A study of the effect of local scour on the flow field near the spur dike

The flow field near a spur dike such as down flow and horseshoe vortex system(HVS)are susceptible to the topographic changes in the local scouring process,resulting in variation of the sediment transport with time.In this study,large eddy simulations with fixed-bed at different scouring stages were conducted to investigate the changes in flow field.The results imply that the bed deformation leads to an increase in flow rate per unit area,which represent the capability of sediment transportation by water,in the scour hole.Moreover,the intensity of turbulent kinetic energy and bimodal motion near the sand bed induced by the HVS were also varied.However,the peak moments between the two sediment transport mechanisms were different.Hence,understanding the complex feedback mechanism between topography and flow field is essential for the local scour problem.

A Comparative Study of Ore-bearing Dikes and a Barren Dike in the Zaozigou Gold Deposit,Western Qinling:Zircon Morphology,U-Pb Chronology and Geochemical Constraints

The Zaozigou gold deposit lies south of the Xiahe-Hezuo regional fault zone in the western Qinling orogenic belt and contains many intermediate to felsic dikes.Diorite porphyry,quartz diorite porphyry and biotite diorite porphyry are mineral-bearing dikes,whereas granite porphyry is unrelated to gold mineralization.To compare the relationship between different dikes and mineralization,this study analyzed the cathodoluminescence(CL)of zircon crystals in all four types of dikes exposed in the Zaozigou deposit,using a zircon typological classification.The formation temperature of the granite porphyry(734°C)was higher than the average temperature of the other three types of dikes(704°C),whereas the former’s alkalinity index(395)was lower than the average alkalinity index of the other three dikes(425).TheΣREE amount of granite porphyry(147.18 ppm)was smaller than the averageΣREE amount of the other three dikes(246.80 ppm)and itsδEu value(0.33)was larger than the averageδEu values of the other three dikes(0.30).The U-Pb ages of zircon in the four types of dikes were relatively consistent with the crystallization ages of approximately 240 Ma,which indicates that all four types of dikes intruded in the Middle Triassic.Compared to the other three ore-bearing dikes,the morphology of the zircon crystals in the barren dikes evolved from S13 to S5 and then returned to S13.These results indicate that the barren dike underwent an increase in temperature and a decrease in alkalinity,which may be an important reason for the absence of mineralization.

Solution to the Breach of the Dike of Keur Bara KAIRE, Located in the Commune of Notto Diobasse in the Department of Thiès, Senegal

This article studies the rupture of the Keur Bara KAIRE dike, located in the commune of Notto Diobasse in the department of Thiès in Senegal. The village is crossed by a stream which collects rainwater from the west to the east, following a natural slope. The overflow of this stream causes serious flooding, leading to the total cutting of the road and the isolation of the population. These floods had tragic consequences, resulting in two losses of human life. To regulate the water level, prevent flooding, and protect agricultural and urban areas from overflows, the Senegalese authorities initiated the project to build the Keur Bara KAIRE dike in 2004, but unfortunately, the latter gave way in 2017. The geotechnical analysis was carried out on samples taken from various points on the site, revealing that the terrain is mainly composed of fine sand and the embankment is made with clayey sand. Morphometric and hydrological investigations highlight that the watershed of the Keur Bara KAIRE dike covers an area of 3.72 km2, with a projected flow of 54.99 m3/s. The resizing of the dike revealed the following data: a length of 132 meters and a height of 3 meters. The spillway is 52.99 meters long with a reservoir height of 1.22 meters. The bay walls have a thickness of 50 cm and the embankments have a slope of 1/2 upstream and downstream. The stability calculation on the broken dike reveals a sliding safety factor (FSG) of 1.84 which complies with the standard and an overturning safety factor (FSR) of 0.13 which is not verified. The surface of the watershed which is equal to 3.72 km2, also the smallest height of precipitation is equal to 234.9 mm and the largest is 664.4 mm, according to the ORSTOM and CIEH methods for hydraulic calculations.

