Field experiment of subgrade vibration induced by passing train in a seasonally frozen region of Daqing

The vibration characteristics and attenuation of the subgrade caused by passing trains in a seasonally frozen region of Daqing, China are investigated. Three field experiments were conducted during different times through the year, in normal, freezing and thawing periods, respectively, and the influence of the season, train speed and train type, is described in this paper. The results show that： （1） the vertical component is the greatest among the three components of the measured vibration near the rail track, and as the distance to the railway track increases, the dominant vibration depends on the season. （2） Compared with the vibration in the normal period, the vertical and longitudinal vibrations increase while the lateral vibration decreases in the freezing period. However, in the thawing period, the vertical and longitudinal vibrations decrease, and the lateral vibration increases. （3） As train speeds increase, the subgrade vibration increases. （4） The vibration induced by a freight train is greater than by a passenger train. These observations provide a better understanding of the vibration and dynamic stability of the subgrade and may be useful in developing criteria for railway and building construction in cold regions.

In-situ experiment investigations of hydrothermal process of highway in deep seasonal frozen soil regions of Inner Mongolia, China

To reveal the influencing factors and changing rules for the hydrothermal interaction process of highway subgrade, the field measurements of Shiwei-Labudalin Highway in Inner Mongolia, China was conducted for 3 years, based on which the freezing-thawing rules and water content changing characteristics were analyzed. The main results show the subgrade presents a frequent freezing-thawing alternation, and the water content of subgrade exhibits an obvious seasonal alternation. The subbase has the maximum water content, while the base has the minimum water content. The change of water flux is concentrated in the thawing period and consistent with the change of temperature gradient. The subbase layer has the most active water flux due to the heat absorption and impermeability of pavement that easily causes the water accumulation in this layer. Therefore, the prevention and treatment for the freezing-thawing disease should be started from heat insulation and water resistance.

Field monitoring of railroad embankment vibration responses in seasonally frozen regions

To investigate the vibration characteristics of a railway subgrade in different seasons, three field experiments were carried out in the seasonally frozen Daqing area of China during spring, smnmer, and winter. The vibration characteristics and attenuation rates of the subgrade induced by passing trains were investigated, and the influences of the season, train speed, train type, train load, and number of train compartments are described in this paper. The results show that： （1） near the rail track the vibration in the vertical direction was more significant than in the lateral and longitudinal directions, and as the distance from the railway track increased, the acceleration amplitudes and the attenuation rates all decreased in all three directions; （2） the acceleration amplitudes and at- tenuation rates decreased in the three different study seasons as the distance from the railway track increased, and the attenuation rates in the freezing period were the largest; and （3） the acceleration amplitude induced by a freight train was greater than that by a passenger train, and the subgrade vibration increased with increasing passenger train speeds when the number of train compart- ments was similar. These results have great significance for enhanced understanding of the characteristics of wain-induced vibra- tion embankment response in seasonally frozen regions, and provide essential field monitoring data on train-induced vibrations in order to improve the performance criteria of railroading in seasonally frozen regions.

Carbon stocks in a highly fragmented landscape with seasonally dry tropical forest in the Neotropics

Background:Global modeling of carbon storage and sequestration often mischaracterizes unique ecosystems such as the seasonally dry tropical forest of the central region of the Gulf of Mexico,because species diversity is usually underestimated,as is their carbon content.In this study,aboveground and soil carbon stocks were estimated to determine the climate mitigation potential of this highly degraded landscape(<25%of forest cover).Results:Tree species in the study area had carbon content values that were 30%–40%higher than the standard value proposed by the IPCC(i.e.,50%).Tropical oak forest in the region,despite its restricted distribution and low species richness,accounted for the highest mean carbon stocks per unit area.The main factors driving spatial variability in carbon stocks were:maximum precipitation,soil organic matter,clay and silt content.No strong relationship was found between aboveground carbon stocks and soil organic carbon in the study area.Quanti-fication of carbon stocks is an important consideration in the assessment of the conservation value of remnants of native vegetation in human-modified landscapes.Conclusions:This study demonstrates the importance of the highly fragmented tropical dry regions of the Neo-tropics in maintaining landscape functionality and providing key ecosystem services such as carbon sequestration.Our results also highlight how crucial field-based studies are for strengthening the accuracy of global models.Furthermore,this approach reveals the real contribution of ecosystems that are not commonly taken into account in the mitigation of climate change effects.

