Hangseok Choi

Pullout Resistance Increase of Soil Nailing Induced by Pressurized Grouting

AbstractPressurized grouting has been frequently adopted in soil-nailing systems that are widely used to improve slope stability. In most geotechnical applications, soil nailing using pressurized grouting has been empirically performed without theoretical validation because the interaction between the pressurized grout and adjacent soil mass is very complicated. The present paper deals with a series of pilot-scale chamber tests performed on four different granite residual soils to evaluate the effect of pressurized grouting on the soil-nailing system. When grout is injected into a cylindrical cavity in the soil mass, the pressure exerted around the cavity perimeter initially increases with time up to a peak value and then gradually decreases to a residual stress. The pressure reduction may result from the seepage of water originally retained in the grout paste into the adjacent soil formation. With the application of pressurized grouting, in situ stresses can be increased by approximately 20% of the injec...

Immune regulatory effects of simvastatin on regulatory T cell-mediated tumour immune tolerance

Statins are potent inhibitors of hydroxyl‐3‐methylglutaryl co‐enzyme A (HMG‐CoA) reductase, and have emerged as potential anti‐cancer agents based on preclinical evidence. In particular, compelling evidence suggests that statins have a wide range of immunomodulatory properties. However, little is known about the role of statins in tumour immune tolerance. Tumour immune tolerance involves the production of immunosuppressive molecules, such as interleukin (IL)‐10, transforming growth factor (TGF)‐β and indoleamine‐2,3‐dioxygenase (IDO) by tumours, which induce a regulatory T cell (Treg) response. In this study, we investigated the effect of simvastatin on the production of IL‐10, TGF‐β and IDO production and the proliferation of Tregs using several cancer cell lines, and Lewis lung cancer (3LL) cells‐inoculated mouse tumour model. Simvastatin treatment resulted in a decrease in the number of cancer cells (3LL, A549 and NCI‐H292). The production of the immune regulatory markers IL‐10, TGF‐β in 3LL and NCI‐H292 cells increased after treatment with simvastatin. The expression of IDO and forkhead box P3 (FoxP3) transcription factor was also increased in the presence of simvastatin. In a murine 3LL model, there were no significant differences in tumour growth rate between untreated and simvastatin‐treated mice groups. Therefore, while simvastatin had an anti‐proliferative effect, it also exhibited immune tolerance‐promoting properties during tumour development. Thus, due to these opposing actions, simvastatin had no net effect on tumour growth.

Slug Test Analysis to Evaluate Permeability of Compressible Materials

The line-fitting methods such as the Hvorslev method and the Bouwer and Rice method provide a rapid and simple means to analyze slug test data for estimating in situ hydraulic conductivity (k) of geologic materials. However, when analyzing a slug test in a relatively compressible geologic formation, these conventional methods may have difficulties fitting a straight line to the semilogarithmic plot of the test data. Data from relatively compressible geologic formations frequently show a concave-upward curvature because of the effect of the compressibility or specific storage (S(s)). To take into account the compressibility of geologic formations, a modified line-fitting method is introduced, which expands on Chirlins (1989) approach to the case of a partially penetrating well with the basic-time-lag fitting method. A case study for a compressible till is made to verify the proposed method by comparing the results from the proposed methods with those obtained using a type-curve method (Kansas Geological Survey method [Hyder et al. 1994]).

Slug Test Analysis in Vertical Cutoff Walls with Consideration of Filter Cake

In constructing a vertical cutoff wall, bentonite-water slurry is frequently used to maintain the stability of sidewalls during excavation before backfilling the trench with less permeable materials to complete the cutoff wall construction. This procedure leads to a thin but relatively impermeable layer, called a filter cake, on the excavation surface. The aim of this paper is to examine the effect of a filter cake on evaluating hydraulic conductivity of the cutoff wall backfill through a slug test analysis with the aid of the verified numerical program, Slug_3D. As an upper bound solution for evaluation of the hydraulic conductivity of the cutoff wall backfill, no-flux boundary conditions for the boundaries of cutoff walls are imposed to consider the effect of filter cakes. The type-curve method and modified line-fitting method are employed to reanalyze the case of EMCON/OWT, Inc., as an example. The previous analysis, without consideration of a filter cake, is compared with the current results that cons...

Compacted soil liner interface strength importance

This paper describes an interesting slope failure in a liner system of a municipal solid waste containment facility during con- struction because the sliding interface is not the geomembrane (GM)/compacted low-permeability soil liner (LPSL) but a soil-soil interface within the LPSL. Some of the lessons learned are as follows: (1) compaction of the LPSL should ensure that each lift is kneaded into the lower lift so a weak interface is not created in the LPSL; (2) the LPSL moisture content should be controlled so it does not exceed the specified value, for example 3-4% wet of optimum, because it can lead to a weak interface in the LPSL; (3) drainage material should be placed over the GM from the slope toe to the top to reduce the shear stresses applied to the weakest interface; and (4) equipment should not move laterally across the slope if it is unsupported but up the slope while placing the cover soil from bottom to top. DOI: 10.1061/(ASCE)GT.1943-5606 .0000556.

