水平分层土层系统等效阻尼比的简化计算方法

在实际工程场地中,很多土层可视为水平分层,各层土的物理和力学性质存在差异,其中包括土的振动阻尼比。本文讨论水平分层土层系统的等效阻尼比的近似计算方法,基于5个不同的加权函数推导了10种等效阻尼比的计算公式。通过2个算例,分别以等效阻尼比为参数计算水平分层土层的地震反应,并与准确解相比较,分析了不同等效阻尼比近似计算方法的计算精度。数值结果表明,若等效阻尼比计算方法选择不恰当,会导致土层地震反应的计算结果出现较大误差。针对2种不同类型的水平分层土层,建议采用基于三角形分布的加权函数来计算土层系统的等效阻尼比。     

Impacts of different vegetation restoration options on gully head soil resistance and soil erosion in loess tablelands

Vegetation restoration is identified as an effective approach to control soil erosion and affects soil detachment and resistance to concentrated flow on the Loess Plateau. However, the effects of vegetation restoration at gully heads in loess-tableland remains unclear. This study was performed to investigate the effects of nine vegetation restoration types at gully heads on soil detachment rate (Dr) and soil resistance to concentrated flow (i.e. soil erodibility, K_r and critical shear stress, τ_c). Undisturbed soil samples were collected from nine vegetation-restored lands and one slope cropland (as the control) and were subjected to a hydraulic flume to obtain Dr values of gully heads under six inflow discharges (0.5–3.5 L s^-1). The results showed that the Dr values of nine revegetated gully heads were 77.11% to 95.81% less than that of slope cropland, and the grassland dominated by Cleistogenes caespitosa and the shrubland dominated by Hippophae rhamnoides had a relatively greater decrease in Dr than those of other seven restoration types. The Dr value of nine revegetated gully heads could be better simulated by stream power than by flow velocity and shear stress and was also significantly affected by soil disintegration rate (positively), soil bulk density, saturated hydraulic conductivity, organic matter content, and water-stable aggregate stability (negatively). Additionally, roots with diameters of 0 to 0.5 mm showed a greater effect on Dr than those with larger diameters. Compared to cropland, the nine restored types reduced K_r by 76.26% to 94.26% and improved τ_c by 1.51 to 4.68 times. The decrease in K_r and the increase in τ_c were significantly affected by organic matter content, water-stable aggregate, mean weight diameter of aggregate and root mass density. The combination of grass species (Cleistogenes caespitosa) and shrub (Hippophae rhamnoides) could be considered the best vegetation restoration types for improving soil resistance of gully heads to concentrated flow. © 2019 John Wiley & Sons, Ltd.     

库水升降条件下考虑饱和渗透系数空间变异性的白水河滑坡渗流变形分析

堆积层滑坡的岩土体渗透系数具有一定的不确定性,且渗透系数是饱和-非饱和渗流分析的重要参数,开展考虑其空间变异性的库岸堆积层滑坡渗流变形分析具有重要意义。以三峡库区中的白水河滑坡为研究对象,基于地面核磁共振技术获取的岩土体渗透系数,分析滑坡体渗透系数的空间变异特征,采用半变异函数方法求得滑坡体渗透系数的竖直波动范围,在此基础上建立渗透系数的非平稳随机场模型。以非侵入式随机有限元的方式开展库水升降两种工况下不确定模型与确定模型的流固耦合模拟,分析两种模型的渗流场、位移变形特征及其差异。结果表明：相比于确定模型,不确定模型孔压改变的滞后性更为明显,且库水下降工况下整体的变形更大,若忽略滑体渗透系数的非平稳空间变异特征将会低估滑坡的实际变形。     

低弗劳德数水流二级消力池水力特性试验研究

针对低弗劳德数水流消能问题,在确定单级消力池和二级消力池体型的基础上,采用物理模型试验方法,分别研究了低弗劳德数水流单级和二级消力池的水力特性和消能结构特性。结果表明,在低弗劳德数水流条件下,二级消力池将原单级消力池出池水面较大波动区变成了适应区,对下游尾水位的适应区间显著增加,出池水面波动更小。同时,单级消力池内流线更加稀疏,流速梯度更小;消力池涡量大小明显低于二级消力池,而雷诺应力明显大于二级消力池;二级消力池内雷诺应力大小分区较单级消力池更明显,表面旋滚区明显大于底部旋滚区,水流更加稳定。相比单级消力池,二级消力池消能率显著提高,且有利于下游河床和岸边的防冲保护,工程应用更为有利。     

