应用于滑坡的拉力型锚索失效机理

拉力型锚索常用于公路边坡支护工程中,在进行锚固体的结构设计时,注浆体与岩石粘结界面的强度往往被高度关注.在广泛调研西南山区失稳破坏的公路边坡时发现,拉力型锚索最为薄弱的部位并非注浆体与岩石粘结界面.因此,设计11种不同配合比的注浆体,将80根拉力型锚索锚固在软岩及硬岩中,采用拉拔试验对锚索的破坏模式进行研究.结果表明:拉力型锚索常见的破坏模式是钢绞线与注浆体之间的脱粘破坏.选择合理的力学计算模型,获得内锚固段两个粘结界面的应力分布弹性解,分析表明:钢绞线与注浆体粘结界面的峰值应力位于锚孔孔口处,应力分布不均匀程度高,致使孔口处的钢绞线注浆体粘结界面首先发生脱粘破坏,脱粘界面以渐进的方式向内锚固段末端传递,最终导致钢绞线从注浆体中旋转拔出.建议上述研究成果在以后的规范修订和锚固工程设计时引起足够的重视.最后,给出了一个钢绞线与注浆体脱粘破坏的工程实例.     

磨刀溪岩石滑坡分析与治理

磨刀溪岩石滑坡由于人工开挖、在支挡不当的情况下产生并逐步扩大。对此,着重采用了工程地质力学法对该滑坡进行了分析,明确了该滑坡为一切层滑坡,其发生发展与岩层的结构面关系密切。在此基础上以推力传递系数法及地基系数等为理论,确定以一排抗滑桩及一排锚索抗滑桩进行支挡,并在下排桩前采用锚索框架对桩前岩土体进行加固,以确保抗滑桩的锚固段不松弛变形,同时结合疏排水的措施对该滑坡予以彻底治理,从实践看最后一次的治理取得了成功。同时分析了前面几次失败的治理经历,从中总结了很多有益的经验和教训,并从治理实践中证明了该滑坡治理措施的合理性和有效性,值得同类工程借鉴。     

冰碛物滑坡中的锚固工程试验

冰碛为冰川搬运和堆积的松散物质,发育在其上的公路滑坡较为少见,缺少相关经验与试验数据。作者考察研究了国内外关于堆积层滑坡的治理现状,结合锚固工程界专家提出的锚固工程研究方向,在现场贴片锚固试验的基础上,对发育在冰碛物上的滑坡体锚固工程进行了专题研究,综合考虑不同锚索型式、不同锚索锚固段长度、不同张拉吨位对锚索锚固段应力分布规律的影响,得出了适用于冰碛物滑坡的锚固试验结论,经过综合比选推荐了一种适用的锚索锚固型式。并结合试验结果通过有限元试算,提出了适宜的建模边界条件。     

岩土工程边坡治理中的预应力锚索技术

岩土工程边坡失稳容易引发较大的安全事故,造成巨大的人员伤亡和财产损失,加强对岩土工程边坡治理成了一个具有理论和实践双重价值的研究课题。本文将详细分析预应力锚索技术在岩土工程边坡治理中应用的优势,探讨岩土工程边坡锚固技术作用机理,并就具体应用提出了几点建议。     

加固含水平软弱层高陡边坡预应力锚索倾角的取值范围

用直线和曲线滑面两种模型，模拟预应力锚索加固含有水平软弱层的高陡边坡的潜在滑动面，通过对锚索加固的力学机理分析来阐述预应力在滑动面主滑方向上产生分力的原因。从锚索受力角度上对锚索倾角的取值范围进行探讨，结合实际造孔过程有不同程度的孔斜或弯曲以及获取较好的锚固灌浆效果，就仰角锚固和俯角锚固两种锚固条件分别得出锚索倾角的取值范围，并以此来判定锚索的预应力是否会在滑动面走向方向上产生不利于坡体稳定的下滑力。     

