Supra-subduction and abyssal mantle peridotites of the Coast Range ophiolite,California

The Coast Range ophiolite (CRO) of California is one of the most extensive tracts of oceanic crust preserved in the North American Cordillera, but its origin has long remained controversial. We present here new data on mineral compositions in mantle peridotites that underlie crustal sections of the ophiolite, and show that these are dominantly refractory harzburgites related to high apparent melting in a supra-subduction zone (SSZ) setting. Abyssal peridotite (characterized by high-Al spinels and relatively high Ti, Na, Nd, Sm, Lu, and Hf in pyroxene) occurs at one location where it is associated with SSZ mantle peridotite and volcanic rocks with both oceanic and arc-like geochemistry. SSZ mantle peridotites (characterized by intermediate-Cr/Al or high-Cr spinels, and by extremely low Ti, Na, Nd, Sm, Lu, and Hf in pyroxenes) are associated with crustal sections containing arc-related volcanic rocks, including boninites. This convergence between conclusions based on crustal lithologies and their underlying mantle sections confirms previous proposals that link the CRO to SSZ processes, and seriously undermines hypotheses that invoke formation of the ophiolite at a mid-ocean ridge spreading center.     

Mechanical Behaviour of Reservoir Rock Under Brine Saturation

Acoustic emissions (AE) and stress–strain curve analysis are well accepted ways of analysing crack propagation and monitoring the various failure stages (such as crack closure, crack initiation level during rock failure under compression) of rocks and rock-like materials. This paper presents details and results of experimental investigations conducted for characterizing the brittle failure processes induced in a rock due to monocyclic uniaxial compression on loading of two types of sandstone core samples saturated in NaCl brines of varying concentration (0, 2, 5, 10 and 15 % NaCl by weight). The two types of sandstone samples were saturated under vacuum for more than 45 days with the respective pore fluid to allow them to interact with the rocks. It was observed that the uniaxial compressive strength and stress–strain behaviour of the rock specimens changed with increasing NaCl concentration in the saturating fluid. The acoustic emission patterns also varied considerably for increasing ionic strength of the saturating brines. These observations can be attributed to the deposition of NaCl crystals in the rock’s pore spaces as well some minor geo-chemical interactions between the rock minerals and the brine. The AE pattern variations could also be partly related to the higher conductivity of the ionic strength of the high-NaCl concentration brine as it is able to transfer more acoustic energy from the cracks to the AE sensors.     

Characterizing Excavation Damaged Zone and Stability of Pressurized Lined Rock Caverns for Underground Compressed Air Energy Storage

In this paper, we investigate the influence of the excavation damaged zone (EDZ) on the geomechanical performance of compressed air energy storage (CAES) in lined rock caverns. We conducted a detailed characterization of the EDZ in rock caverns that have been excavated for a Korean pilot test program on CAES in (concrete) lined rock caverns at shallow depth. The EDZ was characterized by measurements of P- and S-wave velocities and permeability across the EDZ and into undisturbed host rock. Moreover, we constructed an in situ concrete lining model and conducted permeability measurements in boreholes penetrating the concrete, through the EDZ and into the undisturbed host rock. Using the site-specific conditions and the results of the EDZ characterization, we carried out a model simulation to investigate the influence of the EDZ on the CAES performance, in particular related to geomechanical responses and stability. We used a modeling approach including coupled thermodynamic multiphase flow and geomechanics, which was proven to be useful in previous generic CAES studies. Our modeling results showed that the potential for inducing tensile fractures and air leakage through the concrete lining could be substantially reduced if the EDZ around the cavern could be minimized. Moreover, the results showed that the most favorable design for reducing the potential for tensile failure in the lining would be a relatively compliant concrete lining with a tight inner seal, and a relatively stiff (uncompliant) host rock with a minimized EDZ. Because EDZ compliance depends on its compressibility (or modulus) and thickness, care should be taken during drill and blast operations to minimize the damage to the cavern walls.     

Chemical and isotopic compositions of groundwater and stream water in a heavy agricultural basin of Korea

The chemical and isotopic compositions of groundwater and stream water in the Haean basin, Korea, which have been intensively used for agricultural irrigation, were examined. The field parameters and chemical compositions were typical of relatively uncontaminated waters, except for the agricultural impact. The low EC levels indicated that the waters had not experienced any significant geochemical processes such as water-rock interaction and evaporation. The very similar chemical compositions and ionic ratios were also indicative of fast circulation and good hydraulic connection. The oxygen and hydrogen isotopic compositions of most of the samples in wet and dry seasons showed very similar range which indicated a single source for both waters without any significant geochemical alteration. However, in the wet season, evaporation trends were observed in some groundwaters because of inflow of irrigation return flow from a rice paddy field. The isotopes of both waters were affected by the altitude and amount of precipitation.     

Finding least-cost paths across a continuous raster surface with discrete vector networks

The problem of finding the least-cost path from a source point to a destination point can be dealt with by routing across a continuous surface or routing along a discrete network. The solutions within these two contexts are linked to the use of a raster- or a vector-based least-cost path algorithm. This study presents a technique which integrates raster- and vector-based least-cost path algorithms for determining the least-cost path across a continuous raster surface with discrete vector networks. The technique incorporates ancillary vector data sets that are required to examine the travel cost at each link, connections between nodes, and the representation of intersecting links in the discrete vector network into raster-based least-cost path analysis. The integrated technique presented here is applicable to all-terrain vehicle navigation where a continuous raster surface and discrete vector networks need to be considered simultaneously in order to find least-cost paths. This paper describes the concept behind, and details of, the integrated technique. Applications of the technique with synthetic and real-world data sets are also presented. They provide proof that the technique is effective in finding least-cost paths across a continuous raster surface with discrete vector networks.     

