The Table of Contents for this section is available.
The work covered by this section consists of the use of the blasting technique of pre-splitting preparatory to the excavation of rock material in cut areas. Pre-splitting shall be defined as the establishment of a free surface or shear plane in rock by the controlled usage of explosive surface or shear plane in rock by the controlled usage of explosive and blasting accessories in approximately aligned and spaced drill holes.
Pre-splitting of rock shall be done in accordance with the details on the plans and at locations directed by the Engineer.
228-2 CONSTRUCTION REQUIREMENTS.
The drill holes for the pre-split face shall not exceed 3 feet in spacing. They shall remain parallel and shall not deviate from the plane of the proposed slope. When more than one lift is necessary for a pre-split face the drill angle may be steepened to allow a 1 foot offset at the bottom of the holes for drilling equipment to drill the holes for the next lift.
Drill holes for pre-splitting shall not exceed 4 inches in diameter and shall not exceed 25 feet in depth. If satisfactory drill hole alignment is not achieved, the allowable drill hole depth shall be reduced as directed by the Engineer on all subsequent shots in order to minimize divergence.
All drilling equipment used to drill the pre-split holes shall have mechanical devices affixed to the equipment to accurately determine the angle at which the drill steel enters the rock. Pre-split hole drilling will not be permitted if these devices are either missing or inoperative.
Only manufactured cartridge-type explosives with a maximum charge of 3/4 pounds per linear foot of drill hole will be permitted in pre-split holes. The charge shall be evenly spaced by stemming or other approved methods. The bottom 2 feet of the hole may have a charge rate that is double the charge rate for the rest of the hole. There shall be no charge in the top 3 feet of the drill hole and that part of the hole shall be stemmed with sand or 3/8 inch maximum size clean stone.
Production blast holes shall not be closer than 4 feet from the line of pre-splitting. The bottom of production drill holes shall be at least 2 feet higher than the bottom of pre-split drill holes.
Pre-split shots shall extend at least 50 feet ahead of production shots. All of the holes in a pre-split shot shall be fired simultaneously and shall precede the production blasting by at least 25 milliseconds.
The pre-split face shall not deviate more than 1 foot from the line of drill holes except where pre-existing cracks, pockets of soil, seams of soft rock, or the character of rock will unavoidably result in irregularities. Any material behind the pre-split line which is loosened by overblast shall be scaled and removed from the face at no cost to the Department. If deviation from the drill line or overblast occurs, all subsequent shots shall be altered by changing the hole spacing, changing the diameter of holes, changing the rate of charge in the holes, or any combination of these or other measures approved by the Engineer.
The quantity of pre-splitting to be paid for will be the actual number of square yards of rock face which has been pre-split, measured along the finished face of the rock. Deductions for unsatisfactory results will not be made where pre-splitting was performed as directed, provided results were caused by pre-existing conditions of the rock or were not caused by blasting methods.
The quantity of pre-splitting, measured as provided in Article 2283, will be paid for at the contract unit price per square yard for "Pre-Splitting of Rock." Such price and payment will be full compensation for all work covered by this section including but not limited to drilling, explosive, loading of drill holes, and blasting.
Payment will be made under:
Pre-Splitting of Rock Square Yard