2-31 Section 205 – Drilling and Blasting
205.01 DESCRIPTION . This work shall consist of drilling and blasting of rock, in accordance with these specifications, the Plans, and as directed by the Engineer. 205.02 DRILLING AND BLASTING OF SOLID ROCK SUBGRADE . Solid rock subgr ade areas shall be shattered in place to the dimensions shown on the Plans or directed by the Engineer. The area of blasted rock subgrade shall extend sufficiently beyond the beginning and end of cut areas to ensure the shattering of all rock to a depth of 4 feet below the bottom of subbase material elevation. After detonation, any rock protruding above the bottom of subbase shall be removed. When directed by the Engineer, the Contractor shall excavate a trench with conventional earth moving equipment acros s the blasted rock to determine if the rock is sufficiently shattered to a depth of 4 feet below the bottom of subbase. Afterwards, the trench shall be backfilled with the rock removed. 205.03 DRILLING AND BLASTING USING PERIMETER CONTROL . Perimeter contr ol blasting refers to the use of explosives and blasting accessories in carefully spaced and aligned drill holes to produce a final excavation surface or shear plane in the rock along the specified excavation backslope. These blasting techniques are used t o better distribute the explosive charge to minimize damage, such as fracturing and overbreak, backbreak, or endbreak, beyond the final excavation face. This is accomplished by using small diameter, decoupled charges in closely spaced blastholes placed on the perimeter of an excavation. Perimeter control blasting methods include line drilling, presplitting, and precision presplitting.
a.Blasting Personnel .
1.Blasting Contractor . The blasting contractor shall be a company specializing in the use of explosives for breaking rock. The blasting contractor shall be responsible for loading and firing each blast, as well as the design and management of blasting operations.
2.Blaster -in-Charge . The blaster -in-charge shall have total authority over the handling , use and security of explosives, and is responsible for coordinating, planning, and supervising explosives use. The blaster -in-charge shall be responsible for inspecting blast areas after each blast event. The blaster -in-charge will be required to be on -site during blasting.
2-32 (3) Blasting Consultant . The blasting consultant shall have specialized experience and
academic knowledge of commercial explosives, perimeter control blasting applications, vibration, and air -overpressure control. The blasting co nsultant shall use this knowledge to evaluate, plan, and oversee the safe use of explosives in commercial applications in accordance with blasting industry and regulatory standards. The blasting consultant shall review and sign all blasting plans and requi red submittals provided by the blasting contractor. The blasting consultant shall not be an employee of the Contractor or any affiliated companies or suppliers of products to the project and shall not have any conflict - of-interest affiliations with the Age ncy, or other entities involved with the work. The Blasting Consultant shall be required per the Contract documents.
4.Vibration Specialist . The vibration specialist shall be responsible for the vibration and airblast monitoring for blasting events. The vibration specialist shall conduct the operation and deployment of seismographs, geophones, and airblast monitoring equipment for all blasting operations. The vibration specialist shall also be available to discuss vibration results at the request of the A gency. The vibration specialist shall not be an employee of the Contractor or any affiliated companies or suppliers of products to the project and must not have any conflict -of-interest affiliations with the Agency, or other entities involved with the work .
b.Submittals . The Contractor shall submit to the Engineer, the following information for completing the work. Review and acceptance of submittals does not relieve the Contractor of responsibility for the blast results or liability. The Contractor is entirely responsible for the work associated with these submittals.
1.Pre-Construction Submittals . The Contractor shall submit the following information prior to the beginning of the work. Once a complete submittal has been received, the Agency shall be allowed 21 calendar days for the initial review period and shall be allowed 14 calendar days for review of each sub sequent resubmittal. The pre -construction submittals shall be submitted at least 10 working days prior to the pre -blast meeting, outlined in Subsection 205.03(d) . Drilling and blasting operations shall not begin until all of the submittals have been approv ed in writing by the Engineer.
2-33 a. Qualifications .
1.Blasting Contractor . The Contractor shall submit documentation that the blasting contractor has successfully completed at least five blasting projects within the last 3 years with subsurface conditions and blasting of a similar scope and complexity to that anticipated. Docu mentation shall include the names of the general contractor and the owner, descriptions of each past project, and current contact information of a representative of the construction manager or project owner. Contact information shall include at least one v alid phone number.
2.Blaster -in-Charge . The Contractor shall verify that they employ the blaster - in-charge and any alternates assigned to the project. The Contractor shall provide documentation of valid licenses for each blaster -in-charge, including sta te of Vermont Department of Public Safety Explosive License and U.S. Bureau of Alcohol, Tobacco, Firearms and Explosives License. Documentation shall be provided showing that each blaster -in-charge has a minimum of 10 years of experience in blasting with p ast projects of scope and complexity similar to that anticipated. University education in the field of explosive engineering may be submitted by the Contractor to supplement experience per approval of the Engineer. Documentation shall include resumes, refe rences, certifications, project lists, experience descriptions and details. References shall include valid phone numbers for the representatives of the construction manager or project owner from at least 3 past projects involving similar perimeter control blasting. The Contractor shall also provide documentation that each blaster -in-charge attended at least 5 blasting seminars, short courses, or blasting conferences in the last 10 years, and shall include a signed statement from the proposed blaster -in-charge certifying that during the past 5 years they:
2-34 i. Have not been involved in incidents where flyrock traveled within
the active travel way, out of the construction right -of-way, onto private property, caused damage of property, or resulted in injury. ii. Have not had a blasting license restricted or revoked in any state. iii. Have not been fined or sanctioned personally in any way by a regulating authority.
