含泥化夹层反倾岩质边坡动力响应的大型振动台试验

针对含泥化夹层反倾岩质边坡制作相似比为1∶30的试验模型进行大型振动台试验,研究泥化夹层饱水前(天然含水状态)和饱水状态下边坡的加速度和位移响应规律,探讨边坡的破坏模式。试验结果表明:泥化夹层饱水后坡面水平向加速度放大系数小于饱水前;泥化夹层饱水前和饱水后随着相对高度的增加,坡面水平向加速度放大系数呈现非线性增加的趋势,其整体上大于坡体内部的加速度放大系数;坡面位移从下至上在泥化夹层饱水前,呈现出非线性增长特性;饱水后位移呈先增大后减小,临近坡肩处坡面最大,坡面呈现鼓出形态。泥化夹层饱水前,在幅值为0.3g的地震波作用下坡体仅出现坡肩局部掉块;饱水后,输入地震动幅值≥0.4g时,坡体先出现坡肩的局部掉块,随后坡体沿中上部的饱和泥化夹层滑动剪出,与此同时,坡体中上部出现纵向裂隙并与水平裂隙贯通,坡顶被震碎。     

地震作用下双层土裂缝边坡稳定性分析

裂缝常存在于边坡表面，地震作用会大幅降低裂缝边坡稳定性。针对双层土裂缝边坡稳定性问题，定义上下土层分界处高度与边坡高度之比为深度系数以描述双层土的分布，基于极限分析上限定理，构建“点到点”离散运动学机构，并在此机构中引入一条垂直张拉裂缝，结合拟静力法和强度折减法建立能量平衡方程求解裂缝边坡临界高度和安全系数上限解。计算结果与传统上限法进行对比，验证离散运动学机构的有效性及其解的优越性，同时探究土体非均质性及深度系数对裂缝边坡稳定性以及裂缝深度和位置的影响规律。结果表明，地震作用会降低边坡稳定性；随着地震力增大，边坡临界滑动面逐渐加深，裂缝深度略微增大，裂缝位置逐渐远离坡面；对于具体的双层土边坡会存在一个特定的深度系数使边坡安全系数达到最值，同时裂缝会穿越至下层土且深度发生突增。     

强震作用下层状岩质斜坡破坏的大型振动台试验研究

以“5.12”汶川地震背景为基础,对不同岩性组合水平层状岩质边坡进行了大型振动台模型试验研究.文中介绍了振动台试验过程,通过对试验现象的观察处理分析,考察了边坡的破坏现象特征、变形破坏模式.实验结果表明,地震力作用下边坡的变形破坏程度、特征以及稳定性不仅与地震波的类型、加载方向、频率、振幅有关,同时还受边坡的岩体性质、...     

Difference between static and dynamic angle of repose of uniform sediment grains

In the investigation of sediment transport, it is necessary to differentiate various definitions of angle of repose (AoR) available in the literature. The static AoR, composed of upper and lower angle of slope, forms just before and after slope instability, while the dynamic AoR can be observed when sediment grains are moving continuously down an inclined plane. In the present study, a series of laboratory experiments was conducted to measure static and dynamic angle of repose for uniform natural sedi-ments with median diameter of 0.28–4.38 mm. The results show that the different slope angles have different characteristics. The upper and dynamic AoR increase slightly with increasing grain diameter, while the lower AoR is not sensitive to changes in sediment size and may assume a constant value. The average of the upper and lower AoR is equivalent to the dynamic AoR, and the difference between them increases with increasing grain diameter. The present study suggests that the different angles of repose should be treated with caution when applying in investigations of bedload transport, dune migration and local scour development.     