双岸整治下插板透水丁坝调控区水流特性研究

为治理塔里木河新其满#3引水口河段,运用插板透水丁坝进行双岸整治,并采用CCHE2D对塔里木河新其满河段#3引水实体水槽模型进行数值模拟,分析了双岸整治下插板透水丁坝不同间距对各调控区水面线、流速、切应力及分水束流的影响规律。结果表明,受到双岸插板透水丁坝调控作用,在Ⅰ、Ⅱ区形成缓流促淤区、Ⅲ区形成束流冲刷区;随丁坝间距增大,各调控区流速减小,缓流率增大;上游丁坝水位雍高值及切应力越小,下游水位雍高值及切应力越大;在Ⅰ、Ⅱ区分流比减小,Ⅲ区束流率增大。当L=4b时,Ⅰ、Ⅱ区缓流率最大为53.2%、93.8%,分流比最小为7.28%、7.14%,Ⅲ区输水输沙能力较单岸丁坝明显增大且具有一定的分水束流作用。研究成果可完善双岸整治下塔里木河河道整治及防护工程研究理论。

法律何以成为正义——从themis到dike

法律女神忒弥斯代表着西方最早的规范性思想,后来却逐渐为"正义"所取代。themis(法律)与dike(正义)本身有着深刻而密切的联系,由于都具有"审判"的涵义,二者逐渐合流,dike取代了themis而上升为社会生活的主导规范。在这个过程中,本来主要指"审判"的dike吸收了审判过程的"公正"要求,变成了一种伦理品质,即"正义"。dike继承并集成了themis的众多属性,其内涵从司法领域上升到伦理政治的高度,逐渐取代了神法themis。这充分证明,法律的本质就在于正义。

基于UDEC的岩脉侵入角度对隧道安全影响分析

为探究岩脉侵入角度对隧道开挖的影响,文章以泸石高速石棉隧道开挖时地层遭遇不同角度岩脉侵入为工程背景,通过UDEC离散元计算,总结岩脉侵入角度对隧道开挖的影响,给出有效处理措施,并得出以下结论:岩脉和被侵入岩体界面易发生塑性滑移,隧道开挖后岩脉区围岩变形最大,且岩脉区围岩有开裂、滑移和隆起现象,围岩变形随角度的减小而减小。边墙与仰拱连接处轴力、剪力、弯矩均最大,安全系数最小,三种工况均在0.3左右。衬砌轴力、剪力的最大值随角度减小而增大,弯矩受角度的影响较小。岩脉区域的安全系数在向着岩脉倾斜方向更小。岩脉侵入区域隧道开挖应采用岩脉区域局部注浆、封闭仰拱、增大衬砌厚度三种方法来加固围岩和提高衬砌承载能力。

低含沙条件下长江口丁坝群冲淤及水动力变化特点

为研究丁坝群工程在低含沙条件下的保滩效果及其与水动力的响应关系,采用青草沙水库北堤外侧2014—2021年实测水下地形数据,定量分析丁坝群工程实施后区域的滩槽冲淤演变特点,基于MIKE21数值模型模拟丁坝群工程在2014与2021年地形条件下的水动力与正向风浪特点。结果表明:青草沙水库北堤丁坝群工程实施后,坝田滩地在2014—2021年间出现了最大厚度近10 m的淤积,滩地高程淤积至0 m附近后保持稳定、冲淤速度变缓,形成的岸坡比降在1:3~1:5;丁坝群头部无冲刷坑形成,与外侧新桥通道底高程在丁坝群实施前已达到-15 m有关;随着坝田滩地的整体淤高,近主槽侧滩面涨落潮流速均呈增大趋势,模拟条件下的高低潮位、有效波高变幅小于0.03 m,基本未受到坝田淤高的影响。丁坝群工程在低含沙条件下仍具有固沙保滩效果,可为长江口水流冲蚀堤岸的护滩带建设提供基础。

粤西北禾洞地区基性岩脉锆石U-Pb年代学、地球化学特征及其构造意义

粤西北禾洞地区处于南岭成矿带中段,主要产有花岗岩型铀矿床和众多铀矿化异常。区内构造岩浆活动频繁,不仅出露加里东期永和岩体、印支期太保岩体和燕山早期禾洞岩体,而且出露不同类型的岩脉。基性岩脉对于研究壳幔相互作用、地幔物质组成、恢复古构造环境具有重要意义。由于连山县禾洞—太保地区零星出露的镁铁质岩研究程度较低,文章从岩石学、年代学和主微量地球化学等方面探讨了其岩石类型、成岩时代、源区性质及形成的构造背景。基性岩脉的岩性主要为变余辉绿(玢)岩,形成时代为晚侏罗世(154.6 Ma±0.9 Ma)。地球化学分析显示,岩石具低硅(SiO_(2)=45.65%~47.79%),高碱(ALK=4.16%~6.27%),富镁铁(TFeO+MgO=16.22%~17.41%),Mg^(#)(58~62)略低于原始岩浆值,稀土元素总量高,负Eu异常,相对富集大离子亲石元素Rb、U,相对亏损Ba、Sr、Th,且贫Nb、Ta、Ti、Zr、P等高场强元素的特征,指示其为碱性玄武岩系列。各类元素参数特征显示其具壳幔混合的源区性质,可能系俯冲物质交代的富集地幔岩浆上升过程中与地壳围岩发生了同化混染作用,兼具大陆裂谷和俯冲带玄武质岩石的特点。结合中生代区域构造演化历史及成岩成矿地质背景,认为粤西北禾洞地区基性岩脉的形成与古太平洋俯冲引起的陆内岩石圈伸展机制有关。

