Simplified approach for design of raft foundations against fault rupture.Part II:soil-structure interaction

This is the second paper of two, which describe the results of an integrated research effort to develop a four-step simplified approach for design of raft foundations against dip-slip （normal and thrust） fault rupture. The first two steps dealing with fault rupture propagation in the free-field were presented in the companion paper. This paper develops an approximate analytical method to analyze soil-foundation-structure interaction （SFSI）, involving two additional phenomena： （i） fault rupture diversion （Step 3）; and （ii） modification of the vertical displacement profile （Step 4）. For the first phenomenon （Step 3）, an approximate energy-based approach is developed to estimate the diversion of a fault rupture due to presence of a raft foundation. The normalized critical load for complete diversion is shown to be a function of soil strength, coefficient of earth pressure at rest, bedrock depth, and the horizontal position of the foundation relative to the outcropping fault rupture. For the second phenomenon （Step 4）, a heuristic approach is proposed, which ＂scans＂ through possible equilibrium positions to detect the one that best satisfies force and moment equilibrium. Thus, we account for the strong geometric nonlinearities that govern this interaction, such as uplifting and second order （P-△） effects. Comparisons with centrifuge-validated finite element analyses demonstrate the efficacy of the method. Its simplicity makes possible its utilization for preliminary design.

Soil bentonite wall protects foundation from thrust faulting: analyses and experiment

When seismic thrust faults emerge on the ground surface, they are particularly damaging to buildings, bridges and lifelines that lie on the rupture path. To protect a structure founded on a rigid raft, a thick diaphragm-type soil bentonite wall （SBW） is installed in front of and near the foundation, at sufficient depth to intercept the propagating fault rupture. Extensive numerical analyses, verified against reduced-scale （1 g） split box physical model tests, reveal that such a wall, thanks to its high deformability and low shear resistance, ＂absorbs＂ the compressive thrust of the fault and forces the rupture to deviate upwards along its length. As a consequence, the foundation is left essentially intact. The effectiveness of SBW is demonstrated to depend on the exact location of the emerging fault and the magnitude of the fault offset. When the latter is large, the unprotected foundation experiences intolerable rigid-body rotation even if the foundation structural distress is not substantial.

Simplified approach for design of raft foundations against fault rupture.Part I:free-field

Over the past few decades, earthquake engineering research mainly focused on the effects of strong seismic shaking. After the 1999 earthquakes in Turkey and Taiwan, and thanks to numerous cases where fault rupture caused substantial damage to structures, the importance of faulting-induced deformation has re-emerged. This paper, along with its companion （Part Ⅱ）, exploits parametric results of finite element analyses and centrifuge model testing in developing a four-step semi-analytical approach for analysis of dip-slip （normal and thrust） fault rupture propagation through sand, its emergence on the ground surface, and its interaction with raft foundations. The present paper （Part Ⅰ） focuses on the effects of faulting in the absence of a structure （i.e., in the free-field）. The semi-analytical approach comprises two-steps： the first deals with the rupture path and the estimation of the location of fault outcropping, and the second with the tectonically- induced displacement profile at the ground surface. In both cases, simple mechanical analogues are used to derive simplified semi-analytical expressions. Centrifuge model test data, in combination with parametric results from nonlinear finite element analyses, are utilized for model calibration. The derived semi-analytical expressions are shown to compare reasonably well with more rigorous experimental and theoretical data, thus providing a useful tool for a first estimation of near-fault seismic hazard.

活动断层作用下管土有限单元模型研究

为研究断层作用下埋地管道的力学状态,基于管土相互作用理论,采用固定边界壳单元模型、管壳耦合模型、等效弹簧边界模型、管单元模型4种管土作用模型,对比分析管道穿越断层计算效果。结果表明:4种模型得到的计算应变趋势基本一致,其中固定边界壳单元模型、管壳耦合模型、等效弹簧边界模型结果基本吻合,计算应变大于管单元模型。同时,4种模型均得出管道与走滑断层交叉角不宜为90°。在此基础上,提出有限单元适用的断层工况,并给出相关应用建议。

