• Journal of the Korean Society of Hazard Mitigation
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• v.9 no.6
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• pp.41-49
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• 2009

Poor compaction of subgrade soil causes low stiffness and bearing capacity of sublayers so that faulting and differential settlements can be generated between new and old pavement surfaces in case of widening works. However, investigation of verifying the reason of producing the defects in the pavements are not performed in detail. In this study, several in-field tests including PMT and PBT were performed for obtaining stiffness of the sublayers in new and old pavements respectively of an widening project. Then, based on the obtained stiffness values and the measured deformations obtained by specially designed tilt meters, the main reasons of generating different deformations between the old and new pavement sections and the relationship between the deformation and stiffness are verified.

• Geomechanics and Engineering
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• v.20 no.2
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• pp.165-174
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• 2020

The enzyme-induced carbonate precipitation (EICP) method has been investigated to improve the hydro-mechanical properties of natural soil deposits. This study was conducted to explore the stiffness evolution during various stress scenarios. First, the optimal concentration of urea, CaCl₂, and urease for the maximum efficiency of calcite precipitation was identified. The results show that the optimal recipe is 0.5 g/L and 0.9 g/L of urease for 0.5 M CaCl₂ and 1 M CaCl₂ solutions with a urea-CaCl₂ molar ratio of 1.5. The shear stiffness of EICP-treated sands remains constant up to debonding stresses, and further loading induces the reduction of S-wave velocity. It was also found that the debonding stress at which stiffness loss occurs depends on the void ratio, not on cementation solution. Repeated loading-unloading deteriorates the bonding quality, thereby reducing the debonding stress. Scanning electron microscopy and X-ray images reveal that higher concentrations of CaCl₂ solution facilitate heterogeneous nucleation to form larger CaCO₃ nodules and 11-12 % of CaCO₃ forms at the interparticle contact as the main contributor to the evolution of shear stiffness.

• Proceedings of the KSR Conference
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• 2008.06a
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• pp.158-167
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• 2008

The quality control of compacted fills has been carried out by evaluating relative densities and coefficients of soil reaction. These measures have several limitations regarding repeatability and reliability of field measurements, and difficulties to use in the fills including large grain size as gravels and boulders. Also, the density is not directly related to the design parameter such as resilient modulus. A preliminary investigation for the usage of the stiffness as a control measure has been carried out. In the laboratory, the stiffness (P-wave velocity) was measured during compaction tests. The stiffness at the optimal moisture content was proposed to use a target control parameter likewise maximum dry density. A field method to match the target stiffness was also proposed by considering easiness of the method and availability of equipment. The most phenomenal feature of the method is that the control parameter (stiffness) is closely related to resilient modulus and can be consistently used from the design stage to the field control during construction.

• Structural Engineering and Mechanics
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• v.31 no.4
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• pp.453-475
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• 2009

The literature regarding the free vibration analysis of Bernoulli-Euler and Timoshenko beams on elastic soil is plenty, but the free vibration analysis of Reddy-Bickford beams on elastic soil with/without axial force effect using the Differential Transform Method (DTM) has not been investigated by any of the studies in open literature so far. In this study, the free vibration analysis of axially loaded Reddy-Bickford beam on elastic soil is carried out by using DTM. The model has six degrees of freedom at the two ends, one transverse displacement and two rotations, and the end forces are a shear force and two end moments in this study. The governing differential equations of motion of the rectangular beam in free vibration are derived using Hamilton's principle and considering rotatory inertia. Parameters for the relative stiffness, stiffness ratio and nondimensionalized multiplication factor for the axial compressive force are incorporated into the equations of motion in order to investigate their effects on the natural frequencies. At first, the terms are found directly from the analytical solutions of the differential equations that describe the deformations of the cross-section according to the high-order theory. After the analytical solution, an efficient and easy mathematical technique called DTM is used to solve the governing differential equations of the motion. The calculated natural frequencies of one end fixed and the other end simply supported Reddy-Bickford beam on elastic soil using DTM are tabulated in several tables and figures and are compared with the results of the analytical solution where a very good agreement is observed and the mode shapes are presented in graphs.