K-Ar Geochronology of Mesozoic Mafic Dikes in Shandong Province, Eastern China: Implications for Crustal Extension

Based on K-Ar isotope analyses, Mesozoic mafic (and alkali ultramafic) dikes from western and eastern Shandong Province, China, are dated at 88.2±1.70 Ma to 169.5±3.7 Ma with the majority of ages ranging from 90 Ma to 140 Ma. The emplacement of the dikes suggests a major Yanshanian (Cretaceous) crustal extension in Shandong province. Together with other available age data, this study suggests four periods of crustal extension at about 80 Ma, 100 Ma, 120 Ma and 140 Ma, respectively. Besides the effect of collapse of the Yanshanian orogenic belt on the emplacement of the mafic dikes in Shandong in the Cretaceous, the mantle plume and the extensive left-lateral advection and extension of the Tanlu fault also have controlled the crustal extension and the emplacement of the mafic dikes in eastern Shandong and western Shandong, respectively.

Geochemical Characteristics and Genesis of the Luxi-Xianrenzhang Diabase Dikes in Xiazhuang Uranium Orefield, Northern Guangdong Province

The Luxi-Xianrenzhang diabase dikes were emplaced into the eastern part of the Guidong composite granitoids in northern Guangdong Province at the end of the Early Cretaceous. They show tholeiitic features, enrichment in large ion lithophile elements, slight enrichment in light rare earth elements, depletion in Zr and Hf, and basically no depletion in Nb and Ta and no Eu anomaly. They are similar to intraplate basalt in terms of trace element characteristics. They have high εNd（t） values （3.6-4.9）, initial ^87Sr/^86Sr ratios （0.70530-70641） and δ^18O values and Dupal anomaly of Pb isotope compositions. Their Sr-Nd, Pb-Sr, Pb-Nd and Pb-Pb isotopes plot between DMM and EMII, with Pb similar to EMII, Nd relatively close to DMM and Sr in between. This profile suggests that the diabase dikes studied were derived from partial melting of a mantle source that had been subjected to metasomatism by fluids originated from a subduction zone under a tectonic environment of crustal extension and lithosphere thinning in the late Yanshanian.

Experiments and numerical simulations on transport of dissolved pollutants around spur dike

The flow field around a spur dike has three-dimensional characteristics. In order to analyze the influence of the flow field on pollutant transport, based on a compressive volume of fluid （VOF） scheme, the three-dimensional transient compressive pollutant transport model （CPTM） and the cubic equation （CE） bounded differencing scheme were developed. For the calibration and validation of CPTM, laboratory experiments were carried out in a flume with a non-submerged spur dike. The spur dike was angled at 60°, 90°, and 120° from the upstream direction. The simulation results agreed with the experimental results. The simulations and experiments showed that the distribution of pollutant concentration was determined by circumfluence and the main flow. Concentration decay in the circumfluenee zone was slower than that in the main flow. Downstream of the spur dike, the concentration fluctuation became intensive with the increase of spur dike angle.

Identification of Five Stages of Dike Swarms in the Shanxi-Hebei-Inner Mongolia Border Area and Its Tectonic Implications

Dike swarms are generally ascribed to intrusion of mantle-source magma result from extension. Basic dike swarms around the Shanxi-Hebei-Inner Mogolia borders in the northern peripheral area of the North China Craton can be divided into five age groups according to isotopic dating: 1800-1700 Ma, 800-700 Ma, 230 Ma, 140-120 Ma, and 50-40 Ma. Geological, petrological and isotope geochemical features of the five groups is investigated in order to explore the variation of the mantle material composition in the concerned area with time. And the various extensional activities reflected by the five groups of dike swarms are compared with some important tectonic events within the North China Craton as well as around the world during the same period.