断层间相互作用的触震与缓震效应定量评价

本文提出了同震库仑应力改变的基本概念 ,应用Navier Coulomb破裂准则 ,探讨了其求解方法 ,从同震库仑应力改变思想出发 ,结合活动断层地震危险性概率预测方法 ,分析了断层间相互作用导致的触震与缓震效应及其定量表达方法 ,并以鲜水河断裂带为例进行了应用研究 ,检验和评价了断层间相互作用触震与缓震效应的重要性。

中上地壳应变分配模型及其地震学研究意义

应变分配 (Strain Partitioning)作为一种基本应变形式 ,即下地壳和岩石圈地幔内的斜向应变在中上地壳内解藕为相互独立的一个正应变分量和一个剪应变分量的现象。在平面上表现为平行排列、同时活动的走滑断裂系统和相应的正应变构造型式。应变分配是一种极为普遍的构造现象。应变分配的发生主要受主断面倾角、与主应力轴交角、区域应力场状态以及构造带结构和物质组成的影响。作为断层相互作用的一种主要模型 ,应变分配模型的最直接证据来源于地震学方面 ,包括震源机制、震源深度及其分区特征等的研究结果。反过来 ,应变分配模型的建立 ,将在确定震源体的独立性、判断震源发震能力、判断地震序列特征、确定地震发展趋势方面为地震科学研究尤其是地震中长期危险性预测研究提供进一步的理论依据。

场地断裂活动效应的风险分析与评价——以宿迁三线船闸为例

断裂研究是区域和场地稳定性评价以及工程抗震设计中的一项重要的基础性工作。对于有断裂通过的工程场地,从断裂、场地土层和工程三者相互作用的角度出发,开展有针对性的场地断裂活动效应及地震稳定性研究,对保证工程的安全建设和可靠运行有着极为重要的现实意义。本文试以宿迁三线船闸的建设为例,对场地断裂活动效应的风险进行分析与评价。

活动断裂地震危险性的研究现状和展望

本文综述了活动断裂地震危险性研究的历史、发展现状、存在的问题及发展方向。在活动断裂地震危险性研究中,重点论述了在概率分析研究阶段地震复发模式、概率模型、断裂间相互作用以及最大震级的评估等问题,指出未来活动断裂地震危险性分析研究的主要发展方向是多学科资料和研究手段、动力环境分析和力学模型的引入。

断层相互作用的初步讨论

给出了半无限介质中任意倾角的多个已发震矩形断层对邻近任意倾角的潜在活断层共同作用的合应力的解析表达式，从而可以计算震后合应力的调整值，为判断潜在活断层的稳定性提供依据。合应力Ｓｒ中既包括了作用在断层面上的正应力，又包括了断层面上的剪应力，它比单独用一个应力描述应力场更有效。最后。

地震中长期预测研究的进展和方向

综述了地震中长期预测的研究历史和发展现状、存在问题及发展方向。地震中长期预测研究大体可以划分为确定性预测研究和概率性预测研究两个主要发展阶段。已有的预测模型和方法在地震复发模式、不确定性分析、断裂之间的相互作用、单一学科面临的资料缺乏等方面存在许多问题。今后一个时期内，地震中长期预测研究的主要发展方向为：建立地震复发模式、建立大陆板内地震复发间隔的通用概率分布模型、活动断裂定量研究资料的应用、不确定性分析、断裂之间的相互作用及其对地震危险性分析的影响以及多学科、多手段的综合运用等。

断层相互作用产生同震库仑应力改变分布图像

讨论了同震库仑应力改变的基本含义,以及基于静应力位错理论求解同震库仑应力改变的边界元方法,对与发震断层相互平行和相互垂直两种典型构造模式下,断层相互作用产生的同震库仑应力改变进行了数值模拟研究,分别获取了相应条件下的同震库仑应力改变空间分布图像.结果表明:不同构造模式的断层相互作用,其产生的同震库仑应力改变分布图像存在较大差异,在分析和评价断层相互作用产生的同震库仑应力改变,及其对活动断层地震危险性的影响时,应该充分考虑待评价断层与发震断层之间的空间几何关系、断层的性质和产状等特定的构造条件.

