Apparatus and test method for determining flow or no flow conditions of bulk solids

Claim 1

A method of bench scale testing to determine the load at which unsupported consolidated particulate material arched over an outlet of diameter B in the bottom of a full-size container will fail by collapsing and flowing through the outlet, said method comprising the steps of: (a) providing a test cell that is hollow and that includes a sleeve-like portion having an inside surface conforming to a frustrated conical section of height C, having a smaller-diameter end and a larger-diameter end, the test cell further including a plug spanning the larger-diameter end of the frustrated conical section and sized to fit loosely therein so as to be freely movable a limited distance into the space within the conical section and having a concave conical inwardly-facing surface; (b) placing the test cell on a supporting surface with the plug resting on the supporting surface so that the larger-diameter end of the conical section is below its smaller-diameter end; (c) filling the test cell completely full with the particulate material; (d) consolidating the particulate material within the test cell by applying a downward pressure at the smaller-diameter end of the conical section, so that the direction of motion of the particulate material during consolidation is toward the plug; (e) inverting the test cell with the plug and the consolidated particulate material still in it, so that after the inversion the larger-diameter end of the conical section is above its smaller-diameter end; (f) applying a gradually-increasing downward load to the plug to produce failure motion of the particulate material toward the smaller-diameter end of the conical section; and (g) noting the downward load at which failure occurs.

Claim 2

A method of bench scale testing to determine the load at which unsupported consolidated particulate material arched over an outlet of diameter B in the bottom of a full-size container will fail by collapsing and flowing through the outlet, said method comprising the steps of: (a) providing a test cell that is hollow and that includes a sleeve-like portion having an inside surface conforming to a frustrated conical section of height C, having a smaller-diameter end and a larger-diameter end, the test cell further including a plug spanning the larger-diameter end of the frustrated conical section and sized to fit loosely therein so as to be freely movable a limited distance into the space within the conical section and having a concave conical inwardly-facing surface; (b) placing the test cell on a supporting surface with the plug resting on the supporting surface so that the larger-diameter end of the conical section is below its smaller-diameter end; (c) filling the test cell completely full with the particulate material; (d) consolidating the particulate material within the test cell by applying a downward pressure at the smaller-diameter end of the conical section, so that the direction of motion of the particulate material during consolidation is toward the plug; (e) inverting the test cell with the plug and the consolidated particulate material still in it, so that after the inversion the larger-diameter end of the conical section is above its smaller-diameter end; (f) applying a gradually-increasing downward load to the plug to produce failure motion of the particulate material toward the smaller-diameter end of the conical section; and (g) noting the downward load at which failure occurs.

Claim 5

A method of bench scale testing to determine whether or not particulate material will flow, after having been at rest for some time, from a full-size container that requires gravity flow for discharge and that has an outlet of diameter B in its bottom, said method comprising the steps of: (a) providing a test cell that is hollow and that includes a sleeve-like portion having an inside surface conforming to a frustrated conical section of height C, having a smaller-diameter end and a larger-diameter end, the test cell further including a plug spanning the larger-diameter end of the frustrated conical section and sized to fit loosely therein so as to be freely movable a limited distance into the space within the conical section and having a concave conical inwardly-facing surface; (b) placing the test cell on a supporting surface with the plug resting on the supporting surface so that the larger-diameter end of the conical section is below its smaller-diameter end; (c) filling the test cell completely full with the particulate material; (d) consolidating the particulate material within the test cell by applying a consolidation load L c uniformly distributed over the particulate material at the smaller-diameter end of the conical section, so that the direction of motion of the particulate material during consolidation is toward the plug, where L.sub.c =1/2Fγ.sub.1 A, B where F=overpressure factor, γ.sub. = bulk density of the particulate material being tested, A 1 =average cross sectional area of the test cell; and, (e) inverting the test cell with the plug and the consolidated particulate material still in it, so that after the inversion the larger-diameter end of the conical section is above its smaller-diameter end; (f) applying a gradually-increasing downward load to the plug to produce failure motion of the particulate material toward the smaller-diameter end of the conical section; (g) noting the downward load L F at which failure occurs; and, (h) determining whether the noted load L F at which failure occurred is such that ##EQU13## where D is the diameter of the larger-diameter end of the conical section, whereby, if it is, then flow from the full-size container will occur by gravity, but if it is not, then flow from the full size container will not occur by gravity.

