggregating the mean annual frequency of collapse, it is shown that the mean annual frequency of collapse is typically dominated by earthquake ground motion intensities corresponding to the lower half of the collapse fragility curve. Uncertainty in the collapse fragility curve and mean annual frequency of collapse as a function of the number of ground motions used in calculations is also quantified, and it is shown that using a small number of ground motions can lead to unreliable estimates of a structure's collapse risk. The proposed method is shown to significantly reduce the computational effort and uncertainty in the estimate. Copyright © 2012 John Wiley & Sons, Ltd.     

A parametric study of the required seating length for bridge decks during earthquake

During the recent major earthquakes, some bridges suffered severe damage due to the pull-off-and-drop collapse of their decks. This is due to the large differential movements of the adjacent spans of bridges during strong shaking compared to the seating lengths provided. The differential movements are primarily due to the different vibration properties of adjacent spans and non-uniform ground excitations at the bridge supports. This paper analyses the effects of various bridge and ground motion parameters on the required seating lengths for bridge decks to prevent the pull-off-and-drop collapse. The random vibration method is used in the analysis. A two-span bridge model with different span lengths and vibration frequencies and subjected to various spatially varying ground excitations is analysed. Non-uniform spatial ground motions are modelled by the filtered Tajimi–Kanai power spectral density function and an empirical coherency function. Ground motions with different intensities, different cross-correlations and different site conditions are considered in the study. The required seating lengths for bridge decks are calculated. Numerical results are presented and discussed with respect to different bridge vibration and ground motion properties. © 1998 John Wiley & Sons, Ltd.     

Multiobjective heuristic approaches to seismic design of steel frames with standard sections

Seismic design problem of a steel moment‐resisting frame is formulated as a multiobjective programming problem. The total structural (material) volume and the plastic dissipated energy at the collapse state against severe seismic motions are considered as performance measures. Geometrically nonlinear inelastic time‐history analysis is carried out against recorded ground motions that are incrementally scaled to reach the predefined collapse state. The frame members are chosen from the lists of the available standard sections. Simulated annealing (SA) and tabu search (TS), which are categorized as single‐point‐search heuristics, are applied to the multiobjective optimization problem. It is shown in the numerical examples that the frames that collapse with uniform interstorey drift ratios against various levels of ground motions can be obtained as a set of Pareto optimal solutions. Copyright © 2007 John Wiley & Sons, Ltd.     

Effect of ground motion selection methods on seismic collapse fragility of RC frame buildings

Variation in the seismic collapse fragility of reinforced concrete frame buildings predicted using different ground motion (GM) selection methods is investigated in this paper. To simulate the structural collapse, a fiber‐element modelling approach with path‐dependent cyclic nonlinear material models that account for concrete confinement and crushing, reinforcement buckling as well as low cycle fatigue is used. The adopted fiber analysis approach has been found to reliably predict the loss in vertical load carrying capacity of structural components in addition to the sidesway mode of collapse due to destabilizing P–Δ moments at large inelastic deflections. Multiple stripe analysis is performed by conducting response history analyses at various hazard levels to generate the collapse fragility curves. To select GMs at various hazard levels, two alternatives of uniform hazard spectrum (UHS), conditional mean spectrum (CMS) and generalized conditional intensity measure (GCIM) are used. Collapse analyses are repeated based on structural periods corresponding to initial un‐cracked stiffness and cracked stiffness of the frame members. A return period‐based intensity measure is then introduced and applied in estimating collapse fragility of frame buildings. In line with the results of previous research, it is shown that the choice of structural period significantly affects the collapse fragility predictions. Among the GM selection methods used in this study, GCIM and CMS methods predict similar collapse fragilities for the case study building investigated herein, and UHS provides the most conservative prediction of the collapse capacity, with approximately 40% smaller median collapse capacity compared to the CMS method. The results confirm that collapse probability prediction of buildings using UHS offers a higher level of conservatism in comparison to the other selection methods. Copyright © 2017 John Wiley & Sons, Ltd.     

How is collapse risk of RC buildings affected by the angle of seismic incidence?

Despite the undeniable influence of the angle of seismic incidence on seismic demand, limited research has been performed to determine its effect when assessing the probabilistic seismic performance of a structure. Since the ground motion group size has a well-known significant effect on the variability of collapse risk, the joint effect of both the ground motion group size and the angle of seismic incidence on the estimation of collapse risk is investigated. Results show that the two variables have a different effect on the collapse risk estimates, with one affecting the bias in the expected value of the estimates and the other their variability. In order to ensure acceptable levels of variability and bias, practical proposals are made regarding the minimum number of records and angles of seismic incidence that should be considered.     

