Utilizing sediment grain size characteristics to assess the effectiveness of clay–sand barriers in reducing aeolian erosion in Minqin desert area,China

The clay–sand barriers in Minqin desert area,China,represent a pioneering windbreak and sand fixation project with a venerable history of 60 a.However,studies on evaluating the long-term effectiveness of clay–sand barriers against aeolian erosion,particularly from the perspective of surface sediment grain size,are limited and thus insufficient to ascertain the protective impact of these barriers on regional aeolian activities.This study focused on the surface sediments(topsoil of 0–3 cm depth)of clay–sand barriers in Minqin desert area to explain their erosion resistance from the perspective of surface sediment grain size.In March 2023,six clay–sand barrier sampling plots with clay–sand barriers of different deployment durations(1,5,10,20,40,and 60 a)were selected as experimental plots,and one control sampling plot was set in an adjacent mobile sandy area without sand barriers.Surface sediment samples were collected from the topsoil of each sampling plot in the study area in April 2023 and sediment grain size characteristics were analyzed.Results indicated a predominance of fine and medium sands in the surface sediments of the study area.The deployment of clay–sand barriers cultivated a fine quality in grain size composition of the regional surface sediments,increasing the average contents of very fine sand,silt,and clay by 30.82%,417.38%,and 381.52%,respectively.This trend became markedly pronounced a decade after the deployment of clay–sand barriers.The effectiveness of clay–sand barriers in erosion resistance was manifested through reduced wind velocity,the interception of sand flow,and the promotion of fine surface sediment particles.Coarser particles such as medium,coarse,and very coarse sands predominantly accumulated on the external side of the barriers,while finer particles such as fine and very fine sands concentrated in the upwind(northwest)region of the barriers.By contrast,the contents of finest particles such as silt and clay were higher in the downwind(southeast)region of the sampling plots.For the study area,the deployment of clay–sand barriers remains one of the most cost-effective engineering solutions for aeolian erosion control,with sediment grain size parameters serving as quantitative indicators for the assessment of these barriers in combating desertification.The results of this study provide a theoretical foundation for the construction of windbreak and sand fixation systems and the optimization of artificial sand control projects in arid desert areas.

Spatial heterogeneity for grain size distribution of eolian sand soil on longitudinal dunes in the southern Gurbantunggut Desert

The grain size composition, distribution characteristics and spatial variation of eolian sand soil on distinct positions across two longitudinal dunes and interdune areas were studied by means of conventional grain size analysis and geostatistical methods. In the study, 184 samples of eolian sand soil from the 0-30cm layer were systemically collected and measured from two longitudinal dunes and interdunes in the southern Gurbantunggut Desert. The results show that the dominant grain sizes are fine and very fine sands, and the differences of grain size compositions between the distinct geomorphologic positions are significant. The contents of clay and silt are highest on the interdune areas and lowest on the crests, and higher on the leeward slopes than on the windward slopes. The contents of very fine and fine sands are highest on the windward slopes and lowest on the crests. The contents of medium, coarse and very coarse sands are lowest on the interdune lands, and highest on the crests, and are identical on the two slopes. The coarser sizes (phi(1)) and mean sizes (Mz) for eolian sand soil all have a varying tendency from fine to coarse sizes with interdune area -> leeward slope -> windward slope -> crest, and the sorting (sigma) are poorly to well sorted. The results of geostatistical analysis reveal that phi(1), Mz and a values are moderately to strongly spatially autocorrelated. The values of the spatially correlated ranges are phi(1) < sigma < Mz. The spatial variation for these grain size parameters is significant across the longitudinal dune landscape. From the crests towards the bottom of the slope, there is a varying gradient of zonal distribution, and the gradient values on the leeward slopes are larger than sites on the windward slopes.

