The Performance of Drag Embedment Anchors (DEA) by Charles Aubeny, Texas A&M University Robert Gilbert, The University of Texas at Austin Robert Randall, Texas A&M University Evan Zimmerman, Delmar Katelyn McCarthy, The University of Texas at Austin Ching-Hsiang Chen, The University of Texas at Austin Aaron, Drake, Texas A&M University Po Yeh, Texas A&M University Chao-Ming Chi, Texas A&M University Ryan Beemer, Texas A&M University Final Project Report Prepared for Minerals Management Service Under Contract Number M09PC00028 MMS Project Number 645 OTRC Project 32558-A6960 March 2011 OTRC Library Number: 12/10C201 “The views and conclusions contained in this document are those of the authors and should not be interpreted as representing the opinions or policies of Minerals Management Service. Mention of trade names or commercial products does not constitute their endorsement by Minerals Management Service. For more information contact: Offshore Technology Research Center Texas A&M University 1200 Mariner Drive College Station, Texas 77845-3400 (979) 845-6000 or Offshore Technology Research Center The University of Texas at Austin 1 University Station C3700 Austin, Texas 78712-0318 (512) 471-6989 A National Science Foundation Graduated Engineering Research Center Table of Contents Table of Contents ............................................................................................................................. i  List of Tables ................................................................................................................................. iv  List of Figures ................................................................................................................................. v  Executive Summary ........................................................................................................................ x  1.0  Introduction ......................................................................................................................... 1  1.1  Objective .......................................................................................................................... 1  1.2  Background ...................................................................................................................... 3  1.3  Scope of Work .................................................................................................................. 4  1.4  Structure of Report ........................................................................................................... 5  2.0  Small (1:30) Scale Model Tests .......................................................................................... 7  2.1  Introduction ...................................................................................................................... 7  2.2  Experimental Equipment and Facility .............................................................................. 8  2.2.1  Experiment Facility ................................................................................................... 8  2.2.2  Kaolinite Clay ......................................................................................................... 11  2.2.2.1  T-Bar ................................................................................................................... 13  2.2.2.2  Thermo-Plastic Tank ........................................................................................... 14  2.2.2.3  Metal Tank .......................................................................................................... 15  2.2.3  Magnetometer for Tracking ........................................................................................... 16  2.3  Small (1:30) Scale Model Anchor .................................................................................. 17  2.4  Pure Loading Tests ......................................................................................................... 20  2.4.1  Pure Translation Tests ............................................................................................. 20  2.4.1.1  Procedure ............................................................................................................. 20  2.4.1.2  Results ................................................................................................................. 22  2.4.1.3  Analysis ............................................................................................................... 22  2.4.2  Pure Rotation Tests ................................................................................................. 27  2.5  Drag Tests ...................................................................................................................... 29  2.5.1  In-plane drag embedment tests ............................................................................... 30  2.5.2  Out-of-plane Drag Embedment Tests ..................................................................... 45  3.0  Large-Scale Tests .............................................................................................................. 50  i 3.1  Introduction .................................................................................................................... 50  3.2  Experimental Test Arrangements ................................................................................... 50  3.2.1  Carriage and Tow Tank Test Arrangements ........................................................... 51  3.2.2  Sediment Pit Layout and Global Coordinates ......................................................... 54  3.2.3  Sediment (Mud) Mixing Device ............................................................................. 56  3.2.4  Anchor and towline characteristics ......................................................................... 57  3.3  Instrumentation and Data Collection .............................................................................. 59  3.3.1  Pressure Transducer ................................................................................................ 60  3.3.2  Anchor Force Transducer ....................................................................................... 61  3.3.3  Anchor 2-Axis Inclination Sensor .......................................................................... 62  3.3.4  Carriage and Breakout Force Transducer ............................................................... 62  3.3.5  T-bar and Rotational Breakout Tests Force Transducers ....................................... 63  3.3.6  Towline and Chaser Angle Position Sensors .......................................................... 