• 한국지반환경공학회 논문집
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• 제18권10호
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• pp.5-14
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• 2017

In recent years, world has witnessed many man-made activities related to both above and underground blasts. Details on behaviour of shallow foundations subjected to blast loads and induced liquefaction is scarce in literature. In this paper, typical shallow strip foundation in saturated cohesionless soils subjected to both above and underground blasting have been simulated by using finite difference based numerical model FLAC3D. Peak particle velocity (PPV) has been obtained to propose critical values for which bearing capacity failure for shallow foundations with soil liquefaction can occur. Typical results for pore pressure ratio (PPR) for various scaled distances are compared to PPR values obtained by using empirical equation available in literature which shows good agreement. Critical design values obtained in the present study for PPV and PPR to estimate the scaled distance, bearing capacity failure and liquefaction susceptibility can be used effectively for design of shallow strip foundation in cohesionless soil subjected to both above and under ground blast loads.

• Geomechanics and Engineering
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• 제3권2호
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• pp.153-167
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• 2011

Traditional design methods of bearing capacity of shallow foundations are deterministic in the sense that they do not explicitly consider the inherent uncertainty associated with the factors affecting bearing capacity. To account for such uncertainty, available deterministic methods rather employ a fixed global factor of safety that may lead to inappropriate bearing capacity predictions. An alternative stochastic approach is essential to provide a more rational estimation of bearing capacity. In this paper, the likely distribution of predicted bearing capacity of strip footings subjected to vertical loads is obtained using a stochastic approach based on the Monte Carlo simulation. The approach accounts for the uncertainty associated with the soil shear strength parameters: cohesion, c, and friction angle, ${\phi}$, and the cross correlation between c and ${\phi}$. A set of stochastic design charts that assure target reliability levels of 90% and 95%, are developed for routine use by practitioners. The charts negate the need for a factor of safety and provide a more reliable indication of what the actual bearing capacity might be.

• Geomechanics and Engineering
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• 제31권2호
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• pp.223-235
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• 2022

Bearing capacity of shallow foundations is often determined for either dry or saturated soils. In some occasions, foundations may be subjected to external loading which is inclined and/or eccentric. In this study, the ultimate bearing capacity of shallow foundations resting on partially saturated coarse-grained cohesionless and fine-grained cohesive soils subjected to a wide range of combined vertical (V) - horizontal (H) - moment (M) loadings is rigorously evaluated using the well-established limit equilibrium method. The unified effective stress approach as well as the suction stress concept is effectively adopted so as to simulate the behaviour of the underlying unsaturated soil medium. In order to obtain the bearing capacity, four equilibrium equations are solved by adopting Coulomb failure mechanism and Bishop effective stress concept and also considering a linear variation of the induced matric suction beneath the foundation. The general failure loci of the shallow foundations resting on unsaturated soils at different hydraulic conditions are presented in V - H - M spaces. The results indicate that the matric suction has a marked influence on the bearing capacity of shallow foundations. In addition, the effect of induced suction on the ultimate bearing capacity of obliquely-loaded foundations is more pronounced than that of the eccentrically-loaded footings.

• Coupled systems mechanics
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• 제4권4호
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• pp.365-383
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• 2015

Strip footing is an important type of shallow foundations and is commonly used beneath the walls. Analysis of shallow foundation involves the determination of stresses and deformations. Element free Galerkin method, one of the important mesh free methods, is used for the determination of stresses and deformations. Element free Galerkin method is an efficient and accurate method as compared to finite element method. The Element Free Galerkin method uses only a set of nodes and a description of model boundary is required to generate the discrete equation. Strip footing of width 2 m subjected to a loading intensity of 200 kPa is studied. The results obtained are agreeing with the values obtained using analytical solutions available in the literature. Parametric study is done and the effect of modulus of deformation, Poisson's ratio and scaling parameter on deformation and stresses are determined.

• Geomechanics and Engineering
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• 제20권4호
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• pp.345-358
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• 2020

Numerous studies have repeatedly demonstrated the efficiency of using skirts to increase the bearing capacity and to reduce settlement of shallow foundations subjected to static loads. However, no efforts have been made to study the efficiency of using these skirts to reduce settlement produced by machine vibration, although machines are very sensitive to settlement and the foundations of these machines should be designed properly to ensure that the settlement produced due to machine vibration is very small. This research has been conducted to investigate the efficiency of using skirts as a technique to reduce the settlement of a strip foundation subjected to machine vibration. A two-dimensional finite element model has been developed, validated, and employed to achieve the aim of the study. The results of the analyses showed that the use of skirts reduces the settlement produced due to machine vibration. However, the percentage decrease of the settlement is remarkably influenced by the density of the soil and the frequency of vibration, where it rises as the frequency of vibration increases and declines as the soil density rises. It was also found that increasing skirt length increases the percentage decrease of the settlement. Importantly, the results obtained from the analyses have been utilized to derive new dynamic impedance values that implicitly consider the presence of skirts. Finally, novel design equations of dynamic impedance that implicitly account to the effect of the skirts have been derived and validated utilizing a new intelligent data driven method. These new equations can be used in future designs of skirted strip foundations subjected to machine vibration.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2003년도 봄 학술발표회 논문집
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• pp.455-462
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• 2003

The current practice of estimating bearing capacity usually employs the conventional bearing capacity formula originally developed for strip footings under vertical central loading, In order account for the effect of footing shape and eccentricity and inclination of loads, correction factors are introduced in the formula, which are derived based on a number of small-scale model test observations. In this paper, comparison of several formulations of bearing capacity factors, as well as values of these factors, are presented. And the conventional bearing capacity equations are compared with some of other failure loci proposed for cohesive soil. Also, the bearing capacity of shallow foundation estimated by the conventional bearing capacity equations are compared with the experimental load test results.

