砾石床面的空气动力学粗糙度

通过砾石床面的空气动力学粗糙度(Z₀)的风洞实验研究,结果表明,砾石床面的空气动力学粗糙度(Z₀)与砾石粒径、砾石覆盖度和自由风速有关,Bagnold的1/30定律和其它有关空气动力学粗糙度与粗糙元高度的固定比例对砾石床面都不适用。在各种一定砾石覆盖度条件下,砾石床面的Z₀随自由风速的增加而呈指数衰减。在各种一定自由风速条件下,Z₀随砾石覆盖度C的变化遵循二次曲线:Z₀=F₁+F₂C+F₃C^1.5+F₄C²,砾石覆盖度为40%~75%时,Z₀达到最大值。建立了包含自由风速和砾石覆盖度两个因子的Z₀的双因子综合模型。     

路堤荷载下具盖板的浆固碎石桩桩土应力比研究

桩土应力比是反映复合地基工作状态的重要参数,前人做了较多的理论工作,但理论解通常是在桩顶铺设砂垫层情况下推出的。在路堤荷载下浆固碎石桩复合地基一般在桩顶设置盖板,针对浆固碎石桩复合地基的特殊情况,进行了理论模型简化,并且运用极限平衡理论和弹性理论,推导了设置盖板的浆固碎石桩复合地基在路堤荷载下桩土应力比公式,并通过工程实测资料进行了验证,其结果可为浆固碎石桩复合地基的优化设计提供参考。     

The response of a gravel‐bed river planform configuration to flow variations and bed reworking: a modelling study

A 2D depth‐averaged model has been developed for simulating water flow, sediment transport and morphological changes in gravel‐bed rivers. The model was validated with a series of laboratory experiments and then applied to the Nove reach of the Brenta River (Northern Italy) to assess its bed material transport, interpret channel response to a series of intensive flood events (R.I. ≈ 10 years) and provide a possible evolutionary scenario for the medium term. The study reach is 1400 m long with a mean slope of 0.0039 m m^?1. High‐resolution digital terrain models were produced combining LiDAR data with colour bathymetry techniques. Extensive field sedimentological surveys were also conducted for surface and subsurface material. Data were uploaded in the model and the passage of two consecutive high intensity floods was simulated. The model was run under several hypotheses of sediment supply: one considering substantial equilibrium between sediment input and transport capacity, and the others reducing the sediment supply. The sediment supply was then calibrated comparing channel morphological changes as observed in the field and calculated by the model. Annual bed material transport was assessed and compared with other techniques. Low‐frequency floods (R.I. ≈ 1.5 years) are expected to produce negligible changes in the channel while high floods may erode banks rather than further incising the channel bed. Location and distribution of erosion and deposition areas within the Nove reach were predicted with acceptable biases stemming from imperfections of the model and the specified initial, boundary and forcing conditions. A medium‐term evolutionary scenario simulation underlined the different response to and impact of a consecutive sequence of floods. Copyright © 2015 John Wiley & Sons, Ltd.     

Characteristics of sediment in transport in the swash zone of a steep estuarine foreshore

Cross‐shore grading of sediment has been observed on the surface of estuarine beaches but the swash zone processes responsible for this grading have not been measured. This study was conducted to provide an explanation for the cross‐shore grading of sediment on a predominantly sandy estuarine foreshore. Data on wave and swash characteristics and sediment trapped in the uprush and backwash during 25 swash events were gathered from mid‐rising to mid‐falling tide on a small transgressive barrier in Delaware Bay, New Jersey, USA. Sediment is predominantly quartz and feldspar, medium to coarse sands with a gravel fraction of granules and pebbles. Wave energies increased with tidal rise. The percentage of gravel in transport in the uprush and backwash is similar (11% and 13%) during the rising tide when the swash zone is at mid‐foreshore, decreases in the uprush (9%) and increases in the backwash (18%) when the swash zone is on the upper foreshore. When the swash zone is at mid‐foreshore on the falling tide, the quantity of gravel in the backwash (30%) is greater than in the uprush (24%). The low proportion of gravel within the foreshore prior to trapping, and the increase in the percentage of gravel when the waves and swash are on the upper foreshore, suggests that the step is the primary source of gravel high on the foreshore. The size of the step increases as wave heights increase with tidal rise. The rate of delivery of gravel into the swash is enhanced by sediment entrained during wave breaking and interaction of the uprush with the previous backwash. The lag in the rate of step migration relative to breaker migration during the falling tide increases the likelihood of mining gravel from the step and subsequent transport in the uprush and backwash. These findings are important for low energy estuarine beaches sensitive to small changes in tidal range and wave energy that cause sedimentological change across the foreshore.     

