Spread Foundations Research Articles

EVALUATION OF DYNAMIC INTERACTION FACTOR OF RECTANGULAR PILED RAFT FOUNDATION FOR HORIZONTAL AND ROTATIONAL MOTION

The interaction between a building and the soil its foundation is built into is important in evaluating the seismic response of the building. The dynamic impedance of a piled raft foundation depends on a dynamic interaction factor between the raft and pile group. In this paper, numerical analyses were performed to investigate the frequency characteristics of the dynamic interaction factor of a rectangular piled raft foundation with various aspect ratios, subjected to a building inertial force caused by an earthquake. Based on the analytical results, a formula was proposed that considers the aspect ratio of the foundation in evaluatiing the dynamic interaction factor for a rectangular piled raft foundation. It was confirmed that the dynamic impedance calculated by a simplified calculation using the dynamic interaction factor and the dynamic impedances of a spread foundation and pile foundation, corresponds well with the results of the numerical analysis.

Expanded Database Assessment of Design Methods for Spread Foundations under Axial Compression and Uplift Loading

AbstractThis paper compiles two expanded databases—NUS/SpreadFound/919 and NUS/RockFound/270—to evaluate the calculation methods of foundation capacity, where the number is the number of load tests...

<b>Development of Spread Foundation Composed of Micropiles and Soilbags to Reduce Seismic Response of Structures</b>

<b>Development of Spread Foundation Composed of Micropiles and Soilbags to Reduce Seismic Response of Structures</b>

Vibration characteristics of spread foundation pier model with progress of local scouring

Vibration characteristics of spread foundation pier model with progress of local scouring

Analyzing the Effects of Soil-Structure Interactions on the Static Response of Onshore Wind Turbine Foundations Using Finite Element Method

The use of wind turbines to generate electricity has increased in recent years. One of the most important parts of a wind turbine is the foundation, which should be designed accurately because it is influenced by difference forces. Soil cannot carry tension stress; thus, when a wind turbine foundation is applied eccentricity forces, a gap appears between the soil and foundation. The gap will have no positive effect on the ultimate bearing capacity of the foundation. This must be considered when designing the dimensions of an onshore wind turbine on a spread foundation using finite element software in order to avoid error during analysis. In the current study, a spread foundation of an onshore wind turbine was simulated using ABAQUS and PLAXIS-3D software. Based on the results, the effects of Soil-Structure Interaction (SSI), eccentricity of forces, soil strength parameters and the foundation buried depth on static response of the foundation are discussed. The results indicate that the influence of soil-structure interaction is depend on magnitude of eccentricity of forces and depth of foundation, so that soil-structure interaction has little impact on settlement of foundation when eccentricity of forces is less than 1/6 of the diameter of the foundation and this has important effect when the eccentricity forces at an amount exceeding 1/6 of the diameter of the foundation. In addition, this effect decreases with increasing the foundation buried depth and independent of the soil strength parameters (φ´ and C).

Strain Influence Factor Charts for Settlement Evaluation of Spread Foundations based on the Stress–Strain Method

In this paper, the stress–strain method for the elastic settlement analysis of shallow foundations is revisited, offering a great number of strain influence factor charts covering the most common cases met in civil engineering practice. The calculation of settlement based on strain influence factors has the advantage of considering soil elastic moduli values rapidly varying with depth, such as those often obtained in practice using continuous probing tests, e.g., the Cone Penetration Test (CPT) and Standard Penetration Test (SPT). It also offers the advantage of the convenient calculation of the correction factor for future water table rise into the influence depth of footing. As is known, when the water table rises into the influence zone of footing, it reduces the soil stiffness and thus additional settlement is induced. The proposed strain influence factors refer to flexible circular footings (at distances 0, R/3, 2R/3 and R from the center; R is the radius of footing), rigid circular footings, flexible rectangular footings (at the center and corner), triangular embankment loading of width B and length L (L/B = 1, 2, 3, 4, 5 and 10) and trapezoidal embankment loading of infinite length and various widths. The strain influence factor values are given for Poisson’s ratio value of soil, ranging from 0 to 0.5 with 0.1 interval. The compatibility of the so-called “characteristic point” of flexible footings with the stress–strain method is also investigated; the settlement under this point is considered to be the same as the uniform settlement of the respective rigid footing. The analysis showed that, despite the effectiveness of the “characteristic point” concept in homogenous soils, the method in question is not suitable for non-homogenous soils, as it largely overestimates settlement at shallow depths (for z/B < 0.35) and underestimates it at greater depths (for z/B > 0.35; z is the depth below the footing and B is the footing width).

