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- Permanent Link:
- http://digital.auraria.edu/AA00004224/00001
## Material Information- Title:
- A study of static torsional loading on drilled shafts
- Creator:
- Volmer, Brian Paul
- Publication Date:
- 2011
- Language:
- English
- Physical Description:
- xiii, 120 leaves : ; 28 cm
## Subjects- Subjects / Keywords:
- Dead loads (Mechanics) ( lcsh )
Torsion ( lcsh ) Shafts (Excavations) ( lcsh ) Soil mechanics ( lcsh ) Dead loads (Mechanics) ( fast ) Shafts (Excavations) ( fast ) Soil mechanics ( fast ) Torsion ( fast ) - Genre:
- bibliography ( marcgt )
theses ( marcgt ) non-fiction ( marcgt )
## Notes- Bibliography:
- Includes bibliographical references (leaves 115-120).
- General Note:
- Department of Civil Engineering
- Statement of Responsibility:
- by Brian Paul Volmer.
## Record Information- Source Institution:
- |University of Colorado Denver
- Holding Location:
- |Auraria Library
- Rights Management:
- All applicable rights reserved by the source institution and holding location.
- Resource Identifier:
- 747568676 ( OCLC )
ocn747568676 - Classification:
- LD1193.E53 2011m V64 ( lcc )
## Auraria Membership |

Full Text |

A STUDY OF STATIC TORSIONAL LOADING ON DRILLED SHAFTS by Brian Paul Volmer B.S., University of Colorado Denver, 2008 A thesis submitted to the University of Colorado Denver in partial fulfillment of the requirements for the degree of Master of Science Civil Engineering 2011 2011 by Brian Paul Volmer All rights reserved. This thesis for Master of Science degree by Brian Paul Volmer has been approved by Hamid Z. Fardi / / Date Volmer, Brian Paul (M.S., Civil Engineering) A Study of Static Torsional Loading on Drilled Shafts Thesis directed by Professor Nien-Yin Chang ABSTRACT Torsional loading on deep foundations is a topic that has received less attention than other load types, particularly the effects of combined-loading and sequences of loading. This work has investigated some of the above effects, but much more in-depth study is desired. A study of the torsional response of drilled shafts is made using a new nonlinear finite element analysis program, SSI3D, for both cohesive and cohesionless soils. This study includes the influences of combined lateral-torsional and vertical-torsional loading, which are found to be significant in some cases and highly dependent upon the soil type. A comparison between the developed finite element analysis and existing design methodology is made. It is found that some of the design methods compare surprisingly well with the finite element analysis, but some were a bit off. Also, because little full-scale testing has been done for torsional loading and torsional loading testing is by nature more complex than that of the more common vertical or lateral tests, a full-scale torsional load test with accommodation for vertical and/or lateral loading is proposed in the hopes of facilitating a better understanding of the behavior of deep foundations under combined loading in different soils. This abstract accurately represents the content of the candidate's thesis. I recommend its publication. ACKNOWLEDGEMENT My thanks to God, my advisor, my family, and my friends for their support and encouragement, without which this work would have never come to be. I would like to give special thanks to Dr. Nien-Yin Chang (my advisor), Kevin Lee (friend in geotechnical studies), Dr. Hien Nghiem (friend and creator of SSI3D), Paul Volmer (my dad), and Cuong Vu (friend in geotechnical studies) for their distinguished physical insight, criticism, technical support, and patience. I am very grateful for my great friend and fellow student in geotechnical studies Shanna Malcolm, who prepared the greater portion of the drawings shown in this work. Also, I would like to thank the Achievement Rewards for College Scientists Foundation (ARCS) for their financial support in my graduate studies. Their aid is greatly appreciated. TABLE OF CONTENTS Figures........................................................................x Tables......................................................................xiii Chapter 1. Introduction................................................................1 1.1 Background.................................................................1 1.2 Objectives of Research.....................................................2 2. Literature Review..........................................................3 2.1 Introduction..............................................................3 2.2 Full-Scale Testing........................................................3 2.2.1 Stoll (1972).............................................................3 2.2.2 Tawfiq (2000)............................................................5 2.3 Response Theory...........................................................7 2.3.1 ONeill (1964)...........................................................7 2.3.2 Poulos (1975)............................................................8 2.3.3 O'Neill and Dutt (1976).................................................10 2.3.4 Randolph (1981).........................................................12 2.3.5 Chow (1985).............................................................13 2.3.6 Hache and Valsangkar (1988)............................................14 