Variations In Moisture Conditions Research Articles

Stress-Based Model for Interpreting Shear Wave Velocity from Seismic Cone Penetration Tests in Unsaturated Soil

Shear wave velocity is an important parameter for estimating soil properties used in analyzing the dynamic response of soil to seismic loading. This paper focuses on developing a model for predicting shear wave velocity in unsaturated soils. The model was developed primarily for the interpretation of seismic cone penetration tests (SCPTs) in unsaturated soil to account for seasonal variations in moisture conditions. In practice, SCPTs typically occur over a period of days without the option of choosing a wet or dry period. The question becomes, if tests are conducted during a dry period, how can shear wave velocity corresponding to a wetter period be predicted, or vice versa? Answering this question was the primary motivation of this work. The work involved field testing with the seismic cone penetrometer during wet and dry periods and a focused study at three sites involving comparison between field and laboratory testing for shear wave velocity. The model presented in this paper is built upon the significant work of many other researchers with reference to new experimental data obtained by the authors. It is demonstrated that a stress-based model incorporating matric suction can provide reasonable predictions of shear wave velocity and provides a method to interpret the impact of changing moisture content on shear wave velocities determined with SCPTs.

Inter-annual and intra-annual tree-ring oxygen isotope signals in response to monsoon rainfall in northwestern Thailand

We present a new teak ( Tectona grandis L.f.) tree-ring stable oxygen isotope (δ18OTR) chronology from Mae Tuen (MT) site, Tak province, northwestern Thailand at inter-annual (167-year, A.D.1850–2016) and intra-annual (A.D.2006–2016) timescales. The inter-annual δ18OTR chronology showed a significant negative correlation ( r = −0.678, p < 0.01) with the May–October amount of regional rainfall obtained from CRU TS4.03. We established a linear regression model that explained 46.0% of the actual rainfall variance and reconstructed monsoon season rainfall back to A.D.1850. The seasonal variations in moisture conditions were reflected in inter-annual δ18OTR variability. The rainfall amount and δ18O in precipitation (δ18Op) mainly controlled intra-annual variations in teak δ18OTR. These results show that the variation in Thai teak δ18OTR is dominated by rainfall, highlighting the strength of δ18OTR as a monsoon rainfall proxy.

Modeling the effect of creep in paper fibres under the influence of external loading and changes in moisture

Paper is a material exhibiting a complex microstructure that is composed of a network of fibres at the micro-level. When subjected to external loading or variations in moisture conditions over different time scales, changes in strain that are non-linear with respect to time are observed at the sheet level (macro-scale). In order to investigate this time-dependent behaviour of paper, a creep power law model is implemented within a finite element approach at the level of single fibres. This rate-dependent model is found to capture experimental results available in literature for single fibres with a good agreement (both quantitatively and qualitatively). Based on the identified model at the level of single fibres, the time-dependent hygro-mechanical response is upscaled towards the network scale. To this end, random model networks of ribbon shaped fibres are generated and their response is simulated. The network-scale response, emerging from the rate-dependent fibre model, demonstrates the ability to predict the response of networks subjected to relaxation at a constant moisture level. The developed numerical model predicts lower values of overall stress response in single fibres as compared to networks. Also, stress relaxation predicted by the rate-dependent model in the cross-direction of the networks is in agreement with the experimental observations by Johanson and Kubát (1967). Therefore, one of the remarkable findings of the present work is that the developed rate-dependent model is robust enough to capture the sheet scale response also qualitatively. Based on the study of these computational results, a better understanding is achieved regarding the influence of mechanical and rate-dependent properties of single fibres on the hygro-expansion of complete fibre networks, and in particular of paper sheets.

A method for predicting the influence of matric suction changes on CPT tip resistance

The Cone Penetration Test (CPT) is a valuable tool for continuous soil profiling and estimating soil properties. A CPT sounding will often pass through the active zone of an unsaturated soil profile, near the ground surface where moisture conditions and matric suction can vary considerably with depth and time. For many projects, the active zone is also significant to the support of shallow foundations and overlying embankments. However, the strength and stiffness of the unsaturated soils in this zone can be significantly affected by variations in the moisture content and matric suction. Likewise, the cone penetration tip resistance and sleeve friction will be influenced by the variations in moisture conditions and suction. Therefore, it is important to consider the soil moisture conditions when CPTs are conducted relative to the moisture conditions assumed for geotechnical design. This paper presents a method for predicting changes in tip resistance as result of changes in matric suction. The method extends the bearing capacity theory to predict changes in cone tip resistance due to changes in matric suction. CPT data collected at test sites, during wet and dry seasons and representing different soil types, are presented to demonstrate the viability of the proposed method.

