National Academies Press: OpenBook

Relationship Between Erodibility and Properties of Soils (2019)

Chapter: Chapter 4 - Erosion Experiments

« Previous: Chapter 3 - Existing Correlations Between Soil Erodibility and Soil Properties
Page 76
Suggested Citation:"Chapter 4 - Erosion Experiments." National Academies of Sciences, Engineering, and Medicine. 2019. Relationship Between Erodibility and Properties of Soils. Washington, DC: The National Academies Press. doi: 10.17226/25470.
×
Page 76
Page 77
Suggested Citation:"Chapter 4 - Erosion Experiments." National Academies of Sciences, Engineering, and Medicine. 2019. Relationship Between Erodibility and Properties of Soils. Washington, DC: The National Academies Press. doi: 10.17226/25470.
×
Page 77
Page 78
Suggested Citation:"Chapter 4 - Erosion Experiments." National Academies of Sciences, Engineering, and Medicine. 2019. Relationship Between Erodibility and Properties of Soils. Washington, DC: The National Academies Press. doi: 10.17226/25470.
×
Page 78
Page 79
Suggested Citation:"Chapter 4 - Erosion Experiments." National Academies of Sciences, Engineering, and Medicine. 2019. Relationship Between Erodibility and Properties of Soils. Washington, DC: The National Academies Press. doi: 10.17226/25470.
×
Page 79
Page 80
Suggested Citation:"Chapter 4 - Erosion Experiments." National Academies of Sciences, Engineering, and Medicine. 2019. Relationship Between Erodibility and Properties of Soils. Washington, DC: The National Academies Press. doi: 10.17226/25470.
×
Page 80
Page 81
Suggested Citation:"Chapter 4 - Erosion Experiments." National Academies of Sciences, Engineering, and Medicine. 2019. Relationship Between Erodibility and Properties of Soils. Washington, DC: The National Academies Press. doi: 10.17226/25470.
×
Page 81
Page 82
Suggested Citation:"Chapter 4 - Erosion Experiments." National Academies of Sciences, Engineering, and Medicine. 2019. Relationship Between Erodibility and Properties of Soils. Washington, DC: The National Academies Press. doi: 10.17226/25470.
×
Page 82
Page 83
Suggested Citation:"Chapter 4 - Erosion Experiments." National Academies of Sciences, Engineering, and Medicine. 2019. Relationship Between Erodibility and Properties of Soils. Washington, DC: The National Academies Press. doi: 10.17226/25470.
×
Page 83
Page 84
Suggested Citation:"Chapter 4 - Erosion Experiments." National Academies of Sciences, Engineering, and Medicine. 2019. Relationship Between Erodibility and Properties of Soils. Washington, DC: The National Academies Press. doi: 10.17226/25470.
×
Page 84
Page 85
Suggested Citation:"Chapter 4 - Erosion Experiments." National Academies of Sciences, Engineering, and Medicine. 2019. Relationship Between Erodibility and Properties of Soils. Washington, DC: The National Academies Press. doi: 10.17226/25470.
×
Page 85
Page 86
Suggested Citation:"Chapter 4 - Erosion Experiments." National Academies of Sciences, Engineering, and Medicine. 2019. Relationship Between Erodibility and Properties of Soils. Washington, DC: The National Academies Press. doi: 10.17226/25470.
×
Page 86
Page 87
Suggested Citation:"Chapter 4 - Erosion Experiments." National Academies of Sciences, Engineering, and Medicine. 2019. Relationship Between Erodibility and Properties of Soils. Washington, DC: The National Academies Press. doi: 10.17226/25470.
×
Page 87
Page 88
Suggested Citation:"Chapter 4 - Erosion Experiments." National Academies of Sciences, Engineering, and Medicine. 2019. Relationship Between Erodibility and Properties of Soils. Washington, DC: The National Academies Press. doi: 10.17226/25470.
×
Page 88
Page 89
Suggested Citation:"Chapter 4 - Erosion Experiments." National Academies of Sciences, Engineering, and Medicine. 2019. Relationship Between Erodibility and Properties of Soils. Washington, DC: The National Academies Press. doi: 10.17226/25470.
×
Page 89
Page 90
Suggested Citation:"Chapter 4 - Erosion Experiments." National Academies of Sciences, Engineering, and Medicine. 2019. Relationship Between Erodibility and Properties of Soils. Washington, DC: The National Academies Press. doi: 10.17226/25470.
×
Page 90
Page 91
Suggested Citation:"Chapter 4 - Erosion Experiments." National Academies of Sciences, Engineering, and Medicine. 2019. Relationship Between Erodibility and Properties of Soils. Washington, DC: The National Academies Press. doi: 10.17226/25470.
×
Page 91
Page 92
Suggested Citation:"Chapter 4 - Erosion Experiments." National Academies of Sciences, Engineering, and Medicine. 2019. Relationship Between Erodibility and Properties of Soils. Washington, DC: The National Academies Press. doi: 10.17226/25470.
×
Page 92
Page 93
Suggested Citation:"Chapter 4 - Erosion Experiments." National Academies of Sciences, Engineering, and Medicine. 2019. Relationship Between Erodibility and Properties of Soils. Washington, DC: The National Academies Press. doi: 10.17226/25470.
×
Page 93
Page 94
Suggested Citation:"Chapter 4 - Erosion Experiments." National Academies of Sciences, Engineering, and Medicine. 2019. Relationship Between Erodibility and Properties of Soils. Washington, DC: The National Academies Press. doi: 10.17226/25470.
×
Page 94
Page 95
Suggested Citation:"Chapter 4 - Erosion Experiments." National Academies of Sciences, Engineering, and Medicine. 2019. Relationship Between Erodibility and Properties of Soils. Washington, DC: The National Academies Press. doi: 10.17226/25470.
×
Page 95
Page 96
Suggested Citation:"Chapter 4 - Erosion Experiments." National Academies of Sciences, Engineering, and Medicine. 2019. Relationship Between Erodibility and Properties of Soils. Washington, DC: The National Academies Press. doi: 10.17226/25470.
×
Page 96
Page 97
Suggested Citation:"Chapter 4 - Erosion Experiments." National Academies of Sciences, Engineering, and Medicine. 2019. Relationship Between Erodibility and Properties of Soils. Washington, DC: The National Academies Press. doi: 10.17226/25470.
×
Page 97
Page 98
Suggested Citation:"Chapter 4 - Erosion Experiments." National Academies of Sciences, Engineering, and Medicine. 2019. Relationship Between Erodibility and Properties of Soils. Washington, DC: The National Academies Press. doi: 10.17226/25470.
×
Page 98
Page 99
Suggested Citation:"Chapter 4 - Erosion Experiments." National Academies of Sciences, Engineering, and Medicine. 2019. Relationship Between Erodibility and Properties of Soils. Washington, DC: The National Academies Press. doi: 10.17226/25470.
×
Page 99
Page 100
Suggested Citation:"Chapter 4 - Erosion Experiments." National Academies of Sciences, Engineering, and Medicine. 2019. Relationship Between Erodibility and Properties of Soils. Washington, DC: The National Academies Press. doi: 10.17226/25470.
×
Page 100
Page 101
Suggested Citation:"Chapter 4 - Erosion Experiments." National Academies of Sciences, Engineering, and Medicine. 2019. Relationship Between Erodibility and Properties of Soils. Washington, DC: The National Academies Press. doi: 10.17226/25470.
×
Page 101
Page 102
Suggested Citation:"Chapter 4 - Erosion Experiments." National Academies of Sciences, Engineering, and Medicine. 2019. Relationship Between Erodibility and Properties of Soils. Washington, DC: The National Academies Press. doi: 10.17226/25470.
×
Page 102
Page 103
Suggested Citation:"Chapter 4 - Erosion Experiments." National Academies of Sciences, Engineering, and Medicine. 2019. Relationship Between Erodibility and Properties of Soils. Washington, DC: The National Academies Press. doi: 10.17226/25470.
×
Page 103
Page 104
Suggested Citation:"Chapter 4 - Erosion Experiments." National Academies of Sciences, Engineering, and Medicine. 2019. Relationship Between Erodibility and Properties of Soils. Washington, DC: The National Academies Press. doi: 10.17226/25470.
×
Page 104
Page 105
Suggested Citation:"Chapter 4 - Erosion Experiments." National Academies of Sciences, Engineering, and Medicine. 2019. Relationship Between Erodibility and Properties of Soils. Washington, DC: The National Academies Press. doi: 10.17226/25470.
×
Page 105
Page 106
Suggested Citation:"Chapter 4 - Erosion Experiments." National Academies of Sciences, Engineering, and Medicine. 2019. Relationship Between Erodibility and Properties of Soils. Washington, DC: The National Academies Press. doi: 10.17226/25470.
×
Page 106
Page 107
Suggested Citation:"Chapter 4 - Erosion Experiments." National Academies of Sciences, Engineering, and Medicine. 2019. Relationship Between Erodibility and Properties of Soils. Washington, DC: The National Academies Press. doi: 10.17226/25470.
×
Page 107
Page 108
Suggested Citation:"Chapter 4 - Erosion Experiments." National Academies of Sciences, Engineering, and Medicine. 2019. Relationship Between Erodibility and Properties of Soils. Washington, DC: The National Academies Press. doi: 10.17226/25470.
×
Page 108
Page 109
Suggested Citation:"Chapter 4 - Erosion Experiments." National Academies of Sciences, Engineering, and Medicine. 2019. Relationship Between Erodibility and Properties of Soils. Washington, DC: The National Academies Press. doi: 10.17226/25470.
×
Page 109
Page 110
Suggested Citation:"Chapter 4 - Erosion Experiments." National Academies of Sciences, Engineering, and Medicine. 2019. Relationship Between Erodibility and Properties of Soils. Washington, DC: The National Academies Press. doi: 10.17226/25470.
×
Page 110
Page 111
Suggested Citation:"Chapter 4 - Erosion Experiments." National Academies of Sciences, Engineering, and Medicine. 2019. Relationship Between Erodibility and Properties of Soils. Washington, DC: The National Academies Press. doi: 10.17226/25470.
×
Page 111
Page 112
Suggested Citation:"Chapter 4 - Erosion Experiments." National Academies of Sciences, Engineering, and Medicine. 2019. Relationship Between Erodibility and Properties of Soils. Washington, DC: The National Academies Press. doi: 10.17226/25470.
×
Page 112
Page 113
Suggested Citation:"Chapter 4 - Erosion Experiments." National Academies of Sciences, Engineering, and Medicine. 2019. Relationship Between Erodibility and Properties of Soils. Washington, DC: The National Academies Press. doi: 10.17226/25470.
×
Page 113
Page 114
Suggested Citation:"Chapter 4 - Erosion Experiments." National Academies of Sciences, Engineering, and Medicine. 2019. Relationship Between Erodibility and Properties of Soils. Washington, DC: The National Academies Press. doi: 10.17226/25470.
×
Page 114
Page 115
Suggested Citation:"Chapter 4 - Erosion Experiments." National Academies of Sciences, Engineering, and Medicine. 2019. Relationship Between Erodibility and Properties of Soils. Washington, DC: The National Academies Press. doi: 10.17226/25470.
×
Page 115
Page 116
Suggested Citation:"Chapter 4 - Erosion Experiments." National Academies of Sciences, Engineering, and Medicine. 2019. Relationship Between Erodibility and Properties of Soils. Washington, DC: The National Academies Press. doi: 10.17226/25470.
×
Page 116

Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

76 This chapter presents the results of all the erosion experiments performed as part of NCHRP Project 24-43. Section 4.1 of this chapter describes the Soil Erosion Laboratory at Texas A&M University (TAMU) and the testing devices that were built as part of this project. The design plans as well as photographs of each device that was built are presented in this section. Section 4.2 presents the erosion test plan matrix for the project, and Section 4.3 presents the results of the erosion experiments, namely, the mini –jet erosion test (mini-JET), the erosion function appa- ratus (EFA), the hole erosion test (HET), the pocket erodometer test (PET), and the borehole erosion test (BET). Finally, Section 4.4 presents the comprehensive information on the geo- technical properties of all tested samples. Appendix 1 of this report includes all detailed results of the erosion tests, and Appendix 2 presents the spreadsheets of the geotechnical properties of each sample. For each sample that was tested in any erosion device, many photographs and videos were taken before, during, and after the tests. The photographs and videos were collected in a file that is held by the authors. 4.1 TAMU Soil Erosion Lab and Testing Devices The primary step in performing the erosion tests in this study was furnishing the erosion lab with all necessary testing equipment and ensuring that the working conditions at TAMU were satisfactory. HET and JET devices were constructed in the lab, and TAMU’s two EFA machines were refurbished. The work done in constructing the HET and JET devices and the refurbish- ment of the TAMU Soil Erosion Laboratory is summarized below. 4.1.1 Construction of HET Apparatus The HET apparatus was constructed at TAMU in accordance with the work done by Wan and Fell (2002) at the University of New South Wales in Australia. A schematic diagram of this device and the design drawings are presented in Figure 37 to Figure 41. Two dummy tests were conducted to make sure that the constructed apparatus was ready for the testing schedule. Figure 42 shows the final version of the HET apparatus in the Soil Erosion Laboratory at TAMU. 4.1.2 Construction of Mini-JET Apparatus The core part of the mini-JET device was obtained from the Department of Biosystems and Agricultural Engineering at Oklahoma State University. The JET test assembly was then constructed in the TAMU Soil Erosion Laboratory (Figure 43). Two dummy tests were also conducted to ensure that there was no considerable leakage or hindrance with the testing process. Figure 43 shows photos of the JET assembly. C H A P T E R 4 Erosion Experiments

Erosion Experiments 77 Figure 37. Schematic of HET assembly (Wan and Fell 2002).

78 Relationship Between Erodibility and Properties of Soils C.L. CROSS SECTION A-A LONGITUDINAL SECTION Left Cylinder Right Cylinder 25 .5 25.5 63.5 50 .8 55.5 56 .5 53 .0 A A 18 0. 0 180.0 90.0 90 .0 20 mm THK PERSPEX END PLATE 12 mm DIA. HOLE FOR 10 mm DIA. THE BOLT 3 mm DEEP RECESS 12 mm DIA. HOLE FOR MONOMETER 12 mm DIA. HOLE FOR AIR RELEASE VALVE Part A Part B Part C Figure 38. Drawing of the entire HET assembly at a glance (all dimensions in millimeters).

Erosion Experiments 79 17 .5 12.0 18 0. 0 180.0 90.0 90 .0 20 mm THK PERSPEX END PLATE 12 mm DIA. HOLE FOR 10 mm DIA.THE BOLT 3 mm DEEP RECESS 25 .5 25.5 16 mm THK 180x180 PERSPEX END PLATE 35 mm DIA. HOLE FOR OUTLET PIPE 12 mm DIA HOLE FOR 10 mm DIA. TIE BOLT 58 .5 12 .0 19 .5 3.0 63.5 16.0 12 .7 Without DimensionsWith Dimensions A A CROSS SECTION A-A LONGITUDINAL SECTION A A 50 .8 50 .8 Figure 39. Drawings of HET associated with Part A: End Plate (all dimensions in millimeters).

80 Relationship Between Erodibility and Properties of Soils 63.5 3 mm DEEP RECESS 12 mm DIA. HOLE FOR MONOMETER 12 mm DIA. HOLE FOR AIR RELEASE VALVE 63 .5 12 mm DIA. HOLE FOR MANOMETER PERSPEX CYLINDER 101.6 mm INTERNAL DIA. 12 mm DIA. HOLE FOR AIR RELEASE VALVE 17.0 3.0 4. 7 50 .8 12 .7 3.0 50 .8 A A 55.5 Without DimensionsWith Dimensions A A CROSS SECTION A-A LONGITUDINAL SECTION Figure 40. Drawings of HET associated with Part B: Middle Cylinder (all dimensions in millimeters).

Erosion Experiments 81 18 0. 0 180.0 90.0 90 .0 20 mm THK PERSPEX END PLATE 12 mm DIA. HOLE FOR 10 mm DIA. THE BOLT 63.5 50 .8 55.5 56 .5 A A 3 mm DEEP RECESS 25 .5 25.5 Without DimensionsWith Dimensions A A CROSS SECTION A-A LONGITUDINAL SECTION 50 .8 55 .5 53 .01 2. 0 23.0 53 .0 26 .5 3.08.0 3. 5 Figure 41. Drawings of HET associated with Part C: Inlet Plate (all dimensions in millimeters).

82 Relationship Between Erodibility and Properties of Soils Flow rate indicator HET Sample Constant Head Tank U/S & D/S Piezometers Drainage Sump Pump Low Flowmeter Dummy Test Sample Right After the Test Flow Indicator at the Middle of a Dummy Test HET Sample Core at the Middle of a Dummy Test Drainage Hose Inflow: Tap Water Figure 42. Photos of HET assembly at TAMU (U/S = upstream; D/S = downstream).

Erosion Experiments 83 Constant Head System Source Flow Hose Drain Hose Inlet: Tap Water JET Device Outlet: Drain Hose Submergence Tank Support Ring Standard Compaction Sample Mold Scour Gauge Inlet from Source Hose Deflector Plate Rotatable Plate JET nozzle (1/8”) Figure 43. Photos of JET assembly at TAMU.

84 Relationship Between Erodibility and Properties of Soils 4.1.3 Refurbishment of EFA Machines and TAMU Soil Erosion Laboratory The TAMU Soil Erosion Laboratory contains two EFAs. Both machines were repaired and upgraded for the second phase of the project. Figure 44 shows photos of the laboratory, the control desk, and the two EFAs. The difference between the two EFAs is the way the sample extrusion is controlled. In EFA #1, the test operator needs to extrude the sample from the tube manually by pushing the button on the control board of the EFA, while in EFA #2 the extrusion is controlled through the desktop on the control desk; however, one of the operators still needs to stand by the EFA to monitor whether there is any scour on the sample. 4.2 Test Plan Matrix As discussed in Chapter 1, the majority of the erosion tests proposed in this study consisted of laboratory tests performed with devices developed in the TAMU Soil Erosion Laboratory. The remaining tests were associated with field tests conducted on the clay and sand sites at TAMU’s Control Desk EFA #2 EFA #1 General View of the Erosion Lab Figure 44. Photos of the Soil Erosion Laboratory at TAMU showing control desk and the two EFAs.