Claim 6

A method of bench scale testing to determine whether or not particulate material will flow, after having been at rest for some time, from a full-size container that requires gravity flow for discharge and that has an outlet of diameter B in its bottom, said method comprising the steps of: (a) providing a test cell that is hollow and that includes a sleeve-like portion having an inside surface conforming to a frustrated conical section of height C, having a smaller-diameter end and a larger-diameter end, the test cell further including a plug spanning the larger-diameter end of the frustrated conical section and sized to fit loosely therein so as to be freely movable a limited distance into the space within the conical section and having a concave conical inwardly-facing surface; (b) placing the test cell on a supporting surface with the plug resting on the supporting surface so that the larger-diameter end of the conical section is below its smaller-diameter end; (c) filling the test cell completely full with the particulate material; (d) consolidating the particulate material within the test cell by applying a consolidation load L c uniformly distributed over the particulate material at the smaller-diameter end of the conical section, so that the direction of motion of the particulate material during consolidation is toward the plug, where L.sub.c =1/2Fγ.sub.1 A, B where F=overpressure factor, γ.sub. = bulk density of the particulate material being tested, A 1 =average cross sectional area of the test cell; and, (e) inverting the test cell with the plug and the consolidated particulate material still in it, so that after the inversion the larger-diameter end of the conical section is above its smaller-diameter end; (f) applying a gradually-increasing downward load to the plug to produce failure motion of the particulate material toward the smaller-diameter end of the conical section; (g) noting the downward load L F at which failure occurs; and, (h) determining whether the noted load L F at which failure occurred is such that ##EQU13## where D is the diameter of the larger-diameter end of the conical section, whereby, if it is, then flow from the full-size container will occur by gravity, but if it is not, then flow from the full size container will not occur by gravity.

Claim 8

A method of bench scale testing to determine whether or not particulate material will flow, after having been at rest for some time, from a full-size container that requires gravity flow for discharge and that has an outlet of diameter B in its bottom, said method comprising the steps of: (a) providing a test cell that is hollow and that includes a sleeve-like portion having an inside surface conforming to a frustrated conical section of height C, having a smaller-diameter end and a larger-diameter end, the test cell further including a plug spanning the larger-diameter end of the frustrated conical section and sized to fit loosely therein so as to be freely movable a limited distance into the space within the conical section and having a concave conical inwardly-facing surface; (b) placing the test cell on a supporting surface with the plug resting on the supporting surface so that the larger-diameter end of the conical section is below its smaller-diameter end; (c) resting a mold ring that is hollow and that has a cylindrical inside surface of diameter equal to the diameter of the smaller-diameter end of the conical section on top of and coaxial with the test cell to form an upward extension of it; (d) filling the test cell and the mold ring completely full with the particulate material; (e) placing a consolidation load container having an outside diameter slightly less than the inside diameter of the mold ring on top of the particulate material in the mold ring; (f) consolidating the particulate material within the test cell and mold ring by applying a consolidation load L c uniformly distributed over the top of the particulate material in the mold ring by the consolidation load container, so that the direction of motion of the particulate material during consolidation is toward the plug, where ##EQU14## and F=overpressure factor, γ.sub. = bulk density of the particulate material being tested, A 1 =average cross sectional area of the test cell; (g) continuing to apply the consolidation load for an interval of time equal to how long the particulate material in the full-size container has been at rest; (h) removing the mold ring and the particulate material contained in it from the test cell; (i) inverting the test cell with the plug and the consolidated particulate material still in it, so that after inversion the larger-diameter end of the conical section is above its smaller-diameter end; (j) applying a gradually-increasing downward load to the plug to produce failure motion of the particulate material toward the smaller-diameter end of the conical section; (k) noting the downward load L F at which failure occurs; and, (l) determining whether the noted load L F at which failure occurred is such that ##EQU15## whereby, if it is, then flow from the full-size container will occur by gravity, but if it is not, then flow from the full size container will not occur by gravity, where D is the diameter of the larger-diameter end of the conical section.