Application of Three-dimensional Static Analysis to Evaluation of Residual Settlement and Inclination of Spread Foundation Induced by Liquefaction

Application of Three-dimensional Static Analysis to Evaluation of Residual Settlement and Inclination of Spread Foundation Induced by Liquefaction

Foundations of Yangtze River mainstream bridges in China

Until 20 December 2019, more than 160 bridges have been built or are under construction on the Yangtze River in China, among which 132 bridges span the Yangtze River mainstream. This paper statistically summarises the 132 bridges in detail from the aspects of bridge type, span and foundation type. In addition, classic cases are picked out and introduced for each foundation type, and the future development of Yangtze River bridges is proposed. The results show that the cable-stayed bridge is the most widely adopted bridge type; the span of Yangtze River mainstream bridges is mostly concentrated between 400 and 600 m, and obeys a normal distribution; the pier foundation of Yangtze River bridges currently has the following six types: pile foundation, caisson foundation, colonnade foundation, caisson–colonnade composite foundation, caisson–pile composite foundation and spread foundation, among which the pile foundation is the most widely used foundation; there are three types of anchorage foundations for suspension bridges: tunnel anchorage foundation, gravity excavation anchorage foundation and gravity caisson anchorage foundation; and the gravity excavation anchorage foundation is the most popular type because of the ease of construction.

Fractile-based method for selecting characteristic values for geotechnical design with LRFD

Load and resistance factor design (LRFD), also known as partial factor design, is becoming a design method of choice in geotechnical practice. The partial factors (i.e., resistance factor and load factor) to ensure safety are specified in the adopted code; however, engineers still need to select values for the uncertain soil parameters in a design. The selection of these parameter values, often called characteristic values, is quite challenging given soil variability and limited test data. This paper presents a fractile-based method for the selection of the characteristic values for the uncertain soil parameters in a design with LRFD. A framework that considers safety, cost, and robustness is established to determine an appropriate fractile for selecting the characteristic values. This framework is demonstrated with two examples, a drilled shaft in sand and a shallow spread foundation. The results show that robust designs can be achieved using LRFD with the characteristic values obtained through the proposed fractile-based method.

On the interaction between spread foundations and tie-beams under eccentric loading

In framed r.c. or steel structures it is common practice to connect spread footings and strip foundations by means of tie-beams. While such beams are often required to absorb axial forces deriving from horizontal relative displacements at the foundation level, their ability to distribute and reduce the bending moments transferred to the ground is typically neglected. The present work shows that a significant advantage – in terms of foundation size and cost – can be obtained by considering the ability of tie-beams to absorb part of the bending moments which are normally attributed to the foundations alone. To this aim, it is first demonstrated that the distribution of internal forces in the soil-foundation-beam system is exclusively governed by a dimensionless parameter representing the relative rotational stiffness of the system. A simple approach is then proposed to evaluate the actions on both foundation ground and tie-beams, using a numerical model or, alternatively, an approximate method based on the superposition of effects. Finally, some examples are given to point out the usefulness of the proposed approach in terms of reduction of load eccentricity at the foundation bearing level, leading to a sensible reduction of foundations cost.

Reliability-based robust geotechnical design of spread foundations considering multiple failure modes

This paper presents an update for the reliability-based robust geotechnical design (RGD) method in the design of a soil-foundation system by systematically considering four different potential failure modes including: bearing resistance failure of subsoil, excessive foundation settlement, punching and bending failure of the spread foundation. Given the uncertainties in the critical geotechnical and structural parameters, a comprehensive investigation of the reliability and robustness of the soil-foundation system considering both single failure mode and multiple failure modes were conducted in this study. Moreover, the optimal designs of the soil-foundation system with respect to robustness and cost efficiency are found on the premise of satisfying the safety requirements. The results from this study indicate that both the uncertainties of the geotechnical and structural parameters should be taken into account in the RGD of soil-foundation system considering multiple failure modes. Without properly accounting for the width-to-height ratio of the foundation, increase of the footing geometries and the construction cost will not always lead to a safer and robust design. Besides, bearing resistance failure of subsoil has most significant influence on the reliability and robustness of the soil-foundation system and is identified as the control failure mode.