Origin and Distribution of Grain Dolostone Reservoirs in the Cambrian Longwangmiao Formation,Sichuan Basin,China

Dolostones in the Cambrian Longwangmiao Formation have become one of the most significant gas exploration domains in China. Over a trillion cubic meters of gas reservoirs have been discovered in the Gaoshiti-Moxi area; however, the origins and distribution of the dolostone reservoirs are not well understood. This work discussed the geology and geochemistry of the dolostone reservoirs in the Longwangmiao Formation to determine their origin and distribution. Two understandings are acquired： firstly, a carbonate ramp provided excellent conditions for grain beach deposition, while the presence of a hypersaline lake was favorable for the contemporaneous dolomitization of grain beach deposits. Petrographic and geochemical evidence further confirm that the Longwangmiao dolostone was formed during the contemporaneous stage. Secondly, the reservoir characteristics indicate that the grain beach sediments provide material basis for the development of the Longwangmiao dolostone reservoirs. Reservoir dissolution simulation experiments show that the porosity of the reservoirs was formed by dissolution during contemporaneous and burial stages. The dissolution pores formed during the contemporaneous stage were controlled by sequence interfaces. The large scale dissolution vugs formed during the burial stage subsequently spread along the pre-existing porosity and fracture zones. This study therefore identified that the development of grain dolostone reservoirs in a shallow water ramp under arid climatic conditions generally met the following conditions：（1） reefal beach deposits lay a foundation for reservoir development;（2） superficial conditions are an important determining factor for reservoir porosity; and（3） burial conditions provide environment for porosity preservation and modification.

Influence of bimodal grain size distribution on the corrosion behavior of friction stir processed biodegradable AZ31 magnesium alloy

In the present study,AZ31 magnesium alloy sheets were processed by friction stir processing(FSP)to investigate the effect of the grain refinement and grain size distribution on the corrosion behavior.Grain refinement from a starting size of 16.4±6.8µm to 3.2±1.2µm was attained after FSP.Remarkably,bimodal grain size distribution was observed in the nugget zone with a combination of coarse(11.62±8.4µm)and fine grains(3.2±1.2µm).Due to the grain refinement,a slight improvement in the hardness was found in the nugget zone of FSPed AZ31.The bimodal grain size distribution in the stir zone showed pronounced influence on the corrosion rate of FSPed AZ31 as observed from the immersion and electrochemical tests.From the X-ray diffraction analysis,more amount of Mg(OH)_(2) was observed on FSPed AZ31 compared with the unprocessed AZ31.Polarization measurements demonstrated the higher corrosion current density for FSPed AZ31(8.92×10^(−5)A/cm^(2))compared with the unprocessed condition(2.90×10^(−5)A/cm^(2))that can be attributed to the texture effect and large variations in the grain size which led to non-uniform galvanic intensities.

Characteristics of grain size distribution and the shear strength analysis of Chenjiaba long runout coseismic landslide

Study on the grain size distribution characteristics and the frictional strength behavior of the slide deposits are helpful to disclose the landslide runout process and understand the mechanism of a long runout landslide. We performed grain size distribution analysis on samples collected from Chenjiaba landslide induced by Wenchuan earthquake. The grain size distribution of samples from the landslide sections quantitatively depicts a gradual coarsening upward grading from shear zone to the top section. Then a multistage-multiphase ring shearing approach was used to determine a comparative shear strength behavior of samples from each landslide section. In this method, a sample was sheared continuously for large displacement and fast rate on different normal stress conditions. The multiphase shear mode with a maximum of 105 mm/min rate has allowed observing the qualitative change and patterns of the frictional resistance behaviors of soils under different normal stresses. The results of coefficient of friction values under multiphase shear mode have shown substantial post peak shear weakening behaviors after large shear displacement that can be narrated with long runout processes. The shear strength test results indicate that the shear zone samples have developed higher friction angle values compared to overlying section samples, on the last phase of shear process, which may be very important to understand the braking mechanism of a long runout landslide.

