• Journal of the Korean Geotechnical Society
• /
• v.32 no.11
• /
• pp.83-96
• /
• 2016

The surface settlement of the back ground of a braced wall due to the ground excavation has the great influence on the safety of the surrounding area. But it is not easy to predict the settlement of the surrounding area due to proud excavation. Estimation of the settlement of the surface ground induced by the deformation of the braced wall is performed by FEM and empirical method (Peck, Clough etc). In this research, surface settlement of the back ground braced wall depending on the joint dips in rocks during excavating the composit ground was measured at the large scale model test (standard: $0.3m{\times}0.3m{\times}0.5m$). The scale of model test was 1/14.5 and the ground was excavated in ten steps. Earth pressure on the braced wall and ground surface settlement on the back ground of a braced wall were investigated. The surface settlement during the excavation depended on the joint dips in rocks on of the ratio of rock layer. Maximum earth pressure and maximum surface settlement were masured at the same excavation step. In accordance with the increase of the rock layer dips and rock layer ratio, the ground surface settlement increased. The maximum ground surface settlement was 17 times larger at 60 degree joint dips in rocks than that of the horizontal ground conditions. And the position of the maximum surface settlement by empirical method was calculated at the point, which was 17%~33% of excavation depth. In accordance with the increase of the rock layer dips and rock layer ratio, the ground maximum surface settlement increased. The ground surface settlement of composite ground is smaller than that of the empirical.

• Journal of Korean Tunnelling and Underground Space Association
• /
• v.15 no.5
• /
• pp.455-468
• /
• 2013

In recent, various types of steel pipe-roof methods, which is reinforced by mortar after propulsion of steel pipe into the ground, have been used for the construction of trenchless underpass. Integrated steel pipe-roof has flexural stiffness and can resist against overburden load and reduce the stress acting on the concrete underpass structures. Due to arching effect, vertical and horizontal stress distribution around the steel pipe-roof is changing. In this study, therefore, the characteristic of stress distribution around the underpass induced by the construction of integrated steel pipe-roof is investigated by using numerical method. To examine the soil-structure interaction, interface element is introduced. Results show that vertical stress acting on the concrete structure placing inside the steel pipe-roof is significantly reduced due to arching effect and flexural stiffness of integrated steel pipe-roof. Design load can be reduced and effective design of underpass will be available if the earth pressure reduction due to arching effect is considered in the design stage.

• Journal of the Korean GEO-environmental Society
• /
• v.13 no.8
• /
• pp.85-94
• /
• 2012

Evaluation of the smear effect caused by mandrel penetration into soft ground for a vertical drain installation is very important to predict the consolidation time of soft ground improvement. 30 kinds of laboratory model tests considering in situ conditions were conducted to investigate the formation of a smear zone and the decrease of coefficient of permeability in the disturbed zone. Three types(C(clay):M(silt)=1:1, 0.5:0.5, and 0:1) of reconstituted samples were used for 3 dimensional smear zone test. An experimental study was performed focusing on length of mandrel penetration, mandrel shape and size, earth pressure, and ground condition(unit weight and grain size distributions). Laboratory test results show that the length of mandrel penetration is the most critical factor for the formation of smear zone. As a result, the ratio between diameter of the smear zone($d_s$) and that of mandrel($d_m$) at field using long mandrel becomes larger than conventional $d_s/d_m$. The ratio between $d_s$ and $d_m$ ranges from 1.89 and 2.48 with the sample at C:M=1:0. It was also found that the $d_s/d_m$ value with the round shape of the mandrel is smaller than that of diamond one. The value of $d_s/d_m$ decreased with larger mandrel size, lower unit weight, and higher earth pressure. However, higher silt content led to increase of $d_s/d_m$. The ratio between coefficient of horizontal permeability in the smear zone($k_{hs}$) and that of undisturbed zone($k_{ho}$) ranged from 0.70 to 0.85. The test results imply that factors and values affecting $k_{hs}/k_{ho}$ show similar tendency with $d_s/d_m$.

