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Burkett T.B.,Fugro | Gilbert R.B.,University of Texas at Austin | Simpson R.C.,Loadtest United States | Wooley J.A.,Balcones Geotechnical PLLC | And 2 more authors.
Geotechnical Special Publication | Year: 2015

An investigation into the load-settlement behavior of two drilled shafts, founded in shale, is presented. The motivation for this research is to advance the understanding on how drilled shafts react under loading in stiff clays and shales. The objective of this study is to improve the understanding of axial capacities for rock-socketed shafts in hard clays and shales. In order to achieve this objective, the research team measured the strengths within the subsurface material at the test site, estimated the unit side shear and unit end bearing of the shale-shaft interaction by running two axial load tests using the patented Osterberg-Cell (O-Cell) loading technique, and compared the results to the current design methods that are used to predict the axial capacity of drilled shafts. The results of the study concluded that the current methods for estimating unit end bearing developed by the Texas Department of Transportation (TxDOT) and the Federal Highway Administration (FHWA) provide fairly accurate predictions when compared to the measured information However, it was discovered that the measured ultimate side resistance steadily decreased nearing the tip of the shaft. A limited amount of information is currently available for load tests performed in soils with Texas Cone Penetration (TCP) values harder than 2-in per 100 blows. The results presented herein demonstrate the effectiveness of the current design methods for drilled shafts and the non-uniformity of side resistance within one- to two-diameters of the shaft tip. © ASCE 2015.

Senanayake A.,University of Texas at Austin | Rendon E.,Ensoft Inc. | Wang S.-T.,Ensoft Inc. | Gerkus H.,University of Texas at Austin | And 2 more authors.
Proceedings of the Annual Offshore Technology Conference | Year: 2015

The objective of this paper is to address the applicability of using API RP 2GEO (2011) for the design of wind turbine monopile foundations in normally to moderately overconsolidated clays. The study involved three-dimensional numerical modeling using the finite-element method, one-g laboratory model testing, and analysis of field test results. The following conclusions concerning the use of Matlock (1970) soft clay p-y curves for the design of large-diameter monopile foundations are drawn: Numerical modeling and model-scale testing with rigid piles of different diameters indicate that the form of the Matlock (1970) p-y curves, in which the lateral displacement is normalized by pile diameter and lateral soil resistance is normalized by the ultimate resistance, appropriately captures the effect of pile diameter. Field and model testing indicate that the Matlock (1970) p-y models consistently overestimate the lateral displacements at the pile head when used to analyze laterally loaded piles in normally to moderately overconsolidated clays. An approximate version of the Jeanjean (2009) p-y model, in which the Matlock (1970) p-y curves are scaled by p-multipliers calculated at various depths, generally provides a reasonable match to measured lateral displacements at the pile head when a relatively large strain at one-half the undrained shear strength is assumed, i.e., c50 = 0.02. This result applies both to small scale model tests in kaolinite and large-scale field tests in high-plasticity clay. Model tests show that cyclic loading causes the stiffness of the lateral pile-soil response to degrade by 20 to 30 percent. The amount of degradation is dependent on the displacement amplitude and the number of cycles. All of the degradation happens within 100 cycles, after which the stiffness is reasonably constant. Model tests show that the ultimate lateral capacity of the pile is not significantly affected by the previous cyclic loading. Copyright © (2015) by the Offshore Technology Conference All rights reserved.

Stevens R.F.,Fugro | Soosainathan L.,Fugro | Rahim A.,NGI Inc | Saue M.,NGI Inc | And 6 more authors.
Offshore Technology Conference, Proceedings | Year: 2015

