00335.00 284 Section 00335 - Blasting Methods and Protection of Excavation Backslopes Descripti on
00335.00 Scope - This Work consists of excavating in Rock using controlled blasting methods to
achieve smooth, uniform and unfractured backslopes, and produce a free surface or shear plane in the Rock along the specified excavat ion backslope, and Production Blasting to facilitate excavation.
00335.01 Definitions :
Buffer Row - In multiple -row blasts in which perimeter control blasting techniques are used, the first row of production holes immediately adjacent to and drilled along a plane parallel to the perimeter control blast line. The Buffer Row is located between the production holes an d the perimeter controlled blast line. Perimeter Controlled Blasting - The use of explosives and blasting accessories in carefully spaced and aligned drill holes. Perimeter C ontrolled Blasting techniques include Presplitting and Trim (Cushion) Blasting. Presplitting - A Perimeter Control Blasting method in which the perimeter row of blast holes are drilled along the plane of the specified final excavation backslope and that utilizes reduced drill hole spacing and reduced diameter explosives decoupled fro m the drill hole wall, and whose initiation precedes the initiation of the adjacent production holes by a minimum of 25 milliseconds. Production Blasting - Fragmentation blasting in the main excavation area, usually using more widely spaced drill holes than controlled blast holes . Trim (Cushion) Blasting - A perimeter control blasting method in which the initiation of the perimeter row of blast holes drilled along the plane of the specified final excavation backslope follows the initiation of the adjacent production holes within 25 to 75 milliseconds, if production holes are being employed in the blast. Materials
00335.10 Materials - Furnish all explosives and blasting caps that are no more than 1 year old. Each
blasting cap period shall come from one lot number. Construction
00335.40 Blasting Methods :
a.General - Use methods in making excavations that do not shatter or loosen the backslopes and that produce smooth and uniform excavation slopes at the specified Slope angles. These include: • Perimeter Controlled Blasting - Use on the entire length of cut section in Rock or cemented Materials that have backslopes of 1V:0.75H or steeper, even if the main excavation can be ripped. • Production Blasting - Blasting in the mass of Rock to be excavated shall be designed to control flyrock, minimize ground vibration and air blast, and result in loosened and fragmented in-place Rock of a size that can be removed, transported, or crushed to produce specified products. Lay out production blast holes in a consistent pattern that does not affect the perimeter control blast holes. Where production blast holes are made adjacent to Highway s with specified closure restrictions, the volume of material blasted shall n ot exceed the 00335.40 285 Contractor's ability to remove the blasted material from the adjacent Highway within the specified closure time.
b.Safety and Flyrock Control - Use techniques that effectively limit and control flyrock. Clear the site of all Boulders or other material as directed prior to beginning blasting Work . Following every blast, observe the entire blast area for a minimum of 5 minutes before reentering or commencing Work in the area. Be responsible for the storage, transportation, and handling of explosives, their use, and the results of all blasting operations according to 00170.94. Cover all blast areas that are within 200 feet of residences, facilities or above-ground utilities using appropriate blast containment mats or an approved equivalent method. Discontinue blasting operations, as directed, if it is apparent that the methods employed are not producing acceptable results or the safety of the public, the Contractor's employees or adjacent property is being jeopardized.
c.Preblast Surve y - Offer, in writing, to perform a preblast survey for owners and occupants of all buildings, Structure s, and utilities within the distance of the blast specified in 00335.40(e). If the offer is accepted, use an Agency -approved survey form, signed and co mpleted by an independent third party, and submitted to the Engineer and Contractor at least 72 hours before blasting begins. Deliver a copy of the survey form and copies of any photos taken to the owners and occupants.
d.Blasting Plan - Provide a separate blasting plan for each cut that requires blasting, prepared by a person qualified and experienced in blasting Work . Each plan shall cover individual major Rock cut areas or Rock production from a M aterial source. Similar minor Rock cut areas of less than 50 cubic yards, as well as U tility and culvert trenches, may be covered as a group in one generalized blasting plan. Submit the blasting plans for the Engineer's review at least 21 Calendar Day s before beginning drilling for e xcavations or when any Perimeter Controlled Blasting is required . The blasting plans will be reviewed for conformance with the Specifications and any concerns will be discussed with the Contractor. Submit any proposed changes to the blasting plans in wri ting to the Engineer for review before implementation. Submittal of blasting plans is for quality control and record -keeping purposes. Review of blasting plans by the Engineer does not relieve the Contractor of full responsibility for the accuracy and adequacy of the plans and the resulting safety when implemented in the field. Each blasting plan shall contain the full details of the drilling and blasting patterns, vibration, flyrock, and noise reduction methods, blast area security measur es and traffic control that the Contractor proposes to use, and the following information: • Station limits of proposed shot. • Removal of overburden. • Plan and Cross Section diagrams of proposed drill pattern for controlled and production blast holes including Buffer Rows, free face, burden, blast hole spacing, blast hole diameters, blast hole angles, lift height and sub drill depth. Accurately draw to scale and show each cu t area to be blasted. • Loading diagram showing the type, amount and specific gravity of explosives, primers, and initiators, and location depth, and type of stemming. 00335.40 286 • Initiation sequence of production and controlled blast holes including delay times and del ay system. • Manufacturer's product data sheets for all explosives, primers and initiators to be used in the Work .
