石质构件风化层内力学性能变化规律研究

石质构件风化层内力学参数随深度变化的规律是石质古建筑稳定性、耐久性和保护方案研究中重要的内容。本文针对古建筑石质构件风化层不便取样,风化岩样加工易破坏和室内试验只能得出试件整体的力学参数,不能反映风化层内力学参数由表及里逐渐变化的不足,综合运用现场声波测试和室内试验对义乌宋代古月桥(建于1213年)风化条石的抗压强度、弹性模量与深度的关系进行了研究。研究表明,风化层内岩石弹性模量、抗压强度与未风化区域的比值随深度呈较好的负指数关系。     

The southern Rhine graben: A new view of the initial phase

One of the puzzling features of the southern end of the Rhine graben is the Dinkelberg-Tabular Jura block on the eastern shoulder of the graben. It is dissected by a large number of faults, the most notable ones forming a field of narrow little grabens and half-grabens whose bordering faults converge at the level of the Middle Triassic evaporites, which points to décollement at that horizon. The little grabens were traditionally considered to be of Oligocene age, coeval with the main taphrogenesis of the Rhine graben. Two hypotheses were offered for their formation, one ascribing them to extension on the extrados of large basement folds, the other to gravity sliding on paleoslopes. Recent field work uncovered overwhelming evidence for an Eocene age of the little grabens, the time of the initial phase of Rhine graben formation. At that time there were neither large basement folds nor paleoslopes of any significance, and therefore the two hypotheses offered until now do not work. However, the map-view pattern of the field of faults offers a somewhat unusual way out of the dilemma. This pattern is most prominently displayed in the Dinkelberg area north of the Rhine. There a lane of narrow décollement grabens with a mean NNE strike is confined within the NW- striking Dinkelberg graben, which is much wider and rooted in the basement. It is also very shallow, with a subsidence on the order of 100 m. The lane of décollement grabens forms a dextral en-échelon pattern with respect to the Dinkelberg graben, suggesting stretching of the post-evaporite sequence above a basement essentially extended by strike slip. This model, though not as clearly expressed, is also compatible with the data in the rest of the Dinkelberg-Tabular Jura block. It also fits surprisingly well a theoretical model by Withjack and Scheiner (1982) that predicts a dominance of strike-slip in the marginal area of a system consisting of extension superimposed on doming.     

米箭沟尾矿坝料动力特性试验研究

本文对米箭沟尾矿坝料的组成、结构特征和物理力学性质进行分析,运用振动三轴试验确定尾矿坝料的动力特性参数,分析研究动力特性指标模型,得出动应力、动模量、阻尼比、动剪切摸量随动应变的变化规律,以及动应力与破坏振次,孔压比与振次比的变化规律,并提出符合试验结果的孔压模型,对该尾矿坝的地震动力分析及抗震稳定性评价提供一定科学依据和技术指导。     

青藏高原的热力和动力作用对亚洲季风区环流的影响

利用NCEP/NCAR再分析资料,研究了青藏高原热状况的季节变化、动力和热力作用对周围环流,特别是对亚洲热带季风环流的影响。高原对西风带的机械作用在冬季最强,春季次之。冬季的机械作用形成以高原为主,南侧气旋性、北侧反气旋性的"偶极子"偏差环流,它比传统认识的爬坡、绕流的影响范围大得多,遍及东亚的高、低纬度。随着西风带的北移和高原总加热在4月由负变正,南侧气旋性偏差环流增强并逐渐北移,6月形成气旋盘踞整个高原的夏季型。在高原南侧,高原冬季偶极型、夏季加热的作用导致孟加拉湾地区常年存在印缅槽,使得印度半岛的感热加热始终强于中南半岛,而中南半岛上空的潜热加热大于印度半岛。印缅槽的演变存在明显的半年周期,证明2月初和8月初的较强低压槽分别对应冬季高原最强的动力强迫和夏季高原最强的热力强迫。对低纬经向风场的分析还表明,季风爆发前高原的热力作用尤为重要,是导致江南春雨的形成,亚洲季风最早在孟加拉湾东部爆发,最后在印度半岛爆发的原因。     

An experimental study on using MR damper to mitigate longitudinal seismic response of a suspension bridge

In this paper, the seismic response reduction performance of magnetorheological (MR) damper is experimentally investigated for a suspension bridge. First, the force–displacement and force–velocity curves under a range of excitation frequencies, amplitudes and currents are obtained by mechanical behavior test of the RD1097 type MR damper. Then a new non-linear hysteretic model is proposed to model the mechanical behavior of the MR damper and the model parameters are identified from test data. An experimental method, as well as a set of testing setups with the MR damper for longitudinal seismic response reduction of a SDOF generalized system representing the fundamental longitudinal mode of suspension bridge, is developed. Finally, the seismic response reduction experiment subject to three kinds of earthquake excitations, including the Pingsheng Bridge earthquake wave, the El-Centro wave and the Taft wave, is carried out, and nine control cases, including uncontrolled, six passive control schemes with different input currents and two semi-active Bang–Bang control schemes, are tested. The results verify that the seismic response reduction experimental method is feasible and the good performance of seismic longitudinal response reduction of the suspension bridge can be achieved by MR damper. It is also shown that the passive control with optimum input current outperforms the semi-active Bang–Bang controls.     