3.Blasting Consultant . The Contractor shall provide documentation that the blasting consultan t has a minimum of 10 years of experience in using perimeter control blasting on projects of scope and complexity similar to that anticipated. The blasting consultant shall have directly participated in at least three projects of similar scope and complexi ty. Documentation shall include the names of the general contractor and the owner, descriptions of each past project, and current contact information of a representative of the construction manager or project owner. Contact information shall include at lea st one valid phone number.
4.Vibration Specialist . The Contractor shall provide documentation that the vibration specialist has directly participated in at least five rock slope and rock removal projects. The documentation shall contain a description of t he projects, details of the vibration control plans, and modifications made during the project. The documentation shall include the names of the general contractor and the owner, and current contact information of a representative of the construction manag er or project owner. Contact information shall include at least one valid phone number.
b.Preliminary Blast Plan . The Contractor shall submit a preliminary blast plan before beginning drilling, when revised drilling or blasting methods are proposed, or a s directed by the Agency. The preliminary blast plan shall clarify the means and methods anticipated to be used during construction to meet blasting tolerances stated in the Contract. The preliminary blast plan shall include, but not be limited to:
2-35 1. A description of the sequence and procedures to be employed to execute the
anticipated blasting operations including the drilling, blasting, fragmentation size, number of blasts, benching details if applicable, and proposed blasting schedule.
2.A descr iption of drilling methods, including production holes, buffer holes and perimeter control holes as applicable, the type of drills, size and type of drill bits, drill hole inclinations, anticipated subdrill depths, burden between rows, hole spacing within rows, and hole diameter.
3.Figures depicting the ty pical plan and area of blasts with profile and sectional views, free faces, burden, bench or lift heights, station limits, blast limits, hole types, burden, hole spacing, depths, diameters, subdrill depths, and inclination.
4.A description of blasting me thods, including types of anticipated explosives to be used, detonators, boosters, blasting agents, type and amount of stemming, method of primary initiation, sequence of delays, any blank or unloaded holes, and detonation methods and timing and loading di agrams.
5.A description and preliminary calculations of charge -weight -per-delay.
6.Manufacturer’s data sheets and safety data sheets (SDS) on all blasting material and equipment proposed, including the type of explosives, blasting agents, cartridge size s and weights, detonators, blast initiation devices, and other equipment required to perform the blast.
7.Station limits for proposed test blast locations.
8.Technical specifications for blasting mats used to cover blasts, including type, size, weight, and number.
9.Plans for control of water, disposal of spoils, disposal of blasting related equipment, materials and waste, and other significant aspects of the work related to drilling and blasting.
10.An organizational chart identifying the key personn el and points of contact for the portion of the work involving drilling and blasting.
2-36 11. Examples of all forms used in the Contractor’s submissions. Individual
forms may require revision for the Agency’s approval.
12.Signature of the blasting consult ant, confirming they have reviewed the preliminary blast plan.
c.Vibration and Noise Control Plan . The vibration and noise control plan shall include a pre -blast condition survey of all buildings, structures, or utilities within a radius of the blasting a rea limits as specified on the Plans. The Contractor shall also notify the residents and owners of these buildings, structures, or utilities of the scheduled blasting activities. At a minimum, notification shall include a certified letter. The pre -blast condition survey shall be conducted by the vibration specialist. Additional buildings, structures, or utilities outside of the radius of the blasting area limits may require a survey and notification , as directed by the Engineer. The vibration and noise co ntrol plan shall include, but is not limited to:
1.A summary naming the person who performed the pre -blast condition survey, including the address or location, owner, and date and time of the survey.
2.Description and measurements of each building, structure , and utility and its existing condition included in the pre -blast condition survey. The Contractor shall also furnish the Engineer with a list of the residents and owners who were contacted and proof of notification.
3.Photos or digital recordings of all cracks and other damaged, weathered, or otherwise deteriorated structural conditions documented in the pre -blast condition survey. Photos and digital recordings shall contain an accurate date stamp.
4.Safe ground vibration and airblast limits for each building, structure, and utility within the radius of the blasting area limits.
5.Calculations for ground vibration, airblast control, and regression analysis to be used to estimate ground vibrations a nd airblasts.
6.Seismograph and airblast monitoring equipment locations, including a scaled map showing locations and the distance from the center of the blast area to the instrument location.
