• Journal of Soil and Groundwater Environment
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• v.22 no.3
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• pp.27-41
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• 2017

This study dealt with the characteristics and the interrelations of hydrogeological parameters such as hydraulic conductivity, dispersivity and effective porosity of unconsolidated sediments for providing the basic data necessary for the planning of the management and preservation of groundwater quality in the Nakdong River Delta of Busan City, Korea. Groundwater quality in this area has been deteriorated due to seawater intrusion, agricultural fertilizer and pesticide, industrial wastewater, and contaminated river water. The physical properties (grain size distribution, sediment type, sorting) and aquifer parameters (hydraulic conductivity, effective porosity, longitudinal dispersivity) were determined from grain size analysis, laboratory permeability test and column tracer test. Among 36 samples, there were 18 Sand (S), 7 Gravelly Sand (gS), 5 Silty Sand (zS), 5 Muddy Sand (mS), and 1 Sandy Silt (sZ). Hydraulic conductivity was determined through a falling head test, and ranged from $9.2{\times}10^{-5}$ to $2.9{\times}10^{-2}cm/sec$ (0.08 to 25.6 m/day). From breakthrough curves, dispersivity was calculated to be 0.35~3.92 cm. Also, effective porosity and average linear velocity were obtained through the column tracer test, and their values were 0.04~0.46 and 1.06E-04~6.49E-02 cm/sec, respectively. Statistical methods were used to understand the interrelations among aquifer parameters of hydraulic conductivity, effective porosity and dispersivity. The relation between dispersivity and hydraulic conductivity or effective porosity considered the sample length, because dispersivity was affected by experimental scale. The relations between dispersivity and hydraulic conductivity or effective porosity were all in inverse proportion for all long and short samples. The reason was because dispersivity was in inverse proportion to the groundwater velocity in case of steady hydrodynamic dispersion coefficient, and groundwater velocity was in proportion to the hydraulic conductivity or effective porosity. This study also elucidated that longitudinal dispersivity was dependent on the scale of column tracer test, and all hydrogeological parameters were low to high values due to the sand quantity of sediments. It is expected that the hydrogeological parameter data of sediments will be very useful for the planning of groundwater management and preservation in the Nakdong River Delta of Busan City, Korea.

• Economic and Environmental Geology
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• v.45 no.6
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• pp.697-707
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• 2012

The quantitative landslide susceptibility assessment methods can be divided into statistical approaches and geomechanical approaches based on the consideration of the triggering factors and landslide models. The geomechanical approach is considered as one of the most effective approaches since this approach proposes physical slope model and considers geomorphological and geomechanical properties of slope materials. Therefore, the geomechanical approaches has been used widely in landslide susceptibility analysis using the infinite slope model as physical slope model. However, the previous studies assumed constant groundwater level for broad study area without the consideration of rainfall intensity and hydraulic properties of soil materials. Therefore, in this study, landslide susceptibility assessment was implemented using the coupled infinite slope model with hydrologic model. For the analysis, geomechanical and hydrualic properties of slope materials and rainfall intensity were measured from the soil samples which were obtained from field investigation. For the practical application, the proposed approach was applied to Jinbu area, Gangwon-Do which was experienced large amount of landslides in July 2006. In order to compare to the proposed approach, the previous approach was used to analyze the landslide susceptibility using randomly selected groundwater level. Comparison of the results shows that the accuracy of the proposed method was improved with the consideration of the hydrologic model.

• Journal of the Korean Geotechnical Society
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• v.34 no.11
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• pp.21-31
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• 2018

Bucket foundations are widely used in offshore areas due to their various benefits such as easy and fast installations. A bucket is installed using self-weight and the hydraulic pressure difference across the lid generated by pumping out water from inside the bucket. When buckets are installed in high permeable soil such as sands, upward seepage flow occurs around the bucket tip and interior, leading to a decrease in the effective stress in the soil inside the buckets. This process reduces the penetration resistance of buckets. However, the soil inside and outside the bucket can be disturbed due to the upward seepage flow and this can change the soil properties around the bucket. Moreover, upward seepage flow can create significant soil plug heave, thereby hindering the penetration of the bucket to the target depth. Despite of these problems, soil disturbance and soil plug heave created by suction installation are not well understood. This study aims to investigate the behavior of soil during suction installation. To comprehend the phenomena of soil plug heave during installation, a series of small-scale model tests were conducted with different testing conditions. From a series of tests, the effects of tip thickness of bucket, penetration rate, and self-weight were identified. Finally, soil properties inside the bucket after installation were approximated from the measured soil plug heave.