Erosion Experiments 85 RELLIS campus. A total of 168 new erosion tests were planned to be performed during this project. Table 16 shows the experimental plan proposed for this project. A testing matrix was proposed in order to perform all erosion tests in accordance with the progress schedule timeline of the project. Table 17 shows the proposed testing matrix for this project. 4.3 Results of Erosion Tests This section presents the results of all the erosion tests performed during this project. As dis- cussed in the previous section, the following erosion test devices were used: EFA, JET, HET, PET, and BET. Detailed information on the geotechnical properties of all tested samples is presented in Section 4.4. Soil Type Type of Test Total Number of Tests Compare Different Devices 1 clay (man-made) 1 silt (man-made) 1 sand (man-made) 1 gravel (man-made) EFA JET HET PET 16 Check Repeatability of Results 1 clay (man-made) 1 silt (man-made) 1 sand (man-made) 1 gravel (man-made) EFA JET HET PET 16 Organize Demonstration and Comparison of Field Erosion Devices 1 clay 1 sand PET BET ISEEP ISTD 8 Erosion Tests to Develop Equations 14 clays EFA HET JET PET 56 8 silts EFA HET JET PET 32 6 sands EFA HET JET PET 24 4 gravels EFA HET JET PET 16 Total Number of Tests Clays, silts, sands, gravels EFA JET HET PET BET ISEEP ISTD 168 Note: ISEEP = in situ erosion evaluation probe; ISTD = in situ scour testing device. Table 16. Experimental test plan proposed for NCHRP Project 24-43.

86 Relationship Between Erodibility and Properties of Soils FY TIME FRAME TASK # TIME FRAME TASK # TIME FRAME TASK # FY TIME FRAME TASK # TIME FRAME TASK # TIME FRAME TASK # TIME FRAME TASK # TIME FRAME TASK # TIME FRAME TASK # TIME FRAME TASK # TIME FRAME TASK # TIME FRAME TASK # Texas A&M University System Iman SHAFII 24-43 Week 4 (10/22 to 10/29)Week 3 (10/14 to 10/21)Week 2 (10/7 to 10/14)Week 1 (9/29 to 10/7) Percent completed? TARGET Perform erosion tests with different devices using the same prepared soil 100 100 100 100 October 30th to November 30th 4 1 EFA, 1 JET, 1 HET, 1 PET on same as above Clay 1 EFA, 1 JET, 1 HET, 1 PET on same as above Silt 1 EFA, 1 JET, 1 HET, 1 PET on same as above Sand 1 EFA, 1 JET, 1 HET, 1 PET on same as above Gravel 1 EFA, 1 JET, 1 HET, 1 PET w/ soil properties on Clay 1 EFA, 1 JET, 1 HET, 1 PET w/ soil properties on Silt 1 EFA, 1 JET, 1 HET, 1 PET w/ soil properties on Sand 1 EFA, 1 JET, 1 HET, 1 PET w/ soil properties on Gravel4Sept ember 30th toOctober 30th TARGET Check repeatability of results Percent completed? 100 100 100 100 TARGET Week 1 (11/29 to 12/7) Week 2 (12/7 to 12/14) Week 3 (12/14 to 12/21) Week 4 (12/22 to 12/29) Week 1 (10/29 to 11/7) Week 2 (11/7 to 11/14) Week 3 (11/14 to 11/21) Week 4 (11/22 to 11/29) 1 BET, (possibly 1 ISTD) on sand site in RELLIS Campus w/ associated soil properties Percent completed? 100 100 100 100 November 30th to December 30th 4 Organize field erosion devices demonstraation and comparison 1 PET, (possibly 1 ISEEP) on clay site in RELLIS Campus w/ associated soil properties 1 PET, (possibly 1 ISEEP) on sand site in RELLIS Campus w/ associated soil properties 1 BET, (possibly 1 ISTD) on clay site in RELLIS Campus w/ associated soil properties TARGET Week 1 (12/28 to 1/5) Week 2 (1/5 to 1/14) Week 3 (1/14 to 1/21) Week 4 (1/22 to 1/29) December 30th to Jan uar y 30th 5 Erosion tests to develop the equations (14 clay samples) Holidays (Christmas Break) 1 EFA, 1 JET, 1 HET, 1 PETw/ soil properties on Clay #1 Jan uar y 30th to Februar y 30th 5 Erosion tests to develop the equations (14 clay samples) 1 EFA, 1 JET, 1 HET, 1 PET w/ soil properties on Clay #4 1 EFA, 1 JET, 1 HET, 1 PET w/ soil properties on Clay #5 1 EFA, 1 JET, 1 HET, 1 PET w/ soil properties on Clay #2 1 EFA, 1 JET, 1 HET, 1 PET w/ soil properties on Clay #3 Percent completed? 100 100 100 100 1 EFA, 1 JET, 1 HET, 1 PET w/ soil properties on Clay #6 1 EFA, 1 JET, 1 HET, 1 PET w/ soil properties on Clay #7 Percent completed? 100 100 100 100 TARGET Week 1 (1/29 to 2/7) Week 2 (2/7 to 2/14) Week 3 (2/14 to 2/21) Week 4 (2/22 to 2/29) Week 1 (2/29 to 3/7) Week 2 (3/7 to 3/13) Week 3 (3/13 to 3/19) Week 4 (3/19 to 3/29) Februar y 30th to Ma r ch 30th 5 1 EFA, 1 JET, 1 HET, 1 PET w/ soil properties on Clay #8 1 EFA, 1 JET, 1 HET, 1 PET w/ soil properties on Clay #9 Holidays (Spring Break) 1 EFA, 1 JET, 1 HET, 1 PET w/ soil properties on Clay #10 Erosion tests to develop the equations (14 clay samples) Percent completed? TARGET 100 100 100 100 TARGET Week 1 (3/29 to 4/7) Week 2 (4/7 to 4/14) Week 3 (4/14 to 4/21) Week 4 (4/22 to 4/29) Apr il 30th to Ma y 30th 5 Erosion tests to develop the equations (8 silt samples) 1 EFA, 1 JET, 1 HET, 1 PET w/ soil properties on Silt #1 1 EFA, 1 JET, 1 HET, 1 PET w/ soil properties on Silt #2 1 EFA, 1 JET, 1 HET, 1 PET w/ soil properties on Clay #14 Percent completed? 100 100 100 100 Ma r ch 30th to Apr il 30th 5 Erosion tests to develop the equations (14 clay samples) 1 EFA, 1 JET, 1 HET, 1 PET w/ soil properties on Clay #11 1 EFA, 1 JET, 1 HET, 1 PET w/ soil properties on Clay #12 1 EFA, 1 JET, 1 HET, 1 PET w/ soil properties on Clay #13 1 EFA, 1 JET, 1 HET, 1 PET w/ soil properties on Silt #3 1 EFA, 1 JET, 1 HET, 1 PET w/ soil properties on Silt #4 Percent completed? 100 100 100 100 TARGET Week 1 (4/29 to 5/7) Week 2 (5/7 to 5/14) Week 3 (5/14 to 5/21) Week 4 (5/22 to 5/29) TARGET Week 1 (5/29 to 6/7) Week 2 (6/7 to 6/14) Week 3 (6/14 to 6/21) Week 4 (6/22 to 6/29) Ma y 30th to Ju ne 30th 5 Erosion tests to develop the equations (8 silt samples) 1 EFA, 1 JET, 1 HET, 1 PET w/ soil properties on Silt #5 1 EFA, 1 JET, 1 HET, 1 PET w/ soil properties on Silt #6 Ju ne 30th to Ju ly 30th 5 Erosion tests to develop the equations (6 sand samples) 1 EFA, 1 JET, 1 HET, 1 PET w/ soil properties on Sand #1 1 EFA, 1 JET, 1 HET, 1 PET w/ soil properties on Sand #2 1 EFA, 1 JET, 1 HET, 1 PET w/ soil properties on Silt #7 1 EFA, 1 JET, 1 HET, 1 PET w/ soil properties on Silt #8 Percent completed? 100 100 100 100 1 EFA, 1 JET, 1 HET, 1 PET w/ soil properties on Sand #3 1 EFA, 1 JET, 1 HET, 1 PET w/ soil properties on Sand #4 Percent completed? 100 100 100 100 TARGET Week 1 (6/29 to 7/7) Week 2 (7/7 to 7/14) Week 3 (7/14 to 7/21) Week 4 (7/22 to 7/29) TARGET Week 1 (7/29 to 8/7) Week 2 (8/7 to 8/14) Week 3 (8/14 to 8/21) Week 4 (8/22 to 8/29) Ju ly 30th to August 30th 5 1 EFA, 1 JET, 1 HET, 1 PET w/ soil properties on Sand #5 1 EFA, 1 JET, 1 HET, 1 PET w/ soil properties on Sand #6 Erosion tests to develop the equations (4 gravel samples) 1 EFA, 1 JET, 1 HET, 1 PET w/ soil properties on Gravel #3 1 EFA, 1 JET, 1 HET, 1 PET w/ soil properties on Gravel #4 1 EFA, 1 JET, 1 HET, 1 PET w/ soil properties on Gravel #1 1 EFA, 1 JET, 1 HET, 1 PET w/ soil properties on Gravel #2 Percent completed? 100 100 100 100 2017 2016 NCHRP Project No. Research Agency Laboratory Leader NATIONAL COOPERATIVE HIGHWAY RESEARCH PROGRAM TRANSPORTATION RESEARCH BOARD NATIONAL RESEARCH COUNCIL TESTIN G MATRIX Percent completed? 100 100 TARGET Week 1 (8/29 to 9/7) Week 2 (9/7 to 9/14) Ju ly 30th to August 30th 5 Erosion tests to develop the equations (finish 6 sands, start on 4 gravel samples) Table 17. Testing matrix for NCHRP Project 24-43. 4.3.1 Ensuring the Repeatability of Erosion Tests and Field Demonstration The two major topics addressed in this section are 1. Testing the same soil with different erosion testing devices (i.e., EFA, JET, HET, and PET) to evaluate the repeatability of the results for each erosion test, and 2. Organizing field demonstration tests of the PET and the BET.

