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"WATER CONDITIONS"
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Evaluation of groundwater effects on tunnel engineering in loess
Tunnels are commonly constructed in loess with a high water content or saturation degree, which can lead to large ground deformation, structural cracking, and even tunnel collapse during construction, in addition to tunnel leaks, sidewall settlement, and frost damage. A complete understanding of the distribution, source, and effects of groundwater in loess is therefore of critical importance, particularly to comprehensively consider loess landforms and material properties and tunnel design and construction practices. This paper presents a review and analysis of previous studies and 27 typical loess tunnels in China, which indicates three different types of water-rich loess surrounding rocks: natural water-rich loess (type I); excavation disturbance-induced water-rich loess (type II); and surface rainfall infiltration water-rich loess (type III). The formation mechanism, seepage field characteristics, and consequent stress and deformation characteristics of the surrounding rock are explained in detail. Key problems, strategies, solutions, and countermeasures are proposed as a helpful reference for theoretical research, design, construction, and maintenance of tunnel engineering in loess.
Journal Article
Phenology and thermal requirements of the species Cyperus difformis L. in southern Brazil
Cyperus difformis L. is a Cyperaceae, annual, of natural occurrence in marshy environments in southern Brazil, considered a weed in irrigated rice crops. Studies on its development are scarce, especially regarding its cycle and thermal requirements. Therefore, the objective of this work was to determine the base temperature, the thermal sum and the duration of the different sub-periods of the biological cycle of the species. The experiment was carried out at the Campus of the Universidade Federal de Santa Maria – UFSM, Santa Maria, Rio Grande do Sul, in four sowing seasons. In a completely delineated design and factorial scheme involving five soil water conditions (water depth and 50% soil water retention capacity [WRC]) from the sowing, water depth and 50% WRC introduced 21 days after emergence and 100% WRC during the whole cycle, with six repetitions each. Each experimental unit consisted of a cultivated in pot plant with 11 L capacity filled with soil. The cycle of the plants was subdivided into the sowing-emergence sub-periods, emergence-emission of the floral tassel and emission of the floral-maturing physiological tassel, being estimated the thermal requirements for the species. The conditions of the soil water condition the base temperature, the sum of the degree-days and the duration of the species cycle. The base temperature varies for each treatment, the sum of degrees-day decreases with the water deficit and the plants under flood accelerate the biological cycle.
Journal Article
Water : the troubled economic history of the arid tropics
\"From the early twentieth century, a big part of the world - the arid/semiarid tropics - began extracting, storing, and recycling vast quantities of water to sustain population growth and economic development. The idea was not a new one in this geography. It was an intrinsic part of ancient culture, statecraft, and technology. Most ancient projects, however, were local and small in scale. The capability of water extraction on a scale large enough to transform whole regions and create new cities improved in the early twentieth century, giving rise to a sharp break in the long-term population and economic growth pattern from the mid-twentieth century. Ironically, the geography of the arid tropics made transforming landscapes in this way expensive, damaging for the environment, and disputatious. The book describes this troubled history of economic emergence, building on a definition of tropicality\"-- Provided by publisher.
BOOK
Influence of Water on the Mechanical Properties and Failure Behaviors of Sandstone Under Triaxial Compression
Water is a crucial factor that influences the mechanical behavior of rock and can induce failure. The aim of this study was to investigate the effects of water content and water distribution on the mechanical behavior of sandstone subjected to triaxial compression. Sandstone samples under different water states, including dry, unsaturated, saturated, and long-term saturated, were prepared. Some saturated samples were dried in air for different periods to prepare samples that were dry on the outside but remained wet on the inside. The triaxial compression tests were performed on the samples under four confining pressures: 5, 10, 15 and 25 MPa. The results indicated that the water state of a sandstone sample can be characterized by its water content, soaking time, water distribution, and long-term saturation. The different water states can affect remarkably the strength, deformation, and failure pattern of the sandstone samples subjected to triaxial compression. Several empirical equations were established to describe the evolution of the mechanical behavior of sandstone with increasing water content and soaking duration. The nonuniform distribution of water promotes the generation of tensile cracks, while increasing confining pressure promotes the development of shear cracks. The strength of sandstone samples with dry outside and wet inside are lower than that of samples with wet outside and dry inside. What is more, a long-term saturated state increases the strain-softening of the sandstone samples, thereby increasing their deformation and lowering their strength.HighlightsInfluence of water state including water content and water distribution on sandstone is comprehensively investigated by triaxial experiments.A series of predictive empirical equations are established to describe the evolutions of the mechanical properties of sandstone with water content/soaking duration.The strengths of the sandstone samples in the dry outside but wet inside state are smaller than those of samples in the wet outside but dry inside state.A long-term saturated state increases the softening of the rock, thereby increasing the deformation and lowering the strength.Water especially nonuniformly distributed water promotes the propagation of tensile cracks near the surface of the rock.
