• Journal of Korean Tunnelling and Underground Space Association
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• v.12 no.2
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• pp.129-144
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• 2010

The earth pressure acting on the vertical shaft is less than that acting on the retaining wall due to three dimensional arching effect. Thus, it might be essential to estimate the earth pressure actually acting on the shaft when designing the vertical shaft. In this paper, large-sized model tests were conducted as Part II of companion papers to verify the newly suggested earth pressure equation proposed by Kim et al. (2009: Part I of companion papers) that can be used when designing the vertical shaft in cohesionless soils as well as in c-$\phi$ soils and multi-layered soils. The newly developed model test apparatus was designed to be able to simulate staged shaft excavation. Model tests were performed by varying the radius of vertical shaft in dry soil. Moreover, tests on c-$\phi$ soils and on multi-layered soils were also performed; in order to induce apparent cohesion to the cohesionless soil, we add some water to the dry soil to make the soil partially-saturated before depositing by raining method. Experimental results showed a load transfer from excavated ground to non-excavated zone below dredging level due to arching effect when simulating staged excavation. It was also found that measured earth pressure was far smaller than estimated if excavation is done at once; the final earth pressure measured after performing staged excavation was larger and matched with that estimated from the newly proposed equation. Measured results in c-$\phi$ soils and in multi-layered soils showed reduction in earth pressures due to apparent cohesion effect and showed good matches with analytical results.

• Geomechanics and Engineering
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• v.22 no.3
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• pp.227-236
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• 2020

Expansive soils are renowned for their swelling-shrinkage property and these volumetric changes resultantly cause huge damage to civil infrastructures. Likewise, subgrades consisting of expansive soils instigate serviceability failures in pavements across various regions of Pakistan and worldwide. This study presents the use of polypropylene fibers to improve the engineering properties of a local swelling soil. The moisture-density relationship, unconfined compressive strength (UCS) and elastic modulus (E₅₀), California bearing ratio (CBR) and one-dimensional consolidation behavior of the soil treated with 0, 0.2, 0.4, 0.6 and 0.8% fibers have been investigated in this study. It is found that the maximum dry density of reinforced soil slightly decreased by 2.8% due to replacement of heavier soil particles by light-weight fibers and the optimum moisture content remained almost unaffected due to non-absorbent nature of the fibers. A significant improvement has been observed in UCS (an increase of 279%), E₅₀ (an increase of 113.6%) and CBR value (an increase of 94.4% under unsoaked and an increase of 55.6% under soaked conditions) of the soil reinforced with 0.4% fibers, thereby providing a better quality subgrade for the construction of pavements on such soils. Free swell and swell pressure of the soil also significantly reduced (94.4% and 87.9%, respectively) with the addition of 0.8% fibers and eventually converting the medium swelling soil to a low swelling class. Similarly, the compression and rebound indices also reduced by 69.9% and 88%, respectively with fiber inclusion of 0.8%. From the experimental evaluations, it emerges that polypropylene fiber has great potential as a low cost and sustainable stabilizing material for widespread swelling soils.

• Journal of the Korean Geotechnical Society
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• v.34 no.6
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• pp.61-73
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• 2018

When the shear deformation occurs on the slope reinforced with soil nail, a passive earth pressure is induced on the ground around the soil nail and the increase of shear deformation causes the earth pressure variation of the ground and the deformation and member force change of the soil nail. In this study, the shear behavior of the soil nail was analyzed experimentally by inducing the shear deformation in the vertical direction of the soil nail using a large-scale direct shear test equipment and it was verified through numerical analysis. The shear test was performed on the bonded length (6D, 8D, 10D and 12D) of the soil nail separated from the shear surface. As a result, it was observed that the continuous increase of the shear deformation caused the damage of the grout and the effect according to the bonded length was analyzed. Through the model test and the numerical analysis, it was confirmed that the transfer length of the soil nail was 0.2~0.22m, which is larger than 0.1m suggested in the previous study, and the shear zone was in the range of 0.6m from the shear surface.

