Effect of the W-beam central guardrails on wind-blown sand deposition on desert expressways in sandy regions

Many desert expressways are affected by the deposition of the wind-blown sand,which might block the movement of vehicles or cause accidents.W-beam central guardrails,which are used to improve the safety of desert expressways,are thought to influence the deposition of the wind-blown sand,but this has yet not to be studied adequately.To address this issue,we conducted a wind tunnel test to simulate and explore how the W-beam central guardrails affect the airflow,the wind-blown sand flux and the deposition of the wind-blown sand on desert expressways in sandy regions.The subgrade model is 3.5 cm high and 80.0 cm wide,with a bank slope ratio of 1:3.The W-beam central guardrails model is 3.7 cm high,which included a 1.4-cm-high W-beam and a 2.3-cm-high stand column.The wind velocity was measured by using pitot-static tubes placed at nine different heights(1,2,3,5,7,10,15,30 and 50 cm)above the floor of the chamber.The vertical distribution of the wind-blown sand flux in the wind tunnel was measured by using the sand sampler,which was sectioned into 20 intervals.In addition,we measured the wind-blown sand flux in the field at K50 of the Bachu-Shache desert expressway in the Taklimakan Desert on 11 May 2016,by using a customized 78-cm-high gradient sand sampler for the sand flux structure test.Obstruction by the subgrade leads to the formation of two weak wind zones located at the foot of the windward slope and at the leeward slope of the subgrade,and the wind velocity on the leeward side weakens significantly.The W-beam central guardrails decrease the leeward wind velocity,whereas the velocity increases through the bottom gaps and over the top of the W-beam central guardrails.The vertical distribution of the wind-blown sand flux measured by wind tunnel follows neither a power-law nor an exponential function when affected by either the subgrade or the W-beam central guardrails.At 0.0H and 0.5H(where H=3.5 cm,which is the height of the subgrade),the sand transport is less at the 3 cm height from the subgrade surface than at the 1 and 5 cm heights as a result of obstruction by the W-beam central guardrails,and the maximum sand transportation occurs at the 5 cm height affected by the subgrade surface.The average saltation height in the presence of the W-beam central guardrails is greater than the subgrade height.The field test shows that the sand deposits on the overtaking lane leeward of the W-beam central guardrails and that the thickness of the deposited sand is determined by the difference in the sand mass transported between the inlet and outlet points,which is consistent with the position of the minimum wind velocity in the wind tunnel test.The results of this study could help us to understand the hazards of the wind-blown sand onto subgrade with the W-beam central guardrails.

Sand deposit-detecting method and its application in model test of sand flow

Against the background of the sand-flow foundation treatment engineering of Guangzhou Zhoutouzui variable cross-section immersed tunnel, a kind of sand deposit-detecting method was devised on the basis of full-scale model test of sand-flow method. The real-time data of sand-deposit height and radius were obtained by the self-developed sand-deposit detectors. The test results show that the detecting method is simple and has high precision. In the use of sand-flow method, the sand-carrying capability of fluid is limited, and sand particles are all transported to the sand-deposit periphery through crater, gap and chutes after the sand deposit formed. The diffusion range of the particles outside the sand-deposit does not exceed 2.0 m. Severe sorting of sand particles is not observed because of the unique oblique-layered depositing process. The temporal and spatial distributions of gap and chutes directly affect the sand-deposit expansion, and the expansion trend of the average sand-deposit radius accords with quadratic time-history curve.

THE RECORD OF YOUNGER DRYAS EVENT IN EOLIAN SAND DEPOSIT IN QAIDAM BASIN

The Qaidam Basin is one of the main areas where the desert of the Qinghai-Xizang Plateau is distributed.According to the envirotunment records and the age of stratigraphy in Xiaxitai section in southeast part of Qaidam Basin,this paper reached the following conclusions: the desert development, formation of the cold-dry climate, evolution of natural environment and their reverse changes occurred frequently since the late glacial. In eolian sand deposits, the YoungerDryas event clearly appeared, which manifesed a dry-cold climatic period. Now there are two different opinions about theclimatic effect of Younger Dryas. According to the predecessors’ research and the field work of the authors, it is considered that the Younger Dryas event not only exists in different climatic zones of China, but the manifests the unitary drycold climatic effect.

