• The Journal of Engineering Geology
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• v.6 no.3
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• pp.137-153
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• 1996

The purpose of this study is to investigate the possibilities of identifying and detecting underground cavities using seismic waves recorded by the fixed and mobile stations. During 18 months of field work we recorded chemical explosions near the Bongdarn station. Seismic Stations were installed on the free surface and underground inside the Samba mine. The seismograms at the fixed(lorg-term) seismic station show abrupt change of polarization characteristics which can he associated with the appearance of P-to-S converted phase(PS) at 150 ~ 200 msec after the first P arrival. This result indicates that converted phases are generated very near to the Bongdarn station at a depth of 190m. Shear-wave splitting phenomena have also been observeci The time delay between fast shear(fS) and slow shear(sS) waves ranges between 30 and 60 msec(average is 42 msec). However, exact time delay between the fast and the slow shear waves can not be accurately measured because of the very short time delay and limitation of sampling rate. Chemical explosion experiments were recorded at stations along various paths to contrast the seismic response of areas with and without cavities. The seismograms recorded at the stations installed at cavity areas show an abrupt change of polarization characteristics but not on the other stations. Seismic waves propagating through the cavity are characterized by the attenuation of high frequency waves and predominantly low frequency seismic waves after the S wave arrivals.

• Journal of the Korean Geotechnical Society
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• v.37 no.11
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• pp.93-105
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• 2021

In this study, we evaluated the effect of soil fine contents on the formation of underground cavities and ground cave-ins induced by damaged sewer pipes. Simulating the domestic rainfall conditions and ground conditions, model tests were performed under three different fine particle contents conditions (7.5%, 15%, and 25%). By repeating the groundwater supply and drainage twice, ground settlement and the amount of discharged soil were obtained. Also, digital images were taken at regular time intervals during the model tests, and internal displacement and deformation were measured using PIV technique. As the cycles were repeated, the soil with high fine content showed greater resistance to the formation of underground cavities. The ground cave-ins, identified by the collapse of the surface, occurred only when the fine particle content was 15%. It is presumed to be due to the suffusion phenomenon; further study was needed to investigate the effect of fine particle contents on the suffusion phenomenon and associated changes of soil strength.

• Journal of the Korean GEO-environmental Society
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• v.19 no.2
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• pp.5-12
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• 2018

Underground cavities could induce road subsidence, which have been frequently observed in urban areas. Therefore, adequate backfilling materials and the restoring methods of the cavities are required to prevent the road subsidence. The objective of this paper is to evaluate the suitability of backfilling methods using foaming lightweight grouting materials considering the flow values, unit weights, and air contents at slurry and expanded states, and unconfined compressive strengths. The grouting materials consist of water, cement, and foaming agent whose proportions of water, cement, and foaming agent are 25: 25: 1.0 and 25: 25: 1.2. The flow values of the two materials are greater than 200 mm, and their unconfined compressive strengths at 28 days age are smaller than 1.3 MPa. From the results, the two proportions of materials are expected to be effectively used as a backfilling material. However, the material components should be carefully mixed because poor mix of these materials could induce non-homogeneous distribution of air bubbles. The unexpectedly non-homogeneous distribution of air bubbles may induce significant cracks or additional cavities.

• Tunnel and Underground Space
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• v.27 no.4
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• pp.205-216
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• 2017

Fluctuations in groundwater level are the major cause of ground subsidence in the abandoned limestone mine. In this study, evaluation of groundwater flow under three different cases of natural condition, aggregate-filling, temporary drainage in groundwater-saturated limestone mine cavities was executed by 3-dimensional analysis. In the case of aggregate-filling, although the water level both in the upper ground of mine cavities and an agricultural watershed was elevated, it was lower than the water level fluctuation of an agricultural water use and rainfall and the flow rate was similar to the flow rate of natural condition. In the case of temporary drainage, as the water level in the upper ground of mine cavities and an agricultural watershed decrease rapidly and the flow rate has increased by 25times, so the risk of ground subsidence increased.

• Tunnel and Underground Space
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• v.26 no.6
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• pp.455-465
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• 2016

The collapse of underground mine development void for mineral resources can cause the subsidence of ground surface. In order to prevent the subsidence of ground, data such as maps or pictures of past mining site is important information for current mine reclamation works. In particular, mine subsidence management was based on mining maps and pictures. The process of the mining area surveys, safety evaluation, and ground reinforcement are normally possible with information such as maps and pictures in past mining. During the Japanese colonial period and 1960's, a lot of mines were developed in Korea indiscriminately. However, mining information at that time is limited to use. In the future, mining information will become even more rare. MIRECO intends to establish a realistic alternative solution. In this study, the basic numerical information of developed mine tunnels in Korea is statistically reviewed, and advanced underground cavity measuring technology was studied. 4,473 mine tunnel opening data of 1,784 abandoned mines in korea were collected and sorted. As a result of the analysis, the average value of small mine tunnel openings in Korea was 1.982 m in height and 1.959 m in width. The mean value of shape factor was analyzed as 0.485. The summary of these numerical mine data will be helpful for understanding and researching Korean abandoned mines. Therefore, the development of measurement technology for abandoned mine cavities and tunnels is expected to facilitate more effective mine subsidence management works in Korea.