The Geotechnics Sub-Committee of the American Society of Civil Engineers (ASCE) Coasts, Oceans, Ports, and Rivers Institute (COPRI) Marine Renewable Energy (MRE) Committee is preparing a guide document for marine renewable energy foundations. That guide would use standard design codes for fixed foundations and mooring anchors in API RP 2GEO and DNV. The static method of computing axial pile capacity described in API RP 2GEO (2011) is generally used to compute ultimate compressive and tensile capacities of pipe piles driven to a given penetration. Lateral soil resistance -pile deflection (p-y) data for clays and sands are usually developed using procedures proposed by Matlock (1970) and O'Neill and Murchison (1983), respectively, and outlined in API RP 2GEO (2011). Marine energy foundations are unique in several ways. Axial pile capacity computations are usually based on a reasonable lower bound, in contrast to the soil resistance to driving, which is based on a reasonable upper bound. For structures supporting wind turbines, however, underestimating (or overestimating) the soil stiffness could require a change in turbine operation and a loss of power production. Although the classical API method is recognized as an appropriately conservative design method for offshore pile foundations, a prediction method is more well suited for structures supporting wind turbines, such as the CPT-based methods for predicting pile capacity in granular soils presented in API RP 2GEO (2011). If a prediction method is used to compute the soil resistance to driving, the evaluation of pile drivability may be overly conservative. Ageing in both clay and sand should also be taken into account. Wind turbines are often supported on large diameter monopiles. The applicability of the p-y data for such large diameter piles needs to be verified. Finally, marine renewable energy generated by in-stream hydrokinetics, ocean thermal energy conversion, and wave energy converters may be floating devices usually anchored to the seafloor. There are uncertainties in the design and installation of these anchors, which become critical for large sustained tensile loads that may degrade due to creep and cyclic loading. Copyright 2015, Offshore Technology Conference.

Talley K.G.,Texas State University | Arrellaga J.,Ensoft Inc. | Breen J.E.,University of Texas at Austin
Journal of Structural Engineering (United States) | Year: 2014

The research program discussed in this paper included both experimental and computational investigations of structural capacity effects on bridge columns by simulating observed column damage. For the experimental research, scaled models of a column were constructed and fractured using stone-splitting wedges. This method was intended to create the worst-case scenario based on the observed damage in the field: cracks propagating through the core of the columns and effectively cleaving each column into four pieces. The finite-element software ATENA, which models cracking in reinforced concrete, was used for the computational modeling and a parametric study. The computer model was correlated to the experimental results and then used to predict capacities for a variety of deterioration levels. This parametric study was used to determine the critical crack width, which would reduce the capacity of the column to its design load. This predicted critical crack width gives the bridge owner another tool for the evaluation of concrete degradation. This paper focuses on the computational portion of the research. As such, this paper presents a method to mimic existing damage in a finite-element model that the practicing engineer could use in a structural assessment of existing conditions. © 2014 American Society of Civil Engineers.

Han Y.,Fluor Corporation | Wang S.-T.,Ensoft Inc.
Geotechnical Special Publication | Year: 2013

The advances on soil-pile-structure interaction are described in this study. The nonlinearity of soil is accounted for approximately by a boundary zone model, and the curves of stiffness and damping of the nonlinear soil-pile system are provided. The coupled horizontal and rocking vibration of an embedded foundation (including pile cap) is analyzed by four parameters rather than the traditional six parameters. The radiation damping is corrected based on many dynamic tests in the field. The effects of soil-pile-structure interaction on dynamic behaviour are examined based on an engineering case. Three conditions are considered: (1) the soil-pile-structure interaction is accounted for fully; (2) the soil-pile system is flexible, but the structure is assumed to be rigid; and (3) the structure is flexible, but the base foundation is assumed to be rigid. For practical applications, a tower structure supported on piled foundation was examined under seismic loads. The earthquake forces and response were calculated using the time history analysis and response spectrum analysis, and compared with those using the method of equivalent static loads. © 2013 American Society of Civil Engineers.

Ni S.-H.,National Cheng Kung University | Isenhower W.M.,Ensoft Inc. | Huang Y.-H.,Trinity Consultants
Journal of GeoEngineering | Year: 2012

Non-destructive evaluation techniques have been adopted to provide pile construction quality control for many years. In particular, low strain pile integrity test methods have been used to check lengths and integrity of newly installed pile. The pile integrity testing signals acquired from the receivers on pile heads are complicated by defects and undesired background noise. The continuous wavelet transform (CWT) method with time-frequency distribution is adopted to enhance the characteristics of the testing signal to raise the identification ability in experimental cases. The in-situ tests of drilled shaft indicate that testing signals could be displayed in the time-frequency domain at the same time and then be explored at every single time by CWT. CWT can enhance the signal and make more information visible. Coupling CWT and Sonic Echo (SE) methods to interpret and identify the pile integrity visually, easily and quickly is proven, even for long drilled shafts.

