• 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.

• Proceedings of the Korean Society of Soil and Groundwater Environment Conference
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• 2002.04a
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• pp.167-172
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• 2002

Seoul subway system has been constructed to solve traffic difficulties of Seoul metropolitan, and now is the major public transportation. However, the more line has added in the system the deeper the bottom of the tunnel base. And a huge amount of groundwater along the line has seeping into the tunnel. Several subway stations has pumping system to extract the groundwater to the outside and consequently, groundwater table along the line has declined gradually. Groundwater table has dropped about 40 meters at some areas, There was some study for the proper usage of the abstracted groundwater and the project to use the groundwater has launched already by the local government. However. more serious problem is expected on quality degradation of soil and groundwater as the decline of groundwater table along the subway line. This study suggests that the detailed groundwater environmental study should be made as soon as possible for this. If there is any pollution leaking at the surface area of the groundwater depression, the pollution will be seep into the subway tunnel in some day even though the time will be different with the soil material and hydraulic characteristics of the aquifer. And the polluted area of the soil and groundwater would be enlarged along the pathway The study on possibility of the soil subsidence and reducing surface water flow in small creek were also needed. This study suggest one of the counter measurement that restoring the declined groundwater table after groundwater environmental study

• Economic and Environmental Geology
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• v.54 no.2
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• pp.247-257
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• 2021

The study area has been contaminated with explosive materials and heavy metals for several decades. For the design of the pump and treat remediation method, groundwater flow before and during groundwater pumping in a contaminated aquifer system was simulated, calibrated, and predicted using a generalized multidimensional hydrological numerical model. A three-dimensional geologic formation model representing the geology, hydrogeology, and topography of the aquifer system was established. A steady-state numerical simulation with model calibration was performed to obtain initial steady-state spatial distributions of groundwater flow and groundwater table in the aquifer system before groundwater pumping, and its results were illustrated and analyzed. A series of transient-state numerical simulations were then performed during groundwater pumping with the four different pumping rates at a potential location of the pumping well. Its results are illustrated and analyzed to provide primary reference data for the pump and treat remediation method. The results of both steady-state and transient-state numerical simulations show that the spatial distribution and properties of the geologic media and the topography have significant effects on the groundwater flow and thus depression zone.

• The Journal of Engineering Geology
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• v.27 no.3
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• pp.255-265
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• 2017

We have determined the optimal pumping rate of the PW-2 water well (depth=100 m) at Imgokri, Sangju City. Cutting analysis and geophysical logging data reveal water-producing horizons at 26.1-26.5, 28.0-30.0, 33, 58, and 71 m. For pumping rates of 40, 55, 70, 90, and $132m^3/d$ over 70 days, the estimated drawdown from the PW-2 well was 6.48, 11.56, 18.07, 28.99 and 60.26 m, respectively. During a constant-rate pumping test at a rate of $117m^3/d$, the cone of depression intersected an impermeable boundary after 120-150 min of pumping. Therefore, we consider the critical pumping rate for well PW-2 to be $90m^3/d$. After pumping at $90m^3/d$ for 70 days, the calculated drawdown was 28.82-31.27 m. We suggest an optimal pumping rate for well PW-2 of $70-90m^3/d$, as the optimal pumping rate should be similar to the critical pumping rate. Sharp increases in the slope of the time-drawdown relationship, dissolved oxygen concentrations, and oxidation-reduction potential during the constant-rate pumping test indicate the limited development of bedrock aquifers around PW-2.

• Journal of The Geomorphological Association of Korea
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• v.23 no.1
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• pp.35-45
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• 2016

Aiming to elucidate the formation processes of Myeonsan wetland around the ridge from Myeonsan peak to Seokgae pass, this paper analyzes the geomorphic, physical and chemical characteristics of the wetland. The results are as follow: Firstly, resistant bedrock and big boulders distributed on the riverbed of the small channel from the wetland to Seokgaecheon have played a role as a temporary base level. At the upstream part above this point, a wide and shallow depression was formed and developed into a wetland. There was a gorge covered with boulders at downstream part. Secondly, owing to the obstacles at the outlet of wetland, deposits on bed tend to be downstream coarsening. Finally, deposits show weak acidity of pH 5.0~5.7. The source of wetland water is groundwater containing rich Ca and Na. Trees in the wetland help much more Ca accumulated. And deposit biotite and amphibole contained rich Mg have been weathered in the wetland.