Spatial-temporal Patterns of Land Surface Temperature and Influencing Factors Contribution in Fuzhou City

With the intensification of urbanization and global warming, the problems of urban thermal environment are increasingly prominent. On the basis of the remote sensing, geographic information system, geostatistics and multiscale spatial pattern, the spatial-temporal variation characteristics of land surface temperature in urban thermal environment were quantitatively analyzed. The results are as follows: \mathrm{①} Dramatic changes in land use/land cover had occurred from 1993 to 2016 in the study area. The net increase area of construction land was 1 231.04 km², with a change rate of 295.33%. Cultivated land was occupied by construction land. \mathrm{②} The area of middle, sub-high and high temperature zones spread to the surrounding areas gradually with the Minjiang River. The area of sub-low and low temperature zones decreased markedly. \mathrm{③} From 1993 to 2016, the contribution of land surface temperature in different urban districts had the characteristics of uneven spatial and temporal distribution. Meanwhile, there was a positive contribution in the process of land surface temperature rise in Fuzhou while there was a negative contribution in Minqing and Yongtai. Forest/grassland, cultivated land, water body and wetland had a negative contribution during land surface temperature rise while construction land contributed positively. \mathrm{④} According to the multi-distance spatial cluster analysis (Ripley's K function), there was a certain scale in the aggregation and dispersion of land surface temperature, in which the aggregation range and degree of aggregation increased in the study area in 24 years.     

脑动脉粥样硬化斑块中不同类型钙化集合体的矿物学特征及分布规律

钙化是脑动脉粥样硬化的重要指示,并与粥样硬化的发展密切相关。脑动脉粥样硬化斑块钙化灶中存在球状与块状两类不同形貌的矿物集合体,但是关于两类钙化矿物学特征的区别以及其在病灶中空间分布规律的研究仍不充分。选取具有不同程度钙化的脑动脉粥样硬化样品,利用扫描电子显微镜(SEM)及其附带的能谱仪(EDS)、透射电子显微镜(TEM)及其附带的选区电子衍射(SAED)以及拉曼光谱(Raman),对钙化物的形貌、构造以及基于空间分布的物相组成及化学成分的变化进行了研究。研究表明,钙化灶中心由块状钙化构成,周围分布着球状钙化。块状钙化中物相分布不均匀,其中心由碳羟磷灰石(CHA)构成,边缘除CHA外还含有部分无定型磷酸钙(ACP)。球状钙化由白磷钙石(WH)与CHA构成。     

LA-ICP-MS/FT方法在矿床保存研究中的应用——以赣东北德兴铜矿和银山铅锌矿床为例

矿床保存是成矿系统研究的重要组成部分,其中裂变径迹研究是揭示矿床保存条件和程度的有效手段之一。本文建立了LA-ICP-MS/FT方法,该方法获得磷灰石裂变径迹年龄值与已有外探测器法分析结果对比表明这一方法是可行的。基于此方法,对赣东北德兴铜矿与银山铅锌矿进行了磷灰石裂变径迹分析,得到了德兴成矿岩体的磷灰石裂变径迹年龄71.4±8.6 Ma,银山地区英安斑岩的磷灰石裂变径迹年龄为77.1±8.3 Ma。这一结果表明,在区域整体抬升背景下,两个矿区均以较低的剥蚀抬升速率抬升至地表。两个矿区样品磷灰石平均裂变径迹围限长度分别为12.32±1.77μm和12.56±1.91μm,对应Dpar值为2.45±0.19μm和1.84±0.17μm,径迹长度频度分布属于单峰型,证实两个矿区为单向冷却过程且没有遭受后期明显的热扰动。进一步温度‒时间热模拟路径显示,德兴和银山在70 Ma前经历了快速隆升过程,然后开始缓慢抬升,到约20 Ma开始再次快速隆升。结合前人报道的U-Th/He定年结果,100 Ma以来,德兴可能比银山具有相对更高的隆升量(~1 km)。     