山西1303年大地震破裂对相邻断裂段地震复发行为的影响

根据历史地震资料分析了山西断陷带中 3个相连接断裂段的地震复发过程及其与130 3年 8级地震的联系。结果发现 :130 3年大地震破裂曾造成相邻断裂段上地震复发行为发生改变 ,其中 ,北邻断裂段的一次地震被提前了 30 0～ 4 0 0a发生 ,南邻断裂段的另一次地震则被推迟了约 30 0a发生 ,而 130 3年破裂过的一部分断裂面很可能长期处于较低的破坏应力下并以中强地震作调整性活动。在未受到 130 3年破裂影响的时期 ,各断裂段的地震复发均表现出时间可预测行为。通常认为 ,一个断裂段的破裂将会造成相连接的邻段至下一次地震时间间隔的缩短 ,但本文却发现这也可造成邻段至下一次地震时间间隔的延长。

活动断层错动引致土壤与结构互制灾害

由历年灾害性地震事件调查资料显示，除了地盘震动、地盘破坏等原因之外，断盘错动导致上覆土层变形，以921集集地震为例，在断层带附近，大多数结构物均遭受到严重损毁。然而少数结构物即使位于断层带，结构体本身却仅有整体位移或转动而未受损。因此断层作用时覆盖断层带上面的土层，在断层作用中所反映的行为与变形对结构物的影响，是该研究的重点。

基于DAB直流变压器的多电压等级交直流混合配电网故障特性分析

双主动全桥(dual active bridge,DAB)直流变压器能够通过直流线路互联多个电压等级的交流配电网形成交直流混合配电网,该系统的故障类型多样,故障特性复杂,该文对其故障特性进行详细研究。分析该系统发生交流网侧单相接地故障、交流阀侧单相接地故障以及直流母线单极接地故障后的故障特性,研究换流站直流侧电容中点采用直接接地和高阻接地两种接地方式的系统中,DAB对系统故障特性的影响。探究发生上述故障后,系统交流侧和直流侧的相互影响,并进行详细对比分析,提出含DAB系统的故障分析方法。最后,通过Matlab仿真平台对上述分析进行仿真验证,指出DAB对直流侧电容中点直接接地系统故障特性的影响更突出,且DAB能够隔离交直流侧故障的相互影响,为交直流混合配电网接地方式的选择、保护系统的设计等提供理论依据。

基于交互式主动探测的电力综合数据网故障定位算法

针对电力综合数据网对故障定位的准确性和时效性要求,提出一种交互式故障诊断机制,并重点解决该机制中故障定位集的选取问题,提出一种基于交互式主动探测的故障定位集选择算法(IPCA)。建立电力综合数据网与候选定位集的贝叶斯模型,借助贝叶斯网络条件独立性将候选定位集划分为若干子集,并引入探测价值衡量探测的诊断能力,利用探测价值交互更新过程的子模性降低故障定位集选取的时间复杂度。仿真结果显示,IPCA在确保故障定位准确性的同时平均可缩短20%左右的定位时间。

Design of bridges against large tectonic deformation

The engineering community has devoted much effort to understanding the response of soil-structure systems to seismic ground motions, but little attention to the effects of an outcropping fault offset. The 1999 earthquakes of Turkey and Taiwan, offering a variety of case histories of structural damage due to faulting, have （re）fueled the interest on the subject. This paper presents a methodology for design of bridges against tectonic deformation. The problem is decoupled in two analysis steps： the first （at the local level） deals with the response of a single pier and its foundation to fault rupture propagating through the soil, and the superstructure is modeled in a simplified manner; and the second （at the global level） investigates detailed models of the superstructure subjected to the support （differential） displacements of Step 1. A parametric study investigates typical models of viaduct and overpass bridges, founded on piles or caissons. Fixed-head piled foundations are shown to be rather vulnerable to faulting-dnduced deformation. End-bearing piles in particular are unable to survive bedrock offsets exceeding 10 cm. Floating piles perform better, and if combined with hinged pile-to-cap connections, they could survive much larger offsets. Soil resilience is beneficial in reducing pile distress. Caisson foundations are almost invariably successful. Statically-indeterminate superstructures are quite vulnerable, while statically-determinate are insensitive （allowing differential displacements and rotations without suffering any distress）. For large-span cantilever-construction bridges, where a statically determinate system is hardly an option, inserting resilient seismic isolation bearings is advantageous as long as ample seating can prevent the deck from falling off the supports. An actual application of the developed method is presented for a major bridge, demonstrating the feasibility of design against tectonic deformation.