Claim 9

A method of bench scale testing to determine whether or not particulate material will flow, after having been at rest for some time, from a full-size container that requires gravity flow for discharge and that has an outlet of diameter B in its bottom, said method comprising the steps of: (a) providing a test cell that is hollow and that includes a sleeve-like portion having an inside surface conforming to a frustrated conical section of height C, having a smaller-diameter end and a larger-diameter end, the test cell further including a plug spanning the larger-diameter end of the frustrated conical section and sized to fit loosely therein so as to be freely movable a limited distance into the space within the conical section and having a concave conical inwardly-facing surface; (b) placing the test cell on a supporting surface with the plug resting on the supporting surface so that the larger-diameter end of the conical section is below its smaller-diameter end; (c) resting a mold ring that is hollow and that has a cylindrical inside surface of diameter equal to the diameter of the smaller-diameter end of the conical section on top of and coaxial with the test cell to form an upward extension of it; (d) filling the test cell and the mold ring completely full with the particulate material; (e) placing a consolidation load container having an outside diameter slightly less than the inside diameter of the mold ring on top of the particulate material in the mold ring; (f) consolidating the particulate material within the test cell and mold ring by applying a consolidation load L c uniformly distributed over the top of the particulate material in the mold ring by the consolidation load container, so that the direction of motion of the particulate material during consolidation is toward the plug, where ##EQU14## and F=overpressure factor, γ.sub. = bulk density of the particulate material being tested, A 1 =average cross sectional area of the test cell; (g) continuing to apply the consolidation load for an interval of time equal to how long the particulate material in the full-size container has been at rest; (h) removing the mold ring and the particulate material contained in it from the test cell; (i) inverting the test cell with the plug and the consolidated particulate material still in it, so that after inversion the larger-diameter end of the conical section is above its smaller-diameter end; (j) applying a gradually-increasing downward load to the plug to produce failure motion of the particulate material toward the smaller-diameter end of the conical section; (k) noting the downward load L F at which failure occurs; and, (l) determining whether the noted load L F at which failure occurred is such that ##EQU15## whereby, if it is, then flow from the full-size container will occur by gravity, but if it is not, then flow from the full size container will not occur by gravity, where D is the diameter of the larger-diameter end of the conical section.

Claim 10

A method of testing to determine the unconfined yield strength of a particulate material comprising the steps of: (a) providing a test cell that is hollow and that includes a sleeve-like portion having an inside surface conforming to a frustrated conical section of height C, having a smaller-diameter end and a larger-diameter end, the test cell further including a plug spanning the larger-diameter end of the frustrated conical section and sized to fit loosely therein so as to be freely movable a limited distance into the spaced within the conical section and having a concave conical inwardly-facing surface; (b) placing the test cell on a supporting surface with the plug resting on the supporting surface so that the larger-diameter end of the conical section is below its smaller-diameter end; (c) filling the test cell completely full with the particulate material; (d) consolidating the particulate material within the test cell by applying a downward pressure σ c at the smaller-diameter end of the conical section, so that the direction of motion of the particulate material during consolidation is toward the plug, where σ.sub.c =(L.sub.c /A.sub.1)+1/2γ.sub.1 C and L c =consolidation load A 1 =average cross sectional area of the test cell γ 1 =bulk density of the particulate material; (e) inverting the test cell with the plug and the consolidated particulate material still in it, so that after the inversion the larger-diameter end of the conical section is above its smaller-diameter end; (f) applying a gradually-increasing downward load to the plug to produce failure motion of the particulate material toward the smaller-diameter end of the conical section; (g) noting the load L F at which failure occurs; and, (h) calculating the unconfined yield strength by the equation ##EQU16## where h=2.1 for a conical test cell, and where D is the diameter of the larger-diameter end of the conical section.

Claim 11

A method of testing to determine the unconfined yield strength of a particulate material comprising the steps of: (a) providing a test cell that is hollow and that includes a sleeve-like portion having an inside surface conforming to a frustrated conical section of height C, having a smaller-diameter end and a larger-diameter end, the test cell further including a plug spanning the larger-diameter end of the frustrated conical section and sized to fit loosely therein so as to be freely movable a limited distance into the spaced within the conical section and having a concave conical inwardly-facing surface; (b) placing the test cell on a supporting surface with the plug resting on the supporting surface so that the larger-diameter end of the conical section is below its smaller-diameter end; (c) filling the test cell completely full with the particulate material; (d) consolidating the particulate material within the test cell by applying a downward pressure σ c at the smaller-diameter end of the conical section, so that the direction of motion of the particulate material during consolidation is toward the plug, where σ.sub.c =(L.sub.c /A.sub.1)+1/2γ.sub.1 C and L c =consolidation load A 1 =average cross sectional area of the test cell γ 1 =bulk density of the particulate material; (e) inverting the test cell with the plug and the consolidated particulate material still in it, so that after the inversion the larger-diameter end of the conical section is above its smaller-diameter end; (f) applying a gradually-increasing downward load to the plug to produce failure motion of the particulate material toward the smaller-diameter end of the conical section; (g) noting the load L F at which failure occurs; and, (h) calculating the unconfined yield strength by the equation ##EQU16## where h=2.1 for a conical test cell, and where D is the diameter of the larger-diameter end of the conical section.