Performance Simulation of Ground-Coupled Heat Pump(GCHP) System for a Detached House

ABSTRACT:Ground-coupled heat pump(GCHP) systems have been shown to be an environ- mentally-friendly, efficient alternative to traditional cooling and heating systems in both residential and commercial applications. Although some work related to performance evaluation of GCHP systems for commercial buildings has been done, relatively little has been reported on the residential applications. The aim of this study is to evaluate the cooling and heating performances of a vertical GCHP system applied to an artificial detached house(117 m 2 ) in Seoul. For this purpose, a typical design procedure was involved with a combination of design parameters such as building loads, heat pump capacity, borehole diameter, and ground thermal properties, etc. The cooling and heating performance simulation of the system was conducted with different prediction times of 8760 hours and 240 months. The performance characteristics including seasonal system COP, average annual power consumption, and temperature variations related to ground heat exchanger were calculated and compared.Keywords:Ground-coupled heat pump(지열 히트펌프), Vertical ground heat exchanger(수직형 지중열교환기), Detached house(단독주택), Hourly performance simulation(시간대별 성능 분석), Monthly performance simulation(월간 성능 분석)

Modification of the Bouwer and Rice method to a cutoff wall with a filter cake.

The Bouwer and Rice method is a line-fitting method used to estimate the hydraulic conductivity of an aquifer by means of a slug test. When considering a relatively impermeable layer, called a filter cake, which may form at the interface between a cutoff wall and the natural soil formation, the assumptions of the Bouwer and Rice method are violated. A modification of the Bouwer and Rice method is proposed that incorporates the concept of a flow net, whereby the geometry of the cutoff wall and filter cake is effectively considered in estimating the hydraulic conductivity of a vertical cutoff wall.

Characterization of Korean solid recovered fuels (SRFs): an analysis and comparison of SRFs.

To date, Korea has used four species of solid recovered fuels (SRFs) which have been certified by the Environmental Ministry of Korea: refuse-derived fuel (RDF), refused plastic fuel (RPF), tyre-derived fuel (TDF), and wood chip fuel (WCF). These fuels have been used in many industrial boilers. In this study, seven regulatory properties associated with each of the four species: particle size, moisture and ash content, lower heating value (LHV), total chlorine, sulfur, and heavy metals content (Pb, As, Cd, Hg, Cr) were analysed. These properties are the main regulation criteria for the usage and transfer of SRFs in Korea. Different properties of each SRF were identified on the basis of data collected over the last 3 years in Korea, and the manufacturing process problem associated with the production of SRFs were considered. It was found that the high moisture content of SRFs (especially WCF) could directly lead to the low LHV of SRFs and that the poor screening and sorting of raw materials could cause defective SRF products with high ash or chlorine contents. The information obtained from this study could contribute to the manufacturing of SRF with good quality.

PERFORMANCE PREDICTION OF GEOTHERMAL HEAT PUMP (GHP) SYSTEM USING CAST-IN-PLACE ENERGY PILES

ABSTRACT:The aim of this study is to evaluate the performance of the GHP system with 45 cast-in-place energy piles(CEP) for a commercial building. In order to demonstrate the feasibility of a sustainable performance of the system, transient simulations were conducted over 1-year and 20-year periods, respectively. The 1-year simulation results showed that the maximum and minimum temperatures of brine returning from the CEPs were 23.91℃ and 6.66℃, which were in a range of design target temperatures. In addition, after 20 years’ operation, these returning temperatures decreased to 21.24℃ and 3.68℃, and finally reached to stable state. Annual average extraction heat of cast-in-place energy piles was 94.3 MWh and injection heat was 65.7 MWh from the 20 years of simulation results. Finally, it is expected this GHP system can operate with average heating SPF of more than 3.45 for long-term.Keywords:Cast-in-place energy pile(현장 타설 에너지파일), Ground heat exchanger(지중열교환기), Geothermal heat pump system(지열 히트펌프 시스템), Cooling and heating performance(냉난방 성능), Transient simulation(동특성 시뮬레이션)

Hydraulic characteristics of bentonite cake fabricated on cutoff walls

Bentonite cake is usually formed on the excavated trench surface that is supported by the bentonite slurry during construction of slurry cutoff walls. The lower hydraulic conductivity of bentonite cakes formed during construction of slurry cutoff walls in comparison to backfill materials provides an additional benefit. In the present study, the hydraulic conductivities of bentonite cakes made using three different bentonites were estimated using the modified fluid-loss test under various pressures. Both the hydraulic conductivities of bentonite cakes and cutoff-wall backfill are important in evaluating the in situ hydraulic performance of slurry cutoff-wall construction. Three bentonite slurry concentrations of 4, 6, and 8% were used to fabricate bentonite cakes that represent common field conditions. X-ray diffraction, cation exchange capacity, and swell-index data were collected to characterize the bentonites. Two modified methods for analyzing fluid-loss test results were used to estimate bentonite cake hydraulic conductivities. In addition, the viscosity as a function of time was measured to explain the sealing capacities of the bentonite slurries. The bentonite-cake hydraulic conductivities ranged from 2.15×10−11 m/s to 2.88×10−10 m/s, which were 10 to 500 times lower than the cutoff wall backfill design. Experimental results for 4 and 6% bentonite slurries were relatively similar, but the 8% slurries were noticeably different. Calculated bentonite-cake thickness and stress distribution indicated that the local void ratio and hydraulic conductivity may vary across the cake thickness. The considerably lower bentonite-cake hydraulic conductivities compared to the cutoff wall backfill design show its significance in slurry cutoff-wall construction practices.