2.3.7 Georgiadis and Saflekou (1990).........................................14 2.3.8 Lin and Al-Khaleefi (1996).............................................18 2.3.9 Guo and Randolph (1996)................................................19 2.3.10 McVay, Herrera, and Hu (2003).........................................19 2.3.11 Zhang and Kong (2006).................................................20 vi 2.3.12 Hu, McVay, Bloomquist, Herrera, and Lai (2006).........................20 2.3.13 Guo, Chow, and Randolph (2007).........................................23 2.3.14 Kong and Zhang (2008)..................................................23 2.4 Design Methods............................................................23 2.4.1 McVay, Herrera, and Hu (2003)............................................24 2.4.2 Colorado Department of Transportation (2004)............................25 3. A Study Using the Finite Element Method (FEM)..............................27 3.1 Introduction..............................................................27 3.2 Choice of Program.........................................................27 3.3 Program Validation........................................................27 3.4 Choice of Material Models.................................................28 3.4.1 Material Model for Pile..................................................29 3.4.2 Material Model for Soil and Interface...................................29 3.5 Hypothetical Case in Clay.................................................29 3.5.1 Model Development........................................................29 3.5.1.1 Geometric Characteristics..............................................29 3.5.1.2 Material Parameters for Pile...........................................32 3.5.1.3 Material Parameters for Clay...........................................32 3.5.2 Load Cases for Clay......................................................35 3.5.2.1 Pure Torsional Load....................................................35 3.5.2.2 Pure Lateral Load......................................................36 3.5.2.3 Pure Vertical Load.....................................................36 3.5.2.4 Combined Lateral and Torsional Load....................................39 3.5.2.5 Combined Vertical and Torsional Load...................................42 3.6 Hypothetical Case in Sand..................................................44 3.6.1 Model Development........................................................44 3.6.1.1 Geometric Characteristics..............................................44 vii 3.6.1.2 Material Parameters for Pile.............................................46 3.6.1.3 Material Parameters for Sand.............................................46 3.6.2 Load Cases for Sand.......................................................49 3.6.2.1 Pure Torsional Load......................................................49 3.6.2.2 Pure Lateral Load........................................................49 3.6.2.3 Pure Vertical Load.......................................................50 3.6.2.4 Combined Lateral and Torsional Load.....................................54 3.6.2.5 Combined Vertical and Torsional Load.....................................57 4. Comparison of FEM Results with Existing Design Methodology...................59 4.1. Introduction................................................................59 4.2. Consistency in Comparison...................................................59 4.3. Presentation of Design Methods for Clay.....................................60 4.3.1. FDOT Structures Design Office Method......................................60 4.3.2. FDOT District 7 Method....................................................61 4.3.3. CDOT Method in Clay.......................................................62 4.4 Comparison of Methods in Clay...............................................62 4.5. Presentation of Design Methods for Sand.....................................66 4.5.1. FDOT Structures Design Office Method......................................66 4.5.2. FDOT District 5 Method O'Neill and Hanson...............................66 4.5.3. CDOT Method in Sand.......................................................67 4.5.4. FDOT District 7 Method....................................................68 4.6 Comparison of Methods in Sand................................................69 5. Proposal of Torsional Load Test..............................................74 5.1 Introduction................................................................74 5.2 Load Application Apparatuses................................................74 5.2.1 Torsional Load Apparatus...................................................75 viii 5.2.1.1 Wrench..........................................................75 5.2.1.2 Hydraulic System................................................78 5.2.1.3 Reactions.......................................................80 5.2.2 Accommodation for Lateral Load Application........................81 5.2.3 Accommodation for Vertical Load Application.......................83 5.3 Measurement Systems...............................................84 5.3.1 Video Recorded Displacement Measurements..........................84 5.3.2 Measurement of Load