63  3.3.7  Chaser Line Displacement Sensor .......................................................................... 63  3.3.8  Towline and Chaser Cable Apparatus ..................................................................... 64  3.4  Sediment Strength Testing ............................................................................................. 65  3.5  Breakout Devices and Procedures .................................................................................. 67  3.5.1  Normal Breakout Test Apparatus and Procedures .................................................. 67  3.5.2  Transverse Breakout Test Apparatus and Procedures ............................................ 67  3.5.3  Rotational Breakout Test and Procedures ............................................................... 69  3.6  In-plane Towing Test Procedures .................................................................................. 70  3.7  Out-of-Plane Towing Test Procedures ........................................................................... 71  3.7.1  Case 1. Initial Surface and Sub-surface Out-of-Plane ............................................ 71  3.7.2  Case 2. Main Pull Line Out-of-Plane Tests ............................................................ 72  3.7.3  Case 3. Carriage Ladder Mounted Out-of-Plane Tests .......................................... 75  3.8  Dredge/Tow Carriage Operation .................................................................................... 76  3.9  Results of Testing Drag Embedment Anchors ............................................................... 79  3.9.1  In-Plane Results ...................................................................................................... 79  3.9.2  Out-of-Plane Results ............................................................................................... 91  3.9.3  Break-out Results ................................................................................................... 99  ii 3.10  Summary and Conclusions ........................................................................................... 100  4.0  Model Development and Evaluation .............................................................................. 103  4.1  In-Plane Behavior ......................................................................................................... 103  4.1.1  Load Capacity ....................................................................................................... 103  4.1.2  Anchor Line Behavior ........................................................................................... 110  4.1.3  Trajectory during Drag Embedment ..................................................................... 112  4.1.4  Adjustments to In-Plane Behavior Model ............................................................. 116  4.1.5  Comparison of 1:30 Scale Model Tests with Model ............................................ 119  4.2  Out-of-Plane Trajectory Behavior ................................................................................ 138  4.2.1  Theoretical Considerations ................................................................................... 138  4.2.2  Experimental Data ................................................................................................ 145  4.2.3  Example Out-of-Plane Behavior ........................................................................... 158  5.0  Recommended Capacity Curves for Generic Anchor ..................................................... 164  6.  Conclusions and Recommended Future Work ................................................................... 171  References ................................................................................................................................... 178  Appendix I. Large Scale Testing Project Data ............................................................................ 179  Appendix II. Tests in Kaolinite Bed .......................................................................................... 183  Appendix III: Engineering Interpretation of Large-Scale Test Data ......................................... 267  Appendix IV: Delmar DEA Investigation ................................................................................. 291  Appendix V – Tests in Laponite Test Bed .................................................................................. 328  iii List of Tables Table 2.1. Physical properties for 1:30 model anchor ................................................................. 19  Table 2.2. Areas of different surfaces for 1:30 scale model anchor ............................................ 19  Table 2.3. Results and analysis of pure translation loading tests for 1:30 scale model .............. 22  Table 2.4. Summary of Theoretical and Experimental Bearing Capacity Factors for Pure Translational Loading ................................................................................................................... 24  Table 2.5. Table of Bearing Capacity Calculations: In-Plane Shear – Plugged, In-Plane Shear Unplugged, Normal and Out-of-Plane Shear ................................................................................ 25  Table 2.5a. In-Plane Shear ........................................................................................................... 25  Table 2.5b. Normal ...................................................................................................................... 26  Table 2.5c. Out-of-Plane Shear ..................................................................................................... 26  Table 2.6. Results and Analysis of Pure Rotational Loading Tests ............................................ 29  Table 2.7. Comparison of T and N ............................................................................................ 42  a e Table 2.8. Calculated N * Values for tests Performed ................................................................ 43  e Table 2.9. Out of Plane N Values for Tests Performed .............................................................. 49  e Table 3.1. Definitions and characteristics of generic model anchor and instrumentation. ......... 54  Table 3.2. Sediment pit sand, bentonite, and water percentages and bulk density. ..................... 56  Table 3.3. Case 2 out-of-plane pull distance. ............................................................................... 73  Table 3.4. Case 2 out-of-plane offset distances. ......................................................................... 75  Table 3.5. Performance of model drag embedment anchor in-plane test plan. ........................... 