• Journal of the Korean GEO-environmental Society
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• v.16 no.2
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• pp.27-31
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• 2015

In urban area, many design projects related to geotechnical projects are controlled by serviceability rather than stability requirements. Accordingly, control of ground deformation has become more crucial and many researchers have studied soil stiffness. Recent experimental studies on the stress-strain response of Chicago glacial clays showed that the nonlinearity and anisotropy are the two key factors in evaluating the soil stiffness. In this study, experimental results are applied to analyze the deep excavation site locating in downtown Chicago. The stress paths observed from the observation points located behind and front of the supporting wall yield typical stress paths. Changes in soil stiffness nonlinearity and anisotropy were discussed by comparing experimental and computed stress paths. The stiffness anisotropy were significant even at the first few excavations. The stiffness degradation characteristics are significantly different according to relative location to the support wall even at the same elevation.

• Journal of the Korean GEO-environmental Society
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• v.18 no.8
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• pp.5-15
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• 2017

To perform an integrated load analysis carried out to evaluate the stability evaluation of wind turbine generators, the six degree-of-freedom stiffness matrix of foundation, which describes relationships between loads and displacement, is needed. Since the foundation stiffness should accurately reflect the shape of foundation and the condition of soil, it is necessary to calculate the stiffness of the bucket foundation that considers the elasto-plastic behavior of the soil. In this study, finite element analyses were performed for a range of soils and shapes of bucket foundations to estimate the foundation stiffness. Normalized stiffness curves are developed from respective numerical simulations. Proposed results are considered to be useful because they can be directly applied in the design.

• Proceedings of the Korean Geotechical Society Conference
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• 2002.10a
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• pp.427-434
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• 2002

In Korea, there are recently many attempts to expand a temporary soil nailing system into a permanent soil nailing system since the first construction in 1993. In the downtown area, it is important that the relaxation of the ground is minimized in the ground excavation works. Due to these problems, soil nailing systems are often used the flexible facing such as shotcrete rather than the rigid facing such as SCW, CIP, and jet grout types in Korea. The soil nailing systems with rigid facings are used greatly however it is insufficient researches for design and analysis of soil nailing systems with rigid facings. In this study, various laboratory model tests are carried out to examining the influence the rigidity of facings on the global safety of soil nailing system, failure loads, displacement behaviour, axial force acting on the nails, and distribution of earth pressure. Also, the parametric studies are carried out for the typical section of soil nailed walls according to thickness of concrete facings and internal friction angle of soil using the numerical technique as shear strength reduction technique.

• Proceedings of the Korean Geotechical Society Conference
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• 2009.09a
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• pp.976-984
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• 2009

This study proposes a simple method that uses a simple mass-spring model to predict the natural frequency of a soil-pile-structure system in sandy soil. This model includes a pair of matrixes, i.e., a mass matrix and a stiffness matrix. The mass matrix is comprised of the masses of the pile and superstructure, and the stiffness matrix is comprised of the stiffness of the pile and the spring coefficients between the pile and soil. The key issue in the evaluation of the natural frequency of a soil-pile system is the determination of the spring coefficient between the pile and soil. To determine the reasonable spring coefficient, subgrade reaction modulus, nonlinear p-y curves and elastic modulus of the soil were utilized. The location of the spring was also varied with consideration of the infinite depth of the pile. The natural frequencies calculated by using the mass-spring model were compared with those obtained from 1-g shaking table model pile tests. The comparison showed that the calculated natural frequencies match well with the results of the 1-g shaking table tests within the range of computational error when the three springs, whose coefficients were calculated using Reese's(1974) subgrade reaction modulus and Yang's (2009) dynamic p-y backbone curves, were located above the infinite depth of the pile.

• Journal of the Korean Geosynthetics Society
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• v.2 no.2
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• pp.13-24
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• 2003

This paper presents the results of investigation on the effects of foundation stiffness and surface loading on the performance of soil-reinforced segmental retaining walls using the finite element method of analysis. A parametric study was performed by varying the foundation stiffness and the location of surface loading. The results of the analyses indicate that the wall deformation and reinforcement tensile load tend to increase with decreasing foundation stiffness with little variation in the horizontal and vertical stress distributions at the back and the base of the reinforced soil zone. Also revealed is that the increment of reinforcement tensile load due to the presence of surface load may be significantly over-estimated when using the conventional approach. Furthermore, the external stability should be carefully examined when a surface loading is present just behind the reinforced soil zone. The implications of the findings from this study to current design approaches are discussed in detail.