Filtered incremental velocity: A novel approach in intensity measures for seismic collapse estimation

This study evaluates the performance of a new intensity measure, referred to as filtered incremental velocity FIV3, which is computed using time-domain features extracted from an acceleration time series and is aimed at the evaluation of structural collapse. This novel approach focuses on the area under a small number of acceleration pulses in the ground motion instead of focusing on the peak response of linear elastic oscillators as in many recently proposed measures of ground motion intensity. FIV3 is developed based on previous research that has highlighted the close relation between the incremental velocity of a ground motion and its potential to induce large inelastic incursions on structures. However, unlike the original definition of incremental velocity which provides a single level of intensity for a ground motion, this new intensity measure is period-dependent and computed as the sum of the three largest incremental velocities obtained from a low-pass filtered ground acceleration time series. Efficiency and sufficiency with respect to several ground motion parameters such as magnitude, source-to-site-distance, spectral shape, scale factor, and duration are carefully evaluated and compared against those computed with some traditional and recently proposed intensity measures using collapse results from a four-story reinforced concrete frame. Results indicate that FIV3 leads to lower variability of collapse estimates and therefore higher efficiency as well as high sufficiency compared with those of other ground motion intensity parameters indicating that this new intensity measure is a promising parameter for structural collapse risk assessment.     

A new approach of selecting real input ground motions for seismic design: The most unfavourable real seismic design ground motions

This paper presents a new way of selecting real input ground motions for seismic design and analysis of structures based on a comprehensive method for estimating the damage potential of ground motions, which takes into consideration of various ground motion parameters and structural seismic damage criteria in terms of strength, deformation, hysteretic energy and dual damage of Park & Ang damage index. The proposed comprehensive method fully involves the effects of the intensity, frequency content and duration of ground motions and the dynamic characteristics of structures. Then, the concept of the most unfavourable real seismic design ground motion is introduced. Based on the concept, the most unfavourable real seismic design ground motions for rock, stiff soil, medium soil and soft soil site conditions are selected in terms of three typical period ranges of structures. The selected real strong motion records are suitable for seismic analysis of important structures whose failure or collapse will be avoided at a higher level of confidence during the strong earthquake, as they can cause the greatest damage to structures and thereby result in the highest damage potential from an extended real ground motion database for a given site. In addition, this paper also presents the real input design ground motions with medium damage potential, which can be used for the seismic analysis of structures located at the area with low and moderate seismicity. The most unfavourable real seismic design ground motions are verified by analysing the seismic response of structures. It is concluded that the most unfavourable real seismic design ground motion approach can select the real ground motions that can result in the highest damage potential for a given structure and site condition, and the real ground motions can be mainly used for structures whose failure or collapse will be avoided at a higher level of confidence during the strong earthquake. Copyright © 2007 John Wiley & Sons, Ltd.     

Collapse assessment of moment frame buildings,considering vertical ground shaking

While many cases of structural damage in past earthquakes have been attributed to strong vertical ground shaking, our understanding of vertical seismic load effects and their influence on collapse mechanisms of buildings is limited. This study quantifies ground motion parameters that are capable of predicting trends in building collapse because of vertical shaking, identifies the types of buildings that are most likely affected by strong vertical ground motions, and investigates the relationship between element level responses and structural collapse under multi‐directional shaking. To do so, two sets of incremental dynamic analyses (IDA) are run on five nonlinear building models of varying height, geometry, and design era. The first IDA is run using the horizontal component alone; the second IDA applies the vertical and horizontal motions simultaneously. When ground motion parameters are considered independently, acceleration‐based measures of the vertical shaking best predict trends in building collapse associated with vertical shaking. When multiple parameters are considered, Housner intensity (SI), computed as a ratio between vertical and horizontal components of a record (SI_V/SI_H), predicts the significance of vertical shaking for collapse. The building with extensive structural cantilevered members is the most influenced by vertical ground shaking, but all frame structures (with either flexural and shear critical columns) are impacted. In addition, the load effect from vertical ground motions is found to be significantly larger than the nominal value used in US building design. Copyright © 2016 John Wiley & Sons, Ltd.     

Variance of collapse capacity of SDOF systems under earthquake excitations

The variance of collapse capacity is an important constituent of probabilistic methodologies used to evaluate the probability of collapse of structures subjected to earthquake ground motions. This study evaluates the effect of ground motion randomness (i.e. record‐to‐record (RTR) variability) and uncertainty in the deterioration parameters of single‐degree‐of‐freedom (SDOF) systems on the variance of collapse capacity. Collapse capacity is evaluated in terms of a relative intensity defined as the ratio of ground motion intensity to a structure strength parameter. The effect of RTR variability on the variance of collapse capacity is directly obtained by performing dynamic analyses of deteriorating hysteretic models for a set of representative ground motions. The first‐order second‐moment (FOSM) method is used to quantify the effect of deterioration parameter uncertainty. In addition to RTR variability, the results indicate that uncertainty in the displacement at the peak (cap) strength and the post‐capping stiffness significantly contribute to the variance of collapse capacity. If large dispersion of these parameters exists, the effect of uncertainty in deterioration parameters on the variance of collapse capacity may be comparable to that caused by RTR variability. Copyright © 2011 John Wiley & Sons, Ltd.     

昆仑山口西8.1级地震的崩塌发育特点

昆仑山口西8．1级地震造成20余处崩塌体或崩塌带，主要分布在地震地表破裂带附近，以库赛湖以西为主。崩塌可分为基岩崩塌、土体崩塌、冰体崩塌、雪崩4种类型。本文对崩塌的空间分布和发育特点进行了分析，通过与其它大地震相比，认为本次地震崩塌规模较小，除介质岩性、地形地貌、气候等因素外，地震动不十分强烈是崩塌规模偏小的重要原因。这种地表破裂带长而地震动偏弱的现象，是本次地震破裂的重要特点，可能与先存断裂的结构有关。