• Proceedings of the Korean Geotechical Society Conference
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• 2000.11a
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• pp.245-252
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• 2000

Model tests on free standing pile groups and piled footings with varying a pile spacing in two layered soils are carried out. The influence of pile cap on the behaviors of end bearing pile groups is analyzed by comparing the bearing behavior in piled footings with those in a single pile, a shallow footing(cap alone) and free standing pile groups. From the test results, it is found that the bearing characteristics of cap-soil-pile system are related with load levels and pile spacings. Before yield, the bearing resistance by cap is not fully mobilized, however, as the applied load increases, the bearing resistance of cap approaches to that of cap alone and settlement hardening occurs after yield due to the compaction caused by the contact pressure between cap and soil. By the cap-soil-pile interaction, shaft friction and point resistance of piles considerably increase with dependency of pile spacings. In two layered soil, the increasing effect of dilatancy in dense sandy soil adjacent to pile tips, increases the point resistance of pile.

• Geomechanics and Engineering
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• v.4 no.3
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• pp.173-190
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• 2012

With recent growing interests in the Performance-Based Seismic Design and Assessment Methodology, more realistic modeling of a structural system is deemed essential in analyzing, designing, and evaluating both newly constructed and existing buildings under seismic events. Consequently, a shallow foundation element becomes an essential constituent in the implementation of this seismic design and assessment methodology. In this paper, a contact interface fiber section element is presented for use in modeling soil-shallow foundation systems. The assumption of a rigid footing on a Winkler-based soil rests simply on the Euler-Bernoulli's hypothesis on sectional kinematics. Fiber section discretization is employed to represent the contact interface sectional response. The hyperbolic function provides an adequate means of representing the stress-deformation behavior of each soil fiber. The element is simple but efficient in representing salient features of the soil-shallow foundation system (sliding, settling, and rocking). Two experimental results from centrifuge-scale and full-scale cyclic loading tests on shallow foundations are used to illustrate the model characteristics and verify the accuracy of the model. Based on this comprehensive model validation, it is observed that the model performs quite satisfactorily. It resembles reasonably well the experimental results in terms of moment, shear, settlement, and rotation demands. The hysteretic behavior of moment-rotation responses and the rotation-settlement feature are also captured well by the model.

• Structural Engineering and Mechanics
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• v.58 no.6
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• pp.1045-1075
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• 2016

Shallow footings are one of the most common types of foundations used to support mid-rise buildings in high risk seismic zones. Recent findings have revealed that the dynamic interaction between the soil, foundation, and the superstructure can influence the seismic response of the building during earthquakes. Accordingly, the properties of a foundation can alter the dynamic characteristics (natural frequency and damping) of the soil-foundation-structure system. In this paper the influence that shallow foundations have on the seismic response of a mid-rise moment resisting building is investigated. For this purpose, a fifteen storey moment resisting frame sitting on shallow footings with different sizes was simulated numerically using ABAQUS software. By adopting a direct calculation method, the numerical model can perform a fully nonlinear time history dynamic analysis to realistically simulate the dynamic behaviour of soil, foundation, and structure under seismic excitations. This three-dimensional numerical model accounts for the nonlinear behaviour of the soil medium and structural elements. Infinite boundary conditions were assigned to the numerical model to simulate free field boundaries, and appropriate contact elements capable of modelling sliding and separation between the foundation and soil elements are also considered. The influence of foundation size on the natural frequency of the system and structural response spectrum was also studied. The numerical results for cases of soil-foundation-structure systems with different sized foundations and fixed base conditions (excluding soil-foundation-structure interaction) in terms of lateral deformations, inter-storey drifts, rocking, and shear force distribution of the structure were then compared. Due to natural period lengthening, there was a significant reduction in the base shears when the size of the foundation was reduced. It was concluded that the size of a shallow foundation influences the dynamic characteristics and the seismic response of the building due to interaction between the soil, foundation, and structure, and therefore design engineer should carefully consider these parameters in order to ensure a safe and cost effective seismic design.

• Structural Engineering and Mechanics
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• v.48 no.1
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• pp.1-16
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• 2013

The seismic response of RC space frame structures with isolated footing resting on a shallow soil stratum on rock is presented in this paper. Homogeneous soil stratum of different stiffness in the very soft to stiff range is considered. Soil, footing and super structure are considered to be the parts of an integral system. A finite element model of the integrated system is developed and subjected to scaled acceleration time histories recorded during two different real earthquakes. Dynamic analysis is performed using mode superposition method of transient analysis. A parametric study is conducted to investigate the effect of flexibility of soil in the dynamic behaviour of low-rise building frames. The time histories and Fourier spectra of roof displacement, base shear and structural response quantities of the space frame on compliant base are presented and compared with the fixed base condition. Results indicate that the incorporation of soil flexibility is required for the realistic estimate of structural seismic response especially for single storey structures resting on very soft soil.

• Geomechanics and Engineering
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• v.18 no.6
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• pp.575-584
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• 2019

The groundwater level (GWL) is an important subsoil condition for the design of foundation. GWL tends to fluctuate often with seasonal variation, which may cause unexpected, additional settlements with some reductions in the safety margin of foundation. In this study, the effects of fluctuating GWL on the load carrying and settlement behavior of footing were investigated and quantified. A series of model load tests were conducted for various GWL and soil conditions using a hydraulically-controlled chamber system. Changes in load level and rising and falling GWL fluctuation cycle were considered in the tests. Settlements during GWL rise were greater than those during GWL fall. The depth of the GWL influence zone ($\underline{d}_{w,inf}$) varied in the range of 0.3 to 1.5 times footing width and became shallower as GWL continued to fluctuate. Design equations for estimating GWL-induced settlements for footings were proposed. The GWL fluctuation cycle, load level and soil density were considered in the proposed method. Changes in settlement and factor of safety with GWL fluctuation were discussed.

