• Computers and Concrete
• /
• v.1 no.2
• /
• pp.211-226
• /
• 2004

A relatively simple multiple-vertical-line-element macro model has been incorporated into a standard computer code DRAIN-2D. It was used in blind predictions of seismic response of cantilever RC walls subjected to a series of consequent earthquakes on a shaking table. The model was able to predict predominantly flexural response with relative success. It was able to predict the stiffness and the strength of the pre-cracked specimen and time-history response of the highly nonlinear wall as well as to simulate the shift of the neutral axis and corresponding varying axial force in the cantilever wall. However, failing to identify the rupture of some brittle reinforcement in the third test, the model was not able to predict post-critical, near collapse behaviour during the subsequent response to two stronger earthquakes. The analysed macro model seems to be appropriate for global analyses of complex building structures with RC structural walls subjected to moderate/strong earthquakes. However, it cannot, by definition, be used in refined research analyses monitoring local behaviour in the post critical region.

• Journal of the Korean Geosynthetics Society
• /
• v.4 no.3
• /
• pp.45-52
• /
• 2005

Most marine structures are constructed on very soft soil, soil improvements are needed for the area of road, buildings. In this paper, some considerations of several case studies on soil placement method after geotextile placement, known as surface treatment, are done. Considerations of strength applicability on the advanced construction method of sand and soil placement are proposed in this paper. Typical tensile strength of geotextile used in the surface soil stabilization method is 15t/m, and thickness of sand and soil placement between 1.6m and 3.1m. Undrained shear strength of soft clay layer ranges $0.2{\sim}1.2t/m^2$. In order to minimize the difficulties which include soil disturbance, soft soil gush and overturn of vertical drain installation rig more studies are needed.

• Geotechnical Engineering
• /
• v.13 no.1
• /
• pp.47-58
• /
• 1997

The predicted consolidation behavior of in-situ soft clay is quite different from the meas ureal one mainly due to the approximate numerical modelling techniques as well as the uncertainties involved in soil properties and geological configurations. In order to improve the prediction, this paper takes the following pinto consideration : an optimization technique should be adopted for characterizing the in-situ properties from measurements and also an equivalent and efficient model be considered to incorporate the actual 3-D effects. The soil parameters used be the modified Camflay model, which have an effect on the process of consolidation, were back-analyzed by BFGS scheme on the basis of settlements and pore pressures measured in real sites. The optimization technique was implemented in a general consolidation analysis program SPINED. By using the program, one may be able to appropriately analyze the timetependent consolidation behavior of soft deposits.

• Journal of the Korean Geosynthetics Society
• /
• v.17 no.4
• /
• pp.239-249
• /
• 2018

Typically, soft clay improvement is carried out using installation of PVD and surcharge method. According to circumstances, installed PVD has left for a long time due to the change in construction schedule. Therefore, for simulation of this kind of condition, discharge capacity tests were carried out under a series of temperature condition (30, 35, $40^{\circ}C$). The results indicated that under water confinement, the discharge capacities significantly reduced with elapsed time. And, the empirical equation by Miura and Chai (2000) was used for estimating the long-term in-clay discharge capacity. Based on the test results, it is recommended that in term of long-term discharge capacity, Miura and Chai's equation and reliability evaluation using discharge capacity tests under a series of temperature condition may be used.

• Journal of the Korean Geotechnical Society
• /
• v.28 no.11
• /
• pp.41-52
• /
• 2012

Suction drain method can directly apply vacuum pressure to the soft ground through vertical drains so it can make hardening zones around them. These hardening zones make steeply lower the discharge efficiency of the pore water with decreasing permeability. This paper considered a stepped vacuum pressure to minimize a hardening zone which is one of the important parameters that can decrease discharge efficiency. A series of laboratory tests were conducted in order to examine the effect of the hardening zones and to evaluate their effects to the ground improvements with varying durations which applied stepped vacuum pressures(-20kPa, -40kPa, -60kPa and -80kPa) with Busan marine clay. According to strength(CPT), water content test and theoretical investigation indicate a size of the hardening zone within 7cm and the decreasing ratio of permeability about 2.0~4.0. Also, the total settlements are larger for the stepped vacuum pressure than the instant vacuum loading. The application time with vacuum pressure is determined considering the geotechnical properties of the interested clays. Results of numerical analysis show that consolidation behavior is appropriate to measurement for considering hardening zones.

