Section 205 — Rock Blasting

Description

205.01This work consists of rock fragmentation blasting using production and controlled blasting techniques to construct engineered rock cuts.

205.02Definitions.

(a)Production blasting. Blasting using widely spaced blast holes that typically contain larger explosive charges to expedite movement and fragmentation for rock removal. (b) Controlled blasting. Blasting that includes presplit blasting and cushion blasting hole techniques. Controlled blasting uses closely- spaced and carefully aligned blast holes that typically contain lighter charges than production holes to produce stable, aesthetically pleasing ro ck faces with minimal blast damage. Controlled blast holes are the first row of blast holes, normally located within 24 inches of the top of the staked slope.

(1)Presplit blasting. Presplit blasting detonates closely spaced backslope holes before drilling for production blasting or before detonating the production blasting holes to produce a highly controlled, smooth cut face.

(2)Cushion blasting. Cushion blasting is similar to presplitting, except that the detonation of the cushion holes along the backslope is detonated immediately after the detonation of the production and buffer holes, generally resulting in a more natural cut face appearance.

(c)Lift. For rock blasting, a lift is the vertical height of rock fragmented from a single blast.

(d)Mudcapping. The blasting of boulders by placing a quantity of explosives against a rock, boulder, or other object without confining the explosives in a drill hole.

(e)Blockholing. The breaking of boulders by firing a charge of explosives that has been loaded in a drill hole.

Construction Requirements

205.03Regulations. Comply with Federal, state, and local rules and regulations for the purchase, transportation, storage, and use of explosive material. Federal regulations include the following:

(a)Safety and health. OSHA, CFR Title 29, Part 1926, Subpart U.

(b)Storage, security, and accountability. Bureau of Alcohol, Tobacco, and Firearms (ATF), CFR Title 27, Part 555, Commerce in Explosives.

(c)Shipment. DOT, CFR Title 49, Parts 171- 179, 390-397.

(d)National Park Service. For projects in National Park Service lands, comply with National Park Service Director’s Order No. 65, Explosives Use and Blasting Safety .

205.04Qualifications. At least 14 days before starting drilling and blasting work, s ubmit the following for approval:

(a)Blaster- in-charge. Provide an individual to directly supervise the drilling and blasting crew during drilling, loading, and detonation of charges. Include the following:

(1)A résumé describing at least 5 years’ experience as a blaster -in-charge on 3 projects with similar work, and provide a brief description of each project including the owner’s name and contact information; and

(2)Copy of a valid blaster license accepted by the state where the project is located for the type of blasting required.

(b)Blasting crew personnel. Documentation that each blasting crew member has completed at least 24 hours of blasting safety training within the past 5 years or has at least 2 years’ blasting experience along with proof of a Federal Employee Possessor Permit ;

(c)Drillers. A résumé for each drill operator describing at least 1 year ’s experience as a driller ; and

(d)Vibration specialist. A résumé describ ing at least 5 years’ experience as a vibration specialist on projects with similar work.

205.05Blasting Plans . Submit proof of applicable permits, licenses, and a general blasting plan signed by the blaster -in-charge at least 14 days before drilling and blasting operations. Blasting plans are not required for boulder reduction blasts (mudcapping or blockholing).

(a)General blasting plan. Submit a general blasting plan for review and approval. The CO will review and approve the General Blasting Plan within 7 days or return it for corrections. Include the following:

(1)Procedures and sa fety precautions for transporting, handling, storing, loading, and detonating explosives, conducting pre -and post -blast surveys, monitoring blasts, managing misfires, and removing and disposing of excess explosives. (2) Explosives transportation and storage plan, including:

(a)Name, address, and telephone number of explosives suppliers;

(b)Description and license number of explosives transport vehicles, routes to be traveled, proposed hours of travel, and driver qualifications; (c) Magazine and day -box locations;

(d)Explosives and accessories inventory system; and

(e)Contact information for the person responsible for security of project blasting material and supplies.

