INTRODUCTIONInterface 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 2C, 20C, and 40C, 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) ld

(kPa) ld/τpeak

δsec-peak

δsec-ld

G

(kPa)

50 (2C) 16.66 16.34 0.981 18.4 18.1 1494 50 (20C) 18.17 17.52 0.964 20.0 19.3 1677 50 (40C) 18.27 16.77 0.918 20.1 18.5 1709 100 (2C) 31.93 31.82 0.997 17.7 17.7 3009 100 (20C) 34.18 34.18 1.000 18.9 18.9 2978 100 (40C) 37.73 35.58 0.943 20.7 19.6 3752 150 (2C) 58.48 58.05 0.993 20.3 21.2 5106 150 (20C) 55.58 55.36 0.996 20.3 20.3 4913 150 (40C) 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