Soil compaction measurement

Man portable apparatus for the in-situ measurement of the shear modulus of a compacted layer of soil, said apparatus comprising:

• a contact foot for engaging a region of soil corresponding to said compacted layer;
• means for applying a downwardly biasing force to said foot;
• a calibrated spring one end of which is connected to said contact foot;
• means for generating an a.c. drive signal;
• a drive transducer responsive to said drive signal for vibrating another end of said spring thereby to apply a vibratory vertical force to said contact foot;
• a first sensing transducer for sensing motion of said foot and generating a corresponding first output signal;
• means including a second sensing transducer for sensing motion of said other end of said spring and generating a corresponding second output signal;
• circuit means for measuring a component of said first output signal which is in phase with said second output signal thereby to obtain a value for a single parameter which is representative of the shear modulus.

Man portable apparatus for the in-situ measurement of the shear modulus of a compacted layer of soil, said apparatus comprising:

• a contact foot for engaging a region of soil in the order of 4½ inches in nominal diameter;
• means for applying a downwardly biasing force to said foot, said force being in the order of 35 pounds;
• a calibrated spring one end of which is connected to said contact foot;
• means for generating an a.c. drive signal;
• a drive transducer responsive to said drive signal for vibrating another end of said spring thereby to apply a vibratory vertical force to said contact foot;
• a first sensing transducer for sensing motion of said foot and generating a corresponding first output signal;
• means including a second sensing transducer for sensing motion of said other end of said spring and generating a corresponding second output signal;
• circuit means for measuring the component of said first output signal which is in phase with said second output signal thereby to obtain a value for a single parameter which is representative of the shear modulus.

Apparatus for the in-situ measurement of the shear modulus of soil, said apparatus comprising:

• a contact foot for engaging a defined surface area of a region of soil to be measured;
• a drive transducer for shaking said contact foot vertically in response to drive signals applied to the transducer;
• a first sensing transducer for sensing the motion acceleration of said foot and generating a corresponding first output signal;
• means including a second sensing transducer for determining the force applied to said foot and generating a corresponding second output signal;
• means for applying to said drive transducer an a.c. drive signal which progressively varies in frequency over a preselected band at a rate of change of frequency, which also varies with frequency so that, for constant amplitude, energy content varies with frequency;
• circuit means for analyzing said first output signal in relation to said second output signal to obtain a measurement of an in-phase component of said first output signal which then is representative of the shear modulus.

Apparatus for the in-situ measurement of the shear modulus of soil, said apparatus comprising:

• a contact foot for engaging a defined surface area of a region of soil to be measured, said foot including a rigid top portion and a lower, flexible membrane portion, the space between said membrane portion and said top portion being filled with an essentially incompressible liquid for coupling force to said region of soil;
• a drive transducer for shaking said contact foot in response to drive signals applied to the transducer;
• a first sensing transducer for sensing the force applied to said foot and generating a corresponding first output signal;
• a second sensing transducer for sensing the acceleration of soil under said lower membrane portion and for generating a corresponding second output signal;
• means for applying to said drive transducer an a.c. drive signal which progressively varies in frequency over a preselected band;
• circuit means for analyzing said second output signal in relation to said first output signal to obtain a measurement which represents the desired shear modulus.