# US 4,394,051 A · Method of hydrospalling

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- Number: US 4,394,051 A
- Document ID: US4394051A
- Status: Granted
- Kind: A
- Application number: 06/270,038
- Filed: 1981-06-03
- Granted: 1983-07-19
- Earliest claimed: 1981-06-03
- Assignees: The United States of America as represented by the Secretary of the Interior
- Inventors: Martin S. Oudenhoven
- Web page: https://patentgrep.com/patent/US4394051A

## CPC

- E21C 37/06: by making use of hydraulic or pneumatic pressure in a borehole
- E21C: MINING OR QUARRYING

## Abstract

A method of breaking rock from a free surface which uses hydrofracturing to induce rock failure. Initially, a hole is cut in the rock face to a depth suitable for spalling by a high pressure water jet drill. Next, at the bottom of this hole a thin circular slot is hydraulically cut into the rock. The slot's circular axis is cut parallel to the transverse axis of the hole and the slot is made larger than the hole diameter. Following this step, a high pressure packer, with a high pressure tube passing through its center, is inserted into the drill hole. This packer is placed near the bottom of the hole above the slot and inflated. A fluid, like water, under high pressure is pumped down the hole past the packer into the slotted area. This high pressure fluid initiates a tensile fracture in the rock at the circular periphery of the slot. Tension is induced in the rock at this peripheral location due to the small radius of curvature existing there. This circular tensile fracture propagates outward away from the drill hole and upward to the free rock surface. After the rock fragment is broken free, pressure is released from the packer and it is withdrawn from the hole letting the fragment drop. To advance through the rock, the process is continuously repeated with the high pressure fluid being applied to the slotted area over a very short time period.

## Claims

### Claim 1

A method of hydrofracturing in situ rock material from its free surface when the material's tensile strength is much less than its compressive strength comprising the steps of:
(a) forming a small diameter hole no more than 1 inch in diameter to a predetermined depth in the material to be fractured;
(b) cutting a generally circular slot in the material from near the bottom of the hole formed in step a, said slot extending outwardly from the hole and encircling it;
(c) mounting and inflating an elongated packer assembly having a fluid conduit therethrough in the hole, said packer terminating at its end remote from the hole's entrance near the intersection of the hole with the slot formed in step b; and
(d) injecting a fluid under high pressure into said slot's volume through the conduit in the packer assembly to fracture the material with the fracture beginning at or near the periphery of the slot and extending to the material's free surface.

### Claim 2 (depends on 1)

The method of claim 1 wherein step (b) is done with a high pressure water jet and the resulting cut slot is larger at its greatest extent than the transverse dimension of the hole and oriented generally parallel to the free surface.

### Claim 3 (depends on 1)

The method of claim 1 wherein steps (a) and (b) are accomplished by using high pressure fluid jets to form a cut, respectively, into the in situ material.

### Claim 4 (depends on 1)

The method of claim 1 wherein steps (a) to (d) are repeated in that sequence to remove additional material to a greater depth.

### Claim 5 (depends on 1)

The method of claim 1 wherein the ratio of compressive strength of the material to its tensile strength is at least 5 to 1 and step d is accomplished by injecting the fluid through a tubular member placed in the packer assembly.