砂土中等截面桩的上拔机制分析

桩的上拔承载性能的宏观力学现象与桩周土细观结构变化相关,应用细观力学的颗粒流（PFC2D）数值模拟方法对承受上拔荷载作用的桩基进行了分析,数值模拟了上拔荷载作用的桩及桩周土的细观力学特征,研究了桩侧摩阻力的分布、桩周土剪切带的形成过程,较好的再现了桩的荷载－位移关系的实验结果,并与宏观物理实物试验的位移实测结果作了对比分析。分析了土体中剪切带形成过程中的颗粒间的细观变化及其形成过程,当上拔荷载达到极限时,上拔桩的剪切带形成原因是密砂的应变软化效应;颗粒流数值模拟的颗粒接触力与实物物理试验桩侧摩阻力是同一的,数值模拟的荷载-位移曲线与实物物理试验的荷载-位移曲线一致;桩侧摩阻力、桩上拔过程中剪切带的形成过程、桩上拔荷载-位移关系与颗粒流数值模拟的颗粒分布、速度、接触力的细观参数的变化密切相关。桩承受荷载过程中土颗粒细观结构变化的颗粒流仿真,是关于细观力学特征与宏观力学响应的初步研究。     

地震导致山体变形破裂机制地质力学模拟试验研究

地震导致山体变形破裂是一个复杂的演化过程,文中通过一些典型实例的地质分析,总结归纳了高地震烈度区山体变形破裂失稳有一定代表性的倾外层状体斜坡滑坡型、高陡块(层)状体斜坡崩塌型、软弱基座体斜坡滑坡型等3种典型性地质力学模式。自主创新研制、设计、探索了一套振动条件下地质力学模拟试验的设备模型和方法,并对3种典型性地质力学模型进行机制模拟试验。通过变形破裂演化过程模拟再现试验,从中揭示出一些振动条件下变形破裂的典型迹象和重要证据,充分再现了典型地震失稳机制的形成条件、相关性因素以及演化规律,为进一步研究分析提供科学可靠的试验数据和证据。     

扩底桩抗拔承载特性数值分析

基于通用软件ABAQUS,建立了扩底抗拔桩三维弹塑性有限元模型,通过对模型的计算与分析,探讨了扩底桩的抗拔承载特性。为验证数值模型的可靠性,将数值计算得到的荷载－位移关系曲线与试桩资料进行比较,两者吻合较好,表明本文所建立的模型可较好地模拟扩底抗拔桩的工作性状。通过计算与分析,探讨了扩底抗拔桩的轴力、侧摩阻力分布特征,桩身和扩大头周围土体变形与塑性应变的发展规律,以及扩大头的挤压作用对扩大头周围土体竖向应力的影响。同时,通过变动参数研究了扩大头的形状、土体的性质对扩底桩抗拔承载力的影响,结果表明,扩大头直径和扩大头周围土体的性质对抗拔承载力的影响较大,而扩底高度的影响相对较小。     

Climate changes in East China since the Late-glacial inferred from high-resolution mountain peat humification records

High-resolution peat humification records were obtained from Dajiuhu of the Shennongjia Mountains and Qianmutian of the Tianmu Mountains to study climate changes in East China. The analyses of pollen, organic matters, TOC, and Rb/Sr indicate a high degree of peat humification and thus strong decomposition of organic matter when climate was dry. Conversely, when climate was humid, the degree of humification is low because peat was preserved in a waterlogged condition. Peat humification from Dajiuhu occurred not only during the Younger Dryas (about 11.4–12.6 cal ka BP), the Bølling-Allerød Warm Period (12.6–15.2 cal ka BP), and the Oldest Dryas (about 15.2–16.0 cal ka BP), but also during the early Holocene (about 11.4–9.4 cal ka BP), the 8.2 cal ka BP cold event, and the Holocene Optimum (about 7.0–4.2 cal ka BP). Both peat humification records since nearly 5 ka BP are consistent, showing that mountain peatland has synchronous responses to the East Asia monsoon-induced precipitation. The LOI data confirm the above observation. The monsoon precipitation since nearly 5 ka BP recorded in these two peat profiles can be divided into three phases. During 4.9–3.5 ka BP, precipitation amount was high but fluctuated greatly. During 3.5–0.9 ka BP, precipitation amount was low. During 0.9–0 ka BP, degree of humification reduced gradually, indicating the increase of monsoon precipitation. Contrast to other high-resolution records from East China monsoon region shows that the monsoon precipitation records of the two peat profiles since nearly 16 ka BP are controlled by a common forcing mechanism of summer solar radicalization in the Northern Hemisphere.     