Grain Size Distribution of Soils within the Cordillera Blanca, Peru: An Indicator of Basic Mechanical Properties for Slope Stability Evaluation

This paper presents results of a study on the mechanical properties of sandy and gravely soils within the Cordillera Blanca, Peru. The soils were divided into groups according to their origin(glacial, fluvial, or debris flow). The grain size distribution of forty three soil samples was used to classify the soils according to the scheme of the Unified Soil Classification System(USCS). These distributions have then been used to estimate shear strength and hydraulic properties of the soils. There are clear differences between the soils which reflect their divergent origins. The glacial soils normally fit within one of two distinctive groups according to the proportion of fines(Group A, 7%-21.5%; Group B, 21%-65%). The estimation of shear strength at constant volume friction angle and peak shear strength of the glacial sediments with low content of fines was made using published data relating to the measured shear strength characteristics of soils with similar origins and grain size distributions. The estimated values were supported by measurements of the angle of repose taken from fourteen samples from two moraines and by shear tests on samples from one locality. The results of the grain size distribution werealso used to estimate the average hydraulic conductivity using the empirical Hazen formula which results were verified by field infiltration tests at two localities.

Grain-size distribution patterns of suspended sediment in response to hydrodynamics on the Dafeng intertidal flat, Jiangsu, China

Patterns of grain-size distributions of suspended sediment in relation to resuspension, settling, and tidal processes are investigated, based on in situ measurements over the Dafeng intertidal flat, on the Jiangsu coast, in the summer of 2002 and 2003. The suspended sediment here is dominated by fine and very fine silt, with a mean grain-size of 7 - 13 μm. The patterns of the grainsize distributions of suspended sediment during a tidal cycle are characterized by two types： one stable type representing insignificant spatial and temperal variations; and the other bimedal type with significant variations. The main factors influencing the grainsize distributions include resnspension, settling, suspended sediment imported into intertidal flats during the flood phase, and the grain-size distribution of seabed sediment. Resuspension increases the coarse particle content, enhances the mean grain-size of suspended sediment, and results in grain-size distributions for the suspended sediment similar to those of seabed sediment; the settling process has opposite effects on the suspended sediment. When resuspension occurs, the gain-size distributions of suspended sediment in the lower part of water column respond significantly to the current velocity. Where the influence of resuspension and settling processes is weak, the grain-size distributions of suspended sediment appear to be stable and almost identical for the various parts of intertidal flats during different measurement periods. Such distributions are referred to the background grain-size distribution, for which the mean grain-size over the Dafeng intertidal flat is around 7 μm.

GEOMETRIC MODEL AND APPLIED METHOD FOR THE CALCULATION OF GRAIN SIZE DISTRIBUTIONS

Most of the available methods for the calculation of the three dimensional(3D)grain size dis- tribution functions(SDF)are based on the S model and lead a grave systematical error.The origin is the basic supposition of spherical grains in the S model,which does not correspond with the feature of real grains.A new model called A model is developed based on the hypothe- sis of polvhedral grains.The probability functions of the A model and the method to calculate the 3D SDFs using the A model are given in the present paper.The theoretical analyses and experimental tests have demonstrated that the A model reduces the systematical error radical- ly.It is nearly as simple as the so far used S model,but gives much better results in repro- ducing of 3D SDFs from the measured ID or 2D SDFs.

The effect of substrate grain size on burrowing ability and distribution characteristics of Perinereis aibuhitensis

