真空作用面位置对加固效果影响的试验研究

工程中应用广泛的真空预压法和真空-堆载联合预压法主要是指真空作用面位于地表面,通过从上部抽真空实现预压的目的,但对于吹填造陆工程,则不十分合理。通过室内试验模拟上位抽真空和下位抽真空,分别从土体的物理力学性质、沉降量、排水量等几个方面对2种预压方法的加固效果进行了比较分析,阐述了真空作用面位置对加固效果的影响。试验结果表明：下位抽真空的加固效果优于上位抽真空。     

Investigating peat hydrological properties using field and laboratory methods: application to the Lanoraie peatland complex (southern Quebec,Canada)

Flow dynamics within a peatland are governed by hydraulic parameters such as hydraulic conductivity, dispersivity and specific yield, as well as by anisotropy and heterogeneity. The aim of this study is to investigate hydraulic parameters variability in peat through the use of different field and laboratory methods. An experimental site located in the Lanoraie peatland complex (southern Quebec, Canada) was used to test the different approaches. Slug and bail tests were performed in piezometer standpipes to investigate catotelm hydraulic conductivity. Combined Darcy tests and tracer experiments were conducted on cubic samples using the modified cube method (MCM) to assess catotelm hydraulic conductivity, anisotropy and dispersivity. A new laboratory method is proposed for assessing acrotelm hydraulic conductivity and gravity drainage using a laboratory experimental tank. Most of slug tests' recovery curves were characteristic of compressible media, and important variability was observed depending on the initial head difference. The Darcy experiments on cubic samples provided reproducible results, and anisotropy (K_h > K_v) was observed for most of samples. All tracer experiments displayed asymmetrical breakthrough curves, suggesting the presence of retardation and/or dual porosity. Hydraulic conductivity estimates performed using the experimental tank showed K variations over a factor of 44 within the upper 40 cm of the acrotelm. The results demonstrate that the intrinsic variability associated with the different field and laboratory methods is small compared with the spatial variability of hydraulic parameters. It is suggested that a comprehensive assessment of peat hydrological properties can be obtained through the combined use of complementary field and laboratory investigations. Copyright © 2007 John Wiley & Sons, Ltd.     

Imprints of sub-glacial volcanic activity on a glacier surface—SAR study of Katla volcano,Iceland

The Katla central volcano, covered by the fourth largest Icelandic glacier Mýrdalsjökull, is among the most dangerous and active volcanoes in Iceland. Due to the ice cover, several indicators of its volcanic activity can only be identified indirectly. We analysed a total of 30 synthetic aperture radar (SAR) images with special focus on identifying circular and linear depressions in the glacier surface. Such features are indicative of sub-glacial geothermal heat sources and the adjacent sub-glacial tunnel (melt water drainage) system. The time series comprises images from five different SAR sensors (ERS-1, ERS-2, JERS-1/SAR, RADARSAT and ENVISAT-ASAR) covering a time period of 12 years, starting in 1994. Individual SAR scenes only partly map the glacier surface morphology due to the environmental influences on the SAR backscatter intensity. Thus, only surface features detectable in several SAR scenes at the same location were considered and merged to form an overall picture of the surface morphology of Mýrdalsjökull and its modification by sub-glacial volcanic activity between 1994 and 2006. Twenty permanent and 4 semi-permanent ice cauldrons could be identified on the surface of Mýrdalsjökull indicating geothermally active areas in the underlying caldera. An analysis of their size was not possible due to the indistinct outline in the SAR images. The spatial distribution of the geothermally active areas led to a new, piecemeal caldera model of Katla volcano. All cauldrons are connected to tunnel systems for melt water drainage. More than 100 km of the sub-glacial drainage system could be identified under the Mýrdalsjökull in the SAR time series. It has been found that the tunnel systems are not in agreement with estimated water divides. Our results allow improved assessment of areas of potential Jökulhlaup hazard accompanying a sub-glacial eruption.     

桂江流域地下水污染途径及防控措施研究

对桂江流域开展岩溶地下水污染调查发现:流域内地下水污染源分为“三氮”污染源、重金属污染源、有机污染源三类;“三氮”污染源主要包括工业、养殖和生活三类污水、生活垃圾渗滤液、农业施用氮肥等;重金属污染主要来自工矿企业;有机污染来自工业、养殖业。污染途径主要有孤峰平原的分散入渗式、孤峰平原的脚洞灌入式、峰丛洼地的消水洞灌入式、溶丘谷地的入渗式和峰丛峰林谷地的天窗灌入式等五类。并对88组地下水样品测试结果进行多指标地下水污染综合评价,结果表明36.5%的水点为“三氮”污染,多以分散入渗进入地下水,其污染形态呈面状分布;15.3%的水点为重金属污染,主要通过峰丛洼地消水洞灌入式补给和溶丘谷地入渗补给两种途径,呈点状分布于污染场地附近;3.49%的水点为有机污染,主要为分散入渗补给途径,污染呈短线状或点状分布。      