2-37 7. Plan and methods for adequately coupling geophones to the ground surface
at the project location.
8.Certificates of calibration for all monitoring equipment, including recorders, seismographs, sensors, and microphones. The records shall show that the monitoring equipment has been calibrated within 12 months.
9.Examples of all forms used in the Contractor’s submissions. Individual forms may require revision for the Agency’s approval. Any equipment used to monitor the condition of any existing conditions revealed during the pre -blast surveys shall be installed and maintained per the direction and recommendation of the vibration specialist. The vibration specialist shall be responsible for recommending the appropriate equipment to be used.
d.Explosives Transportation, Handling, and Storage Plan . This plan shall include work procedures and safety precautions for the storage, transportation, and handling of explosives including:
1.A list of all authorities having jurisdiction over operations involving the transportation, storage, handling, and use of explosives; c opies of all required blasting permits regarding explosive use and storage; and copies of necessary blasting licenses or authorizations obtained from the state and pertinent localities.
2.A scaled map showing locations where explosives will be kept in tem porary day boxes or delivery vehicles while on site.
3.Information describing how explosives will be inventoried, secured, and guarded to prevent unauthorized use of explosives.
e.Blasting Safety Plan for Use of Explosives . This plan shall include work procedures and safety precautions for the detonation of explosives including:
1.Worker, site, and public safety procedures; blast communication procedures; signage; and equipment details.
2.Means to prevent contamination and deleterious effects to envir onmental and other natural resources.
2-38 3. A complete description of the clearing and guarding procedures that will be
employed to ensure personnel, staff, visitors, and all other persons are at safe locations during blasting. This information shall inclu de details regarding visible warning signs or flags, audible warning signals, method of determining blast area zones, access blocking methods, guard placement and guard release procedures, primary initiation method, and the system by which the blaster -in-charge will communicate clearing and guarding procedures.
4.A description of the equipment and procedures that will be used to monitor the approach of lightning storms and, in the event of such, evacuation and site safety security plans. This includes spec ifications of the lightning detection equipment.
5.Contingency plans for handling of misfires.
6.Fire prevention plan details, including smoking policies, procedures and limitations for work involving any open flames or sparks, description and location of all firefighting equipment, and firefighting and evacuation plans.
2.Pre-Blast Submittals . The Contractor shall submit the following information to the Engineer no later than 8:00 a.m. on the weekday prior to the proposed upcoming blast. The Agency shall be allowed 8 hours to review the submittal and each resubmittal. Reviews will only be conducted on weekdays. Explosive materials shall not be delivered to the site until the submittals have been approved in writing by the Engineer.
a.Pre-Blast Plan . The blaster -in-charge shall submit a pre -blast plan for review by the Engineer. The review of a blasting plan by the Agency shall not relieve the Contractor of responsibility to produce adequate rock breakage, to limit breakage to within the desig n excavation final lines and grades, that project vibration limits are not exceeded, and to ensure that flyrock does not result from the blasting operation. The pre -blast plan shall include, but not be limited to:
1.A scaled drawing showing the location, orientation, number, diameter, and depth of blastholes relative to the specified stations, slopes, lines, and grades.
2-39 2. Calculations showing determinations of maximum charge -per-delay.
3.A detailed log showing the proposed amounts of all explosive s, by type, and stemming used in all charged holes, rock volume calculations, and powder factor calculations.
4.Drawing showing surface initiation and in -hole firing times of all charges.
5.Proposed date and time of blast.
6.A description of methods that will be used to reduce and control flyrock potential.
7.Methods to prevent overbreak, backbreak, endbreak , and loosening of rock not intended to be removed or disturbed by the blast.
8.Locations and distances from the center of the blast area to the seismographs and instruments that will measure ground and air blast vibrations. Locations shall be in degrees latitude and longitude, recorded with a hand -held GPS unit.
9.Proposed location of digital video recorders, from a minimum of two different angles or locations. Videos must be obtained from a location that is close enough to adequately show the blast occ urring.
10.Proposed changes to the preliminary blast plan based on review of the drilling logs.
b.Drill Logs . The blasting contractor shall submit a completed and detailed drill log that includes a record of all holes drilled. An example drill log form i s available from the Agency Geologist per request. At a minimum, drill logs shall include:
1.Project name, date and time of drilling, general weather conditions, and the drilling equipment used.
2.Station limits and bench identification number, if applic able for the drilling operation.
2-40 3. Layout, location, and identification of drill holes. Note that production
holes, buffer holes, presplit or precision presplit holes, and line drilling holes shall be identified as appropriate.
4.Diameter and depth of each drill hole.
5.Planned borehole inclination, drill inclination during operation, final borehole inclination, and any deviation from planned angle at each borehole drilled.
6.Detailed description and depth of key observations and deviations encountered during drilling of each hole, including but not limited to:
i.Jointing or voids. ii. Zones where loss or gain of fluid or air is encountered. iii. Changes in lithology. iv. Changes in the rate of drilling not due to equipment.
v.Color variati on in cuttings. vi. Odors emanating from the drill hole. vii. Soil types encountered. viii. Water bearing zones.