Study on potential evapotranspiration and wet-dry condition in the seasonal frozen soil region of northern Tibetan Plateau

This study was based on the CEOP/CAMP-Tibet observed data at AWS （Automatic Weather Station） of MS3478 in the seasonal frozen soil region of northern Tibetan Plateau from March 2007 to February 2008. The variation characteristics of PE （potential evapotransph＇ation） were analyzed based on the Penman-Monteith method recommended by FAO （the Food and Agriculture Organization of the United Na- lions）. The contributions of dynamic, thermal and water factors to PE were discussed, and the wet-dry condition of the plateau region was further studied. The results indicated that daily PE was between 0.52 mm and 6.46 mm for the whole year. Monthly PE was over 107 mm from May to September, but decreased to less than 41 mm from November to February. Annual PE was 1,037.8mm. In the summer, thermal PE was significantly more than dynamic PE, but conversely in the winter. Annual variation of thermal PE was of sine wave pattern. In addition, drought and semi-drought climate lasted for a long time while semi-humid climate was short. The effect of water and dynamic factors on PE varied considerably with the seasons. Annual variation of thermal PE was of sine wave pattern.

Temporal and Spatial Characteristics of Wave Energy Resources in Sri Lankan Waters over the Past 30 Years

For the survival and development of‘One Belt,One Road’,the present work aimed to evaluate the current situation of wave energy resources around Sri Lankan(SL)waters.Thirty-year ERA-Interim wind data were used to drive the third-generation wave model WAVEWATCH-III,and the seasonal and regional distribution characteristics of wave energy resources in SL waters were analyzed.Furthermore,the optimal season and region that contribute most to wave power in the study area were determined.On the basis of 30-year hindcast wave data,the significant wave height and wave power density,the occurrence of available SWH and rich WPD,the effective storage of wave energy,and the contribution and stability of wave energy were also analyzed.Results show that extremely optimistic wave energy resources are found at the western,southern,and southeastern waters of SL;moreover,the period of June,July,August(JJA)has great advantages in terms of the overall level of WPD,wave energy effective storage,and the contribution rate of wave energy.In addition,the wave energy during JJA is more stable than that of other periods and thus is benefi-cial to the transformation and development of wave energy.This study also provides important guiding value for disaster prevention and reduction,coastal zone management,and coastal development in the crucial region of the 21st Century Maritime Silk Road.

Field monitoring of differential frost heave in widened highway subgrade

In cold regions,the widened subgrade could produce uneven frost heave that is detrimental to the pavement.This study investigates the differential frost heave characteristics in a widened subgrade.The field monitoring system mainly consists of temperature,moisture,and displacement sensors and distributed optical fiber cables for strain measurement.The monitoring results show that the cooling period in the subgrade is longer than the warming period.Water content in the subgrade changes significantly within 0−2 m below the subgrade surface but stabilizes within 2−5 m.The maximum frost heave occurs from February to March.In comparison,the existing subgrade has a longer freezing period and larger heave value,caused by the higher density and water content inside.Water in the existing subgrade migrates into the new one after widening,leading to frost heave reduction in the existing subgrade.Simultaneously,the traffic loads result in the consolidation of the new subgrade,thus reducing the heave value in the second year.In the third year,the water supply from the existing subgrade facilitates the frost heave in the new subgrade.The tensile strain distributions obtained by the distributed optical fiber cables show that the maximum differential frost heave occurs at the joint between the existing and new subgrades.The differential frost heave gradually stabilizes after three years.Finally,an improved frost heave prediction model is developed based on the segregation potential concept and monitoring results.

PRELIMINARY DISCUSSIONS OF BASIC CLIMATIC CHARACTERISTICS OF PRECIPITATION DURING RAINING SEASONS IN REGIONS SOUTH OF CHANGJIANG RIVER AND ITS RELATIONSHIP WITH SST ANOMALIES

Basic climatic characteristics are analyzed concerning the precipitation anomalies in raining seasons over regions south of the Changjiang River (the Yangtze). It finds that the regions are the earliest in eastern China where raining seasons begin and end. Precipitation there tends to decrease over the past 50 years. Waters bounded by 9(S -1(S, 121(E - 129(E are the key zones of SST anomalies that affect the precipitation in these regions over May ~ July in preceding years. Long-term air-sea interactions make it possible for preceding SST anomalies to affect the general circulation that come afterwards, causing precipitation anomalies in the raining seasons in regions south of the Changjiang River in subsequent years.