ASSESSING THE ULTIMATE BEARING CAPACITY OF FOOTING IN A TWO-LAYERED CLAYEY SOIL SYSTEM USING THE RIGID PLASTIC FINITE ELEMENT METHOD

Ultimate bearing capacity formulae for foundations are specified in the guideline published by the Architectural Institute of Japan for the design of building foundations. The rigid plastic finite element method was developed by Tamura and Ohtsuka to estimate the ultimate bearing capacity of footing. Unlike deformation analysis, this method employs limited soil constants; it uses only the strength parameters of cohesion c and friction angle φ as it considers the limit state directly and disregards the deformation of the building and ground. A series of rigid plastic finite element analyses were conducted to compare the ultimate vertical and inclined bearing capacities of spread foundations between the simulation results and the theoretical formula for a two-layered clayey soil system. The change in the failure mode of the ground was discussed using the geometrical ratio between the width of the footing and the height of the surface layer. The strength ratio of the surface and second ground layer was clearly shown to affect the formation of failure mode. The applicability of the rigid plastic finite element method for the assessment of the ultimate bearing capacity of a two-layered clayey soil system was successfully demonstrated.

ULTIMATE VERTICAL BEARING CAPACITY OF CLAYEY SQUEEZE BREAKDOWN USING RIGID-PLASTIC FINITE ELEMENT METHOD

The relations of ultimate bearing capacity for foundations are specified in the guideline published by the Architectural Institute of Japan for design of building foundations. The rigid-plastic finite element method developed by Tamura and Ohtsuka has been employed to estimate the ultimate bearing capacity of footings. The characteristic of this method is that, in contrast to deformation analysis, it applies limited soil constants; only the strength parameters, such as cohesion and friction angle, are used since the method deals with the limit state directly by disregarding the deformation of the building and ground. In this study, a series of rigid plastic finite element analyses were performed to compare the ultimate bearing capacities of spread foundation for clayey squeeze breakdown obtained by simulations and the formulae of the Architectural Institute of Japan. The change in the failure mode of the ground was discussed considering the geometrical ratio between the width of the footing and the surface clay layer. In addition, inclined load was considered for clayey squeeze breakdown. The applicability of rigid plastic FEM to the assessment of ultimate vertical bearing capacity of clayey squeeze breakdown was demonstrated.

Perhitungan Lendutan Pondasi Telapak Dengan Metode Elemen Hingga

Bangunan teknik sipil seperti gedung, jalan dan jembatan bertumpu pada lapisan tanah. Dalampelaksanaan pembangunan sering kali tanah tersebut tidak memenuhi kriteria kekuatan untuk memikulbeban dari struktur di atasnya, sehingga diperlukan suatu pemecahan dalam masalah tersebut. Pondasimemikul beban yang di salurkan oleh kolom sebelum diteruskan ke tanah. Salah satu parameter yangperlu diperhatikan dalam suatu desain pondasi adalah lendutan. Dalam tulisan ini, lendutan pondasitelapak dihitung dengan menggunakan metode elemen hingga. Pondasi diasumsikan sebagai strukturyang rigid dan berada di atas tumpuan elastis/pegas sebagai pengganti pengaruh modulus reaksi tanah.Desain pondasi pelat dimodelkan sebagai persamaan matrik dari perilaku pelat tipis yang dimodifikasiterletak di atas tanah. Studi kasus dilakukan untuk mendapatkan lendutan pada tiap-tiap titik nodal.Dalam metode elemen hingga, pondasi telapak dimodelkan sebagai pelat lentur. Hasil lendutanmaksimum dengan perhitungan manual dan numerik dengan menggunakan software SAP2000.Perbedaan hasil lendutan maksimum dari kedua metode ini diperoleh sebesar 0.28 %.

