基于PFC2D数值模拟的交替压裂中应力阴影效应研究     

夏磊  曾亚武 《岩土力学》2018,39(11):4269-4277

为了探究应力阴影效应对交替压裂中压裂间距选取的影响,基于优化后的颗粒流离散元流固耦合计算模型,模拟并分析了双初始水力裂缝下因应力阴影效应产生的诱导应力的分布情况,并与理论解析解进行对比,证明了该数值方法的合理性。在此基础上,分析了应力阴影效应在不同各向异性地应力场及初始压裂间距条件下对新水力裂缝的起裂压力及扩展形态的影响,研究结果表明：初始各向异性应力场不改变裂缝周边的应力场,不影响新水力裂缝的起裂压力;随着初始压裂间距的减小,应力阴影效应增强,新水力裂缝的起裂压力逐渐增加。初始水力裂缝间距与初始各向异性应力场共同影响新水力裂缝的扩展形态,随着初始水力裂缝间距或初始水平地应力场差异系数的增大,应力阴影对新水力裂缝的扩展方向的影响逐步减弱;初始水力裂缝对新水力裂缝的扩展有一定的限制作用,在一定程度上不利于形成复杂的裂缝网络。根据以上分析结果,对交替压裂中压裂间距的优化进行了定性的探讨。  相似文献   

Coiled nautiloid cephalopods from the British Silurian     

Charles Hepworth Holland 《Proceedings of the Geologists' Association. Geologists' Association》2010,121(1):13-23

Coiled nautiloid cephalopods from the British Silurian are described and their taxonomy revised. The Order Oncocerida is represented by a single specimen of Oxygonioceras oxynotum. Twelve species from the Order Tarphycerida (within which is here subsumed the Order Barrandeocerida) are described: one of Trocholites, two of Ophioceras, two of Catyrephoceras, three of Lechitrochoceras, one of Peismoceras, two of Systrophoceras, and one of Uranoceras. Their distribution, stratigraphical and geographical, is indicated.  相似文献   

扎龙湿地表层沉积物磷的赋存形态及空间分布特征   总被引：2，自引：0，他引：2  

叶华香  臧淑英  贾晓丹  苏丹 《地理与地理信息科学》2012,28(2):108-112

沉积物中不同形态的磷具有不同的地球化学行为和生物有效性,其含量和分布特征包含着许多环境地球化学信息。该文利用SMT法对扎龙湿地表层沉积物中总磷(TP)及各形态磷进行了分析,探讨其空间分布特征及控制因素。结果表明,扎龙湿地表层沉积物TP含量高,接近于富营养化严重的太湖和巢湖,主要分布于核心区和东北部;无机磷(IP)含量稍高于有机磷(OP),其分布特征都与TP相似。IP中的钙结合态磷(Ca-P)和铁铝结合态磷(Fe/Al-P)空间分布差异性较小,Ca-P含量占IP的59.2%。TP及各形态磷含量受粒度、有机质、pH及溶解氧等环境因子的影响,造成扎龙湿地水体富营养化的污染物质主要来自外源;但随着湿地盐碱化加重、生态环境破坏及植被覆盖度下降,沉积物内源磷的释放将成为扎龙湿地水体富营养化的重要来源,将直接加剧水体富营养化程度,尤其增加核心区水体富营养化的风险。  相似文献   

Bab Agnaou gate, Marrakech, Morocco: characterization of original building material and commentary on their state of conservation     

K. Benzzi  B. Tanouti  M. Bouabdelli  A. Alvarez  J. L. Brianso  F. Cherradi 《Environmental Geology》2006,51(2):275-282

Bab Agnaou is the most ancient gate sculpted in stone during the Almohad era (twelfth century). The petrographic and mineralogical studies were carried out in order to characterize the original materials of construction. So the ashlar is a calcareous mudstone, whereas the mortar is one with lime binder. The characterization of the ashlar’s degradation state, based on the mapping of the gate, permitted to highlight the evolution, the extension and the relation between the different weathering forms. Thus it proved to be possible to distinguish the weathering forms related to architecture and the provision of the blocks, from those related to infiltration of water.  相似文献   

