• Journal of the Korean Society for Railway
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• v.13 no.2
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• pp.214-221
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• 2010

The transitional zone between tunnel and earthwork is one of the most vulnerable areas site for railway lines and because of differential settlement due to different stiffness of each supporting layer, it has to conducted a maintenance work constantly. In this study, it is conducted to compare the effect of reinforcement by wheel load and displacement of the sleepers after existing sleepers are replaced with the large sleepers for 20m long in-field transitional zone. Also, numerical parametric study using multi-layer elastic method has been performed to compare rail force, settlement and stresses of ballast while varying size and space of the sleeper. The field test and numerical results show that replacing the large sleepers improves about 10% of total settlement and coefficient of wheel force than conventional sleepers. Effectiveness of improvement is about 9.3%, 4%, 14.5% for rail seat force, settlement of sleepers and ballast pressure respectively with size of sleepers.

• Proceedings of the Korean Geotechical Society Conference
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• 2008.10a
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• pp.1212-1217
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• 2008

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 and the Granulated Blast Furnace Slag (GBFS). In a series of tests, number of strain cycles was changed as n=5-200 and the shear strain amplitude varied from 0.1% to 1.0%. The relative density was also changed as Dr=50, 60 and 70%. From the test results for Toyoura sand and GBFS, it is clarified that the post cyclic settlement is relatively large at the small relative density and becomes large with the shear strain amplitude. When the influence of the direction of cyclic shear is decreases, the post cyclic settlement strain for Toyoura sand is converged to a constant value, but the GBFS is increased with the number of strain cycles.

• Proceedings of the Korean Geotechical Society Conference
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• 2005.03a
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• pp.286-293
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• 2005

In soft ground the settlement criterion usually governs. Therefore, it is very important not only reasonable assessment of the allowable bearing capacity of the soil but also reasonable assessment of settlement. In the previous studies by many other researchers, load concentration ratio and settlement reduction factor are usually proposed for estimating the settlement of granular compaction piles. In the previous studies, the reinforced ground with granular compaction piles is simplified as composite ground and the analysis is performed with in the basis of this assumption. However, the lateral deformation of granular compaction pile could not be considered and only the relative vertical strength between pile and soils could be considered in the analysis. In this study, a method adapting the Tresca failure criterion is proposed for calculating settlement of granular compaction pile. Proposed method can be considered the strength of pile material, pile diameter, installing distance of pile and the deformation behavior of vertical and horizontal directions of pile. In the presented study, large-scale field load test is performed and the results are described. Also, predictions of settlements from the proposed method are compared with the results of the load test. In addition, a series of parametric study is performed and the design parameters are analyzed.

• Magazine of the Korean Society of Agricultural Engineers
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• v.39 no.3
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• pp.128-137
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• 1997

In this study, examined influence of consolidation effect that had affected by location of pump inlet that was set collection well for drainage of pore water discharged by embankment on soft ground through the field test. The results of this study are summarized as follows; 1 Initial consolidation curve value were larger than theoritic value, the cause of these phenomena were thought influence of secondary consolidation and three dimensional strain of soft clay. 2. The settlement value of Hosino method was larger than that of Hyperbolic method, but settlement value of Hyperbolic method was accurate more than that of Hosino method in the prediction of settlement. 3. When pump inlet in collection well came down from GL+O.3m to GL-1.5m, settlement value increased about 10cm and when the ground water level was made insitu after pumping had completed , settlement was expanded about 7~8cm. So it is found that location change of pump inlet bad an influence on settlement remarkably. 4. If location of pump inlet in collection well for large scale estate or wide road site is lowered than original ground level, the settlement will be accelerated effectively, and at this stage automatic pump must be used in pumping.

• Proceedings of the Korean Geotechical Society Conference
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• 2008.10a
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• pp.1712-1716
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• 2008

Performance of ground improvement project using prefabricated vertical drains of condition, in which approximately 10m dredged fill overlies original soft foundation layer in the coastal area has been conducted. From field monitoring results, excessive ground settlement compared to predicted settlement in design stage developed during the following one year. In order to predict the final consolidation behavior, recalculation of consolidation settlements and back analysis using observed settlements were conducted. Field monitoring results of surface settlements were evaluated, and then corrected because large shear deformation was occurred by construction events in the early stages of consolidation. To predict the consolidation behavior, material functions and in-situ conditions from laboratory consolidation test were re-analyzed. Using these results, height of additional embankment is estimated to satisfy residual settlement limit and maintain an adequate ground elevation. The recalculated time-settlement curve has been compared to field monitoring results after additional surcharge was applied.

• Proceedings of the KSR Conference
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• 2004.06a
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• pp.1007-1013
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• 2004

A three-arch NATM tunnel with a total length of 53.5m has been constructed for a metropolitan subway station in Daejon, Korea. The tunnel, whose crown is located 22m below the ground, crosses the old Daejon station underneath. Since the tunnel comprises a very large section (10${\times}$28 m; largest in Korea), it shows complicated mechanical behaviors, especially near portal, due to its short length relative to width. As far as its construction step is concerned, the center tunnel is excavated with pre-excavated pilot tunnel, which is a unique feature of this tunnel (first in Korea) to secure safety during construction and prevent excessive settlements. The both side tunnels are then excavated along with the center tunnel. Since significant amount of settlement was predictable from the design stage, extensive monitoring was performed during construction. During excavation of the side tunnels, unexpected large settlements up to ${\~}$140mm (estimated 41.8 mm at design stage) was measured at the center tunnel. In this paper, we study the causes of this unusually large ground settlement. We believe that the extra-wide tunnel excavation increases the stress influence zone of portal in longitudinal direction and consequently add more settlements to the existing due to excavation and consolidation.