Perinereis aibuhitensis(Grube, 1878) lives in marine sediments of estuary or shoal areas, where substrate has some crucial environmental factors affecting its burrowing and distribution. In order to provide basic data for the habitat selection and suitability evaluations of the artificial aquaculture of P. aibuhitensis, this paper conducted a quantified analysis of its burrowing ability and explored its behavioral preferences in different substrates,including mud(<75 μm), fine sand(125–250 μm), medium sand(250–500 μm), coarse sand(500–2 000 μm), gravel(2 000–4 000 μm) and ceramsite(4 000–8 000 μm). The research results revealed that substrate grain size significantly affected the burrowing time, burrowing rate, burrowing depth and distribution rate(P<0.01).Moreover, P. aibuhitensis demonstrated preferential selections relating to substrate grain sizes, had higher burrowing ability in ceramsite, mud and fine sand compared with other substrates. The strongest burrowing ability and the highest distribution rate were observed in ceramsite. The study indicated that P. aibuhitensis was sensitive to substrate grain size, which also had an impact on its burrowing process and population distribution.In the natural sea, substrates mainly composed of mud and fine sand are fit for aquaculture and stock enhancement. Based on behavioral preferences and ecological rehabilitation function of P. aibuhitensis, this paper proposes a symbiotic system of marine animals and halophytes, and constructs an ecosystem model of"Marine fish-Halophytes-Perinereis aibuhitensis" with P. aibuhitensis as the link.

Fruit Production Distribution and Adjustment Strategies under the Constraint of Grain Security

Grain security is the foundation of national security,and guaranteeing the grain security by every possible means is a development priority for the whole country.Rapid development of the fruit industry satisfies increasing demands of people for fruits,but also presents certain competition for grain production.From the perspective of limited resources and comparative income,this paper analyzed potential threats of fruit production distribution to grain production in farmland and labor resources,and came up with pertinent adjustment strategies.

The grain-size distribution of the suspended particulate matter in the Huanghe Estuary and its adjacent sea area in winter

The grain-size of suspended particulate matter （SPM） in the Huanghe Estuary and its adjacent sea area was investigated with an in situ laser particle size analyzer （LISST-100） in November 2006.The spatial distribution of the grain-size parameters was very complicated.The results show that （1） the mean particle size of SPM ranged from 3.00Φ to 6.41Φ,with an average value of 4.66Φ;（2） the frequency distribution patterns of the SPM grain-size showed three different types,which were mono-mode,dual-mode and tri-mode,respectively;（3） C-M chart suggested that the transportation-processes of the SPM not only included suspended mode,but also the bed load transportation mode.The bed load transportation mode mainly occurred at the bottom layer.The characteristics and space distribution of SPM grain-size might be mainly controlled by sediment discharge of the Huanghe River,hydrodynamics condition,surface sediment types,and biological process within the study area.

Assessment of the Relationship between ESR Signal Intensity and Grain Size Distribution in Shear Zones within the Atotsugawa Fault System, Central Japan

For the first time, a relationship between ESR signal intensity and grain size distribution (sieve technique) in shear zones within the Atotsugawa fault system have been investigated using fault core rocks. The grain size distributions were estimated using the sieve technique and microscopic observations. Stacks of sieves with openings that decrease consecutively in the order of 4.75 mm, 1.18 mm, 600 μm, 300 μm, 150 μm and 75 μm were chosen for this study. Grain size distributions analysis revealed that samples further from the slip plane have larger d50 (average gain size) (0.45 mm at a distance of 30 - 50 mm from the slip plane) while those close to the slip plane have smaller d50 values (0.19 mm at a distance of 0 - 10 mm from the slip plane). This is due to intensive crushing that is always associated with large displacement during fault activities. However, this pattern was not respected in all shear zones in that, larger d50 values were instead observed in samples close to the slip plane due to admixture of fault rocks from different fault activities. Results from ESR analysis revealed that the relatively finer samples close to the slip plane have low ESR signals intensity while those further away (coarser) have relatively higher signal intensity. This tendency however, is not consistence in some of the shear zones due to a complex network of anatomizing faults. The variation in grain size distribution within some of the shear zones implies that, a series of fault events have taken place in the past thus underscoring the need for further investigation of the possibility of reoccurrence of faults.

Optimizing Domain Distribution of Grain Oriented Silicon Steel by Using Antimony as the Laser Surface Alloying Element

For reducing the core loss of grain oriented silicon steel and improving its aging property, a new method, the LLSA by using Sb as the laser surface alloying element, was investigated, and at proper technique conditions rather good result was obtained.