• The Korean Journal of Soil Zoology
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• v.2 no.2
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• pp.83-91
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• 1997

One year study with litter bags(mesh size - 0.4mm, 0.8mm, 1.7mm and 5.0mm) was carried out to investigate the soil invertebrate community in the process of leaf decomposition in Namsan and Kwangreung deciduous forests, which were considered to be under different degrees of environmental selective pressure. Soil animals collected from litter bags were classified into the class of order or higher taxa. Acari and Collembola were major groups: Acari and Collembola were about 60% and 30% of total soil animals in their numbers, respectively. Among minor groups, Dipteria, Araneae, Diplopoda, Coleoptera and Chilopoda were comparatively dominant. In Namsan forest which was considered to be under higher environmental selective pressure than Kwangreung, the densities of Acari and Collembola were somewhat higher than in Kwangreung, although there was no statistically significant difference between two sites. The densities of Chilopoda, Enchytraeidae and Nematoda were much higher in Namsan than in Kwangreung but Diplopoda and Symphyla were much more in Kwangreung. It was expected that those groups could be used as bioindicators. The densities of Acari and Collembola were very low until March and then showed the peak in May. But they decreased slowly until November. There was no significant difference among the mesh sized of litter bags in the densities of Acari and Collembola but other groups of soil invertebrates seemed to be prevented from immigrating into the litter bag of mesh size 0.4mm. Decomposition rate of litter in the litter bag was low in early stage of decomposition. The % residual mass over initial mass at 8 months after litter bag introduction in the field was over 80%. Thereafter, % residual mass decreased more fast and was about 60% at 1 year after bag introduction. There was little evidence for the effects of soil invertebrates upon the litter decomposition in the period of this study. And there was no significant difference between Namsan and Kwangreung or among mesh sizes of litter bags in the decomposition rate.

• Journal of the Korean Geosynthetics Society
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• v.19 no.4
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• pp.65-74
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• 2020

In earth pressure balance (EPB) shield TBM tunnelling, the application of soil conditioning which improves properties of the excavated muck by additives injection, is generally used for enhancing the performance of TBM. Therefore it is important to apply the soil conditioning in the numerical model which simulates excavation performance of TBM equipment, but related studies on a method that simulates soil conditioning are insufficient to date. Accordingly, in this study, an laboratory pressurized vane test apparatus was devised to evaluate the characteristics of conditioned soil. Using the apparatus, the vane shear tests were performed on foam-conditioned soil with different shear rates, and the test was numerically simulated with discrete element method (DEM). Finally, the contact properties of particles in DEM were determined by comparing the results of test and analysis, and it indicates that the applicability of pressurized vane test and DEM model for reproducing soil conditioning in TBM excavation model with DEM.

• Proceedings of the Korean Geotechical Society Conference
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• 2005.03a
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• pp.1047-1054
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• 2005

The purpose of this study is the understanding to changes in the characteristic of soil structure and classification, atterberg limits, undrained shear strength and consolidation of clayey soil dependent on pH of soil pore water. A series of tests including consistency tests, uniaxial compressive tests, vane tests and oedometer tests are performed on. The test results indicated that pH changes in the soil pH resulted in changes in the soil structure and classification, stress-strain behavior. Specially, when pH is conditioned to 7, liquid limit, undrained shear strength and preconsolidation pressure are the largest.

• Proceedings of the Korean Geotechical Society Conference
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• 2008.10a
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• pp.1614-1622
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• 2008

A series of three-dimensional numerical modelling have been conducted to clarify the behaviour of multi-pressurised soil nails with high strength steel pipes. In this study, the soil non-linearity, the soil-nail interaction and staged construction are considered. It has been found that pressurised soil nails can reduce lateral ground movement by 14-21% compared to general soil nails with very low pressure. In addition, ground settlement was reduced when using multi-pressurised soil nails. The pressurised soil nail may result in an increase in the surcharge loading on the ground surface.