三处滑坡工后锚索承载性能现场试验对比分析

工后边(滑)坡预应力锚固工程的长期工作性能是影响锚固工程安全性的一个关键问题。通过一种改进的拉拔检测设备,对重庆三处滑坡工后锚索结构进行了锚索抗拔力检测。通过对各工点检测结果的分析,对各工点锚索结构物当前预应力状态,预应力损失率,锚索安全储备进行了科学判定,为补强整治提供依据。对比分析了造成三处滑坡预应力损失差别较大的原因,岩体蠕变变形及锚索的松弛耦合变形是导致工后锚索预应力损失的主要原因,对于过于松散破碎或含水量较大的滑坡体尽量避免采用预应力锚索结构。通过对比分析各工点工后锚固工程的应力状态及锚索破坏方式表明,锚固段破坏是引起锚固工程失效的主要方式之一,今后锚索工程施工时,应重点注意锚索的长度及注浆等施工质量。对于大型的边(滑)坡中的预应力锚固工程建议安装锚索测力设备,以便时掌握预应力损失情况,及时进行补张拉,防患于未然;对于未安装锚索测力设备的,建议封锚时,预留钢绞线长度大于5 cm,以便工后进行拉拔检测试验。此种改进的拉拔检测设备具有简单、实用、易操作等特点,值得在工后岩土锚固工程长期性能评价领域推广应用。     

岩质边坡锚固参数正交优化分析及应用

岩质边坡防护的最有效措施就是锚固工程。然而锚固参数(包括锚杆或锚索长度、锚固间距、预应力大小等)的选取至今在理论上未能很好解决,在实际工程中也未体现出合理的优化设计。以云沱段狮子包边坡2-2′剖面(K0 85.7 m)为例,运用正交试验设计法分析锚固参数的组合方案,以边坡稳定性系数作为评价指标,分别改变锚固参数,以此分析对边坡稳定性的影响。研究结果表明,对边坡稳定性影响显著的因素由大至小的顺序是:预应力大小、锚固间距、锚杆长度。以此研究结果为该实例的锚固支护参数选取确定了设计方案,最后采用有限差分程序FLAC3D进行了锚固效果数值分析验证。     

岩土工程中边坡治理的岩土锚固技术探讨

随着现代科技的不断发展,施工技术处于进步之中,新材料与新工艺层出不穷,岩土工程施工技术也呈现多元化趋势。岩土锚固技术成为影响岩土工程边坡治理效果的重要方面。结合岩土工程实践,分析影响边坡稳固的因素,对岩土锚固进行全面研究,构建科学合理的技术应用方案,加速岩土锚固技术在边坡治理中的推广与应用,在根本上为岩土工程的顺利开展创造更加优质的条件。     

浅谈边坡稳定性问题及其主要治理措施

我国经济发展十分迅速,对建筑工程发展有促进作用。在建筑工程施工过程中,如果没有及时对潜在的边坡地质灾害进行防治,很可能会在工程建设过程中或完工后产生崩塌、滑坡、泥石流等地质灾害。边坡稳定性问题最主要的原因就是边坡抗滑能力减弱,一旦边坡处于高荷载或暴雨等情况下,就很容易出现变形及下滑现象。因此,在边坡滑坡预防及治理过程中,应根据边坡特征、地质条件及周边环境等,合理选用抗滑桩、预应力锚索（锚杆）、格构梁、土骨架、主动防护网、挡土墙等治理措施。本文简单分析影响边坡稳定性的主要因素,并提出合理的边坡治理原则要求与具体措施。     

刍议岩土工程中边坡治理的岩土锚固技术

在建筑市场的快速发展背景下,新型施工技术、材料、工艺不断出现。尤其是岩土工程中,在边坡治理中使用岩土锚固技术不仅可以提升治理效果,同时也可以降低边坡坍塌率。所以在岩土工程边坡治理中,要制定出合理化施工方案,做好岩土锚固技术推广工作,提高岩土工程施工质量。     

Instability of a High Alpine Rock Ridge: the Lower Arête Des Cosmiques,Mont Blanc Massif,France