深埋煤层开采顶板泥砂溃涌灾害多源信息评价

深埋煤层采场顶板泥砂溃涌灾害是由于泥岩顶板遇水发生松散崩解,在矿压作用下泥砂集中溃入井下的综合性灾害,其灾害发生受到含水层、矿山压力、地质构造等多因素影响。以黄陇煤田照金煤矿为研究区,在灾害发生机理研究的基础上,讨论了灾害发生的主要影响因子,最终选取洛河组含水层富水性、煤层到洛河组含水层距离、宜君组砾岩厚度、煤层上覆杂色泥岩厚度、煤层到杂色泥岩距离、单位面积断层密度、褶皱构造分布和煤层开采厚度8个主控因素,采用层次分析权重赋值方法,确定影响灾害发生的各主控因素权重,构建煤层顶板泥砂溃涌灾害危险性评价数学模型;绘制主控因素专题图并进行栅格赋值,通过信息融合叠加方法将各因素进行叠加,最终形成多源信息融合的照金煤矿煤层顶板泥砂溃涌灾害综合分区。研究结果表明,照金煤矿ZF202工作面所在区域该类灾害发生的危险性高,与实际开采过程中曾发生的“4·25”重大事故发生区域较为吻合,说明本次危险性评价模型构建合理,分区结果可用于指导矿井的开采布设与泥砂溃涌灾害防治。移动阅读      

冻融期东北农田土壤温度和水分变化规律及影响因素分析

为了更好地认识季节性冻融区冻融过程对农田土壤温度和水分的影响, 以吉林省长春市黑顶子河流域为研究对象, 监测了冻融期流域内玉米田和水稻田土壤温度和水分的变化过程。结果表明： 冻融期表层土壤温度主要受积雪厚度影响, 深层土壤温度主要受土壤初始含水率影响。冻结期, 冻结层含水率几乎都呈增加趋势, 其中浅层土壤增幅最大; 冻结速度慢、 初始含水量低、 相邻土层含水量高的土层冻结过程水分增加量更大, 反之则小。融化期, 各下垫面、 土层土壤含水率基本呈下降趋势, 且主要集中在表层0 ~ 30 cm, 水分损失以蒸发为主, 冻结层对土壤蒸发有抑制作用; 冻结层的融化是造成各下垫面不同土层土壤含水率差异, 以及各土层在不同融化阶段土壤含水率差异的主要原因。     

吉林省和龙地区鸡南BIF型铁矿床含矿建造地球化学特征及形成时代

鸡南铁矿床位于吉林省和龙地区,地处华北克拉通北缘与兴蒙造山带接壤的龙岗地块北部,是东北地区发现较早的BIF型铁矿床之一。该矿床铁矿体主要呈层状、似层状、扁豆状赋存于鞍山群鸡南组上段中部层位,含矿岩石以黑云斜长片麻岩、角闪黑云斜长片麻岩、黑云角闪斜长片麻岩及斜长角闪岩为主,为角闪岩相的中低级区域变质岩系;主要矿石类型为条带状磁铁石英岩型和块状磁铁角闪岩型。为确定该矿床含矿建造的原岩、变质时代及构造背景,重点对含矿岩系中的斜长角闪岩进行了岩石地球化学和锆石U-Pb年代学研究。结果表明：斜长角闪岩的地球化学特征表现为富集大离子亲石元素、轻微富集重稀土元素;主量元素质量分数与中性-基性岩类基本相似,结合原岩恢复图解,判断其原岩类型为亚碱性玄武岩（拉斑玄武岩）,形成于弧后盆地背景;LA-ICP-MS锆石U-Pb年代学研究中,2个较老的锆石测点年龄分别为（2 468±15）和（2 469±9）Ma,代表区内峰期变质年龄（约2 460 Ma）,26个锆石测点的测年数据较为集中,加权平均年龄为（2 275±25）Ma,代表区内退变质年龄。通过与国内外典型BIF型铁矿床的对比研究认为,区内的鸡南铁矿与官地铁矿同属Algoma型铁矿床。