A macroscopic damage‐plastic constitutive law for modeling quasi‐brittle fracture and ductile behavior of concrete

A new phenomenological macroscopic constitutive model for the numerical simulation of quasi‐brittle fracture and ductile concrete behavior, under general triaxial stress conditions, is presented. The model is particularly addressed to simulate a wide range of confinement stress states, as also, to capture the strong influence of the mean stress value in the concrete failure mechanisms. The model is based on a two‐surface damage‐plastic formulation. The mechanical behavior in different domains of the stress space is separately described by means of a quasi‐brittle or ductile material response:

相似文献   

四川汶川地震断裂带科学钻探2号孔（WFSD-2）岩性特征和断裂带的结构

以WFSD-2钻孔岩心为研究对象,通过详细的岩心编录和岩石学、构造地质学等研究,识别出该钻孔岩心具有6段岩性,从上向下依次为彭灌杂岩（0-599.31m）、三叠系须家河组二段（599.31-1211.49m）、彭灌杂岩（1211.49-1679.51m）、三叠系须家河组三段（1679.51-1715.48m）、彭灌杂岩（1715.48-2081.47m）、三叠系须家河组四段（2081.47-2283.56m）。彭灌杂岩主要以花岗岩和火山岩为主,三叠系须家河组沉积岩以砂岩、粉砂岩、泥岩、页岩、煤层（线）和砾岩为主。3套彭灌杂岩与三叠系须家河组沉积岩重复出现,时代较老的岩性段逆冲覆盖在新的地层之上,表明龙门山构造带由一系列逆冲岩片叠置而成。岩心中断裂岩较为发育,主要为断层角砾岩、碎裂岩和断层泥,反映出脆性变形作用的特点。通过对断裂岩的统计分析,厘定了20余条产状不同、规模不等的次级断裂带,断裂带宽度和断裂密度峰值显示FZ600、FZ720、FZ782、FZ817、FZ922、FZ951、FZ1449、FZ1681、FZ2082为主要断裂带,其中FZ1681系规模最大的一条断裂。依据断裂岩的组合特征可以将岩心中断裂带的结构以断层泥为核部划分为两大类：对称型断裂带和不对称型断裂带。根据地表破裂带、WFSD-1钻孔岩心中主滑移带位置的几何关系、岩性分层等因素,可推断汶川地震主滑移带应位于FZ1134、FZ1449或FZ1681之中,同时也暗示该地区经常发生类似汶川地震的大地震活动。研究表明,龙门山地区经历了强烈的构造缩短和快速隆升作用,暗示龙门山地区构造活动非常强烈。     

顺层高边坡开挖松动区研究

开挖顺层岩石高边坡,往往需要进行预加固,因而合理确定坡体开挖松动区范围便成为核心问题。根据坡体开挖后的应力和位移状态,给出了开挖松动区的明确定义;结合重庆万州-梁平高速公路沿线各顺层高边坡失稳实例,对顺层高边坡开挖松动区进行了研究,简述了松动区的特点,分析了开挖松动区的影响因素。从岩体结构出发,以开挖深度和岩层倾角为主控元素,对顺层高边坡开挖松动区的长度进行了统计分析,结果表明：岩层倾角在15～30°的砂泥岩顺层高边坡最易产生开挖失稳,且松动区长度与开挖深度有关,二者比值较为集中地分布在2～5之间。     

天然气水合物成矿带的识别技术研究

在天然气水合物的地震资料解释过程中,常规地震剖面上难以识别水合物成矿带的准确位置。通过多年的实践对比研究,认为波形、速度反演、速度模型、流体因子、瞬时振幅、相对极性和能量半衰时等各种地震剖面,能够较好地揭示水合物成矿带的地球物理异常特征。收集整理了一部分国内外对水合物成矿带的识别技术,并提出了在无井的情况下,如何利用波形、速度和各种地震属性剖面所提供的信息来确定水合物成矿带的一些新想法,以期对水合物资源量的评估能提供比较有价值的参考依据。     

土地调查中有关城镇与农村土地面积问题的研究

第二次全国土地调查工作中,城镇与农村地区的土地面积在计算方法上有所不同：农村地区的土地面积是以椭球面为基准的面积,即球面面积;城镇地区的土地面积是以平面为基准的面积,即平面面积。二者之间存在差异并按一定规律变化,当调查区处于投影带边缘附近时,同一图斑的球面面积与平面面积之间的差异达到最大。由于采用不同的计算方法而导致面积数量的差异,在进行农村与城镇有关土地数据整合时会出现矛盾。为了建立城乡统一的土地管理信息系统,保证土地面积的一致性,应当采取相应措施消除二者之间的差异。     

Biostratigraphy of the Garau Formation (Berriasian?–lower Cenomanian) in central part of Lurestan zone,northwest of Zagros,Iran

