• 콘크리트학회지
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• 제24권1호
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• pp.36-41
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• 2012

• Geomechanics and Engineering
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• 제34권4호
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• pp.381-396
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• 2023

The present paper evaluates seismic bearing capacity of rock masses subjected to loads of strip footings using the upper bound method. A general formula was proposed to evaluate the seismic bearing capacity considering both the horizontal and vertical accelerations of the earthquake and the effects of footing embedment depth simultaneously. Modified Hoek-Brown failure criterion was employed for the rock mass. Some comparisons were made with the available solutions and the finite element numerical models to show the accuracy of the developed upper bound formulations. The obtained results show significant improvement compared to the other available solutions. By increasing the horizontal earthquake acceleration from 0.1 to 0.3, the bearing capacity was reduced by up to 39%, while the effect of the vertical earthquake acceleration depends on its direction. An upward acceleration in the range of zero to 0.2 results in an increase in the bearing capacity by up to 24%, while the downward earthquake acceleration has an adverse effect. Also, by increasing the embedment depth of the footing from zero to 5 times the footing width, the value of seismic bearing capacity was raised about 86%. The obtained results were presented as design tables for use in practical applications.

• Geomechanics and Engineering
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• 제38권3호
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• pp.261-273
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• 2024

This study presents a groundbreaking analytical approach to find an exact solution for the bearing capacity of strip footings on reinforced slopes, utilizing the two-phase approach and slip line method. The two-phase approach is considered as a generalized homogenization technique. The slip line method is leveraged to derive the stress field as a lower bound solution and the velocity field as an upper bound solution, thereby facilitating the attainment of an exact solution. The key finding points out the variation of the bearing capacity factor N_γ with influencing factors including the backfill soil friction angle, the footing setback distance from the slope crest edge, slope angle, strength, and volumetric fraction of inclusion layers. The results are evaluated by comparing them with those of relevant studies in the literature considering analytical and experimental studies. Through the application of the two-phase approach, it becomes feasible to determine the tensile loads mobilized along the inclusion layers associated with the failure zone. It is attempted to demonstrate the results by utilizing non-dimensional graphs to clearly illustrate variable impacts on reinforced soil stability. This research contributes significantly to advancing geotechnical engineering practices, specifically in the realm of static design considerations for reinforced soil structures.

• Geomechanics and Engineering
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• 제5권4호
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• pp.363-377
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• 2013

Any structure constructed on the earth is supported by the underlying soil. Foundation is an interfacing element between superstructure and the underlying soil that transmits the loads supported by the foundation including its self weight. Foundation design requires evaluation of safe bearing capacity along with both immediate and long term settlements. Weak and compressible soils are subjected to problems related to bearing capacity and settlement. The conventional method of design of footing requires sufficient safety against failure and the settlement must be kept within the allowable limit. These requirements are dependent on the bearing capacity of soil. Thus, the estimation of load carrying capacity of footing is the most important step in the design of foundation. A number of theoretical approaches, in-situ tests and laboratory model tests are available to find out the bearing capacity of footings. The reliability of any theory can be demonstrated by comparing it with the experimental results. Results from laboratory model tests on square footings resting on sand are presented in this paper. The variation of bearing capacity of sand below a model plate footing of square shape with variation in size, depth and the effect of permissible settlement are evaluated. A steel tank of size $900mm{\times}1200mm{\times}1000mm$ is used for conducting model tests. Bearing capacity factor $N_{\gamma}$ is evaluated and is compared with Terzaghi, Meyerhof, Hansen and Vesic's $N_{\gamma}$ values. From the experimental investigations it is found that, as the depth of sand cushion below the footing ($D_{sc}$) increases, ultimate bearing capacity and settlement values show an increasing trend up to a certain depth of sand cushion.

• Geomechanics and Engineering
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• 제9권3호
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• pp.287-311
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• 2015

The ultimate bearing capacity and failure mechanism of square footings resting on a sand layer over clay soil have been investigated numerically by performing a series of three-dimensional non-linear finite element analyses. The parameters investigated are the thickness of upper sand layer, strength of sand, undrained shear strength of lower clay and surcharge effect. The results obtained from finite element analyses were compared with those from previous design methods based on limit equilibrium approach. The results proved that the parameters investigated had considerable effect on the ultimate bearing capacity and failure mechanism occurring. It was also shown that the thickness of upper sand layer, the undrained shear strength of lower clay and the strength of sand are the most important parameters affecting the type of failure will occur. The value of the ultimate bearing capacity could be significantly different depending on the limit equilibrium method used.