断裂构造对斜坡应力场影响的数值模拟及成灾机理研究

断裂构造及活动强度对斜坡体的应力场分布具有重要的影响。采用基于强度折减法的有限元法,分别以正断层和逆断层与斜坡体的组合关系为例,剖析了断裂构造对斜坡体应力场的影响及成灾机理,揭示了含有断层的斜坡体塑性区的贯通过程。研究表明,包含断层的斜坡体在应力分布特征及斜坡变形破坏机理方面与无断层的斜坡体有较大差别：含断层的斜坡体在坡面和断层面附近的最大主应力迹线与坡面或断层面相平行,在天然状态下,塑性区同时出现在坡脚和断层面后方,随着折减系数的增大,塑性区分别从坡脚和断层面后方向坡体深部和上部发展,直至断层面前后两个塑性区相贯通,坡体发生破坏,并且对坡体变形破坏的影响程度以逆断层最强,其次为正断层,断层不活动时较弱。     

Identifying slope processes over time and their imprint in soils of medium‐high mountains of Central Europe (the Karkonosze Mountains,Poland)

Soils in mountainous areas are often polygenetic, developed in slope covers that relate to glacial and periglacial activities of the Pleistocene and Holocene and reflect climatic variations. Landscape development during the Holocene may have been influenced by erosion/solifluction that often started after the Holocene climatic optimum. To trace back soil evolution and its timing, we applied a multi‐methodological approach. This approach helped us to outline scenario of soil transformation. According to our results, some aeolian input must have occurred in the late Pleistocene. During that time and the early Holocene, the soils most likely had features of Cryosols or Leptosols. Physico‐chemical and mineralogical analyses have indicated that the material was denudated (between late Boreal to the Atlantic) from the ridge and upper‐slope positions forming a colluvium at mid‐slope positions. Later, during the Sub‐Boreal, mass wasting of the remains of silt material deposited at the end of the Pleistocene age on the ridge top seems to have occurred. In addition, the cool and moist conditions caused the deposition of a colluvium at the lower‐slope positions. The next phase was characterized by the transformation of Leptosols/Cambisols into Podzols at upper‐slope or shoulder positions and to Albic Cambisols at mid‐slope positions. During the Sub‐Boreal period, Stagnosols started to form at the lower part of the slope catena. Overall, the highest erosion rates were calculated at the upper‐slope position and the lowest rates at mid‐slope sites. Berylium‐10 (¹⁰Be) data showed that the Bs, BC/C were covered during the Holocene by a colluvium with a different geological composition which complicated the calculation of erosion or accumulation rates. The interpretation of erosion and accumulation rates in such multi‐layered materials may, therefore, be hampered. However, the multi‐methodological reconstruction we applied shed light on the soil and landscape evolution of the eastern Karkonosze Mountains. Copyright © 2017 John Wiley & Sons, Ltd.     

Opportunities for manipulating catchment water balance by changing vegetation type on a topographic sequence: a simulation study

This simulation study explores opportunities to reduce catchment deep drainage through better matching land use with soil and topography, including the ‘harvesting’ (evapotranspiration) of excess water running on to lower land units. A farming system simulator was coupled with a catchment hydrological framework to enable analysis of climate variability and 11 different land‐use options as they impact the catchment water balance. These land‐use options were arranged in different configurations down a sequence of three hydrologically interconnected slope units (uphill, mid‐slope and valley floor land units) in a subcatchment of Simmons Creek, southern New South Wales, Australia. With annual crops, the valley floor land units were predicted to receive 187 mm year^?1 of run‐on water in addition to annual rainfall in 1 in 10 years, and in excess of 94 mm year^?1 in 1 in 4 years. In this valley floor position, predicted drainage averaged approximately 110 mm year^?1 under annual crops and pastures, whereas permanent tree cover or perennial lucerne was predicted to reduce drainage by up to 99%. The planting of trees or lucerne on the valley floor units could ‘harvest’ run‐on water, reducing drainage for the whole subcatchment with proportionately small reduction in land areas cropped. Upslope land units, even though often having shallower soil, will not necessarily be the most effective locations to plant perennial vegetation for the purposes of recharge reduction. Water harvesting opportunities are site specific, dependent on the amounts and frequency of flows of water to lower landscape units, the amounts and frequency of deep drainage on the different land units, the relative areas of the different land units, and interactions with land use in the different slope positions. Copyright © 2007 John Wiley & Sons, Ltd.     

