• Journal of the Korean GEO-environmental Society
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• v.20 no.2
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• pp.49-58
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• 2019

A study on the analysis of underground ground condition using 3D-GPR exploration was carried out in this paper. The test bed was constructed similar to the field, and the detection analysis was carried out for each depth of cavity and underground burial. Through this, we were able to know the permittivity of the ground by inversion, and we could confirm the depth of detection for the joint by accurate calculation. We confirmed the signal waveforms in the cavity under the road through 3D-GPR exploration, analyzed more quantitatively in subjective and empirical analysis. The subsidence and depth of the subsurface settlement can be observed through 3D-GPR survey, and ground condition change after the ground reinforcement can be confirmed through the exploration section.

• Journal of the Korean Geosynthetics Society
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• v.18 no.4
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• pp.299-306
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• 2019

In this study, a model experiment that simulates the behaviour of the ground composed of several compacted layer was intended to measure the loosened area in the event of a ground cavity through a LAD (Loosened area detector). It was confirmed that the size of the cone diameter was affected by the ground composed of fine grain + granulated soil layered through the model soil. In order to select the appropriate cone type, a scale effect experiment was conducted. From the test results, a micro-cone was chosen for the most suitable indoor model experiment. In the case of applying LAD in this study, the loosening condition of the ground was determined by the rapid change in penetration resistance caused by the difference in the boundary surface and relative density due to the compaction of the ground for indoor model testing. The range of loosened area occurring in the cavity was estimated through the penetration resistance characteristics on the ground, and the failure area was identified through the reduction rate of penetration resistance in the loosening area.

• Journal of the Korean GEO-environmental Society
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• v.7 no.3
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• pp.69-76
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• 2006

In this study, an experimental study in sand ground that was prepared by raining method was performed for modeling the bearing capacity behavior of strip footing above a cavity. The critical range of bearing capacity of the strip footing affected by underground cavity was investigated by comparing results between experiment and theory. The size of the critical region depends on several factors such as footing shape, soil property, cavity size and cavity shape. The ultimate bearing capacity was more influenced by the depth of the underground cavity than the eccentricity of the underground. In addition, an underground cavity influences on not only the decrease of the bearing capacity, but also the differential settlement of a strip footing.

• The Journal of Engineering Geology
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• v.27 no.3
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• pp.217-231
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• 2017

The subsidence of ground in urban area can be caused by the occurrence of the cavity and the change in ground volumetric water content. The objective of this study is the detection of abnormal area of ground in urban area where the cavity or the change in ground volumetric water content is occurred by the ground penetrating radar signal. GPR survey is carried out on the test bed with a circular buried object. From the GPR survey, the signals filtered by the bandpass filtering are measured, and the methods consisting of gain function, time zero, background removal, deconvolution and display gain are applied to the filtered signals. As a result of application of the signal processing methods, the polarity of signal corresponds with the relation of electrical impedance of the cavity and the ground in test bed. In addition, the relative permittivity calculated by GPR signal is compared with that of predicted by volumetric water content of the test bed. The relative permittivities obtained from two different methods show similar values. Therefore, the abnormal area where the change in ground volumetric water content is occurred can be detected from the results of the GPR survey in case the depth of underground utilities is known. Signal processing methods and estimation of relative permittivity performed in this study may be effectively used to detect the abnormal area of ground in urban area.

• Journal of Ecology and Environment
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• v.30 no.1
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• pp.49-56
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• 2007

We placed and monitored 2,137 nest boxes to determine how the size of the entrance hole and the box placement influenced nest box selection by secondary cavity-nesting birds and to derive recommendations for the use of nest boxes for management of cavity-nesting birds in forested environments. A total of 566 pairs of seven bird species used the nest boxes from 1997 to 2006, 562 of which were secondary cavity-nesters. Sympatric tits such as varied tits (Parus varius), great tits (P. major), and marsh tits (P. palustris) were common breeding birds in nest boxes, and showed clear preferences for 4.0 cm, 3.5 cm and 3.0 cm nest holes, respectively. Tree sparrows (Passer montanus) and Eurasian nuthatches (Sitta europaea) preferred 4 cm and 3.5 cm holes, respectively. We did not detect selection for the directional orientation for the entrance hole, but the birds appeared to avoid nest boxes that faced steep or gentle upward slopes and those less than 1.8 m from the ground. These results are probably related to avoidance of disturbance and predation. We suggest that diverse species can be supported by the placement of nest boxes with entrance holes of various sizes and that specific species can be targeted by selecting the hole sizes preferred by those species. To attract secondary cavity-nesters, managers should avoid placing nest boxes close to the ground and facing hills. This study also suggests that careful selection and placement of nest boxes is needed to avoid biases in research using nest boxes.