Stereographic Projections of Symmetry Elements and Single Forms on Quasicrystals     

ChenYing PengJue ChenJingzhong LongGuangzhi 《中国地质大学学报(英文版)》2005,16(1):16-23

INTRODUCTIONThe stereographic projection of symmetry ele ments and the single forms of crystals is very system atic in classical crystallography. Shechtman et al.( 1984 ) reported the existence of a metallic solidwhich diffracted electro…  相似文献   

Phosphorus fractions in sediment profiles and their potential contributions to eutrophication in Dianchi Lake   总被引：5，自引：0，他引：5  

Li Gao  Jianmin M. Zhou  Hao Yang  Jie Chen 《Environmental Geology》2005,48(7):835-844

Dianchi Lake is a eutrophic lake in southwestern China. Sediment and the bottom water samples were taken from six sites in the east, west, south, north and center of the lake, respectively, in December 2002. Total phosphorus (TP) concentrations in sediments were high and reached a maximum value of 6.66 g/kg. There was a soluble reactive phosphorus (SRP) concentration gradient at the sediment–water interface. In the present study, sediment P was divided into loosely adsorbed P (NH₄Cl-P), redox-sensitive P (BD-P), metal oxides bound P (NaOH-P), calcium bound P (HCl-P), and organic P (Org-P). At three of the six sites selected, the concentrations of different P forms in sediments followed the order: NaOH-P, Org-P>HCl-P>BD-P>NH₄Cl-P in the profile, and in the southern lake the order was HCl-P>NaOH-P, Org-P>BD-P>NH₄Cl-P in the top 15 cm layers of the sediments. The sediment profiles showed that different forms of P had an increasing trend upward toward the sediment surface. There is a considerable potential for release from the sediment into the overlying water and sediment P could be the dominant factor determining the trophic status of the lake if the external load is reduced. An erratum to this article can be found at  相似文献   

Formation and preservation of open-framework gravel strata in unidirectional flows   总被引：1，自引：0，他引：1  

I. A. LUNT  J. S. BRIDGE 《Sedimentology》2007,54(1):71-87

Open‐framework gravel (OFG) in river deposits is important because of its exceptionally high permeability, resulting from the lack of sediment in the pore spaces between the gravel grains. Fluvial OFG occurs as planar strata and cross strata of varying scale, and is interbedded with sand and sandy gravel. The origin of OFG has been related to: (1) proportion of sand available relative to gravel; (2) separation of sand from gravel during a specific flow stage and sediment transport rate (either high, falling or low); (3) separation of sand from gravel in bedforms superimposed on the backs of larger bedforms; (4) flow separation in the lee of dunes or unit bars. Laboratory flume experiments were undertaken to test and develop these theories for the origin of OFG. Bed sediment size distribution (sandy gravel with a mean diameter of 1·5 mm) was kept constant, but flow depth, flow velocity and aggradation rate were varied. Bedforms produced under these flow conditions were bedload sheets, dunes and unit bars. The fundamental cause of OFG is the sorting of sand from gravel associated with flow separation at the crest of bedforms, and further segregation of grain sizes during avalanching on the steep lee side. Sand in transport near the bed is deposited in the trough of the bedform, whereas bed‐load gravel avalanches down the leeside and overruns the sand in the trough. The effectiveness of this sorting mechanism increases as the height of the bedform increases. Infiltration of sand into the gravel framework is of minor importance in these experiments, and occurs mainly in bedform troughs. The geometry and proportion of OFG in fluvial deposits are influenced by variation in height of bedforms as they migrate, superposition of small bedforms on the backs of larger bedforms, aggradation rate, and changes in sediment supply. If the height of a bedform increases as it migrates downstream, so does the amount of OFG. Changes in the character of OFG on the lee‐side of unit bars depend on grain‐size sorting in the superimposed bedforms (dunes and bedload sheets). Thick deposits of cross‐stratified OFG require high bedforms (dunes, unit bars) and large amounts of aggradation. These conditions might be expected to occur during high falling stages in the deeper parts of river channels adjacent to compound‐bar tails and downstream of confluence scours. Increase in the amount of sand supplied relative to gravel reduces the development of OFG. Such increases in sand supply may be related to falling flow stage and/or upstream erosion of sandy deposits.  相似文献   

