• Journal of the Korean Society of Groundwater Environment
• /
• v.6 no.3
• /
• pp.152-157
• /
• 1999

Oil leaked from underwound storage tanks and leachate from sanitary landfills have been known as contaminant sources of the high-quality groundwater resources. The mobility of contaminants in the aquifer largely depends on the groundwater flow and the determination of associated hydraulic parameters is essential for a proper remediation of contaminated grnundwater. This study aimed at determining an optimum set of hydraulic parameters for an unconfined sandy aquifer of a laboratory scale through comparison of various methods. Results showed that the specific yield obtained from gravity drainage experiment was an average of 0.20 with minor variations in aquifer depths. and the permeabilities obtained from Dupuit approximation and slug test gave similar values of 5.33 cm/min and 5.85 cm/min but the constant head method gave 0.17 cm/min, which is much ion than the other methods. This experimental evidence reveals that the permeability of the unconfined sandy aquifer could be accurately determined by Dupuit assumption or slug tut rather than by constant head method conducted for a disturbed separate soil column.

• Journal of the Korean Geotechnical Society
• /
• v.28 no.2
• /
• pp.71-78
• /
• 2012

Rainfall infiltration test under one dimensional condition is conducted to evaluate the effect of rainfall intensity on seepage velocity and infiltration characteristics for initial unsaturated sediment. Experimental results are compared with those numerical simulations with respect to variations of pore water pressure, degree of saturation and discharge velocity with time, and both results give good agreement. High rainfall intensity tends to increase seepage velocity almost linearly. But it shows rapid increase as rainfall intensity approaches saturated hydraulic conductivity of the sediment. In addition, the upper part of wetting front depth is partially saturated, not fully. Therefore, actual wetting front depth is considered to advance faster than theoretical prediction, which leads to slope instability of unsaturated slope due to surface rainfall.

• Journal of the Korean Society for Railway
• /
• v.11 no.1
• /
• pp.54-60
• /
• 2008

In the trackbed design using elastic multilayer model, the stress-dependent resilient modulus $(E_R)$ is an important input parameter, that is, reflects substructure performance under repeated traffic loading. However, the evaluation method for resilient modulus using repeated loading triaxial test is not fully developed for practical purpose, because of costly equipment and the significantly fluctuated values depending on the testing equipment and laboratory personnel. The this study, the paper will present an indirect method to estimate the resilient modulus using dynamic properties. The resilient modulus of crushed stone, which is the typical material of sub-ballast, was calculated with the measured dynamic properties and the range of stress level of the sub-ballast, and approximated with the power model combined with bulk and deviatoric stresses. The resilient modulus of coarse grained material decreases with increasing deviatoric stress at a confining pressure, and increases with increasing bulk stress. Sandy soil (SM classified from Unified Soil Classification System) of subgrade was also evaluated and best fitted with the power model of deviatoric stress only.

• Korean Journal of Plant Resources
• /
• v.20 no.2
• /
• pp.125-128
• /
• 2007

Plan stability production investigating 1st harvesting degree for maximum leaf quantity enlargement, is as following it summarize result that test for 3 years since 2002 allowing 4 processing such as trunk lower column department harvesting, Foliar and rhizoma growth were tendency that give protective care 1 st harvesting height is short, but there were many the number of tillering crawl, Distribution of rhizome about diameter 5mm low 58%, large rhizome's ratio was high tendency harvesting height is short. Because foliar amount is much harvesting height is short in ground department, 15% rose in soil surface harvesting since 292kg provision per 5cm harvesting 10a, The time of refining the harvest of stems and leaves before drying has reduced when the height of the harvest is low, and the 5cm harvest has decreased 30% compared to the soil surface harvest.

• Journal of the Earthquake Engineering Society of Korea
• /
• v.12 no.1
• /
• pp.43-55
• /
• 2008

The complexity of determining strain associated with shear modulus and damping ratio in torsional tests has been resolved by means of several approaches. Particularly, the modified equivalent radius approach is adequate to when generating the plots of equivalent radius ratio versus strain more effectively over any range of strains in resonant column and torsional shear (RC/TS) tests. The modified equivalent radius approach was applied for hyperbolic, modified hyperbolic, and Ramberg-Osgood models in evaluating damping ratio. Results showed that using a single value of equivalent radius ratio based on conventional equivalent radius approach is not appropriate. A new model was developed to consider the soil damping behavior at small strains as well as hysteretic damping and it was attempted to determine adjustments are required in evaluating strain associated damping when combining the two damping components.

