IIT Gandhinagar  ajanta@iitgn.ac.in  ap@iitgn.ac.in
Soil Testing Lab
 
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Introduction Experimental Setup Data Analysis Results Theory

Bender Element Test

Need and Scope:

Determination of small strain shear modulus of soils in the laboratory by propagating a shear wave through the specimen, measure its velocity, and calculate the small strain shear modulus using density & shear wave velocity of the material. Shear waves can be generated and measured by small pieces of piezoceramic called bender elements, which can be installed at the end caps of specimens in commonly used triaxial setup. The piezoceramic bender element is an electro-mechanical transducer, which is capable of converting mechanical energy either to or from electrical energy.

Concept:

Shear wave velocity determination in sands is important for analyzing and predicting safety of various structures located on it. The initial tangent shear modulus (Gmax) of soil, also termed as small strain shear modulus of soil, is a fundamental parameter used in various kinds of geotechnical analysis especially in earthquake geotechnical engineering and soil dynamics. There is an increasing interest in using small strain shear modulus to define the state of sand so as to use non-destructive techniques for site characterization. The value of shear modulus depends on a number of parameters, including void ratio, confining stress, soil structure, degree of saturation, temperature, stress history, and time.

At strains within the elastic range, typically 10-4% or less, the stiffness is represented by shear wave velocity, and in turn small strain shear modulus. This parameter is useful for the design and analysis of earthquake resistant foundations, vibrating machine foundations, vibration isolation measures, analysis of soil-structure interaction problems and design of shallow and deep foundations. Some of the real life situations, where these studies are of great importance are: impact of an earthquake on structures such as buildings, roads, embankments, railway track formations, monitoring soil stabilization,

The strain level in engineering structures lies in the small strain range, and thus the small-strain modulus (Gmax) of geotechnical fill materials is a key parameter in defining the material response to static loading. It is now treated as a fundamental property of soil. Gmax is also important in small-strain dynamic analyses such as those used to predict soil behaviour during earthquakes, explosions, or machine and traffic vibrations.


 
 
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