Chemical characteristics of aerosols in the Kuroshio area     

Chen Liqi  Yu Qun  Yang Xulin  Tang Rongkun 《中国海洋湖沼学报》1993,11(4):351-359

Aerosol samples were collected with a Sierrer Model 235 cascade impactor in the marine atmosphere over the Kuroshio area in consecutive four seasons from 1987 to 1988. Na, Cl, Al, V, and water soluble and acid soluble Mn, Fe, Pb, Cu, V, Cd were determined by neutron activation analysis and atomic absorption spectrophotometry, respectively. Seawater source chemical species in the aerosols appeared in high content in large over 3.6 μm diameter particles, and crustal source vanadium appeared in 3.6 μm diameter particles, but pollution source vanadium appeared in less than 0.52 μm diameter particles. Trace metals in the aerosols mostly had the highest concentration of water soluble metals on fine particles, and acid soluble metals on large particles. The concentrations of trace metals in the aerosols were higher in autumn and winter, lower in spring and summer. Funds from the National Natural Science Foundation of China.  相似文献   

河湾形态演变的自组织及其稳定性          下载免费PDF全文

汪富泉  曹叔尤  丁晶 《水科学进展》2001,12(1):7-16

运用自组织理论和方法建立河湾的演化方程.结合Fokker-Planck方程解析解的性质与Langevin方程的动力学特征,推断河湾演变的基本规律如对称破缺、形态转变、演变趋势及速度等.然后根据数学模型与理论分析结果,研究长江洲湾,下荆江尺八口、上车湾、碾子湾等实际河湾演变的自组织规律及其稳定性特征.理论推导结果与实际观测资料基本一致  相似文献   

Three Dimensional Plate Kinematics in Romania     

Dinter  Georg  Schmitt  Günter 《Natural Hazards》2001,23(2-3):389-406

Since 1996 the Collaborative Research Center (CRC) 461``Strong Earthquakes: A Challenge for Geosciences andCivil Engineering' is funded by the DeutscheForschungsgemeinschaft (German Research Foundation) asa German contribution to the UN initiative``International Decade of Disaster Reduction' (IDNDR).A central project of this CRC is the subproject B1``Three Dimensional Plate Kinematics in Romania', whichis installed to detect borders of the geotectonicplates in Romania, to quantify their three-dimensionalmovement rates and to determine in detail thedeformation of each geotectonic unit in the VranceaRegion as a contribution to the research of thetectonic cause of the intermediate depth earthquakesin this region. These aims shall be accomplished byrepeated GPS-measurements in a network which has beeninstalled in 1997 and measured until now in 1997 and1998. This network is consisting of 26 stations,covering an area of 250 km × 380 km with the Vranceaarea as the centre. The geodetic frame is given by sixstations of the CEGRN (Central European GeodynamicRegional Network) of the CEI-initiative CERGOP, forwhich coordinates and velocities in a global tectonicscenario are available. The paper gives informationabout the tectonic background, the geodetic network,the GPS-measurements and the achieved accuracies andfirst results of deformation analyses. It is shownthat until now no significant deformations could bedetected. But the extension of the GPS network andremeasurements with time intervals of two years willallow statements about the recent crustal movementswithin the lifetime of the CRC 461.  相似文献