超长灌注桩桩-土界面剪切试验研究

为研究超长灌注桩桩侧与土体接触界面的剪切力学行为,采用大型界面剪切仪,开展混凝土与粉质黏土、粉细砂土接触界面剪切试验。针对钻孔灌注桩泥浆护壁施工特点及后注浆工艺的应用,在混凝土与粉细砂土界面设置膨润土泥皮或膨润土泥皮与水泥浆,以研究泥皮及存在泥皮时注浆对界面剪切性状的影响。试验结果表明：界面剪切应力随剪切位移增加逐步达到极限值,之后,剪切应力保持基本不变或出现软化现象;土体类型及法向应力大小对界面剪切力学行为具有较大的影响;粉细砂土-混凝土界面摩擦角与土体有效内摩擦角相近,存在泥皮时,界面摩擦角降低达40%,泥皮的润滑作用较大地削弱了界面的剪切性能;存在泥皮情况下,注浆后界面摩擦角较泥皮界面提高近1倍,水泥浆的注入不仅消除了泥皮产生的不利影响,也有利于进一步改善界面剪切性能,提高其抗剪强度;泥皮及注浆对界面剪切应力与剪切位移关系亦有较大的影响;界面剪切作用对土体具有一定的影响范围,并在接触界面附近土体中逐渐形成剪切破坏带,剪切过程中界面呈现出由剪切位移阶段逐步过渡至剪切滑移阶段;此外,在剪切过程中,不同界面类型的土体变形存在较大差异。     

Impact of reach geometry on stream channel sensitivity to extreme floods

Predicting spatial and temporal variations in bank erosion due to extreme floods presents a long‐standing challenge in geomorphology. We develop two methodologies for rapid, regional‐scale assessments of stream reaches susceptible to channel widening. The first proposes that channel widening occurs when unit stream power exceeds a critical threshold (300 W/m²). The second is motivated by the observation that widening often occurs at channel bends. We introduce a new metric, the bend stress parameter, which is proportional to the centripetal force exerted on a concave bank. We propose that high centripetal forces generate locally high bank shear forces and enhance channel bank erosion. We test both metrics using the geomorphic signature of Tropical Storm Irene (2011) on the White and the Saxtons Rivers, Vermont. Specifically, we test if reaches where significant channel widening occurred during Irene required one or both metrics to exceed threshold values. We observe two distinct styles of channel widening. Where unit stream power and bend stress parameter are high, widening is usually due to bank retreat. Elsewhere widening is usually due to the stripping of the upstream end of mid‐channel islands. Excluding widening associated with the stripping of the heads of mid‐channel islands, almost all the widening (> 98%) occurred along reaches identified as susceptible to widening. The combined metrics identify up to one‐quarter of the reaches lacking susceptibility to channel widening. Copyright © 2014 John Wiley & Sons, Ltd.     

A comparison of wetness indices for the prediction of observed connected saturated areas under contrasting conditions

For lack of other widely available spatial information, topography is often used to predict water fluxes and water quality in mesoscale watersheds. Such data have however proven to be misleading in many environments where large and flat valley bottoms and/or highly conducive soil covers determine water storage and water transport mechanisms. Also, the focus is generally on the prediction of saturation areas regardless of whether they are connected to the catchment hydrographic network or rather present in isolated topographic depressions. Here soil information was coupled with terrain data towards the targeted prediction of connected saturated areas. The focus was on the 30 km² Girnock catchment (Cairngorm Mountains, northeast Scotland) and its 3 km² sub‐catchment, Bruntland Burn in which seven field surveys were done to capture actual maps of connected saturated areas in both dry and humid conditions. The 1 km² resolution UK Hydrology of Soil Types (HOST) classification was used to extract relevant, spatially variable, soil parameters. Results show that connected saturated areas were fairly well predicted by wetness indices but only in wet conditions when they covered more than 30% of the whole catchment area. Geomorphic indices including information on terrain shape, steepness, aspect, soil texture and soil depth showed potential but generally performed poorly. Indices based on soil and topographic data did not have more predictive power than those based on topographic information only: this was attributed to the coarse resolution of the HOST classification. Nevertheless, analyses provided interesting insights into the scale‐dependent water storage and transport mechanisms in both study catchments. Copyright © 2013 John Wiley & Sons, Ltd.     

Nitrate dynamics in a rural headwater catchment: measurements and modelling

This study was designed to improve our understanding of, and mechanistically simulate, nitrate (NO₃) dynamics in a steep 9.8 ha rural headwater catchment, including its production in soil and delivery to a stream via surface and subsurface processes. A two‐dimensional modelling approach was evaluated for (1) integrating these processes at a hillslope scale annually and within storms, (2) estimating denitrification, and (3) running virtual experiments to generate insights and hypotheses about using trees in streamside management zones (SMZs) to mitigate NO₃ delivery to streams. Total flow was mathematically separated into quick‐ and slow‐flow components; the latter was routed through the HYDRUS software with a nitrogen module designed for constructed wetlands. Flow was monitored for two years. High surface‐soil NO₃ concentrations started to be delivered to the stream via preferential subsurface flow within two days of the storm commencing. Groundwater NO₃‐N concentrations decreased from 1.0 to less than 0.1 mg l^?1 from up‐slope to down‐slope water tables, respectively, which was attributed to denitrification. Measurements were consistent with the flushing of NO₃ mainly laterally from surface soil during and following each storm. The model accurately accounted for NO₃ turnover, leading to the hypotheses that denitrification was a minor flux (<3 kg N ha^?1) compared to uptake (98^?127 kg N ha^?1), and that SMZ trees would reduce denitrification if they lowered the water table. This research provides an example of the measurement and modelling of NO₃ dynamics at a small‐catchment scale with high spatial and temporal resolution. Copyright © 2013 John Wiley & Sons, Ltd.     

