Byung-Sik Chun

A Study on Applications of Polyurethane Injection Material for Ground Improvement

The physical and chemical properties of polyurethane-yielding two-component liquid injection mixture and those of the resulting polyurethane solid foam for chemical grouting were investigated. From the chemical experiments on the factors influencing the properties of polyurethane, it was investigated that the behaviors of polyurethane-yielding liquid material and those of the produced polyurethane solid foam were greatly affected by the ground conditions such as temperature, water content and density of soil. The ground reinforcing and water-blocking effects of polyurethane grouting were examined through the field case history of tunnel excavation of the subway under construction.

Application of Constitutive Model to Predict the Behavior of EPS-Geofoam

EPS (Expanded Polystyrene)-geofoam, a super light weight material, has the unit weight of 20–30 kg/m3 and is used as one of the methods acquiring the safety for settlement and bearing capacity. There are a few constitutive models for the selection of the EPS-geofoam fill which is essential to the determination of the fill configuration and the settlement calculation. However, it is difficult to determine the parameters of its model. In this paper, therefore, a practical nonlinear constitutive model developed from the results of drained triaxial compression tests was proposed. The proposed nonlinear numerical constitutive model was applied to a large scale model test and to a field construction in Japan. The predictions agree well with the measurements.

Enhanced Heavy Metal Sorption by Surface-Oxidized Activated Carbon Does Not Affect the PAH Sequestration in Sediments

We examined the sorption of heavy metals and polycyclic aromatic hydrocarbons (PAHs) to surface-oxidized activated carbon (AC) and its effect on the distribution of those compounds in sediments. Created surface oxygen groups on AC enhanced the sorption of copper, which is superior in sorption competition, in the marine sediments. In case of cadmium, aqueous chemistry altered by AC addition, such as pH, has greater impact on the bioavailability according to the result of a sequential extraction combined with the pore water concentration measurements. Oxidized AC exhibited 2.3 times more adsorption of reduced bioavailable copper while 23% of bioavailable cadmium was adsorbed onto unmodified AC. No significant changes in BET surface area, pore volume, and AC/water distribution coefficient (KAC) of PAHs were observed with surface-oxidized AC. The largest difference in KAC after the oxidation was only 0.14 log unit. Consequently, freely dissolved aqueous concentrations of PAHs were reduced by more than 96% for all tested ACs in a week despite the increased Cu sorption on AC. This indicates that enhanced metal sorption by surface oxidation of AC is less significant in controlling bioavailability of PAHs in sediments than particle size or sorbent dose.

A study on using acoustic emission in rock slope with difficult ground — focused on rainfall

This study attempted to predict slope failures by applying AE techniques to a rock slope with a history of collapse. Damage levels were assessed on the basis of the AE characteristics estimated by conducting laboratory tests on simulated slope failures. The test results showed that the specimen showed a very high degree of failure at the initial stage of loading, which was analyzed using the AE characteristics to assess the damage levels. The variation in the measured number of AE hits and AE events in field tests may indicate minute variations in the slope. The measured values appeared to be insignificant as they were less than the minimum criterion for damage. An analysis of rainfall, which is an important factor in slope behavior, showed that as rainfall increased, the number of AE hits and AE events also increased. In particular, when the cumulative rainfall was constant, the cumulative number of AE hits and AE events appeared to converge, indicating that the cumulative rainfall and the number of AE hits are closely connected. When applying AE techniques to a slope that has a high probability of failure, the failure prediction of the specific location and the early prediction of failure behavior on rock slopes became possible.

A Study on the Ground Reinforcement of Jeju Scoria Layer by Chemical Grouting

Recently, public works becoming bigger in Jeju are implemented various kinds of ground reinforcement method including the chemical grouting method. In this study, we have been investigated on the proper material and the injection condition for the excellent injection effect and the excellent strength of injection material and the permanent waterproof and reinforcement through the experiment. The kind of injection material has been selected through the uniaxial compression test and the endurance test of injection material as the chamber test. An experiment was performed with model ground made of scoria, the injection performance of selected material has been identified through the evaluation test of injection range using the decision test of injection amount and the calibration chamber test. As a result of test, it has been analyzed that MSG appeared to have the excellent strength, durability and injection performance all compared with the ordinary cement, this result is judged to be possible as the ancillary data of design at time of design and construction with the chemical grouting method in the future.

Strength and Permeability of Biostabilized Sand

Shallow backshore sands in the coastal zone are continually left in a relatively loose state due to coastal processes and human behavior. Because of this, backshore construction usually involves some form of soil improvement or alternative foundation design. To address these issues, an investigation into the application of an eco-friendly organic acid for soil improvement is conducted. Test results show the organic acid focuses on the proliferation of local microbes to cement and restructure the sand matrix, thus making the application a more sustainable option. Unconfined compression, California bearing ratio, and permeability tests were performed to assess the degree to which the sample sand was improved. After 96 days, results showed compressive strength to increase by at least 60 % and a decrease in permeability of at least 49 %. California bearing ratios increased modestly. The results are promising and shed some light into the application of an organic acid for soil improvement.

Correlation between Compressive Strength and Unit Weight of Lightweight Foamed Controlled Low Strength Material (CLSM) Using Coal Ash

With the increase in the application of CLSM using coal ash, we performed a basic research on CLSM material, laying focus on the correlation between compressive strength and unit weight of lightweight foamed CLSM. The unconfined compression strength is a criterion for the judgment of the possibility of re-excavation and an important factor determining the economy, efficiency, and excavation character. However, to know the quantitative compression strength value takes a certain amount of time, because the applicability of unconfined compression strength of CLSM is judged by the standard of 28days. Therefore, in this study the relation between compressive strength and unit weight (foam slurry unit weight, apparent unit weight) is analyzed focusing on lightweight foamed CLSM. We also suggested a formula which can easily predict the 28-day compressive strength only using unit weight value without the need to cure the slurry for 28 days.

Vibration Characteristics of Embedded Piles Carrying a Tip Mass

The vibration characteristics of fully and partially embedded piles with flexibly supported end carrying an eccentric tip mass are investigated. The pile model is based on the Bernoulli-Euler theory and the soil is idealized as a Winkler model for mathematical simplicity. The governing differential equations for the free vibrations of such members are solved numerically using the corresponding boundary conditions. The lowest three natural frequencies and corresponding mode shapes are calculated over a wide range of non-dimensional system parameters: the rotational spring parameter, the relative stiffness, the embedded ratio, the mass ratio, the dimensionless mass moment of inertia, and the tip mass eccentricity.