• Proceedings of the Korean Geotechical Society Conference
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• 2005.03a
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• pp.57-64
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• 2005

Since the allowable bearing capacities of piles in weathered/fractured rock are mainly governed by settlement, the load-displacement behavior of the rock socketed pile should be well known. To predict pile head settlement at the design stage, the exact understanding of the load-transfer mechanisms is essential. Therefore, in this research, the load-transfer mechanisms of drilled shaft socketed into weathered rock was investigated. For that, 5 cast-in-place concrete piles with diameters of 1,000 mm were socketed into weathered gneiss. The static axial load tests and the load-transfer measurements were performed to examine the axial resistant behavior of the piles. A comprehensive field/laboratory testing program on weathered rock at the field test sites was also performed to describe the in situ rock mass conditions quantitatively. And then, the effect of rock mass condition on the load transfer mechanism was investigated. The side shear resistance of the pile in moderately weathered rock reached to yielding point at a few millimeter displacements, and after that, the rate of resistance increment dramatically decreased. However, that in the highly /completely weathered rock did not show the obvious yielding point, and gradually increased showing the hyperbolic pattern until with the relatively high displacement (>10 mm). The end bearing-displacement curves showed linear increase at least until with the base displacement of approximately 10 mm, regardless rock mass conditions.

• Geotechnical Engineering
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• v.14 no.5
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• pp.181-190
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• 1998

One-Dimensional Nonlinear Consolidation Model(NCM) ivas developed by using an Extended Power Function Model, which could represent the compressibility of soils. A nonlinear finite element program for NCM was developed to analyze the porewater pressure dissipation and the settlement of saturated soils. Parameters used in compressibility model could be easily obtained from conventional oedometer test data. This model has been applied to Yansan-Mulgum area for the comparison with the results of CONSOL program and that of Terzaghi theory. A Good The rates of consolidation predicted by this model and CONSOL were faster than that of conventional Tergaghi theory, for they consider the nonlinear characteristics of soils. Consolidation curves of this model were located between Terzaghi and CONSOL curves. Consolidation curves near drainage boundary, where effective stress valied rapidly, seemed to reflect the variations of compressibility of sails. Consolidation curves near drainage boundary obtained from this model were composed of two parabolic curves. Intersection of the parabolic curves occurred when effective stress reached the value of preconsolidation stress. Moreover, thin model could be used to represent the effect of magnitude of applied load. whereas CONSOL and Terazghi theory could not.

• Journal of the Korean GEO-environmental Society
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• v.9 no.3
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• pp.61-68
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• 2008

Side friction is often neglected in the analysis of the results of a consolidation test when the specimen has a high ratio of diameter to height. As the height of a specimen increases, however, side friction becomes important. This paper presents an investigation of the effect of side friction on consolidation test results for normally consolidated kaolinite slurry. Consolidation tests were performed to obtain settlement, pore pressure, compressibility, and hydraulic conductivity of kaolinite slurry. The compressibility relationship is corrected for side friction using a modified form of Taylor (1942) analytical solution. Numerical simulations using the CS2 piecewise-linear model are compared with settlement and excess pore pressure measurements. Experimental results show improved agreement with a modified CS2 model in which the effect of side friction is considered. The numerical and experimental results indicate that the side friction is an important factor affecting the rate of consolidation as well as the compressibility relationship for the specimen.

• Journal of the Korea institute for structural maintenance and inspection
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• v.14 no.2
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• pp.137-144
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• 2010

Up to now, common studies of top base have concentrated upon bearing capacity and settlement by in-situ loading test in Japan and Korea. But most of all preceding study for top base must analyze how to deliver overburden loading on bottom of foundation. Therefore, in this study, the stress delivery mechanism of Top-Base Foundation developed in Japan and Floating Top Base developed in Korea is investigated through numerical analysis and laboratory model test. Analyzing the load delivery mechanism of top base, it was found that the division rate of load reduction of top base for overburden load was largest in peripheral skin friction between the top base and the crushed stone. Further, total stress dispersion angle of Top-Base Foundation including internal stress dispersion effect of top base was $41.8^{\circ}$ and total stress dispersion angle of Floating Top Base was $44.5^{\circ}$.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.16 no.1
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• pp.18-26
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• 2004

In order to accelerate the rate of consolidation settlement, to reduce settlement, and to increase bearing capacity for soft ground under quay, sand compaction pile method (SCP) has usually been applied. SCP-reinforced ground is composite soil which consists of the sand pile and the surrounding soft soil. One of main important considerations in design and analysis for SCP-reinforced soils is stress concentration ratio according to area replacement ratio. In this paper, the numerical analysis was conducted to investigate characteristics of stress concentration ratio in composite ground. It was found that stress concentration ratio of composite ground is not constant as well as depends on several factors such as area replacement ratio, depth of soft soil, and consolidation process. The values of stress concentration ratio increase during loading stage due to stress transfer of composite soil, and reach up to 2.5∼12 according to area replacement ratio at the end of construction. After the end of consolidation, however, these values are converged to 2.5 to 6.0 irrespective of area replacement ratio due to increase in effective stress of soft soil during consolidation process.

