Vertically loaded piles in non-homogeneous media

Analytical methods for the axial responses of piles can be classified under three broad categories of (1) simple but approximate analytical solutions, (2) one-dimensional numerical algorithms, (3) full axisymmetric analyses using boundary or finite element approaches. The first two categories rely on the so-called load transfer approach, with interaction between pile and soil determined by independent springs distributed along the pile shaft and at the pile base. The non-linear spring stiffness is related to the elastic–plastic properties of the actual soil partly by empirically based correlations and partly by theoretical arguments based on simplified models of the pile–soil system. This paper presents new closed-form solutions for the axial response of piles in elastic–plastic, non-homogeneous, media. The solutions fall in the first of the three categories above, and have been verified through extensive parametric studies using more rigorous one-dimensional and continuum analyses. The effect of non-homogeneity and partial slip on the load and displacement profiles along the pile shaft is explored, and comparisons are presented with experimental data. © 1997 John Wiley & Sons, Ltd.     

Climatic and non-climatic lake-level changes inferred from a Plio-Pleistocene lacustrine complex of Catalonia (Spain): palynology of the Tres Pins sequences

A 27-m sequence of deposits from the Plio-Pleistocene Banyoles-Besalú lacustrine complex, at Tres Pins, N.-E. Spain, shows lithological, carbonate, pollen and spores, and ostracode-gastropod evidence of climatic and lake-level change. Upland pollen taxa from the lowermost zones 1, 3 and 5, show that the area was forested and indicate a progressive deterioration of the climate. Zone 2 (steppe vegetation) corresponds to a global glacial stage, with mild temperatures, if the comparison to modern analogues is valid. Only minor climate fluctuations occurred subsequently. Aquatic vegetation and micritic sediment facies show a pelagic environment during pollen zones 1 and 3 and a littoral one during pollen zone 5. A short-term lowering of the water level (sandy algal micrite and slightly brackish waters) occurred in zone 2, as a result of severe droughts. Subzone 2c records progressive recovery of the forest. The coarse lithology and the high carbonate content, however, continue to indicate shallow waters. The fluctuation marked by zone 4 (extensive marsh vegetation and spring waters) may be due to a lake-level decrease caused by karst activity, or by lower precipitation with only slight cooling, or more probably by a relative lake-level decrease caused by natural infilling. The sediment of pollen zone 4, a sandy algal micrite, indicates the development of a littoral bench at the core site. From pollen zone 4 to pollen zone 5 an evolution from lakeward to landward position occurred. In zone 2, droughts existed at least during the spring growing season, and probably also during the rest of the year. In subzone 2c, a shift to spring precipitation occurred. In contrast, during pollen zone 4, if there was a decrease in precipitation, it did not take place during the summer growing season.     

Recent sedimentary histories of shallow lakes in the guatemalan savannas

Shallow basins in the savannas of Peten, Guatemala filled with water after 305±55 BP (calibrated age+1430–1660 AD). Aguadas Chimaj and Chilonche possess dilute waters and iron-rich, clayey sediments that are poor in Ca and Mg, reflecting the highly weathered nature of riparian soils. Low ²¹⁰Pb flux rates to Chimaj (0.085 pCi cm^-2 yr^-1) and Chilonche (0.134 pCi cm^-2 yr^-1) are attributed to low ²²²Rn emission rates from the nearby Caribbean Sea. Mean sediment accumulation rates in Chimaj and Chilonche for the past 150 years are 0.015 g cm^-2 yr^-1 and 0.047 g cm^-2 yr^-1 respectively. Forest expansion after 305 BP is documented in pollen profiles from the small aguadas and larger Lake Oquevix. Regional reforestation postdates the 9th century Classic Maya collapse and coincides with indigenous depopulation that was a consequence of European intrusion that began in the early 1500s. The timing of forest regrowth indicates the importance of historical anthropogenic factors in controlling Peten's vegetation. Nevertheless, other sedimentological lines of evidence (e.g. lithology, algal remains and charcoal particles) suggest that changing climate and/or local hydrology may have played a role in the reforestation process.     

A multi‐mechanism constitutive model for plastic adaption under cyclic loading

As is well known, granular soils under cyclic loading dissipate a large amount of energy and accumulate large irreversible strains. Usually, with time, this second effect reduces and the accumulation rate decreases with the number of cycles until obtaining a sort of ideal stationary cyclic state at which ratcheting disappears. In this paper, only this ideal state is taken into consideration and simulated by means of a multi‐mechanism constitutive model for plastic adaptation. For this purpose, the concept of cycle is discussed, many different categories of cyclic stress/strain paths are considered and some theoretical issues concerning both the flow and the strain‐hardening rules are tackled. Even though the paper focuses on soil behaviour, the conclusions can be extended to all materials exhibiting ratcheting due to volumetric behaviour.Copyright © 2013 John Wiley & Sons, Ltd.     

