• Journal of the Korean Geotechnical Society
• /
• v.25 no.4
• /
• pp.19-29
• /
• 2009

In this study, a numerical analysis was performed to predict the sequential behavior of anchored retaining wall where the failure accident took place, and verified accuracy of prediction through the comparisons between prediction and field measurement. The emphasis was given to the wall behaviors and the variation of sliding surface based on the two different methods of elasto-plastic and finite element (shear strength reduction technique). Through the comparison study, it is shown that the bending moment and the soil pressure at construction stages produce quite similar results in both the elasto-plastic and finite element method. However, predicted wall deflections using elasto-plastic method show underestimate results compared with measured deflections. This demonstrates that the elasto-plastic method does not clearly consider the influence of soil-wall-reinforcement interaction, so that the tension force (anchor force and earth pressure) on the wall is overestimated. Based on the results obtained, it is found that finite element method using shear strength reduction method can be effectively used to perform the back calculation analysis in the anchored retaining wall, whereas elasto-plastic method can be applicable to the preliminary design of retaining wall with suitable safety factor.

• Journal of the Korean Geotechnical Society
• /
• v.26 no.2
• /
• pp.23-32
• /
• 2010

This study was especially conducted to find out the characteristics of the lightweight air-mixed soil (slurry density 10 kN/$m^3$) containing silt related to water. Compression strength, permeability, and capillary height of the lightweight air-mixed soil were studied, and also to support these studies, the structure of that soil was analyzed in detail. Air bubbles of various sizes are inside the lightweight air-mixed soil, and its distribution in a location is almost constant. A numerous tiny pores are inside the air bubbles so that the lightweight air-mixed soil can be saturated with water. Porosity is also estimated through the image analysis. Peak strength of the lightweight air-mixed soil is not dependent on water, but behavior of stress-strain is affected by the water. Permeability is about $4.857{\times}10^{-6}cm/sec$, which is a little bit higher than the clay's permeability. Capillary rise occurs rapidly at the beginning of the test until the lapse of 100 minutes and then its increase rate becomes slow. The capillary rise causes the increase of the density of the lightweight air-mixed soil, and thus it is required to pay attention to this phenomenon during structure design and maintenance of the lightweight air-mixed soil.

• Journal of the Korean Geotechnical Society
• /
• v.26 no.10
• /
• pp.61-68
• /
• 2010

A pilot-scale model test was performed to estimate the availability of new material, Fe-loaded zeolite, as the filling material in permeable reactive barrier (PRB) against the contaminated groundwater with both Cd and Cr(VI). Aquifer was simulated by filling up a large scale soil tank with sands, and mobilizing the water flow by the head difference of water level in both ends of the tank. Then, the mixture of concentrated Cd and Cr(VI) solution was injected into the aquifer to form a contaminant plume, and its behavior through Fe-loaded zeolite barrier was monitored. The test results showed that Fe-loaded zeolite barrier successfully treated the contaminant plume containing both Cd and Cr(VI) and that the immobilized contaminants in the barrier were not desorbed or released. The results indicated that the Fe-loaded zeolite could be a promising material in PRBs against the multiple contaminants with different ionic forms like Cr(VI) and Cd.

• Journal of the Korean Geotechnical Society
• /
• v.26 no.3
• /
• pp.5-12
• /
• 2010

In this study, in order to clarify the effect of the direction of cyclic shear on the post-earthquake settlement the multi-directional shear tests were carried out for Toyoura Japan standard sand, Genkai natural sand, Kaolinite and the Granulated Blast Furnace Slag (GBFS). The diameter and the height of the specimen are 75 mm and 20 mm, respectively. In a series of tests, the number of strain cycles was adjusted as n=5, 20, 30, 100, 200 and the shear strain amplitudes were varied from 0.1% to 1.0%. The relative densities of each samples were also adjusted as Dr=50, 60 and 70%. From the test results for Toyoura sand and GBFS, it is clarified that the post-earthquake settlement is relatively large at the small relative density and becomes large with the shear strain amplitude. When the influence of difference on the direction of cyclic shear decreases, the post-earthquake settlement strain for Toyoura sand is converged to a constant value, but the GBFS increases with the number of strain cycles. In addition, the post-earthquake settlement is in the order of Kaolinite > Toyoura sand > Genkai sand > GBFS.

• Journal of the Korean Geotechnical Society
• /
• v.26 no.12
• /
• pp.5-17
• /
• 2010

Coarse granular material is used as important fill material in most of large embankments such as railway, road, dam and so on. Therefore, the accurate design parameters of the coarse granular material are necessarily required in design and construction. The behavior of the coarse granular material was not well understood because of the lack of large testing equipment capable of coarse granular material. A large triaxial testing system was developed in this research, capable of large specimens of 500 mm, 300 mm and 150 mm in diameter. In the new large triaxial testing system, the load cell is installed inside the triaxial cell and axial displacement is measured locally on a specimen in order to improve control and measurement in small strain level. Urethane specimens of 300 mm and 50 mm in diameter were prepared. The large triaxial tests were performed on the 300 mm diameter urethane specimens while RC/TS and impact echo tests on the 50 mm diameter urethane specimens to verify this testing system. In this verification test results, we could ascertain the reasonable test results of the KRRI large triaxial testing system.