Claim 15

A method of bench scale testing to determine the load at which unsupported consolidated particulate material arched over an outlet of width B in the bottom of a full-size container will fail by collapsing and flowing through the outlet, said method comprising the steps of: (a) providing a test cell that is hollow and that includes a sleeve-like portion of rectangular cross section having an inside surface conforming to a frustrated wedge of height C, having a smaller end and a larger end, the test cell further including a plug spanning the larger end of the frustrated wedge and sized to fit loosely therein so as to be freely movable a limited distance into the space within the frustrated wedge and having a concave trough-like inwardly-facing surface; (b) placing the test cell on a supporting surface with the plug resting on the supporting surface so that the larger end of the frustrated wedge is below its smaller end; (c) filling the test cell completely full with particulate material; (d) consolidating the particulate material within the test cell by applying a downward pressure at the smaller end of the frustrated wedge, so that the direction of motion on the particulate material during consolidation is toward the plug; (e) inverting the test cell with the plug and the consolidated particulate material still in it, so that after the inversion the larger end of the frustrated wedge is above its smaller end; (f) applying a gradually-increasing downward load to the plug to produce failure motion of the particulate material toward the smaller end of the frustrated wedge; and, (g) noting the downward load at which failure occurs.

Claim 16

A method of bench scale testing to determine the load at which unsupported consolidated particulate material arched over an outlet of width B in the bottom of a full-size container will fail by collapsing and flowing through the outlet, said method comprising the steps of: (a) providing a test cell that is hollow and that includes a sleeve-like portion of rectangular cross section having an inside surface conforming to a frustrated wedge of height C, having a smaller end and a larger end, the test cell further including a plug spanning the larger end of the frustrated wedge and sized to fit loosely therein so as to be freely movable a limited distance into the space within the frustrated wedge and having a concave trough-like inwardly-facing surface; (b) placing the test cell on a supporting surface with the plug resting on the supporting surface so that the larger end of the frustrated wedge is below its smaller end; (c) filling the test cell completely full with particulate material; (d) consolidating the particulate material within the test cell by applying a downward pressure at the smaller end of the frustrated wedge, so that the direction of motion on the particulate material during consolidation is toward the plug; (e) inverting the test cell with the plug and the consolidated particulate material still in it, so that after the inversion the larger end of the frustrated wedge is above its smaller end; (f) applying a gradually-increasing downward load to the plug to produce failure motion of the particulate material toward the smaller end of the frustrated wedge; and, (g) noting the downward load at which failure occurs.

Claim 19

A method of bench scale testing to determine whether or not particulate material will flow, after having been at rest for some time, from a full-size container that requires gravity flow for discharge and that has an outlet of width B in its bottom, said method comprising the steps of: (a) providing a test cell that is hollow and that includes a sleeve-like portion of rectangular cross section having an inside surface conforming to a frustrated wedge of height C, having a smaller end and a larger end, the test cell further including a plug spanning the larger end of the frustrated wedge and sized to fit loosely therein so as to be freely movable a limited distance into the space within the frustrated wedge and having a concave trough-like inwardly-facing surface; (b) placing the test cell on a supporting surface with the plug resting on the supporting surface so that the larger end of the frustrated wedge is below its smaller end; (c) filling the test cell completely full with particulate material; (d) consolidating the particulate material within the test cell by applying a consolidation load L c uniformly distributed over the particulate material at the smaller end of the frustrated wedge, so that the direction of motion of the particulate material during consolidation is toward the plug, where L.sub.c =Fγ.sub.1 A.sub.1 B where F=overpressure factor, γ.sub. = bulk density of the particulate material being tested, A 1 =average cross sectional area of the test cell; (e) inverting the test cell with the plug and the consolidated particulate material still in it, so that after the inversion the larger end of the frustrated wedge is above its smaller end; (f) applying a gradually-increasing downward load to the plug to produce failure motion of the particulate material toward the smaller end of the frustrated wedge; (g) noting the downward load L F at which failure occurs; and, (h) determining whether the noted load L F at which failure occurred is such that ##EQU17## whereby, if it is, then flow from the full-size container will occur by gravity, but if it is not, then flow from the full-size container will not occur by gravity, where D is the width of the larger end of the test cell.

