Showing papers on "Foundation (engineering) published in 2007"

Failure envelopes for offshore shallow foundations under general loading

Abstract: The interaction of vertical, horizontal and moment (VHM) loads acting on a shallow foundation is complex, and it is becoming increasingly popular to represent ultimate limit states under general VHM loading as failure envelopes in three-dimensional load space. General loading is of particular interest offshore, where harsh environmental conditions lead to large horizontal and moment foundation loads. Shallow foundations with peripheral skirts that penetrate into the seabed are used to resist large lateral and overturning forces. During undrained loading, tensile resistance can be mobilised on the underside of the base plate by suctions developed within the skirt compartment. This paper presents failure envelopes and kinematic mechanisms for undrained ultimate limit states of circular skirted foundations in uniform and heterogeneous deposits under general VHM loading based on finite element results. An approximating method is proposed that permits accurate prediction of ultimate limit states under a full range of general loading.

Centrifuge model tests on geotextile-reinforced slopes

Abstract: This paper addresses the static response of geotextile-reinforced slopes resting on a firm foundation to the self-weight loading imposed in a geotechnical centrifuge at pre-failure and at failure. ...

Improving wildfire preparedness: Lessons from communities across the U.S.

Abstract: Communities across the U.S. have been taking action to adapt to the wildfire risk they face. In a series of case studies conducted in 15 communities, researchers identified and described four elements that form the foundation for community wildfire preparedness: landscape, government, citizens, and community.

Tests on reinforced concrete deep beams

Abstract: Reinforced concrete deep beams are commonly used in structures as load distribution elements, such as transfer girders, pile caps, folded plates, and foundation walls. These members frequently have several supports and web openings to facilitate essential services.

Method and apparatus for wind power foundation

Abstract: An apparatus and method for a wind power foundation. An embodiment of a wind power plant includes a tower having a top and a bottom. The plant also includes an assembly, the assembly including a transition piece that is coupled with a concrete cap. The assembly has a top and a bottom, with the top of the assembly being coupled with the bottom of the tower. The plant also includes a jacket structure. The jacket structure has a top and a bottom and multiple legs, with the bottom of the assembly being coupled with the top of the jacket structure.

Experimental and numerical study of soil-reinforcement effects on the low-strain stiffness and bearing capacity of shallow foundations

Abstract: This paper presents results of meticulous laboratory testing and numerical simulations on the effect of reinforcement on the low-strain stiffness and bearing capacity of shallow foundations on dry sand. The effect of the location and the number of reinforcement layers is studied in the laboratory, whereas numerical simulations are used to study the reinforcement-foundation interaction. Laboratory tests show an increase of 100, 200, and 275% not only in bearing capacity but also in low-strain stiffness (linear load–displacement behaviour) of a square foundation when one, two, and three layers of reinforcement are used, respectively. The specimen preparation technique is found to be crucial for the repeatability and reliability of the laboratory results (less than 5% variability). Numerical simulations demonstrate that if reinforcements are placed up to a depth of one footing width (B) below the foundation, better re-distribution of the load to deeper layers is achieved, thus reducing the stresses and strains underneath the foundation. Numerical simulations and experimental results clearly identify a critical zone between 0.3 and 0.5B, where maximum benefits not only on the bearing capacity but also on the low-strain stiffness of the foundation are obtained. Therefore, soil reinforcement can also be used to reduce low-strain vibrations of foundations.

Health On the Net Foundation (HON)

Abstract: To achieve this mission, HON established a criteria for trustworthy health information websites, the HON Code of Conduct HONcode, reached by a consensus among webmasters, citizens and medical experts. HON develops vertical health search engines to provide access to quality and adapted online health information with the HONcode certified websites forming a “confidence-space” where citizens can safely explore and search their information options.

Impedance of flexible suction caissons

Abstract: The dynamic response of offshore wind turbines is affected by the properties of the foundation and the subsoil. The aim of this paper is to evaluate the dynamic soil-structure interaction of suction caissons for offshore wind turbines. The investigations include evaluation of the vertical and coupled sliding-rocking vibrations, influence of the foundation geometry and examination on the properties of the surrounding soil. The soil is simplified as a homogenous linear viscoelastic material and the dynamic stiffness of the suction caisson is expressed in terms of dimensionless frequency-dependent coefficients corresponding to different degrees of freedom. The dynamic stiffness coefficients for the skirted foundation are evaluated using a three-dimensional coupled boundary element/finite element model. Comparisons with known analytical and numerical solutions indicate that the static and dynamic behaviours of the foundation are predicted accurately using the applied model. The analysis has been carried out for different combinations of the skirt length, Poisson's ratio of the subsoil and the ratio of the soil stiffness to the skirt stiffness.

