The expandable jacket consists of the rubber membrane surrounding the cylindrical specimen, circular segmental metal plates surrounding the rubber membrane, and elastomeric rubber bands or rings around the segmental plates to permit uniform radial expansion and maintain uniform diameter of the specimen during the test and thereby providing accurate values of deviator stress, volume change characteristics and shear strength of soil specimen. To determine the three-dimensional coefficient of consolidation and coefficient of consolidation in horizontal direction, the flexible ring consists of all above structural components of expandable jacket except that a filter fabric or paper is wrapped around the cylindrical specimen, and then rubber membrane is mounted surrounding the filter paper or paper. The calibration device for calibration of the expandable jacket and flexible ring shall provide the magnitude of correction to be made in deviator stress and lateral resistance provided by the rubber bands or rings during the test.

A large-scale direct shear apparatus for direct shear test of multi-size cylindrical undisturbed soil samples, comprising an external framework, a sample shear box, a horizontal loading device, a vertical loading device, and a control system. The sample shear box is disposed within the external framework and includes an upper shear box, a lower shear box, and a base. The horizontal loading device includes a horizontal drive motor equipped with a load sensor, a horizontal mechanical loading mechanism, and an upper shear box connection structure. The horizontal drive motor is installed on one inner side of the external framework and contacts the lower shear box via the horizontal mechanical loading mechanism. The upper shear box connection structure is fixed to the other inner side of the external framework and contacts the upper shear box. The vertical loading device includes a vertical drive motor and a vertical mechanical loading mechanism.

A large-scale direct shear apparatus for direct shear test of multi-size cylindrical undisturbed soil samples, comprising an external framework, a sample shear box, a horizontal loading device, a vertical loading device, and a control system. The sample shear box is disposed within the external framework and includes an upper shear box, a lower shear box, and a base. The horizontal loading device includes a horizontal drive motor equipped with a load sensor, a horizontal mechanical loading mechanism, and an upper shear box connection structure. The horizontal drive motor is installed on one inner side of the external framework and contacts the lower shear box via the horizontal mechanical loading mechanism. The upper shear box connection structure is fixed to the other inner side of the external framework and contacts the upper shear box. The vertical loading device includes a vertical drive motor and a vertical mechanical loading mechanism.

A device for measuring strain and volume of a soil sample including an enclosure adapted to receive a soil sample within another enclosure. A base adapted to hold the sample enclosure. The device also has a plurality of moveable arms located between the enclosures which may be a spaced distance apart and adapted to move around the sample. Cameras as included on the arms.

Methods and apparatus for evaluation of an earth formation including evaluating a core sample obtained from the formation. Methods include using a change in measurements of at least one stress parameter of the core sample, such as radial strain, axial stress, and acoustic emission counts, over time responsive to an applied stress to estimate imminent rock failure in the core sample. This may include estimating the imminent rock failure using differences between portions of a curve generated based on the measurements.

A device for a low stress triaxial test includes a test platform; a pressure chamber disposed on the test platform; a base disposed on the pressure chamber and fixed to the test platform; a support disposed on the test platform; a servo motor disposed on the support; a loading piston connected to the servo motor and penetrating into the pressure chamber; an axial force sensor disposed on the loading piston; a top cap detachably connected to the loading piston and covering the sample; a first pipeline connected to the base and passing through the test platform to connect with a measurement system; a second pipeline connected to the pressure chamber and passing through the test platform to connect with a confining pressure control system; and a third pipeline connected to the first pipeline and the top cap. The device can ensure the accuracy and authenticity of test results.

The present disclosure discloses a test method for reducing test error in shear strength of a root-soil composite, belonging to the field of agricultural engineering testing methods. The method includes: sampling with a ring knife perpendicular to an actual shear surface to ensure consistency between a direction of the actual shear surface of the root-soil composite and a shear surface direction in a direct shear test; determining a shear strength of soil in each layer within an actual shear depth range by stratifying with a minimum thickness of the ring knife; and planning an annular sampling area and performing sampling in various directions along the annular area, thereby reducing test error in determining shear characteristics of the root-soil composite from three aspects.