Development Of Recommended Resistance Factors For Drilled Shafts In Weak Rocks Based On O Cell Tests
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Development Of Recommended Resistance Factors For Drilled Shafts In Weak Rocks Based On O Cell Tests
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Author : Xiaoming Yang (Writer on geotechnical engineering)
language : en
Publisher:
Release Date : 2010
Development Of Recommended Resistance Factors For Drilled Shafts In Weak Rocks Based On O Cell Tests written by Xiaoming Yang (Writer on geotechnical engineering) and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2010 with Load factor design categories.
From October 1, 2007, the new bridges on federal-aid funded projects are mandated to be designed to meet American Association of State Highway and Transportation Officials (AASHTO) Load and Resistance Factor Design (LRFD) Bridge Design Specifications. LRFD is a simplified form of reliability-based design. By multiplying calibrated factors to load and resistance components, the designed structure will maintain a specific level of reliability (or probability of failure). By concept, the load and resistance factors should be calibrated by large number of test data; however, they are often unavailable in geotechnical engineering. Significant efforts are needed to calibrate load and resistance factors based on test data of good quality. In this study, 26 O-Cell test data were collected from Kansas, Colorado, Missouri, Ohio, and Illinois. Seven methods available in the literature were selected to estimate the load capacities of 25 out of 26 drilled shafts. The "FHWA 0.05D" method was found to yield the closest and conservative predictions of the nominal resistances to the representative values; therefore, it was adopted in this study when calibrating the resistance factors for Strength Limit State design. These test data were analyzed and used to calibrate side and base resistance factors for drilled shafts in weak rock. Resistance factors were calibrated at two different target reliability indices: 2.3 (i.e., failure probability, Pf ~ 1/100) for shafts with greater redundancy and 3.0 (Pf ~ 1/1000) for shafts with less redundancy. Side resistance factors were calibrated from two different datasets of measured resistance: total side resistance and layered unit side resistance. The resistance factors calibrated from layered unit side resistance are considered more reliable, therefore, they are recommended for design. The recommended resistance factors from this study are compared with those in AASHTO specifications. Some of those calibrated resistance factors from this study are considerably lower than those in AASHTO specifications. The main reasons for such lower resistance factors are mainly attributed to the low efficiency of the FHWA design method and the limited quality and number of O-Cell test data. These resistance factors may be improved by increasing the size and the quality of the test data in the future. At present, field load tests on drilled shafts are recommended as an alternative to using lower resistance factors, which will also accumulate more test data for future improvement.
Model Uncertainties In Foundation Design
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Author : Chong Tang
language : en
Publisher: CRC Press
Release Date : 2021-03-17
Model Uncertainties In Foundation Design written by Chong Tang and has been published by CRC Press this book supported file pdf, txt, epub, kindle and other format this book has been release on 2021-03-17 with Technology & Engineering categories.
Model Uncertainties in Foundation Design is unique in the compilation of the largest and the most diverse load test databases to date, covering many foundation types (shallow foundations, spudcans, driven piles, drilled shafts, rock sockets and helical piles) and a wide range of ground conditions (soil to soft rock). All databases with names prefixed by NUS are available upon request. This book presents a comprehensive evaluation of the model factor mean (bias) and coefficient of variation (COV) for ultimate and serviceability limit state based on these databases. These statistics can be used directly for AASHTO LRFD calibration. Besides load test databases, performance databases for other geo-structures and their model factor statistics are provided. Based on this extensive literature survey, a practical three-tier scheme for classifying the model uncertainty of geo-structures according to the model factor mean and COV is proposed. This empirically grounded scheme can underpin the calibration of resistance factors as a function of the degree of understanding – a concept already adopted in the Canadian Highway Bridge Design Code and being considered for the new draft for Eurocode 7 Part 1 (EN 1997-1:202x). The helical pile research in Chapter 7 was recognised by the 2020 ASCE Norman Medal.
