Soil and rock shear tester

A device for determining the shear strength of rock and soil, comprising:

• anchoring means for supporting said device within a bore drilled in the material being tested, said borehole having a longitudinal axis;
• a shaft slidably mounted on said anchoring means and having a longitudinal axis coextensive with said longitudinal axis of said borehole;
• a plurality of cylinder blocks slidably mounted on said shaft;
• a pair of shear heads mounted opposite one another on each of said cylinder blocks so as to define an expansion compartment within said cylinder block, each of said shear heads having a plurality of teeth for engagement with the material to be tested;
• a fluid supply means for providing compressed fluid to said expansion compartments whereby each of said pairs of shear heads is expanded simultaneously from a first retracted position to a second expanded positon;
• said shear heads of each successive shearing unit applying progressively greater normal force on said material being tested while in said expanded position;
• means for applying an axial force along said shaft to each of said shearing units;
• a shear head retracting means for retracting said shear heads from said expanded position to said retracting position after the material engaged by said teeth of said shear head shears;
• and
• means for sequentially transferring said axial force from one pair of shear heads to the next succeeding pair of shear heads after the material engaged by the preceeding pair of shear heads shears.

A method of in situ determination of soil and rock properties by drilling a borehole in the material to be tested, comprising:

• introducing into said borehole a device for determining the shear strength of the material to be tested, said device including an anchoring means for supporting said device within said borehole, a shaft slidably attached to said anchoring means having a longitudinal axis coextensive with that of said borehole, a plurality of shearing units slidably attached to said shaft, and means for sequentially applying an axial force along said shaft to each of said shearing units, each of said shearing units having a cylinder block slidably mounted on said shaft and a pair of shear heads slidably mounted opposite one another on said cylinder block so as to define an expansion compartment within said cylinder block, said shear heads being movable between a first retracted position and a second material-engaging expanded position;
• anchoring said device with respect to said borehole;
• moving said shearing heads of all of said shearing units from said retracted position to said expanded position simultaneously;
• applying normal forces on the material to be tested, said normal force being progressively greater at each succeeding shearing unit;
• sequentially applying an axial force along said shaft to each of said shearing units until the material engaged by said pair of shear heads of each unit is successively sheared;
• moving each pair of shear heads from said expanded position to said retracted position after the material engaged by said pair of shear heads has sheared;
• and
• determining the shearing strength of the material to be tested from the known applied normal and shear forces.