MEASUREMENT OF BASE AND SUBGRADE LAYER STIFFNESS USING BENDER ELEMENT TECHNIQUE

Abstract eng:
Base and subgrade soil stiffnesses are important parameters for material characterization in highway construction. During and after pavement construction, it is very important and cost-effective to have a reliable technique that can measure the stiffness of in-situ base and subgrade layers accurately and quickly. The new highway design guide proposed by AASHTO requires such measurement be conducted. A new field-testing technique has been developed to measure small-strain shear modulus of soils (which can be converted into elastic modulus) using the bender element technique. The device used in this method includes a pair of cone penetrometers, each fitted with two bender elements, which can be pushed into the base, subbase and subgrade layers. A pulse generated by a function generator is used to activate the transmitters. Vibration of the transmitters produces shear waves that propagate through the soil in the horizontal and inclined directions and are captured by the receivers. Then from the measured shear wave velocities, soil stiffness can be determined. The technique is compared with current practice of soil stiffness determination based on the CBR test.

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