Multi‐criteria evaluation and least‐cost path analysis for optimal haulage routing of dump trucks in large scale open‐pit mines

A new raster‐based GIS model that combines multi‐criteria evaluation and least‐cost path analysis was developed to determine the optimal haulage routes of dump trucks in large scale open‐pit mines. The model logic can consider multiple criteria simultaneously (i.e. speed, water body, ore body, curve, visibility, haul road maintenance) and can rate the adverse factor scores of truck movement using fuzzy membership functions. After establishing the weights of five factors by pairwise comparisons, the average adverse score grid can be generated by the weighted linear combination of factor and constraint scores. New software, called Dump Traveler, was implemented to improve the availability of the developed model. An application to the Roto South pit in the Pasir open‐pit coal mine, Indonesia, showed that the software can provide rational solutions to determine the optimal routes on truck haulage operations. Moreover, the layout of available haul roads can be evaluated to consider the trade‐off between road maintenance costs and the potential for traffic jams. Variations of weights for factors were found to be sensitive to the optimal haulage routes determined by least‐cost path analysis. The software provides both optimal routes on truck haulage operations and approximately estimated travel times along the routes, therefore it can support other truck dispatching software that mainly considers scheduling problems.     

Geotechnical parameter estimation in tunnelling using relative convergence measurement

Accurate estimation of geotechnical parameters is an important and difficult task in tunnel design and construction. Optimum evaluation of the geotechnical parameters have been carried out by the back‐analysis method based on estimated absolute convergence data. In this study, a back‐analysis technique using measured relative convergence in tunnelling is proposed. The extended Bayesian method (EBM), which combines the prior information with the field measurement data, is adopted and combined with the 3‐dimensional finite element analysis to predict ground motion. By directly using the relative convergence as observation data in the EBM, we can exclude errors that arise in the estimation of absolute displacement from measured convergence, and can evaluate the geotechnical parameters with sufficient reliability. The proposed back‐analysis technique is applied and validated by using the measured data from two tunnel sites in Korea. Copyright © 2005 John Wiley & Sons, Ltd.     

Calculation of Intercepted Volume of Sewer Overflows： a Model for Control of Nonpoint Pollution Sources in Urban Areas

The authors discovered large differences in the characteristics of overflows by the calculation of 1） intercepting volume of overflows for sewer systems using SWMM model which takes into consideration the runoff and pollutants from rainfalls and 2） the intercepted volume in the total flow at an investigation site. The intercepting rate at the investigation point of CSOs showed higher values than the SSDs. Based on the modeling of the receiving water quality after calculating the intercepting amount of overflows by considering the characteristics of outflows for a proper management of the overflow of sewer systems with rainfalls, it is clear that the BOD decreased by 82.9%-94.0% for the discharge after intercepting a specific amount of flows compared to the discharge from unprocessed overflows.     

Daily streamflow modelling and assessment based on the curve‐number technique

A cell‐based long‐term hydrological model (CELTHYM) that can be integrated with a geographical information system (GIS) was developed to predict continuous stream flow from small agricultural watersheds. The CELTHYM uses a cell‐by‐cell soil moisture balance approach. For surface runoff estimation, the curve number technique considering soil moisture on a daily basis was used, and release rate was used to estimate baseflow. Evapotranspiration was computed using the FAO modified Penman equation that considered land‐use‐based crop coefficients, soil moisture and the influence of topography on radiation. A rice paddy field water budget model was also adapted for the specific application of the model to East Asia. Model sensitivity analysis was conducted to obtain operational information about the model calibration parameters. The CELTHYM was calibrated and verified with measured runoff data from the WS#1 and WS#3 watersheds of the Seoul National University, Department of Agricultural Engineering, in Hwaseong County, Kyounggi Province, South Korea. The WS#1 watershed is comprised of about 35·4% rice paddy fields and 42·3% forest, whereas the WS#3 watershed is about 85·0% forest and 11·5% rice paddy fields. The CELTHYM was calibrated for the parameter release rate, K, and soil moisture storage coefficient, STC, and results were compared with the measured runoff data for 1986. The validation results for WS#1 considering all daily stream flow were poor with R², E² and RMSE having values of 0·40, ?6·63 and 9·69 (mm), respectively, but validation results for days without rainfall were statistically significant (R² = 0·66). Results for WS#3 showed good agreement with observed data for all days, and R², E² and RMSE were 0·92, 0·91 and 2·23 (mm), respectively, suggesting potential for CELTHYM application to other watersheds. The direct runoff and water balance components for watershed WS#1 with significant areas of paddy fields did not perform well, suggesting that additional study of these components is needed. Copyright © 2002 John Wiley & Sons, Ltd.     

Does El Niño-Southern Oscillation affect the precipitation in Korea on seasonal time scales?

A number of studies in the past two decades have attempted to find the relationship between the precipitation in Korea and the El Niño-Southern Oscillation (ENSO) on various time scales. Comprehensive analyses of station precipitation data in Korea for the 61-year period, 1954-2014, in this study show that the effects of ENSO on the seasonal precipitation in Korea are practically negligible. The correlation between summer precipitation and ENSO is insignificant regardless of the intensity, type (e.g., eastern-Pacific or central-Pacific), and stage (e.g., developing, mature, or decaying) of ENSO. Somewhat meaningful correlation between ENSO and precipitation in Korea occurs only in the ENSO-developing fall. Because summer rainfall accounts for over half of the annual total and fall is a dry season in Korea, the overall effects of ENSO on precipitation in Korea are practically nonexistent.