Influence of gravel segregation on gluing solution solidification in a railway ballast     

Chung Fang  Yusin Lee  Yung-Jung Lin  Li-Sin Lu  Po-Chen Chen 《Acta Geotechnica》2017,12(3):605-614

Influence of gravel segregation on gluing solution distribution in a realistic railway ballasts is investigated numerically. The rheological characteristics of the gluing solution are accounted for by using a coupled elasto-visco-plastic stress model with an asymptotic time increasing viscosity. The realistic railway ballast is accomplished by using the vertex identification technique, in which the regulations of the gravel composition in ballast practice are followed. Specifically, a uniformly distributed one and a segregated one induced by the difference in gravel size and gravel shape are generated. The rheological model of the gluing solution and twofold ballasts are incorporated into the finite element code of ANSYS\(^{\copyright }\) to study the flow characteristics and time-dependent solidification of the gluing solution. Relatively concrete vertical and lateral gravel–gravel adhesion in twofold ballasts can be generated by using denser network arrangement of the gluing solution; the vertical penetration in the uniform ballast is slightly deeper than that in the segregated ballast, while a slightly reverse tendency in the lateral extension near the upper and central parts appears. However, the difference in the solidified gluing solution distributions in both ballasts is essentially insignificant, indicating that the influence of the gravel segregation needs not necessary to be taken into account in gluing practice when percolation is not taken into account.  相似文献   

Spatial assessment of groundwater quality in the Jangseong region,South Korea     

Mesfin Benti Tolera  Seunghyuk Park  Sun Woo Chang  Il-Moon Chung 《Environmental Earth Sciences》2017,76(15):545

A total of 129 groundwater samples were collected in the Jangseong region of South Korea to characterize and evaluate groundwater quality and its suitability for irrigation and domestic uses. Samples were chemically analyzed for major ions, pH, electrical conductivity, and total dissolved solids following standard methods. The AquaChem 2014.2 model linked with PHREEQC was used for the statistical analysis and characterization of the hydrochemistry of the groundwater. The analysis showed that in all samples Ca–HCO₃ was the leading water type and that the abundance of major cations was in the order Ca > Na > Mg > K, and of anions in the order HCO₃ > Cl > SO₄ > F. According to the correlation analysis, Ca showed strong interdependence with HCO₃, suggesting that these parameters may have originated from common sources. Saturation index calculations indicated that all samples were undersaturated with respect to aragonite, calcite, dolomite, fluorite, gypsum, halite, and siderite, and oversaturated with respect to goethite and hematite. The irrigation suitability analysis revealed that groundwater in the Jangseong area can be used for irrigation without any restrictions based on EC, sodium adsorption ratio, percent sodium, residual sodium carbonate, Kelley ratio, permeability index, and the US Salinity Laboratory diagram analysis. The drinking water suitability analysis made for major parameters by comparison with the WHO guidelines indicates that the groundwater in the area is suitable for drinking except in some samples with high nitrate–N concentrations. The elevated nitrate concentrations in the groundwater are likely an indicator of agricultural pollution.  相似文献   

A review of conventional techniques for subsurface characterization of landslides     

J. David Rogers  Jaewon Chung 《Environmental Earth Sciences》2017,76(3):120

Naturally occurring landslides can be difficult to characterize and often exhibit anomalies in controlling geometry and consistency. The characterization of landslides in engineering geology practice is usually based on program of subsurface exploration; focused on identifying subsurface materials, structure and stratigraphy, hydrologic conditions, and appropriate strength parameters. On native slopes bereft of anthropogenic modification (excavation), geomorphic evidence of previous movement and its relative depth and scale are often discernible to the experienced eye. This paper seeks to describe the various techniques that have been successfully employed in site-specific subsurface investigations of prehistoric landslides. These include considerations of limiting geometry (for planning subsurface exploration and sampling), overcoming problems with site access, exploratory trenches, small diameter borings, downhole logging of large diameter borings, and geophysical techniques. These procedures can be combined to develop more realistic cross sections along the vector of maximum landslide movement, so the displaced mass can be realistically analyzed. The respective advantages and disadvantages of these techniques are discussed, with baseline references on subsurface exploration.  相似文献   

Predicting landslides for risk analysis — Spatial models tested by a cross-validation technique   总被引：3，自引：3，他引：0  