Rock Socketed Shafts For Highway Structure Foundations
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Author : John P. Turner
language : en
Publisher: Transportation Research Board
Release Date : 2006
Rock Socketed Shafts For Highway Structure Foundations written by John P. Turner and has been published by Transportation Research Board this book supported file pdf, txt, epub, kindle and other format this book has been release on 2006 with Bridges categories.
TRB's National Cooperative Highway Research Program (NCHRP) Synthesis 360: Rock-Socketed Shafts for Highway Structure Foundations explores current practices pertaining to each step of the design process, along with the limitations; identifies emerging and promising technologies; examines the principal challenges in advancing the state of the practice; and investigates future developments and potential improvements in the use and design of rock-socketed shafts.
Drilled Shafts In Rock
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Author : Lianyang Zhang
language : en
Publisher: CRC Press
Release Date : 2004-05-15
Drilled Shafts In Rock written by Lianyang Zhang and has been published by CRC Press this book supported file pdf, txt, epub, kindle and other format this book has been release on 2004-05-15 with Technology & Engineering categories.
Drilled shafts in rock are widely used as foundations of heavy structures such as highway bridges and tall buildings. Although much has been learned about the analysis and design of drilled shafts in rock, all the major findings are published in the form of reports and articles in technical journals and conference proceedings. This book i
Study Of Side Shear Stress Development For Drilled Shafts In Very Weak Porous Limestone Using Axial Load Transfer Analyses
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Author : Matias R. Frediani
language : en
Publisher:
Release Date : 2023
Study Of Side Shear Stress Development For Drilled Shafts In Very Weak Porous Limestone Using Axial Load Transfer Analyses written by Matias R. Frediani and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2023 with Civil engineering categories.
This thesis presents a series of axial load transfer analyses performed to investigate the mobilization of side shear stresses of drilled shafts installed in a very weak, porous limestone formation in Puerto Rico (PR). The numerical analyses presented are predictions of two axial load tests carried out on instrumented drilled shafts installed in very weak, porous limestone at a test site located in northwest PR. The field test component was performed by a former MS student of the research group of Dr. Pando when employed by the University of Puerto Rico at MayaguÌ8ez. The test site involved an outcrop of a very weak, porous, and highly weathered limestone with a representative unconfined compressive strength (UCS) of 2.7 MPa, and an average rock quality designation (RQD) of 34%. Descriptions of the test site and the rock characterization are provided in this MS thesis. The main objective of this thesis was to investigate the mobilization of the side shear stresses of the two test drilled shafts installed in this unique very weak, porous limestone and assess whether load transfer analyses are suitable to predict the observed experimental behavior. The first focus of this study was to evaluate whether existing static methods could reasonably predict the measured ultimate side shear stresses, also referred to as unit shaft resistance. A total of 10 static methods were evaluate and the range of predictions of the unit shaft resistance was found to be very large, highlighting the need to improve our capability of predicting this important design parameter. Furthermore, the measured ultimate side shear stress values at the PR test site were found to be above the upper bound of the range of predicted values using the selected static methods. The higher measured unit shaft resistance values are attributed to limitation of the selected static methods that are solely based on only the intact rock UCS, and do not incorporate other important variables such as the surface roughness of the rock socket walls or stiffness ratio between drilled shaft and surrounding rock mass. The second focus of this MS thesis was to evaluate the ability to capture the axial load transfer mechanisms of the test drilled shafts and the experimental axial load versus settlement curves using load transfer analyses. The load transfer analyses behavior of the axial load tests was simulated using 1D finite element models of the deep foundation and springs using nonlinear T-Z curves to represent the development of the side shear stresses as a function of level of relative movement between the foundation and the rock. The literature review identified two T-Z curves formulations for very weak limestone. One formulation is from McVay and Niraula (2004) who proposed T-Z curves developed from centrifuge tests on simulated Florida limestone. The second formulation is a model developed by Asem and Gardoni (2019) based on a comprehensive database of drilled shaft load tests on very weak to weak rock. These two T-Z formulations were used to predict the experimental load-settlement curves. The predictions using the McVay and Niraula (2004) were much stiffer than the observed behavior. A modified T-Z formulation, based on the Asem and Gardoni (2019) was found to yield the best predictions and exhibit more flexibility because it depends not only on the unit shaft resistance but also on the stiffness or modulus of deformation of the rock mass. The modified load-transfer model was found to be reasonably adequate to predict the measured experimental behavior of the two test drilled shafts installed in the unique, very weak, porous limestone rock from the karst formation in northwest PR.