Erosion Experiments 87 For the purpose of ensuring the repeatability of the erosion tests, man-made samples of all four types of soils (gravel, sand, silt, and clay) were prepared and tested using the EFA, JET, HET, and PET. Table 18 shows the primary description of the soils tested for the purpose of ensuring repeatability. Thirty-two samples were tested. The first letter in the sample name refers to the soil type. The second letter refers to the first letter of each apparatus type. The number at the end of the sample name is 1 if the sample was being tested for the first time, and 2 if it was being tested for the second time to ensure repeatability. For example, CJ-2 means that the sample is a clay that was tested with the JET for the second time to evaluate the repeat- ability of this device. The results of the work done to check the repeatability of erosion tests for each sample are described in the following sections: • Section 4.3.1.1, Ensuring the Repeatability of the EFA; • Section 4.3.1.2, Ensuring the Repeatability of the PET; • Section 4.3.1.3, Ensuring the Repeatability of the HET; and • Section 4.3.1.4, Ensuring the Repeatability of the JET. 4.3.1.1 Ensuring the Repeatability of the EFA Clay Samples (CE-1 and CE-2). The prepared clay samples were a mixture of 60% porcelain Grolleg kaolin plus 40% bentonite. Both samples were remolded and compacted to reproduce the target condition listed in Table 18. Results of the EFA tests on CE-1 and CE-2 are presented in Figure 45 and Figure 46 against velocity and shear stress, respectively. Both samples can be categorized as medium erodibility (Category III). The critical velocities for CE-1 and CE-2 were 1.18 and 1.04 m/s, respectively. The critical shear stress values for CE-1 and CE-2 were 7.59 and 5.93 Pa, respectively. The results of each EFA test are also presented in the format of an EFA result spreadsheet in Appendix 1. Figure 47 shows an example of the EFA result spreadsheet for Sample CE-1. Silt Samples (ME-1 and ME-2). The silt samples were 100% porcelain Grolleg. Both samples were remolded and compacted to reproduce the target condition listed in Table 18. Results of the EFA tests on ME-1 and ME-2 are presented in Figure 48 and Figure 49 against velocity and shear Soil Type Description Erosion Test Sample Name Target Water Content (%) Target Wet Unit Weight (kN/m3) Gravel Pea gravel from Lowes, College Station, Texas HET JET EFA PET GH-1 & GH-2 GJ-1 & GJ-2 GE-1 & GE-2 GP-1 & GP-2 10 20 Sand Mixture of 20% bentonite + 80% silica sand (60–80) from Armadillo Clay & Supplies Co., Austin, Texas HET JET EFA PET SH-1 & SH-2 SJ-1 & SJ-2 SE-1 & SE-2 SP-1 & SP-2 10 19 Silt Porcelain Grolleg kaolin from Armadillo Clay & Supplies Co., Austin, Texas HET JET EFA PET MH-1 & MH-2 MJ-1 & MJ-2 ME-1 & ME-2 MP-1 & MP-2 18 16 Clay Mixture of 60% porcelain Grolleg kaolin + 40% bentonite from Armadillo Clay & Supplies Co., Austin, Texas HET JET EFA PET CH-1 & CH-2 CJ-1 & CJ-2 CE-1 & CE-2 CP-1 & CP-2 15 14 Table 18. Description of the soils used to ensure repeatability of erosion tests.

(a) Logarithmic Scale (b) Natural Scale Figure 45. EFA test results based on velocity for ensuring the repeatability of the EFA on clay samples. (b) Natural Scale (a) Logarithmic Scale Figure 46. EFA test results based on shear stress for ensuring the repeatability of the EFA on clay samples.

Erosion Experiments 89 Erosion Rate vs. Shear Stress Erosion Rate vs. Velocity Figure 47. EFA result spreadsheet for CE-1. (a) Logarithmic Scale (b) Natural Scale Figure 48. EFA test results based on velocity for ensuring the repeatability of the EFA on silt samples.

90 Relationship Between Erodibility and Properties of Soils stress, respectively. Both samples can be categorized as high to medium erodibility (Categories II to III). The critical velocities for ME-1 and ME-2 were 0.1 m/s. The critical shear stress values were measured as 0.1 Pa. Sand Samples. The sand samples were a mixture of 20% bentonite and 80% silica sand 60–80. Both samples were remolded and compacted to reproduce the target condition listed in Table 18. Results of the EFA tests on SE-1 and SE-2 are presented in Figure 50 and Figure 51 against velocity and shear stress, respectively. Both samples can be categorized as medium erodibility (Category III). Gravel Samples. The gravel samples were pea gravel. Both samples were remolded and compacted to reproduce the target condition listed in Table 18. Results of the EFA tests on GE-1 and GE-2 are presented in Figure 52 and Figure 53 against velocity and shear stress, respectively. Both samples can be categorized as medium to low erodibility (Categories III to IV). The critical velocities for GE-1 and GE-2 were 1.44 and 1.5 m/s, respectively. The critical shear stress values were measured as 17.63 and 19.13 Pa, respectively. 4.3.1.2 Ensuring the Repeatability of the PET The PET was performed on the top surface of each sample prior to each EFA test. As dis- cussed in Chapter 2, the PET consists of 20 applications of a jet of water at 8 m/s by squeezing the trigger of a water pistol positioned 50 mm from the sample face. The jet hits the sample surface at the same location at one end of the sample. The depth of the hole formed on the (a) Logarithmic Scale (b) Natural Scale Figure 49. EFA test results based on shear stress for ensuring the repeatability of the EFA on silt samples.

(a) Logarithmic Scale (b) Natural Scale Figure 50. EFA test results based on velocity for ensuring the repeatability of the EFA on sand samples. (a) Logarithmic Scale (b) Natural Scale Figure 51. EFA test results based on shear stress for ensuring the repeatability of the EFA on sand samples.

Figure 52. EFA test results based on velocity for ensuring the repeatability of the EFA on gravel samples. (a) Logarithmic Scale (b) Natural Scale Figure 53. EFA test results based on shear stress for ensuring the repeatability of the EFA on gravel samples. (a) Logarithmic Scale (b) Natural Scale

Erosion Experiments 93 sample surface is then measured and entered in the PET erosion categories chart. The PET was conducted three times at different areas on the top end of each sample. The results of the PET show reasonable repeatability for each soil type (Table 19). As discussed in Chapter 2, the results of the PET can be associated with the erosion category chart (Figure 54). All the points fall within the medium erodibility range (Category III) on this chart. Comparison of the results of the PET with the results of EFA shows compliance between the two tests. 4.3.1.3 Ensuring the Repeatability of the HET Clay Samples (CH-1 and CH-2). The clay samples were a mixture of 60% porcelain Grolleg kaolin plus 40% bentonite. Results of the HETs on CH-1 and CH-2 are presented in Figure 55 and Figure 56, respectively. The HET results are plotted as erosion rate (mm/h) against hydraulic shear stress. The HET plots include several fluctuations resulting from the errors associated with the constant head system both upstream and downstream. Note that Wan and Fell (2002) had the same type of curves and estimated the critical shear stress by fitting a best line on each plot. The critical shear stress values were measured as 70 and 67 Pa for CH-1 and CH-2, respectively. As explained in Chapter 2, HET results begin with a decrease in erosion rate and an increase in shear stress; thereafter, both erosion rate and shear stress begin increasing. The first part of the Sample Result (mm) Sample Result (mm) Clay Sand CP-1 2.11 SP-1 5.4 CP-2 3.0 SP-2 4.22 Silt Gravel MP-1 5.33 GP-1 na MP-2 5.3 GP-2 na Note: na = not applicable. It is not feasible to perform the PET on gravel samples. Table 19. Results of the PET on each sample. Figure 54. Erosion categories for the samples tested with the PET.

94 Relationship Between Erodibility and Properties of Soils curve is typically attributed to the thickness of the disturbed zone resulting from drilling the 6 mm hole in the center of the sample. The second part of the curve corresponds to the erosion of the undisturbed soil. To predict the critical shear stress, the erosion part of the fitted erosion curve is extended (see the dashed tangent line in Figure 55) to cross the horizontal axis. The shear stress associated with the obtained point is the critical shear stress. It should be noted that the dashed line is determined according to the operator’s interpretation. Therefore, the critical shear stress and slope of shear stress in the HET are subjective. The erosion part of the CH-1 and CH-2 test result curves were plotted in the erosion category chart. It can be concluded that both samples place in the low erodibility range (Category IV) (Figure 57). The main reason that the curves are in two different shear stress ranges is that the Figure 55. HET data for Sample CH-1. Figure 56. HET data for Sample CH-2.