80  Table 3.6. Model drag embedment anchor out-of-plane test plan. .............................................. 92  Table 3.7. Model drag embedment anchor breakout test plan. .................................................... 99  Table 4.1. Significant Features of Large and Small Scale Laboratory Model Tests ................. 108  Table 4.2. Comparison of Large and Small Scale In-Plane Test Results .................................. 110  Table 4.3. Anchor Parameters used in Small-Scale Test Comparisons to Model ...................... 119  Table 4.4. Test bed Parameters used in Small-Scale Test Comparisons to Model .................... 123  Table 4.5 Tilt v of Plane of Trajectory: Model Predictions versus Measurement ..................... 159  Table 5.1. Generic Anchor Holding Capacity Relations, A/b2 = 1500, 50-degree fluke-shank f angle with Bearing Factor N =4 .................................................................................................. 166  e Table 5.2. Generic Anchor Holding Capacity Relations, A/b2 = 1500, 50-degree fluke-shank f angle with Bearing Factor N =5 .................................................................................................. 167  e Table 5.3. Generic anchor holding capacity relations for wire anchor lines with 100-m drag distance, 50-degree fluke-shank angle with N =4 ....................................................................... 169  e Table 5.4. Generic Anchor Holding Capacity Relations, A/b2 = 1500, 36-degree fluke-shank f angle ............................................................................................................................................ 170  iv List of Figures Figure 2.1. Loading frame ............................................................................................................. 8  Figure 2.2. Loading device ............................................................................................................ 9  Figure 2.3. Load cell ................................................................................................................... 10  Figure 2.4. Data acquisition and control system .......................................................................... 11  Figure 2.5. Water Content vs. Undrained Shear Strength (Lee 2008) .......................................... 12  Figure 2.6. T-Bar test .................................................................................................................... 13  Figure 2.7. Drill with steel paddle and mixing process in the thermoplastic tub ........................ 14  Figure 2.8. Thermo Plastic Tank on Elevated Platform ............................................................... 15  Figure 2.9 - Testing Facility.......................................................................................................... 16  Figure 2.10. Testing Facility for use of the Magnetometer .......................................................... 17  Figure 2.11. 1:30 Scale Model Anchor ......................................................................................... 18  Figure 2.12. Area 1 through 7 presented in Table 2.2 ................................................................. 19  Figure 2.13. Magnetometer attached to 1:30 scale model ........................................................... 20  Figure 2.14. In-plane Shear Test Orientation (Left: Just Anchor and Right: With Magnetometer Sensor) .......................................................................................................................................... 21  Figure 2.15. Out-of-plane Shear Orientation  Figure 2.16. Normal Orientation. ..................... 21  Figure 2.17. Test setup for pure rotational loading test ............................................................... 27  Figure 2.18. Attachment of the Anchor to the Threaded Rod for each Orientation .................... 28  Figure 2.19. Testing Tracks in Metal Tank .................................................................................. 30  Figure 2.20. Example Test Configuration for In-Plane Drag Embedment Test .......................... 31  Figure 2.21. Trajectory of an In-Plane Drag Embedment Tests .................................................. 32  Figure 2.22. Illustration of In-plane Drag test with Steep Anchor Line ...................................... 34  Figure 2.23. Illustration of In-plane Drag Test with Magnetometer ............................................ 35  Figure 2.24. Out-of-plane drag test data with the Magnetometer ................................................ 36  Figure 2.25. Effect of Initial Pitch Angle on Pitch and the Trajectory ....................................... 37  Figure 2.26. Line Displacement vs. Load cell readings and Interpolated Trajectory ................. 39  Figure 2.27. Example of Undrained Shear Strength Profile ........................................................ 41  Figure 2.28. N vs. Line Displacement and Embedment Depth ................................................. 44  e Figure 2.29. Variation in dn/ds throughout Drag Distance .......................................................... 44  Figure 2.30. Trajectory for Out-of-plane Test ............................................................................. 47  Figure 2.28. Out-of-plane drag test data with the Magnetometer. ............................................... 48  Figure 3.1. Schematic of the Dredge/Tow Tank in the Haynes Coastal Engineering Laboratory at Texas A&M University. ................................................................................................................ 51  Figure 3.2. General test configuration with the main pull line (grey) and data acquisition chaser line (dashed). ................................................................................................................................. 52  Figure 3.3. Pull angle adjustments ............................................................................................... 52  Figure 3.4. Instrumentation used for drag embedment testing. ................................................... 53  Figure 3.5. Bracket detail. ............................................................................................................ 53  v Figure 3.6. Sediment mixture operation outside and discharging sediment into sediment pit in the towing flume. .......................................................................................................................... 55  Figure 3.7. Sediment pit global coordinates and profile. ............................................................. 55  Figure 3.8. Support structure and sediment pit. ........................................................................... 