Basin-Scale Sand Deposition in the Upper Triassic Xujiahe Formation of the Sichuan Basin, Southwest China: Sedimentary Framework and Conceptual Model

The Upper Triassic Xujiahe （须家河） Formation in the Sichuan （四川） Basin, Southwest China is distinctive for the basin-scale sand deposition. This relatively rare sedimentary phenomenon has not been well interpreted. Here we addressed this issue by discussing sedimentary framework and conceptual model. Analysis of sedimentary setting implied that the basin received transgression during the deposition. It had multiple provenance supplies and river networks, as being surrounded by old- lands in multiple directions including the north, east and south. Thus, the basin was generally charac-terized by coastal and widely open and shallow lacustrine deposition during the Late Triassic Xujiahe period. This is similar to the modern well-known Poyang （鄱阳） Lake. Therefore, we investigated the framework and conceptual model of the Sichuan Basin during the Xujiahe period with an analogue to the Poyang Lake. Results show that the conceptual model of the deposition can be divided into transgressive and regressive stages. The first, third and fifth mem- bers of the formation are in transgressive stage and the deposits are dominated by shore and shallow lacustrine mud. In contrast, the deposition is mainly of braided river channel sand deposits during the regressive stage, mainly including the second, fourth and sixth members of the formation. The sand deposited in almost the entire basin because of the lateral migration and forward moving of the cross networks of the braided rivers. The multiple alternations of short and rapid transgression and relatively long regression are beneficial to the basin-scale sand deposition. Thus, the main channel of the braided river and its extensional areas are favorable for the development of hydrocarbon reservoir. This provides practical significance to the reservoir evaluation and exploration. In addition, the results also justify the relatively distinctive sedimentary phenomenon in the study area and may also have im- plications for understanding the large-scale sand deposition elsewhere.

Eolian sand deposition and its environmental significance in the northeastern margin of the Qinghai-Xizang Plateau

The dry climate which appeared about 8-7 Ma ago in South Asia has been interpreted as results of the intensification of Asian monsoon caused by the uplift of the Qinghai-Xizang Plateau at its maximum altitude around that time. Whether it is or not, it is a critical problem. A total of 55 samples were taken from the Tertiary red earth and Quaternary lacustrine deposits and loess in the Linxia Basin which is located in the northeastern margin of the

A Study of the Adsorption of Molecular Deposition Filming Flooding Agent MD-1 on Quartz Sand

Molecular deposition filming flooding (MDFF) is a novel oil recovery technique based on the thermopositive monolayer electrostatic adsorption of the MDFF agent on different interfaces within reservoir systems. In this paper, the adsorption property of the MDFF agent, MD-1, on quartz sand has been studied through adsorption experiments at different pH and temperatures. Experimental data are also analyzed kinetically and thermodynamically. The results show that the adsorption of MD-1 on quartz sand takes place mainly because of electrostatic interactions, which corresponds to adsorption that increases with pH. Kinetic analyses show that at a higher pH the activation energy for adsorption gets lower and, therefore, the adsorption becomes quicker for MD-1 on quartz sand. Thermodynamic analyses show that pH plays an important role in the adsorption of MD-1 on quartz sand. At a higher pH, more negative surface charges result in the increase of electrostatic interactions between MD-1 and quartz sand. Therefore, the saturated adsorption amount increases and more adsorption heat will be released.