Rendon E.A.,Ensoft Inc. | Manuel L.,University of Texas at Austin
Wind Energy | Year: 2014

Accurate prediction of long-term 'characteristic' loads associated with an ultimate limit state for design of a 5-MW bottom-supported offshore wind turbine is the focus of this study. Specifically, we focus on predicting the long-term fore-aft tower bending moment at the mudline and the out-of-plane bending moment at the blade root of a monopile-supported shallow-water offshore wind turbine. We employ alternative probabilistic predictions of long-term loads using inverse reliability procedures in establishing the characteristic loads for design. Because load variability depends on the environmental conditions (defining the wind speed and wave height), we show that long-term predictions that explicitly account for such load variability are more accurate, especially for environmental states associated with above-rated wind speeds and associated wave heights. Copyright © 2012 John Wiley & Sons, Ltd. Copyright © 2012 John Wiley & Sons, Ltd.

Vasquez L.F.G.,Ensoft Inc. | Maniar D.R.,Stress Engineering Inc. | Tassoulas J.L.,University of Texas at Austin
Journal of Geotechnical and Geoenvironmental Engineering | Year: 2010

We outline the development of a computational procedure for finite-element analysis of suction-caisson behavior, highlighting its unique features and capabilities. The procedure is based on a description of clayey soil as a two-phase medium: a water-filled porous solid. Nonlinear behavior of the solid phase is represented by means of a bounding-surface plasticity model. An algorithm is developed for frictional contact in terms of effective normal stress. Furthermore, a special remeshing scheme is introduced facilitating the simulation of the installation process, tracking the caisson penetration path and avoiding numerical complications in the vicinity of the caisson-soil interfaces. To illustrate the use of the proposed computational procedure and examine its validity, complete simulations of available laboratory tests on model suction caissons are conducted. Results are presented and discussed for test-bed preparation (consolidation) followed by caisson installation by self-weight and suction, setup (reconsolidation), and axial pullout. The overall agreement between computations and measurements is good. Possible improvements are identified and recommendations are made regarding future studies. © 2010 ASCE.

Wang S.-T.,Ensoft Inc. | Vasquez L.,Ensoft Inc. | Xu D.,Ensoft Inc.
Geotechnical Special Publication | Year: 2013

One of the most important features of flexible retaining walls is that wall deformations highly influence the distribution of earth pressures on the wall. The deflection of flexible retaining walls is controlled by the flexural rigidity of the wall and the soil pressure generated based on the permissible movement of the wall. The conventional method of design for flexible retaining walls is based on a limit-equilibrium theory that searches the force equilibrium by assuming the soils engaged around the wall are all in the limit state. The limit-equilibrium analysis does not take into account the nonlinear mobilization of soil reaction with wall deflection. The application of soil-structure interaction (SSI) to the design of flexible retaining walls means that the deformation of the structural system is analyzed based on the mobilized earth pressure and soil resistance along the wall. Such analyses will result in the most appropriate selection of the size and configuration of the wall, and for the tieback, while ensuring that deformations throughout the system are acceptable. The method introduced in this paper is to model the structural elements in terms of overall behavior and to use nonlinear p-y curves for modeling the passive resistance of soils due to lateral deformation of embedded wall sections. This paper will discuss the modifications of p-y curves that are needed to take into account the configuration of the wall system (group effects), the unsymmetrical driving forces in the backfill side, the soil resistance in the penetration side, and the long-term effect from the sustained loads. © 2013 American Society of Civil Engineers.

Ensoft Inc. | Date: 2010-11-11

A base for holding a wind turbine tower is disclosed. The base includes individual shaft piles, a base cap and anchoring units. The base cap includes reinforcement inserts and is connected to each of the individual shaft piles. The anchoring units are embedded in the base cap and extend in an anchoring direction from the base cap at anchoring locations for anchoring the wind turbine tower to the base cap. Each of the reinforcement inserts extend in a radial direction relative to a center axis of the wind turbine tower. At least one of the plurality of reinforcement inserts, at a radius of the center axis adjacent to an anchoring location of a respective anchoring unit, has a portion of the respective reinforcement insert extending along the anchoring direction.

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