(3)Area security plan including explosives and general site security, methods of site communication, pre -and post -blast signage and audible signaling systems, road closure requirements, and pre-blast notification for affected agencies or entities.

(4)Manufacturer’s technical and safety data sheets for proposed explosives, primers, initiators, and related blasting devices and accessories.

(5)Excavation plans and equipment lists for pre -blast dressing and access roads, and benches for drilling and blasting operations. (6) Typical scaled plan and section views for both production and controlled blasting. Include the following:

(a)Stationing intended for each typical blast plan;

(b)Maximum blast length and free face;

(c)Hole spacing, hole inclination, hole depth, hole diameter, and burden;

(d)Stemming depth, decking method and materials (if required), and subdrill depth;

(e)Powder factor, charge weight per delay; and

(f)Initiation method, sequence, and delay times.

(7)Methods for limiting dust and noise.

(8)Fire watch plan including number of post-blast observers and duration of the fire watch.

(9)Contingency plan for blast flyrock containment, including a drawing and description of the proposed containment system designs. Do not deliver explosives to the project until the general blasting plan is accepted. Submit revisions and updates within 48 hours of changes in the above information. Do not blast until revisions and updates to the general blasting plan are approved.

(b)Site-specific blasting plans and general plan revisions and updates. Submit site -specific blasting plans after approval of the general blasting plan or at times there is a change in drilling a nd blasting methods provided in the general blasting plan. Allow 3 days for approval. Do not start drilling until the plan is approved. Include the following:

(1)Proposed excavation sequence;

(2)Station limits and plan view of the proposed blast, showing how the proposed blast fits into the lift excavation sequence;

(3)Elevations of the tops and bottoms of each lift;

(4)Scaled drawings for each blast showing access, containment, plan and section views of drill patterns, clearing limits, free face, burden, blast hole lo cations, blast hole spacing, subdrill depths, lift height, blast hole diameters, and blast hole angles;

(5)Loading diagram for each blast showing powder factor, charge weight per delay, type and quantity of explosives, primers, initiators, locations of decking, and range of stemming depths for substantial variations within the drill pattern;

(6)Initiation method and sequence of blast holes for each blast. Include delay times, delay system, and downhole firing times;

(7)Flyrock, air-blast overpressure (noise), and ground vibration control measures;

(8)Estimated volume of in -place rock to be blasted. Include the total length of production and controlled blast hole; (9) Location and orientation of significant joints, fractures, faulting, bedding planes or other rock mass structural features that affect the site-specific blasting plan; (10) Post-blast rockfall conta inment designs and procedures; and

(11)If structures are within an area of ground vibration or air- blast overpressure concern, prepare an attenuation study with information for the affected structures. Develop a plot of peak particle velocity versus peak frequency according to the United States Department of the Interior, Bureau of Mines Report of Investigation 8507 (RI 8507) . From this plot, determine the values of peak particle velocity and peak frequency that will not damage each structure in the site -specif ic blast plan.

205.06Pre -Blast Condition Survey and Vibration Monitoring and Control. The Contractor is responsible for damage resulting from blast related ground vibrations and air -blast overpressures. Determine the need for vibration monitoring depending on soil and rock conditions, blasting parameters as outlined in the blasting plan, and proximity of buildings, structures, utilities, and sensitive natural features that may be subject to damage from ground vibrations or air -blasts. If vibration monitoring is required, comply with the following requirements:

(a)If not specified in the contract, establish referenceable blasting criteria for buildings, structures, utilities, and natural features that conform to Federal, state, and local rules and regulations. Present blasting criteria in terms of distance of the facility or feature from blasting, maximum allowable peak particle velocity limits versus structure type, maximum allowable peak particle velocity and peak frequency as determined by RI 8507, and air overpressure structure damage limits.

(b)Conduct a pre -blast condition survey of nearby buildings, structures, utilities, and natural features potentially damaged by blasting- related ground vibrations or air -blast. Document the natural frequency of each affected structure or feature. Use a survey method acceptable to the Contractor’s insurance company. Submit a copy of pre -blast condition survey records with the site -specific blasting plans for CO review.