ROLE OF NaCl IN ORE-FORMING OF SAND-SHALE TYPE COPPER DEPOSITS

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Spatial configuration of sand and mud in the lacustrine nearshore sand bar deposits and its geological implications

Different configurational orders of sand bodies and interlayers in lacustrine nearshore sand bar reservoirs frequently interact,causing complicated genesis and distribution of argillaceous sediments,as well as other issues.This paper investigates the spatial configuration of sand and mud in the sand bar reservoir,and analyzes its internal structure.Modern sand bar deposits in the Xiashan Lake,Shandong Province,China,were analyzed and compared with the sand bar reservoirs of the Member 2 of the Paleogene Shahejie Formation in the Banqiao Sag,China.The configurational mode of sand bar deposits was explored from the perspective of the spatial distribution and composition relationships between sand and mud.Based on the alternate deposition characteristics of sand and mud in the longitudinal direction,lacustrine nearshore sand bars can be divided into three sedimentary combination patterns:thin-sand and thin-mud interbed pattern,thick-mud thick-sand pattern,and thin-mud thick-sand pattern.Their mud components manifest as the deposition of fine-grained lithofacies of multiple genetic types.These include(semi-)deep lacustrine mud,sand and mud interbedded beach,argillaceous sediments in the water retention area behind the bar,and fall-silt seams that resulted from flood discharge.By summarizing the specific developmental locations and sequential relationships of each fine-grained argillaceous facies in modern sand bar deposits,a depositional process-based argillaceous sediment composition model is proposed.Based on this,this paper discusses the spatial configuration of sand bodies and argillaceous sediments in sand bar reservoirs,and introduces the typical stratigraphic structures of sand bars in two environments,i.e.,vertical superposition and lateral migration.In lacustrine nearshore sand bar reservoirs,the deposition and preservation degrees of mud mainly depend on three factors:accommodation space change,frequency of base-level cycles,and exposure-erosion time.These in turn influence the continuity and relative contents of sand and mud in reservoirs.The distribution of argillaceous sediments forms different orders of interlayers,which affects the heterogeneity and fluid percolation of sand bar reservoirs.Clarifying the space-matching relationship of sand and mud in sand bar deposits provides geological models and information parameters for the refined characterization and modeling of the internal configuration of sand bar reservoirs.Furthermore,this work offers guidance for the optimal adjustment of reservoir development strategies or the optimization of reservoir development plans.

Modeling of Deposition Process of Particulate Organic Matter (POM) with Sand on Vegetated Area in a River

The transport and deposition of particulate organic matter (POM) in river streams has recently received much attention as one of important ecological processes in rivers. We focused on interacted behaviors of sand particles in bed load and POM in vegetated area on sand bars. The purpose of this study is to clarify the characteristics of deposition of POM with bed load on sandbars with the riparian vegetation. A basic experiment on POM transport and deposition with vegetation is conducted in a laboratory flume. It demonstrates that several issues still remain to be future investigated. In particular, the shear due to the bed roughness in the vegetated area and the transport and deposition process of sand particles and POM are required to be described by the proper modeling which will be introduced into a simulation model of various fluvial processes. The main results of this study are that ripples are formed by bed load in riparian vegetation and POM deposition is promoted by ripple behavior. Based on these results, the POM deposition with ripples in vegetated area is described by a conceptual model which will affect various aspects in ecosystem management based on fluvial processes.

兰新高速铁路开孔挡风墙周围沙粒沉积与侵蚀特征数值模拟研究

设置在路基上的挡风墙起到了有效防风作用,但是由于其阻碍作用,对路基造成了严重的积沙危害。因此,基于Fluent欧拉双流体模型,对兰新高速铁路沿线既有下部开孔挡风墙周围风沙两相流运动特性进行数值模拟研究,得到挡风墙周围的流场分布规律以及沙粒沉积与侵蚀特征。结果表明:随着来流风速的增大,路堤迎风侧坡脚处的漩涡强度逐渐衰弱直至消失;路堤背风侧漩涡整体位置往背风侧方向移动,且漩涡涡量增加,导致沙粒反向侵蚀区域增加;迎风侧边坡处的沙粒沉积区域逐步减小,沙粒侵蚀区域逐步增加;北侧线路逐渐出现侵蚀区域,而风速对南侧线路沉积侵蚀区域的变化影响较小。在强风地区,布设挡风墙时应考察线路上风向的地表情况,地表松散、沙源丰富时宜同时采取防沙治沙措施,以达到减缓线路积沙危害的目的。

