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381.
Six submarine slope canyons in an area of the northwestern Mediterranean, offshore from the Ebro River and Delta, were surveyed with bathymetric swathmapping (SeaBeam) and mid-range side-looking sonar (SeaMARC I). All of the canyons have slightly winding paths with concave-upwards gradients that are relatively steep shallower than 1,200 m. Two major types of canyons are identified on the basis of their morphologic character at the base of the slope; Type-I canyons lead to an unchannelled base-of-slope deposit and Type-II canyons are continuous with channel-levee systems that cross the rise.Four Type-I canyons were surveyed in the area. Two of these are broad, U-shaped, steep (average gradients of 1:14), do not indent the shelf, and terminate downslope at debris-flow deposits. These two canyons, the most northern in the area, have rounded heads with extensive gullies separated by knife-edge ridges. Relief of the canyon walls is about equal on both sides of the canyons, although the right-hand walls (looking downslope) are generally steeper. The other two Type-I canyons in the area are similar in that they do not indent the shelf, but they are much smaller and shallower and coalesce before terminating in the base-of-slope region. The two Type-II canyons that feed leveed-channels are U-shaped with flatter floors, longer profiles and gentler gradients than Type-I canyons. They are closer to the Valencia Valley and have relatively small cross-sectional areas.We propose a four-stage evolutionary sequence to explain the development of the canyons observed in this section on the prograding Ebro margin. During the initial stage, slumping and erosion on the slope creates a network of small gullies. During the next stage, headward growth of one (or more) gully leads to a major indentation of the shelf. This is the critical factor for developing a channel that will incise the slope and provide a major conduit for moving sediment to the basin. Stage 3 is characterized by the development of a continuous channel accompanied by levee growth across the lobe. In the final stage, the channel-levee system becomes inactive either through destruction by mass wasting, infilling of the channel, or loss of the major sediment source. 相似文献
382.
383.
针对兰州某小区商住楼已形成不均匀沉降的地基,根据场地施工条件、地基条件和建筑物的结构特征,对该工程地基选择了高压旋喷注浆法进行加固,加固结果表明:加固前及加固初期地基沉降速率较大,加固施工完成后沉降速率变小,加固完成两个月后沉降稳定,加固效果良好。通过该工程实践表明:高压旋喷注浆法在复杂地基中对既有建筑物的加固处理虽然是可行的,但同时必须根据地基土的特点采取相应的切实可行的技术措施,才能使地基加固处理达到预期的效果。其加固原理既有旋喷桩的托换加固之功效,又有静压注浆加固之作用。 相似文献
384.
Automated classifications of topography from DEMs by an unsupervised nested-means algorithm and a three-part geometric signature 总被引:7,自引:3,他引:7
An iterative procedure that implements the classification of continuous topography as a problem in digital image-processing automatically divides an area into categories of surface form; three taxonomic criteria–slope gradient, local convexity, and surface texture–are calculated from a square-grid digital elevation model (DEM). The sequence of programmed operations combines twofold-partitioned maps of the three variables converted to greyscale images, using the mean of each variable as the dividing threshold. To subdivide increasingly subtle topography, grid cells sloping at less than mean gradient of the input DEM are classified by designating mean values of successively lower-sloping subsets of the study area (nested means) as taxonomic thresholds, thereby increasing the number of output categories from the minimum 8 to 12 or 16. Program output is exemplified by 16 topographic types for the world at 1-km spatial resolution (SRTM30 data), the Japanese Islands at 270 m, and part of Hokkaido at 55 m. Because the procedure is unsupervised and reflects frequency distributions of the input variables rather than pre-set criteria, the resulting classes are undefined and must be calibrated empirically by subsequent analysis. Maps of the example classifications reflect physiographic regions, geological structure, and landform as well as slope materials and processes; fine-textured terrain categories tend to correlate with erosional topography or older surfaces, coarse-textured classes with areas of little dissection. In Japan the resulting classes approximate landform types mapped from airphoto analysis, while in the Americas they create map patterns resembling Hammond's terrain types or surface-form classes; SRTM30 output for the United States compares favorably with Fenneman's physical divisions. Experiments are suggested for further developing the method; the Arc/Info AML and the map of terrain classes for the world are available as online downloads. 相似文献
385.
土工袋加固地基原理及其工程应用 总被引:4,自引:0,他引:4
介绍土工袋加固地基的原理、基本特性,及其在房屋地基加固、路基加固、堤防加固及构筑挡墙等非膨胀土地基中的工程应用实例与处理膨胀土地基的应用可能性。 相似文献
386.
基于有限差分强度折减法的略阳电厂边坡稳定性分析 总被引:2,自引:0,他引:2
将强度折减理论应用于边坡稳定性分析中,借助FLAC/SLOPE有限差分分析程序,选择弹塑性Mohr-Coulomb模型及其破坏准则,以大唐略阳电厂边坡作为工程实例,分析了该边坡的稳定性,并与传统的Bishop法、Janbu法等方法计算所得边坡稳定系数进行了对比分析。结果表明,有限差分强度折减法能更加真实地反映边坡的实际情况,求得的边坡稳定系数更接近边坡的实际稳定状态,显示出其在边坡稳定性分析中的一定优势。 相似文献
387.