• Proceedings of the Korean Society of Crop Science Conference
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• 2017.06a
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• pp.315-315
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• 2017

In Japan, more than 80 % of soybean growing area is converted fields and excess water is one of the major problems in soybean production. For example, recent study (Yoshifuji et al., 2016) suggested that in the fields of shallow groundwater level (GWL) (< 1m depth), rising GWL even in a short period (e.g. 1 day) causes inhibition of soybean growth. Thus it becomes more and more important to predict GWL and soil moisture in detail. In addition to conventional surface drainage and underdrain, FOEAS (Farm Oriented Enhancing Aquatic System), which is expected to control GWL in fields adequately, has been developed recently. In this study we attempted to predict GWL and soil moisture condition at the converted field with FOEAS in Biwa lake reclamation area, Shiga prefecture, near the center of the main island of Japan. Two dimensional HYDRUS model (Simuinek et al., 1999) based on common Richards' equation, was used for the calculation of soil water movement. The calculation domain was considered to be 10 and 5 meter in horizontal and vertical direction, respectively, with two layers, i.e. 20cm-thick of plowed layer and underlying subsoil layer. The center of main underdrain (10 cm in diameter) was assumed to be 5 meter from the both ends of the domain and 10-60cm depth from the surface in accordance with the field experiment. The hydraulic parameters of the soil was estimated with the digital soil map in "Soil information web viewer" and Agricultural soil-profile physical properties database, Japan (SolphyJ) (Kato and Nishimura, 2016). Hourly rainfall depth and daily potential evapo-transpiration rate data were given as the upper boundary condition (B.C.). For the bottom B.C., constant upward flux, which meant the inflow flux to the field from outside, was given. Seepage face condition was employed for the surrounding of the underdrain. Initial condition was employed as GWL=60cm. Then we compared the simulated and observed results of volumetric water content at depth of 15cm and GWL. While the model described the variation of GWL well, it tended to overestimate the soil moisture through the growing period. Judging from the field condition, and observed data of soil moisture and GWL, consideration of soil structure (e.g. cracks and clods) in determination of soil hydraulic parameters at the plowed layer may improve the simulation results of soil moisture.

• Geomechanics and Engineering
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• v.22 no.2
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• pp.173-185
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• 2020

Calcareous soil is originated from marine biogenic sediments and weathering of carbonate rocks. The formation history for calcareous sediment includes complex physical, biological and chemical processes. It is preferably selected as the major fill materials for hydraulic reclamation and artificial island construction. Calcareous sands possess inter pores and complex shape are liable to be damaged at normal working stress level due to its fragile nature. Thus, the engineering properties of calcareous soil are greatly affected by its high compressibility and crushability. A series of triaxial shear tests were performed on calcareous sands derived from South China Sea under different test conditions. The effects of confining pressure, particle size, grading, compactness, drainage condition, and water content on the total amount of particle breakage for calcareous soil were symmetrically investigated. The test results showed that the crushing extent of calcareous sand with full gradation was smaller than that a single particle group under the same test condition. Large grains are cushioned by surrounding small particles and such micro-structure reduces the probability of breakage for well-graded sands. The increasing tendency of particle crushing for calcareous sand with a rise in confining pressure and compactness is confirmed. It is also evident that a rise in water content enhances the amount of particle breakage for calcareous sand. However, varying tendency of particle breakage with grain size is still controversial and requires further examination.

• Journal of the Korean Institute of Landscape Architecture
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• v.30 no.3
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• pp.86-93
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• 2002

The objectives of this research were to investigate the effect of serpentine as a new soil conditioner for growth of turfgrass. To achieve the goal, pure sand or mixtures of sand and serpentine with various ratios were tested for soil physical properties and the growth effects of perennial ryegrass and zoysiagrass growth were compared. Major results of this research are summarized as follows; 1) Hydraulic conductivity of 10~30% serpentine mixtures were observed within the range of 1010~901mm/h which is good for USGA recommendation. Experimental results of pH and EC for various mixtures indicated that the 10% serpentine mixture was the most suitable for turfgrass growth. 2) Perennial ryegass treated with 10% serpentine mixture showed the highest visual quality(p<0.01) among all treatments. And serpentine treatment was more effective to improve visual quality of perennial ryegrass than that of zoysiagrass. The treatment of 10% serpentine had better visual qualities than that of 20% in both of zoysiagrass and perennial ryegrass. Treatment with the right amount of serpentine extends green period for one to two weeks during early winter in both zoysiagrass and perennial ryegrass. 3) In perennial ryegrass, the treatment of 10% serpentine resulted in an increase of total dry weight compare with those of zeolite or barley stone, and also dramatically promoted the dry weight by 15% compared with sand 100%(control). Total dry weight of zoysiagrass treated with 10% serpentine was 9％ higher than that of san. These results indicated that serpentine can be a good soil conditioner for both zoysiagrass and perennial ryegrass when it is blended with sand within a range of 10 to 20% by volume.