• Journal of the Korean GEO-environmental Society
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• v.15 no.11
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• pp.21-27
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• 2014

In this study, the prediction methods for the crest settlement after impounding and the maximum internal settlement during dam construction were proposed through the analysis on settlement data at 46 monitored points of 37 Center-Cored Rockfill Dams (CCRDs). Results from this analysis provided that the crest settlement increases with elapsed time, and from the relationship between the dam height and the maximum internal settlement during dam construction, it is confirmed that the internal settlement was largely evaluated when the coarse-grained material was used as the dam core. This internal settlement increased in proportion to the dam height. In addition, the crest settlement of the CCRD with the core compacted with fine-grained material was relatively large. It is expected that the results of this study would provide the practical tool for the design, construction and management of CCRDs.

• KDI Journal of Economic Policy
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• v.42 no.1
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• pp.57-95
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• 2020

As a case study of an ex-post evaluation of regulations, in this paper I evaluate the 'uniform settlement rate requirement', a regulation that was introduced in 1986 and that was applied to the international telephone market in the U.S. for more than 20 years. In a bilateral market between the U.S. and a foreign country, each U.S. firm and its foreign partner jointly provide international telephone service in both directions, compensating each other for terminating incoming calls to their respective countries. The per-minute compensation amount for providing the termination service, referred to as the settlement rate, is determined by a bargaining process involving the two firms. In principle, each U.S. firm could have a different settlement rate for the same foreign country. In 1986, however, the Federal Communications Commission introduced the Uniform Settlement Rate Requirement (USRR), which required all U.S. firms to pay the same settlement rate to a given foreign country. The USRR significantly affected the relative bargaining positions of the U.S. and foreign firms, thereby changing negotiated settlement rates. This paper identifies two main routes through which the settlement rates are changed by the implementation of the USRR: the Competition-Induced-Incentive Effect and the Most-Favored-Nation Effect. I then empirically evaluate the USRR by estimating a bargaining model and conducting counterfactual experiments aimed at measuring the size of the two effects of the USRR. The experiments show remarkably large impacts due to the USRR. Requiring a uniform settlement rate, for instance, results in an average 32.2 percent increase in the negotiated settlement rates and an overall 13.7 percent ($3.43 billion) decrease in the total surplus in the U.S. These results provide very strong evidence against the implementation of the USRR in the 1990s and early 2000s.

• Geomechanics and Engineering
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• v.15 no.3
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• pp.851-859
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• 2018

There are two primary causes of the ground movement due to tunnelling in urban areas; firstly the lost ground and secondly the groundwater depression during construction. The groundwater depression was usually not considered as a cause of settlement in previous research works. The main purpose of this study is to analyze the combined effect of these two phenomena on the transverse settlement trough. Centrifuge model tests and numerical analysis were primarily selected as the methodology. The characteristics of settlement trough were analyzed by performing centrifuge model tests where acceleration reached up to 80g condition. Two different types of tunnel models of 180 mm diameter were prepared in order to match the prototype of a large tunnel of 14.4 m diameter. A volume loss model was made to simulate the excavation procedure at different volume loss and a drainage tunnel model was made to simulate the reduction in pore pressure distribution. Numerical analysis was performed using FLAC 2D program in order to analyze the effects of various groundwater depression values on the settlement trough. Unconfined fluid flow condition was selected to develop the phreatic surface and groundwater level on the surface. The settlement troughs obtained in the results were investigated according to the combined effect of excavation and groundwater depression. Subsequently, a new curve is suggested to consider elastic settlement in the modified Gaussian curve. The results show that the effects of groundwater depression are considerable as the settlement trough gets deeper and wider compared to the trough obtained only due to excavation. The relationships of maximum settlement and infection point with the reduced pore pressure at tunnel centerline are also suggested.

• Journal of Korean Society of Environmental Engineers
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• v.27 no.5
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• pp.486-490
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• 2005

Fine recycled-concrete aggregates(RCAs) instead of natural sand were tested for a foundation material under sewage conduit system, which was evaluated based on foundation settlement at various conditions. To obtain this applicability of RCAs, the settlement behavior was simulated with FLAC program based on the difference of material properties, and immediate settlement behaviors and the change of material properties under the simulated drainage conditions also tested at the various loading conditions in the laboratory. Finally, large-scale settlement test in the field was conducted to prove the above feasibilities. Subsequently, the amount of settlement from the FLAC simulation was calculated under $5.0{\times}10^{-6}\;m$ and the extent of settlement and property changes (porosity, permeability and waster absorption) was not noticeable from the laboratory experiments. Also, settlement monitoring from the field experiment showed the consistent results with laboratory experiments except for the consolidation settlement(=5 mm) of the round below the foundation. In summary, adopting fine RCAs as a foundation material for sewage conduit system was resonable based of geotechnical point of view.