• Geomechanics and Engineering
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• v.14 no.5
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• pp.479-489
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• 2018

In this paper, a comparative study of the effects of soil modelling on the interaction between tunnelling in soft soil and adjacent piled structure is presented. Several three-dimensional finite element analyses are performed to study the deformation of pile caps and piles as well as tunnel internal forces during the construction of an underground tunnel. The soil is modelled by two material models: the simple, yet approximate Mohr Coulomb (MC) yield criterion; and the complex, but reasonable hardening soil (HS) model with hyperbolic relation between stress and strain. For the former model, two different values of the soil stiffness modulus ($E_{50}$ or $E_{ur}$) as well as two profiles of stiffness variation with depth (constant and linearly increasing) were used in attempts to improve its prediction. As these four attempts did not succeed, a hybrid representation in which the hardening soil is used for soil located at the highly-strained zones while the Mohr Coulomb model is utilized elsewhere was investigated. This hybrid representation, which is a compromise between rigorous and simple solutions yielded results that compare well with those of the hardening soil model. The compared results include pile cap movements, pile deformation, and tunnel internal forces. Problem symmetry is utilized and, therefore, one symmetric half of the soil medium, the tunnel boring machine, the face pressure, the final tunnel lining, the pile caps, and the piles are modelled in several construction phases.

• Geomechanics and Engineering
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• v.29 no.4
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• pp.435-449
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• 2022

In this paper, unreinforced and geogrid-reinforced soil foundations were modeled by discrete element method and this performed under surface strip footing loads. The effects of horizontal position of geogrid, vertical position, thickness, number, confining pressure have been investigated on the footing settlement and propagation of tensile force along the geogrids. Also, interaction between rectangular tunnel and strip footing with and without presence of geogrid layer has been analyzed. Experimental results of the literature were used to validation of relationships between the numerically achieved footing pressure-settlement for foundations of reinforced and unreinforced soil. Models and micro input parameters which used in the numerical modelling of reinforced and unreinforced soil tunnel were similar to parameters which were used in soil foundations. Model dimension was 1000 mm* 600 mm. Normal and shear stiffness of soils were 5*10⁵ and 2.5 *10⁵ N/m, respectively. Normal and shear stiffness of geogrid were 1*10⁹ and 1*10⁹ N/m, respectively. Loading rate was 0.001 mm/sec. Micro input parameters used in numerical simulation gain by try and error. In addition of the quantitative tensile force propagation along the geogrids, the footing settlements were visualized. Due to collaboration of three layers of geogrid reinforcements the bearing capacity of the reinforced soil tunnel was greatly improved. In such practical reinforced soil formations, the qualitative displacement propagations of soil particles in the soil tunnel and the quantitative vertical displacement propagations along the soil layers/geogrids represented the geogrid reinforcing impacts too.

• Proceedings of the Korean Geotechical Society Conference
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• 2005.10a
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• pp.689-697
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• 2005

The soil nailing system at permanent slope reinforcement is used with various facing methods in Korea. Also, pressure-injected grout technique is variously applied to many structures. However, most design of the pressure-injected grout technique have been carried out empirically because of complicated mechanisms associated with the behavior of surrounding soils and the hardening process of cement grout. Therefore this study, a newly modified soil nailing technology named as the PGSN (Pressure Grouting Soil Nailing) system with fabric form is developed to increase the global stability. Up to now, the PGSN system has been estimated mainly focusing on an establishment of the design procedure. In the present study, numerical study are carried out to evaluate potential failure surface and minimum factor of safety including facing stiffness and expanded radius of cemented grout by SSR (Shear Strength Reduction) technique. Also, results of numerical analysis are carried out for the typical section of soil nails slope using $FLAC^{2D}$ program for expanded effective radius by pressure grouting.

• Proceedings of the Korean Geotechical Society Conference
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• 2008.10a
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• pp.1397-1403
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• 2008

Soil compaction works are essential to construction of dams, breakwaters and roads in order to avoid unexpected settlement/deformation of superstructures. Taking advantage of oscillating accelerometer, this research was made to complement existing methods for assessment of soil stiffness. In order to examine the validity of compaction-degree suggested in the study, tests on vibration characteristics using accelerometers was also performed. Test results for sand and gravel mixtures and Korean standard sands were compared and evaluated by conventional assessment methods under varying conditions as of input frequency, size of loading plate and relative density.

• Coupled systems mechanics
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• v.13 no.3
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• pp.187-200
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• 2024

This paper presents a numerical model for buckling analysis of slender piles, such as micropiles. The model incorporates geometric nonlinearities to provide enhanced accuracy and a more comprehensive representation of pile buckling behavior. Specifically, the pile is represented using geometrically nonlinear beams with the von Karman deformation measure. The lateral support provided by the surrounding soil is modeled using the spring approach, with the spring stiffness determined according to the undrained shear strength of the soil. The numerical model is tested across a wide range of pile slenderness ratios and undrained shear strengths of the surrounding soil. The numerical results are validated against analytical solutions. Furthermore, the influence of various pile bottom end boundary conditions on the critical buckling force is investigated. The implications of the obtained results are thoroughly discussed.