Using a multiscale, probabilistic approach to identify spatial-temporal wetland gradients

Abstract Wetlands are highly dynamic ecosystem components that fluctuate dramatically in inundation and persistence of water both within and across years. However, these systems are commonly classified in a deterministic, discrete manner that does not reflect inherent spatial and temporal variation. Developing a methodology to identify gradients in water inundation is critical given the dynamic nature of wetlands. We present a methodology that applies probabilistic estimates, derived from a nonparametric model, to predict wetlands along a gradient in ephemerality, or degree of water inundation. We applied this model across four sampling areas in the Plains and Prairie Pothole Region (PPPR) in the U.S. Northern Great Plains. We developed a model relationship between high-resolution (RapidEye) and moderate resolution (Landsat) satellite sensor data. This allowed us leverage the benefits of high spatial resolution data and a long temporal series of freely available mid-resolution data to characterize water persistence in wetlands. To obtain measures of wetland inundation across a gradient of ephemerality, we estimated wetland probabilities across a temporal series reflecting large variation in moisture conditions. We found that a nonparametric statistical approach was highly effective in predicting wetlands of varying size and ephemerality. Our predictions were strongly supported with low error (RapidEye 3.1–15%, Landsat 0.3–1.5%). Probabilistic predictions of wetland ephemerality contribute valuable information needed for management and policy decisions, especially given potential alterations to wetland ephemerality and ecosystem services under climate change. Using predicted gradients in wetland ephemerality over time will enable researchers and land managers to more effectively capture nuance in ecosystem condition, function, and change.

Effect of water during freeze–thaw cycles on the performance and durability of lime-treated gypseous soil

Research on the freeze–thaw durability of soils in general and on the variation in moisture conditions in particular is vital for both economic and stability reasons. The present study is an attempt to further understand the process of freeze–thaw deterioration under two different test procedures (an open system with water uptake during thawing and a closed system with only initial water content), by measuring the strength, gas permeability, mineralogical, and microstructural properties of lime-treated gypseous soil. The study involved fine-grained soil with different gypsum contents (0%, 5%, 15%, and 25%) of soil dry weight. The soil samples were treated with 3% lime and cured for 28days at 20°C, then subjected to 12 freeze–thaw cycles in both open and closed systems, following the ASTM test procedure. A detailed parametric study (laboratory study) was conducted in order to understand the behavior of these soils. Results show that the tested characteristics of the soil samples depended considerably on the water available during the freeze–thaw procedure and on the gypsum content. Unconfined compressive strength decreased and gas permeability increased with increasing gypsum content and number of freeze–thaw cycles. The water content of the soil samples is a key parameter of the stability of earth structures under freeze–thaw conditions.

Investigating Resilient Modulus Interdependence to Moisture for Reclaimed Asphalt Pavement Aggregates

A variety of factors affect the overall performance of the material within pavement structure, with moisture content susceptibility being recognized as one of the most important factors that is known to directly affect the resilient modulus of granular base layer materials and consequently the overall performance of pavement structures. While the effect has been widely investigated for virgin aggregate, more limited research has been undertaken to quantify the effect of various moisture conditions on base layer materials containing reclaimed asphalt pavement (RAP) material. The present study aims to examine the effect of moisture on the resilient modulus of base layer materials containing RAP and a direct comparison to a virgin aggregate is presented, in order to identify potential variations in performance. Specifically more in depth information is provided regarding the sensitivity of RAP to variations in moisture conditions. Resilient modulus determination was performed, via laboratory triaxial testing on materials with varying RAP percentages and moisture contents and compared to the behavior of a course grained virgin aggregate material under similar conditions. For the current research the investigated RAP material exhibited modulus values that are equivalent or exceed those of a virgin aggregate utilized for base material at OMC and below. More details outlining the variations in modulus under various loading conditions are presented.

