• Journal of Korean Tunnelling and Underground Space Association
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• v.9 no.1
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• pp.49-62
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• 2007

A new earth pressure equation acting on the vertical shafts in cohesionless soils has been proposed by modifying the equations proposed by others. In order to verify the modified equation, model tests which can control uniform wall displacement with depth to radial direction were conducted. Model tests were performed with three different wall friction angles and two different relative densities. The measured values were larger than estimated values when assuming $\lambda=1$ ; smaller than those when assuming $\lambda=1-sin\phi$. The parameter, $\lambda$ is the ratio of tangential stress to vertical stress and is the most critical value in proposed equation. A method which can estimate the earth pressure on vertical shafts in layered soils is also proposed by reasonably assuming the failure surface of layered soils and using the modified equation. In order to verify the proposed method, in-situ measurement data have been collected from the three in-situ vertical shafts installed in layered soils. Most of earth pressures converted from measured data match reasonably well with estimated values using proposed method.

• Journal of the Korean Geotechnical Society
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• v.28 no.2
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• pp.23-31
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• 2012

The purpose of this study is to analyze earth pressure acting on a circular shaft-tunnel considering arching effect by centrifuge modeling test on sands. The centrifuge testing method provides a way to model an in-situ stress state condition with a stress gradient within a laboratory specimen. A small-scale model of circular shaft-tunnel, which has a real diameter of 6.0 m and height of 15.0 m, was designed and tested twice under 75g-level. Additionally, an effect of excavation was presented by separating two segments of circular shaft wall to find behavioral properties and strength of earth pressure along with excavating ground. The test results were compared with those of the proposed earth pressure equation. The test results showed that earth pressure decreased by about 70% in comparison with existing two-dimensional earth pressure. This fact might be attributed to three-dimensional arching effects.

• 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.

• Journal of Korean Tunnelling and Underground Space Association
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• v.11 no.2
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• pp.117-129
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• 2009

Several researches have been done to estimate the earth pressure on a vertical circular shaft considering three dimensional arching effect and verified them by conducting model tests. However, any equation suggested so far is not applicable in case of multi-layered soils and/or C-${\phi}$ soils. In this study, new equation for estimating the earth pressure acting on the vertical shaft in c-${\phi}$ soils is proposed. A parametric study is performed to investigate the significance of the cohesion when estimating the coefficient of earth pressure in C-${\phi}$ soils and estimating earth pressures in vertical shafts. A method which can estimate the earth pressure on vertical shafts in layered soils is also proposed by assuming a failure surface in layered soils and using the modified equation. This paper is Part I of companion papers focusing on the theoretical aspect of model developments; the experimental verification will be made in Part II.

• Journal of the Korean GEO-environmental Society
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• v.9 no.4
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• pp.63-76
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• 2008

This research was carried in order to improve design technique for the vertical shaft of which design guide has not been proposed clearly. The deformation tendency of vertical shaft and distribution of the earth pressure around shaft were reviewed with both of theoretical earth pressure distribution suggested in design criteria and measured data which had been gained from 2 constructing shaft. The distribution of earth pressure applied on the vertical shaft was similar with the result of previous theory for the earth pressure proposed by Shin (2007). Moreover it was observed that asymmetric deformation and earth pressure around vertical shaft were caused by inhomogeneity and anisotropy of the ground. The asymmetric earth pressure ratio ($R_p$) in soil and weathered rock were divergent according to the shape ratio. In addition, it is more reasonable that the value of asymmetric earth pressure ratio ($R_p$) is considered less than 0.35 in the case of constructing shaft under rock.

• Journal of Korean Tunnelling and Underground Space Association
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• v.13 no.6
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• pp.431-450
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• 2011

When a circular vertical shaft is constructed below the groundwater level, additional forces caused by groundwater flow besides horizontal effective stresses will act on the wall. The inward direction of the groundwater flow will be inclined to the vertical wall and its direction will change depending on the wall depth. In this paper, to figure out the effect of seepage forces acting on the circular vertical shaft, the slope of the inclined flow varying with the depth is divided into vertical and horizontal components to derive the coefficient of earth pressure considering the seepage pressure and to obtain the vertical stress by taking the seepage pressure into account. The control volume in this study is assumed to be the same with that of the dry ground condition within which the earth pressure is acting on the wall by the creation of the plastic zone during shaft excavation. An example study shows that the vertical stress increases by about 1.4 times and the horizontal earth pressure increases up to 2.5 times compared to the dry ground condition. The estimated values from the proposed equation considering seepage forces and the calculated values from numerical analysis with "effective stress plus seepage force" show similar values, which verifies appropriateness of the proposed equation to estimate the earth pressure under the seepage condition.

• Journal of the Korean GEO-environmental Society
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• v.7 no.4
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• pp.15-24
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• 2006

It is well known that earth pressure on the cylindrical open caisson and cylindrical retaining wall of a shaft is less than that at-rest and in plane strain condition because of the horizontal and vertical arching effects due to wall displacement and stress relief. In order to examine the earth pressure distribution of a cylindrical wall, model tests were performed in dry sand for the care of constant wall displacement with depth. Model test apparatus which can control wall displacement, wall friction, and wall shape ratio was developed. The effects of various factors that influence earth pressure acting on the cylindrical retaining wall of a shaft were investigated.

• Journal of the Korean Geotechnical Society
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• v.15 no.4
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• pp.261-277
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• 1999

The horizontal and vertical earth pressures in backfill space which is narrowly excavated like ditch are affected by the share of ditch backfill space and the wall friction between excavated surface and backfill soil. In this paper, for the excavated surface the Handy's equation of a symmetric vertical case and the Kellogg's equation of a symmetric sloped one are modified to show the minor principal stress arch for the unsymmetrical excavated backfill space. Compared with the soil test box result, a similarity in magnitude and distribution of backfill earth pressure shows that the earth pressure has been observed. The backfill earth pressure in unsymmetrically sloped space has been shown twice as much as the one in vertically excavated space and also remarkable decline of arching for the former case. It is verified that the earth pressure equation should account the shape and size of backfill space to calculate the earth pressure for similar structure to the one handled in this study.

• Journal of Korean Tunnelling and Underground Space Association
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• v.9 no.2
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• pp.143-155
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• 2007

The earth pressure acting on a circular shaft wall is smaller than that acting on the wall in plane strain condition due to the three dimensional axi-symmetric arching effect. Accurate estimation of the earth pressure is required for the design of the shaft wall. In this study, the stress model considering the decrease of earth pressure due to the horizontal and vertical arching effect and the influence of shape ratio (shaft height/radius) is proposed. In addition, model test on the sandy soil is conducted and a comparison is made between the stress model and the test results. The comparison shows that the proposed stress model is in agreement with test results; decrease of shape ratio (increase of radius) leads to stress state equal to the plane strain condition and approximate stress distribution is found between stress model and model test results.

• Journal of the Korean Geotechnical Society
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• v.38 no.1
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• pp.35-45
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• 2022

When constructing a cylindrical vertical shaft through the open-cut method, the walls are generally designed to be temporary flexible walls that allow a certain level of displacement. The earth pressure applied to the flexible walls acts as an external force and its accurate estimation is essential for reasonable and economical structure design. The earth pressure applied to the flexible wall is closely interrelated to the plastic deformation of the surrounding ground. This study simulated a stepwise excavation for constructing a cylindrical vertical shaft through a centrifugal model test and evaluated the continuous deformation behaviors of the surrounding ground through digital image analysis.