laboratory apparatus and methodology for evaluating water erosion rates of erodible rock and ...

135 Pages·2004·2.98 MB·English

LABORATORY APPARATUS AND METHODOLOGY FOR DETERMINING
WATER EROSION RATES OF ERODIBLE ROCK AND COHESIVE SEDIMENTS

By

MATTHEW A. TRAMMELL

A THESIS PRESENTED TO THE GRADUATE SCHOOL
OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT
OF THE REQUIREMENTS FOR THE DEGREE OF
MASTER OF SCIENCE

UNIVERSITY OF FLORIDA

2004
Copyright 2004

by

Matthew A. Trammell
To my Parents, Sister, and Family
ACKNOWLEDGMENTS
I would like to thank Dr. Max Sheppard, my graduate advisor and supervisory
committee chairman, for his assistance, guidance, and support throughout my master’s
career here at the University of Florida. I would also like to thank Dr. David Bloomquist,
my supervisory committee cochair, for presenting me with this research opportunity and
also for his support and guidance throughout my time here. Again, I would like to thank
both my committee chairmen for their trust and confidence in my work performed during
this research. A well-deserved thanks goes to the staff of the Coastal and Oceanographic
Engineering Laboratory. Without the help of Vernon Sparkman, Chuck Broward, and
Danny Brown, the construction and setup of the apparatus and all of the associated
electronics would not have been possible.
I would also like to thank Dr. Robert Thieke for serving on my supervisory
committee as well as for his guidance and support throughout my undergraduate and
graduate years here at the University of Florida. My appreciation is extended to Dr.
Michael McVay and Dr. Frank Townsend for their assistance in helping me understand
the behavior of cohesive sediments. I would also like to extend my most sincere
appreciation to Matthew Henderson and Kenneth Kerr. Their previous research and
assistance in the designing of the apparatus were invaluable to the research presented in
this thesis.
I would also like to say thank you to the Florida Department of Transportation for
its financial support and supplemental research assistance. I am very grateful to the staff
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of the State Materials Office in Gainesville, Florida, including Dr. David Horhota and
Summer Hartley for their time and assistance with this research.
Last, but certainly not least, I would like to express my love and gratitude for my
parents and family. Without their unconditional love and support throughout not only my
college career but my whole life, I would not have made it to where I am today.
I Thank Them All So Much!!!!

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TABLE OF CONTENTS

page

ACKNOWLEDGMENTS.................................................................................................iv
LIST OF TABLES.............................................................................................................ix
LIST OF FIGURES.............................................................................................................x
ABSTRACT.....................................................................................................................xiii
CHAPTER

1 INTRODUCTION........................................................................................................1
1.1 Definition of Scour and Scour Modes....................................................................3
1.1.1 General Scour...............................................................................................4
1.1.2 Contraction Scour.........................................................................................5
1.1.3 Local Scour...................................................................................................6
1.2 HEC-18 Guidelines.................................................................................................7
1.3 Purpose and Scope................................................................................................10
1.3.1 Purpose.......................................................................................................11
1.3.2 Scope..........................................................................................................12

2 BACKGROUND AND LITERATURE REVIEW....................................................13
2.1 What is Rock?.......................................................................................................13
2.2 Classification of Rock...........................................................................................14
2.3 Erosion Process of Rock.......................................................................................15
2.4 Current Methods for Predicting Scour of Rock....................................................16
2.4.1 HEC-18.......................................................................................................16
2.4.1.1 “Scourability of Rock Formations” Memorandum..........................16
2.4.1.2 Scour Competence of Rock..............................................................17
2.4.1.2.1 Geologic, Geomorphology, Stream Stability, and Geotechnical
Analysis...................................................................................................18
2.4.1.2.2 July 19, 1991 “Scourability of Rock Formations” Memorandum18
2.4.1.2.3 Flume Tests...................................................................................18
2.4.1.2.4 Erodibility Index...........................................................................19
2.5 What is a Cohesive Material?...............................................................................19
2.6 Cohesive Material Classification..........................................................................21
2.7 Erosion Process of Cohesive Materials................................................................23
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2.8 Current Methods for Predicting Scour in Cohesive Materials using HEC-18......25
2.9 Previous Rock and Cohesive Sediment Erosion Experiments.............................28
2.9.1 The Erosion Function Apparatus (EFA).....................................................28
2.9.2 Sediment Erosion at Depth Flume (SEDflume).........................................30
2.9.3 Adjustable Shear Stress Erosion and Transport Flume (ASSET)..............32
2.9.4 Rotating Erosion Test Apparatus (RETA).................................................34

3 SEDIMENT EROSION RATE FLUME (SERF).......................................................38
3.1 Design Challenges and Objectives.......................................................................38
3.2 Background of the Sediment Erosion Rate Flume...............................................40
3.3 Sediment Erosion Rate Flume for Measuring Rock
and Cohesive Material Erodibility.........................................................................42
3.3.1 Sediment Erosion Rate Flume....................................................................42
3.3.2 Monitoring and Control of the SERF.........................................................45
3.4 Advantages of the SERF.......................................................................................48
3.5 Limitations of the SERF.......................................................................................49
3.6 Experimental Procedures......................................................................................50
3.6.1 Overview of the Testing Procedure............................................................50
3.6.2 Data Acquisition Procedure........................................................................52
3.6.2.1 SeaTek Program...............................................................................52
3.6.2.2 Stepper Motor Programs..................................................................53
3.6.2.3 Erosion Rate Test Program..............................................................54
3.6.3 Data Analysis..............................................................................................55