Erosion Experiments 95 initial head condition for CH-1 and CH-2 differed because of the unexpected change in the test condition at the time of test (815 mm and 360 mm, respectively); however, when the erosion part of the curves is tracked, both curves cross the horizontal axis at a critical shear stress of 70 Pa. It is important to notice that higher initial heads in the HET lead to greater shear stress ranges at the soil–water interface. Therefore, the user should be aware of the desired shear stress range before performing HET. For high erodible geomaterials such as silt, the erosion function is better captured in an HET with a low initial head; however, for more erosion-resistant geo- materials such as dense high-plasticity clay, performing the HET with higher initial heads would better capture the erosion function. The results of all HETs are also presented in the format of an HET result spreadsheet in Appendix 1. Figure 58 shows an example of the HET result spreadsheet for Sample CH-1. Silt Samples (MH-1 and MH-2). The silt samples were 100% porcelain Grolleg kaolin. Results of the HETs for MH-1 and MH-2 are presented in Figure 59 and Figure 60, respectively. The critical shear stress was measured as 50 and 46 Pa for CH-1 and CH-2, respectively. The erosion functions of MH-1 and MH-2 were plotted in the erosion category chart and fell in the medium erodibility category (Category III) (Figure 61). The initial head was 330 mm and 321 mm for MH-1 and MH-2, respectively. Sand Samples (SH-1 and SH-2). As said earlier, the sand samples were a mixture of 20% bentonite plus 80% silica sand 60–80. The HET results for SH-1 and SH-2 are presented in Figure 62 and Figure 63, respectively. The critical shear stress values were measured as 111 and 108 Pa for CH-1 and CH-2, respectively. For the purpose of comparison and populating the NCHRP-Erosion spreadsheet, the erosion part of the SH-1 and SH-2 test result curves was plot- ted in the erosion category chart. Both erosion curves fell at the boundary between medium and low erodibility (Categories III and IV) (Figure 64). The initial head was 514 and 508 mm for SH-1 and SH-2, respectively. Gravel Samples (GH-1 and GH-2). The HET can only be performed in soils in which a horizontal hole can hold up and be self-supporting (i.e., fine-grained soils). Therefore, the HET was not conducted for the gravel samples. Figure 57. Erosion part of the clay HET curves plotted on the erosion category chart.

Figure 58. HET result spreadsheet for Sample CH-1.

Erosion Experiments 97 Actual test data Tangent line Fitted curve Figure 59. HET data for Sample MH-1. Actual test data Tangent line Fitted curve Figure 60. HET data for Sample MH-2. Figure 61. Erosion part of the silt HET curves plotted on the erosion category chart.

98 Relationship Between Erodibility and Properties of Soils Actual test data Tangent line Fitted curve Figure 62. HET result for Sample SH-1. Actual test data Tangent line Fitted curve Figure 63. HET result for Sample SH-2. Figure 64. Erosion part of the sand HET curves plotted on the erosion category chart.

Erosion Experiments 99 4.3.1.4 Ensuring the Repeatability of the JET As discussed Chapter 2, for every JET the operator records the depth of the hole being created at the center of the sample as a function of time under a constant head condition. The collected data are then backanalyzed to estimate two main erodibility parameters: critical shear stress and erosion rate. Three techniques are used to interpret the JET results: (1) the Blaisdell solution, (2) the iterative solution, and (3) the scour depth solution. Figure 65 shows an example of reading inputs during a JET and a sample JET spreadsheet. Each method gives a different set of erodibility parameters: critical shear stress (tc), and detachment coefficient (kd), which is the linear slope of the early part of the erosion curve in the erosion rate–shear stress plot. It is the test operator’s duty to find the best solution for interpreting JET results. In addition, since one of the goals of this research project was to establish relationships between soil erod- ibility and engineering properties, it was very important to understand each solution well and choose a consistent method of data interpretation for all JET results. The three interpretation techniques are summarized below. Blaisdell Solution. The most established solution in the literature is the Blaisdell solution, which was developed and used by Hanson and Cook (1997, 2004). This technique was created on the basis of a hyperbolic function (Blaisdell et al. 1981) to model the development of the scour hole. The details of this hyperbolic function are not discussed here; however, it is worth noting that this function employs the real-time depth of the scour hole and the velocity of the water jet at the nozzle to predict the maximum depth of erosion, at which the hole stops being eroded. Thereafter, the estimated equilibrium depth is used to measure the critical shear stress (Equation 57): (57)0 2J J c p e t = t ×     where Je = equilibrium depth, Jp = potential core length (nozzle diameter × 6.2), and t0 = maximum shear stress at the soil–water boundary. The value of kd is then determined by using the least squares derivation between the real time and predicted time. Further information is provided in Chapter 2, Section 2.1.6. It was found in the literature that this technique highly underpredicts the values of tc and kd. After many jet tests were run, letting the sample erode until it reached the equilibrium depth, it was observed that the equilibrium depth estimated with the Blaisdell solution was typically lower than the actual equilibrium depth. This consequently leads to underprediction of the critical shear stress and, subsequently, the detachment coefficient (kd). The other issue with the Blaisdell solution was the high variability of the critical shear stress (Simon et al. 2010; Cossette et al. 2012). Iterative Solution. In an effort to improve the Blaisdell solution and reduce the scatter in tc versus kd, Simon et al. (2010) developed the iterative solution. In this technique, the results of tc and kd from the Blaisdell solution are used for the next iteration to minimize the root mean square deviation between the real time and predicted time; however, many examples showed that the same variation in results was often observed. Scour Depth Solution. The scour depth solution was developed by Daly et al. (2013). The big difference between this technique and the other two is that it solves for kd and tc at the same

(a) (b) Figure 65. Example of (a) reading inputs during a JET, (b) sample JET spreadsheet.

Erosion Experiments 101 time. As shown in Figure 65, the plot of scour depth versus time is better predicted by the scour depth solution. With this method, the JET should be run until the sample stops eroding in the center (i.e., reaches the equilibrium depth). To date, JET results are often reported by using the Blaisdell solution technique. However, new studies by Daly et al. (2015) and Khanal et al. (2016) have reported JET results in the form of all three solution techniques. Khanal et al. (2016) have investigated the influence of the operator-dependent variables, such as reading interval, ending time, and pressure head setting on JET results interpreted with all three solutions. It has been partially concluded that the scour depth solution gives the most accurate results in terms of scour depth versus time. This solution also makes fewer assumptions [e.g., assuming the final equilibrium depth (Je) or the predicted time] as compared with the Blaisdell and iterative solutions. Because the scour depth solution makes fewer assumptions than the Blaisdell and iterative solutions, JET results obtained with the scour depth solution were selected for comparison with the erosion results obtained from the HET and the EFA. However, one of the disadvantages of the scour depth solution occurs in the case where the soil is very resistant to erosion. In this case, it is rarely possible to end with the equilibrium depth; therefore, the iterative solution is better for pre- dicting subtle changes in scour depth and obtaining the equilibrium depth, and, consequently the erodibility parameters. For this project, the JET results are reported according to all three solutions discussed above. For the regression analyses presented in the next chapters, the scour depth solution is used as the primary solution, except in special cases in which use of the iterative solution or Blaisdell solution was more appropriate. Clay Samples (CJ-1 and CJ-2). Table 20 shows the results of the three solutions—Blaisdell, iterative, and scour—for CJ-1 and CJ-2. Reasonable repeatability was observed for all three techniques. The results of all JET tests are presented in the format of a JET result spreadsheet in Appendix 1. Figure 66 shows an example of the JET result spreadsheet for Sample CJ-1. Silt Samples (MJ-1 and MJ-2). Table 21 shows the JET results obtained for Samples MJ-1 and MJ-2. A reasonable repeatability is observed for all three techniques. Sand Samples (SJ-1 and SJ-2). Table 22 shows the JET results obtained for Samples SJ-1 and SJ-2. Except for the iterative solution, reasonable repeatability was observed, especially for the critical shear stress values. Gravel Samples (GJ-1 and GJ-2). Like the HET, the JET can only be performed in fine- grained soils. Therefore, the JET was not conducted for the gravel samples. 4.3.1.5 Field Erosion Device Demonstration As shown in Table 16, the erosion testing included organizing field demonstration tests of the BET device, the PET, and, possibly, North Carolina State University’s ISEEP and FHWA’s ISTD. Letters were sent to the appropriate staff at North Carolina State University and FHWA Sample Blaisdell Solution Iterative Solution τc(Pa) kd(cm3/N.s) τc (Pa) kd (cm3/N.s) CJ-1 5.79 0.59 5.8 3.82 CJ-2 4.81 0.53 4.92 3.76 Scour Depth Solution τc (Pa) kd(cm3/N.s) 8.8 2.56 6.74 1.19 Table 20. JET results for Samples CJ-1 and CJ-2.

102 Relationship Between Erodibility and Properties of Soils Figure 66. JET result spreadsheet for Sample CJ-1.

Erosion Experiments 103 to invite them to participate in the field demonstration tests. However, North Carolina State University did not have the funds necessary to bring the ISEEP to College Station, and FHWA declined because it was working on improving the ISTD and thus was not ready to contribute to this project. It was decided to perform the feasible available field tests at the National Geotechnical Experimentation Site at TAMU’s RELLIS Campus. These tests include the BET and the PET on both sand and clay sites. Terracon Consultants, Inc., of Conroe, Texas, provided neces- sary equipment to perform the field demonstration for this project. This section presents the results of the BET in clay and sand sites. The following BET procedure was undertaken at both sites: 1. Sampling was done at from 2 to 5 ft, from 6 to 9 ft, and from 10 to 13 ft in a 14-ft-deep borehole with 3-in. diameter Shelby tubes. Three 3-ft-long Shelby tube samples were taken every 4 ft. A 3-in. drill bit was used if necessary. 2. Insert the mechanical caliper and measure the diameter versus the depth (Figure 67). 3. Circulate the drilling fluid for 1 min to flush the borehole (Figure 68). 4. Insert the mechanical caliper and measure the diameter versus the depth. 5. Withdraw the mechanical caliper. 6. Insert NW drilling rods down to 6 in. above the bottom of the hole and circulate drilling fluid for 15 min at maximum pump velocity. 7. Withdraw the drilling rods. 8. Insert the mechanical caliper and measure the diameter versus the depth. 9. Withdraw the mechanical caliper. 10. Insert NW drilling rods 6 in. above the bottom of the hole and circulate the drilling fluid for 15 min at half the previous rate. 11. Withdraw the drilling rods. 12. Insert mechanical caliper and the measure diameter versus the depth. 13. Withdraw the mechanical caliper. 14. Insert NW drilling rods 6 in. above the bottom of the hole and circulate drilling fluid for 15 min at a flow rate to be decided in the field. 15. Withdraw the drilling rods. 16. Insert the mechanical caliper and measure the diameter versus the depth. 17. Withdraw the mechanical caliper. 18. Plot the data and adjust the procedure. Blaisdell Solution Scour Depth Solution Iterative Solution Sample τc(Pa) kd(cm3/N.s) τc (Pa) kd(cm3/N.s) τc (Pa) kd (cm3/N.s) MJ-1 1.9 1.45 1.74 1.4 4.74 5.22 MJ-2 1.37 1.02 3.89 2.12 3.63 5.2 Table 21. JET results for Samples MJ-1 and MJ-2. Blaisdell Solution Scour Depth Solution Iterative Solution Sample τc(Pa) kd(cm3/N.s) τc (Pa) kd(cm3/N.s) τc (Pa) kd (cm3/N.s) SJ-1 4.10 1.34 8.30 5.56 5.15 10.54 SJ-2 4.06 0.73 8.03 3.59 3.96 5.48 Table 22. JET results for Samples SJ-1 and SJ-2.