据孢粉分析黑龙江嘉荫地区晚白垩世气候变化对恐龙绝灭的影响

黑龙江省嘉荫地区是中国境内发现恐龙最早的地区,自恐龙化石被发现以来在该区进行过大量的发掘,但对恐龙生活环境和灭绝原因一直没有解释。本研究将产恐龙的晚白垩世地层由下而上划分为永安村组、太平林场组、渔亮子组和富饶组,其中产恐龙化石和大量孢粉化石。孢粉化石由下而上可识别为Polypodiaceaesporites-Monosulcites-Beaupreaidites、Cyathidites-Taxodiaceaepollenites-Aguilapollenites和Classopollis-Ephedripites-Sphagnumsporites组合。根据含恐龙地层中的孢粉化石组合变化和沉积物特征分析,认为晚白垩世本区总体属湿暖的亚热带气候环境。孢粉化石组合的变化显示当时出现暖湿至干热气候条件的演变。嘉荫群上部渔亮子组中膏岩层和耐高温、抗盐碱的克拉梭粉（Classopollis）麻黄粉（Ephedripites）组合在短时间内的大量出现,说明晚白垩世末期出现有短暂的干热气候,这种气候的突然转变以及伴随的生态系统的紊乱可能是嘉荫地区恐龙大量死亡的重要原因,但不排除诸如天外星体碰撞地球、大规模火山喷发等引发白垩纪末恐龙全球灭绝的因素,后者更可能是引起气候变化的直接因素。     

新疆藜科花粉形态研究

利用光学显微镜和扫描电子显微镜对新疆分布的14属25种藜科植物花粉形态进行了观察和测量,记录了鉴定特征。为了适应当前孢粉分析研究的需要,根据花粉的大小,孔径等特征,将藜科花粉分为4个型态属型。     

Anthropogenic perturbations to the trophic structure in a permanent hypersaline shallow lake: La Salada de Chiprana (north-eastern Spain)

The changes in the trophic state in the Salada de Chiprana (north-eastern Spain) over two quite different seasonal cycles (1989, 1994/95) were studied. During the former cycle, the lake was permanently stratified, and was biogenically meromictic, and in the latter, showed no apparent stratification. The main variables related to the physico-chemical changes observed can be attributed to the effect caused by the increase in the nutrient loading. The large amounts of nutrients (total-N and total-P) and organic matter are due to the use of the lake as a reservoir for water discharged from irrigation. Two remarkable effects of the change are the permanent mixing of the water column and the immobilization of phosphorus in the form of ionic species and solid phases that are not available to the biota especially primary producers (phytoplankton, periphyton, microbial mats). The results of the present study emphasize the fragility of (hyper) saline ecosystems to anthropogenic disturbances such as increases in freshwater inflow and nutrient inputs. Likewise, the study reveals the failure of conservation criteria that have been used to manage this lake, especially those which refer to the control of freshwater, nutrient-rich influents.     

Paleolimnological environment indicated by the diatom and pollen assemblages in an alpine lake in Taiwan

Yuanyang Lake (24°35N, 121°24E), located at an altitude of 1,670 m within a nature preserve in northern Taiwan, is an acidic lake. Remains of diatoms and pollen from a 3.72-m sediment core were used to elucidate the relationships between the vegetation of the watershed and the paleolimnological environment. Past pH, saprobity level, and total P of the lake were inferred from the diatom assemblages and were analyzed with respect to changes in the terrestrial vegetation. The inferred pH values fluctuated only slightly, whereas the inferred saprobity level increased markedly towards the sediment surface. In the topmost sediment, a slight drop in the inferred pH was associated with a lowering in the saprobity index. This was interpreted as a possible result of recent anthropogenic acidification and changes in productivity related to changes in acidity. Based on pollen analyses, we conclude that Chamaecyparis persisted over at least the last four thousand years in the watershed. The vegetation in the watershed changed little during this period of time, which is consistent with the constancy of inferred pH values. A positive correlation between the inferred pH and ¹³C values of the sediments was found.     

The Holocene vegetation history of the Khibiny Mountains: implications for the post‐glacial expansion of spruce and alder on the Kola Peninsula,northwestern Russia

Pollen and peat botanical investigations of the Lutnermayok peat bog, Kola Peninsula, northwestern Russia, were carried out, and 21 surface pollen samples were studied. Combined with previous studies our data form the basis for the vegetation history over the last 7000 yr of the Khibiny Mountains. Pinus sylvestris was the dominant species between 7000 and 5000 yr BP and Picea obovata penetrated to the Khibiny Mountains ca. 5500/5300 yr BP. Since 4500 yr BP, Picea replaced Pinus in major parts of the area and dominated the forest cover. Picea immigrated to the Kola Peninsula after 7000 yr BP. There were two paths of spruce migration: from the southeast and the southwest. Grey alder, Alnusincana, immigrated to the Kola Peninsula from the southwest and northwest about ca. 8000 yr BP. Grey alder has been restricted to its modern range since 4000 yr BP. The range of vertical movement of the treeline in Khibiny Mountains during the last 700 yr was 240–260 m, which corresponds to an amplitude of summer temperature change of 2°C. Copyright © 1999 John Wiley & Sons, Ltd.     

载铝离子树脂用于天然水降氟试验

将载铝离子树脂作为吸附Ｆ的滤料,用于天然水的除Ｆ。经地热水（４７℃）现场中试表明,每一级的吸附作用,Ｆ降低量ρ（Ｆ）为２￣３ｍｇ／Ｌ。用载铝离子树脂处理天然水,树脂上的铝离子与水中的Ｆ产生选择性吸附,可将高氟水改良为符合国家标准的饮用水,而不会在水中引入其它离子。