Application...................................85 5.3.2.1 Tolerance Analysis of Applied Load Measurements.................90 5.3.3 Measurement of Pile Displacement..................................97 5.3.3.1 Above Ground Surface............................................97 5.3.3.2 Below Ground Surface...........................................102 5.4 Summary of Equipment for Proposed Test.............................105 6. Summary.............................................................107 7. Conclusions.........................................................110 8. Recommendations for Future Research.................................112 References.............................................................115 IX LIST OF FIGURES Figure 2.1 Test Setup by Stoll (1972)...............................................4 2.2 Load-Rotation Curve by Stoll (1972).....................................4 2.3 Test Setup by Tawfiq (2000).............................................6 2.4 Basis of 1-Dimensional Numerical Model by O'Neill (1964)................8 2.5 Comparison of Calculated and Measured Model Torsional Responses by Poulos (1975)..........................................................9 2.6 Comparison of Solution by Poulos and Model Test in Clay by O'Neill and Dutt (1976)...........................................................10 2.7 Comparison of Solutions by Poulos and Model Tests in Sand by O'Neill and Dutt (1976)...........................................................11 2.8 Discretization of Pile by Chow (1985)...................................13 2.9 Model for FEM by Georgiadis and Saflekou (1990).........................15 2.10 Axial Response Due to Axial Loading alone by Georgiadis and Saflekou (1990).......................................................16 2.11 Axial Response Due to Combined Torsional-Axial Loading by Georgiadis and Saflekou (1990)...................................................17 2.12 Torsional Load Response by Lin and Al-Khaleefi (1996)..................18 2.13 Reduction in Lateral Capacity Due to Torsion by Hu, McVay, Bloomquist, Herrera, and Lai (2006)...............................................22 3.1 Geometric Arrangement of FEA Model in Clay...............................31 3.2 Pure Torsional Load Response in Clay....................................38 3.3 Pure Lateral Load Response in Clay......................................38 3.4 Pure Vertical Load Response in Clay ....................................39 3.5 Combined Lateral-Torsional Load Response in Clay........................41 x 3.6 Lateral Response Due to Torsion in Clay.................................41 3.7 Combined Vertical-Torsional Load Response in Clay.......................43 3.8 Vertical Response Due to Torsion in Clay................................43 3.9 Geometric Arrangement of FEA Model in Sand..............................45 3.10 Pure Torsional Load Response in Sand....................................52 3.11 Pure Lateral Load Response in Sand .....................................53 3.12 Pure Vertical Load Response in Sand....................................53 3.13 Combined Lateral-Torsional Load Response in Sand.......................56 3.14 Lateral Response Due to Torsion in Sand................................56 3.15 Combined Vertical-Torsional Load Response in Sand......................58 3.16 Vertical Response Due to Torsion in Sand...............................58 4.1 Comparison of FDOT District 7 and CDOT Method with FEA for Clay.........64 4.2 Comparison of FDOT District 7 and CDOT Method with FEA for Clay........65 4.3 Comparison of FDOT SDOF and District 7 Method with FEA for Sand........71 4.4 Comparison of All Design Methods with FEA for Sand.....................71 4.5 Comparison of FDOT SDOF and District 7 Method with FEA for Sand........72 4.6 Comparison of All Design Methods with FEA for Sand.....................72 5.1 Typical Wrench Design...................................................76 5.2 Typical Wrench Design..................................................76 5.3 Typical Wrench Design..................................................77 5.4 Isolated Lateral Load Application to Torsional Load Test...............82 5.5 Lateral Load Application in a Rotationally Displaced State..............82 5.6 Isolated Vertical Load Application for Lateral Pile Test (ASTM, 2009 a).83 5.7 Geometrical Description of Load Application.............................87 5.8 Profile of Relative Displacement Measurement of Arm Ends................89 5.9 Plan View of Relative Displacement Measurement of Arm Ends...............89 xi 5.10 Rotated Coordinate System.............................................93 5.11 Measurement Device Setup for Test Pile Displacements ..........98 5.12 Measurement Device Setup for Test Pile Displacements ..........99 5.13 Depiction of an Above Ground Pile Displacement in the General Sense..101 5.14 Mohr's Representation of Pure Torsional Load on a Cylinder ..........104 5.15 Test Pile Instrumented for Displacement Measurement..................105 xii LIST OF TABLES Table 4.1 Properties for Analysis of Hypothetical Cases.........................60 4.2 Design Capacities for Methods in Hypothetical Clay Case..............63 4.3 Design Capacities for Hypothetical Cases in Sand......................70 5.1 Perfect Measurement of Maximum Applied Load