Influence of Rigidity and Load Condition on the Contact Stress and Settlement Deformation of a Spread Foundation

Abstract The distribution of the contact stress between a spread foundation and subsoil has been regarded as a classic issue in geotechnical engineering. Previous studies on this problem mainly focused on rigid foundations under axial loads, usually with width-to-height ratios (w/h) of 2.5 or less. However, flexible foundations are much more widespread in engineering applications. To investigate the effect of rigidity on the contact stress distribution and settlement deformation under axial and eccentric compression, two series of model tests on spread foundations (with w/h ratios from 2.5 to 4.0) placed on silty sand and clay were conducted. The results indicate that, under axial load, the contact stress in the central area of the rigid foundation is smaller than that around the edges. However, as the aspect ratio increases, the opposite occurs. Furthermore, in the eccentric compression progress, the w/h ratio (representing the rigidity of a foundation) has an important impact on the pressure distribution. A clear asymmetric distribution of pressure was observed under the eccentric load, and the maximal stress appears around the edges of the eccentric side under the rigid foundations, while under the flexible foundations the maximal stress appears in the central area. These research results can provide a practical reference for engineering applications with flexible foundations.

Comparison of Spread Foundation Design in Case of Inhomogeneous Subsoil

Paper deals with designing spread foundation on inhomogeneous subsoil by PN- 81/B-03020, by Meyerhof and Hanna and by procedure often applied in Slovakia. The approach using substitute foundation, the approach using punching shear failure and the approach using shear surface are introduced. Three approaches were applied to design foundation on inhomogeneous subsoil for two cases: stronger soil underlain by weaker soil and vice versa. In case stronger soil underlain by weaker soil, PN-81/B-03020 prescribes to determine size of substitute foundation based on soil types (cohesive or cohesionless), distance from foundation base to the weaker soil top and also width of real foundation. Meyerhof and Hanna prescribe to determine adhesive force and passive force per unit length of the vertical planes crossing foundation sidewall. By Meyerhof and Hanna, adhesive force depends on cohesion of stronger layer and also on ratio between bearing capacity of stronger soil and weaker soil. Meyerhof and Hanna also introduce punching shear coefficient, depending on angle of internal friction of stronger soil and ratio between bearing capacity of stronger soil and weaker soil. In case weak layer underlain by strong layer, PN-81/B-03020 prescribes to ignore bearing capacity of strong layer, Meyerhof and Hanna prescribe to determine bearing capacity of both layers. Meyerhof and Hanna prescribe to take into account distance from foundation base to the stronger soil and also depth of failure surface beneath the foundation in the thick bed of the upper weaker soil layer. The procedure often applied in Slovakia does not differ above mentioned two cases and prescribes for both cases to found probably shear surface, to determine average values of subsoil shear strength parameters and unit weight, based on which a bearing capacity of inhomogeneous subsoil will be determined. The results show that in the case stronger soil underlain by weaker soil, foundation sizes obtained by three approaches are different. Results also show that in case weaker layer underlain by stronger layer, neglecting the stronger layer leads to uneconomical design.

A Study on Prediction of Settlement for Spread Foundation Building by Liquefaction

A Study on Prediction of Settlement for Spread Foundation Building by Liquefaction

Simplified method of estimating the dynamic impedance of a piled raft foundation subjected to inertial loading due to an earthquake

Simplified method of estimating the dynamic impedance of a piled raft foundation subjected to the seismic forces of building is presented. Parametric analysis was first performed to calculate the impedance of piled raft, spread, and pile foundations in the frequency domain. Base on calculated impedances, arbitrary functions were newly derived to describe the dynamic interaction factor between the raft and the pile group that constitute the piled raft foundation. It is possible to easily evaluate the impedance of piled raft foundations using the equation for the dynamic interaction factor along with the impedances of the corresponding spread and pile foundations.

CALCULATION METHOD OF HORIZONTAL DISPLACEMENT AND SOIL SPRING FOR SPREAD FOUNDATION BASED ON ELASTIC THEORY

The calculation method of horizontal soil spring for spread foundation proposed in this paper is able to assess horizontal soil springs of various individual foundation groups with considering interactions among spread foundations. In addition, the horizontal soil spring of the spread foundation with complex shape can be easily evaluated due to discretizing aggregate of circular foundation. The validity of the calculation method was confirmed by comparing calculated results against those of elastic finite element analysis and elastic theory.

Soil freezing and the depth of spread foundations

This paper presents the possibility for setting heated building foundations at a depth lower than the level of „zero” isothermal line. In order for the foundation not to be susceptible to damage due to its exposure to negative temperatures, an appropriate thermal insulation was proposed. For the suggested thermal insulation - by means of numerical methods - a calculation of temperature distribution in the vicinity of the foundations was carried out. Based on the analysis of the obtained results, an optimal setting depth for insulated foundations was proposed.