• Earthquakes and Structures
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• 제16권6호
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• pp.691-704
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• 2019

This study simulates the responses of large-scale bridge piers under pseudo-dynamic tests to investigate the performance of four types of numerical models that consider the nonlinear behavior of the pier and the rocking behavior of the footing. In the models, beam-column elements with plastic hinges are used for the pier, two types of foundation models (rotational spring and distributed spring models) are adopted for the footing behavior, and two types of viscous damping models (Rayleigh and dashpot models) are applied for energy dissipation. Results show that the nonlinear pier model combined with the distributed spring-dashpot foundation model can reasonably capture the behavior of the piers in the tests. Although the commonly used rotational spring foundation model adopts a nonlinear moment-rotation property that reflects the effect of footing uplift, it cannot suitably simulate the hysteretic moment-rotation response of the footing in the dynamic analysis once the footing uplifts. In addition, the piers are susceptible to cracking damage under strong seismic loading and the induced plastic response can provide contribution to earthquake energy dissipation.

• Geomechanics and Engineering
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• 제18권6호
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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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• 재33권6호
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• pp.543-552
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• 2023

The design of foundations based on a deterministic approach may not be safe and reliable occasionally, since soils sometimes show considerable spatial variability, and thus, significant uncertainties in turn affect the estimation of footing bearing capacity. The design of footing on cohesionless stratums on the basis of reliability analysis has not received much attention. This paper performs two-dimensional random finite difference analyses of shallow strip footings on a spatially variable frictional soil considering correlation structure. Friction angle (ϕ) is considered as a log-normally distributed random variable and Monte Carlo Simulation is then performed to determine the statistical response based on the random fields. A new approach reliability-based safety factor is defined based on various reliability levels by considering the coefficient of variation of ϕ and correlation length in both the horizontal and vertical directions. The comparison of the probabilistic safety factor and the conventional one illustrates the limitations of the deterministic safety factor and provides insight into how the heterogeneity of soils properties affects the required safety factor. Results show that the conventional safety factor of 3 can be conservative in some cases, especially for soil with low values of mean ϕ and COV_ϕ.

• Geomechanics and Engineering
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• 제20권5호
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• pp.371-384
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• 2020

A settlement prediction method based on shear wave velocity measurements and soil nonlinearity was recently developed and verified by means of centrifuge tests. However, the method was only applicable to heavily overconsolidated soil deposits under enlarged yield surfaces. In this study, the settlement evaluation method was refined to consider the stress history of the sublayer, based on an overconsolidation ratio evaluation technique, and thereby incorporate irrecoverable plastic deformation in the settlement calculation. A relationship between the small-strain shear modulus and overconsolidation ratio, which can be determined from laboratory tests, was adopted to describe the stress history of the subsurface. Based on the overconsolidation ratio determined, the value of an empirical coefficient that reflects the effect of plastic deformation over the elastic region is determined by comparing the overconsolidation ratio with the stress increment transmitted by the surface design load. The refined method that incorporate this empirical coefficient was successfully validated by means of centrifuge tests, even under normally consolidated loading conditions.

• 한국지반공학회논문집
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• 제20권8호
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• pp.5-14
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• 2004

얕은기초의 설계에 있어 작용하중에 의한 침하량 산정은 기초의 지지력 산정과 함께 매우 중요한 고려사항이다. 상부구조물에 의한 설계하중이 지표면의 기초지반에 직접 작용하는 얕은기초의 경우, 기초지반의 거동은 일반적으로 완전 선형탕성도 아니며, 파괴에 도달한 소성상태도 아닌 비선형 응력-변형률의 거동을 보이게 된다. 이러한 지반의 비선형성은 침하량 산정에 있어 매우 중요한 요소로 간주될 수 있으나, 실제 설계에 있어서는 대표탄성계수의 적용에 의한 간편법이 보편적으로 적용되고 있다. 일반적으로 사질토지반에 놓인 얕은기초 침하량 산정은 표준관입시험(SPT)나 콘관입시헙(CPT) 등의 현장시험 결과를 토대로 이루어진다. 본 연구에서는 비선형 유한요소해석에 의한 얕은기초 하중-침하량 분석을 수행하였으며, 기존의 탄성론에 근거한 침하량 산정법과의 비교분석 또한 수행하였다. 이와 같은 해석을 통하여 콘관입시헙(CPT) 결과에 근거한 새로운 얕은기초 침하량 산정법 및 얕은기초 설계법을 제안하였다.