• Geotechnical Engineering
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• v.6 no.3
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• pp.13-30
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• 1990

In this paper, response of pile foundations under seismic loading is studied for use in aseismic design of deep foundations. Both the pseudostatic methods such as subgrade reaction theory by Reese, and elastic analysis by Poulos, and the dynamic methods proposed by, respectively, Prakash and Gazetas, are used for this study. The top displacements and maximum bending moments of example piles are obtained by each method mentioned above, and the results by each method are compared among others. The group pile effects are also considered approximately. The calculated results are compared with experimental results obtained by Novak in 1984. The pseudostatic methods, combined with dynamic group interaction factors, and the dynamic method proposed by Gazetas which considers both kinematic interaction and inertial interaction, separately, estimate the top displacements reasonably well : the method by Prakah or the pseudostatic methods combined with static group interaction factors may overestimate the top displacements and bending moments as well. Therefore, it is recommended to the the simple elastic analysis combined with dynamic group interaction factors for aseismic design of pile foundatins and to confirm the results by the Gaz etas' dynamic methods.

• Geotechnical Engineering
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• v.8 no.4
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• pp.5-16
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• 1992

The main purpose of this the sutdy is to develop the reinforced earth structure design method considering induced stresses and deflections resulting from placement and compaction of soil. In this paper, the new reinforcement Geolog developed by the author is also introduced which is being used as one of the effective earth reinforcing structure against compaction induced stresses. This study adopted the Seed's bilinear model in the estimation of the com paction induced stresses and compute the peak lateral stresses during compaction by doubled Boussinessq's elastic solution of mirror image theory, thereafter, calculate the residual compaction induced lateral stresses from the above peak lateral stress by the residual fraction. It is considered to be reasonable that the compaction induced stresses be added to the lateral earth pressures estimated from conventional gravity analysis considering the actual stresses during service life of the structures. "GEOLOG", a composite of steel bar and attached concrete stopper is found to be effective against tension and pull - out failure. In this paper, the design method considering the compaction induced stresses and the effect of Geolog reinforcement is suggested for the remforced earth structures where backkfill settlement on displacements are not allowed as in the cases of the bridge abutments or double faced reinforcement earth structures.tructures.

• Journal of the Korean Geotechnical Society
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• v.21 no.10
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• pp.49-60
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• 2005

This paper presents the results of an investigation on the effects of design variables on the behavior of geosynthetic-reinforced modular block walls in a tiered arrangement using the finite-element method of numerical analysis. A parametric study was performed by varying the offset distance between the tiers and reinforcement length of the lower and upper tier using verified finite-element model. The finite-element analysis provided relevant information on the mechanical behavior of the tier wall and interaction mechanism between the upper and lower tier, which was otherwise difficult to obtain from the limit-equilibrium analysis based current design approaches. Practical implications of the findings obtained from this study in the current design approaches are discussed in great detail.

• Journal of the Korean Geotechnical Society
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• v.21 no.10
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• pp.99-112
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• 2005

The ground excavation in the urban area induces in general ground movement and subsequent damage on the adjacent building structures. So the essentials in the designing stage are the prediction of ground movement induced by the ground excavation and the damage risk assessment of buildings adjacent to the excavation. A propsed prediction method of the ground movement induced by the strutted excavation has been studied with due consideration of the existing ground movement prediction methods. A building damage risk assessment method based on the angular distortion and the horizontal strain derived from the green-field ground movement is also proposed. These methods have been applied successfully in the on-going deep excavation project in Singapore.

• Journal of the Korean Geotechnical Society
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• v.20 no.3
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• pp.97-106
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• 2004

In case of tunnel construction with a shallow soil cover in cohesionless soils or highly weathered rocks, reinforcement measures are required for a tunnel stability during the tunnel construction. Recent developments show that the use of Umbrella Arch Method(UAM) as tunnel reinforcement and water cut-off in domestic projects has increased. Unfortunately, guidelines for the design and construction of UAM have not been established, only empirical designs and applications in tunnel construction have been performed so far. In this study, behaviour of the steel pipes installed on the tunnel roof was analyzed through the monitoring of bending and axial stresses of the pipes with the advance of the tunnel face. The monitoring results were used in the establishment of the loading mechanism around the pipe. This paper suggests, the guidelines used in the determination of the total length, overlapping length and lateral spacing of the reinforcing pipes obtained from the established loading mechanism.