长江武汉段天兴洲低滩沉积物粒度端元对河流-风成沙丘沉积环境的指示意义

河床沙波向风成沙丘演变的过程具有特殊的沉积动力机制。笔者等以68份长江武汉段天兴洲洲头低滩沉积物的粒度分布数据为例,利用端元分析方法从每个粒度分布中分离提取4个粒度端元组分(EM1、EM2、EM3和EM4),探讨了河流—风成沙丘不同沉积环境中粒度端元的异同。研究结果表明:EM1和EM3组分在粒度分布中占比与沉积物粒度中值分别呈较好的线性正相关和负相关;河流沉积物主要由EM1、EM2和EM3组成的跳跃方式搬运,对应滚动次总体的EM4组分占比5%~10%,少悬浮搬运;风成沙纹沉积物主要包括两段跳跃次总体,以EM2组分为主、EM1和EM3组分为辅,少EM4组分;沙丘背风面沉积物主要靠颗粒流顺坡滑塌,以EM2组分为主、EM1和EM3组分为辅,含占比约为5%的EM4组分;未被风成沙纹覆盖的沙丘波谷沉积物记录了河流和小型滞水洼地的沉积特征,代表滚动次总体的EM4组分占比7%~15%,悬浮次总体占比可达20%。本文提取的沉积物粒度端元为弱风环境中河道内局部小型河流—风成沙丘的沉积环境和演化过程研究提供了参考。

大风区高速铁路路基双侧挡风墙周围沙粒沉积数值模拟研究

兰新高速铁路横穿多个大风区,对其安全运营造成严重影响。为降低强风对线路的危害,在大风区修筑大量防风构筑物,其中以路基挡风墙最为常见,挡风墙降低了风害的影响,但是带来严重的线路积沙问题。通过数值模拟研究不同风速下路基双侧挡风墙周围的流场特征,利用风产生的壁面剪切应力与沙粒剪切应力的比值确定地表沙粒沉积与侵蚀类型。研究发现,气流在两道挡风墙之间分别形成一个顺时针涡流和一个逆时针涡流,在第二道挡风墙背风侧形成一个顺时针大涡,随着来流风速增大,漩涡尺寸和涡流强度均在增大;由于涡流的存在,部分沙粒被卷走,路堤背风坡附近以及路基面上的沙粒沉积显著减少,当来流风速为24、30 m/s时,南北侧线路道床面均出现沙粒反向侵蚀;单双侧挡风墙的积沙规律对比结果表明,设置双侧挡风墙时,线路积沙显著减少。研究揭示了大风区铁路双侧挡风墙周围路基面上的沙粒沉积规律,对未来风区铁路的防护建设具有指导意义。

上砂下黏地层中桩-筒复合基础V-H承载特性

海上风机基础不仅受自重等竖向力V作用,也因水流、波浪和风等影响而承受水平荷载H。为探讨上砂下黏地层中一种由单桩和吸力筒组成的新型海上风机桩-筒复合基础受V-H组合作用时的承载特性,自主设计完成了一系列室内桩-筒复合基础V-H组合加载模型试验,获得不同组合参数下桩-筒复合基础的荷载-位移曲线和桩身弯矩分布曲线,并绘制出V-H承载力包络线。在此基础上,采用ABAQUS建立了上砂下黏地层中桩-筒复合基础三维数值分析模型,经模型验证与参数分析,进一步讨论了砂土厚度、筒径、筒高以及加载高度等参数对桩-筒复合基础承载特性的影响曲线,并拟合出桩-筒复合基础承载力简化计算公式,分析结果表明:桩-筒复合基础能显著提高桩身水平承载力,增幅达30%~90%,且增加筒径比增加筒高更有利于提高基础水平承载力;上部砂土层较厚时,桩-筒复合基础存在一个使复合基础水平承载力达到最大的预加竖向荷载最佳值,其值随不同载荷工况在(0.4~0.7)Vult范围内变化。