Tectonic dynamics and correlation of major earthquake sequences of the Xiaojiang and Qujiang-Shiping fault systems, Yunnan, China

The N-S trending Xiaojiang fault zone and the NW-SE trending Qujiang-Shiping fault zone are adjacent active fault systems and seismogenic zones associated with strong and major earthquakes in Yunnan, China. To understand the interaction of the two fault systems, and its probable influence on earthquake occurrences, this paper conducts a synthetic study based on data of active tectonics, historical earthquakes, relocated small earthquakes, GPS station velocities and focal mechanism resolutions. The study makes several conclusions. （1） The active southward motion of the western side of the Xiaojiang fault zone （i.e. the side of the Sichuan-Yunnan block） has a persistent and intensive effect on the Qujiang-Shiping fault zone. The later fault zone has absorbed and transformed the southward motion of the western side of the former fault zone through dextral strike-slip/sheafing as well as transverse shortening/thrusting. （2） Along the Xiaojiang fault zone, the present sinistral strike-slip/sheafing rate decreases from 10 and 8 mm/a on the northern, central and central-southern segments to 4 mm/a on the southern segment. The decreased rate has been adjusted in the area along and surrounding the Qujiang-Shiping fault zone through reverse-dextral faulting and distributed sheafing and shortening. （3） The tectonic-dynamic relation between the Xiaojiang fault zone and the Qujiang-Shiping fault zone is also manifested by a close correlation of earthquake occurrences on the two fault zones. From 1500 to 1850 a sequence of strong and major earthquakes occurred along the Xiaojiang fault zone and its northern neighbor, the Zemuhe fault zone, which was characterized by gradually accelerating strain release, gradually shortening intervals between M≥7 events, and major releases occurring in the mid to later stages of the sequence. As a response to this sequence, after an 88-year delay, another sequence of 383 years （from 1588 to 1970） of strong and major earthquakes occurred on the Qujiang-Shiping fault zone, and had the same features in accelerating strain release and its temporal course. （4） Since there has been no M≥7 event for 177 years on the Xiaojiang fault zone, the potential risk of a strong or major earthquake occurring on this fault zone in the future should be noticed and studied further.

活动断层的构造地球化学研究现状

活动断层在形成演化过程中经常伴随很多复杂的构造地球化学作用,并导致诸如应力矿物的生长、断层泥矿物颗粒表面微形貌的形成、气体同位素异常等地质现象的出现,它们都可以用来判识活动断层的活动性、启闭性以及断裂带的三维展布状况,尤其是断裂带的深度等问题。因此,有关活动断裂带的断层泥、流体地球化学以及相关的水—岩相互作用等问题一直吸引众多科学家的密切关注,并在许多领域取得了丰硕的成果。但是,由于构造地质作用的极端复杂性,构造地球化学研究也仍然存在一些需要深入探究的科学问题。

基于双核处理器的主动磁悬浮轴承容错控制架构

为了满足针对多自由度磁悬浮支承系统的故障诊断与实时控制需求,提出一种基于异构的双核处理器ARM+DSP架构。硬件配置上以数字信号处理器(digital signal processing,DSP)作为从处理器执行多个环路的故障监测;而高级精简指令集处理器(advanced RISC Machines,ARM)作为主控制器执行转子位置控制算法,并根据从控制器的故障重构控制器而实现容错;软件结构上提出基于双核处理器的信息交互、任务分配与执行的设计方法,设计了双向中断来协调控制与监控代码间的执行时序。试验得到系统故障诊断与实时容错控制仅需1.8 ms,能够满足系统需求。试验结果证明了本研究所提出架构的有效性。