7.Any unrecovered equipment left in a drilled hole.
8.Any collapse of drilled holes or backfilling of holes for any reason.
9.Signature of t he drill operator acknowledging review of the data contained in the drill log.
10.Signature of the blaster -in-charge acknowledging review of the data contained in the drill logs.
2-41 c. Borehole Tracking Report . The blasting contractor shall submit a bore hole tracking
report. An example borehole tracking report form is available from the Agency Geologist upon request. For each perimeter control blasthole, this shall include, but is not limited to:
1.Perimeter control blasthole number, correlated to drill logs.
2.Measured depth (the total length of the blasthole measured along the actual borehole path).
3.Design inclination.
4.Average azimuth. 5.. Average inclination. 6.. Deviation from the inclination shown on the Plans.
7.True vertical depth (measured vertically from the surface down to the depth of the borehole).
8.Drilled offset.
9.Difference between deviation and drilled offset.
10.A statement stating the number of holes in conformance with the specification tolerances for inclination, t he number of holes not in conformance, and the amount to which they are out of tolerance.
11.Description of corrective measures taken for blastholes that are out of tolerance.
12.Signed copy of measured data.
3.Post-Blast Submittals . The Contractor shall submit the following information for approval not less than 48 hours after each blast and before any further blasting operations can continue. Post -blast reports must be completed and accepted by the Agency before the next pre-blast plan is submitted . The Agency shall be allowed 8 hours to review the submittal and each resubmittal. Reviews will only be conducted on weekdays.
2-42 a. Post-Blast Report . The blaster -in-charge shall submit a post -blast report to provide
a full detailed account of the blast . An example post -blast report is available from the Agency Geologist upon request. This shall include, but is not limited to:
1.Blast Details .
i.Blast number, date, time, station location, and weather conditions. ii. Final burden, spacing and number of holes blasted. iii. Calculated volume of blast. iv. Explosive details, including, load parameters, including type, quantity, size, weight of explosives, per type, overall total, and stemming type and depths.
v.Maximum charge weight per delay, for product ion holes and perimeter control blastholes . vi. Total number and type of delays used, number of holes for each delay period, and sequence of time delay. vii. Typical blasthole profiles showing the details of the loading, including subdrilling. viii. Numb er of blasting mats used, type, placement, or other methods to control flyrock.
2.Overall Performance Details .
i.Relative quality of rock fragmentation, including identifying high - bottom areas. ii. Evidence of backbreak, overbreak, endbreak or blast damage along the new slope face including within any half barrel casts. Include station limits and estimated dimensions of damage.
2-43 iii. Amount and measured distance of flyrock ejected.
iv. Any inters ections or areas of over loading or under loading as shown in the constructed rock slope face.
v.A section that includes an evaluation by the blaster -in-charge and blasting consultant of the blast performance. vi. Corrective actions to the blast design and methods should the results of the blasting violate any section of the specification, or the tolerances and intent shown on the Plans.
3.Digital Video Records of Blast .
i.The recordings shall be labeled to identify the blast and location of camera ( e.g. Blast 01 – Position A). ii. Video recordings shall begin at least 10 seconds before the blast and continue recording until there is no evidence of visible dust.
b.Vibration and Airblast Data and Report . The vibration specialist shall submit vibratio n and airblast data. This shall include, but is not limited to:
1.Instruments used.
2.Name of qualified observer and interpreter.
3.Blast number and date.
4.The location of the blast (station and offset, latitude and longitude, and elevation) and the blast area center location (station and offset, latitude and longitude, and elevation).
5.A scaled map showing the location of the blast and the seismographs.
6.Surface material type the geophone has been coupled to at the recording station and the coup ling method.
2-44 7. Summary report from each seismograph, including, but not limited to:
i.Peak particle velocity and frequency of the peak. ii. Peak particle displacement. iii. Peak acceleration. iv. Peak vector sum.
v.Distance from blast center. vi. Maximum charge weight per delay. vii. Airblast overpressure. viii. Confirmation that the vibration data shows conformation with the vibration limits. ix. Calibration verification.
8.Ground vibration and airblast regression analysis, relating s caled distance (square root) to peak particle velocity, and scaled distance (cube root) to airblast pressure level.
9.A dated and signed copy of records of all seismograph ground vibrations and airblast readings.
c.Flyrock Report . If flyrock travels wit hin the active travel way, out of the construction right -of-way, onto private property, causes damage of property, or results in injury, the blasting contractor shall file a flyrock report. This report shall be reviewed by the blasting consultant and submi tted to the Engineer for approval before blasting operations resume. This shall include, but is not limited to:
1.Cause of the flyrock.
2.Methods used to prevent the flyrock, if used.
2-45 3. Methods to be employed on subsequent blasts to reduce the thro w of
flyrock.