Rockfalls are dominant in the rock slopes and rock ridge morphodynamics in high mountain areas and endanger people who pass along or stay there, as well as infrastructure that host them (cable cars, refuges). Risks are probably greater now because of fast permafrost degradation and regression of surface ice, two consequences of the atmospheric warming of the last decades. These two commonly associated factors are involved in the instability of rock slopes by modifying the mechanical behaviour of often ice‐filled rock fractures and the mechanical constraints in the rock masses. This paper examines over 15 years the instability of the lower Arête des Cosmiques on the French side of the Mont Blanc massif. Its vulnerability is due to the presence of a high‐capacity refuge on its top (3613 m a.s.l.). In 1998, a part of the refuge was left without support when a collapse of 600 m³ occurred immediately below it. Since this date, reinforcement work has been carried out in this area, but the whole ridge has been affected by around 15 relatively shallow rockfalls. Through a multidisciplinary approach, this article assesses the role of the cryospheric factors in the triggering of these rockfalls.     

泥石流堆积特征及其斜坡稳定性评价

以往对泥石流的研究多集中在活动泥石流及其危害方面，边坡稳定性评价中，常据泥石流堆积体边坡看作均质边坡。通过对川西山区若干典型泥石流堆积边坡的研究，划分了泥石流的堆积类型，发现泥石流堆积边坡并非一种完全均质边坡，而是一种具有控制性沉积结构面的堆积边坡，并论述了不同类型泥石流堆积边坡的控坡要素及其边坡稳定性。     

Assessment of geomorphic hazards in connection with permafrost occurrence in the Zugspitze area (Bavarian Alps, Germany)

In the Zugspitze area (Bavarian Alps, Germany), permafrost conditions are present in limestone bedrock and in regolith. Distribution is strongly dependent on topography in the east–west oriented mountain crest with steep north- and south-facing slopes. Numerous structures mainly for tourist purposes (cable car and recreation buildings, ski-lift masts, rack-railway tunnel, tunnel with supply facilities) are situated in the area, and several of them are placed on ground with permafrost. Results from a temperature measurement programme and distribution modelling show that for some of these constructions, the effects of permafrost degradation have to be considered in terms of stability of the foundations.The permafrost limit is close to the summit crest, and therefore, stability evaluations for the constructions in this area have to bear in mind the possible warming or even melting of ice within the bedrock crevasses caused by climate warming. Stability of the foundations as well as stability of rock walls in this area will probably be affected by a shifting of the permafrost limit. Constructions in the Zugspitzplatt area are already affected by the melting ground ice, and stabilizing measures have to be evaluated for several foundations where subsidence is likely to occur.Besides the local results, the study provides for the first time data on permafrost distribution in the northern Alpine margin based on standard methods of BTS measurements and numerical modelling.     

Use of Thermal Infrared Multispectral Scanner (TIMS) imagery to investigate upslope particle size controls on arid piedmont morphology

Geomorphic differences between slopes backing two distinct desert piedmont types provide a proxy indicator for the kind of landform developed at the corresponding mountain base. Here, the term ‘bedrock pediment’ describes subaerial bedrock platforms that emanate from a mountain base while ‘alluvial slope’ describes suballuvial bedrock platforms that extend from the mountain. Mountain slopes backing bedrock pediments have been demonstrated to be mantled by larger clast sizes than corresponding slopes backing alluvial slopes in the Phoenix region, Arizona, USA. The present research focuses on using the disparate particle sizes between slopes backing bedrock pediments and alluvial slopes as an indicator for the piedmont form developed at the mountain base, and uses high-resolution remotely sensed digital data as a medium for quantitative landform assessments. A gravel + bedrock versus soil index developed from airborne midinfrared multispectral imagery acquired by the Thermal Infrared Multispectral Scanner (TIMS) indicates the presence of slopes mantled with larger particle sizes versus slopes mantled with smaller particle sizes and greater soil coverage. Two test areas confirm the applicability of this method and further demonstrate the usefulness of high-resolution midinfrared multispectral imagery as a geomorphic tool in arid regions.     