西藏羌塘盆地东南缘晚白垩世—古近纪砾岩层砾组特征及其地质意义

通过对环绕聂荣微陆块分布的晚白垩世—古近纪砾岩层的沉积特征和砾组特征分析,结合区域地质情况,阐述了砾岩层的性质、成因、来源、搬运方式及其所反映的构造背景等。研究表明,本套砾岩层为近—中距离搬运的冲洪积作用的产物,砾岩层砾石成分复杂,含量各异,分选性好,其古水流呈现单一水流特征,水动力条件相对较稳定,砾性和砾向分析指示砾石主要来源于聂荣微陆块、班公怒江缝合带以及其周边高山地区,反映冲积为主、洪积为辅的山前或山麓水系分布的沉积特征。结合区域资料综合分析,晚白垩世时期,聂荣微陆块北部地区发生隆升,形成东北高西南低的古地理格局;进入古近纪时期,在继承先前的古地理构造格局基础上,测区整体隆升。由此推断,晚白垩世时期青藏高原的隆升遍布班公—怒江缝合带以北地区,古近纪时期青藏高原整体发生隆升。     

嵩山地区登封群地层的新认识

嵩山地区位于华北克拉通南缘,是我国记录前寒武纪地质的典型地区之一。但以往对该区偏重于地球化学的研究,对地层学的研究相对薄弱,尤其是太古界登封群地层研究程度很低。在野外实地调查,实际测量研究整个登封群地质剖面时,发现登封群存在的一个宏观的粒序,从老羊沟岩组到金家门岩组再到郭家窑岩组,所含砾石粒径存在一个总体变小,数量由多变少的规律。     

大同--运城高速公路某软基复合地基检测结果分析

以山西大运高速公路某段软基处理为例,从挤密碎石桩的加固机理和破坏方式入手,通过对软基复合地基的原位测试结果分析,得出碎石桩不但提高了地基的承载力,增加了桩间土的强度,减少了地基沉降,而且消除或减轻了地基的液化,使复合地基承载力达到了设计要求,特别是为以后在高速公路修筑中的软基处理提供了参考资料.     

毛乌素沙漠风积砂地层碎石桩载荷试验研究

在榆林地区典型风积砂地层中开展了碎石桩复合地基载荷试验,通过试验对碎石桩有效桩长及承载力等方面进行了探索性研究.通过试验得到天然地基临塑荷载为128kPa,极限荷载320kPa;碎石桩单桩临塑荷载为1019.2kPa,极限荷载不小于3312.4kPa;桩间土临塑荷载为318kPa,极限荷载1590kPa;复合地基临塑荷...     

砾石层覆盖区煤田高精度三维地震勘探技术在张家口蔚县单侯井田的应用

以张家口蔚县单侯井田三维地震勘探为例,在松散厚砾石层覆盖区使用可控震源组合激发进行三维地震勘探,获得了较高质量的原始资料.地震资料经精细处理及三维多属性地质解释,断层的断点清晰、自然,煤层缺失区反射波特征明显,褶曲(向斜、背斜)显示明显.在使用炸药震源难以取得较好地质成果的厚砾石层覆盖区,使用可控震源组合激发取得了较满...     

1961-2005年新疆区域分级雨日(量)的气候特征

利用新疆区域108个常规气象观测站的逐日降雨资料对新疆区域1961-2005年分级雨日(量)的气候特征进行研究.按日雨量的大小分成4个等级:小雨(0.1～6.0 mm)、中雨(6.1～12.0 mm)、大雨(12.1～24.0 mm)和暴雨(≥24.1 mm),有效雨日(量)为上面4个等级雨日(量)的总和.结果发现:新...