• Journal of the Korean Geotechnical Society
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• v.37 no.7
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• pp.13-23
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• 2021

If roads, bridges, buildings, etc. are built on the ground with soft clay or organic soil, there may be a lot of problems in geotechnical engineering such as settlement and stability due to the large settlement and lack of bearing capacity. In extreme cases, it may appear due to shear failure or collapse of the constructed structure, so a ground improvement method is indispensable to increase the strength of the ground and to suppress settlement. In this study, the settlement according to each groundwater level condition was analyzed using the measurement results for the groundwater level conditions, one of the important factors in predicting the settlement in dredged and reclaimed ground, and the groundwater level conditions applied to the settlement analysis were proposed by comparing it with settlement generated 5 years after construction. As a result of the analysis, it is judged that it is reasonable to apply the measured groundwater level during construction and the low water ordinary neap tide (L.W.O.N.T) during load application for the groundwater level in the settlement analysis. In addition, in the case of the dredged and reclaimed ground, it is estimated that the water pressure acting on the clay layer is nonlinear, as the result of the observations of the head of water at the observation points above and below the in-situ clay layer were different.

• Journal of the Korean Geotechnical Society
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• v.30 no.10
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• pp.19-31
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• 2014

In order to investigate ground state change visually in physical model during centrifuge testing, electrical resistivity survey was adopted. Commercial resistivity survey equipment verified at various in-situ sites was utilized. The resistivity survey equipment installed in centrifuge facility was remotely controlled through intranet and electrical resistivity images obtained while centrifuge testing was being checked by real-time inversion. To verify the stable operation of the developed resistivity survey system, preliminary tests were conducted. Model ground was uniformly constructed using unsaturated soil and saline water was dropped on the ground surface to simulate contaminant flow situation. During the 10 g centrifuge tests, electrical resistivity was continuously detected and the testing results were compared with those of identically carried out 1 g centrifuge tests. In addition, the electrical resistivity was directly measured immediately after the centrifuge test by open cutting the model. Finally, reliability of electrical resistivity survey in the centrifuge test was verified by comparing those testing results.

• Journal of the Korean Geotechnical Society
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• v.39 no.12
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• pp.103-114
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• 2023

Monitoring the site of an underground construction wall is crucial to confirm the stability of the supports and ground due to excavation. In particular, it is essential to maintain the accuracy of a load cell gauge, which identifies the load of the support transmitted from the excavated ground. However, research on verification methods and regulations that can identify the accuracy of load cell gauges at construction sites is inadequate, which is a problem as load cell gauges are installed without proper performance inspections. In this study, performance tests were conducted by a complete investigation of load cell gauges sold in Korea and comparing them with foreign products to determine defect causes. In addition, the criteria for selecting a load cell gauge were presented, and the results of this study were considered to help select a highly reliable load cell gauge.

• Geophysics and Geophysical Exploration
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• v.11 no.4
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• pp.326-334
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• 2008

The resistivity method has been used to image the electrical properties of the subsurface. Especially, this method has become suitable for monitoring since data could be rapidly and automatically acquired. In this study, we developed a time-lapse inversion algorithm for the interpretation of resistivity monitoring data. The developed inversion algorithm imposes a big penalty on the model parameter with small change, while a minimal penalty on the model parameter with large change compared to the reference model. Through the numerical experiments, we can ensure that the time-lapse inversion result shows more accurate and focused image where model parameters have changed. Also, applying the timelapse inversion method to the leakage detection of an embankment dam, we can confirm that there are three major leakage zones, but they have not changed over time.

• Journal of Korean Tunnelling and Underground Space Association
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• v.17 no.4
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• pp.441-455
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• 2015

In the present study, a face safety monitoring system was developed that will enable judging collapse risks on faces during tunnel construction to secure workers' safety. This system enables detecting abnormal behaviors of faces by analyzing the displacement of faces measured in real time using the x-MR control chart technique. In addition, an algorithm to judge false alarms was developed so that abnormal behaviors of faces and errors occurring in the process of work can be distinguished from each other by comparing the number of measured values exceeding the management criteria and moving range k. The results of the present study are applicable to real-time monitoring of behavior on the face in dangerous ground sections to minimize damage to workers.