Sandra G. Catane Hillel B. Cabria Cristituto P. Tomarong Jr Ricarido M. Saturay Jr Mark Albert H. Zarco Winston C. Pioquinto 《Landslides》2007,4(1):85-90
On 17 February 2006, a rockslide-debris avalanche cascaded down the steep slope of Mt. Can-abag, burying the entire village
of Guinsaugon in St. Bernard, Southern Leyte, Philippines. Casualties include 139 dead with 980 still missing and presumed
dead, making it perhaps the most catastrophic landslide in Philippine history. The landslide started at the ridge top along
a fault plane associated with the active Philippine Fault Zone. It started as a block slide that transformed into an avalanche.
The entire event lasted for only a few minutes. Estimated maximum landslide velocity is 120–130 m/s. The landslide left behind
a deep, wedge-shaped scarp. The central part of the deposit exhibits a hummocky topography typical of avalanches, in contrast
to the flatter surface of the debris-flow-type marginal deposit. High amounts of soil in the matrix were derived from the
scouring of ancient landslide deposits and rice fields in the valley. The landslide has a total area of 3.2 km2 and a runout distance of 4.1 km. Estimated volume of debris is approximately 20 Mm3. At least four streams were dammed by the landslide debris. Intense precipitation and earthquakes preceding the landslide
are the potential triggers. Preliminary back analyses assuming a planar and wedge slip surface yielded very low factors of
safety even under dry conditions. A more rigorous analysis of the failure mechanism of the landslide is needed. 相似文献
388.
A high-resolution history of vegetation and climate history on Sunda Shelf since the last glaciation
Karl STATTEGGER 《中国科学D辑(英文版)》2007,50(1):75-80
This paper presents 16500-year-long high-resolution pollen and spore records from sediments of core 18287 on the continental slope of the southern South China Sea. In the period of 16.5―13.9 ka B.P., the low-mountain rainforest dominated the continental slope of the South China Sea. And in the period of 13.9―10.2 ka B.P., the lowland rainforest and ferns expanded greatly, while the low-mountain rainforest shrank, which indicated a warming at the last deglaciation. Also during this period, the pollen sedi-mentation rates reduced sufficiently. This might imply a rise of the sea level and therefore the sub-mergence of the shelf, resulting in the broadening of the distance between the source area and the slope. After 10.2 ka B.P, decreasing of the fern indicates the early Holocene (10.2―7 ka B.P.) is a cold period, while the increasing of fern marks the rising temperature (7―3.6 ka B.P.). 相似文献
389.
Numerical model simulations of sea-breeze circulations in the presence of idealized topography are subjected to dimensional
analysis in order to capture the dynamics of the sea-breeze circulation combined with an upslope-flow circulation. A secondary
objective is to reconcile previous results based on observations. The analysis is based on a scaling analysis of sea-breeze
speed, depth and volume flux. This study is motivated by the fact that the literature of sea breezes interacting with upslope
flows is generally qualitative. Results show clear scaling regimes and strong interaction between the two thermally driven
circulations. We distinguish three regimes, depending on slope length, slope angle, stability and surface heat flux. The first
and third regimes obey the scaling laws of pure sea-breeze scaling. The second regime shows a significant decrease in the
scaled volume flux relative to pure sea-breeze scaling. Dynamical relations in the second regime show a strong influence on
the circulation of upslope stable air advection. 相似文献
390.
Classification of Vertical Wind Speed Profiles Observed Above a Sloping Forest at Nighttime Using the Bulk Richardson Number 总被引:5,自引:0,他引:5
Hikaru?KomatsuEmail author Norifumi?Hotta Koichiro?Kuraji Masakazu?Suzuki Taikan?Oki 《Boundary-Layer Meteorology》2005,115(2):205-221
Wind speed profiles above a forest canopy relate to scalar exchange between the forest canopy and the atmosphere. Many studies have reported that vertical wind speed profiles above a relatively flat forest can be classified by a stability index developed assuming wind flow above a flat plane. However, can such a stability index be used to classify vertical wind speed profiles observed above a sloping forest at nighttime, where drainage flow often occurs? This paper examines the use of the bulk Richardson number to classify wind speed profiles observed above a sloping forest at nighttime. Wind speed profiles above a sloping forest were classified by the bulk Richardson number Ri B . Use of Ri B distinguished between drainage flow, shear flow, and transitional flow from drainage flow to shear flow. These results suggest that Ri B is useful to interpret nighttime CO2 and energy fluxes above a sloping forest. Through clear observational evidence, we also show that the reference height should be high enough to avoid drainage-flow effects when calculating Ri B . 相似文献