全球海底光缆传输网络的节点职能与鲁棒性评价

海底光缆传输网络是全球信息传递和要素流动的重要基础设施支撑,国家或地区在全球海底光缆网络中的节点职能和对网络鲁棒性的影响事关国家信息通信安全。在此背景下,研究基于全球网络基础设施Infrapedia数据库,提取了1991—2017年近30年全球光缆分布数据,运用复杂网络分析方法,研究了不同国家或地区在全球光缆网络中承担“传输职能”和“枢纽职能”的特征及其演变,并探究了全球海底光缆网络的鲁棒性。研究发现：①国家或地区的信息传输职能和枢纽职能具有不同的模式;其中信息传输职能较为扁平化,且呈明显廊道格局,咽喉海峡沿线的国家或地区占据重要位置;信息枢纽职能具有明显的等级结构。②毗邻海峡的地缘战略位置、背靠强劲的国家实力、增长迅速的市场需求等共同塑造了全球海底光缆网络中的重要节点。③部分节点（尤其是高中间中心性的节点）发生故障会导致整个网络功能的大幅下降。研究从避免海底光缆链接的单一性、提升全球枢纽职能等方面提出了维护我国海底信息传输安全的启示。     

Effects of environmental change on scree slope development throughout the postglacial period in the Chic-Choc Mountains in the northern Gaspé Peninsula, Québec

The combined study of present-day processes and stratigraphic data, has permitted the reconstruction of the dynamics of scree slopes of the northern Gaspé Peninsula throughout the postglacial period. In this region, liberated progressively from beneath an ice cover between 13,500 and 10,000 years BP, the scree slopes have to be seen as an integral part of a regional geosystem. Evolution of these slopes has been rapid, influenced by local paraglacial conditions (glacio-isostatic rebound, glacio-eustatic fluctuations, and re-equilibration of glacially over-steepened rockwalls) which operated against a backdrop of Late Glacial and Holocene climatic fluctuations. During the Younger Dryas and part of the Early Holocene period, as the foot slopes emerged from beneath the Goldthwait Sea, the basal part of several scree slopes advanced onto marine terraces as lobate rock glaciers, under the influence of a periglacial climate, characterised by permafrost. Many scree slopes continued to transfer debris downslope after regional establishment of a closed forest cover at ca. 7250 years BP. Forest colonisation in the early pre-emergent phase of the postglacial period was retarded, due to constant replenishment of the debris removed from the foot slopes by marine processes. In the later post-emergent phase, development of a complete forest cover has only been possible on slopes where the summit rockwall segment has been completely eliminated, a condition not yet fulfilled for many geomorphologically active scree slopes of the region. In fact, both of these paraglacial influences have been diachronous on a regional scale. Advance upslope of the forest front on the scree slopes appears to have been slow, difficult and subject to periodic regressions of possible climatic origin, as indicated by numerous buried soils in colluvial stratigraphic sequences, and for the past 150 years by dendro-ecological studies. Stratigraphic exposures, along with direct observation of slope events, have revealed the operation of a large variety of debris transfer processes, including niveo-aeolian sedimentation and frost-coated clast flows, the latter representing an important process first recognised on the scree slopes of Gaspésie.     

Automated classification of landform elements using object-based image analysis

This paper presents an automated classification system of landform elements based on object-oriented image analysis. First, several data layers are produced from Digital Terrain Models (DTM): elevation, profile curvature, plan curvature and slope gradient. Second, relatively homogenous objects are delineated at several levels through image segmentation. These object primatives are classified as landform elements using a relative classification model, built both on the surface shape and on the altitudinal position of objects. So far, slope aspect was not used in classification. The classification has nine classes: peaks and toe slopes (defined by the altitudinal position or the degree of dominance), steep slopes and flat/gentle slopes (defined by slope gradients), shoulders and negative contacts (defined by profile curvatures), head slopes, side slopes and nose slopes (defined by plan curvatures). Classes are defined using flexible fuzzy membership functions. Results are visually analyzed by draping them over DTMs. Specific fuzzy classification options were used to obtain an assessment of output accuracy. Two implementations of the methodology are compared using (1) Romanian datasets and (2) Berchtesgaden National Park, Germany. The methodology has proven to be reproducible; readily adaptable for diverse landscapes and datasets; and useful in respect to providing additional information for geomorphological and landscape studies. A major advantage of this new methodology is its transferability, given that it uses only relative values and relative positions to neighboring objects. The methodology introduced in this paper can be used for almost any application where relationships between topographic features and other components of landscapes are to be assessed.     