• Journal of the Korean Geosynthetics Society
• /
• v.21 no.1
• /
• pp.11-21
• /
• 2022

In this study, the individual vacuum seepage consolidation method, a new soft ground improvement method, was developed to supplement the conventional suction drain method (individual vacuum preloading method) and the geotechnical behavior was predicted through numerical analysis. If the individual vacuum seepage consolidation method applied, the effect of accelerating settlement and increasing the amount of settlement was high when the aquifer was located in the middle or at the bottom of the layer to the target improvement layer. It was found that the pumping amount in the aquifer does not affect the settlement behavior when it exceeds a certain level. Even vacuum pumping wells were installed in various locations, such as inside or outside of the embankment, the difference in settlement and horizontal displacement was insignificant. In addition, it was predicted that the settlement rate was the fastest and the horizontal displacement (inward) was large when both methods were carried out at the same time. Since this method can reach the target settlement amount very quickly, it was confirmed that it is possible to increase the spacing of vertical drain, thereby securing economic feasibility.

• Journal of the Korean GEO-environmental Society
• /
• v.16 no.2
• /
• pp.53-58
• /
• 2015

The Pre-loading method has been widely used for the soft ground stabilization but long construction times and the transport of large quantities of fill material are required. To shorten the construction periods, the vertical drain method is generally applied simultaneously. But the high costs of the fill materials along with environmental damages remain as the main difficulties to apply this method. Therefore, a complimentary way to reduce both the height of the embankment and the consolidation time is needed. In this study, the electro-osmosis method, which is able to shorten the consolidation time and minimize the damage of the environment, was performed with a model test. The results show that as the voltage increases the consolidation settlements, consolidation drainage and shear strength also increase while the water content decreases.

• Journal of the Korean GEO-environmental Society
• /
• v.13 no.12
• /
• pp.35-42
• /
• 2012

There are many large-scale coastal region landfill and land development by loading to use territory efficiently, this regions are mostly soft clay ground. Constructing structures and road on the soft ground bring about engineering problems like ground shear fracture and a big amount of consolidation by bearing capacity. Improvement of soft soil is required to secure soil strength and settlement control. In improvement of soft soil, predict for the amount of settlement based on field surveyed reports are important element for estimating pre-loading banking height and the final point of consolidation. In this study, there is calculating theoretical settlement by analyzing field surveyed report and ground investigation to improvement of soft soil with pre-loading and vertical drain method. And present settlement prediction method reflect soil characteristics in Gimpo Hangang site by analysing prediction settlement and observational settlement during compaction using hyperbolic, ${\sqrt{s}}$, Asaoka method.

• Journal of the Korean Geotechnical Society
• /
• v.27 no.10
• /
• pp.5-12
• /
• 2011

This study was focused on the reactivity of furnace slag against cadmium to design the vertical drain method with reactive column for improving contaminated sea shore sediment. The kinetic sorption test was performed by changing the initial concentration and pH. Using pseudo-second-order model, the reactivity of furnace slag was quantitatively analyzed. Equilibrium removal amount ($q_e$) of furnace slag increased and rate constant ($k_2$) decreased with the increase of initial cadmium concentration. With the increase of pH, the equilibrium removal amount ($q_e$) and rate constant ($k_2$) increased in the same initial concentration. Required retention time was related to the inverse of the product of the equilibrium removal amount ($q_e$) multiplied by rate constant ($k_2$). The required retention time could be used to design the length of reactive column.

• Journal of Industrial Technology
• /
• v.25 no.B
• /
• pp.63-71
• /
• 2005

This paper is an experimental result of investigating lateral soil movements at piled bridge abutments by using the centrifuge model facility. Three different centrifuge model experiments, changing the methods of ground improvement at bridge abutment on the soft clayey soil (no improvement, preconsolidation and plastic board drains (PBD), sand compaction pile (SCP) + PBD), were carried out to figure out which method is the most appropriate for resisting against the lateral soil movements. In the centrifuge modelling, construction process in field was reconstructed as close as possible. Displacements of abutment model, ground movement, vertical earth pressure, cone resistance after soil improvement and distribution of water content were monitored during and after centrifuge model tests. As results of centrifuge model experiments, preconsolidation method with PBD was found to be the most effective against the lateral soil movement by analyzing results about displacements of abutment model, ground movement and cone resistance. Increase of shear strength by preconsolidation method resulted in increasing the resistance against lateral soil movement effectively although SCP could mobilize the resistance against lateral soil movement. It was also found that installment with PBD beneath the backfill of bridge abutment induced effective drainage of excess pore water pressure during the consolidation by embanking at the back of the abutment and resulted in increasing the shear strength of clay soil foundation and eventually increasing the resistance of lateral soil movement against piles of bridge abutment.