Claim 20

A method of bench scale testing to determine whether or not particulate material will flow, after having been at rest for some time, from a full-size container that requires gravity flow for discharge and that has an outlet of width B in its bottom, said method comprising the steps of: (a) providing a test cell that is hollow and that includes a sleeve-like portion of rectangular cross section having an inside surface conforming to a frustrated wedge of height C, having a smaller end and a larger end, the test cell further including a plug spanning the larger end of the frustrated wedge and sized to fit loosely therein so as to be freely movable a limited distance into the space within the frustrated wedge and having a concave trough-like inwardly-facing surface; (b) placing the test cell on a supporting surface with the plug resting on the supporting surface so that the larger end of the frustrated wedge is below its smaller end; (c) filling the test cell completely full with particulate material; (d) consolidating the particulate material within the test cell by applying a consolidation load L c uniformly distributed over the particulate material at the smaller end of the frustrated wedge, so that the direction of motion of the particulate material during consolidation is toward the plug, where L.sub.c =Fγ.sub.1 A.sub.1 B where F=overpressure factor, γ.sub. = bulk density of the particulate material being tested, A 1 =average cross sectional area of the test cell; (e) inverting the test cell with the plug and the consolidated particulate material still in it, so that after the inversion the larger end of the frustrated wedge is above its smaller end; (f) applying a gradually-increasing downward load to the plug to produce failure motion of the particulate material toward the smaller end of the frustrated wedge; (g) noting the downward load L F at which failure occurs; and, (h) determining whether the noted load L F at which failure occurred is such that ##EQU17## whereby, if it is, then flow from the full-size container will occur by gravity, but if it is not, then flow from the full-size container will not occur by gravity, where D is the width of the larger end of the test cell.

Claim 22

A method of bench scale testing to determine whether or not particulate material will flow, after having been at rest for some time, from a full-size container that requires gravity flow for discharge and that has an outlet of width B in its bottom, said method comprising the steps of: (a) providing a test cell that is hollow and that includes a sleeve-like portion of rectangular cross section having an inside surface conforming to a frustrated wedge of height C, having a smaller end and a larger end, the test cell further including a plug spanning the larger end of the frustrated wedge and sized to fit loosely therein so as to be freely movable a limited distance into the space within the frustrated wedge and having a concave trough-like inwardly-facing surface; (b) placing the test cell on a supporting surface with the plug resting on the supporting surface so that the larger end of the frustrated wedge is below its smaller end; (c) resting a mold frame that is hollow and that has a rectangular inside surface of dimensions equal to those of the smaller end of the frustrated wedge on top of and registered with the test cell of form an upward extension of it; (d) filling the test cell and the mold frame completely full with the particulate material; (e) placing a consolidation load container having outside dimensions slightly less than the inside dimensions of the mold frame on top of the particulate material in the mold frame; (f) consolidating the particulate material within the test cell and mold frame by applying a consolidation load L c uniformly distributed over the top of the particulate material in the mold frame by the consolidation load container, so that the direction of motion of the particulate material during consolidation is toward the plug, where L.sub.c =Fγ.sub.1 A.sub.1 B and F=overpressure factor, γ.sub. = bulk density of the particulate material being tested, and A 1 =average cross sectional area of the test cell; (g) continuing to apply the consolidation load for an interval of time equal to how long the particulate material in the full-size container has been at rest; (h) removing the mold frame and the particulate material contained in it from the test cell; (i) inverting the test cell with the plug and the consolidated particulate material still in it, so that after inversion the larger end of the frustrated wedge is above its smaller end; (j) applying a gradually-increasing downward load to the plug to produce failure motion of the particulate material toward the smaller end of the frustrated wedge; (k) noting the downward load L F at which failure occurs; and, (l) determining whether the noted load L F at which failure occurred is such that ##EQU18## whereby, if it is, then flow from the full-size container will occur by gravity, but if it is not, then flow from the full-size container will not occur by gravity, where D is the width of the larger end of the test cell.