• Korean Journal of Soil Science and Fertilizer
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• v.41 no.4
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• pp.273-278
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• 2008

This study was carried out in order to test unsaturated hydraulic conductivity estimation of van Genuchten's and Campbell's models using one-step outflow method through Tempe pressure cell. The undisturbed soil cores (columns) were taken from Ap1, B1 and C horizons of Songjeong series (the fine loamy, mesic family of Typic Hapludults). After the saturated hydraulic conductivity Ks of the cores was determined by constant head method, water outflow rate and retentivity of cores were measured in Tempe pressure cell. Fitted curves by models accorded to measured data except for both end of pressure range. In near-saturated condition, measured water retention characteristics showed a relatively better fitness with Campbell's model than van Genuchten's. The soil unsaturated conductivity estimated by Campbell's model was higher than by van Genuchten's. In Ap1 and B1 horizon, the soil unsaturated conductivities obtained by one-step outflow method went between van Genuchten's and Campbell's hydraulic functions, slightly closer to van Genuchten's. In C horizon, van Genuchten's model had better fitness with the one-step outflow data. Consequently, van Genuchten's model generally had better fitness with measured hydraulic conductivity than Campbell's model at the soil water potential range of -10~-75 kPa, especially in C1 horizon. In near-saturated condition, Campbell's model could be thought as relatively accurate hydraulic model, because of the better fitness of Campbell's model with soil water retention data than van Genuchten's model.

• Journal of Soil and Groundwater Environment
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• v.18 no.4
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• pp.1-7
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• 2013

Subcritical water which acts as organic solvent with increasing temperature and pressure because dielectric constant and viscosity decrease can be used to remediate PAHs-contaminated soil. Factors influencing on extraction were studied with varying the water temperature $200{\sim}275^{\circ}C$, extraction time 0~90 min, flow rate 10~100 mL/min and pressure 3.9~10MPa. 300 g of soil sample which was contaminated with PAHs(naphthalene, phenanthrene, fluoranthene and pyrene; 423, 420, 539 and 428 mg/kg of initial concentration) was packed into the cell and placed to reactor and then the subcritical water was pumped through the cell for PAHs extraction. Naphthalene was removed almost 100% at relatively low temperature ($200^{\circ}C$). The removal rate of phenanthrene, fluoranthene, and pyrene increased by 8, 26, and 23% when the temperature increased from 200 to $275^{\circ}C$; and it was gradually increased as extraction time increased from 0 to 90 min. Decreasing removal rate when water flow rate increased from 10 to 30 mL/min, but there was no significant change after 30 mL/min. This is supposed due to channeling phenomenon. The pressure was not an effective factor for extraction of PAHs in this study. Based on the results, the importance of effective factor was in following sequence: temperature >> time > flow rate.

• Proceedings of the Korean Geotechical Society Conference
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• 2009.03a
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• pp.419-433
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• 2009

Pressure grouting is a common technique in geotechnical engineering to increase the stiffness and strength of the ground mass and to fill boreholes or void space in a tunnel lining and so on. Recently, the pressure grouting has been applied to a soil-nailing system which is widely used to improve slope stability. The soil-nailing design has been empirically performed in most geotechnical applications because the interaction between pressurized grouting paste and the adjacent ground mass is complicated and difficult to analyze. The purpose of this study is to analyze the increase of pullout resistance induced by pressurized grouting with the aid of performing laboratory model tests and field tests. In this paper, two main causes of pullout resistance increases induced by pressurized grouting were verified: the increase of residual stress; and the increase of coefficient of pullout friction. From the laboratory tests, it was found that residual stress in borehole increases by pressurized grouting and dilatancy angle could be estimated by cavity expansion theory using the measured wall displacements. From the field test results, the pullout resistance of soil-nailing with pressurized grouting was found to be 10% larger than that of soil-nailing with gravitational grouting, mainly caused by mean normal stress increase and dilatancy effect. So, the pullout resistance could be estimated by considering these two effects. The radial displacement increases with dilatancy angle increase and the dilatancy angle decreases with injection pressure increase. The measured pullout resistance obtained from field tests is in good agreement with the estimated one from the cavity expansion theory.