• Journal of the Korean Geotechnical Society
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• v.39 no.9
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• pp.13-24
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• 2023

To investigate the stability of temporary retaining walls during excavation, it is essential to develop reverse analysis technologies capable of precisely evaluating the properties of the ground and a learning model that can assess stability by analyzing real-time data. In this study, we targeted excavation sites where the C.I.P method was applied. We developed a Deep Neural Network (DNN) model capable of evaluating the stability of the retaining wall, and estimated the physical properties of the ground being excavated using a Differential Evolution Algorithm. We performed reverse analysis on a model composed of a two-layer ground for the applicability analysis of the Differential Evolution Algorithm. The results from this analysis allowed us to predict the properties of the ground, such as the elastic modulus, cohesion, and internal friction angle, with an accuracy of 97%. We analyzed 30,000 cases to construct the training data for the DNN model. We proposed stability evaluation grades for each assessment factor, including anchor axial force, uneven subsidence, wall displacement, and structural stability of the wall, and trained the data based on these factors. The application analysis of the trained DNN model showed that the model could predict the stability of the retaining wall with an average accuracy of over 94%, considering factors such as the axial force of the anchor, uneven subsidence, displacement of the wall, and structural stability of the wall.

• Journal of Korean Tunnelling and Underground Space Association
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• v.25 no.1
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• pp.13-26
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• 2023

Recently, as the development of underground spaces has become active due to rapid urbanization and population density, interest in the ground behavior according to the construction of underground spaces is increasing. In large cities with high population density and many buildings, ground subsidence has a great impact on structures and there may be a risk of collapse, so the analysis of ground behavior due to underground construction is essential. Previous studies have been conducted on the subsidence pattern of the surface and the deformation of the tunnel when constructing the tunnel, but analysis has rarely been conducted by using actual topographic information. Therefore, this study analyzed the difference in ground behavior between the actual topography and the flat topography. As a result, it was confirmed that ground settlement occurs at higher elevations, such as in mountainous topography, and when the numerical analysis is performed considering topographical information, the crown settlement of the tunnel is up to about approx. It showed a difference of 10 mm, and it was found that the sensitivity was less in the case of displacement of tunnel wall compared to the crown settlement and ground settlement. The numerical analysis considering the actual GIS-based topographic information presented in this study can be used to obtain more accurate surface subsidence data to understand the behavior of the upper structure due to tunnel excavation.

• Journal of the Korean Geotechnical Society
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• v.22 no.8
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• pp.77-88
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• 2006

In this study, the lateral behavior of Pile-Bent structures subjected to lateral loading was evaluated by a load-transfer approach. An analytical method based on the Beam-Column model and nonlinear load transfer curve method was proposed to consider material non-linearity (elastic and yielding) and $P-{\Delta}$ effect. Special attention was given to the lateral deflection of Pile-Bent structures depending on different soil properties, lateral load, slenderness ratio based on pier length and reinforcing effect of casing. From the results of the parametric study, it is shown that the increase of lateral displacement in a pile is much less favorable for an inelastic analysis than for an elastic analysis. It is found that for inelastic analysis, the maximum bending moment is located within a depth approximately 3.5D(D: pile diameter) below ground surface, but within 1.5D when $P-{\Delta}$ effect is considered. It is also found that the magnitude and distribution of the lateral deflections and bending moments on a pile are highly influenced by the inelastic analysis and $P-{\Delta}$ effect, let alone soil properties around an embedded pile.

• Journal of the Korean Geotechnical Society
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• v.39 no.7
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• pp.57-67
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• 2023

Slope failures during rainfall have been observed in mountainous areas of South Korea as a result of the presence of solar power facilities. The seepage behavior and pore pressure distribution differ from typical slopes due to the presence of impermeable solar panels, and the load imposed by the solar power structures also affects the slope behavior. This study aims to develop a method for evaluating the stability of slopes with solar power facilities and to analyze vulnerable points by considering the maximum slope displacement. To assess the slope stability and predict behavior while considering rainfall seepage, a combined seepage analysis and finite difference method numerical analysis were employed. For the selected site, various variables were assumed, including parameters related to the Soil Water Characteristic Curve, strength parameters that satisfy the Mohr-Coulomb failure criterion, soil properties, and topographic factors such as slope angle and bedrock depth. The factors with the most significant influence on the factor of safety (FOS) were identified. The presence of solar power facilities was found to affect the seepage distribution and FOS, resulting in a decreasing trend due to rainfall seepage. The maximum displacement points were concentrated near the upper (crest) and lower (toe) sections of the slope.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.28 no.3C
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• pp.179-186
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• 2008

Pressuremeter test estimates the deformational properties of soil from the relationship between applied pressure and the displacement of cavity wall. It is general to utilize the reloading curve for the estimation of deformational properties of soil because the initial loading curve can be affected by the disturbance caused by boring. On the other hand, the instrumental resolution or the variation of measured data makes it hard to estimate the maximum shear modulus from pressuremeter test results. This study suggested the methodology estimating the maximum shear modulus from pressuremeter test directly, based on the curve fitting of reloading curve. In addition, the difference was taken into account between the stress state around the probe in reloading and that of the in-situ state. Pressuremeter tests were conducted for 15 cases using a large calibration chamber, together with a number of reference tests. The maximum shear moduli taken from suggested method were compared with those from empirical correlation and bender element test.