循环剪切荷载作用下软土的力学性状研究

利用从现场取得的原状土样,通过室内动三轴试验对循环荷载作用下的变形、孔压和强度特性进行研究。试验研究主要考虑了周围固结压力、循环剪切应力比、荷载频率和循环次数等因素的影响。研究表明,在循环荷载作用下,孔隙水压力和轴向应变均是一个波动上升的过程。当循环应力比增大时,动孔隙水压力变化幅值显著增加,而残余孔压也较大。同时,孔隙水压力值也随着周围压力的增大而明显增大。当作用荷载频率比较大时,需要更多的循环次数才能达到小频率作用荷载能达到的孔隙水压力值。但是,随着循环荷载作用次数的增加,频率对孔隙水压力的影响有减小的趋势。     

秦岭大巴山地形对陕南强降水的影响研究

通过对地形敏感性试验的数值分析,认为大巴山使秦岭山脊、汉江河谷降水减小;使秦岭东南坡和渭河河谷下游强降水增加,大巴山本身降水增加幅度最大;大巴山峡口地形将大量暖湿气流向北输送,在秦岭南侧和东侧的迎风坡上产生强降水,而峡口两侧由于地形阻挡气流通过,使其下游地区降水减少。秦岭使大巴山和汉江河谷、陕北降水增加,使山脉本身降水减少,秦岭山脉对降水的影响主要是通过地形产生的垂直次级环流实现的;秦岭的地形高度变化与山脊降水量具有反相关关系,与山谷降水量关系不明显。     

钙质砂的工程性质研究进展与展望

钙质砂是一种海洋生物成因、碳酸钙含量50%的特殊岩土介质,由于其成因与特殊的组构导致工程力学性质有别于常规的陆源砂,从而引起国内外学者的重视。本文总结了钙质砂国内外研究现状,对其成因与分布、力学性质、钙质砂中基础类型的研究进行了详细的阐述; 以南沙群岛某岛礁修建机场跑道为例,探讨了珊瑚礁地层建设大型工程的可行性。指出今后要加强钙质砂颗粒破碎微观机理研究以及其对钙质砂力学性质的影响机制,建立相应的力学模型; 加强钙质砂中各类基础受力性质研究以及基础设计参数取值研究; 针对岛礁工程的建设,加强岛礁工程地质、岩土体结构与力学性质、礁体稳定性等研究。     

含方解石脉石炭系灰岩单轴压缩的变形破裂特点

沉积岩形成后由于构造运动和热液运移而导致节理裂隙中晶体生长形成岩脉充填,方解石脉充填节理裂隙后与母岩形成整体,公路隧道及边坡工程中会经常遇到岩体中充填有大量的方解石脉。方解石脉与围岩之间的边界由于形成地质结构,所以对于岩体在应力作用下的力学响应具有重要作用,另外方解石脉的充填厚度也会显著影响到岩体的整体力学行为。本次研究从贵州省惠水至兴仁高速公路工程野外露头采集了含有不同厚度方解石脉的石炭纪石灰岩,考虑到不同厚度方解石脉充填以及区域长期降雨过程中水对岩石力学行为影响这两个重要因素,首先对天然以及饱和后的岩石切片开展了矿物组构的统计分析,然后在实验室制备了标准圆柱形岩石试样并开展了天然以及饱和后的单轴压缩力学实验。通过单轴压缩实验获得了试验过程的全应力-应变曲线,针对破裂后试样采用工业CT扫描及三维重构获得了岩石试样中的裂缝形态特点。经过对饱和以及天然状态下含不同厚度方解石岩脉灰岩的力学行为和裂缝分布的分析发现,由于方解石岩脉厚度和含水饱和度的增加,其单轴受压状态下整体塑性显著增加且强度明显降低,岩石饱和后矿物组构的变化以及方解石脉厚度的增加对其力学行为以及破裂模式有明显影响。另外随着方解石脉厚度变化而导致的力学行为变化表明,方解石岩脉充填在岩石中不仅形成地质结构面而影响其力学行为,另外由于与母岩形成整体抵抗变形而导致其力学行为产生显著变化。