Claim 23

A method of bench scale testing to determine whether or not particulate material will flow, after having been at rest for some time, from a full-size container that requires gravity flow for discharge and that has an outlet of width B in its bottom, said method comprising the steps of: (a) providing a test cell that is hollow and that includes a sleeve-like portion of rectangular cross section having an inside surface conforming to a frustrated wedge of height C, having a smaller end and a larger end, the test cell further including a plug spanning the larger end of the frustrated wedge and sized to fit loosely therein so as to be freely movable a limited distance into the space within the frustrated wedge and having a concave trough-like inwardly-facing surface; (b) placing the test cell on a supporting surface with the plug resting on the supporting surface so that the larger end of the frustrated wedge is below its smaller end; (c) resting a mold frame that is hollow and that has a rectangular inside surface of dimensions equal to those of the smaller end of the frustrated wedge on top of and registered with the test cell of form an upward extension of it; (d) filling the test cell and the mold frame completely full with the particulate material; (e) placing a consolidation load container having outside dimensions slightly less than the inside dimensions of the mold frame on top of the particulate material in the mold frame; (f) consolidating the particulate material within the test cell and mold frame by applying a consolidation load L c uniformly distributed over the top of the particulate material in the mold frame by the consolidation load container, so that the direction of motion of the particulate material during consolidation is toward the plug, where L.sub.c =Fγ.sub.1 A.sub.1 B and F=overpressure factor, γ.sub. = bulk density of the particulate material being tested, and A 1 =average cross sectional area of the test cell; (g) continuing to apply the consolidation load for an interval of time equal to how long the particulate material in the full-size container has been at rest; (h) removing the mold frame and the particulate material contained in it from the test cell; (i) inverting the test cell with the plug and the consolidated particulate material still in it, so that after inversion the larger end of the frustrated wedge is above its smaller end; (j) applying a gradually-increasing downward load to the plug to produce failure motion of the particulate material toward the smaller end of the frustrated wedge; (k) noting the downward load L F at which failure occurs; and, (l) determining whether the noted load L F at which failure occurred is such that ##EQU18## whereby, if it is, then flow from the full-size container will occur by gravity, but if it is not, then flow from the full-size container will not occur by gravity, where D is the width of the larger end of the test cell.

Claim 24

A method of testing to determine the unconfined yield strength of a particulate material comprising the steps of: (a) providing a test cell that is hollow and that includes a sleeve-like portion of rectangular cross section having an inside surface conforming to a frustrated wedge of height C, having a smaller end and a larger end, the test cell further including a plug spanning the larger end of the frustrated wedge and sized to fit loosely therein so as to be freely movable a limited distance into the space within the frustrated wedge and having a concave trough-like inwardly-facing surface; (b) placing the test cell on a supporting surface with the plug resting on the supporting surface so that the larger end of the frustrated wedge is below its smaller end; (c) filling the test cell completely full with particulate material; (d) consolidating the particulate material within the test cell by applying a downward pressure θ c at the smaller end of the frustrated wedge, so that the direction of motion of the particulate material during consolidation is toward the plug, where σ.sub.c =L.sub.C /A.sub.1 +γ.sub.1 C and L c =consolidation load A 1 =average cross sectional area of the test cell and γ 1 =bulk density of the particulate material; (e) inverting the test cell with the plug and the consolidated particulate material still in it, so that after the inversion the larger end of the frustrated wedge is above its smaller end; (f) applying a gradually-increasing downward load to the plug to produce failure motion of the particulate material toward the smaller end of the frustrated wedge; (g) noting the load L F at which failure occurs; and, (h) calculating the unconfined yield strength by the equation ##EQU19## where h=1.1 for a rectangular test cell, and where D is the width of the larger end of the test cell.

Claim 25

A method of testing to determine the unconfined yield strength of a particulate material comprising the steps of: (a) providing a test cell that is hollow and that includes a sleeve-like portion of rectangular cross section having an inside surface conforming to a frustrated wedge of height C, having a smaller end and a larger end, the test cell further including a plug spanning the larger end of the frustrated wedge and sized to fit loosely therein so as to be freely movable a limited distance into the space within the frustrated wedge and having a concave trough-like inwardly-facing surface; (b) placing the test cell on a supporting surface with the plug resting on the supporting surface so that the larger end of the frustrated wedge is below its smaller end; (c) filling the test cell completely full with particulate material; (d) consolidating the particulate material within the test cell by applying a downward pressure θ c at the smaller end of the frustrated wedge, so that the direction of motion of the particulate material during consolidation is toward the plug, where σ.sub.c =L.sub.C /A.sub.1 +γ.sub.1 C and L c =consolidation load A 1 =average cross sectional area of the test cell and γ 1 =bulk density of the particulate material; (e) inverting the test cell with the plug and the consolidated particulate material still in it, so that after the inversion the larger end of the frustrated wedge is above its smaller end; (f) applying a gradually-increasing downward load to the plug to produce failure motion of the particulate material toward the smaller end of the frustrated wedge; (g) noting the load L F at which failure occurs; and, (h) calculating the unconfined yield strength by the equation ##EQU19## where h=1.1 for a rectangular test cell, and where D is the width of the larger end of the test cell.