• Proceedings of the Korean Society of Soil and Groundwater Environment Conference
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• 2005.10a
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• pp.59-61
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• 2005

In Korea, hundreds of abandoned and closed coal and metallic mines are present in the steep mountain valleys due to the depression of the mining industry since the late 1980s. From these mines, enormous amounts of coal waste were dumped on the slopes, which causes sedimentation and acid mine drainage (AMD) to be discharged directly into streams causing detrimental effects on soil and water environments. A limestone slurry by-product (lime cake) is produced from the Solvay process in manufacturing soda ash. It has very fine particles, low hydraulic conductivities ($10^{-8}{\sim}10^{-9}cm/sec$), high pH, high EC due to the presence of CaO, MgO and $CaCl_2$ as major components, and traces of heavy metals. Due to these properties, it has potential to be used as a neutralizer for acid-producing materials. A field plot experiment was used to test the application of lime cake for reclaiming coal wastes. Each plot was 20 x 5 m (L x W) in size on a 56% slope. Treatments included a control (waste only), calcite ($CaCO_3$), and lime cake. The lime requirement (LR) for the coal waste to pH 7.0 was determined and treatments consisted of adding 100%, 50%, and 25% of the LR. The lime cake and calcite were also applied in either a layer between the coal waste and topsoil or mixed into the topsoil and coal waste. Each plot was hydroseeded with grasses and planted with trees. In each plot, surface runoff and subsurface water were collected. The lime cake treatments increased the pH of coal waste from 3.5 to 6, and neutralized the pH of the runoff and leachate of the coal waste from 4.3 to 6.7.

• Journal of the Korea Safety Management & Science
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• v.18 no.4
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• pp.1-9
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• 2016

In recent years, urban areas occurred several times a sinkhole. In Korea, this limestone area where the sink hole sink holes occur based on not much was seen as a very rare phenomenon. However, the occurrence of accidents in recent Subsidence and urban areas is occurring in the limestone sinkhole may yet see another one called artificial Subsidence phenomenon. Subsidence in urban areas can have various causes, such as depression groundwater level changes due to the influence of soil, underground, etc. underground utilities by anthropogenic actions. But a lot of research on natural sinkhole by geological experts continued steadily since the past Subsidence that occurred in recent years the city has become an urgent problem to formulate a countermeasure to be very concerned about the human and material damage. In this study, the city by analyzing existing research on the causes and countermeasures of Subsidence recently released look at the announced sinkhole, published statistics and cases of Subsidence data, and overseas corresponding practices in each relevant agencies and to suggest measures for local Subsidence.

• Journal of Korea Soil Environment Society
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• v.2 no.1
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• pp.51-61
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• 1997

The objective of this study is to evaluate the feasibility of Pumping-and-Treatment system (PTS) for remediation of the saturated zones contaminated with NAPLs. A simulation is carried out for the removal of DNAPLs (denser-than-water non-aqueous phase liquids) and LNAPLS (lighter-than-water non-aqueous phase liquids) distributing at and below the water table. In the study, LNAPL and DNAPL are assumed to be n-hexane and 1,1-dichloroacetone, respectively. The model system studied consists of four heterogeneous soil layers with different permeabilities. Groundwater flows through the bottom layer and a pumping well is located under the initial water table. The time-driven deformation of the water table and removal efficiency of contaminants are estimated after vacuum application to the inlet of the well. In the calculation, FVM (Finite Volumetric Method) with SIMPLEC algorithm is applied. Results show that removal efficiencies of both DNAPL and LNAPL are negligible for the first 5 days after the PTS operation. However, when the cone-shape water table is formed around the inlet of the pumping well, the rapid removal rate is obtained since NAPLs migrate rapidly through the curvature of the water table. The removal efficiency of DNAPL is estimated to be higher than that of LNAPL due to the gravity. The results also show that the fluctuation or cone-shaped depression of the water table enhances the removal efficiency of NAPLs in saturated zones. The simulation results could provide a basis of the PTS design for the removal of NAPLs in saturated zones.