Earthquake fault rupture—shallow foundation interaction in undrained soils: a simplified analytical approach

Abstract: The interaction between normal or reverse fault ruptures and shallow foundations resting on a homogeneous undrained soil layer is investigated. After performing a thorough set of non-linear finite element simulations, three simple kinematic mechanisms are proposed to predict the conditions for the fault rupture to be diverted by the foundation. The results obtained by both numerical and analytical approaches are in good agreement, and support the adequacy of the proposed mechanisms. A relationship is established for assessing the minimum foundation bearing load needed for diversion of the fault rupture trace, either normal or reverse. This relationship is proved to be independent of the fault type and dip angle, so that it can be applied easily for engineering applications, even in the absence of specific tectonic information.

The Relativity of Foundation Effectiveness: The Case of Community Foundations:

Abstract: This article proposes that efforts to understand and achieve greater foundation effectiveness would be advanced by expanding the discussion to be more attuned to the relative and context-dependent ...

Probabilistic Seismic Assessment of Structure, Foundation and Soil Interacting Systems

Abstract: This report presents research on the probabilistic seismic performance evaluation of a structural-geotechnical interacting system. The system comprises a bridge, its foundation, and the supporting soil. The investigation includes a study on probabilistic performance evaluation methodologies, development of a multiplatform and hybrid simulation framework, verifications of numerical models of structural and geotechnical systems in comparison with measured data, and the derivation of fragility curves of a bridge in Central and Eastern United States. Seismic performance evaluation procedures are studied using a benchmark threestory, reinforced concrete (RC) building structure. Three probabilistic performance evaluation methods are applied: the Monte Carlo simulation, response surface, and SACFEMA methods. The analysis of benchmark structure shows that the effect of random variability in structural materials is small compared to the effect of input ground motion. When Peak Ground Acceleration (PGA) is used as an intensity measure, the derived vulnerability curves highly depend on ground motion sets. Three different simulation methods results in similar vulnerability curves. The computational cost are the most expensive when the Monte Carlo simulation is adopted. Methodologies for soil-structure-interaction analysis are introduced, including the newly developed multiplatform, multiresolution hybrid simulation framework. These methodologies and numerical models of soil-structure-interaction systems are verified through comparison with field measurements and experimental results. The soil-structure interacting system is verified through analyses of a heavily instrumented bridge which recorded several sets of ground motions. The verification study of soil-structure interacting system shows that detailed and meticulously developed analytical models are capable of replicating measurements of the response of complex bridge systems subjected to strong ground motion. Seismic vulnerability curves of a reference bridge in the Central and Eastern United States (CEUS) are derived employing the aforementioned methods with and without soilstructure interaction. A typical highway over-crossing bridge representing one of the most common bridge types in the CEUS is selected. Four different approaches of SoilStructure Interaction (SSI) are tried: (a) Abutments and foundations are assumed to be fixed, (b) Conventional lumped spring approaches are adopted to model abutments and foundations, (c) Lumped springs for abutments and foundations are estimated from Finite Element (FE) analysis of geotechnical system, and (d) Multiplatform simulation is conducted. All four of the methods shows that abutment bearings in transverse direction are most vulnerable components. Failure probability of the bridge system is highly dependent on the failure probability of abutment bearings. Considering that simplified methods for SSI analysis include larger assumptions than fully coupled methods and that the multiplatform simulation is verified with measured responses from instrumented bridge, the use of multiplatform simulation is suggested if computational power and resources for FE modeling are affordable.

Foundations and Earth Retaining Structures

Abstract: Chapter 1. Review Of Basic Soil Mechanics. Chapter 2. Foundation Loads, Stresses And Strains In Soils. Chapter 3. Analytical, Numerical Methods And Observational Methods For Foundation Design. Chapter 4. Settlement, Strength And Deformation Parameters From Laboratory Tests. Chapter 5. Site Characterization. Chapter 6. Uncertainties In Foundation Design, Foundation Design Philosophy And Methodologies. Chapter 7. Design Of Shallow Foundations. Chapter 8. Pile Foundations. Chapter 9. Mat Foundations. Chapter 10. Stability Of Earth Retaining Walls -- Rigid And Flexible Walls. Chapter 11. Mechanical Stabilized Earth (Mse) Walls And Other Retaining Walls. Appendix A. Appendix B. Appendix C.

Settlement of Shallow Circular Foundations with Structural Skirts Resting on Sand

Abstract: This paper presents the findings of an experimental study concerning a method of reducing the settlement of shallow circular foundations on sand. It involves the use of structural skirts fixed to the edges of foundations. The experiments were performed in a large tank setting and the footing was instrumented in order to measure normal stresses and settlement. A series of tests were conducted to study the settlements of a circular footing with and without structural skirts. Test results indicate that this type of reinforcement reduces the settlement of subgrade and modifies the stress-displacement behaviour of the footing. A settlement Reduction Factor (SRF) was proposed, which takes into account the influence of various parameters that affect settlements. Results show that the use of structural skirts can produce enhanced settlement reduction in the range of 0.1 to 1.0 depending on stress applied and skirt depth. Given these levels of settlements reduction, it is concluded that the use of structural skirts to reduce the settlement of shallow foundations on dense sand is of practical significance. Further testing is recommended for different foundation shapes with structural skirts resting on different soil types.