• Geomechanics and Engineering
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• v.31 no.5
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• pp.477-488
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• 2022

Pile composite foundation (PCF) has been commonly applied in practice. Existing research has focused primarily on semi-infinite media having equal pile lengths with little attention given to the effects of inclined bedrock and dissimilar pile lengths. This investigation considers the effects of inclined bedrock on vertical loaded PCF with dissimilar pile lengths. The pile-soil system is decomposed into fictitious piles and extended soil. The Fredholm integral equation about the axial force along fictitious piles is then established based on the compatibility of axial strain between fictitious piles and extended soil. Then, an iterative procedure is induced to calculate the PCF characteristics with a rigid cap. The results agree well with two field load tests of a single pile and numerical simulation case. The settlement and load transfer behaviors of dissimilar 3-pile PCFs and the effects of inclined bedrock are analyzed, which shows that the embedded depth of the inclined bedrock significantly affects the pile-soil load sharing ratios, non-dimensional vertical stiffness N₀/wdE_s, and differential settlement for different length-diameter ratios of the pile l/d and pile-soil stiffness ratio k conditions. The differential settlement and pile-soil load sharing ratios are also influenced by the inclined angle of the bedrock for different k and l/d. The developed model helps better understand the PCF characteristics over inclined bedrock under vertical loading.

• Proceedings of the KSR Conference
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• 2006.05b
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• pp.661-666
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• 2006

• Structural Engineering and Mechanics
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• v.33 no.1
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• pp.47-66
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• 2009

Radiation damping due to wave propagation in unbounded domains may cause a significant reduction of structural vibrations when excited near resonance. Here a novel matrix-valued algebraic Pad$\acute{e}$-like stiffness formulation in the frequency-domain and a corresponding state equation in the time domain are elaborated for a soil-structure interaction problem with a layered soil excited in a transient manner by a flexible rotor during startup and shutdown. The contribution of radiation damping caused by a soil-layer upon a rigid bedrock is characterized by the corresponding amount of critical damping as it is used in structural dynamics.

• Journal of the Earthquake Engineering Society of Korea
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• v.6 no.1
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• pp.7-11
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• 2002

By focusing on the resonant vibration mode of soil-underground structure system, this paper obtained dynamic soil stiffness and easy sliding conditions at the interface between soil and underground structure. Multi-step method is employed to isolate two primary causes of soil-structure interaction. Mohr-Coulomb criterion is used to determine the threshold level of the sliding. To find out the conditions the interface slides easily, parametric studies are performed about the factors governing sliding, which are the size and location of underground structures, ground condition, the configuration of surface deposit and interface friction coefficients.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 1997.10a
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• pp.42-49
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• 1997

In this paper, the method for soil-structure interaction analyses in the time domain is proposed. The far field soil region which is the outside of the artificial boundary is modeled by using explicit frequency-dependent two dimensional infinite elements which can include multiple wave components propagating into the unbounded medium. Since the dynamic stiffness matrix of the far field soil region using the proposed infinite elements is obtained explicitly in terms of exciting frequencies and constants in the frequency domain, the matrix can be easily transformed into the displacement unit-impulse response matrix, which corresponds to a convolution integral of it in the time domain. To verify the proposed method for soil-structure interaction analyses in the time domain, the displacement responses due to an impulse load on the surface of a soil layer with the rigid bed rock are compared with those obtained by the method in the frequency domain and those by models with extend finite element meshes. Good agreements have been found between them.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 1998.10a
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• pp.335-342
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• 1998

A soil-structure interaction (SSI) experiment is being conducted in a seismically active region in Hualien, Taiwan. To obtain earthquake data for quantifying SSI effects and providing a basis to benchmark analysis methods, a 1/4-th scale cylindrical concrete containment model similar in shape to that of a nuclear power plant containment was constructed in the field where both the containment model and its surrounding soil, surface and sub-surface, are extensively instrumented to record earthquake data. In between September 1993 and May 1996, fifteen earthquakes with Richter magnitudes ranging from 4.2 to 6.2 were recorded. The recorded data were analyzed to provide information on the response characteristics of the Hualien soil-structure system, the SSI effects and the ground motion characteristics. The ground response data were analyzed for their variations with depth, with distance from the model structure, and at the same depths along downhole arrays. Variations of soil stiffness and soil-structure system frequencies were also evaluated against maximum ground motion. In addition, the site soil properties were derived based on correlation analysis of the recorded data and then correlated with those from the geotechnical investigation data.