A comparison of landslide rates following helicopter and conventional cable-based clear-cut logging operations in the Southwest Coast Mountains of British Columbia

A comparison of landslide rates following helicopter and conventional, cable-based, clear-cut logging was carried out using results from two independent terrain attribute studies in the Eldred and Lois River watersheds in the Southwest Coast Mountains of British Columbia. Landslides initiating from directly within a road prism were excluded from the study in order to focus the comparison on landslides related primarily to conventional versus helicopter yarding methods. A landslide rate of 0.02 landslides/ha was observed in 162 terrain polygons logged by helicopter 8 years prior to this study. Landslide rates in 38 gullied polygons were 0.06 landslides/ha. No landslides were observed in 124 open-slope polygons. Over a similar 8-year average period, 0.03 landslides/ha were observed in 142 cable-yarded terrain polygons; 0.06 and 0.02 landslides/ha occurred in gullied and open-slope polygons, respectively. t-Tests indicate that total landslide rates are not significantly different following helicopter and conventional logging; however, a dichotomy exists between gullied and open-slope terrain polygons. Landslide rates are not significantly different in gullied terrain but are significantly higher on open-slopes following conventional cable logging. Consequently, landslides appear to have a greater potential to occur in open-slope terrain following conventional logging, but differences in gullied polygons are less likely. Increased post-logging landslide rates in conventionally logged, open slopes are more likely the result of undetected road-related drainage changes than differences between helicopter and conventional yarding-related ground disturbance.     

Water table control on rill initiation and implications for erosional response

On sloping sandy agricultural soil sites near Toronto, Canada, summer storms adequate to generate runoff occur frequently, but rill development occurs mainly in spring when snowmelt or rainfall-induced runoff occurs above frozen subsoil. This suggests that on low and moderate slopes on these soils rill initiation is controlled primarily by hydraulic impedance close to the surface, rather than critical hydraulic conditions in runoff. Laboratory flume experiments were carried out on 10 m slopes at 1.5°, 5° and 9° with loamy sand/clay composite soil sample to test this hypothesis. Runoff with hydraulic conditions adequate for rill initiation occurred rapidly in most tests, but on 1.5° and 5° slopes little knickpoint scour or sediment transport occurred before water table development. This coincided with reduced surface soil strength, knickpoint scour and marked increase in sediment discharge, particularly on 5° slopes where increase was 20- to 30-fold. Further increase in sediment discharge occurred when water tables reached the surface. On 9° slopes runoff occurred more quickly, with higher hydraulic values. Significant rill incision and sediment discharge occurred well before water table development, and ultimately reached much higher values than on lower slopes. Results show that soil erodibility can change dramatically over short time periods during storms due to soil moisture conditions, and that the presence of a hydraulic impedance close to the surface which causes a perched water table to develop can strongly influence rill incision and sediment transport. The influence is unlikely to be marked on soils which are very erodible regardless of moisture conditions, or on extremely resistant soils. It will also be limited on very gentle or steep sites, but can be a significant factor in rill development on intermediate slopes.     

Road-cut slope topography and stability relationships in St Lucia,West Indies

Slope topography is shown to be a significant factor in controlling the porewater pressures in road-cut slopes in the residual volcanic soils of St Lucia, West Indies. It is shown that this control diminishes as the permeability of the material decreases. This finding is confirmed by stability envelopes in which ‘stable’ and failed slopes are examined as a function of slope topography and material properties.