09.02.2013 Views

WATER JET CONFERENCE - Waterjet Technology Association

WATER JET CONFERENCE - Waterjet Technology Association

WATER JET CONFERENCE - Waterjet Technology Association

SHOW MORE
SHOW LESS

Create successful ePaper yourself

Turn your PDF publications into a flip-book with our unique Google optimized e-Paper software.

DISCUSSION<br />

NAME: George Savanick<br />

COMPANY: Twin Cities Research Center, Minn., MN<br />

QUESTION: "It is difficult to see how unconsolidated material can be fractured. Would<br />

you please enlarge upon your use of the term 'fracture'?"<br />

ANSWER: It is certainly true that the term "fracture" implies there is a fracture toughness<br />

associated with the material. In the Florida demonstration, the soil was cohesionless<br />

material thus having negligible toughness. In the text, I have tried to use the term<br />

separation. The resistance to separation opening is principally the in situ compressive<br />

stress field which is altered at the tip of the separation by the hydraulic pressure applied<br />

along the separation surface. The distribution of this separation opening pressure is a<br />

function of the separation shape, slurry properties and pumping rate. There are, therefore,<br />

similarities between the separation process which occurred in the unconsolidated<br />

sediments and hydraulic fracture in deep rock formations from an analytical standpoint.<br />

Although I do not pretend to thoroughly understand the difference in behavior<br />

between these two processes, I feel that the major differences are in stability of the<br />

material at the separation tip. I hypothesis that the cohensionless soil below the<br />

groundwater table will experience a reduction in pore pressure as the separation extends<br />

thus leading to temporary liquefaction at the tip. This localized soil density reduction will<br />

redistribute with time spreading away from the unsupported separation tip. The length of<br />

unsupported tip is dependent on the deformation of the soil as there is a critical minimum<br />

width of separation or gap beyond which the ground supporting slurry will not penetrate<br />

within the separation. The localized density reduction yields a localized change in soil<br />

modulus which alters the size and orientation of the stress field at the separation tip. This<br />

alteration in stress field orientation will thus alter the direction of separation or "fracture"<br />

propagation as predicted by rock fracture theories. This direction of propagation is the<br />

characteristics of greatest significance to the Block Displacement process.<br />

327

Hooray! Your file is uploaded and ready to be published.

Saved successfully!

Ooh no, something went wrong!