• Journal of the Korean GEO-environmental Society
• /
• v.8 no.3
• /
• pp.19-25
• /
• 2007

Stone columns is the ground improvement method which composed of compacted gravel or crushed stone inserted into the soft ground consisting of loose sand and clay. There are many difficulties in quantitative analysis of soil-pile interaction because settlement behavior of stone columns is affected by various parameters. In this study, various parameters of behavior of end-bearing group piles are investigated by load tests. Finally, the improved characteristics of soft ground and the influence of design parameters are investigated in this study using PR (performance ratio) value. From the PR value calculation and test results, we know that settlement behavior of stone columns is affected by area replacement ratio of composite ground, diameter of column rather than embedment ratio and mat.

• Geotechnical Engineering
• /
• v.9 no.3
• /
• pp.35-48
• /
• 1993

This paper was focused on the design and construction of stone columns as a method of reinforcements in slightly soft clay or loose silty sand overlying the firm strata. It was intended to find out the effects of soil improvement by field tests in Kwangmyoung Haan Site by comparing the test results performed before and after the installation of stone columns . The results of this experimental study are as follows : the hearing capacity was increased by 3.33 times and the SPT N -valued was increased by 3.9 times by installing the stone columns : the stone column method can cut down the construction cost almost 35% compared to the precast concrete pile method in economic viewpoints.

• Journal of the Korean Geotechnical Society
• /
• v.16 no.1
• /
• pp.65-73
• /
• 2000

An elasto-plastic constitutive model was proposed, in which the behavior at small-to-large strain level can be modeled. The proposed model is based on the anisotropic hardening description with the generalization of isotropic hardening rule and the total stress concept. From a mathematical approach it was proved that the model includes the previous successful models. The model was verified by a series of resonant column tests, torsional shear tests and triaxial tests, and the proposed model predicted small-to-large strain behavior more consistently and accurately than the hyperbolic model and the Ramberg-Osgood model for a weathered granitic soil. In addition, the nonlinearity under small strain condition was predicted appropriately for the torsional shear test results.

• Proceedings of the Korean Geotechical Society Conference
• /
• 2005.03a
• /
• pp.308-319
• /
• 2005

Piezo-ceramics are special materials which transform energy between mechanical and electrical forms. Bender-elements are composite materials consisting of thin piezo-ceramics and elastic shims, and are widely used as actuators and transducers in the field of electronics, robotics, autos and mechatronics utilizing the effectiveness of energy transformation capability. In geotechnical engineering, commercial bender-elements are used in laboratory as source and receiver in the measurements of soil stiffness. The elements were built by using various metal shims sandwiched between piezo-ceramics and coating over the composite in the research. A pair of elements were buried in a concrete block and used as source and receiver to measure the stiffness of the concrete. The test results were verified by comparing with the resonant column testing results. In a preliminary stage of the development of an in-situ seismic testing equipment using bender-elements for soft clay materials, shear waves were generated and measured by burying the elements in the barrel of kaolinite and water mixture. The measured shear wave signals were so distinct for the first-arrival pick that applicability of the elements in the field measurements is very promising.

• Journal of Soil and Groundwater Environment
• /
• v.28 no.1
• /
• pp.1-14
• /
• 2023

In this study, column tests using relatively uniform Jumunjin sand media were conducted to evaluate the feasibility of calcium polysulfide (CaS_x, CPS) in removing high concentration of Zn²⁺ in groundwater. The injected CPS solution reacted rapidly with Zn²⁺ in artificial groundwater and effectively reduced Zn²⁺ by more than 99% through metal sulfide precipitation. Since the density (d = 1.27 g/cm³ ) of CPS solution was greater than that of water, CPS solution settled down rapidly while capturing Zn²⁺ and formed stable CPS layer similar to dense nonaqueous phase liquid. Mass balance analysis on Zn²⁺ in CPS solution suggested that CPS solution effectively reacted with Zn²⁺ to form metal sulfide precipitates except for high groundwater seepage velocity of 400 cm/d. With greater groundwater seepage velocity, injected CPS did not completely dissolve at the CPS-water interface, but a partially-misible CPS layer continuously moved and reacted with Zn²⁺+ in the direction of groundwater flow. Since hydraulic conductivity (K_h) decreased slightly due to the generated metal precipitates in the inter-pores of media, injection of CPS solution should be optimized to prevent clogging. As evidenced by both XRF and SEM/EDS results, ZnS precipitates were clearly observed through the reaction between the CPS solution and Zn²⁺. Further study is warranted to evaluate the feasibility of CPS to remove high-concentration heavy metalcontaminated groundwater in complex and heterogeneous media.