• Structural Engineering and Mechanics
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• 제52권3호
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• pp.507-523
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• 2014

Shell foundations have been employed as an alternative for the conventional flat shallow foundations and have proven to provide economical advantage. They have shown considerably improved performance in terms of ultimate capacity and settlement characteristics. However, despite conical shell foundations are frequently used in industry, the theoretical solutions for bearing capacity of these footings are available for only triangular shell strip foundations. The benefits in design aspects can be achieved through theoretical solutions considering shell geometry. The engineering behavior of a conical shell foundation on mixed soils was investigated experimentally and theoretically in this study. The failure mechanism was obtained by conducting laboratory model tests. Based on that, the theoretical solution of bearing capacity was developed and validated with experimental results, in terms of the internal angle of the cone. In comparison to the circular flat foundation, the results show 15% increase of ultimate load and 51% decrease of settlement at an angle of intersection of $120^{\circ}$. Based on the results, the design chart of modified bearing capacity coefficients for conical shell foundation is proposed.

• Geomechanics and Engineering
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• 제14권1호
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• pp.51-60
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• 2018

The foundations are classified into shallow and deep, which have important differences: in terms of geometry, the behavior of the soil, its structural functionality, and its constructive systems. The shallow foundations may be of various types according to their function; isolated footings, combined footings, strip footings, and slabs foundation. The isolated footings are of the type rectangular, square and circular. The combined footing may be rectangular, trapezoidal or T-shaped in plan. This paper presents a new model for T-shaped combined footings to obtain the most economical contact surface on the soil (optimal dimensioning) to support an axial load and moment in two directions to each column. The new model considers the soil real pressure, i.e., the pressure varies linearly. The classical model uses the technique of test and error, i.e., a dimension is proposed, and subsequently, the equation of the biaxial bending is used to obtain the stresses acting on each vertex of the T-shaped combined footing, which must meet the conditions following: The minimum stress should be equal or greater than zero, and maximum stress must be equal or less than the allowable capacity that can withstand the soil. To illustrate the validity of the new model, numerical examples are presented to obtain the minimum area of the contact surface on the soil for T-shaped combined footings subjected to an axial load and moments in two directions applied to each column.

• Geomechanics and Engineering
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• 제18권4호
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• pp.391-406
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• 2019

The aim of this paper was to study the influence of the footing shape and the effect of the roughness of the foundation base on the bearing capacity of shallow foundations on rock masses. For this purpose the finite difference method was used to analyze the bearing capacity of various types and states of rock masses under the assumption of Hoek-Brown failure criterion, for both plane strain and axisymmetric model, and considering smooth and rough interface. The results were analyzed based on a sensitivity study of four varying parameters: foundation width, rock material constant (mo), uniaxial compressive strength and geological strength index. Knowing how each parameter influences the bearing capacity depending on the footing shape (circular vs strip footing) and the footing base interface roughness (smooth vs rough), two correlation factors were developed to estimate the percentage increase of the ultimate bearing capacity as a function of the footing shape and the roughness of the footing base interface.

• 한국지반공학회지:지반
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• 제12권3호
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• pp.127-148
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• 1996

최근에 들어 사면이나 사면 근처에 교대등과 같이 기초하중이 비교적 큰 구조물들이 시공되는 예가 점차 많아지는 경 향을 보이고 있다. 그러나 일반적으로 사면 또는 사면 근처 에 설치되는 기초의 경우는 수평지반에 비해 지지력이 현저하게 떨어지기 때문에, 말뚝이나 케이슨 등과 같은 고가의 깊은기초들이 주로 사용되고 있는 실정이다. 따라서 토목섬유 또는 metal strip등의 보강재를 이용하여 사면을 보강하는 경제적인 공법이 필요시 되고,또한 이와같은 공법에 관련된 합리적인 기초지지력 해석법의 제시가 요구되고 있다. 본 연구에서는 사면 근처에 설치되는 얕은 기초의 지지력 보강을 목적으로 strip등의 보강재를 설치할 경우, 'wide slab effect' 개념등 Huang및 Binquet-Lee등이 모형실험등을 통해 제시한 파괴매카니즘 및 Boussinesq해법 등을 토대로 하여 보강사면에 대한 기초지지력 해석법을 제시하였다. 본 해석법에서는 soil dilatancy 등의 영향에 의한 깊이별 보강재-주변흙 사이의 마찰계수 변화를 함수형태로 표현하여 보강재주변흙 사이의 상호작용을 부분적으로 고려하였으며, 아울러 본 연구를 통해 제시된 기초지지력 해석법의 적합성 검토를 위해 Huang등이 제시한 모형실험결과와 서로 비교하였다. 이외에도, 설계에 관련된 여러 변수들이 기초지지력에 미치는 영향에 대해서도 분석이 이루어졌다.