Pavement thickness and stabilised foundation layer assessment using ground-coupled GPR

Experimental results from field and laboratory investigations using a ground-coupled ground penetrating radar (GPR), dielectric measurement, magnetic imaging tomography (MIT) and dynamic cone penetrometer (DCP) tests are presented. Dielectric properties of asphalt pavement and stabilised and unstabilised pavement foundation materials were evaluated in the laboratory in frozen and unfrozen conditions. Laboratory test results showed that dielectric properties of materials back-calculated from GPR in comparison to dielectric gauge measurements are strongly correlated and repeatable. For chemically stabilised materials, curing time affected the dielectric properties of the materials. Field tests were conducted on asphalt pavement test sections with different foundation materials (stabilised and unstabilised layers), drainage conditions and layer thicknesses. GPR and MIT results were used to determine asphalt layer thicknesses and were compared with measured core thicknesses, while GPR and DCP were used to assess foundation layer profiles. Asphalt thicknesses estimated from GPR showed an average error of about 11% using the dielectric gauge values as input. The average error reduced to about 4% when calibrated with cores thicknesses. MIT results showed thicknesses that are about 9% higher than estimated using GPR. Foundation layer thicknesses could not be measured using GPR due to variations in moisture conditions between the test sections, which is partly attributed to variations in gradation and drainage characteristics of the subbase layer.

Increasing range mismatching of interacting species under global change is related to their ecological characteristics

ABSTRACTAim We investigate the importance of interacting species for current and potential future species distributions, the influence of their ecological characteristics on projected range shifts when considering or ignoring interacting species, and the consistency of observed relationships across different global change scenarios.Location Europe.Methods We developed ecological niche models (generalized linear models) for 36 European butterfly species and their larval host plants based on climate and land‐use data. We projected future distributional changes using three integrated global change scenarios for 2080. Observed and projected mismatches in potential butterfly niche space and the niche space of their hosts were first used to assess changing range limitations due to interacting species and then to investigate the importance of different ecological characteristics.Results Most butterfly species were primarily limited by climate. Species dwelling in warm areas of Europe and tolerant to large variations in moisture conditions were projected to suffer less from global change. However, a gradient from climate to host plant control was apparent, reflecting the range size of the hosts. Future projections indicated increased mismatching of already host‐plant‐limited butterflies and their hosts. Butterflies that utilize plants with restricted ranges were projected to suffer most from global change. The directions of these relationships were consistent across the scenarios but the level of spatial mismatching of butterflies and their host plants increased with the severity of the scenario.Main conclusions Future changes in the co‐occurrence of interacting species will depend on political and socio‐economic development, suggesting that the composition of novel communities due to global change will depend on the way we create our future. A better knowledge of ecological species characteristics can be utilized to project the future fate and potential risk of extinction of interacting species leading to a better understanding of the consequences of changing biotic interactions. This will further enhance our abilities to assess and mitigate potential negative effects on ecosystem functions and services.

Channel and Vegetation Change on the Cimarron River, Southwestern Kansas, 1953–2001

Little is known about historical channel change along rivers on the Great Plains of the United States. Focused on a 113 km reach of the Cimarron River, southwestern Kansas, this study revisits the site of Schumm and Lichty's (1963) work that documented channel changes between 1874 and 1960. Based on field and archival evidence from Seward and Morton Counties, Kansas, we find that channel narrowing, which began in the 1940s, continues to the present. Between 1953 and 2001, the mean channel width of the Cimarron River decreased by 114 m, or 75 percent, although channel narrowing and the expansion of riparian vegetation were more pronounced in some locations than in others. The channel changes and increase in riparian vegetation both appear to have been caused by a decrease in annual peak flows, which favored in-channel sedimentation and the expansion of riparian vegetation. The decrease in annual peak flows coincided with a reduction in the annual variation in moisture conditions, as measured by the Palmer Drought Severity Index. Agricultural practices and groundwater withdrawals have likely contributed to the decline in peak flows since 1970.

The variation of moisture conditions in China during the last 2000 years

AbstractUtilizing more than 50,000 reports of droughts and floods found in local records we have reconstructed the history of moisture conditions in eastern China for the last 2000 years. The area studied extends eastward of Gansu province and is situated between Inner Mongolia in the north and Zhejiang in the south. Separate analyses are presented for the semi‐arid, semi‐wet and wet subdivisions of this area. It was possible to develop moisture indices with a time resolution of 5 years in each subregion. The time series of the moisture index presented for the semi‐wet area extends over the period AD 1–1950, while for the other two subregions the period covered is AD 251–1950.Each of the climatic subdivisions is found to undergo prolonged periods of dryness and wetness. The frequency of alternation between dry and wet conditions increases from the semi‐arid region to the semi‐wet region to the wet region. The variations of moisture conditions in the whole area of eastern China is compared with known changes in the level of the Caspian Sea. The variations in the two regions are found to be coherent.

Adaptation of Crocidura Hirta Peters to variation in moisture conditions in Southern Africa

Adaptation of Crocidura Hirta Peters to variation in moisture conditions in Southern Africa