Magnitude.................95 5.2 Measurements of Maximum Applied Load Magnitude with Error.............95 5.3 Tabulation of Error Due to Various Load Application Components........96 5.4 Summary of Equipment for Proposed Load Test..........................106 xiii 1. Introduction 1.1 Background Torsional loading on deep foundations is a topic that seems to have received less attention than that of other load types. This lack of attention seems to be due to the great value attached to understanding the commonly more critical vertical and lateral load types. Nevertheless understanding pile response due to torsional loading is an important concern and has been proven to be critical in some circumstances. Additionally, understanding torsional loading seems to be gaining importance as some structures are now requiring greater torsional loads of deep foundations. In recent years the Florida Department of Transportation (FDOT) has enforced the replacement of cable supported traffic signals and the like with mast and arm supports in southern Florida to meet the large loads brought on by hurricanes (Hu, McVay, Bloomquist, Herrera, and Lai, 2006). These mast and arm type signal supports cause the associated foundational support tremendous torsional loading and are an excellent example of the practical application for a better understanding of torsionally loaded deep foundations. Other examples of practical applications are power line towers, slender buildings, and especially offshore platforms (Kong and Zhang, 2008). Upon a review of literature it was found that there exists a dearth of information regarding the response of deep foundations under combined loading. This lack of information is even more pronounced when the combined loading scenario involves torsion. The attention that torsional loading has received has been primarily focused upon pure torsional loading without consideration of the influences from axial and lateral loads. However, numerical and physical models developed by (Hu, McVay, Bloomquist, Herrera, and Lai, 2006) and (Georgiadis and Saflekou, 1990) suggest that the interaction between lateral and torsional loading and axial and torsional loading is significant. This suggestion is further substantiated by the full scale lateral- torsional testing performed by (Tawfiq, 2000). Because it is almost inconceivable that torsional loading be present without significant lateral and vertical loads for all practical problems, it is felt that the influences of combined loading are important and should be considered when analyzing torsionally loaded deep foundations. Full scale testing gives the most reliable results for the determination of deep foundation safety. Unfortunately full scale testing is currently only performed for limited types of loading. Upon review of literature it was found that the full scale testing methods used to study the performance of deep foundations under torsional loading are somewhat behind that of other load types. In fact only two sets of full scale torsional tests are known to have ever been performed. These torsional tests; however, lacked the full scale testing standards currently available to that of lateral and vertical testing. 1.2 Objectives of Research This work is written to satisfy a number of objectives. The first is to review the available literature regarding the full scale testing, behavior, and design of deep foundations under torsional loading. The second is to perform a simple study of the response of drilled shafts under torsional loading, including the effects of combined lateral-torsional and vertical-torsional loading, using the Finite Element Method (FEM). The third objective is to compare the results found by the FEM with existing theory and design methods. And the fourth and last objective is to propose a reasonable full scale torsional load testing method. 2 2. Literature Review 2.1 Introduction This literature review is concerned with the determination of deep foundation response to torsional loading. The results, methods, and instruments associated with full-scale testing are of prime importance as this testing yields the most accurate results for deep foundation behavior. Additionally, the methods by which the torsional behavior of piles may be predicted are of important consideration as are the methods that are used to design such foundations. The following is broken up into three sections. The first section reviews past full- scale torsional tests, the second reviews methods by which torsional response may be determined, and the third reviews methods used in design to estimate the ultimate torsional resistance of piles. 