• Journal of the Korean Geotechnical Society
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• v.35 no.12
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• pp.123-134
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• 2019

This study presents dynamic responses of circular pipe models as a part of fundamental studies on dynamic stability monitoring of the large circular steel pipe cofferdam with the ship collision. Small-scaled laboratory experiments are performed with a single and bolted circular steel pipes with a diameter, thickness, and height of 30, 0.4, 90 cm, respectively. The bolted circular steel pipe is configured with three segments of 30 cm in height. Circular steel pipe models are embedded in a soil tank, all 1 m in length, width, and height. The thickness of soil in the soil tank is set at 23 cm. The ship collision is simulated with a hammer impacting. The dynamic responses are investigated with different water levels of 25, 40, 55, and 70 cm. Experimental results show that a signal energy decreases with increasing water level. More sensitive reduction in the energy appears for the bolted circular steel pipe. A predominant frequency decreases with increasing water level for both single and bolted steel pipes. The minor reduction in the frequency appears for the bolted circular steel pipe under the water level of 70 cm. This study suggests that the signal energy and frequency response is useful for the dynamic stability monitoring of the large circular steel pipe cofferdam.

• Journal of the Korean Geotechnical Society
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• v.38 no.11
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• pp.43-54
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• 2022

The settlement at the railroad foundation is often the leading cause of track irregularity and potential derailment. The control of such deformation is considered necessary in track maintenance practice. Nevertheless, the monitoring process performed by in situ surveying requires an excessive amount of manpower and cost. The InSAR, a remote sensing technique by RADAR satellite, is used to overcome such a burden. The PS-InSAR technique is preferred for a long-term precise monitoring method. However, this study aims to obtain relatively brief analysis results from only two satellite images using the D-InSAR technique, while a minimum of 25 images are required for PS-InSAR. This study verifies the precision of D-InSAR within a few millimeters by inspecting railroad facilities and land settlements in Korea Railroad Research Institute's test track with images from TerraSAR-X Satellite. Multiple corner reflectors were adopted and installed on an embankment and the building roof to raise the surface reflectivity. Those reflectors were slightly adjusted periodically to verify the detecting performance. The results revealed the optimum distance between corner reflectors. Further, the deformation of railway tracks, slopes, and concrete structures was analyzed successively. In conclusion, this study indicates that the D-InSAR technique effectively monitors the short-term deformation of a broad area such as railway structures.

• Journal of the Korean Geotechnical Society
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• v.26 no.5
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• pp.37-48
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• 2010

In this study, the seepage flow monitoring method by the hydraulic head loss rate was developed for the purpose of application to offshore construction site enclosed by cofferdams in which seepage force varies periodically. The amount of the hydraulic head loss rate newly defined in this graph was in a range between 0 and 1. The zero of the rate means the existence of flow with no seepage resistance. The 1 of the rate means no seepage flow through the ground. The closer to 1 the coefficient of determinant in the hydraulic head loss graph is, the more the ground through which seepage water flows is stable. The closer to 0 the coefficient of determinant in the hydraulic head loss graph is, the more the ground through which seepage water flows was unstable and the higher the possibilities of existence of empty space or of occurrence of piping on the seepage flow pass in the ground is. The hydraulic head loss graph makes it possible to monitor sensitively the situation of seepage flow state, and the graph helps to understand easily the seepage flow state at the specific section on the whole cofferdam.

• Journal of the Korean Geotechnical Society
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• v.40 no.4
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• pp.61-68
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• 2024

Monitoring the injection degree of biopolymers in soils is required in estimating the performance of biopolymer-treated grounds. In this study, the degree of saturation and injection process of biopolymer solutions in sandy soils were evaluated using electrical resistivity. To assess the changes in electrical resistivity according to the contents of the biopolymer solutions, electrical resistivities were measured for Jumunjin sand-xanthan gum biopolymer solution (weight concentration of 0.5%) mixtures with different degrees of saturation of 20%, 40%, 60%, 80%, and 100%. In addition, electrical resistivities were measured at eight layers in oven-dried Jumunjin sand during the upward injection of the xanthan gum biopolymer solution to monitor the injection process. Experimental results showed that the electrical resistivity decreased as the degree of saturation of the mixture increased, and their relationship was constructed. During the injection of the xanthan gum biopolymer solution into the sandy soils, the electrical resistivity decreased and converged and the degree of saturation at each layer could be estimated on the basis of the above-constructed relationship. This study demonstrated that electrical resistivity may be an effective physical property for monitoring the injection degree of biopolymer solutions in the ground.

• Proceedings of the Korean Geotechical Society Conference
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• 1999.03a
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• pp.293-300
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• 1999

The maintenance for the stability of tunnel, especially on downtown area, careful check must be considered during construction stage and after. Moreover we have to achieve the stability of tunnel by ground improvement and reinforcement when ground condition is bad or tunnel failures under the various ground conditions. In this paper, it is presented the case of tunnel failure and the state of restoration by ground reinforcements at seoul subway $\bigcirc$-$\bigcirc$ construction site. For the purpose of ground reinforcement, first, curtain wall was established by chemical grouting. Secondly, cement milk grouting was carried by upper part of tunnel crown. Also Boreholes loading test and tunnel monitoring were carried by in failure site for the long term stability of tunnel.