Chang-Jo Chung  Andrea G. Fabbri   《Geomorphology》2008,94(3-4):438

A landslide-hazard map is intended to show the location of future slope instability. Most spatial models of the hazard lack reliability tests of the procedures and predictions for estimating the probabilities of future landslides, thus precluding use of the maps for probabilistic risk analysis. To correct this deficiency we propose a systematic procedure comprising two analytical steps: “relative-hazard mapping” and “empirical probability estimation”. A mathematical model first generates a prediction map by dividing an area into “prediction” classes according to the relative likelihood of occurrence of future landslides, conditional by local geomorphic and topographic characteristics. The second stage estimates empirically the probability of landslide occurrence in each prediction class, by applying a cross-validation technique. Cross-validation, a “blind test” here using non-overlapping spatial or temporal subsets of mapped landslides, evaluates accuracy of the prediction and from the resulting statistics estimates occurrence probabilities of future landslides. This quantitative approach, exemplified by several experiments in an area near Lisbon, Portugal, can accommodate any subsequent analysis of landslide risk.  相似文献   

Effects of spilled oil on microbial communities in a tidal flat     

Katayama Y  Oura T  Iizuka M  Orita I  Cho KJ  Chung IY  Okada M 《Marine pollution bulletin》2003,47(1-6):85-90

Effects of spilled oil on microbial communities in tidal flats were examined by use of a simulator for a tidal flat ecosystem. The simulator is composed of a wave generator, a tide control device, and a tidal flat. Sediment for the tidal flat was obtained at a natural tidal flat in Hiroshima Bay, Japan. After stabilizing the benthic organisms, fuel oil C was added to the surface of the flat at 1 lm(-2). Although the total number of micro-organisms remained at 1.5-3.5 x 10(9) cells g(-1) dry sediment irrespective of the addition of oil, bacterial communities which were analyzed based on the 16S rDNA showed clear changes after the addition of fuel oil C and after a subsequent recovery period. Bacterial colonies were randomly isolated from the oil-supplemented sediment during the experiments, and the isolates were examined for susceptibility to hydrocarbons in order to screen the oil-susceptible bacteria. The proportion of oil-susceptible bacteria in the isolates decreased with the addition of the oil. Oil-susceptible bacteria showed an inability to assimilate petroleum compounds as well as an inhibition of growth. The possibility of using oil-susceptible bacteria as an indicator of bioremediation in tidal flats was discussed.  相似文献   

210Pb-derived sediment accumulation rates in the southwestern East Sea (Sea of Japan)     

G. H. Hong  S. H. Kim  C. S. Chung  D.-J. Kang  D.-H. Shin  H. J. Lee  S.-J. Han 《Geo-Marine Letters》1997,17(2):126-132

 Recent sediment accumulation rates are 18–230 mg cm^-2 yr^-1 (0.02–0.2 cm yr^-1) based on excess ²¹⁰Pb activity profiles in the southwestern part of the East Sea (Sea of Japan). Assuming no mixing beneath surface mixed layers, ²¹⁰Pb-derived sediment accumulation rates are 18–32 mg cm^-2 yr^-1 in the northern part of the Yamato Ridge and the Ulleung Basin, 29–136 mg cm^-2 yr^-1 in the Korea Plateau, and 230 mg cm^-2 yr^-1 in the southern shelf. These values generally agree with long-term sedimentation rates estimated from dated ash layers. Received: 6 October 1995 / Revision received: 31 May 1996  相似文献   

Early Cretaceous gabbroic complex from Yinan,Shandong Province: petrogenesis and mantle domains beneath the North China Craton   总被引：12，自引：1，他引：11  

Yi-Gang?XuEmail author  Jin-Long?Ma  Xiao-Long?Huang  Yoshiyuki?Iizuka  Sun-Lin?Chung  Yan-Bin?Wang  Xiang-Yang?Wu 《International Journal of Earth Sciences》2004,93(6):1025-1041