e.Blasting Notification - Notify all owners and occupants of buildings, Structure s, and utilities that are within the following distances o f the blasting areas: • 300 feet for shots using less than 50 pounds of explosives per time delay of 15 milliseconds. • 600 feet for shots using between 50 and 250 pounds of explosives per time delay of 15 milliseconds. • 1,250 feet for shots using more than 25 0 pounds of explosives per time delay of 15 milliseconds. Provide notification, in writing, once, at least 48 hours before blasting begins, and again on the Day the blasting operations occur . Do not begin detonation of the blast until the Agency represen tative is ready to videotape the blast, or until the Engineer is prepared to witness the blast.
f.Blasting Test Sections - Demonstrate the adequacy of each proposed blasting plan by means of test shots in each cut or excavation before beginning full -scale blasting. Do not proceed with remaining drilling and blasting until acceptable test blast results have been demonstrated to the satisfaction of the Engineer. In areas where Perimeter Controlled Blasting techniques are being employed, drill and blas t short representative test sections not exceeding 100 feet in length. Excavate a section not less than 20 feet wide exposing the full height of the lift for examination. In areas where no Perimeter Controlled Blasting techniques are being employed, determine effectiveness of the test section based on the material placement, cut slope stability, fragmentation and control of ground vibration, air blast and flyrock. Do not drill ahead of the test blast area, except as provided in 00335.41(a)(6), until the test section has been evaluated. The Contractor may be directed to use test section lengths less than 100 feet. If the results of the test shots are unacceptable revise the methods, techniques and procedures, at no additional cost to the Agency, so that the results achieved will be acceptable. No further drilling and blasting will be allowed until the revised methods are reviewed according to 00335.40(d) and verified by additional test shots. If, during the progress of the Work , the methods of drilling and blasting do not produce acceptable results within the tolerances specified, drill, blast and excavate additional test sections until a technique is determined that will produce acceptable results.
g.Blasting According to Plan - After the Engineer has reviewed the blasting plan and determined that test sections have demonstrated acceptable results, perform all perimeter controlled and Production Blasting according to the plan that produced acceptable results. Notify the Engineer when any changes in conditions or results are observed. On the Day of each blasting occurrence and before detonation of the blast, the supervisor or blasting specialist in charge shall certify, in writing, that the shots being carried out are consistent with the reviewed blasting plan.
h.Blasting Report - Submit a blasting report detailing the blast outcome within 48 hours of making each blast. Include in the report the following: 00335.41 Drill logs and notes regarding conditions encountered in the drill holes, including a description of encountered subsurface conditions such as open joints, soft or fractured Rock zones, groundwater conditions, hole alignment, and drilling problems. Any var iations from the submitted Blasting Plan, including any changes to explosives type or amount, loading dimensions, hole spacing, and initiation sequence and delay times. All blast monitoring documentation. • A copy of the color video recording of the blast ar ea(s), with sound, high definition (at least 1080p resolution, 24 fps) , in a format commonly used for viewing with a computer or DVD player. The video recording must show an unobstructed view of the blast area, framed to show both above and below the blas t area. Begin recording at least 10 seconds before the blast, and continue recording until there is no visible dust. Use a free standing recording device that is not a cell phone or similar device, as approved by the Engineer. Submit the type of recordi ng device to be used at least 7 Calendar Days before the blast. • A comment section that includes the Contractor's evaluation of the blast performance, any unusual conditions or situations during the blast, and any misfires . • Details of all damage incurred and details of all neighbors ' complaints or comments.
i.Suspension of Blasting - If damage to existing facilities or adjacent property occurs due to blasting, immediately suspend blasting and report damage to the Engineer. Discontinue blasting operation s if the methods of drilling and blasting do not produce acceptable results within the tolerances specified. Before resuming blasting operations, revise the Blasting Plan and take other appropriate measures as necessary to correct the unacceptable blastin g results. Submit the revised Blasting Plan to the Engineer. Do not resume blasting until authorized by the Engineer.
00335.41 Controlled Blasting Methods :
a.Presplitting:
1.Attach mechanical devices to all drilling Equipment used to drill the presplit holes to determine, within an accuracy of 1 degree, the angle at which the drill steel enters the Rock.
2.Drill presplit holes with a minimum diameter of 2 1/2 inches and a maximum diameter of 3 inches.
3.Start presplit drill holes along the presplit line within 3 inches of the dimensions shown on the blasting plan. Holes located beyond this tolerance will be rejected. Completely fill the rejected holes with stemming material at no additional cost to the Agency. Drill new presplit holes with the proper spacing. Rejected holes will not be measured for payment.
