Development of the PETS Toolbox Boulder Splitting Capability Calculator

Lessons Learned from Jackson Hole, Wyoming

During the Practical Explosives Training School (PETS) conducted in Jackson Hole, Wyoming, we had the opportunity to work with an experienced team of blasters responsible for removing large boulders located near critical engineering structures and infrastructure.

One of the major challenges facing the blasting team was how to safely remove oversized boulders while minimizing vibration, flyrock, airblast, and potential impacts on nearby structures. Because of these concerns, the team selected a non-detonating double-base propellant system known as NXBurst.

Unlike conventional explosives, NXBurst cartridges do not detonate. Instead, they deflagrate, producing high-pressure gases that generate tensile fractures within the rock mass. This process allows the blaster to split the rock in a controlled manner while significantly reducing many of the hazards commonly associated with traditional blasting operations.

The NXBurst cartridges were initiated using a non-electric initiation system combined with surface delays to control the firing sequence and improve crack propagation throughout the boulder.

As part of the training, students and instructors observed numerous boulder-splitting operations and evaluated the effectiveness of different drilling patterns, burden-and-spacing relationships, stemming methods, and delay-timing sequences. These field observations provided valuable information regarding how double-base propellant systems perform under actual operating conditions.

One of the most important outcomes of the training was calibrating the PETS Toolbox Boulder Splitting Capability Calculator.

The purpose of this calculator is to provide drillers and blasters with a practical engineering tool that can be used to estimate:

• Boulder volume
• Estimated rock weight
• Number of drill holes required
• Hole burden and spacing
• Hole depth
• Number of cartridges required (We used 1 per hole)
• Stemming requirements
• Delay timing recommendations
• Split likelihood
• Field risk level

The calculator is intended to provide a starting design that can be refined through field experience and site-specific calibration.

Importance of Field Validation

No calculator can fully account for the variability found in natural rock masses. Rock strength, jointing, weathering, natural fractures, and confinement conditions all influence splitting performance.

For this reason, field validation is essential.

After each shot, the blaster should document:

• Rock type
• Boulder dimensions
• Hole diameter and depth
• Burden and spacing
• Number of cartridges
• Delay timing
• Stemming method
• Splitting results
• Venting observations
• Rifling observations
• Flyrock observations

Over time, these data can be used to refine the design factors and develop site-specific design tables that improve future performance.

Venting and Rifling

During the Jackson Hole training, two recurring field issues were identified:

Venting: Venting occurs when high-pressure gases escape from the hole collar before sufficient pressure develops within the rock mass.

Rifling: Rifling occurs when high-pressure gases travel along the stemming column and eject stemming material from the collar of the hole.

Both conditions reduce the amount of useful energy available for rock fracture because gas pressure is released to the atmosphere instead of being confined within the borehole.

In simple terms:

The longer the pressure remains inside the hole, the more work it can perform on the rock.

Improving Confinement

One method currently being evaluated by PETS involves placing approximately 2–3 inches of non-hardening modeling clay at the collar of the hole above the crushed-stone stemming column.

The objective is to:

• Improve gas retention
• Reduce venting
• Reduce rifling
• Reduce collar ejection
• Improve fracture propagation
• Increase splitting efficiency

Only the upper 2–3 inches of the collar should be sealed with clay. The remainder of the hole should continue to use angular crushed-stone stemming to provide controlled confinement and safe gas release.

Continuous Improvement

The PETS Toolbox Calculator is intended to evolve as additional field data becomes available.

Every shot provides valuable information. Every successful split improves our understanding of the relationship between:

• Rock properties
• Boulder geometry
• Hole design
• Stemming effectiveness
• Delay timing
• Double-base propellant performance

By collecting and analyzing field results, blasters can move from trial-and-error practices toward repeatable engineering procedures that improve safety, productivity, and overall splitting performance.

PETS Philosophy

Measure → Calculate → Drill → Load → Stem → Time → Fire → Evaluate → Improve

The goal is not simply to split rock, but to continuously improve the process through observation, documentation, and engineering analysis.