56  Figure 3.9. Sediment mixing device. ........................................................................................... 57  Figure 3.10. S ediment surface after recent mixing. ..................................................................... 57  Figure 3.11. Anchor fluke angle settings. .................................................................................... 58  Figure 3.12. Anchor dimensions and centroid. ............................................................................ 59  Figure 3.13. Anchor instruments layout. ..................................................................................... 60  Figure 3.14. Pressure transducer mounted on bottom side of model anchor. .............................. 61  Figure 3.15. Anchor force transducer attached to shank of model anchor. ................................. 61  Figure 3.16. Anchor pitch and roll sign convention. ................................................................... 62  Figure 3.17. Chaser line displacement sensor. ............................................................................. 64  Figure 3.18. Towline pulley apparatus (right) and chaser cable apparatus. ................................ 65  Figure 3.19. Tow and chaser line angle convention. ................................................................... 65  Figure 3.20. T-bar sediment strength measurement device. ........................................................ 66  Figure 3.21. T-bar test locations. ................................................................................................. 67  Figure 3.22. Transverse breakout test apparatus. ......................................................................... 68  Figure 3.23. Model anchor rotational coordinates. ...................................................................... 69  Figure 3.24. Rotational breakout setup pictures. ......................................................................... 70  Figure 3.25. In-plane initial anchor placement. ........................................................................... 71  Figure 3.26. Case 1 surface out-of-plane. .................................................................................... 72  Figure 3.27. Example paths for 15° out-of-plane. ....................................................................... 74  Figure 3.28. Pull paths for 30° and 45° out-of-plane. ................................................................. 74  Figure 3.29. Ladder mounted out-of-plane pull path example ................................................... 76  Figure 3.30. Dredge/tow carriage and sediment pit (left) and model anchor being lifted out of the mud after a test (right). ............................................................................................................ 77  Figure 3.31. Dredge/tow carriage control console (left) and sediment pit with mud mixer (right). ....................................................................................................................................................... 77  Figure 3.32. Manual control system (left) and PC control system and horizontal position laser mounted on the dredge/tow carriage (right). ................................................................................. 78  Figure 3.33. Computer screen for tow carriage operation during model drag embedment anchor testing. ........................................................................................................................................... 79  Figure 3.34. In-plane anchor measurements for test number 10. ................................................ 82  Figure 3.35. In-plane measurements for chaser, anchor, displacement, and pitch and roll for test 10................................................................................................................................................... 83  Figure 3.36. In-plane anchor measurements for test 13. .............................................................. 84  Figure 3.37. In-plane angle measurements for test 13. ................................................................ 85  Figure 3.38. Six locations sediment strength profile for March 25, 2010. ................................. 86  Figure 3.39. Test 10 (0.42ft/s) and test 13 (0.62 ft/s) in-plane 50° sample results. ..................... 87  vi Figure 3.40. In-Plane 0.42 ft/s Test 10 (50°) and Test 2 (36°). .................................................... 89  Figure 3.41. Effect of towing angle, tow speed, and fluke angle on the force measured at the shank pad eye and the towing line. ............................................................................................... 90  .Figure 3.42. Effect of tow angle, fluke angle, and tow speed on anchor penetration depth as measured by pressure sensor mounted on bottom of model anchor fluke. ................................... 91  Figure 3.43. Example Test 98 Out-of-Plane Data Time Delay .................................................... 94  Figure 3.44. Out-of-Plane Test 98 and 100 Comparisons ........................................................... 95  Figure 3.45. Effect out of plane pull angle on maximum penetration increase after initial embedment for the model anchor with 36o and 50o fluke angles. ................................................ 97  Figure 3.46. Maximum force at the model anchor shank padeye for three out of plane pull angles after initial embedment. ..................................................................................................... 98  Figure 3.47. Model anchor roll angle as a result of out of plane pull angle. ............................... 98  Figure 4.1. Definition Sketch of Anchor and Anchor Line System ........................................... 104  Figure 4.2. Definition Sketch of Force System on Anchor ........................................................ 104  Figure 4.3. Measured Anchor Bearing Factors, Large-Scale Anchor ........................................ 107  with 50-degree Fluke-Shank Angle ............................................................................................ 107  Figure 4.3. Anchor Line Geometry for Various Soil Strength Profiles; the soil strength parameter *= kz/s , where k=strength gradient, z=pad-eye depth, s =mudline undrained shear u0 u0 strength ........................................................................................................................................ 112  Figure 4.4. Measured Anchor Trajectory ................................................................................... 115  Figure 4.5. Measured Anchor Line-Fluke Angle, Large-Scale Anchor with 50-degree Fluke- shank Angle ................................................................................................................................ 