• Journal of the Korean Geotechnical Society
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• v.19 no.6
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• pp.307-323
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• 2003

In this study the pilot test of C.G.S (Compaction Grouting System) as injection method by low slump mortar was performed and the results were analyzed in order to find out the application of this method to the soft ground and the effect of settlement restraint. The site for pilot test is adjacent to apartments supported by pile foundations. Sand drain method was performed previously as countermeasures against settlement, but settlement occurs continuously because this ground is very soft. Site investigations such as SPT, CPT and vane shear test were performed to determine the characteristics of ground improvement after the installation of C.G.S. Field measurements were performed on purpose to find out the displacement of ground during the installation of C.G.S. From the results of this study, C.G.S method can be optimized by the control of radius, space, depth, injection material and injection pressure. C.G.S improves soft ground with radial consolidation of adjacent soft ground. Considering that increase of N value to about 3, C.G.S can be considered as an effective method to increase the bearing capacity as well as constrain the settlement of soft ground. It is also expected to be economic and effective in the improvement of ground when it is used in applicable sites.

• Geomechanics and Engineering
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• v.19 no.4
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• pp.315-327
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• 2019

Deep excavations for development of subway systems in metropolitan regions surrounded by adjacent buildings is an important geotechnical problem, especialy in Tabriz city, where is mostly composed of young alluvial soils and weak marly layers. This study analyzes the wall displacement and ground surface settlement due to deep excavation in the Tabriz marls using two dimensional finite element method. The excavation of the station L2-S17 was selected as a case study for the modelling. The excavation is supported by the concrete diaphragm wall and one row of steel struts. The analyses investigate the effects of wall stiffness and excavation width on the excavation-induced deformations. The geotechnical parameters were selected based on the results of field and laboratory tests. The results indicate that the wall deflection and ground surface settlement increase with increasing excavation depth and width. The change in maximum wall deflection and ground settlement with considerable increase in wall stiffness is marginal, however the lower wall stiffness produces the larger wall and ground displacements. The maximum wall deflections induced by the excavation with a width of 8.2 m are 102.3, 69.4 and 44.3 mm, respectively for flexible, medium and stiff walls. The ratio of maximum ground settlement to maximum lateral wall deflection approaches to 1 with increasing wall stiffness. It was found that the wall stiffness affects the settlement influence zone. An increase in the wall stiffness results in a decrease in the settlements, an extension in the settlement influence zones and occurrence of the maximum settlements at a larger distance from the wall. The maximum of settlement for the excavation with a width of 14.7 m occurred at 6.1, 9.1 and 24.2 m away from the wall, respectively, for flexible, medium and stiff walls.

• Journal of the Korean Geotechnical Society
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• v.18 no.3
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• pp.51-59
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• 2002

This paper deals with development of a damage risk assessment system for adjacent buildings to under-passing tunnel face considering 3D-ground movement. The system consists of building and ground information module, monitoring data module, settlement evaluation module, and building damage risk assessment module. The major modules, settlement evaluation module and building damage assessment module, are based on settlement estimation model suggested by Attewell et al (1982) and the building damage assessment method by Mair et al. (1996). After estimating 3D-ground movements due to tunneling with settlement evaluation module, damage assessment far buildings is performed using building damage risk assessment module. The developed system has two major functions; 1) calculation of 3D-settlement with ground loss ($V_{s}$)or maximum settlement ($w_{max}$) and inflection point (i) using various empirical formulae, monitoring data, numerical results, and so on; 2) assessment of damage risk for adjacent buildings of arbitrary section with position change of tunnel face. The field data given by Boscadin and Cording (1989) leer the case of two-storied masonry building near the Metro tunnel in Washington D.C. was simulated to verify the applicability of the developed system.

• Explosives and Blasting
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• v.17 no.4
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• pp.67-88
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• 1999

Ground settlements induced by tunnel excavation cause the foundations of the neighboring superstructures to deform. An expert system called NESASS was developed to analyze the structural safety of such superstructures. NESASS predicts the trend of ground settlements to be resulted from tunnel excavation and carries out a safety analysis for superstructures on the basis of the predicted ground settlements. Using neural network techniques, NESASS learns a data base consisting of the measured ground settlements collected from numerous actual fields and infers a settlement trend at the field of interest. NESASS calculates the magnitudes of angular distortion, deflection ratio, and differential settlement of the structure and, in turn, determines the safety of the structure. In addition, NESASS predicts the patterns of cracks to be formed on the structure using Dulacskas model for crack evaluation. In this study, the ground settlements measured from the Seoul subway construction sites were collected and sorted with respect to the major factors influencing ground settlement. Subsequently, a database of ground settlement due to tunnel excavation was built. A parametric study was performed to verify the reliability of the proposed neural network structure. A comparison of the ground settlement trends predicted by NESASS with the measured ones indicates that NESASS leads to reasonable predictions. An examples is presented in this paper where NESASS is used to evaluate the safety of a structure subject to deformation due to tunnel excavation near to the structure.