Sensitive high resolution ion microprobe (SHRIMP) zircon U–Pb ages, geochemical and Sr-Nd-Pb isotopic data are reported for the gabbroic complex from Yinan (Shandong Province) with the aims of characterizing the nature of the Mesozoic mantle beneath the North China Craton. The Yinan gabbros contain alkali feldspar and biotite, and are characterized by moderate Mg#, high SiO₂, low FeO and TiO₂ contents and a strong enrichment of light rare earth elements [(La/Yb)_n=11–50], but no Eu anomaly. They have low Nb/La (0.07–0.29), radiogenic ⁸⁷Sr/⁸⁶Sr (0.710) and unradiogenic _Nd(t) (–15 to –13). These crustal fingerprints cannot be attributed to crustal contamination, given the lack of correlation between isotopic ratios and differentiation indices and the unreasonably high proportion of crustal contaminant (>20%) required in modeling. Instead, compositional similarities to contemporaneous basalts from nearby regions imply that the Yinan gabbros were not significantly affected by crystal cumulation. Isotopic data available for the Mesozoic mafic magmas reveal two distinct mantle domains beneath Shandong. While the EM1-like domain (with low ⁸⁷Sr/⁸⁶Sr) is confined to western Shandong, the mantle beneath eastern Shandong is dominated by EM2-type (with high ⁸⁷Sr/⁸⁶Sr) affinities. This aerial distinction suggests that the EM2-like signature of the Yinan gabbros may have been inherited from westerly-subducted Yangtze crust during the Triassic North China-South China collision. Emplacement of the Yinan gabbros (127 Ma) is likely affiliated with the widespread and protracted extension during the late Mesozoic in this region.  相似文献   

Neighbourhood redevelopment and the making of a housing middle class: Can gentrification explain China’s spatial and social changes?     

Chung  Him 《GeoJournal》2021,86(3):1375-1388

GeoJournal - This paper addresses the relationship between spatial change and social process in China. Studies in Anglo-American and European cities usually suggest middle classes move into a...  相似文献   

Time series analyses of hydrological parameter variations and their correlations at a coastal area in Busan,South Korea     

Sang Yong Chung  Venkatramanan Senapathi  Selvam Sekar  Tae Hyung Kim 《Hydrogeology Journal》2018,26(6):1875-1885

Monitoring and time-series analysis of the hydrological parameters electrical conductivity (EC), water pressure, precipitation and tide were carried out, to understand the characteristics of the parameter variations and their correlations at a coastal area in Busan, South Korea. The monitoring data were collected at a sharp interface between freshwater and saline water at the depth of 25 m below ground. Two well-logging profiles showed that seawater intrusion has largely expanded (progressed inland), and has greatly affected the groundwater quality in a coastal aquifer of tuffaceous sedimentary rock over a 9-year period. According to the time series analyses, the periodograms of the hydrological parameters present very similar trends to the power spectral densities (PSD) of the hydrological parameters. Autocorrelation functions (ACF) and partial autocorrelation functions (PACF) of the hydrological parameters were produced to evaluate their self-correlations. The ACFs of all hydrologic parameters showed very good correlation over the entire time lag, but the PACF revealed that the correlations were good only at time lag 1. Crosscorrelation functions (CCF) were used to evaluate the correlations between the hydrological parameters and the characteristics of seawater intrusion in the coastal aquifer system. The CCFs showed that EC had a close relationship with water pressure and precipitation rather than tide. The CCFs of water pressure with tide and precipitation were in inverse proportion, and the CCF of water pressure with precipitation was larger than that with tide.  相似文献   

DEM modeling of hydraulic fracturing in permeable rock: influence of viscosity,injection rate and in situ states     

Kang Duan  Chung Yee Kwok  Wei Wu  Lu Jing 《Acta Geotechnica》2018,13(5):1187-1202

Hydraulic fracturing in permeable rock is a complicated process which might be influenced by various factors including the operational parameters (e.g., fluid viscosity, injection rate and borehole diameter) and the in situ conditions (e.g., in situ stress states and initial pore pressure level). To elucidate the effects of these variables, simulations are performed on hollow-squared samples at laboratory scale using fully coupled discrete element method. The model is first validated by comparing the stress around the borehole wall measured numerically with that calculated theoretically. Systematic parametric studies are then conducted. Modeling results reveal that the breakdown pressure and time to fracture stay constant when the viscosity is lower than 0.002 Pa s or higher than 0.2 Pa s but increases significantly when it is between 0.002 and 0.2 Pa s. Raising the injection rate can shorten the time to fracture but dramatically increase the breakdown pressure. Larger borehole diameter leads to the increase in the time to fracture and the reduction in the breakdown pressure. Higher in situ stress requires a longer injection time and higher breakdown pressure. The initial pore pressure, on the other hand, reduces the breakdown pressure as well as the time to fracture. The increase in breakdown pressure with viscosity or injection rate can be attributed to the size effect of greater tensile strength of samples with smaller infiltrated regions.  相似文献