海洋天然气水合物发育顶界的模拟计算

天然气水合物顶界的确定对于其资源评价十分重要,但目前还没有很好的方法来确定.本文利用在甲烷-硫酸根（SMI）界面硫酸根与甲烷所消耗的量相等和水-天然气水合物二相体系甲烷溶解度模型,建立了水合物顶界埋深计算的数学模型,并考虑硫酸根氧化有机质和微生物原位甲烷生成的影响.计算的ODP1245和IODP1327站位水合物顶界埋深分别为53 mbsf和83 mbsf,与钻探获得的水合物顶界埋深相吻合.     

Seismic traveltime inversion of 3D velocity model with triangulated interfaces

Seismic traveltime tomographic inversion has played an important role in detecting the internal structure of the solid earth. We use a set of blocks to approximate geologically complex media that cannot be well described by layered models or cells. The geological body is described as an aggregate of arbitrarily shaped blocks, which are separated by triangulated interfaces. We can describe the media as homogenous or heterogeneous in each block. We define the velocities at the given rectangle grid points for each block, and the heterogeneous velocities in each block can be calculated by a linear interpolation algorithm. The parameters of the velocity grid positions are independent of the model parameterization, which is advantageous in the joint inversion of the velocities and the node depths of an interface. We implement a segmentally iterative ray tracer to calculate traveltimes in the 3D heterogeneous block models. The damped least squares method is employed in seismic traveltime inversion, which includes the partial derivatives of traveltime with respect to the depths of nodes in the triangulated interfaces and velocities defined in rectangular grids. The numerical tests indicate that the node depths of a triangulated interface and homogeneous velocity distributions can be well inverted in a stratified model.     

Interannual meridional displacement of the East Asian upper-tropospheric jet stream in summer

On the interannual timescale, the meridional displacement of the East Asian upper-tropospheric jet stream (EAJS) is significantly associated with the rainfall anomalies in East Asia in summer. In this study, using the data from the National Centers for Environmental Prediction-Department of Energy (NCEP/DOE) reanalysis-2 from 1979 to 2002, the authors investigate the interannual variations of the EAJS‘s meridional displacement in summer and their associations with the variations of the South Asian high (SAH) and the western North Pacific subtropical high (WNPSH), which are dominant circulation features in the upper and lower troposhere, respectively. The result from an EOF analysis shows that the meridional displacement is the most remarkable feature of the interannual variations of the EAJS in each month of summer and in summer as a whole. A composite analysis indicates that the summer (June-July-August, JJA) EAJS index, which is intended to depict the interannual meridional displacement of the EAJS, is not appropriate because the anomalies of the zonal wind at 200 hPa (U200) in July and August only, rather than in June, significantly contribute to the summer EAJS index. Thus, the index for each month in summer is defined according to the location of the EAJS core in each month. Composite analyses based on the monthly indexes show that corresponding to the monthly equatorward displacement of the EAJS, the South Asian high (SAH) extends southeastward clearly in July and August, and the western North Pacific subtropical high (WNPSH) withdraws southward in June and August.     

苏德尔特构造带贝14块兴安岭群层序地层分析

以层序地层学理论为指导,利用岩心、测井、地震资料相结合的分析手段,建立了苏德尔特构造带贝14块兴安岭群的层序地层等时格架,将兴安岭群划分为3个三级层序和短期中期基准面旋回。分析了个层序的主要构型及其成因,认为盆地由断陷向凹陷转化,沉积速率也随之降低,盆地各层序的厚度由厚变薄。兴安岭群内部层序界面多为沉积间断,不同沉积时期的岩性、物性以及沉积物叠置关系具有明显的韵律性变化。层序发育明显受构造活动的控制,幕式构造活动是构成层序主要构型的成因。     

An Engineering Application Tool for Visual Assessment of the Equilibrium Beach

An engineering application tool for prediction of the static equilibrium bay(Beach Mod)is established to describe two bay shape formulas by use of the programming software "MATLAB" with a graphic user interface(GUI).The tool is user-friendly for engineering students for the design of beach shapes.This tool was tested through application on three types of beaches in Taiwan and Australia.By implementing the concept of Headland Control,the Beach Mod program allows users to draw a structure and create an artificial headland.The results indicate that Beach Mod can efficiently forecast beach changes as well as MEPBAY,a competing software package,while boasting a better user interface.     

Seston transport and deposition in Pelorus sound,south Island,New Zealand

Transport of seston (suspended sediment) in Pelorus Sound is controlled by tides and freshwater inflow. During high freshwater inflow, a moderately stratified estuarine circulation may be superimposed on the tidal circulation, but the latter dominates and transports seston seawards and landwards with the ebb and flood phases respectively. With extreme freshwater inflow, the estuarine circulation gains impetus and most seston is rapidly transported seaward in the low saline surface layer.

Irrespective of circulation there is a persistent trend in seston concentrations. Highest values occur at the sound's head because of the influence of nearby Pelorus and Kaituna Rivers and because of resuspension of bottom sediment by strong tidal currents. Seston concentrations wane along the sound until near the entrance, where values increase as a result of greater production of biogenic seston and because additional seston is brought in from Cook Strait with the flood tide. This trend parallels variability in the thicknesses of muddy bottom sediments. Muds are thick at the head where an extensive delta extends from the river mouths; muds gradually thin seaward and then thicken markedly in the vicinity of the sound entrance.

Seston weight and composition patterns and 3.5 kHz seismic profiles indicate Pelorus Sound acts as a double‐ended sediment trap. The upper reaches receive and retain river‐derived seston, whereas the sound entrance traps seston derived from Cook Strait. This situation appears to hold for both high and extremely high influxes of sediment.