中国东部海域地壳-上地幔瑞利波速度结构研究

为了进一步了解中国东部沿海及相邻海域的地壳－上地幔结构特征,对该区域的构造演化历史、地震活动及深部构造等方面研究提供一些基础资料,利用３１个数字地震台记录的高质量瑞利波资料,采用一种新的混合路径频散的网格反演方法（Ｏｃｃａｍ方法）,对中国东部海域瑞利波群速度横向不均匀分布进行了初步研究．根据反演得到的１０-１５０ｓ共３６个中心周期的群速度分布特征,以及几个典型地点的剪切波速度结构的深度变化,对研究区域内各构造单元的划分以及它们在速度结构和上地幔低速层埋深等方面的特征进行了讨论。     

Seismic stability analysis of fractured rock slopes by yield design theory

This paper deals with the problem of stability of fractured rock slope located in seismic area. The rock mass is crossed by two sets of fractures which are considered to be planar, parallel and persistent. The effects of both horizontal seismic coefficient and strength characteristics of fractures are addressed. The analysis is based upon the kinematic approach of the yield design theory and the pseudo-static method as well. The fundamental inequality of the kinematic approach is invoked and the failure of the fractured rock slope is considered through simple translational mechanism involving a one-partsliding block. Rigorous upper bounds of the so-called stability factor for the structure under study of given slope angle, strength properties of constituent materials and seismic loads are obtained. The results are presented in the form of stability charts relating the estimated upper bound solutions to the friction angle of fractures.The used procedure highlights the destabilizing effects of the seismic loadings and is capable of conducting parametric studies. Furthermore, the results obtained far from various sets of data show good performance and further research work is planed to extend the analysis to include a large number of sub-problems.     

Pyroclastic flow deposits of the 1991 eruption of Volcán de Colima,Mexico

The April 16, 1991, eruption of Volcán de Colima represents a classical example of partial dome collapse with the generation of progressively longer-runout, Merapi-type pyroclastic flows that traveled up to 4 km along the El Cordoban gullies (East, Central and West). The flows filled the gullies with block-and-ash flow deposits up to 10 m thick, of which, after 7 years of erosion, only remnants remained in the El Cordoban West and East gullies. The El Cordoban Central gully, however, provided a well-preserved and incised longitudinal section of the 1991 deposits. The deposits were emplaced as proximal and distal facies, separated by a change in slope angle from >30° to <20°. The proximal facies consists of massive, clast-supported flow units (up to 1 m thick) with andesite blocks locally supported by a matrix of coarse ash and devoid of segregation structures or grading. The distal facies consists of a massive, matrix-supported deposit up to 8 m thick, which contains dispersed andesite blocks in a fine ash matrix. In the distal facies, a train of blocks marks flow-unit upper boundaries and, although sorting is poor, some grading is present. Thin, finely stratified, or dune-bedded layers of fine ash material are locally present above or below units of both facies. Sedimentologic parameters show that the size or fraction of large pyroclasts (larger than –1 ) decreases from proximal to distal facies, as the percentage of matrix (0 to 4 ) increases, especially immediately beyond the break in slope. We propose that the propagation of the Colima pyroclastic flows is critically dependent on local slope angle, the presence of erodible slope debris, and the decrease in grain size with distance from the vent. The progressive fining is probably caused by some combination of erosion, clast breakup and deposition of larger pyroclasts, and is itself influenced by the slope angle. In the proximal region, the flows moved as granular avalanches, in which interacting grains ground each other and erosion occurred to produce an overriding dilute ash cloud. The maximum runout distance of the avalanches was controlled by the angle of repose of the material, and the volume and grain size of source and eroded material. Because the slope angle is close to the repose angle for this debris, granular avalanches were not able to propagate far beyond the change in slope. If, however, an avalanche had enough mass in finer grain size fractions, at least part of the flow continued beyond the break in slope and across the volcano apron, propagating in a turbulent state and depositing surge layers, or in an otherwise settling-modified state and depositing block-and-ash flow layers.Editorial responsibility: T Druitt     