Stability of the Guiding Dike in Yangtze Estuary Under the Wave Load

During the construction of the guiding dike in the Yangtze Estuary, some of the caisson structures sank into the soil for 1 -5 m or slid about 20 m away from the original place when a strong storm attacked this area. Dynamic triaxial tests were carried out to simulate the behavior of foundation soils under wave loading. The test results show that the excessive settlement and lateral movement of the caissons are due to the weakening of the soft clay strength during the strong storm. The test results also show that the ability of the soft clay to resist the wave force will be greatly increased when the soft soil samples are suitably improved. Based on the test results, an improvement method combining vertical drains with surcharge loading was proposed to strengthen the foundation soil. On the improved soil foundation, the dike has been reconstructed and undergone several strong storms without any damage. A finite element approach has been developed for analyzing the settlement and stability of the dike under the action of strong storm.

Minimum critical thickness of dike for ore-bearing fluid injection:A new approach applied to the Shihu gold deposit,Hebei Province,North China

According to the metallogenic theory by transmagmatic fluid （TMF）, one magmatic intrusion is a channel of ore-bearing fluids, but not their source. Therefore, it is possible to use TMF＇s ability for injection into and for escaping t^om the magmatic intrusion to evaluate its ore-forming potential. As the ore-bearing fluids cannot effectively inject into the magmatic intrusion when the magma fully crystal- lized, the cooling time and rates viscosity varied can be used to estimate the minimum critical thickness of the intrusion. One dimensional heat transfer model is used to determine the cooling time for three representative dikes of different composition （granite porphyry, quartz diorite and diabase） in the Shihu gold deposit. It also estimated the rates viscosity varied in these time interval. We took the thickness of dike at the intersection of the cooling time -- thickness curve and the rates viscosity varied versus thick- ness curve as the minimum critical thickness. For the ore-bearing fluids effectively injecting into the magma, the minimum critical thicknesses for the three representative dikes are 33.45 m for granite porphyry, 8.22 m for quartz diorite and 1.02 m for diabase, indicating that ore-bearing dikes must be thicker than each value. These results are consistent with the occurrence of ore bodies, and thus they could be applied in practice. Based on the statistical relationship between the length and the width of dikes, these critical thicknesses are used to compute critical areas： 0.0003--0.0016 km2 for diabase, 0.014--0.068 km2 for quartz diorite and 0.011-0.034 km2 for granite porphyry. This implies that ore- bearing minor intrusions have varied areas corresponding to their composition. The numerical simulation has provided the theoretical threshold of exposed thickness and area of the ore-bearing intrusion. These values can be used to determine the ore-forming potentials of dikes.

Risk Analysis and Assessment of Overtopping Concerning Sea Dikes in the Case of Storm Surge

Risk analysis and assessment relating coastal structures has been one of the hot topics in the area of coastal protection recently. In this paper, from three aspects of joint return period of multiple loads, dike failure rate and dike continuous risk prevention respectively, three new risk analysis methods concerning overtopping of sea dikes are developed. It is worth noting that the factors of storm surge which leads to overtopping are also considered in the three methods. In order to verify and estimate the effectiveness and reliability of the newly developed methods, quantified mutual information is adopted. By means of case testing, it can be found that different prior variables might be selected dividedly, according to the requirement of special engineering application or the dominance of loads. Based on the selection of prior variables, the correlating risk analysis method can be successfully applied to practical engineering.

Ordovician Granitoids and Silurian Mafic Dikes in the Western Kunlun Orogen, Northwest China:Implications for Evolution of the Proto-Tethys

The western Kunlun orogen in the northwest Tibet Plateau is related to subduction and collision of Proto-and Paleo-Tethys from early Paleozoic to early Mesozoic. This paper presents new LA-ICPMS zircon U-Pb ages and Lu-Hf isotopes, whole-rock major and trace elements, and Sr–Nd isotopes of two Ordovician granitoid plutons(466–455 Ma) and their Silurian mafic dikes(～436 Ma) in the western Kunlun orogen. These granitoids show peraluminous high-K calcalkaline characteristics, with(^(87)Sr/^(86)Sr)_i value of 0.7129–0.7224, ε_(Nd)(t) values of -9.3 to -7.0 and zircon ε_(Hf)(t) values of -17.3 to -0.2, indicating that they were formed by partial melting of ancient lower-crust(metaigneous rocks mixed with metasedimentary rocks) with some mantle materials in response to subduction of the Proto-Tethyan Ocean and following collision. The Silurian mafic dikes were considered to have been derived from a low degree of partial melting of primary mafic magma. These mafic dikes show initial ^(87)Sr/^(86)Sr ratios of 0.7101–0.7152 and ε_(Nd)(t) values of -3.8 to -3.4 and zircon ε_(Hf)(t) values of -8.8 to -4.9, indicating that they were derived from enriched mantle in response to post-collisional slab break-off. Combined with regional geology, our new data provide valuable insight into late evolution of the Proto-Tethys.