• Geomechanics and Engineering
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• v.32 no.2
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• pp.193-207
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• 2023

In general, the numerous classical approaches available in the literature can anticipate the settlement of shallow foundations. As long as the footings are not in close proximity to other subsurface buildings, the findings achieved using these methods are legitimate and acceptable. However, due to increased urbanisation and land scarcity, footings are frequently built close together. As a result, these footings' settlement behaviour differs from those of isolated footings. A simpler approach for assessing the settlement behaviour of two square or rectangular footings placed in close proximity is presented in this work. A Parametric study has been carried out to examine the interference effect on the settlement of these footings placed in close vicinity on the surface of a homogeneous, isotropic and elastic soil medium. The interaction factors are examined by varying the different aspect ratios (L/B), clear spacing ratio (S/B) and intensity of loading on the right footing with respect to the left footing. Further, variation of the settlement ratio (δ/B) with respect to embedment depth ratio D_f/B is examined. For square and rectangular footings, the interference settlement profile is also investigated by varying the clear spacing ratio (S/B) and the degree of loading. The results were compared to 3D finite element analysis and experimental data that were available.

• Journal of Industrial Technology
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• v.24 no.B
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• pp.95-105
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• 2004

This paper is an experimental and numerical research works about the effects of the b earing capacity of sloped rubble mound on the density of rubble mound and the position of footing. Centrifuge model tests were performed to investigate the bearing capacity of rubble m ound by changing the density of rubble mound and the location of loading in forms of s trip loading to simulate the caisson. Materials of rubble mound used in the model tests were crushed rocks having similar value of uniformity coefficient to the value in field. Two different relative densities of 80% and 90% were prepared during tests. The dimens ions of centrifuge model were trapezoidal shape of model mound having the bottom wid th of mound, 30cm and height of mound, 10cm. Gravity level applied during the centrif uge test was 50G. Surcharge loading in the forms of strip loading was applied on the t op of the sloped model mound. Tests were carried out by changing the position of loadi ng. The rigid model footing was located in the center of top of the model rubble mound and the edge of model footing was at the crest of mound. Test results were analyzed by using the limit equilibrium methods proposed by Meyer hof(1957) and Bowles(1982) and the numerical approach with FLAC being available com mercially software. For the numerical estimations with FLAC, the rubble mound was si mulated with the constitutive relationship of Mohr-Coulomb elasto-plastic model.

• Smart Structures and Systems
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• v.29 no.3
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• pp.513-522
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• 2022

Due to the importance of accurate analysis of bearing capacity in civil engineering projects, this paper studies the efficiency of two novel metaheuristic-based models for this objective. To this end, black hole algorithm (BHA) and multi-verse optimizer (MVO) are synthesized with an artificial neural network (ANN) to build the proposed hybrid models. Based on the settlement of a two-layered soil (and a shallow footing) system, the stability values (SV) of 0 and 1 (indicating the stability and failure, respectively) are set as the targets. Each model predicted the SV for 901 stages. The results indicated that the BHA and MVO can increase the accuracy (i.e., the area under the receiving operating characteristic curve) of the ANN from 94.0% to 96.3 and 97.2% in analyzing the SV pattern. Moreover, the prediction accuracy rose from 93.1% to 94.4 and 95.0%. Also, a comparison between the ANN's error decreased by the BHA and MVO (7.92% vs. 18.08% in the training phase and 6.28% vs. 13.62% in the testing phase) showed that the MVO is a more efficient optimizer. Hence, the suggested MVO-ANN can be used as a reliable approach for the practical estimation of bearing capacity.

• Geomechanics and Engineering
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• v.28 no.6
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• pp.547-557
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• 2022

Dune sands are poorly graded collapsible soils lacking fines. This experimental study explored the technical feasibility of sustainable invigoration of fine waste materials to improve the geotechnical properties of dune sand. The fine waste considered in this study is fine marble waste. The fine waste powder was mixed with dune sand at different contents (5, 10,15, 20, 25, 50%), where the gradation, void ratio, compaction, and shear strength characteristics were assessed for each fine marble waste -dune sand blend. The geotechnical properties of the dune sand-fine marble waste mix delineated in this study reveal the enhancement in compaction and gradation characteristics of dune sand. According to the results, the binary mixture of dune sand with 20% of fine marble waste gives the highest maximum dry density and results in shear strength improvement. In addition, a numerical study is conducted for the practical application of the binary mix in the field and tested for an isolated shallow foundation. The elemental analysis of the fine marble waste confirms that the material is non-contaminated and can be employed for engineering applications. Furthermore, the numerical study elucidated that the shallow surface replacement of the site with the dune sand mixed with 20% fine marble waste gives optimal performance in terms of stress generation and settlement behavior of an isolated footing. For a sustainable mechanical performance of the fine marble waste mixed sand, an optimum dose of 20% fine marble waste is recommended, and some correlations are proposed. Thus, for improving dune sand's geotechnical characteristics, the addition of fine marble waste to the dune sand is an environment-friendly solution.

• Proceedings of the Korean Geotechical Society Conference
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• 2010.03a
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• pp.1073-1076
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• 2010

Shallow foundations of various columns such as traffic signs, CCTVs, traffic lights, street lights, steel telephone poles and so on are made by cast-in-situ concrete method. However, typical cast-in-situ method has many problems because of the long duration of construction, occupation of sidewalks and low strength of the concrete after curing. In order to solve the problems, field load tests for the prefabricated DSF foundation made by combination of column and foundation was conducted to know load-deformation behavior by torsional tests.