Paraglacial modification of slope form

The morphological consequences of paraglacial modification of valley-side drift slopes are investigated at six sites in Norway. Here, paraglacial slope adjustment operates primarily through the development of gully systems, whereby glacigenic sediment is stripped from the upper drift slope and redeposited in debris cones downslope. This results in an overall lowering of average gradient by up to 4·5° along gully axes. In general, slope profile adjustment appears to be characterized by a convergence of slope profiles towards an ‘equilibrium form’ with an upper rectilinear slope gradient at 29°± 4° and a range of concavities of approximately 0·0 to 0·4. After initial rapid incision, further gully deepening is limited, but gullies become progressively wider as sidewall gradients decline to c. 25°, after which parallel retreat appears to predominate. The final form of mature paraglacial gully systems consists of an upper bedrock-floored source area, a mid-slope area of broad gullies whose sidewalls rest at stable, moderate gradients, and a lower slope zone where gullies discharge onto the surfaces of debris cones and fans. Some gullies appear to have attained this final form and have stabilized following exhaustion of readily entrainable sediment within decades of gully initiation. At most sites, paraglacial activity has transformed steep drift-mantled valley sides into gullied slopes where an average of c. 2–3 m of surface lowering has taken place. At the most active sites, these average amounts imply minimum erosion rates averaging c. 90 mm a⁻¹ since gully initiation, which highlights the extreme rapidity of paraglacial erosion of deglaciated drift-mantled slopes. Copyright © 1999 John Wiley & Sons, Ltd.     

Point process-based modeling of multiple debris flow landslides using INLA: an application to the 2009 Messina disaster

We develop a stochastic modeling approach based on spatial point processes of log-Gaussian Cox type for a collection of around 5000 landslide events provoked by a precipitation trigger in Sicily, Italy. Through the embedding into a hierarchical Bayesian estimation framework, we can use the integrated nested Laplace approximation methodology to make inference and obtain the posterior estimates of spatially distributed covariate and random effects. Several mapping units are useful to partition a given study area in landslide prediction studies. These units hierarchically subdivide the geographic space from the highest grid-based resolution to the stronger morphodynamic-oriented slope units. Here we integrate both mapping units into a single hierarchical model, by treating the landslide triggering locations as a random point pattern. This approach diverges fundamentally from the unanimously used presence–absence structure for areal units since we focus on modeling the expected landslide count jointly within the two mapping units. Predicting this landslide intensity provides more detailed and complete information as compared to the classically used susceptibility mapping approach based on relative probabilities. To illustrate the model’s versatility, we compute absolute probability maps of landslide occurrences and check their predictive power over space. While the landslide community typically produces spatial predictive models for landslides only in the sense that covariates are spatially distributed, no actual spatial dependence has been explicitly integrated so far. Our novel approach features a spatial latent effect defined at the slope unit level, allowing us to assess the spatial influence that remains unexplained by the covariates in the model. For rainfall-induced landslides in regions where the raingauge network is not sufficient to capture the spatial distribution of the triggering precipitation event, this latent effect provides valuable imaging support on the unobserved rainfall pattern.     

不同厚度层状边坡动力响应的模型试验研究

采用振动台物理模拟试验方法,以4种不同覆土厚度的层状边坡模型为研究对象,水平输入振幅逐渐增大的正弦波加速度,分析了结构面上覆不同厚度土层对动力作用下边坡的稳定影响.研究了在动力作用下边坡的破坏位置和性质、破坏形式及最危险覆土厚度,验证了坡面放大效应与高程的关系,采用MIDAS/GTS软件对模型试验进行振型分析,分析了模型边坡的自振频率与覆土厚度的变化关系.试验结果表明：①模型破坏时最先出现的裂缝在边坡的中上部,且6 cm覆土厚度的模型对振动的响应最大,对应到实际工程中时12m厚度土层覆盖的边坡是最应该注意防护的.②不同厚度的土层破坏的形式不同：当土层厚度较薄时模型破坏较迅速,基本沿结构面发生整体滑动破坏,且滑动呈现一定的流体特性;当覆土较厚时裂缝先在模型中上部出现,随着振动的持续裂缝继续发展,最后发生整体性崩塌.③随着高程的增加峰值加速度总体呈放大趋势,但最大值出现在边坡中上部而非坡顶,说明不仅均质边坡有加速度的高程放大效应,层状边坡也具有加速度的高程放大效应.     