(c)If ground vibration or air -blast damage is possible, monitor each blast with digital recording seismographs and approved air -blast monitoring equipment calibrated within the last year. Locate monitoring equipment according to the directions of the vibration specialist. Place at least three recording stations be tween the blast area and closest susceptible structures, utilities, and immediately adjacent to natural features. Place one of the three recording stations on the critical structures. For ground vibration monitoring, use self -triggering seismographs that c an measure peak air blast overpressure and record particle velocity, displacement, and acceleration for three mutually perpendicular components of vibration in the range generally found for controlled blasting. Provide instruments with internal calibration and triaxial orthogonal transducers with flat frequency response from 2 to 250 hertz with a sampling rate of at least 1000 data points per second with sufficient memory to store the full blasting sequence and their locations. Provide seismographs that can produce a permanent digital time history file for each ground motion episode.

(d)Control ground vibrations and air -blast overpressures with adjustments to delay sequences and maximum allowable charge weights per delay. Verify allowable charge weights per del ay by conducting representative trial blasts and measuring ground vibrations and air -blast overpressure levels. Prepare an attenuation study that will enable prediction of the peak particle velocity in any component (longitudinal, transverse, or vertical) on the surface of all structures. Conduct test blasts with blast plan modifications that limit ground vibrations and air -blast overpressures to levels that will not cause damage to nearby buildings, structures, utilities, and or natural features as determi ned by the vibration specialist. Submit a copy of the attenuation study results and predicted maximum allowable peak particle velocity and peak frequency for each structure based on a plot of peak particle velocity versus peak frequency according to RI 8507.

(e)Record each blast using digital video equipment from two locations that clearly show the entire proposed blast site, preferably from locations on both sides or by unmanned aircraft system above the blast. Provide digital videos with sound, with a minimu m 1080p resolution, and in a common file format for viewing.

(f)Ensure blasting operations incorporate collected data and findings from vibration monitoring by having the vibration specialist interpret seismograph and air- blast records.

(g)Submit a copy of the interpreted seismograph and air -blast records with a certifying signature by the vibration specialist. If actual peak particle velocity versus peak frequency measurements exceeds those predicted for a structure, adjust the site -specific blast plans for the actual structural response to the blasting.

205.07Test Blasting. Before starting full- scale drilling and blasting, demonstrate adequacy of the site - specific blasting plan by drilling, blasting, and excavating a test blast up to 100 linear feet, as measur ed along the roadway centerline, with proposed containment measures in- place. Conduct the test blast at an approved location within the planned excavation area. Space blast holes for presplit and cushion blasting no more than 30 inches apart for the initia l test blast. Adjust the spacing based on the results of the test blasts for each excavation in differing geology as approved. Use the approved spacing in the full- scale blasting or subsequent test blasts if necessary. A test blast is unacceptable if it re sults in excessive flyrock, potentially damaging ground vibrations or air-blasts, unplanned overbreak and backbreak, excessive damage to the final rock cut face, or results in unwanted overhangs. If a test blast is unacceptable, revise the site -specific bl asting plan and conduct additional test blasts until the combination of blast hole pattern spacing, timing, controlled blast hole alignment, and charges produce acceptable results.