4.Control the drilling operations to ensure that presplit hole alignment does not vary from the plane of the planned Slope by more than 9 inches either parallel or normal to the Slope. Presplit holes exceeding these limits will not be paid for unless, in the Engineer's opinion, satisfactory Slopes are being obtained.
5.The length of presplit holes for any individual lift shall not exceed 30 feet unless the Contractor can demonstrate to the Engineer's satisfaction that hole alignment can be maintained within the above tolerances. Upon satisfactory demonstration, and with written permission of the Engineer, the length of holes may be increased to a maximum of 60 feet. If more than 5 percent of the presplit holes are misaligned in any one lift, reduce the height of the lifts until the 9-inch alignment tolerance is met. 00335.42
6.Drill presplit holes a minimum of 30 feet longitudinally beyond the limits of the production holes to be detonated or to the end of the cut. Unless otherwise allowed by the Engineer in writing, remove all overburden, including any loose or decomposed Rock, before drilling the Presplitting holes.
7.When the cut height will require more than one lift, a maximum offset of 18 inches between lifts will be allowed to allow for drill Equipment clearance. Adjust the Slope angle of lower lifts to compensate for drill offsets and any drift that may have occurred in upper lifts.
8.Use only explosives manufactured specifically made for Presplitting in the presplit holes. The maximum diameter of explosives used in presplit holes shall not be greater than half the diameter of the presplit hole. Bulk ammonium nitrate and fuel oil (ANFO) is not allowed in the presplit holes.
9.Determine that the presplit hole is free of obstructions for its entire depth before placing charges. Exercise all necessary precautions so the placing of the charges will not cause caving of material from the walls of the holes.
10.Detonation of explosives in each hole in a presplit shot may be delayed, providing the hole-to-hole delay is no more than 25 milliseconds.
11.Drill the presplit holes with a minimum spacing of 10 times the presplit hole diameter, and a maximum spacing of 14 times the presplit hole diameter.
b.Trim (Cushion) Blasting - When the horizontal distance from the new proposed slope face to the existing Rock face is less than 15 feet, the Contractor may trim blast instead of Presplitting. The requirements in 00335.41(a) for Presplitting also apply to trim blasting, by changing the words "presplit" and "Presplitting" to "trim blasting". If trim blasting burdens are less than 6 feet or zones of weakness in the Rock are observed, submit a hole loading diagram that reflects the site conditions.
c.Buffer Row - Locate the buffer hole line a minimum of 3 feet away from the perimeter control blast line, or 1 foot for every inch of buffer hole diameter, whichever is greater. Space Buffer Row holes 3 to 5 feet center-to-center. The explosive load in buffer holes shall not exceed 50 percent of the full explosive load that could be placed in a 3-inch production hole. Initiation of the buffer holes shall be on a delayed sequence toward a free face.
00335.42 Production Blasting - Do not drill any row of production blast holes closer than 6 feet to
the perimeter controlled blast line. Where necessary to minimize damage to the Rock backslope, a row of buffer holes may be drilled between the perimeter controlled blast line and the production blast holes. Except for the bottom lift, do not extend production holes below the bottom of the controlled blast holes. Do not exceed 6-inch diameter for production holes. Detonate production holes on a delay sequence documented in the blasting plan.
00335.43 Scaling - Remove all loose, hanging, or potentially dangerous Rock on the excavated
surface by scaling during the completion of the excavation of each lift or test section. Do not begin drilling the next lift until this Work has been completed, as directed. Scale the slopes throughout the Contract at the frequency required to remove loose or overhanging material. Use a suitable standard steel mine scaling rod to hand-scale the slopes. Other methods such as machine scaling, hydraulic splitters or light blasting may be used instead of, or to supplement, hand-scaling, if allowed. 00335.90 Measurement
00335.80 Measurement - The quantities of perimeter controlled blast holes will be measured on the
length basis and will be determined by dividing the cut slope surface area by the perimeter controlled blast hole spacing. The cut slope surface area will be determined by Cross Section measurement from the top of the blasted Rock to the finished ditch bottom elevation. The quantities shown in the Contract Schedule of Items have been computed from a theoretical plan length using 30-inch hole spacing. The actual quantities will depend on field conditions and results from blasting test sections. Payment
00335.90 Payment - The accepted quantities of perimeter controlled blast holes will be paid for at
the Contract unit price, per foot, for the item "Perimeter Controlled Blast Holes". Payment will be payment in full for furnishing and placing all Materials, and for furnishing all Equipment, labor, and Incidentals necessary to complete the Work as specified. No separate or additional payment will be made for blasting, scaling, or loosening materials for excavation. When the Contract Schedule of Items does not indicate payment for Work performed under this Section, no separate or additional payment will be made. Payment will be included in payment made for the appropriate items under which this Work is required. 00340.00
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Source: Oregon Standard Specifications for Construction, 2024 Edition. Pages 350–355 of 1,268. View official source ↗