甘肃青土湖地区不同类型沙丘的表沙理化特征及其环境意义

沙丘表层沉积物的理化特征在揭示风沙的来源、沉积过程、风化作用等方面具有重要作用。本研究采用野外实地采样和实验室分析方法分析了甘肃青土湖地区不同类型沙丘表层沉积物的粒度和地球化学特征。结果表明:(1)青土湖地区沙丘表层沉积物以细砂为优势粒级,平均含量达72.08%,其次为极细砂,黏粒成分很少。频率分布曲线为单峰分布,概率累积曲线表现为三段式,反映出沉积环境较为稳定。(2)研究区沙丘表层沉积物常量元素以SiO2为主,平均含量为76.40%,其次为Al2O3和CaO,平均含量分别为5.05%、3.74%。微量元素以Cr、Mn、Co、Sr、Ba、Ti、Ce和P为主,平均含量均>100 mg/L。(3)Y、Zr和Y/Zr、Rb/Zr双变量图、A-CNK-FM图解表明巴丹吉林沙漠和腾格里沙漠为其沙源。风沙搬运过程中的磨蚀、风选作用是研究区富集Fe、Mg元素的主要原因。此外,下伏湖相沉积物就地起砂,石羊河冲积物也为其提供了部分沙物质。(4)A-CN-K和A-CNK-FM三角模式图表明研究区风化程度较弱,处于初期脱Na、Ca阶段。在沙丘固定过程中成土作用增强但淋溶作用减小,这是由于植被的影响导致半固定、固定沙丘Na、Ca含量较高。

松辽盆地南部砂岩型铀矿储层结构与铀成矿作用

以松辽盆地南部DL地区砂岩型铀矿为目标,在沉积学背景研究的基础上,开展铀储层结构与铀成矿作用研究。通过钻孔数据统计及系统的取样分析并编制铀储层非均质性图件,精细地刻画了姚家组铀储层的几何形态和复杂结构,充分展示了铀储层的定量非均质性。结果显示,区内灰色砂体多为原生灰色砂体,而下氧化带在沉积期后经历了较强的表生流体改造,为后生氧化带,矿体主要分布于河道砂体分岔处,以及从无隔挡层到隔挡层突然变厚的河道砂体边缘而非河道中央,其形态受氧化还原界面控制以板状为主。综合分析认为,表生流体成矿作用经历了晚白垩世姚家组含矿主岩预富集与表生流体叠加改造成矿2个阶段。通过对比DL地区储层结构对铀成矿的控制作用,在BL地区优选出3片找矿靶区,为下一步的勘查工作提供理论依据。

砂土场地桩-筒复合基础地震响应离心振动台试验

地震作用容易引起砂土地基中的海上风机基础液化失效,单桩-筒型复合基础(简称桩-筒复合基础)结合了单桩基础和吸力筒基础的优势,是一种新颖的海上风机基础形式。针对砂土场地桩-筒复合基础地震响应,开展干砂及饱和砂的单桩和桩-筒复合基础的离心振动台试验,采用白噪声和具有不同频谱成分的地震波进行激振,得到两种基础形式在砂土场地中的自振频率、超孔压累积、风机加速度响应以及基础弯矩分布等。结果表明:饱和场地中筒基下的浅层土体,其超孔压累积会有所衰减,加速度幅值则被相应放大;饱和场地中单桩浅部弯矩响应较大,风机产生明显的残余位移,相比单桩,桩-筒复合基础加速度响应更大,但其在限制水平位移方面具有明显优势。研究结论对于桩-筒复合基础的抗震分析具有参考价值。