4 LABORATORY RESULTS.......................................................................................57
4.1 Verification of Shear Stress Measurement...........................................................57
4.2 Repeatability Analysis of the SERF.....................................................................61
4.3 Analysis of Rock Cores........................................................................................62
4.3.1 Limerock.....................................................................................................63
4.3.2 Clayey Rock...............................................................................................64
4.4 Analysis of Cohesive Sediment Cores..................................................................65
4.4.1 Bubble Bump Cohesive Sediment Core.....................................................65
4.4.2 Modeling Clay............................................................................................67

5 CONCLUSIONS........................................................................................................69
5.1 Critical Shear Stress Analysis...............................................................................69
5.2 Repeatability Analysis..........................................................................................70
5.3 Analysis of Rock Cores........................................................................................71
5.3.1 Limerock Analysis......................................................................................72
5.3.2 Clayey Rock...............................................................................................73
5.3.3 Comparison of Erosion Rates between the SERF and the RETA..............73
5.4 Analysis of Cohesive Sediment Cores..................................................................73
5.4.1 Bubble Bump Cohesive Sample.................................................................73
5.4.2 Modeling Clay Sample...............................................................................76
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5.4.3 Correlation between Geotechnical Properties and Erosion Rates..............78

6 CONTINUING RESEARCH AND DESIGN MODIFICATIONS...........................79
6.1 Continuing Research.............................................................................................79
6.1.1 Correlation between Erosion Rates and Geotechnical Properties of
Sediments.........................................................................................................79
6.1.2 Evaluation of Rock and Cohesive Material at Actual Bridge Locations....80
6.1.3 Evaluation of Erosion Rates versus Applied Shear Stress Accounting For
Suspended Sediment in the Flow.....................................................................80
6.2 Design Modifications and Recommendations......................................................81
6.2.1 New Control / Data Acquisition Computer................................................81
6.2.2 Improved Flushing System and Drain........................................................81
6.2.3 Water Temperature Control System...........................................................82
6.2.4 Modifications to the Flume Sections..........................................................82

APPENDIX

A SCHEMATIC DRAWINGS AND PHOTOGRAPHS OF THE SERF.....................84
B SERF TESTING MADE EASY.................................................................................96
B.1 SeaTek Ranging System......................................................................................96
B.2 LabView Control Programs.................................................................................99
B.2.1 Simple Movement Program.....................................................................100
B.2.2 Pressure and Temperature Program.........................................................101
B.2.3 Erosion Rate Testing Program.................................................................102
B.3 Pump Controls....................................................................................................109

C SERF Testing Procedures.........................................................................................112
C.1 Erosion Rate Pre-Test Procedure.......................................................................112
C.2 Sediment Sample Preparation Procedure...........................................................113
C.3 Erosion Rate Testing Procedure (for Cohesive or Cohesionless material)........114
C.4 Erosion Rate Testing Procedure (for 2.3” Diameter Rock Core)......................116
C.5 Critical Shear Stress Test Procedure..................................................................117

LIST OF REFERENCES.................................................................................................119
BIOGRAPHICAL SKETCH...........................................................................................121
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LIST OF TABLES
Table page

4-1 Shields Curve Fit Equations.....................................................................................59
4-2 Description of Motion at Observed Critical Shear Stress........................................60
4-3 Results of Critical Shear Stress Examination...........................................................60
5-1 Results of Critical Shear Stress Examination...........................................................69

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LIST OF FIGURES
Figure page

1-1 Graphical representation of the modes in which scour affects a bridge structure......4
1-2 Structure induced flows and their respective flow patterns.......................................7
3-1 Schematic diagram of the SeaTek transducer array.................................................46
4-1 Plot of three separate erosion rate tests....................................................................62
4-2 Plot of erosion rate vs. shear stress for a cohesive sediment....................................67
4-3 Plot of erosion rate vs. shear stress for the modeling clay sample...........................68
5-1 Plot of erosion rate vs. applied shear stress for the final three tests performed for
the repeatability analysis..........................................................................................71
5-2 Erosion rate vs. shear stress plot for the bubble bump cohesive sample..................74
5-3 Erosion rate vs. shear stress for the modeling clay sample......................................77
A-1 Schematic drawing of the Sediment Erosion Rate Flume........................................84
A-2 Schematic drawing of the profile view of the SERF................................................85
A-3 Photograph of the SERF at the University of Florida. SERF control office is in the
background...............................................................................................................85
A-4 Side view of the test section, showing the stepper motor, test cylinder, SeaTek
transducer, and the pressure transducer....................................................................86
A-5 Top view of the test section showing the SeaTek transducer along with the camera
and test cylinder.......................................................................................................86
A-6 Back side view of the test section, showing the window, camera, SeaTek
transducer, and the test cylinder containing a sand sample......................................87
A-7 Back side of test section, showing window, SeaTek transducer, and the test cylinder
containing a sand sample..........................................................................................87
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