西秦岭新生代以来地质构造过程对青藏高原隆升和变形的约束

西秦岭位于青藏高原东北缘重力梯度带内,是高原物质向北、向东扩展的前缘,其新生代以来地质构造 地貌过程应该是印度板块-欧亚板块的碰撞造山过程和高原隆升过程的一部分。通过对西秦岭内部中-新生代沉积、变形及地貌记录的初步综合分析,得出如下初步认识:(1)根据西秦岭中-新生代红层沉积岩石组合和构造变形特征,可以分为晚侏罗世-早白垩世、晚白垩世-古近纪和新近纪三个构造层,分别对应于西秦岭新生代3个构造演化阶段。(2)西秦岭晚白垩世-古近纪构造层的褶皱缩短和区域断裂带的逆冲推覆发生在古近纪末期-新近纪初期,与整个青藏高原主要逆冲推覆构造事件同步,说明印度板块与欧亚板块碰撞的构造应力在古近纪末已波及至西秦岭。(3)西秦岭新近纪以来经历了一个构造相对稳定的侵蚀夷平期,于36 Ma之前形成了以晚白垩世-古近纪构造层侵蚀面、前新生代碳酸盐地层的岩溶夷平面为标志的主夷平面以及夷平面发育过程中形成新近纪近水平的、以红色粘土岩为主要特征的细碎屑沉积。这一夷平面可以作为高原组成部分的西秦岭隆升的基准面。该夷平面现今高程自西向东逐渐降低,反映了西秦岭隆升呈现自西向东连续的扩展。(4)青藏高原南部构造变形方式在中新世发生了由逆冲推覆 褶皱缩短向伸展走滑的构造转换,而在西秦岭内部却并未发生这样的构造转换,仍然以逆冲构造为主,只是西秦岭北缘的边界断层在中-晚更新世才发生逆冲 左旋走滑作用,这可能指示了青藏高原东北缘晚新生代构造变形的走滑作用只是构造块体边界与构造挤压应力方向下非正交的应力分解所致,同时也可能反映了作为西秦岭块体整体滑移和块体内部的收缩变形并行不悖。(5)由GPS观测数据确定的区域位移场应该指示了现今西秦岭块体的整体缓慢的向东移动,地震机制解确定的构造应力是下地壳向东蠕动拖曳脆性上地壳的整体运动,西秦岭地壳厚度由西向东逐渐增厚是西部由于南北向缩短增厚的下地壳向东扩展流动的结果,增厚地壳的均衡抬升是西秦岭地貌面高度变化的内在原因。     

LIVESTOCK VERSUS “WILD BEASTS”: CONTRADICTIONS IN THE NATURAL PATRIMONIALIZATION OF THE PYRENEES

ABSTRACT. The Pyrenees are becoming an environmental reservoir. The acute human depopulation experienced during the twentieth century and the progressive appropriation of large parts of the mountainous territory by the state in order to implement conservation policies have resulted in the return, via reintroduction or natural regeneration, of bears, wolves, beavers, river otters, marmots, mouflon, feral goats, and deer, among other species. This development, however, has not occurred without social and scientific controversy and leads to questions about territorialization and governmentality. Herders perceive wild animals as unregulated public property subsidized by the work of the local populace. Agriculturalists see their fields trespassed on a daily basis by animals they cannot kill because of their protected status. Ranchers, under extremely strict sanitation regulations, see their animals coming into contact with these unchecked wild populations. The work and living space of the mountain communities has fallen under the jurisdiction of external institutions and constituencies that value conservation and ecotourism above local subsistence.     

Analytical modelling of multi‐mass flexible rocking structures

This paper presents a new analytical model for describing the large rocking response of an elastic multi‐mass structure resting on ideally rigid ground. Using the experimental results from a rocking steel column, the ability of the proposed analytical model to estimate the rocking and translational acceleration response under free vibration, pulse and earthquake excitations is evaluated. It is observed that the classical treatment of impact may result in an unrealistically large transfer of energy to vibrations. Therefore a new Dirac‐delta type impact model that spreads the effects of impact over time and space is proposed. The use of a Dirac‐delta model and accurate restitution factors play a pivotal role in prediction of rocking and acceleration responses. In order to characterize the nonlinear response better, a modal analysis of the linearized system is proposed. With this approach, the vibration mode frequencies and shapes during rocking action were determined. A comparison of analytical and experimental modal estimations suggests good agreement. The results emphasize that the vibration characteristics of several vibration modes are affected by rocking action, and these modes may be excited at impact. Copyright © 2016 John Wiley & Sons, Ltd.     