• Journal of the Korean Geotechnical Society
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• v.33 no.11
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• pp.45-57
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• 2017

Temperature change affects consolidation behavior of soft clays. The increase of temperature in soft clays induces the increase of pore water pressure. The dissipation of the excess pore water pressure decreases volume and void ratio. Also, the consolidation rate is accelerated by high temperature which induces the decrease of viscosity of pore fluid. The effects of temperature on the consolidation behavior such as consolidation settlement, consolidation time, and pore water pressure were investigated in this study. A numerical analysis of hydro-mechanical (HM) and thermo-hydro-mechanical (THM) behavior was performed. The combination of heat injection and sand drain for consolidating the soft ground, with varying temperature (40 and $60^{\circ}C$) and sand drain diameter (40, 60, and 80 mm), was considered. The results show that the temperature inside soil specimen increases with the increase of the temperature of heating source and the diameter of sand drain. Moreover, the heat injection increases the excess pore water pressure and, accordingly, induces additional settlement in overconsolidated (OC) state and reduces the consolidation time in normally consolidated (NC) state.

• Geomechanics and Engineering
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• v.18 no.2
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• pp.189-203
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• 2019

Brine leakage is a common phenomenon during construction facilitated by artificial freezing technique, threatening the stability of frozen wall due to the continual thawing of already frozen domain. This paper takes the frequently encountered soft clay in Wujiang District as the study object, and remolded specimens were prepared by mixing calcium chloride solutions at five levels of concentration. Both the deformation and pore water pressure of frozen specimens during thawing were investigated by two-stage loading tests. Three sections were noted from the changes in the strain rate of specimens during thawing at the first-stage load, i.e., instantaneous, attenuated, and quasi-stable sections. During the second-stage loading, the deformation of post-thawed soils is closely correlated with the dissipation of pore water pressure. Two characteristic indexes were obtained including thaw-settlement coefficient and critical water content. The critical water content increases positively with salt content. The higher water content of soil leads to a larger thaw-settlement coefficient, especially at higher salt contents, based on which an empirical equation was proposed and verified. The normalized pore water pressure during thawing was found to dissipate slower at higher salt contents, with a longer duration to stabilize. Three physical indexes were experimentally determined such as freezing point, heat conductivity and water permeability. The freezing point decreases at higher salt contents, especially as more water is involved, like the changes in heat conductivity. The water permeability maintains within the same order at the considered range of salt contents, like the development of the coefficient of consolidation. The variation of the pore volume distribution also accounts for this.

• Journal of the Korean Geotechnical Society
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• v.25 no.11
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• pp.117-130
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• 2009

In this paper, a series of laboratory chamber tests were carried out to evaluate the applicability of a porous concrete pile fabricated with recycled aggregates (RAPP) for the soft ground improvement. While performing the laboratory chamber tests for the RAPP, the surface settlement, excess pore pressure and vertical stress distribution with time were compared with those of SCP provided by You (2003) under the same experimental condition. In addition, the experimental results were compared with the numerical simulation using ABAQUS in this study. The results show that the settlement reduction is significantly enhanced due to the stress-sharing mechanism between the RAPP and soil formation by stress concentration on the RAPP. Furthermore, the comparison of consolidation rate shows that the RAPP can accelerate consolidation as well, which behaves as a vertical drain.

• Geomechanics and Engineering
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• v.32 no.4
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• pp.427-443
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• 2023

Across the globe, rapid urbanization demands the construction of basements for car parking and sub way station within the vicinity of high-rise buildings supported on piled raft foundations. As a consequence, ground movements caused by such excavations could interfere with the serviceability of the building and the piled raft as well. Hence, the prediction of the building responses to the adjacent excavations is of utmost importance. This study used three-dimensional numerical modelling to capture the effects of twin excavations (final depth of each excavation, H_e=24 m) on a 20-storey building resting on (4×4) piled raft. Because the considered structure, pile foundation, and soil deposit are three-dimensional in nature, the adopted three-dimensional numerical modelling can provide a more realistic simulation to capture responses of the system. The hypoplastic constitutive model was used to capture soil behaviour. The concrete damaged plasticity (CDP) model was used to capture the cracking behaviour in the concrete beams, columns and piles. The computed results revealed that the first excavation- induced substantial differential settlement (i.e., tilting) in the adjacent high-rise building while second excavation caused the building tilt back with smaller rate. As a result, the building remains tilted towards the first excavation with final value of tilting of 0.28%. Consequently, the most severe tensile cracking damage at the bottom of two middle columns. At the end of twin excavations, the building load resisted by the raft reduced to half of that the load before the excavations. The reduced load transferred to the piles resulting in increment of the axial load along the entire length of piles.

• Journal of Ocean Engineering and Technology
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• v.25 no.6
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• pp.110-115
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• 2011

Numerouslong-term consolidation and secondary compression settlements may occur in Busan clay, which is astructured soft clay and consists of a thick clay deposit. As a surcharge load is applied to soils, soils experience different stress paths with depth. Therefore, it is necessary to study the long-term consolidation behavior of Busan clay considering stress conditions such as OC or NC states. In this study, a series of long-term consolidation tests were performed to investigate the consolidation characteristics of Busan clay for 20 days. The undisturbed clay samples were taken from 3 sites located in the Nakdong River estuary. The results showed that the creep rate of the Busan clay gradually decreased with time, which indicated that the secondary compression settlement decreased with time. In addition, the experimental results for 3 samples showed that the ratios were about 0.0363 and 0.051, respectively.