104 Relationship Between Erodibility and Properties of Soils Figure 67. Photographs taken from the mechanical caliper (3 arms) in closed-arm and opened-arm conditions. Figure 68. Circulating the drilling fluid in the borehole in order to flush.

Erosion Experiments 105 A photograph of the pump and the flow meter assembly on the drill rig is shown in Figure 69. One borehole in the sand site and one borehole in the clay site were drilled with 3-in.-diameter hollow stem augers. The drilling rods used to circulate the drilling fluid were 2.75 in. in diam- eter, which leaves an empty space of almost one-quarter inch between the drilling rods and the borehole wall. During the test, the flow rate is constantly monitored with the in-line flow meter shown in Figure 69; therefore, the velocity of the fluid in the borehole can be obtained by dividing the flow rate by the annular space between the drilling rod and the borehole wall. Results of the BET for clay and sand are discussed in the following sections. BET at the Clay Site. One borehole was drilled to the depth of 14 ft. The borehole was located at the following coordinates: N 30o.38.104′, W 096o.29.348′. Soil was classified as CH throughout the borehole. As described earlier for the BET procedure, the zero reading was measured after 1 min of flushing at a flow of 36 gallons per minute (gpm) (0.002271 m3/s). After that, three different flows of 35 gpm (0.002208 m3/s), 21 gpm (0.001325 m3/s), and 33 gpm (0.002082 m3/s) were generated in the borehole and maintained for 10 min each. The mechanical caliper shown in Figure 67 was used to obtain the diameter profile after each flow. Figure 70 shows the caliper readings at five different stages: 1. Before flushing: right after the borehole was drilled and before the 1-min flushing was done. 2. After flushing: after 1 min of flushing. 3. Reading 1: after 10 min of 35-gpm flow. 4. Reading 2: after 10 min of 21-gpm flow. 5. Reading 3: after 10 min of 33-gpm flow. The caliper readings at each of the aforementioned stages were obtained in two runs to make sure that the readings were repeatable. For all the cases, an acceptable overlay was observed, and the repeatability of the caliper readings was confirmed. The borehole diameter profiles shown in Figure 70 portray the averaged diameter profile between the first and second runs at each stage. Figure 70 clearly shows that, before any calculations of the erosion rate were made, there was a weak sand fissure at the proximity of the depth of 7.5 to 8.5 ft that caused much greater diameter enlargement. This observation is indeed an example of one of the most important advantages of the BET as compared with many other erosion tests in catching a continuous erodibility profile at a site prior to construction of bridges, levees, dams, and so forth. Figure 69. Photograph of the pump and the in-line flow meter assembly on the drill rig.

106 Relationship Between Erodibility and Properties of Soils While Figure 70 shows the borehole diameter profile at different stages during the test, it must be noted that the erosion function curve (i.e., the plot of the average erosion rate versus the fluid velocity) was constructed separately for each 2-ft interval (i.e., 2–4 ft, 4–6 ft., 6–8 ft, 8–10 ft, and 10–12 ft). Table 23 gives the flow rates, velocities, and time of application of each velocity for the BET at the clay site. Figure 71 shows the erosion function curves for each of the 2-ft intervals. As discussed in Chapter 2, Section 2.2.3, the BET has two component tests: the lateral bore- hole erosion test (LBET) associated with the increase in diameter of the borehole and the bottom borehole erosion test (BBET) associated with the increase in depth below the bottom of the drill- ing rods during the flow. The LBET is very similar in concept to the HET but with a larger hole and a vertical flow direction. The BBET is much like an in situ jet erosion test. The increase in depth at the bottom of the borehole in the BBET was monitored after each stage; however, these measurements did not lead to a reasonable erosion rate at the bottom of the hole. The main reason was that, as the wall of the borehole was being eroded, some eroded materials would settle and remain at the bottom of the borehole; therefore, the measurements of the bottom depth did not necessarily represent the actual erodibility of the soil at that depth. This issue, however, was not confronted during the BET at the sand site. The results of the LBET and BBET are included below in the discussion of the BET at the sand site. Figure 72 shows the results of some earlier EFA tests performed on samples taken from the same depths at the clay site. These EFA tests were performed about 1 year earlier than the Figure 70. Clay borehole diameter profile at different stages during the BET.

Erosion Experiments 107 Flow (m3/s) Velocity (m/s) Duration (min) Change in Profile (Figure 70) Depth = 2 to 4 ft 0.002271 1.967 1 Before flushing to after flushing 0.002208 1.308 10 After flushing to Reading 1 0.001325 0.773 10 Reading 1 to Reading 2 0.002082 1.063 10 Reading 2 to Reading 3 Depth = 4 to 6 ft 0.002271 2.639 1 Before flushing to after flushing 0.002208 1.444 10 After flushing to Reading 1 0.001325 0.967 10 Reading 1 to Reading 2 0.002082 1.431 10 Reading 2 to Reading 3 Depth = 6 to 8 ft 0.002271 2.450 1 Before flushing to after flushing 0.002208 1.280 10 After flushing to Reading 1 0.001325 0.669 10 Reading 1 to Reading 2 0.002082 0.687 10 Reading 2 to Reading 3 Depth = 8 to 10 ft 0.002271 N/A 1 Before flushing to after flushing 0.002208 0.596 10 After flushing to Reading 1 0.001325 0.418 10 Reading 1 to Reading 2 0.002082 0.433 10 Reading 2 to reading 3 Depth = 10 to 12 ft 0.002271 2.242 1 Before flushing to after flushing 0.002208 1.188 10 After flushing to Reading 1 0.001325 0.621 10 Reading 1 to Reading 2 0.002082 0.712 10 Reading 2 to Reading 3 Table 23. Flow, velocity, and time for the BET at clay site. 100,000 1,000 100 10 1 0.1 10,000 Er os io n Ra te (m m /h r) Figure 71. Results of lateral BET: erosion function curves for each 2-ft interval at the clay site.

108 Relationship Between Erodibility and Properties of Soils BET. Also, the boring from which samples were taken for EFA testing was not the same as or close to the boring done for the BET. These two factors as well as different flow conditions in the EFA and BET could be the main reasons that the EFA and BET results did not match perfectly. Clearly, there is a gap between the results of the two tests; however, in both tests, most erosion was observed in soil layers deeper than 6 ft. Existence of a weak sand fissure in the proximity of 8 ft made a big difference in the erosion resistance of the borehole in the clay site. BET at the Sand Site. One borehole was drilled to the depth of 12 ft. The borehole was located at the following coordinates: N 30o.38.301′, W 096o.27.606′. The soil was classified as SC throughout the borehole. Similar to the BET procedure, the borehole was flushed for almost 30 s at a flow of 37 gpm (0.002334 m3/s). After that, flows of 34 gpm (0.002145 m3/s) and 38 gpm (0.002397 m3/s) were generated in the borehole and maintained for 7 min each. The mechani- cal caliper shown in Figure 67 was used to obtain the borehole diameter profile after each flow. Figure 73 shows the caliper readings at four different stages during the test: 1. Before flushing: right after the borehole was drilled and before the 30-s flushing was done. 2. After flushing: after 30 s of flushing. 3. Reading 1: after 7 min of 34-gpm flow. 4. Reading 2: after 7 min of 38-gpm flow. As with the BET at the clay site, caliper readings at each of the aforementioned stages were obtained in two runs to ensure that the readings were repeatable. For all the cases, an accept- able overlay was observed, and the repeatability of the caliper readings was confirmed. The borehole diameter profiles shown in Figure 73 portray the averaged diameter profile between the first and second runs at each stage. It is clearly shown that the diameter enlargement at depths closer to the ground surface (0–3 ft) was significantly greater than at other depths. While Figure 73 shows the borehole diameter profile at different stages during the BET, it must be noted that the erosion function curve (i.e., plots of the average erosion rate versus the fluid velocity) was constructed separately for each 2-ft interval (i.e., 1–3 ft, 3–5 ft, 5–7 ft, 7–9 ft, and 9–11 ft). Table 24 gives the flow rates, velocities, and time of application of each velocity for the BET at the sand site. Figure 74 shows the erosion function curves for each of the 2-ft intervals. 100,000 1,000 100 10 1 0.1 10,000 Er os io n Ra te (m m /h r) Figure 72. EFA results: erosion function curves for each 2-ft interval at the clay site.