205.08Blasting. Use explosives and initiating devices less than 1 year old. Locate explosives magazines at approved sites. Inspect the pre-blast area and submit the proposed extent of pre-blast clearing and dressing for approval. Blasting with angle -drilled or fan -drilled holes is only allowed during initial pioneering operations to establish access to the top of cut. Controlled blasting requirements are applicable to pioneering work. Before drilling, remove overburden, soil, and loose or decomposed rock along the top of the excavation for a distance of at least 30 feet beyond the end of the production hole drilling limits, or to the end of the cut. Record and maintain a log of each blast hole drilled identifying the depth, color, and character of the cuttings, penetration rate, hole collar location and hole orientation, loss of drilling air, groundwater, and other pertinent information. Before initiating the blast, prepare a blast plan map and submit it showing designated hole numbers along with individual hole logs completed, dated, and signed by the driller. Ensure blast holes are free of obstructions for the entire depth before placing charges. Take necessary precautions when placing charges so caving of material from the walls of the holes and the hole collar will not occur. Mitigate uncontrolled gas pressure loss during blasting and excessive blast noise by stemming the upper portion of blast holes with appropriate dry granular material passing the ½ -inch sieve. Do not stem holes with drill cuttings or trash. Blast according to the approved site -specific blasting plan. Use blasting mats, rockfall containment systems, and other protective devices to prevent damage to surrounding features.

(a)Production blasting. When conducting cushion blasting or presplitting, drill a lighter -loaded buffer row of production holes on a parallel plane adjacent to the controlled blast line to minimize blast damage to the final slope. Drill production blast holes a maximum of 4 inches in diameter to a depth such that unbroken rock does not extend above the finish surface. Drill production blast holes to the design depth. If more than 5 percent of the production blast holes in a lift do not conform to the design depth requirements, redrill the shallow holes to the proper depth. Except when subdrilling, do not drill production blast holes below the base plane of the controlled blast holes. Drill production blast holes within two drill hole diameters of the planned collar location. If more than 5 percent of the drill hole collars in a lift are out of tolerance, fill each hole outside of the loca tion tolerance with crushed stone and redrill. Detonate production holes in a controlled delay sequence.

(b)Controlled blasting. Use controlled blasting to form the final cut face on rock cuts where the staked slope ratio is 1⅓V:1H or steeper and the slope height is more than 10 feet above the ditch grade. Use drilling equipment that accurately controls the angle of the drill as it enters the rock. Select a lift height and conduct drilling operations so the blast hole spacing and downhole alignment does not va ry more than 8 inches from the proposed spacing and alignment. If more than 5 percent of the holes exceed the variance, reduce the lift height and modify drilling operations until the holes are within tolerance. Drill holes a maximum of 3 inches in diamete r and within 3 inches of the staked collar location. Fill and redrill blast holes outside of the location tolerance if more than 5 percent of the hole collars in a lift are outside of the location tolerance. Fill the blast holes with crushed stone before redrilling. Drill the controlled blast hole line at least 30 feet beyond loaded production holes or to the end of the cut. Do not exceed 30 feet for bench height or drill hole length. Limit subdrilling of holes to one -half of the hole spacing or 24 inches, whichever is deeper. Offset lifts up to 24 inches horizontally to allow for drill equipment clearance. Remove benches resulting from the drilling offset. Compensate for drift that may occur in the upper lifts. Adjust the drill inclination angle or the init ial drill collar location to obtain the required typical section. Limit drilling to one -half of the hole spacing or 24 inches, whichever is deeper. Do not use bulk ammonium nitrate and fuel oil for controlled blasting. Only use standard explosives manufactured specifically for controlled blasting in controlled blast holes, unless approved. For explosives in controlled blast holes use a maximum diameter no greater than one- half of the diameter of the presplit hole. (c) Revising blasting p lans. Stop drilling and blasting operations, and submit a revised site -specific blasting plan according to Subsection 205.05(b) , if the following occur:

(1)Slopes are unstable;

(2)Slopes exceed overbreak tolerances within the limits of the excavation or as determined by the CO for the site geology; (3) Unwanted overhangs, ridges, or ledges are created;

(4)Excessive blast damage occurs within the limits of the excavation or as determined by the CO;

(5)Poor fragmentation results in oversize material requiring secondary b lasting and rehandling;

(6)Safety of the public is jeopardized;

(7)Property or natural features are endangered;

(8)Excessive or uncontrolled flyrock is generated;

(9)Excessive ground vibration or air -blast overpressure occurs where damage to buildings, structures, utilities, or natural features is possible; or

(10)Desired slope or rock face conditions are not produced. Dress the cut face by removing or stabilizing cut face rock that is loose, hanging, or potentially dangerous after each blast. Dress the cut face by approved methods. Leave minor irregularities or surface variations in place if they do not create a hazard. Excavate and remove m aterial outside the neat line slopes which is unstable and a potential hazard. D rill the next lift only after the slope stabilization and blast cleanup work is complete.

