Means for determining the shear strength of earth in situ

Claim 1

Apparatus for in situ measurement of the torsional shear strength of earth located in advance of the remote end of a bore hole comprising: a torsion shaft having a vaned end axially insertable into earth in advance of the remote end of a bore hole, said shaft terminating a nominal distance outward from the end of the bore hole; torque-generating means associated with said shaft to urge rotation thereof; anchor means including radial vanes engageable with the earth at the remote end of said bore hole, said anchor means surrounding said shaft between its vaned end and said torque-generating means; rigid structure fixedly coupling said anchor means and said torque-generating means; means located between said torsion shaft vaned end and said torque-generating means for sensing resistance to rotation of said shaft to torque applied thereto by said torque-generating means, said means for sensing resistance being operative to produce an electrical signal proportionate to the degree of resistive forced sensed; means for transmitting said signal to external of the bore hole; means for measuring the strength of such signal; gravity actuated means operable to insert said vaned shaft and said anchor means into and to engage earth at the remote end of a bore hole; and said gravity-actuated means comprising expandible-retractible members associated with said rigid structure, and said bore is provided with a liner to engage said members when extended to apply the weight thereof to said rigid structure.