• Tunnel and Underground Space
• /
• v.20 no.5
• /
• pp.352-359
• /
• 2010

Stability of twin tunnels depends on the pillar width and the ground condition. In this study, large scale model tests were conducted for investigating the influence of the pillar width of twin tunnels on their behavior in the regular horizontal jointed rock mass. Jointed rocks was composed of concrete blocks. Pillar width of twin tunnels varied in 0.29D, 0.59D, 0.88D and 1.18D, where D is the tunnel width. During the test, pillar stress, lining stress, tunnel distortion, and ground displacement were measured. Lateral earth pressure coefficient was kept in a constant value 1.0. As a result, it was found that the pillar stress and the displacement of the ground and tunnel were increased by decreasing pillar width. The maximum displacement rate was measured just after the upper excavation in each construction sequence. And the maximum influence position was the right shoulder of the preceeding tunnel at the pillar side. It was also found that for the stability assessment the inner displacement was more critical than the crown displacement. The influence zone was formed at the pillar width 0.59D~0.88D that was smaller than 0.8D~2.0D, which was proposed by experience for a good ground condition. And it would be concluded that horizontal joints could also influence on the stability of the twin tunnels.

• Journal of the Korean Geotechnical Society
• /
• v.26 no.7
• /
• pp.7-16
• /
• 2010

Stress history increases the residual horizontal stress of granular soil and, consequently, the penetration resistance. This study analyzes the effect of stress history on the cone resistance ($q_c$), horizontal stress index ($K_D$) and dilatometer modulus ($E_D$) of CPT and DMT from calibration chamber specimen in OC as well as NC state. Test results show that the normalized cone resistance by mean effective stress correlates well with the relative density and the state parameter, whereas the normalized cone resistance by vertical effective stress is a little affected by stress history. The influence of stress history is more reflected on $K_D$ than $E_D$ and $q_c$. The $K_D/K_0$, in which the effect of stress history on $K_D$ is compensated by the at-rest coefficient of earth pressure, $K_0$, is related to relative density, state parameter and the normalized cone resistance by mean effective stress. It is also observed that the normalized dilatometer modulus by mean effective stress ($E_D/{\sigma}_m'$) shows a unique correlation with the state parameter, regardless of stress history.

• The Journal of the Convergence on Culture Technology
• /
• v.5 no.3
• /
• pp.345-349
• /
• 2019

In Korea, the mountainous area occupies more than 70% of the whole country, cutting of earth slope that cuts a part of the ground surface is widely used when building infrastructures such as road, railroad, and industrial complex construction. In recent years, regulations on environmental damage have become more strict, and various methods have been developed and applied. Among them, Concrete-Panel Retaining Wall technique is actively applied. Concrete-Panel Retaining Wall is a method to resist horizontal earth pressure by forming a wall by attaching a precast retaining wall to the front of the support material and increasing the shear strength of the disk through reinforcement of the support material. Soil nailing, earth bolt, and ground anchor are used as support material. Among them, ground anchor is a more aggressive reinforcement type that introduces tensile load in advance to the steel wire, and a large concentrated load acts on the front panel. This concentrated load is a factor that creates cracks in the concrete panel and reduces the durability of the retaining wall itself. In this study, steel pipe sleeves and reinforcements were purchased at the anchorage of the panel to prevent cracks, and by applying bumpy shear keys to the end of the panel, the weakness of the individual behavior of the existing grout anchors was improved. The problem of degraded landscape by exposure to front concrete of retaining wall and protrusion of anchorage was solved by the production of natural stone patterns and the construction of sections that do not protrude the anchorage. In order to verify the effectiveness of anti-crack sleeves and reinforcements used in the null, indoor testing and three-dimensional numerical analysis have been performed, and the use of steel pipe sleeves and reinforcements has demonstrated the overall strength increase and crack suppression effect of panels.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.19 no.5
• /
• pp.263-274
• /
• 2018