Journal Article
Study on the influence of revetment on the evolution law of river channel morphology in the wandering section of Tarim river
The fluvial geomorphology of wandering rivers exhibits distinctive characteristics that distinguish them from other river types. Understanding the mechanisms underlying water-sediment dynamics and bank protection density in the morphological adjustment processes of wandering rivers is of considerable scientific and practical importance. Utilizing multi-temporal remote sensing imagery spanning from 2013 to 2023, this study systematically quantifies the morphological characteristics of a 65-km reach extending from Sanyuankou to Tarim River’s Third Bridge through comprehensive extraction of key geomorphological parameters along the central sandbank line. The investigation employs an integrated approach combining hydrological datasets to elucidate the quantitative relationships governing thalweg migration patterns in successive meander bends under constrained boundary conditions. The analytical results demonstrate that the asymmetric distribution of bank protection density, characterized by relatively low values on both left and right banks during 2013–2017, significantly influenced fluvial geomorphological processes, resulting in irregular variations in the sandbar index (
) and extensive thalweg migration. Quantitative analysis revealed a significant reduction in the sandbar index (
) from 4.31 during 2013–2017 to 2.80 in the subsequent period (2018–2022), representing a 35% decrease. With the increase in riparian density, the magnitude of the thalweg oscillations was most substantially franked in typical continuous bend reaches compared to other channel reaches. An empirical formula was developed to predict the thalweg swing width in successive river bends under fixed boundary conditions, taking into account the interplay between water-sediment dynamics and bend revetment parameters. The formula’s validity was confirmed through empirical testing, which demonstrated a strong correlation between the computed results and the observed data. The research results have important reference significance for the prediction of river regime in continuous bends of wandering rivers.
Journal Article
Effects of arbuscular mycorrhizal fungi on maize nitrogen uptake strategy under different soil water conditions
Aims
Arbuscular mycorrhizal fungi (AMF) could influence plant abilities of total nitrogen (N) acquisition. Global changes have been influencing availabilities of different N forms and water resources in soil. However, it is uncertain whether and how AMF colonization affects plant uptake and preference of different N forms and how are they affected by soil water conditions.
Methods
We conducted a pot experiment with
Funneliformis mosseae
(a common arbuscular mycorrhizal fungal species) colonized and non-colonized maize (
Zea mays
L.) growing at low and high water conditions, the growth medium contained much more nitrate (NO
3
−
) than ammonium (NH
4
+
).
Results
F. mosseae
colonization and high water availability increased maize biomass and total N uptake. Enhanced water supply increased proportional contributions of NH
4
+
to colonized and non-colonized maize because high water conditions may increase NH
4
+
accessibility to maize.
F. mosseae
colonization weakened proportional contributions and preference of NH
4
+
in maize, indicating that AMF enable plants to prefer using the more abundant N form and develop more beneficial N uptake strategies considering that NO
3
−
was more dominant than NH
4
+
in growth medium. Furthermore, maize NH
4
+
preference was decreased by
F. mosseae
colonization more under high than low water conditions. This demonstrated greater effects of AMF on regulating plant N uptake strategies in soils with greater water availability.
Conclusions
This work revealed the regulation of AMF colonization on plant N uptake strategies under different soil water conditions. The findings enriched our knowledge of plant N use in the context of global changes.
Journal Article