The spatial distribution of major and trace elements of surface sediments in the northeastern Beibu Gulf of the South China Sea

A multi-index analysis including grain size, major and trace elements is performed on the surface sediments from the northeastern Beibu Gulf to trace the sources of the sediments and to understand the controlling factors for elements distribution. The mean grain size exhibits a wide variation ranging from 0.09Φ to 8.05Φ with an average value of 5.33Φ. The average contents of major elements descend in an order of c(SiO_2)>c(Al_2O_3)>c(Fe_2O_3)>c(CaO)>c(MgO)>c(K_2O)>c(Na_2O)>c(TiO_2)>c(P_2O_5)>c(MnO), while those of trace elements exhibit a descending order of c(Sr)>c(Rb)>c(V)>c(Zn)>c(Cr)>c(Pb)>c(Ni)>c(Cu)>c(As). On the basis of elementary distribution characteristics and statistical analyses, the study area is divided into the four zones: Zone I is located in the northeastern coastal area of the gulf, which receives large amount of fluvial materials from local rivers in Guangxi and Guangdong, China, and the Qiongzhou Strait; Zone Ⅱ is located in the center of the study area, where surface sediments exhibits a multiple source; Zone Ⅲ is located in the Qiongzhou Strait, where surface sediments are dominated by materials from the Zhujiang River and Hainan; Zone IV is located in the southwest of the study area, where surface sediments are mainly originated from the Red River and Hainan. The statistical analyses of sediment geochemical characteristics reveal that the grain size, which is mainly influenced by hydrodynamics and mineral composition of terrigenous materials, is the leading factor controlling the elementary distribution.Meanwhile, impacts from anthropogenic activities and marine biogenic process will also be taken into consideration.

Distribution and characteristics of gravelly soil liquefaction in the Wenchuan M_s 8.0 earthquake

In this paper,a distribution map of gravelly soil liquefaction that was caused by the Wenchuan M8.0 earthquake in China is proposed based on a detailed field investigation and an analysis of geological soil profiles. The geological background of the earthquake disaster region is summarized by compiling geological cross sections and borehole logs. Meanwhile,four typical liquefied sites were selected to conduct sample drillings,dynamic penetration tests (DPT),and shear wave velocity tests,to understand the features of liquefied gravelly soil. One hundred and eighteen (118) liquefied sites were investigated shortly after the earthquake. The field investigation showed:(1) sandboils and waterspouts occurred extensively,involving thousands of miles of farmland,120 villages,eight schools and five factories,which caused damage to some rural houses,schools,manufacturing facilities and wells,etc.; (2) the Chengdu plain is covered by a gravelly soil layer with a thickness of 0 m to 541 m according to the geological cross sections; (3) there were 80 gravelly soil liquefied sites in the Chengdu plain,shaped as five belt areas that varied from 20 km to 40 km in length,and about ten gravelly soil liquefied sites distributed within Mianyang area; and (4) the grain sizes of the sampled soil were relative larger than the ejected soil on the ground,thus the type of liquefied soil cannot be determined by the ejected soil. The gravelly soil liquefied sites are helpful in enriching the global database of gravelly soil liquefaction and developing a corresponding evaluation method in further research efforts.