Erosion Experiments 109 Figure 75 shows the results of some earlier EFA tests performed on the samples from the sand site. The sand samples tested in the EFA were mixed from different depths and constructed in the laboratory to represent a similar condition in the field. The EFA results are acceptably con- sistent with the BET results, specifically for soil deeper than 5 ft. As mentioned earlier, the first 5 ft showed significant erosion during the BET. One of the reasons for much greater erosion in depths closer to the ground surface was that as the test was being performed, the cohesionless sand wall on top of the borehole became weaker and began to erode more as compared with deeper layers. In the deeper layers, however, more reasonable erosion was observed. One of the reasons that better consistency between the EFA and BET results was observed for the sand samples may be that the borings used for the BET and EFA were close to each other and, there- fore, soils from same depth were more similar than was the case with the clay site. The BET results discussed above are all associated with the increase in the diameter of the borehole (LBET). For the sand borehole, the depth increase at the bottom of the borehole was also monitored (BBET). The erosion function curve for the bottom of the sand borehole is shown in Figure 76. Briaud et al. (2017a) showed that the flow velocity of the jet eroding the borehole was almost equal to the average velocity of the flow in the annular space between the drilling rods and the borehole wall at depths close to the jet nozzle. For this study, the aver- age velocity of the flow for the depth of 9–11 ft was chosen to represent the velocity of the jet at the bottom of the borehole. The BBET results presented in Figure 76 show a higher erosion rate than the LBET result for the depth of 9–11 ft in Figure 74. Figure 73. Sand borehole diameter profile at different stages during the BET.

110 Relationship Between Erodibility and Properties of Soils Flow (m3/s) Velocity (m/s) Duration (min) Change in profile (Figure 73) Depth = 1 to 3 ft 0.002334 0.518 0.5 Before flushing to after flushing 0.002145 0.147 7 After flushing to Reading 1 0.002397 0.102 7 Reading 1 to Reading 2 Depth = 3 to 5 ft 0.002334 0.548 0.5 Before flushing to after flushing 0.002145 0.179 7 After flushing to Reading 1 0.002397 0.162 7 Reading 1 to Reading 2 Depth = 5 to 7 ft 0.002334 2.453 0.5 Before flushing to after flushing 0.002145 1.555 7 After flushing to Reading 1 0.002397 1.191 7 Reading 1 to Reading 2 Depth = 7 to 9 ft 0.002334 1.652 0.5 Before flushing to after flushing 0.002145 0.988 7 After flushing to Reading 1 0.002397 0.721 7 Reading 1 to Reading 2 Depth = 9 to 11 ft 0.002334 1.207 0.5 Before flushing to after flushing 0.002145 0.769 7 After flushing to Reading 1 0.002397 0.647 7 Reading 1 to Reading 2 Table 24. Flow, velocity, and time for the BET at sand site. 100,000 1,000 100 10 1 0.1 10,000 Er os io n Ra te (m m /h r) Figure 74. LBET results: erosion function curves for each 2-ft interval at the sand site.

Erosion Experiments 111 100,000 1,000 100 10 1 0.1 10,000 Er os io n Ra te (m m /h r) Figure 75. EFA results: erosion function curves for each 2-ft interval at the sand site. 100,000 1,000 100 10 1 0.1 10,000 Er os io n Ra te (m m /h r) Figure 76. BBET results: erosion function associated with the bottom of the sand borehole. 4.3.2 Erosion Tests Performed Using Many Different Soils This section discusses the running of different erosion tests on many natural samples. More than 128 erosion tests (32 EFA, 32 JET, 32 HET, and 32 PET) were performed on 14 natural clay, 8 silt, 6 sand, and 4 gravel samples. Many of these tests were performed on natural samples taken from Terracon’s Houston office. Some were collected from the Alcona Dam near Oscoda, Michigan; the Tittabawassee River in Midland, Michigan; Crane Creek in California; and Free- port and Lissie, Texas. After Hurricane Harvey, Iman Shafii, lead engineer on NCHRP Project 24-43, joined the Geotechnical Extreme Events Reconnaissance (GEER) team supported by the National Science Foundation. During this major effort, 15 samples from different locations were obtained and brought to the TAMU Soil Erosion Laboratory for erosion testing (primarily for EFA testing).

112 Relationship Between Erodibility and Properties of Soils Because of the limitations of each erosion testing device, a few challenges confronted the investigating team during the erosion testing phase. The following revisions were made to the testing plan: 1. HET testing on clay and silt samples: The HET was primarily conducted on remolded samples instead of natural samples, following the advice of the panel. 2. HET testing on sand and gravel (6 tests on sand and 4 tests on gravel): The HET could not be properly conducted on sand and gravel samples due to the limitations associated with its setup. In all cases, the hole drilled in sand samples collapsed. For gravel samples, this test clearly was not feasible. Therefore, it was decided to increase the number of erosion tests on any other sample (mostly coarse-grained samples) using other erosion tests (i.e., EFA and PET) to make up for the number of erosion tests promised in the proposed testing matrix. 3. JET testing on gravel (4 tests on gravel): The JET test also is not designed for gravel samples. Therefore, no JET results were reported for gravel samples. A summary of the tested samples presented in this section is given in Table 25. The majority of Table 25 is incorporated with intact samples; however, some cohesionless samples were remolded in the laboratory to follow the testing matrix shown in Table 17. Erosion result spreadsheets, as described in earlier sections, were prepared for each tested sample separately. Appendix 1 shows the results of the EFA, JET, and HET for all samples tested in this project. The total number of tests performed during this project turned out to be more than the 168 erosion tests promised in the proposed testing matrix. Test and Sample Name Collected From Date Collected Site INTACT SAMPLES EFA and PET B-1 (23–25 ft) G2 Consulting Group, LLC Dec. 2016 Tittabawassee River, Midland, Michigan B-7 (22–24 ft) B-9A (25–27 ft) B-9A (29–31ft) B-7-16 @ 8.5 ft Barr Engineering Co. Nov. 2016 Alcona Dam, Oscoda, Michigan B-7-16 @ 11.6 ft B-7-16 @ 13.5 ft B-7-16 @ 15.3 ft B-9-16 @ 16.1 ft B-9-16 @ 17.3 ft B-11-16 @18 ft B-11-16 @ 20.5 ft B-12-16 @ 18.1 ft B-12-16 @ 18.9 ft B-12-16 @ 20.5 ft B-13-16 @ 19 ft B-13-16 @ 20.5 ft B-13-16 @ 23.5 ft B-2 (13–15 ft) Terracon, Houston Oct. 2016 Beaumont Formation, Texas B-6 (0–2 ft) B-1 (4–6 ft) B-1 (28–30 ft) B-8 (2–4 ft) 5694 Table 25. Summary list of tested samples.

Erosion Experiments 113 B-2 (8–10 ft) B-2 (13–15 ft) B-3 (8–10 ft) B-4 (8–10 ft) B-5 (4–6 ft) B-5 (6–8 ft) B-6 (0–2 ft) B-2 (8–10 ft) Terracon, Houston Winter 2016 Lissie Formation Texas B-3 (10–12 ft) B-8 (2–4 ft) Terracon, Houston Winter 2016 Alluvium, Freeport TexasB-13 @ 20 ft B-13 @ 18 ft B-9A @ 26 ft G2 Consulting Group, LLC Dec. 2016 Tittabawassee Midland, Michigan B-9A @ 27 ft B-1 (23–25 ft) B-7 (22–24 ft) GEER Sample #2 GEER Sept. 2017 Bay City Bridge, Texas B-1 (12.5–14.5 ft) American Geotechnics April 2017 Crane Creek, California GEER Sample #1 Geotechnical Extreme Events Reconnaissance (GEER) Sept. 2017 Port Aransas Bridge, Texas GEER Sample #2 Bay City Bridge, Texas GEER Sample #3 GEER Sample #4 GEER Sample #5 GEER Sample #6 San Louis Pass, Texas GEER Sample #7 GEER Sample #8 Levee at Brazos River, Texas GEER Sample #9 Rosenberg Culvert Bridge, Texas GEER Sample #10 JET and PET B-1 (2–4 ft) Terracon, Houston Oct. 2016 Beaumont Formation, TX B-1 (4–6 ft) B-1 (8–10 ft) B-1 (10–12 ft) B-1 (13–15 ft) B-1 (18–20 ft) B-1 (28–30 ft) B-2 (2–4 ft) Test and Sample Name Collected From Date Collected Site Table 25. (Continued). (continued on next page)

114 Relationship Between Erodibility and Properties of Soils Test and Note: Shading indicates not applicable. Sample Name Collected From Date Collected Site Clay #9 Clay #10 Clay #11 Clay #12 Clay #13 Clay #14 Silt 1 Silt 2 Silt 3 Silt 4 Silt 5 Silt 6 Silt 7 Teton Dam Core REMOLDED SAMPLES EFA and PET Teton Dam 1 Teton Dam 2 Teton Dam 3 Sample 2 (FHWA) S-0-0-0 Sand #1 Sand #2 Gravel #1 Gravel #2 Gravel #3 Gravel #4 JET and PET Teton Dam Core S-0-0-0 Sand #1 Sand #2 Sample 2 (FHWA) HET and PET Clay #1 Clay #2 Clay #3 Clay #4 Clay #5 Clay #6 Clay #7 Clay #8 Table 25. (Continued).