Numerical simulation of vibrational response characteristics of railway subgrades with insulation boards

This study presents a numerical method based on the surface temperature data and the ground temperature increase in Daqing for predicting temperature field distribution in the Binzhou Railway subgrade and analyzing the temporal and spatial distribution of freeze−thaw status of railway subgrade.The calibrated numerical method is applied to simulate the temperature field distribution and roadbed vibrational response of the railway subgrade with a thermal insulation layer at different seasons.The results show the following:(1)The thermal insulation layer can remarkably increase the soil temperature below it and maximum frost depth in the subgrade.(2)Thermal insulation can effectively reduce the subgrade vibration and protect it from frost damage.(3)Given that the strength requirements are met,the insulation layer should be buried as shallow as possible to effectively reduce the subgrade vibration response.The research findings provide theoretical support for the frost damage prevention of railway subgrades in seasonally frozen regions.

Size-resolved aerosol water-soluble ions at a regional background station of Beijing, Tianjin, and Hebei, North China

The characteristics of water-soluble ions in size-resolved particulate matter were investigated usingion chromatography at Shangdianzi, a regional background station of Beijing, Tianjin, and Hebei. Seasonal total concentrations of ions （Na＋, Mg2＋, IC, Ca2＋, NH＋4, Cl-, SO2-4 and NO-3） were 75.5 ± 52.9 μg/m3 in spring, 26.5 ± 12.3 Bg/m3 in summer, 22.7 ± 20.4 μg/m3 in autumn, and 31.1 ± 23.9 μg/m3 in winter, respectively. The secondary ions （NO3, SO2-4 and NH＋4）, mainly associated with fine particles, accounted for 84.2% in spring, 82.1% in summer, 81.5% in autumn and 76.3% in winter of all ions. Strong correlations were found between NH＋4 and SO2-4 （r = 0.95, p 〈 0.01） as well as NH＋4 and NO-3 （r = 0.90, p 〈 0.01） in fine particles; while in coarse particles, correlations between Mg2＋ and NO-3 （r = 0.80, p 〈 0.01）, and Ca2＋ and NO2＋ （r = 0.85, p 〈 0.01） were found. The concentrations of Na＋, IC, Mg2＋, Ca2＋, NH＋4, Cl-, NO3, and SC2-4 were 2.02, 0.81, 0.36, 1.65, 9.58, 4.01, 18.9, and 18.4 μg/m3 in particulate matter from southeast-derived air masses, which were typically 1.58-3.37 times higher than in northwest trajectories. Thus, concentrations of water-soluble ions at this background station were heavily influenced by regional transport of serious pollution derived from biomass burning, coal combustion, industrial and vehicle exhaust emissions from Beijing, Tianjin, and Hebei.

Variations in soil moisture over the ‘Huang-Huai-Hai Plain＇ in China due to temperature change using the CNOP-P method and outputs from CMIP5

In this study, the variations in surface soil liquid water(SSLW) due to future climate change are explored in the‘Huang-Huai-Hai Plain'(‘3H') region in China with the Common Land Model(CoLM). To evaluate the possible maximum response of SSLW to climate change, the combination of the conditional nonlinear optimal perturbation related to the parameter(CNOP-P) approach and projections from 10 general circulation models(GCMs) of the Coupled Model Intercomparison Project5(CMIP5) are used. The CNOP-P-type temperature change scenario, a new type of temperature change scenario, is determined by using the CNOP-P method and constrained by the temperature change projections from the 10 GCMs under a high-emission scenario(the Representative Concentration Pathway 8.5 scenario). Numerical results have shown that the response of SSLW to the CNOP-P-type temperature scenario is stronger than those to the 11 temperature scenarios derived from the 10 GCMs and from their ensemble average in the entire ‘3H' region. In the northern region, SSLW under the CNOP-P-type scenario increases to0.1773 m^3 m^(-3); however, SSLW in the scenarios from the GCMs fluctuates from 0.1671 to 0.1748 m^3 m^(-3). In the southern region,SSLW decreases, and its variation(–0.0070 m^3 m^(-3)) due to the CNOP-P-type scenario is higher than each of the variations(–0.0051 to –0.0026 m^3 m^(-3)) due to the scenarios from the GCMs.