• Proceedings of the Korean Society of Soil and Groundwater Environment Conference
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• 2004.09a
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• pp.37-47
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• 2004

In Korea, over three hundreds of the coal mines were closed or abandoned due to the depression of the mining industry since the late 1980s. Many of them locate in the steep mountain valleys and the coal mine wastes had been disposed without a proper treatment From these mines, enormous amounts of coal mine overburdens have been abandoned in the slopes and the ample amounts of acid mine drainage (AMD) from either portal or overburdens have been discharging directly to the streams, causing the detrimental effects on soil and water qualities. Objectives of this research were to reclaim the coal mine overburdens using the lime waste cake from the soda ash production by stabilizing the overburden slopes, introducing the vegetation alleviate the environmental problems caused by the closed coal mines. The percentages of the grass distribution ratio (%) and the surface coverage ($\textrm{cm}^2$) in each treatment plot were determined during June to August after seed spraying grasses such as orchard grass (Dactylis glomerata L), Kentucky Bluegrass (Poa pratensis L.) and Eulalia (Miscanthus sinensis Anderss) at the end of May. The grasses covered only 15.5 % of the coal overburden plot at the early stage but the coverage was increased with time to 33% in August. Growth of such grasses was enhanced with the combined treatments of lime waste and topsoil resulting in the increased surface coverage by the grasses. The Increment of the surface coverage from June to August was higher with lime waste treatments. The distribution percentages and surface coverage were highest when the lime wastes were treated at 25 % of the lime requirement. This might be related with the high salt contents in the hire wastes. Results demonstrated that the amounts of lime wastes at 25% of the lime requirement were sufficient for neutralizing the acidic coal overburden and introducing the re-vegetation. Either layering between the coal waste and topsoil or mixing with coal overburdens could be adopted as the lime waste treatment method. The combined treatment of lime wastes and topsoil was recommended for re-vegetation in the coal overburden slopes. The lime wastes from the soda ash production might have a potential to be recycled for the reclamation of the abandoned coal mines to alleviate the environmental problems associated with coal mine waste.

• The Journal of Engineering Geology
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• v.27 no.2
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• pp.153-164
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• 2017

The geological factors for causing ground subsidence are very diverse. It can be affected by any geological or extrinsic influences, and even within the same geological factor, the soil depression impact factor can be determined by different physical properties. As a result of reviewing a large number of papers and case histories, it can be seen that there are seven categories of ground subsidence factors. The depth and thickness of the overburden can affect the subsidence depending on the existence of the cavity, whereas the depth and orientation of the boundary between soil and rock are dominant factors in the ground composed of soil and rock. In case of soil layers, more various influencing factors exist such as type of soil, shear strength, relative density and degree of compaction, dry unit weight, water content, and liquid limit. The type of rock, distance from the main fracture and RQD can be influential factors in the bedrock. When approaching from the hydrogeological point of view, the rainfall intensity, the distance and the depth from the main channel, the coefficient of permeability and fluctuation of ground water level can influence to ground subsidence. It is also possible that the ground subsidence can be affected by external factors such as the depth of excavation and distance from the earth retaining wall, groundwater treatment methods at excavation work, and existence of artificial facilities such as sewer pipes. It is estimated that to evaluate the ground subsidence factor during the construction of underground structures in urban areas will be essential. It is expected that ground subsidence factors examined in this study will contribute for the reliable evaluation of the ground subsidence risk.