Erosion Experiments 115 4.4 Soil Geotechnical Properties Soil index tests were conducted for all samples tested by any erosion testing device. The geotechnical tests included unit weight (ASTM D7263-09), moisture content (ASTM D2216-10), Atterberg limits (ASTM D4318-17), mini vane shear test (ASTM D4648), pocket penetrom- eter, sieve analysis (ASTM 422), hydrometer analysis (ASTM D7928-17), USCS (ASTM D2487-17), AASHTO classification, and specific gravity test (ASTM D854-14). Existing rel- evant geological information such as latitude and longitude, origin, water table data of the samples, and so forth were also recorded for each sample when possible. All this information was compiled in a comprehensive two-page soil properties spreadsheet for each sample. As an illustration, Figure 77 and Figure 78 show the two pages of the completed soil properties spreadsheet for sample B-7-16 (13–15.5 ft). Such spreadsheets were developed for all the soil samples that were tested with different erosion testing devices. Appendix 2 contains all the soil properties spreadsheets developed for this project. h d 98.99% WC (%) 13.04% 13.59% Notes: Plasticity Index Notes: Pocket Penetrometer was 2.32 mm Limits Average Plastic Limit (%) 49 0.083 Plastic Limit 3.1 11.5 20-30 22 Liquid Limit (%) 13.50 Dry Density Wet Density 0.25 0.0041 0.538 131.52 Sample # Core depth at middle (ft) Wc+s (gr) Ws (gr) Wc+s (gr) Core Diameter (ft) 0.25 Notes: Sample Dimensions Depth of upper side of the core (ft) 13.667 height (ft) 0.083 Depth of middle of the core (ft) 13.709 height (mm) 25.315 Depth of lower side of the core (ft) 13.750 Moisture Content 8 7 Ws (gr) 8.9 Container # Weight of Container (gr) Dry 1 13.50 45 1 9.9 Wet Layer depth (ft): Layer thickness (ft) Page 1 of 2B-7-16 (top) Iman Shafii B-7-16 5-Dec Clay From : Form # 0916 Sample name Operator Bore hole ID Date Layer type 13 To : 15.5 2.5 25-35 25 7.6 7.9 Core depth at middle (ft) 27.19% # of blows (mm) 13.50 WC (%) 1 1 9.1 9.6 10.1 Wet Wc+s (gr)* Dry Wc+s (gr) 7.35 12.5 O 46.00 0.9 Liquid Limit 26.96% 1 2 3 11.52 A1 Test # Container # Weight of Container (gr) 13.32% Notes: Wc+s (gr)* Wc+s (gr)Dish # Weight of Dish (gr) 12.7 11.31 1 5.6 13.87% Test # Core deoth (ft) Liquidity Index 1.9 6.2 45 W 1 13.5 2 13.5 15-25 20 1 15.6 14.6 D (mm) H (mm) 7 27.14% Weight of Solids (gr) Sample Height (ft) Moisture (%) Weight of Water (gr) 31.88% 30.30% 27.13% Dry Density (pcf) 104 Wet Density (kN/m3) 20.7 Wet Density (pcf) 131.5 Dry Density (kg/m3) 1658.2 Dry Density (kN/m3) 16.3 Sample Diameter (ft) Sample Volume (ft3) Sample weight (lb) Wet Denisty (pcf) Density Calcs. 19 29 90 Rotation Rate (o/min) Mini Vane Shear Test Su (kPa) Pocket Penetrometer Unconfined Strength OSHA Category 66 Type A tsf or kg/cm2 kPa 2.5 239.2 0 5 10 15 20 0 5 10 15 20 25 30 35 M oi st ur e Co nt en t (% ) # of blows y = -0.0096x + 0.5119 R² = 0.9943 26% 27% 28% 29% 30% 31% 32% 33% 15 20 25 0 M oi st ur e Co nt en t (% ) # of blo s Figure 77. Page 1 of soil properties spreadsheet for B-7-16 (13–15.5 ft).

116 Relationship Between Erodibility and Properties of Soils 0.003 21.5 0.01340 7.0 0.003 21.5 0.01340 7.6 0.003 21.5 0.01340 8.0 0.003 21.5 0.01340 8.40 0.003 21.4 0.01341 8.8 0.003 21.1 0.01348 9.4 0.003 20.8 0.01357 10.1 0.003 20.5 0.01356 10.5 0.003 20.0 0.01365 11.0 0.003 19.0 0.01386 11.8 0.003 18.9 0.01386 12.8 D (mm) % susType Time 5 2 1 0.50 K CC 0.99954 1.0305 1.03201.035 1.0235 1.0285 1.03 1.0315 1.0335 1.017 1.02 1.022 1.0265 2 1 0.5 0.266667 0.083333 240 60 30 15 22.1 Error (%) 0.0% Temp. (oC) 44.21 53.69 60.00 64.74 72.64 80.53 85.27 90.00 96.32 Specific Gravity (ASTM D854-14) L cm 0.018483 0.028049 0.038837 0.053432 0.071536 0.074000 Rh T (oC) K Gs, 20c 2.643412 Mρws,tMs 36422.4101.92 248.6996 0.9978 Mp (gr) Vp (mL) ρw (g/mL) Mpw,t (g) 350.06 Gt 2.64 451.8 469.1 33.161.0105 1.0140 303.7 340.7 377.8 0.001320 0.003073 0.005845 0.008022 gr of pass ing 200 100.00 1.0170 % of fine 39.58 29.69155.6 207.4 251.8 281.5 48.06 53.72 57.96 65.03 89.52 86.23 80.58 76.33 72.09 1.0190 1.0205 1.0230 1.0255 1.0270 1.0285 400.0 422.2 0.011135 1406 240 60 30 15 1406 Largest Particle (mm) Mass of Portion (gr) 24.7 6.2 5.2 Retained (gr) 6.9 2.2 0.0 Percent reta ined (%) 345.7 506.2 ∑ soil mass after sieve (gr) 321 501 0.27 0.08 200 363 369.2 Pan 4.76 151H Sieve+soi l (gr) 4.8 51.4 Air-dried weight (gr) 11 Oven-dried weight (gr) 10.9 D60 (mm) Cc Cu Gravel Fraction (%) 0 Sand Fraction (%) Fine Content (%) D10 (mm) Hygroscopic Correction Factor 0.990909091 Elapsed Time (min) 0.006620.0013N/A89.5%9.5% Reading (rh)Hydrometer Analysis (ASTM 422) USCS Classification AASHTO Classification CL#VALUE!#VALUE!0.01335 A-6 (10.3) 469.1 18.8 100.0 10.5 D30 (mm) 829.1 335.8 524 317 360 Sieve weight (gr) Geologic Category 1-General Geologic Information (i.e. Location, Color, etc.) 2- Cemented, uncemented, desiccated, overconsolidated, normally consolidated 3-Geologic Coordinates 1 2 3 Alcona Dam, Brown Cemented N/A Percent passed (%) 100 Particle Size Distribution (ASTM 422) Page 2 of 2 40 Sieve # Opening (mm) 4 Largest Particle (mm) Mass of Portion (gr) 5244.8 B-7-16 (top) Iman Shafi i Form # 0916 Sample name Operator D50 (mm) 1.0135 100.0 0.43 97.8 0.15 93.1 0.07 89.5 0.00 0.0 0 10 20 30 40 50 60 70 80 90 100 0.001 0.010 0.100 1.000 10.000 Pe rc en t Pa ss in g by W ei gh t ( % ) Grain Size (mm) Figure 78. Page 2 of soil properties spreadsheet for B-7-16 (13–15.5 ft).

Next: Chapter 5 - Organization and Interpretation of the Data »
Relationship Between Erodibility and Properties of Soils Get This Book
×
MyNAP members save 10% online.
Login or Register to save!
Download Free PDF

Analysis of the erodibility of geomaterials is important for the study of problems related to soil erosion such as bridge scour, embankment overtopping erosion, and stream stability. Erodibility is the relationship between the soil erosion rate and fluid velocity or hydraulic shear stress. Since different soils have different geotechnical properties, their erosion rates vary.

The TRB National Cooperative Highway Research Program's NCHRP Research Report 915: Relationship Between Erodibility and Properties of Soils provides reliable and simple equations quantifying the erodibility of soils on the basis of soil properties.

The report presents a detailed analysis of the issue. In addition, the project that developed the report also produced a searchable spreadsheet that uses statistical techniques to relate geotechnical properties to soil erodibility. The spreadsheet, NCHRP Erosion, includes a searchable database that includes compiled erosion data from the literature review and a plethora of erosion tests. It contains equations that may be used to estimate the erosion resistance of soil and determine whether erosion tests are needed.

The following appendices to NCHRP Report 915 were published online in a single Appendices Report:

Appendix 1 – Erosion Test Results Spreadsheets

Appendix 2 – Geotechnical Properties Spreadsheets

Appendix 3 – First and Second Order Statistical Analysis Results

Appendix 4 – Deterministic Frequentist Regression Analysis

Appendix 5 – Probabilistic Calibration Results

  1. ×

    Welcome to OpenBook!

    You're looking at OpenBook, NAP.edu's online reading room since 1999. Based on feedback from you, our users, we've made some improvements that make it easier than ever to read thousands of publications on our website.

    Do you want to take a quick tour of the OpenBook's features?

    No Thanks Take a Tour »
  2. ×

    Show this book's table of contents, where you can jump to any chapter by name.

    « Back Next »
  3. ×

    ...or use these buttons to go back to the previous chapter or skip to the next one.

    « Back Next »
  4. ×

    Jump up to the previous page or down to the next one. Also, you can type in a page number and press Enter to go directly to that page in the book.

    « Back Next »
  5. ×

    To search the entire text of this book, type in your search term here and press Enter.

    « Back Next »
  6. ×

    Share a link to this book page on your preferred social network or via email.

    « Back Next »
  7. ×

    View our suggested citation for this chapter.

    « Back Next »
  8. ×

    Ready to take your reading offline? Click here to buy this book in print or download it as a free PDF, if available.

    « Back Next »
Stay Connected!