安徽省太湖县刘羊河金红石砂矿地质特征及找矿标志研究

在太湖县刘羊河金红石砂矿区开展的地质填图、重砂测量、钻探等地质工作基础上,总结了刘羊河金红石砂矿区域地质、矿区地质、矿床地质特征,确定了砂矿体赋存于第四系全新统的砂层及砂砾层中。认为:矿床成因类型为河谷冲积型,砂矿体形状受地貌控制,与河谷形状一致;大别山前剥蚀丘陵区内次级地貌单元一侵蚀堆积河谷区有利于砂矿的形成和保存;大别山岩群桥岭岩组和新元古代变质侵人岩及石英脉中的矿物为本区金红石重要的物质来源;地貌特征、物源母岩、重砂异常是金红石砂矿重要的找矿标志。以期为安徽省大别山南部潜山、太湖一带进一步开展金红石砂矿床找矿工作提供参考。

沉积方向对珊瑚砂动剪切模量及阻尼比的影响

复杂地质赋存环境下珊瑚砂具有显著的各向异性特征,颗粒的沉积方向显著影响其动力特性。对南沙岛礁珊瑚砂开展均等固结的共振柱试验,探究了珊瑚砂颗粒的沉积方向角φ(沉积面与水平面的夹角)和初始有效固结围压σ0’对其动剪切模量G和阻尼比λ的影响。在给定φ下,G随剪应变幅值γ_(a)增大而减小的速率随σ0’的增大而增加;给定σ0’下,G随γ_(a)增大而减小的速率随φ增大呈现先减后增的趋势,φ=60°时G—γ_(a)曲线位于最下方。最大动剪切模量G_(0)随φ的增大表现出先减后增的现象,且φ对G_(0)的影响随σ0’的增大而降低。建立了考虑φ和σ0’影响的修正Hardin模型,预测和量测的G_(0)值偏差小于10%。动剪切模量比G/G_(0)—γ_(a)曲线对φ不敏感,结合修正Hardin模型和Davidenkov骨架曲线预测和量测的G值偏差小于15%。在陈国兴等(2006)提出的阻尼比经验模型中引入φ影响的修正项,预测和量测的λ值偏差小于20%。

威海市东部滨海新城海域海砂资源分布及特征

对威海东部滨海新城海域海底底质样品、浅地层剖面、地质钻探、多波束测量等资料进行了分析,探讨了该区海砂资源的类型、分布特征及沉积环境。结果表明:研究区海砂资源主要分布于鸡鸣岛和苍家岛潮沟附近,均为埋藏砂矿,以粉砂和细砂为主,含泥量较高,可用作回填用砂。研究区埋藏砂矿主要形成于晚更新世末期,成因类型主要有古冲积、残留和海积等类型。

鄂尔多斯盆地五蛟西地区长6段单砂体叠置特征研究

沉积微相控制下的单砂体发育类型、频率和叠置样式,控制了储层的连通性和井间剩余油的分布。本次研究综合利用丰富的岩心、测井和分析测试资料,在沉积微相精细刻画基础上,对鄂尔多斯盆地五蛟西地区三叠系延长组长6段单砂体发育特征和叠置样式进行精细研究。结果表明:五蛟西地区长6段岩性以粉砂岩、细砂岩、含泥砾或泥岩撕裂屑的细砂岩和泥岩为主,发育沉积微相类型主要为砂质碎屑流、浊流和半深湖泥3种。长6段垂向上可识别出5~8期单砂体,单砂体叠置类型包括孤立型、叠加型以及切叠型3种;平面上单层砂体多以枝状、网状、局部片状展布。湖平面升降导致的可容纳空间(A)变化及沉积物供给速度(S)匹配关系是控制单砂体空间发育特征的关键性因素。研究区长6段自下而上,随着A/S比值的变化,单砂体类型垂向上由叠加型、切叠型逐渐向孤立型、局部叠加型变化,平面上由网状、枝状向局部片状演化。