205.09Reporting.

(a)Post-blast. Prepare a post -blast report. Submit the report within 3 days following a blast and before drilling for the next blast. Include the following:

(1)Results of the blast. Include overbreak, blast damage, noise levels, flyrock, drill trace retention, fragmentation, material containment, material rehandling requirements, and misfires;

(2)Proposed changes for future site -specific blasting plans that will prod uce acceptable results if blasting objectives were not met; (3) Proposed repairs or stabilization plans for unstable or blast damaged backslopes;

(4)A detailed blasting plan modified to show significant changes in pattern, loading, or timing;

(5)Drilling logs for ea ch hole completed (dated and signed by the driller) that identify the depth, color, and character of the cuttings. Include the penetration rate, hole collar location, hole orientation, and conditions that adversely affected drilling or explosives loading operations;

(6)Depth measurements of production and controlled blast holes;

(7)A drawing or sketch showing the direction of blast, the face, or faces, hole numbers, and the physical blast layout; (8) Measurement of overbreak quantities following lift mucking;

(9)Date an d time of loading and detonating the blast; and

(10)Name and signature of the blaster -in-charge.

(b)Monitoring. Submit copies of the digital videos after each blast. Do not continue drilling and blasting operations until the video has been received and reviewed by the CO. Allow 24 hours for review. If vibration or air- blast monitoring is required, submit a vibration and air -blast report within 3 days following a blast and before drilling for further blasting. Do not drill until directed. Include the following:

(1)Type of vibration or air-blast recording station used and instrument identification numbers;

(2)Name of vibration specialist observing the blast and interpreting vibration and air -blast data;

(3)Blast identification number and location of blast;

(4)Distance and direct ion of ground vibration and air -blast overpressure recording stations from the blast area;

(5)Type of material the ground vibration recording stations were sitting on at the time of the blast;

(6)Maximum applicable charge weight per delay;

(7)Peak displacement, par ticle velocity , and frequency recorded at each ground vibration sensor location;

(8)Peak overpressure recorded at each air -blast sensor location;

(9)Dated and signed copy of instrument records;

(10)Post-blast condition survey noting changes from the pre-blast survey ; and

(11)Comments on success of the blast in terms of adherence to established ground vibration or air-blast criteria and management practices. If failing to meet ground vibration and air- blast criteria and management objectives, submit proposed changes to future site -specific blasting plans that will produce acceptable results.

(c)Close -out. Before demobilizing from the project site, submit a written statement signed by the blaster -in-charge certifying:

(1)Blast holes loaded with explosive material have been either detonated or unloaded and disposed of properly; and

(2)Blasting is complete and explosive material has been removed from the project site.

205.10Acceptance. Material for rock blasting will be evaluated under Subsectio ns 106.02 and 106.03. Rock blasting will be evaluated under Subsections 106.02 and 106.04.

Measurement

205.11Measure the S ection 205 pay items listed in the bid schedule according to Subsection 109.02 and the following as applicable: When measuring controlled blasting by the square foot, measure the face blast as shown in the blasting plan. When measuring controlled blast holes by the linear foot, measure the actual length of drilling recorded in the post- blast reports. Controlled blast holes include the row of holes lying closest to the trim line. Do not measure presplit blast holes with more than 8 -inch misalignment. Do not measure production blast holes. Do not measure dressing of the cut face rock.

Payment

205.12The accepted quantities will be paid at the contract price per unit of measurement for the Secti on 205 pay items listed in the bid schedule. Payment will be full compensation for the work prescribed in this Section. See Subsection 109.05 . Section 206. — RESERVED