• Geotechnical Engineering
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• v.13 no.4
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• pp.95-108
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• 1997

For normally consolidated clay, several researchers have developed a number of theoretical time factors to determine the coefficient of consolidation However, depending on the assumptions and analytical techniques, it could considerably vary even for a specific degree of consolidation. In this paper, a method is proposed to determine a consistent coefficient of consolidation over all ranges of degree of consolidation by applying the concept of the Optimum Design Technique. The initial excess pore pressure distribution is assumed to be obtainable by the successive spherical cavity expansion theory. The dissipation of pore pressure is simulated by means of two dimensional linear-uncoupled axisymmetric consolidation analysis. The minimization of the differences between the measured and the predicted excess pore pressures was carried by BFGS unconstrained optimum design algorithm with one dimensional golden section search technique. By analyzing numerical and real field examples, it can be found that the adopted optimum technique gives a consistent and convergent results.

• Geotechnical Engineering
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• v.10 no.3
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• pp.79-96
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• 1994

A tunnel design expert system entitled NESTED is developed using the artificial neural network. The expert system includes three neural network computer models designed for the stability assessment of underground openings and the estimation of correlation between the RMR and Q systems. The expert system consists of the three models and the computerized rock mass classification programs that could be driven under the same user interface. As the structure of the neural network, a multi -layer neural network which adopts an or ror back-propagation learning algorithm is used. To set up its knowledge base from the prior case histories, an engineering database which can control the incomplete and erroneous information by learning process is developed. A series of experiments comparing the results of the neural network with the actual field observations have demonstrated the inferring capabilities of the neural network to identify the possible failure modes and the support timing. The neural network expert system thus complements the incomplete geological data and provides suitable support recommendations for preliminary design of tunnels in rock masses.

• Computers and Concrete
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• v.24 no.5
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• pp.459-468
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• 2019

The stability and safety of concrete plug structure of diversion tunnel is crucial for the impoundment of upstream reservoir in hydropower projects. The ongoing Wudongde hydropower plant in China plans to adopt straight column plugs and curved column plugs to replace the traditional expanded wedge-shaped plugs. The performance of the proposed new plug structures under high water head is then a critical issue and attracts the attentions of engineers. This paper firstly studied the joint bearing mechanism of plug and surrounding rock mass and found that the quality and mechanical properties of the interfaces among plug concrete, shotcrete, and surrounding rock mass play a key role in the performance of plug structures. By performing geophysical and mechanical experiments, the contact state and the mechanical parameters of the interfaces were analyzed in detail and provide numerical analysis with rational input parameters. The safety evaluation is carried out through numerical calculation of plug stability under both construction and operation period. The results indicate that the allowable water head acting on columnar plugs is 3.1 to 7.4 times of the designed water head. So the stability of the new plug structure meets the design code requirement. Based on above findings, it is concluded that for the studied project, it is feasible to adopt columnar plugs to replace the traditional expanded wedge-shaped plugs. It is hoped that this study can provide reference for other projects with similar engineering background and problems.

• Geomechanics and Engineering
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• v.31 no.6
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• pp.573-582
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• 2022

The geometry of the gravity-type anchorage changes depends on various factors such as the installation location, ground type, and relationship with the upper structure. In particular, the anchorage geometry embedded in the ground is an important design factor because it affects the pull-out resistance of the anchorage. This study examined the effect of four parameters, related to anchorage geometry and embedded ground conditions, on the pull-out resistance in the gravity-type anchorage through two-dimensional finite element analysis, and presented a guide for major design variables. The four parameters include the 1) flight length of the stepped anchorage (m), 2) flight height of the stepped anchorage (n), 3) the anchorage heel height (b), and 4) the thickness of the soil (e). It was found that as the values of m increased and the values of n decreased, the pull-out resistance of the gravity-type anchorage increased. This trend is related to the size of the contact surface between the anchorage and the rock, and it was confirmed that the value of n, which has the largest change rate of the contact surface between the anchorage and the rock, has the greatest effect on the pull-out resistance of the anchorage. Additionally, the most effective design was achieved when the ratio of the step to the bottom of the anchorage (m) was greater than 0.7, and m was found to be an important factor in the pull-out resistance behavior of the anchorage.

• Journal of the Korean Geotechnical Society
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• v.26 no.7
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• pp.71-80
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• 2010

Korea is considered to be a seasonal frozen soil area that thaws in the spring, and freezes in winter. In the current design codes for anti-freezing layer, the thickness of anti-freezing layer is calculated by the depth frozen due to the temperature condition. Therefore, there is a tendency of over-design and applying uniform thickness without the consideration of thermal stability, bearing capacity and frost susceptibility of materials. So, it is essential to study the structural appropriateness of pavement layer and bearing capacity besides the seasonal and mechanical properties of pavement materials to take an appropriate and reasonable design of the road structure. In this paper, the evaluation of frost susceptibility on subgrade, ant-freezing layer, subbase was conducted by means of the mechanical characteristics and model experiment. The temperature, heaving amount, unfrozen water contents and freezing depth of soil samples, the subgrade, anti-freezing layer, subbase soils of road construction site were measured to determine the frost susceptibility.