• Proceedings of the Korean Geotechical Society Conference
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• 2005.10a
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• pp.330-335
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• 2005

Reliable predictions of the movement of earth retaining structures and the ground adjacent to braced walls in urban excavation are often difficult due to many variable factors. The ground settlement and the damage of adjacent structures in urban excavation has been an important issue. Therefore, the stability of the adjacent structures must be secured with the excavation support and research on the protection of adjacent structure is necessary. This study showed a countermeasure method for case of damage behavior in urban excavation.

• Journal of the Korean GEO-environmental Society
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• v.10 no.6
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• pp.35-48
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• 2009

An excessive ground displacement occurs with excavating tunnel in a fault zone because the fault has properties of soft ground in generally. It may have had a bad influence to adjacent structure. So, rapid reduction of ground strength by groundwater inflow should be prevented. It must be established for an impervious and reinforcing effect of ground to ensure a tunnel stability. The ground settlement and reinforcing effects were estimated by numerical analyses on tunnel through 570 m sector in Yangsan fault zone of Keongbu high-speed railway. Settlements evaluated by numerical analysis is similar to those calculated by using equation of Loganathan & Poulo. It was shown that reliable estimate of ground settlement by applying a prediction equation is possible. Applicability of adopted tunnel reinforcement method in fault zone was investigated by results of pilot construction and numerical analysis. Results from this study indicate that the adopted reinforcement method make tunnel displacements and member stresses restrain in design criteria.

• Proceedings of the Korean Geotechical Society Conference
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• 2006.03a
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• pp.268-275
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• 2006

Excavation works of cylindrical shafts and tunnels for the construction of a variety of infrastructures have been frequently going on in the urban areas. When ground excavations of cylindrical shafts and shallow tunnels proceed in the ground condition of high water level and silt particle component, ground water drawdown involving soil particle migration causes loosening of ground around tunnels and shafts, causes settlement and deformation of ground. Damages due to ground sinking and differential settlement can occur in the adjacent ground and structures. The extent and possibility of damage relevant to ground water drawdown and soil particle migration can't be so precisely expected in advance that we will face terrible damages in case of minor carefulness. This paper introduces two examples of construction management where using incremental deformation graph of inclinometer, we noticed the possibility of soil migration due to ground water drawdown in the excavation process of vertical shaft and shallow tunnel, analysed a series of measurement data in coupled connection, properly prepared countermeasures, so came into safe and successful completion of excavation work without terrible damages. The effort of this article aims to improve and develop the technique of design and construction in the coming projects having similar ground condition and supporting method.

• Journal of the Korean GEO-environmental Society
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• v.17 no.8
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• pp.39-44
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• 2016

Ground deformation around construction site in urban area where typically adjacent structures are located needs to be strictly controlled. Accordingly, it is very important to precisely monitor the ground deformation. Settlement beacon is typically employed to measure the ground deformation, but meanwhile the rapid development in electronic technology enables 3D image scanner to become available for measuring the ground deformation profile in usual construction sites. With respect to the profile measurement, the 3D scanner has an advantage, whereas its accuracy is somewhat limited because it does not measure the displacement directly. In this paper, we developed a conditional merging technique to combine the ground displacement measured from settlement beacon and the profile measured by the 3D scanner. Synthetic ground deformation profile was generated to validate the proposed technique. It is found that the ground deformation measurement error can be reduced significantly via the conditional merging technique.

• Proceedings of the Korean Geotechical Society Conference
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• 1996.03a
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• pp.65-86
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• 1996

• Geomechanics and Engineering
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• v.21 no.2
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• pp.95-102
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• 2020

Population concentration in urban areas has led traffic management a central issue. To mitigate traffic congestions, the government has planned to construct large-cross-section tunnels deep underground. This study focuses on estimating the damage caused to frame structures owing to tunnel excavation. When constructing a tunnel network deep underground, it is necessary to divide the main tunnel and connect the divergence tunnel to the ground surface. Ground settlement is caused by excavation of the adjacent divergence tunnel. Therefore, predicting ground settlement using diverse variables is necessary before performing damage estimation. We used the volume loss and cover-tunnel diameter ratio as the variables in this study. Applying the ground settlement values to the settlement induction device, we measured the extent of damage to frame structures due to displacement at specific points. The vertical and horizontal displacements that occur at these points were measured using preattached LVDT (Linear variable differential transformer), and the lateral strain and angular distortion were calculated using these displacements. The lateral strain and angular distortion are key parameters for structural damage estimation. A damage assessment chart comprises the "Negligible", "Very Slight Damage", "Slight Damage", "Moderate to Severe Damage", and "Severe to Very Severe Damage" categories was developed. This table was applied to steel frame and concrete frame structures for comparison.