Bedload hysteresis in a glacier‐fed mountain river

Sediment transport during flood events often reveals hysteretic patterns because flow discharge can peak before (counterclockwise hysteresis) or after (clockwise hysteresis) the peak of bedload. Hysteresis in sediment transport has been used in the literature to infer the degree of sediment availability. Counterclockwise and clockwise hysteresis have been in fact interpreted as limited and unlimited sediment supply conditions, respectively. Hysteresis has been mainly explored for the case of suspended sediment transport, but it was rarely reported for bedload transport in mountain streams. This work focuses on the temporal variability of bedload transport in an alpine catchment (Saldur basin, 18.6 km², Italian Alps) where bedload transport was monitored by means of an acoustic pipe sensor which detects the acoustic vibrations induced by particles hitting a 0.5m‐long steel pipe. Runoff dynamics are dominated by snowmelt in late spring/early summer, mostly by glacier melt in late summer/early autumn, and by a combination of the snow and glacier melt in mid‐summer. The results indicate that hysteretic patterns during daily discharge fluctuations are predominantly clockwise during the snowmelt period, likely due to the ready availability of unpacked sediments within the channel or through bank erosion in the lower part of the basin. On the contrary, counterclockwise hysteresis tend to be more frequent during late glacier melting period, possibly due to the time lag needed for sediment provided by the glacial and peri‐glacial area to be transported to the monitoring section. However, intense rainfall events occurring during the glacier melt period generated predominantly clockwise hysteresis, thus indicating the activation of different sediment sources. These results indicate that runoff generation processes play a crucial role on sediment supply and temporal availability in mountain streams. Copyright © 2014 John Wiley & Sons, Ltd.     

Evapotranspiration and canopy characteristics of two lodgepole pine stands following mountain pine beetle attack

Over the past decade, British Columbia (BC), has experienced the largest mountain pine beetle (MPB) outbreak on record. This study used the eddy‐covariance (EC) technique to examine the impact of the MPB attack on evapotranspiration (E) and associated canopy characteristics of two lodgepole pine stands with secondary structure (trees, saplings and seedlings surviving the attack) located in central BC. MPB‐06, an 85‐year‐old almost pure stand of pine trees, was first attacked in 2006, and by 2010, ~80% of the trees had been killed. MPB‐03, a 110‐year‐old stand with an overstory consisting of over 90% pine and a developed sub‐canopy, was first attacked in 2003 and by 2007 had > 95% pine canopy mortality. EC measurements began in August 2006 at MPB‐06 and in March 2007 at MPB‐03, and continued for four years. Annual total E ranged from 226 mm to 237 mm at MPB‐06, and from 280 to 297 mm at MPB‐03, showing relatively little year‐to‐year change at both sites over the four years. Increased E from the accelerated growth of the surviving vegetation (secondary structure, shrubs and herbs) compensated for reduction in E due to the death of the overstory. Monthly average daytime canopy conductance, the Priestley–Taylor (α), and the canopy–atmosphere decoupling coefficient (Ω) steadily increased during the growing season reaching approximate maximum values of 5 mm s^?1, 0.75 and 0.12, respectively. Potential evapotranspiration was approximated using a vapour pressure deficit‐dependent α obtained at high soil water content. Calculated water deficits indicated some water‐supply limitation to the surviving trees and understory at both sites. Rates of root zone drainage during the growing season were low relative to precipitation. Copyright © 2013 John Wiley & Sons, Ltd.     

Protolith ages and deformation mechanism of metamorphic rocks in the Zhangbaling uplift segment of the Tan-Lu Fault Zone

Protolith ages and Indosinian deformation mechanism of metamorphic rocks in the Zhangbaling uplift segment of the Tan-Lu Fault Zone are important, unsolved problems. Our LA-ICP-MS zircon dating work indicates that protolith ages of the greenschist-facies Zhangbaling Group are 754–753 Ma, and those of the amphibolite-facies Feidong Complex are 800–745 Ma. These rocks belong to the earliest cover of the Yangtze Plate. Their ages and metamorphic features suggest that the rocks did not come from the Dabie Orogen. The Indosinian structures in the Zhangbaling Group and lower Sinian strata formed in a flatlying ductile detachment zone with a shear sense of top-to-the-SSW whereas those in the underlying Feidong Complex are characterized by ENE-WSW inclined folds developed under a ductile regime. It is suggested therefore that the sinistral Tan-Lu Fault Zone of the Indosinian period is buried under the Hefei Basin west of the Zhangbaling uplift segment and the uplift segment is a displaced block neighboring the fault zone. Detachment deformation between the upper rigid and lower ductile crust during displacement of the Zhangbaling uplift segment resulted in the formation of the flat-lying ductile detachment zone and its underlying drag fold zone of a ductile regime. The protolith ages and deformation mechanism in the Zhangbaling uplift segment further prove sinistral origination of the Tan-Lu Fault Zone during the continent-continent collision of the North China and Yangtze plates and support the indentation model for the two-plate collision that considers the Tan-Lu Fault Zone as an oblique convergence boundary.