• Journal of the Korean GEO-environmental Society
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• v.21 no.12
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• pp.5-10
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• 2020

In this study, the evolution of soil engineering property values according to excavation was analyzed through the inverse analysis for the OO deep excavation site located in Incheon. The stiffness of the ground was updated by comparing the horizontal wall deformation of the excavation support wall calculated by the finite element analysis at each stage of excavation and the value measured using an inclinometer. The updated stiffness was used to predict the response of the excavation support wall in the next excavation step. The finite element analysis method using the Hardening Soil model was used, and the stratum where the excavation support wall is located was selected as the stratum for the inverse analysis. The inverse analysis results showed that the stiffness value at the stiffness value at the initial stage of excavation is larger than the stiffness used in the original design. As the excavation proceeds, the stiffness calculated through the second inverse analysis was found to decrease compared to the value derived by the first inverse analysis. Therefore, it can be stated that the deformation of the excavation support wall can be accurately calculated through finite element analysis when an appropriate stiffness value is input according to the excavation stage.

• Tunnel and Underground Space
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• v.20 no.4
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• pp.267-276
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• 2010

In modern rock engineering practice, fully grouted rock bolting is actively employed as a major supporting system, so that understanding the behavior of fully grouted rock bolts is essential for the precise design of rock bolting. Despite its importance, the supporting mechanism of rock bolts has not been fully understood yet. Since most of existing analytical models for rock bolts were developed by drastically simplifying their boundary conditions, they are not suitable for the bolts of in-situ condition. In this study, 3-D elastic FE analysis of fully grouted rock bolts has been conducted to provide insight into the supporting mechanism of the bolt. The distribution of shear and axial stresses along the bolt are investigated with the consideration of different boundary conditions including three different displacement boundary conditions at the bolt head, the presence of intersecting rock joints, and the variation of elastic modulus of adjacent rock. The numerical result reveals that installation of the faceplate at the bolt head plays an important role in mobilizing the supporting action and enhancing the supporting capabilities of the fully grouted rock bolts.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.11
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• pp.604-609
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• 2016

This study evaluated the long-term performance of RSR (Reinforced Subgrade for Railways) technology which increases the railway line capacity without the need for additional land. Its characteristics include the use of a short reinforcement with rigid wall, which make it possible to apply it in confined spaces. The 7m high and 40m long testbed employed to evaluate the long-term performance was designed and constructed near Jupo station on the Chang-hang line. This line, located close to a local bus route, had collapsed at the subgrade following heavy rainfall. The performance of the new type of subgrade was verified with long term measurements over a 2 year period including the surface and ground settlement, horizontal displacement of the wall, tensile strain of the reinforcement, and settlement of the rail top on the side track. Based on the results of the measurements made until now, we concluded that it had sufficient safety and serviceability for use as a railway subgrade. It is expected that RSR technology could be frequently used at sites which lack the necessary construction materials for an embankment and are located close to functional railway lines and boundaries, in order to settle civil complaints.

• Journal of the Korean GEO-environmental Society
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• v.16 no.10
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• pp.15-22
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• 2015

In this study, to evaluate the long-term behavior characteristics and the loss of prestress force, the long-term measurement of the tensile anchors in the actual construction was performed and the results were analyzed comparing with the existing estimation. As the reinforcement member used for the purpose of slope stability or uplift-resisting of the permanent structure, etc, the permanent anchor should maintain the functions during the performance period of the structure differently from the temporary anchor. However, as the time passes by, since the relaxation and the creep of the anchor occur constantly, the management for the loss of tensile force is essential to perform the functions stably. So far, the loss of the tensile force has been estimated according to the reduction of the prestress using elasticity theory and using the relaxation value according to the type of tension member and the test using the long-term measurement is limited. Therefore, in this study, the site condition and the ground were investigated for the tensile anchor in the actual construction and the long-term measurement results more than 500 days was analyzed by installing the loadcell, inclinometer and the groundwater level gauge. In addition, the long-term behavior characteristics were evaluated by comparing the disposition of the measured earth retaining wall and the tension force loss of the anchor with the existing interpretation results. In the evaluation results, the most of the tension force loss occurs within 90 days and the loss was measured less than the estimated values.

• Journal of Korean Association for Spatial Structures
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• v.11 no.2
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• pp.129-138
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• 2011

Construction methods for underground structure are classified as bottom-up, up-up, and top-down methods depending on the procedure of construction related to a superstructure. In top-down construction methods, building's main structure is built from the ground level downwards by sequentially alternating ground excavation and structure construction. In the mean time, the main structure is also used as supporting structure for earth-retaining wall, which results in the increased stability of the earth-retaining wall due to the minimized deformation in adjacent structures and surrounding grounds. In addition, the method makes it easy to secure a field for construction work in the downtown area by using each floor slabs as working spaces. However top-down construction method is often avoided since an excavation under the slab has low efficiency and difficult environment for work, and high cost compared with earth anchor method. This paper proposes a combined construction method where semi-open cut is selected as excavation work, slurry as earth -retaining wall and CWS as top-down construction method. In the case study targeted for an actual construction project, the proposed method is compared with existing top-down construction method in terms of economic feasibility, construction period and work efficiency. The proposed construction method results in increased work efficiency in the transportation of earth and sand, and steel frame erection, better quality management in PHD construction, and reduced construction period.