• Tunnel and Underground Space
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• v.2 no.2
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• pp.237-250
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• 1992

The cavities formed by the excavation of coal seam cause unstable within rock body, leading to large displacement around adjacent roadway. This displacement brings the closure of roadway and deformation of support. Therefore, it is necessary to understand and predict the deformation characteristics of roadway while coal seam is under excavation. In this study, the observed displacements are compared with the calculated ones through the analysis using Linear Boundary Element Mothod under the elastostatic conditions, in order to determine the virgin stress state and deformation modulus which affect the deformation characteristices.

• Tunnel and Underground Space
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• v.1
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• pp.32-38
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• 1991

9 nuclear power plants are presently in operation in Korea. They produce radioactive waste of which the most long-lived radioactive elements need to be safely stored for hundreds of thousands of years, isolated from humanity and the environment. The safe disposal of high level radioactive waste in mined cavities requires knowledge of the mechanical. thermal and fluid flow characteristics of rock as perturbed by a thermal pulse The literature review was performed to assemble data on the following properties: modulus tensile strength compressive strength thermal expansion specific heat, thermal conductivity thermal diffusivity and permeability.

• Journal of Korean Tunnelling and Underground Space Association
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• v.21 no.5
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• pp.699-715
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• 2019

Recently, in urban areas, cavities and ground collapse adjacent to underground structures are frequently reported. Several studies on the cavity generation by structure cracks have been made, however they are focused on the cause of cracks and settlement of the ground. In this paper, soil particle and groundwater discharge through pipe cracks and cavity generation mechanism are investigated. The theoretical analysis of the groundwater, which is the main factor of the drainage of the soil particles, and the particle transport mechanism and flow characteristics were investigated. An experimental model test was carried out to identify the mechanism of cavity generation by underground buried pipe cracks. The soil particle weight of discharge through the cracks, and the movement characteristics of the particles were analyzed using PIV. In this study, it is clearly identified that soil particle movements, cavity generation and ground collapse that occur in the ground are basically caused by the movement of groundwater.

• Geophysics and Geophysical Exploration
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• v.11 no.4
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• pp.368-372
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• 2008

This study evaluates the usefulness and capability of surface electrical resistivity technique for identifying the weak zones or subsurface cavities in karst area with limestone formation. Weak zones or cavities near surface can be potentially dangerous and several problems are associated with collapse of roads or buildings accompanied by subsidence phenomena. In this paper, both two and three dimensional resistivity investigation were conducted to investigate subsidence along a road in Yongweol-ri, Muan-gun, South Korea. The results of the resistivity survey using dipole-dipole array provide a clear view of the weathered regolith, the distribution of weak zones or cavities and bedrock. Several low resistivity areas were identified and subsequent drilling led to the discovery of several weak zone or clay-filled underground cavities. The drilling results show excellent correlation with the resistivity images. It is illustrated, the ability of electrical technique to produce high resolution images of subsurface, which are useful for subsidence assessment. Also the results of this study have demonstrated that two and three dimensional electrical resistivity surveys are useful for delineating the subsidence area. Based on resistivity imaging, the map of hazardous zone has been developed.

• Tunnel and Underground Space
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• v.31 no.4
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• pp.211-220
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• 2021

Tunnel collapse often occurs during deep underground tunneling (> 40 m depth) in South Korea. Natural cavities as well as water supply pipes, sewer pipes, electric power cables, artificial cavities created by subway construction are complexly distributed in the artificial ground in the shallow depths of the urban area. For deep tunnel excavation, it is necessary to understand the properties of the ground which is characterized by porous elements and various geological structures, and their influence on the stability of the ground. This study analyzed geological factors for risk assessment in deep excavation in South Korea based on domestic and overseas case study. As a result, a total of 7 categories and 38 factors were derived. Factors with high weights were fault and fault clay, differential stress, rock type, groundwater and mud inrush, uniaxial compressive strength, cross-sectional area of tunnel, overburden thickness, karst and valley terrain, fold, limestone alternation, fluctuation of groundwater table, tunnel depth, dyke, RQD, joint characteristics, anisotropy, rockburst and so forth.