1. INTRODUCTION
Interface shear behavior is an integral part of design
of geotechnical structures including foundations and
earth retaining structures. Steel pile deep
foundations, steel sheetpiles for hydraulic control,
and steel strips used for reinforcing soil are three
common applications that incorporate soil/steel
interfaces. Temperature variability exists for many
geotechnical structure applications including
variations due to ground surface seasonal
temperature fluctuations, extreme climates,
industrial facilities that include significant heating or
cooling, and energy piles. Limited temperature-
dependent interface shear strength data has been
reported in the existing literature.
Changes in surface texture of steel due to abrasion
against soil can affect interface shear response. Pit
formation and uniform indentations on steel surfaces
by abrasive particle movement under a confined load
and shear force displacement were observed by
several studies. The study presented herein was
conducted to assess the shear response of sand-
steel interfaces with particular emphasis on
characterization of the surface texture properties of
the steel components.
EXPERIMENTAL TEST PROGRAM
Interface direct shear tests were conducted for sand-
steel interfaces at varying normal stress conditions
and at varying temperatures. Surface texture
characteristics were determined using an optical
interferometer.
•A medium well-graded sand was used for testing.
The sand was classified as SW (well graded sand)
according to USCS and tested in a dry condition.
Relative density was 75% for all tests.
•Rigid steel plates used as the interface surface was
A36 milled sheet steel (3.2mm thickness). The steel
plates were supported with rigid box beam spacers.
Specimens were tested in as-received conditions and
subsequent to constant designated temperatures
for a minimum of 24 hours before shearing.
This study was partly supported by the Global Waste
Research Institute. The optical interferometer was obtained
through NSF MRI Grant No. 1039995. Mr. Flores was
supported by NSF REU Site Grant No. 1263337.
RESULTS
Temperature Effects on Sand-Steel Interface Shear and Quantification of Post-
Shear Surface Texture Characteristics of Steel
CONCLUSIONS
ACKNOWLEDGEMENTS
Testing Apparatus
Direct Shear Device Sled Schematic Thermal-Insulated Enclosure
Each temperature sheared three samples at different confining stresses.
Andrew Flores, E.I.T., Derek Manheim, E.I.T., Jim Hanson, Ph.D., PE, and Nazli Yessiler, Ph.D.
Failure Envelopes for sand/steel interfaces
Results of Interface Shear Tests
3-D Representation of Virgin and Tested Steel
Surfaces Documenting Characteristic pitting (b)
and Longitudinal Grooving (c)
Areal Scale Fractal Analysis of Steel Specimens in
the Machine Direction as a Function of Confining
Stress (left) and Temperature (right)
Interferometer Images
Before shearing
After shearing
Test Materials
•Interface shear strength of dry sand with steel was not
highly sensitive to temperature. Resulting peak interface
friction angles were 20.1°, 19.9°, and 19.0° for tests
conducted at 2°C, 20°C, and 40°C, respectively.
•The shapes of the shear stress-strain curves generally
indicated slightly strain hardening behavior. tl-d/τpeak
ranged from 0.95 to 1.0.
•Ratios of interface friction angle to internal angle of
friction (d/f) were 0.45, 0.45, and 0.43 for peak conditions
and 0.49, 0.49, and 0.46 for large-displacement conditions
for 2°C, 20°C, and 40°C, respectively.
•Surface texture characteristics provided evidence of
both particle rolling (resulting in random pitting) and
sliding (resulting in uniform grooving)
•Overall, the response of interface shear and changes to
surface texture were determined to be a coupled
response to confining stress and temperature. A
threshold stress of 150 kPa was identified as a level
required to produce significant changes in surface
texture of smooth steel.
Test
τpeak
(kPa)
τld
(kPa)
τld/τpeak δsec-peak δsec-ld G
(kPa)
50 (2°C) 16.66 16.34 0.981 18.4 18.1 1494
50 (20°C) 18.17 17.52 0.964 20.0 19.3 1677
50 (40°C) 18.27 16.77 0.918 20.1 18.5 1709
100 (2°C) 31.93 31.82 0.997 17.7 17.7 3009
100 (20°C) 34.18 34.18 1.000 18.9 18.9 2978
100 (40°C) 37.73 35.58 0.943 20.7 19.6 3752
150 (2°C) 58.48 58.05 0.993 20.3 21.2 5106
150 (20°C) 55.58 55.36 0.996 20.3 20.3 4913
150 (40°C) 49.13 49.13 1.000 18.1 18.1 4762
Areal Scale Fractal Analysis of Steel Specimens In
the Cross-Machine Direction
Interface Shear and Interferometer Analysis