Load bearing and load anchoring, ground to structure foundation pier

Abstract: A foundation plate accepts a structural member such as a beam or post. The foundation plate uses weep holes to prevent water damage to the structural member. Anchor slots allow the use of earth screws or other means to secure the foundation plate. Additional protection to the structural member is provided by the slope and shape of the foundation plate.

Centrifuge seismic modeling of pile-supported wharves

Abstract: Five pile-supported wharf models were dynamically tested in a large-scale geotechnical centrifuge at UC Davis, California. Models representing pile-supported wharf configurations common in the United States were subjected to recorded acceleration time histories. Model variations included single-lift, multi-lift, and cut-slope rock dike configurations with foundation layers of loose liquefiable sand, marine clay, or dense sand, or a combination thereof. In addition, zones of soil were placed to model soil improvement. Structural elements representing pile-supported wharf geometries were placed within the models; some models included all vertical piles, while two of the models included batter piles. In addition, single piles were placed in two of the models and subjected to static cyclic lateral load tests. All models were extensively instrumented with nearly 100 instruments recording accelerations, pore pressures, linear deformations, and pile strains. This paper summarizes the design, construction, and testing of these complex models, and includes a brief summary of the results and recommendations for future modeling.

Design and Construction Considerations for Offshore Wind Turbine Foundations

Abstract: With the growing energy needs of the world and the sustainable nature of wind energy this sector is a highly innovative growth industry. The past years have seen the industry develop and test not only more efficient, but also much larger wind turbines than those that are in current use. The next generation of wind turbines that are on the drawing boards are gigantic in size. These huge dimensions of the proposed wind turbines will put large demands on the foundations. As an increasing number of wind farms are being planned offshore in water depths of over 40 m, the combination of water depth and the increased windmill tower heights and rotor blade diameters create loads that make foundation design very complex. Moreover, offshore foundations are exposed to additional loads such as ocean currents, storm wave loading, ice loads and potential ship impact loads. All of these factors pose significant challenges in the design and construction of wind turbine foundations. This paper presents the various issues facing the designer in designing and constructing wind turbine tower foundations. Current practices are summarized to assist developers in foundation type selection and design.Copyright © 2007 by ASME

Bored concrete pile foundation distributing optical fiber sensing detecting method and system

Abstract: The present invention relates to a distributed optical-fibre sensing detection method for cast-in-place pile foundation. It is characterized by that it utilizes the sensing property of optical fibre for strain, so that the optical fibre can be implanted in the cast-in-place pile. When the concrete is solidified or loaded externally, said concrete and its peripheral concrete can produce synchronous deformation, its produced strain extent is the strain valve of said pile-body concrete. The invented sensing technique is a distributed data acquisition, namely, it can obtain the strain data of every point of pile-body. Said invention can utilize these data to implement detection and analysis of cast-in-place pile.

Foundation construction for superstructures

Abstract: The installation of a foundation at a selected location enables a superstructure to be installed and supported in a desired attitude such as a vertical attitude at the foundation. An installation template is placed at the selected location and support sites on the installation template can be adjusted so that the installation template will support the foundation subassembly in a manner such that the superstructure can be supported in said desired attitude. The foundation subassembly is placed onto the installation template using a lifting subassembly that is secured to the foundation subassembly. The foundation subassembly is fixed in place by concrete or the like into which the foundation assembly is inserted. The superstructure can then be secured to the foundation subassembly. The superstructure and the foundation assembly can be elongated lengthwise relative to their lateral dimensions, and the superstructure can comprise a post adapted to hold a panel for deflecting road noise.

Gravity foundation for tidal stream turbine

Abstract: An arrangement for mounting at least one tidal turbine and its associated support structures 4 in a river or sea bed, characterised by mounting the turbine and associated support structures 4 upon a base/foundation structure 8,15 of such weight as to withstand forces acting to displace it The base/foundation structure 8,15 may be pre-assembled an transportable to a required location where it may be lowered to the sea or river bed The base/foundation structure 8,15 may include voids 16 fillable with ballast when in position Expandable members such as jacks or expandable elastomeric tubes 19 may be used to level the base/foundation 8,15 on the sea/river bed The base/foundation may also be further secured by means of elongate fasteners driven into the sea/river bed

Assessing foundation stability and soil-structure interaction through integrated geophysical techniques: A case history in Rome (Italy)

Abstract: We present a case history in which several geophysical methods were used to investigate a five-floor residential building, constructed from reinforced concrete, which has been seriously damaged by differential settlement. The results from various geophysical methods (electrical resistivity tomography, seismic refraction, multichannel analysis of surface waves, cross-hole seismic surveys) were integrated and correlated to give an overall picture of the subsoil geometry and characteristics in the area under investigation, with particular regard to the stiffness properties and the degree of saturation. The ability of geophysics to investigate non-invasively has proven successful for dealing with buildings affected by foundation instability. The resolution of the results obtained from experimental data provides additional insight into the geological scenario and the causes of the settlement. Moreover, geophysical data may be used as a guide to optimize borehole locations for coring and soil specimen collection, which are necessary steps in designing the restoration intervention.