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Klammler H.,Federal University of Bahia | McVay M.,University of Florida | Lai P.,05 Suwannee St. | Horhota D.,State Materials Office
Journal of Geotechnical and Geoenvironmental Engineering | Year: 2013

Reliability-based design, such as LRFD, aims at meeting desired probability of failure levels for engineered structures. The present work attempts to contribute to this field by analyzing the influence of spatially variable soil/rock strength on the axial resistance uncertainty of single and multiple shafts in group layouts. This includes spatial variability over the individual shaft surfaces, effects of limited data, random measurement errors, and workmanship. A possible correlation between boring data inside or near the footprint of a foundation and the foundation itself is considered. In a geostatistical approach, spatial averaging (upscaling) and a degenerate case of ordinary kriging are applied to develop variance reduction charts and design equations for a series of foundation group layouts (single, double, triple, and quadruple). For the potential situation of an unknown horizontal correlation range at a site, the worst case scenarios are identified and demonstrated in an example problem. Resulting probabilities of failure are applied to the whole foundation (i.e., group) rather than single objects. It is found that a boring at the center of a group footprint can significantly reduce resistance prediction uncertainty, especially under the worst case scenario for unknown horizontal correlation range. In contrast, independent of the presence of a center boring or not, the uncertainty reduction through additional borings becomes small, once four or five borings are available. © 2013 American Society of Civil Engineers. Source


Thiyyakkandi S.,University of Florida | McVay M.,University of Florida | Bloomquist D.,University of Florida | Lai P.,05 Suwannee St.
Journal of Geotechnical and Geoenvironmental Engineering | Year: 2013

With increased urbanization, deep foundation (bridges, signage, walls, etc.) selection is moving toward the minimization of disturbance and installation time, as well as addressing quality control and assurance issues. Unfortunately, many types of deep foundations involve noise and vibration during installation (e.g., driven piles) or integrity and reduced resistance issues (e.g., drilled shafts, both conventional and post grouted tip, continuous flight auger piles). This paper presents a new foundation type, a jetted and grouted precast pile, which uses the advantages of several proven deep foundation installation techniques. The installation of the new pile is comprised of three distinct phases: (1) pressurized water-jetting of a precast pile into the ground; (2) side grouting of the pile; and (3) tip grouting. The pile has two separate side grouting zones, each with its own grout delivery system. Each grout zone is covered with a semirigid membrane, which results in radial expansion of the soil during side grouting and horizontal orientation of the major principal stress. Small-scale testing revealed excellent bonding between the pile and the grout, as well as improved mobilized pile-soil skin and tip resistance. Both experimental and FEM modeling of the grouting and axial loading were performed on various sized jetted and grouted precast piles in cohesionless soil. On the basis of this study, a methodology that predicts expected grout pressures during grouting, unit side and tip resistance, and the load-displacement response of a pile in cohesionless soil is proposed. Further testing and research is required to validate the proposed methodology before it can be implemented in practical situations. © 2013 American Society of Civil Engineers. Source


Tran K.T.,University of Florida | McVay M.,University of Florida | Herrera R.,05 Suwannee St. | Lai P.,05 Suwannee St.
Computers and Geotechnics | Year: 2012

A technique is presented to estimate the nonlinear skin friction of a driven pile using monitored strains and accelerations at the top and bottom of a pile during a hammer blow. The scheme is based on a numerical solution of the 1-D wave equation with nonlinear static skin friction and viscous stiffness proportional damping. The soil-pile system is divided into pile segments based on pile length and the frequency content of the measured signal. Each segment is characterized with independent multilinear (bilinear loading with independent unloading) soil skin friction. The measured strains at the top and bottom of the pile are used to solve for the unknowns, including proportional damping and the loading and unloading stiffness of each pile segment from a least square error comparison of measured and computed particle velocities at the top and bottom of the pile. The technique was applied to four full-scale piles driven into layered sand and clay deposits with measured ultimate static skin frictions varying from 700 to 2700. kN. The analysis was carried out on five separate beginning of restrike blows within 1. week of the static load tests. The approach was shown to give consistent (within 20%) predicted skin frictions vs. displacements of the measured static load test results. © 2011 Elsevier Ltd. Source


Tran K.T.,University of Florida | McVay M.,University of Florida | Herrera R.,05 Suwannee St. | Lai P.,05 Suwannee St.
Soil Dynamics and Earthquake Engineering | Year: 2011

A numerical technique is presented to estimate ultimate skin friction of a driven pile using instrumentation installed at the top and bottom of a pile. The scheme is based on an analytical solution of the 1D wave equation with static skin friction and damping along with a genetic algorithm for solution. Specifically, acceleration and strains measured at both the top and bottom of the pile are used to develop an observed Green's function, which is matched to an analytical Green's function, which is a function of secant stiffness and viscous damping. Requiring 1-3. s of analysis time per blow, the algorithm provides a real time assessment of average skin friction along the pile. The technique was applied to four driven piles having ultimate skin frictions varying from 700 to 2000. kN, with the predicted skin frictions generally consistent with measured static load test results. © 2011 Elsevier Ltd. Source

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