• Korean Journal of Soil Science and Fertilizer
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• v.35 no.6
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• pp.335-343
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• 2002

Methods of bedsoil analysis were difficult to be applied universally because use and material of bedsoil are diverse from country to country. Korean Standard Methods for Bedsoil Analysis was developed to measure the water content, water retention, and saturated hydraulic conductivity. Fifty-three samples for horticultural bedsoil and nine samples for paddy rice bedsoil in the current market were collected. Water content of bedsoil was determined using gravimetric method through $105^{\circ}C$ oven-dry for 16 hours, but different calculations between horticultural and paddy rice bedsoils were chosen according to different predominant component, plant residue or mineral. Water content percentage of horticultural bedsoil was calculated as [(weight of sample before oven-dry - weight of sample after oven-dry)/(weight of sample before oven-dry)]${\times}100$, while that of paddy rice bedsoil as [(weight of sample before oven-dry - weight of sample after oven-dry)/(weight of sample after oven-dry)]${\times}100$. Water retention was measured at water potential -0.5, -1, -3, -5, -7, -10 kPa by Sandbox method and saturated hydraulic conductivity was measured by constant head method using acryl cylinder (${\Phi}5cm{\times}L\;20cm$). By new 'Korean Standard Methods of Bedsoil Analysis', the average water content of horticultural bedsoil was obtained 46.34%(w/w) and that of paddy rice bedsoil 16.89%. For horticultural bedsoil, easily available water(EAW), water buffering capacity(WBC), and optimal matric potential(OMP) was estimated at 28.4%, 7.01%, and -5.60 kPa, respectively. Optimal moisture content was 44.41% and average saturated hydraulic conductivity for bedsoils was estimated at $28.4cm\;min^{-1}$.

• Journal of Korean Society of Environmental Engineers
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• v.28 no.3
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• pp.265-269
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• 2006

This study was to investigate the effect of acidic leachate on the landfill liner system and healing of cracks by using industrial by-products; BFS(Blast Furnace Slag) and FA(Fly Ash). From the results of pH measurement, for OPC(Ordinary Portland Cement) and DM(Dredged Mud) mixtures immersed acidic leachate, the initial pH($4.5{\sim}5.5$) was heavily increased to approximately 10 after 60 days experiment due to the production of 2 mole $OH^-$ which was occurred by hydrolysis of CaO and MgO etc.. Meanwhile, the initial pH of acidic leachate immersed DM mixtures with BFS and FA respectively was lasted for longer period as compared to the comparison. The reason was that production of low Ca C-S-H hydrates which stabilized in acidic liquid. The physical properties(compressive strength, hydraulic conductivity) of DM mixtures added BFS and FA was improved. It was concluded that the dissolution of hydrates was disturbed by high alkalinity of BFS and FA.

• Proceedings of the Korean Society of Agricultural Engineers Conference
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• 1999.10c
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• pp.294-300
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• 1999

After researching the physical properties of the concrete included Rice Husk Ash(RHA concrete) and workability of fresh concrete admixed RHA, we have tested durability of RHA-concrete against freeaing and thawing in the winter using rapid freezing and thawing test method(KS F 2456) . There aretwo hypotheses to explain the failure mechanism of a freezing and thawing action. First, the hydraulic pressure in the pores of freezing concrete make an internal stress of concrete structures outbreaking micro crack in the face of concrete, Second, Frost action causing damage to cement paste repeatedly come from soil frost action, freezing water in the capillaries. Initial Relative Dynamic Modulus of Elasticity (DME) was biggest in cae of unit binder weight 600kgf/㎥ and relative dynamic modulus of elasticity increased until 300cycles. In general , initial relative DME was proportional to unit binder weight . Relative DME was decreased in proportion to unit binder weight in the case of 300, 400, 500kgf/㎥ , but relative DME fo the others remained more than 90% until 300 cycles. It was not good effect of intermixed RHA to concrete in case of below unit binder weight 300kgf/㎥ and the resistance of freezing and thawing was not good either.

• Geotechnical Engineering
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• v.8 no.3
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• pp.51-60
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• 1992

This paper represents the physical and engineering characteristics of admixed liners obtained from several laboratory tests. Fly ash and weathered granitic soil are selected as primary materials, and bentonite and cement are used as additives. The results show that the maximum dry density reaches peak values at 5% and 25% of bentonite for Seochon and Samchonpo fly ash respectively, and for the weathered granitic soil, the maximum dry density increases continuously as the amount of bentonite increases. The strength of the admixed materials is not sensitive to the bentonite content, although it increases when the additives is cement. The required amount of bentonite to reach the hydraulic conductivity less than 10-7cm/sec are 18, 30, 10% of the sample weights for Seochon and Samchonpo fly ashes and the weathered granitic soil. The amount of additives show significant differences and depend on the grain size and their distributions and the amount of fine content in the primary materials