4.Plans to prevent future encroachments of private property if applicable.
d.Misfire Report . If a misfire is discovered, the blasting contractor shall file a misfire report. This report shall be reviewed by the blasting consultant and submitted to the Engineer for approval before blasting operations resume. This includes, but is not limited to:
1.Cause of the misfire.
2.How the misfire was discovered.
3.Procedure followed for handling the unexploded explosives.
4.Methods to be employed on the subsequent blasts to prevent future misfires.
c.Site Preparations . The blasting limits as shown in the Plans shall be cleared of all vegetation, overburden, and boulders prior to beginning blasting work. Use of explosive charges is not permitted to blast boulders or remove less than 3 feet of rock above grade. Boulders shall be broken in a manner that s hall not dislodge them and cause them to move downslope. The methods allowed for boulder breaking include hydraulic splitter and hydraulic hammer. Alternative methods of boulder removal may be proposed by the Contractor and submitted to the Engineer for ap proval.
d.Pre-Blast Meeting . A pre -blast meeting shall be held prior to the start of drilling and blasting work and shall be attended by the Agency, the Contractor, the blasting contractor, blaster -in-charge, blasting consultant, and vibration specialis t. The pre -blast meeting shall be conducted to clarify the construction requirements for the work, to coordinate construction activities, and to identify contractual relationships and responsibilities. The pre -construction submittals, outlined in Subsectio n 205.03(b)(1) , shall be submitted at least 10 working days prior to the pre -blast meeting.
e.Public Meeting . To better inform the public about anticipated drilling and blasting operations, at the request of the Engineer, the Contractor shall make their blasting consultant, blasting contractor, and vibration specialist prepare for and participate in a public mee ting conducted by the Engineer. The participants shall be prepared to answer any questions regarding the blasting operations, ground vibrations, airblast overpressure, and flyrock expected to impact the public.
2-46 (f) Blasting Progress Meetings . At the re quest of the Agency, meetings may be held at any time during
the project to review the progress of the blasting operations, discuss modifications to the methods and procedures of the written blast plan, or discuss issues with upcoming blasts. Blasting prog ress meetings shall be attended by the Agency, the Contractor, the blasting contractor, and other interested parties.
g.Explosive Material Handling and Storage . Explosives shall be handled, transported, used, controlled, stored, and monitored in accorda nce with Subsection 107. 10.
h.Test Blasting Program . Prior to commencing full -scale blasting operations, the blasting contractor shall drill, blast , and muck test sections, up to 100 feet in length, to determine if their proposed blast design, including hole spacing, timing, and charges, will meet the objectives of the Contract. If more than one blast design is tested in one test blast, each design section shall be at least 20 feet in length along the final face surface. All requirements for blasting oper ations covered elsewhere in this specification shall apply to the blasting carried out in conjunction with the test blast. The blasting contractor will not be allowed to drill ahead of the test blast until the results have been evaluated and approved by th e Engineer. If the results of the test blasts are unsatisfactory, then, notwithstanding the Engineer’s prior review of such methods, the blasting contractor shall adopt revised methods as necessary to achieve the required results. Unsatisfactory test blast results include an excessive amount of overbreak, backbreak, or endbreak beyond the indicated lines and grade, flyrock, ground vibration, airblast or violation of other requirements within these specifications, or unsatisfactory c ondition of the constructed rock slope face, such as not producing a uniform rock slope face. No additional compensation will be allowed for costs incurred by the blasting contractor in adopting revised blasting methods necessary to produce an acceptable t est blast. If the Engineer suspends blasting operations after full scale blasting has begun, test blasts will be required before full scale blasting can resume.
2-47 (i) Blasting Methods .
1.Types of Perimeter Control Blasting .
a.Line Drilling . Line drilling is defined as a controlled perimeter excavation technique consisting of a series of closely spaced holes that are not loaded with explosives and are drilled along the excavation line. The line drill hole spacing shall be no greater than twice the line drill hole diameter as stated in the Plans.
b.Presplitting . Presplitting is defined as a method of controlled blasting utilizing a row of closely spaced, lightly loaded blastholes placed on the perimeter of the excavation and fired before the p roduction holes. The presplit blastholes shall be a minimum of 2 inches and maximum of 3 inches in diameter. The presplit holes shall be drilled with a minimum spacing of 10 times the presplit hole diameter and a maximum spacing of 12 times the presplit h ole diameter. Presplit hole loads are limited to 0.35 pounds of explosive per foot of blasthole. The maximum diameter of explosives used in presplit holes shall not be greater than half the diameter of the presplit hole. Presplit blastholes shall be fired before production holes. If presplitting and production holes are fired within the same blast, all presplit blastholes shall be fired at least 25 milliseconds before the production blastholes are detonated. Line drilling along final walls may be requ ired at corners where presplit lines meet. Subdrilling 2 feet below ditch bottom will be allowed to facilitate removal of the toe berm.
c.Precision Presplitting . Precision presplitting is defined as utilizing more closely spaced blastholes than presplitti ng with lighter explosives loads. This method of perimeter control matches the strength of the explosives to the strength requirements of the rock to cause the web of rock between the precision presplit holes to fail in tension with the minimum energy need ed and to create the split without damaging the constructed rock cut face. The precision presplit blastholes shall be a minimum of 2 inches and maximum of 3 inches in diameter. The precision presplit holes shall be drilled with a minimum spacing of 4 time s the precision presplit hole diameter and a maximum spacing of 8 times the precision presplit hole diameter. Subdrilling 2 feet below ditch bottom will be allowed to facilitate removal of the toe berm.