The structure and sedimentology of relict talus,Trotternish, northern Skye,Scotland

Sections up to 3·5 m deep cut through the upper rectilinear segment of relict, vegetated talus slopes at the foot of the Trotternish escarpment reveal stacked debris-flow deposits intercalated with occasional slopewash horizons and buried organic soils. Radiocarbon dating of buried soil horizons indicates that reworking of sediment by debris flows predates 5·9–5·6 Cal ka BP , and has been intermittently active throughout the late Holocene. Particle size analyses of 18 bulk samples from these units indicates that c. 27–30 per cent of the talus deposit is composed of fine (<2 mm) sediment. Sedimentological comparison with tills excludes a glacigenic origin for the talus debris, and the angularity of constituent clasts suggests that in situ weathering has been insignificant in generating fine material. We conclude that the fine sediment within the talus is derived primarily by granular weathering of the rockwall, with syndepositional accumulation of both fine and coarse debris, implying that c. 27–30 per cent of rockwall retreat since deglaciation reflects granular weathering rather than rockfall. The abundance of fines within the talus deposits is inferred to have been of critical importance in facilitating build-up of porewater pressures during rainstorms, leading to episodic failure and flow of debris on the upper parts of the slope. A wider implication of these findings is that the mechanical properties of talus slopes cannot be regarded as those of free-draining accumulations of coarse clasts, and that models that treat talus slopes as such have limited value in explaining their form and evolution. Our findings lend support to models that envisage the upper straight slope on talus accumulations as the product of mass-transport as well as rockfall, and indicate that episodic debris flow has been the primary agent of mass-transport at this site. © 1998 John Wiley & Sons, Ltd.     

Effects of hillslope topography on runoff response in a small catchment in the Fudoji Experimental Watershed,central Japan

We investigated the role of different hillslope units with different topographic characteristics on runoff generation processes based on field observations at two types of hillslopes (0·1 ha): a valley‐head (a convergent hillslope) and a side slope (a planar hillslope), as well as at three small catchments having two types of slopes with different drainage areas ranging from 1·9 to 49·7 ha in the Tanakami Mountains, central Japan. We found that the contribution of the hillslope unit type to small catchment runoff varied with the magnitude of rainfall. When the total amount of rainfall for a single storm event was < 35 mm, runoff in the small catchment was predominantly generated from the side slope. As the amount of rainfall increased (>35 mm), the valley‐head also began to contribute to the catchment runoff, adding to runoff from the side slope. Although the direct runoff from the valley‐head was greater than that from the side slope, the contribution from the side slope was quantitatively greater than that from the valley‐head due to the proportionally larger area occupied by the side slope in the small catchment. The storm runoff responses of the small catchments reflected the change in the runoff components of each hillslope unit as the amount of rainfall increased and rainfall patterns changed. However, similar runoff responses were found for the small catchments with different areas. The similarity of the runoff responses is attributable to overlay effects of different hillslope units and the similar composition ratios of the valley‐head and side slope in the catchments. This study suggests that the relative roles of the valley‐head and side slope are important in runoff generation and solute transport as the catchment size increases from a hillslope/headwater to a small catchment. Copyright © 2011 John Wiley & Sons, Ltd.     