In this study, the applicability and external/internal stability of a MSEW abutment with a slab were investigated. Structural analysis of slab bridges between 10 ~ 20.0 m and thicknesses of 0.7 ~ 0.9 m was carried out to calculate the reaction forces due to dead and live loads acting on the bridge supports. The slab bridge with a length of 20.0 m satisfied the allowable contact pressure of 200 kPa for the true MSEW abutment. Because the external stability of the true MSEW abutment was dominated by the geometry of the MSE wall, the change in the factor of safety due to the load of the super-structure is small. Because the stiffness of the foundations is fixed and the load of the super-structure is increased, the factor of safety of the bearing capacity was reduced. As the load of the super-structure was increased, the horizontal earth pressure of the true MSEW abutment increased greatly. As a result, the pullout and fracture of the uppermost reinforcement, which are the factors of safety, did not meet the design criteria. Therefore, it is necessary to increase the pullout resistance and the long-term allowable tensile force of the reinforcement placed on the top of the reinforced soils to ensure efficient design and performance of a true MSEW abutment.

• Geotechnical Engineering
• /
• v.12 no.6
• /
• pp.185-198
• /
• 1996

EPS is increasingly used as a filling material in soft ground. The beneficial effects of the use of EPS derive from minimizing the stress increment, which, in turn, increases the bearing capacity and reduces the settlement. EPS can also be used as a backfill material for retaining walls and abutments to reduce the horizontal earth pressure. However, there is no rational application for the selection of the EPS fill which is essential to the selection of the filling configuration and the settlement calculation. In this paper, therefore, the nonlinear numerical model developed from the results of triaxial compression tests is applied to the construction of EPS and verified through the comparison between the prediction and in-situ measurements.

• Proceedings of the Korean Geotechical Society Conference
• /
• 2003.06a
• /
• pp.65-81
• /
• 2003

During the last few decades in Korea, the development of hillside or mountain areas has rapidly increased for infrastructure construction such as railroads, highways and housing. Many landslides have occurred during these constructions. Also, the amount and scale of damage caused by landslides have increased every year. In the case of Far East Asia including Korea, the damage of landslides is consequently reported during the wet season. In this paper, the effect of stabilizing piles on slope stability is checked and the behavior of slope soil and piles are observed throughout the year by field measurements in the large-scale cut slopes. In particular a large-scale cut slope situated on the construction site for the express highway in Donghae, Korea. First of all, The behavior of the slope soil was measured by inclinometers during slope modification. Landslides occurred in this area due to the soil cutting for slope modification. The horizontal deformations of slope soil gradually increased and rapidly decreased at depth of sliding surface indicating that the depth of sliding surface below the ground surface can be predicted. On the basis of being able to predict the depth of the sliding surface, stabilizing piles were designed and constructed in this slope. To ensure the stability of the reinforced slope using stabilizing piles, an instrumentation system was installed. The maximum deflection of piles is measured at the pile head and it is noted that the piles deform like deflection on a cantilever beam. The maximum bending stress of piles is measured at the soil layer. The pile above the soil layer is subjected to lateral earth pressure due to driving force of the slope, while pile below soil layer is subjected to subgrade reaction against pile deflection. As a result of research, the effect and applicability of stabilizing piles in large-scale cut slopes could be confirmed sufficiently.

• Journal of the Korean Geotechnical Society
• /
• v.32 no.8
• /
• pp.47-59
• /
• 2016

Rocking behavior of shallow foundation reduces the superstructure load during earthquake. However, because of deficiency of understanding of rocking mechanism and soil permanent deformation, it has not been applied to real construction. In this study, slow cyclic tests were conducted for embedded shallow foundations with various slenderness ratio via centrifuge tests. From the variation of earth pressure 'soil rounding surface' phenomenon which makes maximum overturning moment equal to ultimate moment capacity was observed. Rocking and sliding behavior mechanism was evaluated. Also, nonlinear behavior and energy dissipation increase as rotation angle increases. And ultimate moment capacity of embedded foundation is larger than that of surface foundation. Finally, adequate ultimate moment capacity can be suggested for seismic design through this study.