2-48 (2) Production Blasting . Production blasting is blasting in the mass of rock to be excavated
and shall be designed to control flyrock, minimize ground vibration and airblast, and result in loosened and fragmented rock suitable for excavation using conventional earth moving equipme nt. Production blastholes shall be in a consistent pattern that does not affect the perimeter control blastholes . To control blasting effects, the blasting contractor shall maintain a burden distance that is not more than one half the bench height and bet ween 25 times and 35 times the diameter of the explosive charge in the blasthole . If the first row of production holes adjacent to the presplit face are intended to be buffer holes, they shall be drilled no less than 4 feet from the presplit line and shall mainta in a stand -off distance between the production explosive charges and the presplit line of no less than three 3 feet. Sub drilling 2 feet below ditch bottom will be allowed to facilitate removal of the toe berm.
3.Buffer Holes . Buffer holes are located between the production holes and the perimeter control blast line. Buffer holes may be battered at the same angle as the presplit face or may be vertical.
4.Blasthole Drilling .
a.General Requirements . All blastholes shall be co vered after drilling to keep overburden and debris from falling into the holes. All blastholes shall be marked with the hole number and depth. Blastholes shall be free of obstructions for their entire depth.
b.Equipment . The blasting contractor shall con trol drilling operations using proper equipment and techniques to ensure that no hole deviates from the tolerance set for both depth and alignment. All drilling equipment used to drill blastholes shall be equipped with an electro - mechanical or electronic device that accurately determines the angle, within 1 degree, at which the drill steel enters the rock. Drilling will not be permitted if these devices are either missing or inoperative.
2-49 c. Tolerances . The blasting contractor will be required to use a borehole alignment
unit affixed to a laser profiler to determine blasthole orientation on all perimeter control blastholes. The blasting contractor shall submit the borehole tracking data as outlined in Subsection 205.03(b)(2)c. This requirement may be waived temporarily when, in the opinion of the Engineer, the borehole alignment is satisfactory. Required borehole tracking may be reinstated at the discretion of the Engineer. Any blastholes deviating from alignment on the plane of the planned slope, eith er parallel or normal to the slope, by more than the tolerances shown on the Plans, shall be refilled with crushed stone stemming or cementitious grout, re -drilled at the proper location and at the proper alignment, and borehole tracked, at no additional cost to the Agency.
5.Blasthole Loading . The blastholes shall be cleaned out prio r to loading to remove cuttings, collapses, or other debris, including removal of water if using non -water -resistant explosives. All blastholes shall be checked and measured before any explosives are loaded into any of the holes to eliminate any safety haz ard resulting from drilling near loaded holes. Stemming material used in production holes shall consist of dry, unfrozen, angular crushed stone having an optimum average diameter of 0.05 times the diameter of the blasthole . Drill cuttings shall not be use d as stemming, with the exception of precision presplit blastholes. If fractional portions of standard explosive cartridges are used, they shall be firmly affixed to the detonating cord in such a manner that the cartridges will not slip down the detonating cord nor bridge across the hole. Spacing of fractional cartridges along the length of the detonating cord shall not exceed 30 inches center to center and shall be adjusted to produce the desired results. Continuous column cartridge types of explosives use d with detonating cord shall be assembled and affixed to the detonating cord in accordance with the explosive manufacturer’s instructions, a copy of which shall be furnished to the Engineer. The bottom charge of a presplit or precision presplit hole may be larger than the line charges but shall not be large enough to cause overbreak. The top charge of the presplit or precision presplit hole shall be placed far enough below the collar, and reduced sufficiently, to avoid overbreaking and heaving. The upper po rtion of all presplit and precision presplit holes, from the topmost charge to the hole collar, shall be stemmed.
2-50 (6) Required Mucking of Constructed Blast Face . The Contractor shall complete mucking
following each blast to allow inspection of the rock cut, approval of the blast face, and allow for adjustments to the blast design for subsequent blasts . All rock on the constructed cut face that is loose, hanging, or which creates a potentially dangerous situation due to risk of rockfall occurring shall be removed to the satisfaction of the Engineer during or upon completion of the mucking. Drilling and loading for the next blast will not be allowed until the required mucking of the previous blasts has been completed and the face is approved. If subsequent blasting causes damage to an already approved area, then the damaged areas will be readdressed to the satisfaction of the Engineer.
j.Stabilization . Stabilization of the rock cut shall be performed in accordance with Section 221 and as directed by the Engineer, as needed. If subsequent blasting causes damage to an already approved stabilized area, then the area may be required to be restabilized at t he discretion of the Engineer.
k.Vibration and Noise Control . The vibration specialist shall submit the pre -blast condition survey as outlined in Subsection 205.03(b)(1)c. The vibration specialist shall establish the safe ground vibration and airblast limit for each building, structure, and utility within the radius of the blasting area limits, as specified on the Plans.