Variability of thermal structure off Georgia,winter 1978

Temperatures recorded over the Georgia shelf and at near-bottom locations on the slope are compared with records of thermocline elevation from inverted echo sounders on the slope and with shore wind observations, for the period January to April 1978.Both upwelling and downwelling events are observed. Upwelling events are associated with upwelling-favorable wind and/or Gulf stream frontal eddies. Strong upwellings are accompanied by risings of the thermocline over the slope, but some weaker eddies occur without noticeable thermocline disturbance. Downwelling events are associated with onshore meander crests of the Gulf Stream, and sometimes with downwelling-favorable wind. The influence of downwelling does not extend seaward of the upper slope.A long-term (1 month) variation of the thermal structure is observed at the shelf break and under the Gulf Stream. It is related to a filament of cold water on the slope, varying in path and size. This cold filament appears to be Antarctic Intermediate Water which is variably advected through the Straits of Florida. Theory suggest that the variability may be caused by changes in the thermocline depth and tilt across the Gulf Stream in response to transport fluctuations.     

Impact of the Rainfall Intensity and Seepage on Slope Stability in Loess Plateau

In recent years, with the increase of traffic construction in mountainous areas in China, road slope traffic accidents have become more and more common. In addition, natural disasters such as landslides, collapses and subgrade settlements caused by rainfall, driving load, seasonal variation and groundwater distribution are frequent. In particular, rainfall is one of the most common factors leading to slope instability (landslide). Therefore, this paper proposes the seep module based on the application software Geo-studio, and analyzes the slope soil parameters and slope stability under five types of rainfall conditions:light rain (10 mm/d), moderate rain (25 mm/d), heavy rain (50 mm/d), rainstorm(100 mm/d), and torrential rain (250 mm/d). The critical safety factor under rainfall intensity is fitted with nonlinear curve by sine function. The results show that the fitting curve of rainfall intensity and safety factor on the upper slope is excellent. The residual points are evenly distributed in the belt area of±0.1, and the data basically conform to the nonlinear sine model, indicating that the curve plays an essential role in slope health diagnosis.     

基于拟动力法的顺层岩质边坡稳定性极限分析

基于极限分析上限法的原理,结合随时间变化的拟动力法,考虑地震、水力和坡顶超载作用下建立含张拉裂缝的顺层岩质边坡极限分析模型,并推导出边坡安全系数的表达式。结构面采用合理的水压力分布形式,且强度参数采用非等比例折减,分析边坡前缘是否堵塞,水平和竖向地震系数、张裂缝积水深度和坡顶超载对边坡安全系数的影响。分析表明:边坡前缘堵塞、水平地震系数、张裂缝积水深度和坡顶超载的增加,降低边坡的稳定性;竖向地震系数的增加提高了边坡的稳定性。随着非等比例折减相关系数的增加,边坡稳定性显著提高。因此结构面参数的变化规律需要得到关注。     

RELATIONSHIP OF SEDIMENT PRODUCTION BETWEEN HILLSLOPE AND GULLY SLOPE IN A SMALL BASIN IN THE BILLY LOESS REGION, NORTH CHINA

SomepeOPlehaverecognizedtheSPatialvariationoflandionnsandgeomorphicPeainthehillyloessregion,NOIthClam(Chenetal.1988).SuchvariationshaVe~linkedtotheverticalzonationofsoilerosionandsedimentproduedoninthisarea(Catetat.1994).HoWeVer,noneOftheStlldiesaPProachtheProbleminaqUantitativemanner.NorweretherelationsbetweensoilerosionPr~sontheoneban4andhydrologicandghgogicalcharacteristicsofthevariouSslopezonesontheother,dearlyestatiIisned.Inaaamon,~stubbesintheareahaveprtridtahotoshowthe~rtanceo…     

Simulation of rainfall-runoff and watershed convergence process in the upper reaches of Heihe River Basin, July 2002

The watershed flow concentration scheme in the distributed hydrology-soil- vegetation model (DHSVM) is coupled with the mesoscale atmospheric model MM5 version 3.5, in which the Oregen States University land surface model (OSULSM) was involved. The flood event which happened in July 2002 in the upper reaches of Heihe river basin is simulated and the surface flow convergence process is shown with this coupled model. It has been concluded that times water head reaches each place of the basin are different. Water amount at each point is split-flow proportionally as the drops in elevation between it and neighbor points. Large part of the water amount pass away in greater slope direction and small part pass away in smaller slope one.Adding of the slope convergence makes the atmospheric model redistributes the surface water laterally.