• Journal of electromagnetic engineering and science
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• v.14 no.3
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• pp.306-313
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• 2014

A Fabry-Perot resonator cavity antenna for Ku-band application is presented in this paper. The Fabry-Perot cavity is formed by a ground plane and a frequency selective surface (FSS) made of a circular hole array. The cavity resonance is excited by a single-feed microstrip patch located inside the cavity. The measured results show that the proposed antenna has an impedance bandwidth of approximately 13% ($VSWR{\leq}2$) and a 3-dB gain bandwidth of approximately 7%. The antenna produces a maximum gain of 18.5 dBi and good radiation patterns over the entire 3-dB gain bandwidth. The antenna's very thin profile, high directivity, and single excitation feed make it promising for use in wireless and satellite communication applications in a Ku-band frequency.

• Journal of the Korean Geotechnical Society
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• v.35 no.11
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• pp.37-49
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• 2019

In order to analyze the effect of burial depth on the generation of ground cavities and cave-ins, a series of model experiments with different height of model ground were performed. Digital images of the model ground were captured to evaluate the internal deformation of the model grounds by adopting the PIV (Particle Image Velocimetry) technique. Additionally, the vertical displacement at the surface, the size of the cavity, and the weight of the discharged soil were measured in each test. The results indicate that the model ground with low burial depth, which does not satisfy the criterion, was more vulnerable to ground cavities and cave-ins than the model ground with high burial depth.

• Journal of the Korean Geotechnical Society
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• v.34 no.8
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• pp.27-36
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• 2018

The collapse behavior of ground subsidence caused by continuous loss of particles depends on the saturated condition and density of the ground. In this study, types of ground subsidence were classified based on the saturated condition and each type was performed on the different relative density to analyze the influence factors on the collapse behavior by distinct element method. According to analysis results, the relatively small amount of settlement occurred on the dense ground and a cavity was created under dense-unsaturated ground. In contrast, loose ground showed the large amount of settlement and collapsed immediately without cavity formation even if the unsaturated ground was simulated. The results demonstrated that because the relative density has influence on the mechanical interlocking and saturated condition has influence on the inter-particle force, these are important factors to change the collapse behavior.

• Journal of Korean Tunnelling and Underground Space Association
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• v.20 no.2
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• pp.287-303
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• 2018

In recent years, the occurrence of ground subsidence phenomenon is frequent in Korea. The Korean government has enacted a special law on underground safety and the law will be enforced from January 1, 2018. Under this new law, underground excavation should be assessed for underground safety impacts. After excavation construction, periodic geophysical surveys should be conducted to investigate the occurrence of underground cavities. When underground cavities were discovered, the underground safety was assessed through numerical analysis. However, it is controversial because the method of numerical modeling the discovered underground cavity is due to be established. In this study, the effect of the depth of the underground cavity from the shape of the underground cavity to the underground cavity was studied using a continuum analysis program. In this study, a method to reflect the shape of the underground cavity to the numerical modeling is presented. The relationship between the shape and depth of the underground cavity, and the factor of safety calculated by the shear strength reduction method (SSR) is presented. The results of this study are expected to form the basic data on underground safety impact assessment.

• Journal of the Korean Geosynthetics Society
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• v.17 no.4
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• pp.141-155
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• 2018

Recently, the number of ground subsidence resulting from underground cavity has been increased. Accordingly, the importance of restoration of stress release zone around the underground cavity has been emphasized. The stress release zone is composed of low density soils having extremely low stiffness and degree of compaction, which can lead to additional cavity expansion and collapse of overlying ground. Therefore, in this study, the suitability of restoration method of underground cavity using expansive material for reinforcement of stress release zone around the cavity is verified. The basic physical properties and expansion characteristics of the expansive material were examined. The experiment equipment capable simulating of stress release zone was developed and is used to investigate the effect of expanding material on stress release zone. The stress release zone was simulated using the spring in numerical analysis. The factors of the volume ratio of the underground cavity to the expansion material, the degree of stress relaxation, and the shape of the cavity were varied in numerical simulations, and the behavior of stress release zone was analyzed based on the numerical analysis results. Analysis variables are factors that affect each other. Also, filling of underground cavity and capacity of restoration of stress release zone were confirmed when the expansive material was inserted into underground cavity.