Utilizing Load Tests And Site Investigation Data To Predict Design Load Capacities For Drilled Shafts In Different Geologic Formations
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Author : Hosam Salman
language : en
Publisher:
Release Date : 2022
Utilizing Load Tests And Site Investigation Data To Predict Design Load Capacities For Drilled Shafts In Different Geologic Formations written by Hosam Salman and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2022 with Engineering categories.
Precise predictions of the design capacities of drilled shafts on weak rock formations is vital for a better design of foundations. Irregularities in rock formations due to weathering cause discrepancies in actual bearing capacities and evaluating the bearing capacity typically requires frequent in-situ testing, using load test shafts at smaller intervals, which is time consuming and expensive. The typical design in Texas currently utilizes in-situ design charts that are developed based on Texas Cone Penetrometer (TCP) blow counts. This approach is found to have limitations related to maximum number of blows, rock characterization, and difficulty in incorporating influential parameters. Problematic soils in the North Central Texas region often lead practitioners to choose deep foundations, but the current design charts do not distinguish between the various types of rock or degradable materials such as intermediate geomaterials (IGM) or shale formations,and the software currently used for deep foundation capacity design does not incorporate all of the influential parameters.The purpose of this study is to better predict and assess the design parameters that are being used for deep foundation design and to improve the current drilled shaft design by either modifying the existing charts or developing new design charts for various types of rock formations such as limestone, sandstone, and intermediate geomaterials (IGM) such as shales. (IGMs are very soft to-medium hard rocks such as shale.) The principal goal and contribution of this research is to improve the methods for predicting drilled shaft design capacities by accounting for the geologic formations and learning from past projects. The following objectives were achieved to fulfill this goal: I. A database was compiled to employ statistical learning methods, as the applicability of a statistical learning outcome relies heavily on the type of database used and there were no databases that contained site investigation data in conjunction with load test data from drilled shaft projects. A database of site investigation data and load test data was compiled from projects undertaken in various geologic formations including shale,Woodbine shale, sandstone, and limestone. About 22 projects used for regression and validation, and approximately 38 load tests were performed for this research.II. Statistical correlations were developed between TCP, unconfined (uniaxial) compressive strength (Qun), dry unit weight, moisture content, recovery, rock quality designation, skin friction, and end bearing. About 96 predicted equations were developed to accommodate the various geologic formations. III. Design charts were developed to predict drilled shaft capacities, accounting for geologic formations and weathered conditions. This research discusses the advantages of the most recent load tests performed on drilled shafts in various design-build projects in the United States and on various types of geologic formations. Several loads tests, such as the Statnamic and bi-directional (O-cell) load cell tests (Osterberg) have been performed on various geologic formations distributed across the Dallas Fort Worth area. Various tables and plots were presented for each formation to show the Pearson correlations matrix and data distribution of each engineering parameter. The research demonstrated how the data were classified and sorted into 45 subsets per three classification systems per the FHWA guidelines to ensure the identification of the best fit regression and model of each geologic formation. It also discussed the challenges of the database such as missing data and outliers, provided methods to resolve these challenges, and showed the distribution of the engineering parameters. Over-designed (OD) or under-predicted (UP) and under designed (UD) or over-predicted (UP) foundation capacities are two common forms of negative variabilities that need to be avoided. Reducing the OD and UD requires the correct assessment of the rock quality and properties. It is always recommended to perform more field load testing to better optimize and predict the appropriate design charts.This research can be directly applied to many bridge design and foundation projects across the globe to ensure that the projects are designed to be safe, long lasting and provides cost savings to the agencies.