1.Vibration Control and Monitoring . The vibration s pecialist shall monitor ground vibrations and airblast at each building, structure, and utility within the radius of the blasting area limits, as specified on the Plans.
a.Locations .
1.A minimum of 3 seismographs shall be used for every blast event. Th e vibration specialist shall be responsible for guaranteeing the appropriate number of seismographs are used in blasting operations. Locations shall be included in the vibration and noise control plan, as outlined in Subsection 205.03(b)(1)c. , and be appro ved by the Engineer. The vibration data collected by these seismographs will be used to ensure excessive vibration is not being transmitted into the rock mass beyond the presplit face.
2.The placement of seismographs and geophones shall be made with the concurrence of the Agency and the vibration specialist.
2-51 3. Whenever vibration damage to adjacent structures is possible, the blasting
contractor shall monitor each blast with approved seismographs located between the blast area and the closest structur es subject to blast damage.
4.The geophones shall be affixed to exposed bedrock or buried sufficiently in natural soils to ensure full coupling.
b.Equipment .
1.All vibration measuring equipment shall be used in accordance with the standards established by the Vibration Section of The International Society of Explosives Engineers.
2.The seismographs used shall be capable of recording peak particle velocity in the three mutually perpendicular components of vibration in the range generally found with per imeter control blasting, the vector sum of these peak particle velocities, and the frequency history of the vibrations.
3.The vibration measuring equipment shall be calibrated within 12 months of the time of use and operated by properly trained personnel.
c.Limits .
1.The peak particle velocity and dynamic displacement of each component shall not be allowed to exceed the safe limits of the nearest structure subject to vibration damage or at areas designated in the Plans, as determined by the vibration sp ecialist, and as approved by the Engineer.
2.Airblast and Noise Control . The vibration specialist shall conduct airblast monitoring for each blast.
a.Location .
1.The vibration specialist shall be responsible for guaranteeing the appropriate number of airblast monitoring instruments are used in blasting operations. Locations shall be included in the vibration and noise control plan, as outlined in Subsection 205.03( b)(1)c. , and be approved by the Engineer.
2-52 2. Airblast monitoring equipment shall be installed between the main blasting
area and the nearest structures subject to blast damage, annoyance, or at areas designated on the Plans.
b.Equipment .
1.The equipm ent used to measure the airblast shall be of the type specifically manufactured for that purpose and shall be approved by the Engineer.
2.The equipment shall be calibrated within 12 months of the time of use and operated by properly trained personnel.
c.Limits .
1.Peak overpressure shall be held below 130 decibels at the nearest structures or other designated locations when measured using a 0.1 Hz high-pass linear peak method.
2.Appropriate blasthole patterns, detonation systems, and stemming shall be used to prevent venting of blasts and to minimize airblast and noise levels produced by the blasting operations.
3.The overpressure limit shall be lowered if it proves too high based on damage or complaints.
3.Vibration and Airblast Data and Report . The vibration specialist shall submit the vibration and airblast data and report as outlined in Subsection 205.03(b)(3)b. The vibration specialist shall keep an up -to-date database of the vibration data that shall include ground vibration and airblast d ata for each blast event. The database shall include regression analysis of both ground vibration and airblast data. The information from this database shall be made available to the Agency upon request.
l.Flyrock .
1.Flyrock Control . Where flyrock cou ld cause property damage or injury to the public, the following shall apply:
2-53 a. The blasting contractor shall protect all overhead and underground utilities prior to
blasting and immediately repair or replace any utilities damaged by the blasting operations. If the blasting contractor wishes to temporarily relocate any utility lines that lie near a blast zone, they shall have written approval from the governing utilities and pay all relocation costs.
b.Where required by the Engineer, the exposed faces of the blast shall also be covered with blasting mats or other suitable materials t o prevent formation of any flyrock. The method of covering shall be approved by the Engineer.
2.Flyrock Report . If flyrock travels within the active travel way, out of the construction right - of-way, onto private property, causes damage to state or priva te property, or results in injury, the blasting contractor shall file a flyrock report as outlined in Subsection 205.03(b)(3)c.
m.Suspension of Blasting . Blasting operations may be suspended by the Engineer as outlined in Subsection 107. 10.
n.Safety . The Agency shall have the authority to prohibit or halt the Contractor’s blasting operations if it is apparent that through the methods being employed the blasted slopes are unstable or that the safety and convenience of the traveling public is bei ng jeopardized.
1.Warnings and Signals . Warnings and signals shall be in accordance with Subsection 107.10.
2.Lightning Protection . Lightning protection shall be in accordance with Subsection 107. 10.