• Journal of the Korean Geotechnical Society
• /
• v.23 no.6
• /
• pp.37-51
• /
• 2007

In this study, pile load tests have been carried out to develop new P-y curves and then, to investigate the effects of pile rigidities on laterally loaded offshore drilled shafts in Incheon marine clay. This paper consists mainly of two parts: the first part, performance of a series of lateral load tests on small- and full-scale piles under one- and two-way loadings and the second part, comparison between the measured and predicted results by using O'Neill's and Matlock's clay models. Based on the results obtained, it is shown that relatively good agreements in bending moments and lateral displacements were obtained between the measured results using calculated P-y curves and predicted ones by O'Neill's and Matlock's clay models. The cases were considered with varying rigidity factors based on pile diameter, length and subgrade soil reaction. Through comparisons, it is found that soil P-y curve influences highly the behavior of flexible pile rather than that of rigid pile.

• Journal of the Korean Geotechnical Society
• /
• v.23 no.5
• /
• pp.77-88
• /
• 2007

Lateral earth pressure and horizontal displacement of the diaphragm walls constructed in multi-soil layers were analyzed by the field instrumentation from six building construction sites in urban area. The distribution of the developed earth pressure of the anchored diaphragm walls during excavation shows approximately a trapezoid diagram. The maximum earth pressure of anchored diaphragm walls corresponds to $0.45{\gamma}H$ and the earth pressure acts at the upper part of the walls. The maximum earth pressure is two times larger than the empirical earth pressure of flexible walls in sands suggested by Terzaghi and Peck(1967), Tschebotarioff(1973), and Hong and Yun(1995a). The horizontal displacement of diaphragm walls is closely related with supporting systems such as struts, anchors, and so on. The horizontal displacement of anchored walls shows less than 0.1 percent of the excavated depth, and the horizontal displacement of strutted walls shows less than 0.25 percent of the excavated depth. Therefore, the restraining effect of horizontal displacement to the anchored diaphragm walls is larger than the strutted diaphragm walls. In addition, since the horizontal displacement of the diaphragm walls is lower than the criterion, $\delta=0.25%H$, used for control the anchored retention wall using soilder piles, the safety of excavation sites applied with the diaphragm walls is pretty excellent.

• Journal of the Korean Geotechnical Society
• /
• v.23 no.11
• /
• pp.77-85
• /
• 2007

This paper investigates the mechanical characteristics of composite geo-material which was developed to reuse both dredged soils and bottom ash. The composite geo-material used in this experiment consists of dredged soil taken from the construction site of Busan New Port, cement, air foam and bottom ash. Bottom ash is a by-product generated at the Samcheonpo thermal power plant. Several series of laboratory tests were performed to investigate behavior characteristics of composite gee-material, in particular the reinforcing effect by mixing bottom ash. The experimental results of composite geo-material indicated that the stress-strain relationship and the unconfined compressive strength are strongly influenced by mixing conditions. Especially it was observed that the compressive strength of composite geo-material increased with an increase in bottom ash content due to reinforcing effect by the bottom ash. Compressive strength of composite geo-material increased with the increase in curing time. The 28-day strength of composite geo-material is $1.7{\sim}1.8$ times higher than the 7-day strength. The moist unit weight strongly depended on air-foam content as well as bottom ash content added to the composite goo-material. In composite geo-material, secant modulus ($E_{50}$) also increased as its compressive strength increased due to the inclusion of bottom ash.

• Journal of the Korean Geotechnical Society
• /
• v.24 no.5
• /
• pp.107-115
• /
• 2008

This paper is performed to examine the effect of creep during the primary consolidation and the applicability of the Yin's EVP (Elasto-Visco-Plastic) model. In ordinary consolidation theories using the elastic model, the primary consolidation process can be expressed but the secondary consolidation process cannot. It is due to the viscosity, which can express the secondary consolidation, and is sometimes related to the scale effect (difference of the thickness of clay layer between laboratory sample and field condition) such as hypotheses Type A and Type B shown by Ladd et al. (1977). Usually, the existence of the creep during the primary consolidation has been conformed and the Type B is well acceped. On the other hand, from the large-scaled consolidation tests the intermediate characteristic between Type A and Type B was proposed as Type C by Aboshi (1973). In this study, to clarify the effect of creep on the settlement-time relation during the primary consolidation in detail, Type B consolidation tests were performed using the separate-type consolidation test apparatus for a peat and clay. Then the test results were analyzed by using Yin's EVP Model (Yin and Graham, 1994). In conclusion, followings were obtained. At the end of primary consolidation, the compression for the subspecimens should not be the same because of the difference of the excess pore water pressure dissipation rate. And the average settlement measured by the separate-type consolidometer coincides with the analyzed one using the Yin's EVP model. As for the dissipation of the excess pore water pressure, however, the measured excess pore water pressure dissipates faster compared with the Yin's model.

• Journal of the Korean Geotechnical Society
• /
• v.24 no.12
• /
• pp.113-120
• /
• 2008

One-dimensional site response analysis is widely used to simulate the seismic site effects. The equivalent linear analysis, which is the most widely used type of site response analysis, is essentially a linear method. The method applies constant shear modulus and damping throughout the frequency range of the input motion, ignoring the dependence of the soil response on the loading frequency. A new type of equivalent linear analysis method that can simulate the frequency dependence of the soil behavior via frequency-strain curve was developed. Various forms of frequency-strain curves were proposed, and all curves were asserted to increase the accuracy of the solution. However, its validity has not been extensively proven and the effect of the shape of the frequency-strain curve is not known. This paper used two previously proposed frequency-strain curves and three additional curves developed in this study to evaluate the accuracy of the frequency-dependent equivalent linear method and the influence of the shape of the frequency-strain curves. In the evaluation, six recordings from three case histories were used. The results of the case study indicated that the shape of the frequency-strain curve has a dominant influence on the calculated response, and that the frequency dependent analysis can enhance the accuracy of the solution. However, a curve that results in the best match for all case histories did not exist and the optimum curve varied for each case. Since the optimum frequency-strain curve can not be defined, it is recommended that a suite of curves be used in the analysis.