Deposition of organic rich black shales and dark gray argillaceous limestones in the Berriasian–Turonian interval has been documented in many parts of the world. Northwest of Zagros, Iran (Lurestan zone), thin bedded black shales and marls, dark gray argillaceous limestones and fissile limestone layers, having bitumen, of the Garau Formation are deposited. For biostratigraphic studies two stratigraphic sections including one surface section (Kuzaran) and one subsurface section (Naft well) were selected, respectively. In this study, 61 foraminiferal species belonging to 17 genera have been identified, and 12 biozones were recognized. Based on fossils distribution and biozones identification, the age of the Garau Formation is Berriasian?–early Cenomanian. In addition, the micropalaeontological study demonstrated a variety of widespread morphological changes in planktonic foraminifera assemblages (e.g., the elongation of the final chambers, appearance of twin chambers in the last whorl). These changes coincide with deposition of argillaceous limestones and marls rich in organic matter, indicating oceanic anoxic events. On this basis, three oceanic anoxic events such as OAE1a, OAE1b and OAE1d were recognized in Naft well section and two (OAE1b and OAE1d) in Kuzaran section.     

Electromagnetic emissions during dilating fracture of a rock

A lot of experiments on electromagnetic emissions (EMEs) have been reported under axial compressive fracture, shear fracture, indentation fracture and stick–slip (friction) in lab and blasting in situ, but there are rare reports on the in-lab experimental work on EMEs during dilating fracture of a rock which is helpful in studying and understanding EMEs related to slow earthquakes and the earthquakes due to volcanic activities and water level changes of reservoirs. Therefore, in the present paper in order to check whether there are detectable EMEs during dilating fracture of a rock in lab, dilating fracture experiments were conducted. The dry cuboid specimens of initially intact granodiorite and limestone were tested inside magnetic field free space (MFFS) at room temperature. We arranged evenly 20 EME antennas whose resonance frequencies range from 2.5 kHz to 540 kHz close to rock specimens. Our experimental results strongly indicate that detectable EMEs could generate during dilating fracture of a rock. They were recorded only associated with some but not all phases of fracture. Their waveforms often took on the trend that a peak arrived at first and then attenuated sharply and followed by a series of low-amplitude oscillations. The electromagnetic (EM) signals after eliminating the effects of EME antennae via deconvolution had the maximum peak-to-peak amplitudes of about 80.0 mV and 40.5 mV for granodiorite and limestone, respectively. Their main spectral components often concentrated in the band of several kHz to ∼60 kHz and of several kHz to ∼280 kHz. The emission of electrons and charged particles from fracture surfaces and/or micro-fracture electrification could be possible mechanisms for our experimental results.     

气井水力压裂有效缝长评估及影响因素研究

为了准确确定气井压后有效缝长及其影响因素,提高川西须家河气藏水力压裂针对性,对于具备生产历史拟合条件的气井,利用数值模拟软件进行了生产历史拟合获得有效水力裂缝缝长,与采用净压力拟合方法获得的水力裂缝支撑缝长进行对比和拟合,获得了有效缝长和支撑缝长的关系式,计算了川西须家河储层单井压后有效缝长;采用灰色关联分析理论分析了各个参数对有效缝长的影响程度和对压裂设计的启示。结果表明：压后有效缝长与支撑缝长具有较强相关性(Le=00584 Lp1359 3),有效缝长明显比支撑缝长短;施工参数(特别是用液量)是影响须家河储层有效缝长的关键,而储层和隔层间应力差则是影响有效缝长的重要客观因素。该研究方法为水力压裂压后评估和提高压裂设计水平提供了较好的借鉴。     

冷冻固定化优势菌群处理含甲醛苯酚废水

包气带土壤中氨氮污染迁移规律已成为近年来国内外学者研究的重点,目前在氨氮污染迁移规律研究中采用柱实验模拟以及软件模拟的方法较多,土壤生物技术则广泛应用于污染物降解领域,而在污染物迁移规律研究中应用较少。本文采用变性梯度凝胶电泳(DGGE)技术、16S rRNA序列分析技术以及典范对应分析相结合,对华北平原3个典型氨氮污染区土壤表层至包气带剖面微环境的细菌垂直分布特征及群落结构进行研究。结合污染区土壤理化性质分析,认为包气带土壤剖面的细菌群落中存在着与氮循环、硫酸盐代谢等过程偶联的优势细菌类群,说明土壤微环境中细菌群落分布明显受氨态氮、硝态氮、亚硝态氮和硫酸盐的分布影响,进一步表明污染土壤优势菌群的群落结构信息是描述包气带土壤环境氨氮污染物迁移规律的重要参数。     

二连盆地可地浸砂岩型铀成矿的再认识

笔者从铀成矿条件入手 ,分析了二连盆地在基底演化期、含矿建造形成期以及后生改造成矿期各阶段对可地浸砂岩型铀矿的控制作用 ,认为二连盆地在含矿建造形成期是由众多分割性强的 ,构造演化和沉积变迁自成体系 ,并具有多物源、近物源特点的小凹陷所组成。同时 ,综合其他控制砂岩型铀矿的因素 ,确定了二连盆地是以发育潜水 层间氧化带砂岩型铀矿为其主要成矿类型 ,且矿床规模以中、小型为主 ,具有成群成带产出的特点。