3.Misfires .
a.Post-Blast Check . The blasting contractor shall observe the entire blast area following a blast to guard against rockfall before commencing work in the cut. The delay between blasting and allowing anyone but the blaster -in-charge to enter the area is needed to make sure t hat no misfires have occurred. It is the blaster -in-charge’s responsibility to go into the blast area and check all holes to make sure that they have detonated. If any holes have not fired, these misfires will be handled by the blaster -in-charge before ot hers enter the work area.
2-54 b. Handling . When it is discovered that that complete detonation of all charges did not
occur, only critical personnel involved in the blasting operation or excavation of the unexploded material will be allowed within the est ablished blasting area. Access to the site shall be restricted until the blaster -in-charge indicates that the site is safe. If the misfire poses problems that cannot be safely corrected by the blaster -in- charge, a consultant, or an explosives company representative skilled in correcting misfires shall be consulted to resolve the problem. Compliance with this or any other provision in the Contract shall not relieve the Contractor of responsibility for any damage or injuries caused by, related to , or arising out of blasting or associated blasting activities. Costs associated with resolving misfire problems will be the sole responsibility of the Contractor.
c.Misfire Report . If a misfire is discovered, the blasting contractor shall file a misfire report as outlined in Subsection 205.03(b)(3)d. 205.04 METHOD OF MEASUREMENT . The quantity of Drilling and Blasting of Solid Rock Subgrade to be measured for payment will be the number of square yards of subgrade plan area drilled and detonated in accord ance with this section, measured at the bottom of subbase. The number of cubic yards of excavation required by the Engineer to inspect the depth of shattered and rearranged rock, computed at a maximum width of 30 inches, will be measured for payment as Tre nch Excavation of Earth. Any area designated as Trench Excavation of Rock will not be included in the measurement and payment for Drilling and Blasting of Solid Rock Subgrade. The quantity of Drilling and Blasting Using Perimeter Control to be measured for payment will be the number of cubic yards of rock blasted and mucked to the constructed rock slope face limits shown on the Plans. 205.05 BASIS OF PAYMENT . The accepted quantity of Drilling and Blasting of Solid Rock Subgrade will be paid for at the Contract unit price per square yard. Payment will be full compensation for performing the work specified including any necessary stripping of rock below the bottom of subbase and refilling with approved material to the bottom of subbase, the removal of blaste d subgrade rock that may swell above subgrade, and its disposition on the project as shown in the Plans or as directed by the Engineer. Excavation and backfill required to inspect the depth of broken rock below subgrade will be paid for at the Contract uni t price per cubic yard for Trench Excavation of Earth.
2-55 The accepted quantity of Drilling and Blasting Using Perimeter Control will be paid for at the Contract
unit price per cubic yard. Payment will be full compensation for clearing, grubbing, and remo ving overburden prior to blasting; drilling, borehole profiling, loading of blastholes; performing blasting; mucking and removal of the excavated rock; vibration and noise control; and for furnishing all labor, tools, equipment, and incidentals to complete the work. Payment for preparing and making required submittals will not be made separately but will be considered incidental to the work under this section. Payment will be made under: Pay Item Pay Unit 205.1000 Drilling and Blasting of Solid Ro ck Subgrade ................................ ......... Square Yard 205.2000 Drilling and Blasting Using Perimeter Control ................................ ........ Cubic Yard
2-56 Section 206 – Rock Slope Scaling
206.01 DESCRIPTION . This work shall consist of excavating loose and dilated rock on slopes. This work includes high -angle construction to be completed via hand scaling using industrial rope access methods or machine scaling. 206.02 SUBMITTALS . The Contractor shall submit to the Engineer the following information for completing the work. Work shall not begin until the submittals have been approved in writing by the Engineer.
a.Qualifications . Not less than 14 calendar days prior to beginning any rock slope scaling, the Contractor shall provide qualifications of Contractor’s personnel to the Engineer. The Contractor shall provide written evidence that the rock slope hand scaling foreman has a minimum of 5 years of demonstrated scaling experience as a foreman and rock slope hand scalers have a minimum of 2 years of demonstrated scaling experience. Operators for machine scaling shall have at least 1 year of demonstrated experience in machine scaling rock slopes.
b.Work Plan . Not less than 14 calendar days prior to beginning the work, the Contractor shall submit a detailed work plan for each rock slope to be scaled. The plan shall include:
1.The proposed rope access methods and safety plan.
2.The proposed construction sequence and schedule.
3.The types of equipment and tools to be utilized during the proposed work.
4.The number of rock slope scaling crews and the numbers of qualified working supervisors and qualified scalers in each crew.
5.The number of qualified machine sca ling operators.
6.Rock removal and disposal plan for rock debris generated from the rock slope scaling work.
7.Full details of protection measures to be used during rock slope scaling that shall protect the roadway from scaled rock.
Source: Vermont Standard Specifications for Construction, 2024 Edition. Pages 171–195 of 1,380.