Influence of Spur Dike on Hydrodynamic Exchange Between Channel and Shoal of Generalization Estuary in Physical Model Test

Widely applied in maintaining estuarial waterway depth, the spur dike has played an important role in currents and sediment exchange between channel and shoal and sediment back-silting in the channel. Through establishing a generalized physical model at a bifurcated estuary and conducting current tests under the joint action of runoff and tide, the influence of the spur dike length on current exchange between channel and shoal is analyzed. Results show that when the spur dike length reaches a certain value, the direction of the flow velocity shear front between the channel and shoal will change. The longer the spur dike, the larger the transverse fluctuating velocity at the peak of flood in the channel shoal exchange area, while the transport of the transverse hydrodynamics is obvious in the process of flood. There is an optimum length of spur dike when the shear stress in the channel and the longitudinal velocity in flood and ebb reach the maximum, and the flow velocity will decrease when the spur dike length is smaller or larger than the optimum. For a certain length of spur dike, the larger the channel shoal elevation difference, the larger the peak longitudinal flow velocity in the middle of the navigation channel in flood and ebb. However, the transverse flow velocity will first decrease and then increase. The transverse transportation is obvious when the channel shoal elevation difference increases.

Jurassic granitoid dike in Luodian, Guizhou Province: discovery and geological significance

In this paper, the Jurassic granitoid dike that intrudes into Permian diabase was reported in Luokun,Luodian County, south Guizhou. Zircon LA-ICP-MS U–Pb dating of the granitoid dike yielded an age of 164.3 ± 2.4 Ma with the e Hf(t) range from + 7.8 to + 12.1. The high contents of SiO_2(65.2%–66.8%) and total alkali(Na_2O + K_2O: 9.01%–9.95%), and low contents of Mg, Fe, Ca, P and Ti show the characteristics of alkali-rich granite. The total contents of rare earth elements range from 289.90 to 394.23 ppm. The Rb, Ba, K, Th, U and other LILE, Ta, Sr, P, Ti are enriched, and heavy rare earth elements are depleted. Petrogeochemical characteristics show that the dike was derived from a partial melting of newly-grown basaltic crust, and contaminated by crustal materials before experiencing strong fractional crystallization. The dike was formed in the intraplate post-orogenic extension stage and indicates that parental magma rose to the shallow crust through a fault. This provides new evidence of tectonic and mantle-crust magmatic activities and may contribute to regional Au mineralization in southern Guizhou and neighboring areas.

Simulation of flow pattern at rectangular lateral intake with different dike and submerged vane scenarios

A comprehensive understanding of the sediment behavior at the entrance of diversion channels requires complete knowledge of threedimensional(3 D) flow behavior around such structures. Dikes and submerged vanes are typical structures used to control sediment entrainment in the diversion channel. In this study, a 3 D computational fluid dynamic(CFD) code was calibrated with experimental data and used to evaluate flow patterns, the diversion ratio of discharge, the strength of secondary flow, and dimensions of the vortex inside the channel in various dike and submerged vane installation scenarios. Results show that the diversion ratio of discharge in the diversion channel is dependent on the width of the flow separation plate in the main channel. A dike perpendicular to the flow with a narrowing ratio of 0.20 doubles the ratio of diverted discharge in addition to reducing suspended sediment input to the basin, compared with a no-dike situation, by creating the outer arch conditions. A further increase in the narrowing ratio decreases the diverted discharge. In addition, increasing the longitudinal distance between consecutive vanes(Ls) increases the velocity gradient between the vanes and leads to a more severe erosion of the bed, near the vanes.

Validation of an operational forecasting system of sea dike risk in the southern Zhejiang Province, South China

In this study,an operational forecasting system of sea dike risk in the southern Zhejiang Province,South China was developed based on a coupled storm-surge and wave model.This forecasting system is important because of the high cost of storm-surge damage and the need for rapid emergency planning.A comparison with astronomical tides in 2016 and the validation of storm surges and high water marks of 20 typhoons verified that the forecast system has a good simulation ability.The system can forecast relatively realistic water levels and wave heights as shown under the parametric atmospheric forces simulated in a case study;the sea dikes in credible high risk were mainly located in the estuaries,rivers,and around the islands in the southern Zhejiang.Therefore,the forecast system is applicable in the southern Zhejiang with a support to the effective prevention from typhoon storm-surge damage.