Grain size characteristics of the carbonate-free fraction of surface sediments from the Southwest Indian Ridge area and its geological significance

The carbonate-free fraction of 20 surface sediments collected from the ultraslow-spreading Southwest Indian Ridge(SWIR) was studied by grain size analysis and mineralogical analysis with X-ray powder diffraction(XRD),stereo microscopy and scanning electron microscopy(SEM). The characteristics of the carbonate-free fraction of the sediments were obtained, and related influential factors were discussed. The results show that the mean grain size of this fraction is in 1.96Φ–8.19Φ, with poorly sorting and unimodal, bimodal or irregular bimodal distribution patterns. Four grain size end members of the fraction are derived with the End Member Model method. The finest end member EM1 shows a significant contribution of terrigenous materials of the aeolian input and sediment carried by the bottom current. End member EM2 with medium size mainly reflects sediment of a siliceous bioclast origin. EM3 and EM4 are interpreted as representing the coarser volcanic materials related to bedrock weathering or volcanic activities. Multi-provenance is the dominant factor controlling the grain size pattern of the carbonate-free fraction of the sediments in that area. In addition, sediment transport processes such as the bottom current and wind are the minor factors that influence the grain size distribution of the carbonate-free fraction sediments.

Discussion on the Hillert Theory of Normal Grain Growthwith a Modified Monte Carlo Simulation

On the basis of analyzing some limitations in the existing algorithm, a modified Monte Carlo methodwas proposed to simulate two-dimensional normal grain growth. With the modified method. the simulated time exponent of grain growth attained n=0.49±0.01, which is very close to the theoretical value of the steady graingrowth n=0.5, indicating the possibility to investigate the total process of normal grain growth. The relationbetween the Hillert and the von Neumann equations were studied and identified, the Hillert's basic equation hasbeen found to hold during the normal grain growth. The grain size distribution was found to van continuouslyand slowly with the simulated time in the total growth process, the lognormal and the Hillert functions may betwo types of the expression forms during its transition, and the later seemingly corresponds at the distribution ofthe steady stage were n≈0.50.

Symptom of the Shrunk-Grain Panicle and the Change Characteristics in Its Grain

Over the past two years, an abnormal growth phenomenon Jiangsu Province of China. The phenomenon is described in called shrunk-grain panicle has occurred in a large area in details by figures and characters in this article. The method with a japonica rice Wuyujing 3 as the experimental material, the characteristics of grain morphology distribution and the grain weight were studied. Normal and shrunk-grain panicles were sampled from several representative areas. The length, width, and weight of the normal grains were distributed as regular, continuous, and single peaks. Plant growth typically had a right-leaning tendency. On the contrary, the distribution of the grain morphology and weight were irregular and nearly double that of the shrunk-grain panicle. The proportion of the cumulative distribution in the two kinds of peaks was closely related to the degree of shrunk-grain panicle. The article discusses the phenomenon＇s symptoms, problems, and diagnosis.

IMPACT OF CLIMATE ON GRAIN YIELD PER UNIT AREA IN CHINA DURING THE YEARS OF 1949～1992

The grain yield per unit area in China has been increasing from 1949 to 1992 with annual fluctuations, which was caused by both policies and monsoon climate. The total grain yield is divided into trend yield, which reflects the influence of economic factors, and climate yield, which reflects the impact of climate factors. The results of grain and climate yield by EOF (empirical orthogonal function) method show that the grain yield in the eastern China is higher and more fluctuating than that in the western region. The spatial and temporal distributions of climate yield were divided into four patterns. Regional unanimity of climate yield variation is the first and main spatial pattern, and then there are the spatial patterns of north-south difference and east-west difference in some years. Generally, climate conditions are good for grain yield during the 1950s and 1980s all over the country.

Evaluation of the location parameter in Weibull distribution of CTOD testing results of high strength steel weldments

In this paper, the location parameter δ_(a) in Weibull distribution i.e. the lower limiting CTOD toughness of high strength steel weldments is evaluated from Gleeble simulated coarse grained specimens. The Charpy-V transition temperature obtained from these specimens is transformed to a fracture toughness K_(IC) value at a given temperature using Sanz' relation. Then, the location parameter a is δ_(a) evaluated. The predicted location parameter arrives at agreement with the lowest CTOD value as obtained from thick multilayer weldments. The improvement of the fracture toughness of multilayer weldments needs the increase of the lowering limiting CTOD.toughness i.e. the toughness of the coarse grained zone.