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Title: Compressional and Shear Wave Velocities for Artificial Granular Media Under Simulated Near Surface Conditions

Compressional and Shear Wave Velocities for Artificial Granular Media Under Simulated Near Surface Conditions Laboratory ultrasonic experiments were made on artificial soil samples in order to observe the effects of slight overburden, sand/clay ratio and pore fluid saturation on compressional and shear wave velocities. Up to several meters of overburden were simulated by applying low uniaxial stress of about 0.1 MPa to a restrained sample. Samples were fabricated from Ottawa sand mixed with a swelling clay (Wyoming bentonite). The amount of clay added was 1 to 40 percent by mass. Most measurements were made under room-dry conditions, but some measurements were made for fully-saturated sand-clay mixtures and for partially-saturated sand samples. For the dry sand-clay samples, compressional (P) velocities were low, ranging from about 200 to 500 m/s for the mixtures at low stress. Shear (S) velocities were about half of the compressional velocity, about 70 to 250 m/s. Dramatic increases in all velocities occurred with small uniaxial loads, indicating strong nonlinearity. Composition and grain packing control the mechanical response at grain contacts and the resulting nonlinear response at low stresses. P and S velocities are sensitive to the amount of clay added, even at low concentrations. At these low equivalent overburden conditions, adhesion and capillarity at grain contacts affect wave amplitudes, velocities, and more » frequency content in the partial saturation case. « less
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Publication Date:
OSTI Identifier:OSTI ID: 827625
Report Number(s):UCRL-JC-142935
R&D Project: EMSP 70108; TRN: US200426%%166
Resource Type:Conference
Resource Relation:Conference: The Society of Exploration Geophysicists International Exposition and 71st Annual Meeting, San Antonio, TX (US), 09/09/2001--09/14/2001; Other Information: PBD: 9 Sep 2001
Research Org:Lawrence Livermore National Lab., CA (US)
Sponsoring Org:USDOE Office of Environmental Management (EM) (US)
Country of Publication:United States
Language:English
Subject: 54 ENVIRONMENTAL SCIENCES; 58 GEOSCIENCES; ADHESION; AMPLITUDES; BENTONITE; CLAYS; EXPLORATION; METERS; MIXTURES; OVERBURDEN; SAND; SATURATION; SHEAR; SOILS; STRESSES; SWELLING; ULTRASONIC WAVES; VELOCITY