1917年海河流域洪涝灾害过程重建

洪涝灾害历来是影响中国的主要自然灾害之一。根据历史文献记载及观测资料,从天气过程、水文过程、受灾情况等方面对1917年海河流域洪涝灾害的自然过程作了详细梳理。得出以下结论： (1) 1917年洪涝灾害呈现由台风袭扰→集中降水→山洪暴发/河流决口→积水/淹没→受灾的成灾过程。 (2) 7月份2次台风带来大范围暴雨,集中性降水出现于7月20—28日,沿燕山、太行山分布,而9月份2次台风带来的暴雨则使灾情更加严重。 (3) 1917年海河流域各河于7月中旬开始涨溢、决口,9月中旬上游降雨结束后,中下游水位趋于稳定并下降,10月份以后洪水才迟缓退去,而洪水泛滥引发的涝灾影响一直延续到1918年。 (4) 1917年洪涝灾害在海河南系和北系都有发生,南系尤为严重,共造成156个县受灾。受灾田亩级数在5级以上的区域主要集中于海河干流沿线、南运河沿线以及河北省文安县等低洼地区。     

基于不同DEM数据源的胶东半岛流域特征提取对比与分析

基于SRTM和ASTER GDEM两种DEM数据源,以胶东半岛为研究区,应用ArcMap水文分析(Arc HydroTools)扩展模块和"burn in"算法,提取河网及流域范围。结果显示,集水面积阈值变化直接影响数字河网密集度。对胶东半岛而言,采用分辨率为90m×90m的SRTM数据可较好地提取河网水系及划分流域;提取的11个主要流域,充分体现了胶东半岛地区的流域特征。     

格林函数表象积分对打桩排水的计算

在动力作用下饱和桩周土排水会对基桩工程性质产生很大影响,研究桩-土动力作用的排水计算很有必要。通过连续介质力学方法,利用两相饱和介质Biot动力方程固相与流相频域格林函数解答,结合排水状态Lamb表象积分,得到集中力作用下饱和土圆柱基桩排水量计算公式。按该公式计算了江苏省金坛市开发区联合中策橡胶项目基地在打桩施工中基桩的理论排水量,并与现场实测排水量对比,发现计算与实际测试的排水量相对误差较小,实际工程桩测试的平均每击排水量期望值为4.82 L,与计算排水量相对误差为34%。可以认为,该方法用于动力作用下饱和土基桩排水计算是合适的。但由于计算是在桩-土弹性系统的假定下进行的,没有考虑土的非线性变形影响,有待于进一步研究,使其更加符合实际。     

高扬程虹吸保障条件分析与合理管径选择数值模拟

富水性斜坡易产生滑坡进而形成泥石流,斜坡排水是防止地质灾害的重要手段。虹吸排水具有实时性和免动力等优势,但因斜坡排水涉及高扬程,在虹吸管内的低压环境中流动液体会发生强烈的空化现象,从而产生气液两相流。在间歇性虹吸排水过程中,如果不及时将析离的气泡带走,气泡会积聚在虹吸管顶点附近,最终破坏虹吸过程。通过对管内两相流型分析,发现只有形成完整的弹状流,才能将气泡带走,保证虹吸的长期有效。采用流体数值计算软件FLUENT的VOF模型,分别对管径为4、5、6、8 mm的虹吸管内气液两相流型进行模拟。结果表明：管径小于5 mm的条件下,表面张力起主要作用,形成完整弹状流;管径大于6 mm的条件下,形成附壁弹状流。该结论通过物理模型试验也得到证明。     

不同力源作用下九江地震台井水位仪与伸缩仪的体应变响应分析

根据潮汐因子计算结果,确定了井水位观测格值。又由线应变和水位与体应变转换公式,分别计算了在固体潮、大气压、强远震和承压含水层排水作用下伸缩仪与水位仪的的体应变响应量,二者相对变化率(体应变比值)在0.242~0.668之间,分析比较了二者的响应特征,并初步解释了水位与应变同步变化的物理机制。     

Erosion of an active fault scarp leads to drainage capture in the Amazon region,Brazil

Far from the continental margin, drainage basins in Central Amazonia should be in topographic steady state; but they are not. Abandoned remnant fluvial valleys up to hundreds of square kilometers in size are observed throughout Amazonia, and are evidence of significant landscape reorganization. While major Late Miocene drainage shifts occurred due to initiation of the transcontinental Amazon River, local landscape change has remained active until today. Driven either by dynamic topography, tectonism, and/or climatic fluctuations, drainage captures in Amazonia provide a natural experiment for assessing the geomorphic response of low‐slope basins to sudden, capture related base‐level falls. This paper evaluates the timing of geomorphic change by examining a drainage capture event across the Baependi fault scarp involving the Cuieiras and Tarumã‐Mirim River basins northwest of the city of Manaus in Brazil. A system of capture‐related knickpoints was generated by base‐level fall following drainage capture; through numerical modeling of their initiation and propagation, the capture event is inferred to have occurred between the middle and late Pleistocene, consistent with other studies of landscape change in surrounding areas. In low‐slope settings like the Amazon River basin, base‐level fall can increase erosion rates by more than an order of magnitude, and moderate to large river basins can respond to episodes of base‐level fall over timescales of tens to hundreds of thousands of years. Copyright © 2013 John Wiley & Sons, Ltd.