2.2 Full-Scale Torsional Load Testing 2.2.1 Stoll (1972) Stoll performed the only known full-scale pure torsional load tests on piles. Two tests were performed on steel cylindrical piles in sand in hopes of determining the vertical frictional resistance of such. Each pile was 10.75 inches in diameter. One pile was embedded in 55 ft of soil and the other in 70 ft. The testing apparatus is considered elegant in nature. A simple beam was symmetrically affixed about each pile center so that equal and opposite loads could be applied via hydraulic cylinders to the beam ends creating a pure couple as shown in Figure 2.1. Pile displacements were measured at the pile head by way of dial indicators. The load displacement diagram obtained from the testing is also shown in Figure 2.2 3 side shear Figure 2.1: Test Setup by Stoll (1972) 100 7 80 60 3 & o 40 t 20 S' K V / / / r 7 l / Tes \ pile v-e 1 i i r / / f ^m. T Test pile A-3 f- -p / 4' r V 1 _ 2 xFxl 2 1 1 L i / / i / 1 1 t , / / M, i ' i 1 i -L 0.02 0.04 0.06 0.08 0.10 0.12 a -angle of twist at top of pile (radians) 0.14 Figure 2.2: Load-Rotation Curve by Stoll (1972) 4 2.2.2 Tawfiq (2000) Tawfiq performed the only other known full-scale torsional load tests on piles. Three combined simultaneous lateral and torsional load tests were performed on drilled shafts 4 ft in diameter and 20 ft in embedment in profiles inclusive of both sand and clay. A heavy beam end was affixed to each pile head and load was applied via hydraulic ram to the opposing beam end such that a combined lateral and torsional load resulted as shown in Figure 2.3. Pile displacement was measured by monitoring the movement of laser beams from the lasers mounted on the pile head and strain gages which were placed at various depths. Also, slope indicators were installed in the test shafts for lateral rotational displacement measurements and ultimately lateral defection calculation From the testing of this work it was concluded by the author that combined lateral loading may significantly increase the torsional capacity of a pile. 5 Figure 2.3 Test Setup by Tawfiq (2000) I Beam Stiffener at Both Sides of the Beam 12" x 12" Steel Tube Beam Filled with Concrete V"' \ InstnmMed Shalt Polymer Slurry Mineral Slurry Figure 2.22 Field Test Arrangement 2.3 Response Theory The following presents the available literature on the theoretical response of piles subjected to torsional loading. 2.3.1 O'Neill (1964) O'Neill developed a 1-dimensional numerical model capable of handling nonlinear behavior for piles under torsion. The basis of this numerical scheme is the mechanical model shown in Figure 2.4 where the pile is broken up along the length into a number of discrete elements. By this method, piles of various geometric and both piles and soil profiles of various material properties may be handled. The developed computational model was verified against model testing performed in the laboratory. However, the computational inputs came from the results of the model testing used for verification. Also, no attempt to develop solutions to the response of torsionally loaded piles upon a basis of commonly available soil parameters from practical site investigation is made. Thus, the practical benefits of this work are extremely limited. 7 + T + 8 + M RIGID ELEMENT N- I RIGID ELEMENT N RIGIO ELEMENT N+ I Figure 2.4: Basis of 1-Dimensional Numerical Model by O'Neill (1964) 2.3.2 Poulos (1975) Poulos developed parametric solutions to the response of piles under torsion. Although the methods of solution may accommodate pile-soil slip at the interface, the theory of elasticity seems to be relied upon for the solutions. From the solutions developed it was found that, except for stiff piles, the amount of pile embedment does not significantly affect the torsional response of the pile and that the load transfer from pile to soil drops off rapidly with depth. Poulos performed a number of both torsional and axial load tests on model piles in clay. The model piles were constructed of aluminum rod with diameters ranging from 0.5 inches to 1.5 inches and lengths ranging from 6 inches to 20 inches. 8 It was found that if the modulus of rigidity was back-calculated from the axial testing, it could be used, with the developed solutions, to estimate the torsional response with fairly good agreement as shown in Figure 2.5. Also, the adhesion at the pile-soil interface was back-calculated from both the torsional and axial load model tests. A strong agreement was found. Figure 2.5: Comparison of Calculated and Measured Model Torsional Responses by Poulos (1975) 9 2.3.3 O'Neill and Dutt (1976) A discussion by O'Neill and Dutt (1976), shows that the solutions given by Poulos (1975) are accurate for loadings up to 40 percent of the total resistance, however, for loadings greater than this the solutions deviate greatly from the actual response of model pile tests performed by the authors as shown in Figures 2.6 and 2.7. (Note: the dashed line is that of Poulos and the solid is the measured response.) The authors felt that this deviation was partly due to a variance in shear stress along the pile interface with rotational failure. O'Neill and Dutt (1976) suggested that as the top of a pile rotates, under torsional loading, the shear stresses along the interface near the top reach a limiting value and are reduced (fail) while the shear stresses along the interface at greater depths increase causing a sort of progressive failure and overall variance in shear stresses at the interface which leads to a nonlinear response. Figure 2.6: Comparison of Solution by Poulos and Model Test in Clay by O'Neill and Dutt (1976) 10 pile head toachie. inch-pounds Figure 2.7: Comparison of Solutions by Poulos and Model Tests in Sand by O'Neill and Dutt (1976) 11 2.3.4 Randolph (1981) Presented an expression for the torsional response of piles which may be written as; d2(p 2utq ~dz2=XGf)] t0 (2.1) where
modulus, and (GJ)p is the torsional rigidity of the pile. By way of hyperbolic and
(3.22)
(3.34)
8 = 31.5 |