117  Figure 4.6. Trajectory Model Corrected for Effect of Initial Anchor Orientation ..................... 118  Figure 4.7. Comparison of Trajectory at Shackle and Fluke ...................................................... 120  Figure 4.8. Tension Ratio through Drag Embedment Test ........................................................ 121  Figure 4.9. Values of θ throughout Drag Distance .................................................................. 122  af Figure 4.10. Test A. 7/12/2010_IP_Track 2_2, in soil with linearly increasing undrained shear strength profile ............................................................................................................................ 124  Figure 4.11. Test B. 10/20/2010_IP_Black Tub_2 in soil with constant, remolded undrained shear strength profile ................................................................................................................... 126  Figure 4.11. Test B (cont.). 10/20/2010_IP_Black Tub_2 in soil with constant, remolded undrained shear strength profile .................................................................................................. 127  Figure 4.12. Comparison of Test A and Test B ......................................................................... 128  Figure 4.13. Comparison of Model and Measured results with different anchor lines .............. 130  Figure 4.14. Varying Su gradient, k ............................................................................................ 131  Figure 4.15. Varying the Shear Strength at the mudline, S ..................................................... 133  u0 Figure 4.16. Comparison of Linearly Increasing S and Constant S ........................................ 134  u u Figure 4.17. Varying the Initial Tow Angle of the Anchor Line ................................................ 135  Figure 4.18. Varying the Distance from the Start of the test to the Pulley ................................. 136  vii Figure 4.19. Comparison of the 1:30 scale model acrylic anchor and an equivalent 1:30 scale model steel anchor ...................................................................................................................... 137  Figure 4.20. Definition sketch for out-of-plane loading ............................................................ 139  Figure 4.21. Illustration of Oblique Plane Containing Anchor Chain ....................................... 140  Figure 4.22. Transformed Coordinate System for Out-of-Plane Loading .................................. 142  Figure 4.23. Anchor in plane of chain ........................................................................................ 143  Figure 4.24. Horizontal and Vertical Tow Line Angles during 15-Degree Out-of-Plane Loading, Haynes Test 96 ............................................................................................................................ 147  Figure 4.25. Measured x-z Trajectory during 15-Degree Out-of-Plane Loading, Haynes Test 96 ..................................................................................................................................................... 147  Figure 4.26. Measured x-y Trajectory during 15-Degree Out-of-Plane Loading, ..................... 148  Haynes Test 96 ............................................................................................................................ 148  Figure 4.27. Measured y-z Trajectory during 15-Degree Out-of-Plane Loading, ..................... 148  Haynes Test 96. ........................................................................................................................... 148  Figure 4.28. Horizontal and Vertical Tow Line Angles during 30-Degree Out-of-Plane Loading, Haynes Test 98 ............................................................................................................................ 149  Haynes Test 98 ............................................................................................................................ 149  Figure 4.30. Measured x-y Trajectory during 30-Degree Out-of-Plane Loading, ..................... 150  Haynes Test 98 ............................................................................................................................ 150  Figure 4.31. Measured y-z Trajectory during 30-Degree Out-of-Plane Loading, ..................... 150  Haynes Test 98 ............................................................................................................................ 150  Figure 4.32. Measured Orientation of Oblique Plane Relative to Original Plane of Loading for 15-Degree Out-of-Plane Loading, Haynes Test 96 ..................................................................... 153  Figure 4.33. Measured Orientation of Oblique Plane Relative to Original Plane of Loading for 30-Degree Out-of-Plane Loading, Haynes Test 98 ..................................................................... 153  Figure 4.34. Definition Sketch for Anchor Roll and Anchor Line Tilt ..................................... 154  Figure 4.35. Measurement of Anchor Roll and Oblique Plane Tilt during 15-Degree Out-of- Plane Loading, Haynes Test 96 .................................................................................................. 154  Figure 4.36. Measurement of Anchor Roll and Oblique Plane Tilt during 30-Degree Out-of- Plane Loading, Haynes Test 98 .................................................................................................. 155  Figure 4.37. Measured Effective Bearing Factor during 15-Degree Out-of-Plane Loading, .... 157  Haynes Test 96 ............................................................................................................................ 157  Figure 4.38. Measured Effective Bearing Factor during 30-Degree Out-of-Plane Loading, .... 157  Haynes Test 98 ............................................................................................................................ 157  Figure 4.39. Predicted effect of 18-degree out-of-plane loading on anchor trajectory .............. 160  Figure 4.40. Predicted effect of 18-degree out-of-plane loading on anchor load capacity ........ 160  Figure 4.41. Predicted effect of 30-degree out-of-plane loading on anchor trajectory .............. 161  Figure 4.42. Predicted effect of 30-degree out-of-plane loading on anchor load capacity ........ 161  Figure 4.43. Predicted effect of increase in bearing factor on anchor trajectory during 15-degree out-of-plane loading .................................................................................................................... 162  viii