Drilled Shafts
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Author : Michael W. O'Neill
language : en
Publisher:
Release Date : 1999
Drilled Shafts written by Michael W. O'Neill and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 1999 with Foundations categories.
Geotechnical Safety And Risk V
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Author : T. Schweckendiek
language : en
Publisher: IOS Press
Release Date : 2015-10-09
Geotechnical Safety And Risk V written by T. Schweckendiek and has been published by IOS Press this book supported file pdf, txt, epub, kindle and other format this book has been release on 2015-10-09 with Technology & Engineering categories.
Geotechnical Risk and Safety V contains contributions presented at the 5th International Symposium on Geotechnical Safety and Risk (5th ISGSR, Rotterdam, 13-16 October 2015) which was organized under the auspices of the Geotechnical Safety Network (GEOSNet) and the following technical committees of the of the International Society of Soil Mechanics and Geotechnical Engineering (ISSGME): • TC304 Engineering Practice of Risk Assessment & Management • TC205 Safety and Serviceability in Geotechnical Design • TC212 Deep Foundations • TC302 Forensic Geotechnical Engineering Geotechnical Risk and Safety V covers seven themes: 1. Geotechnical Risk Management and Risk Communication 2. Variability in Ground Conditions and Site Investigation 3. Reliability and Risk Analysis of Geotechnical Structures 4. Limit-state design in Geotechnical Engineering 5. Assessment and Management of Natural Hazards 6. Contractual and Legal Issues of Foundation and (Under)Ground Works 7. Case Studies, Monitoring and Observational Method The 5th ISGSR is the continuation of a series of symposiums and workshops on geotechnical risk and reliability, starting with LSD2000 (Melbourne, Australia), IWS2002 (Tokyo and Kamakura, Japan), LSD2003 (Cambridge, USA), Georisk2004 (Bangalore, India), Taipei2006 (Taipei, Taiwan), the 1st ISGSR (Shanghai, China, 2007), the 2nd ISGSR (Gifu, Japan, 2009), the 3rd ISGSR (Munich, Germany, 2011) and the 4th ISGSR (Hong Kong, 2013).
Applications Of Statistics And Probability In Civil Engineering
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Author : Michael Faber
language : en
Publisher: CRC Press
Release Date : 2011-07-15
Applications Of Statistics And Probability In Civil Engineering written by Michael Faber and has been published by CRC Press this book supported file pdf, txt, epub, kindle and other format this book has been release on 2011-07-15 with Technology & Engineering categories.
Under the pressure of harsh environmental conditions and natural hazards, large parts of the world population are struggling to maintain their livelihoods. Population growth, increasing land utilization and shrinking natural resources have led to an increasing demand of improved efficiency of existing technologies and the development of new ones. A
Design Of Rock Socketed Drilled Shafts
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Author : Jamal Nusairat
language : en
Publisher:
Release Date : 2006
Design Of Rock Socketed Drilled Shafts written by Jamal Nusairat and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2006 with Bridges categories.
This project was aimed at evaluating and developing design methods for laterally loaded drilled shafts socketed in rock. Five lateral load tests on rock socketed drilled shafts with full range of instrumentation were conducted in Ohio. Detailed instrumentation included the use of vibrating wire strain gages, inclinometers, dial gages, and load cells. P-y curves representing site-specific lateral shaft-rock interaction were deduced from strain data. Field testing included the use of a borehole pressuremeter/dilatometer to obtain measurements that were correlated with rock mass strength and deformation parameters as well as with p-y curves. A comparison was made between the baseline p-y curves deduced from strain data of lateral load tests, the p-y curves predicted by using Reese's interim criterion, and the p-y curves from the pressuremeter tests in rock. A new hyperbolic p-y criterion for rock is proposed based on the field test data and extensive theoretical work. Validation of the proposed p-y criterion of rock was carried out by comparing the predictions of shaft deflections and bending moments using the hyperbolic p-y criterion against actual lateral load tests results. Based on the findings of this study, a complete solution for the design of drilled shafts socketed in rock or intermediate geomaterials under lateral loads is provided.