Attachment to C-408M/96-19
July 1, 1996
COMMONWEALTH OF PENNSYLVANIA
Department of Transportation
CLASS 1, CLASS 1A, AND CLASS 1B EXCAVATION
Supplementing the Specifications
Publication 408M dated 1996
SECTION 203.3(b)2. Presplit Blasting Method.
Revise completely as follows:
SECTION 203.3(b)2. Presplit Blasting Method:
Prior to start of presplit blasting, excavate material overlying rock or hard shale to the elevation directed; also excavate those areas not designated for presplit blasting at ends of the excavation section.
Presplit in accordance with the following criteria:
Drilling depth increments- not to exceed 30 feet
Maximum diameter of holes- 3½ inches
Spacing of holes - 18 inches minimum, 36 inches maximum
Explosives- manufactured for presplit blasting: cartridge-type less than or equal to one-half the diameter of presplit hole up to a maximum of 1½ inches.
Arrange a meeting with the Engineer to discuss presplit blasting operation at least two weeks prior to anticipated start of operation, or when a change in drilling and presplit blasting method is proposed. One week prior to the meeting submit a presplit blasting plan to the Engineer, with a copy for the Project Geotechnical Engineer, for review.
Have presplit blasting plan contain complete details on drilling, blasting patterns and controls to be used, including, the following information as a
Station limits of test area and presplit blast section.
Plan and section views of drill pattern, including blasthole spacing, blasthole diameters, blasthole angles, lift height, and subdrill depth for test area and presplitlast section
Loading diagram showing type and amount of explosives per foot, stemming.
Initiation sequence of blastholes, including delay times and delay system.
Manufacturers data sheets for all explosives, primers, and initiators to be employed.
At beginning of operation, and when material of different characteristics is encountered, construct
test sections approximately
25 feet in length to determine optimum spacing, size, and loading of holes for presplitting. Test sections may have varied loadings and hole spacings, depths, and sizes. Use an overall test area up to 100 feet in length.
Presplit blast the first test area using 30 foot maximum lifts and four 25 foot sections with holes spaced at 18, 24, 30, and 36 inches.
Upon completion of the presplit blasting test, expose test area for the Engineer and Project Geotechnical Engineer to examine and evaluate. Prepare presplit blasting plan for full scale operations based on evaluation of loads and hole spacing in presplit blasting test. Adjust presplit blasting lift based on presplit blasting test evaluation.
Drill presplit holes within 3½ inches of the staked collar location. A hole outside the 3½ inch tolerance will be rejected.
Control drilling operations by the use of proper equipment and technique to ensure no hole deviates from indicated slope by more than 12 inches either parallel or normal to slope after blasting.
Holes out of 12 inch alignment tolerance or 3½ inches staked collar location, will be deducted from the payment.
If more than 5% of presplit holes in any lift are
misaligned, reduce height of lifts in 10 foot increments until 12 inch alignment tolerance is met.
An offset bench 2 feet in width will be allowed when excavation is deeper than drilling depth increment, to accommodate drill head to slope for each lift. Stake offset benches for toe of completed slope to coincide with indicated toe of slope.
Complete presplit slopes prior to blasting interior portions of excavation by separate operations or use time delay initiators which will fracture slope before charges detonate in interior portion. In either case, extend presplitting holes to end of excavation, or not less than 50 feet beyond limits of interior portion.
Submit, to the Engineer, copies of seismic records showing generated frequencies and particle velocities for each blast.
SECTION 203.4(d) Presplit Blasting.
Revise first sentence as follows:
Measured on lineal foot of acceptable presplit blast holes with appropriate deductions for holes not drilled within tolerance as specified in Section 203.3(b).
Back to 408M/96 Table of Contents.
Back to Construction Publications