# Chapter 6: The Blast Design Process

The blast design process is composed of a combination of interrelated parameters for the blast that incorporate the principles discussed in chapter 14. This chapter's discussion assumes that the best design for rock breakage should be evaluated for its maximum downstream benefit, and that only unavoidable overriding factors should alter that design.

Historically, blasters have been solely responsible for evaluating design parameters and designing the blast, but they typically did not evaluate downstream processes. Today blasters may find that in some operations, there are services and products available to help with the blast design process in part or in total. Some do the complex analysis of delay timing, and some simulate the rock breakage process based on explosive performance and geologic properties. With or without technology the objective is to break the rock with an explosion is based on the same principles discussed in Chapter 14.

Many limiting factors are identified in the documents, evaluations, inspections and equipment availability indicated in figure 6.1. These factors can change up until the time of the blast. Some factors are generally known early in the process, and some are not known until the design is completed. For this reason the blast designer should be prepared to make changes.

Before the design process begins a very specific objective and set of goals should be clearly stated and agreed to by all project "stakeholders".

## Stakeholder

A stakeholder is a person who has a specific responsibility for blast results or one that may be impacted by blasting operations.

Many times a design is simply a repetition of one used before. Although this process is fast, it is ineffective if conditions have changed at the blast site. For example, if the drill needs to be replaced the borehole diameter may change and the job site may not provide adequate space for its setup and mobility requirements. A drill change may require changes in multiple design parameters. If the proper explosives are not available, inappropriate substitutions may occur. Proceeding with the design without making necessary adjustments invariably leads to less than satisfactory performance and some stakeholder dissatisfaction. If site changes occur that cannot be incorporated, the blaster-in-charge should be prepared to postpone or cancel the blast until satisfied rather than take unwarranted risks.

![Figure 6.1: Blast design process](images/046.png)

*Figure 6.1 – Blast design process.*

Ultimately blast designs specify four basic parameters: (1) borehole locations, (2) explosives selections, (3) borehole loading schemes describing the size and position of charges within each borehole, and a (4) delay diagram that describes the sequence of detonations.

## Objective And Goals

A blasting project has only one objective—break rock—for a specific operation. The operation dictates the degree and type of breakage required. Table 6.1 suggests some common blasting objectives. For any blast there may be one or more goals to enhance one aspect of the design. Multiple goals should be ranked in order of priority. Multiple project goals may conflict and require different final designs and its anticipated outcomes.

Often different goals require different design provisions. Safety is always the overriding goal. In the end, every blast should produce (1) minimal damage to the remaining rock mass and (2) a hazard free post blast area. Some goals often represent different stakeholder responsibilities. Blasters and designers can find themselves between conflicting directives. The blast design obviously becomes the technical plan to best break the rock and satisfy as many goals as possible. Goals should be organized in the most appropriate goals order and the project as not penalized due to performance.

The designer's focus on a single objective helps achieve good results, effectively incorporate changes due to limiting factors, and avoid problems.

### Basic Blasting Objectives

| **Objective** | **Intention** |
|---|---|
| Fragment size distribution | Mining and quarrying |
| Fature handling ease | Trenching |
| | Excavations where the broken rock is not the final product |
| | Breaking oversize material |
| Stable final wall or surface | Presplit / trim |
| | Final standing width or radius |

*Table 6.1 – Basic blasting objectives.*

Since all goals are important, it is imperative they are clearly documented in writing and prioritized by the stakeholders. Some typical blasting goals are listed in table 6.2.

### Typical Blasting Goals

| **Goal** | **Purpose** |
|---|---|
| Fragmentation | Optimize digging and hauling |
| Rock displacement | Control face bursting |
| Diggability | Improve Excavator performance |
| Muckpile control | Improve material flow |
| Vibration control | Provide for public protection |
| Final condition of the remaining rock mass | Ensure regulatory compliance |
| | Preserve next blasting surface |
| | Preserve post blast access roads |
| | Control ore dilution or damage |
| Cost | Optimize or control overall process cost on individual line item cost. |

*Table 6.2 – Typical blasting goals.*

Documentation helps evaluate blast results. It is not uncommon for different goals to require different design provisions. For example the best fragmentation size distribution may satisfy the mill or crusher operator but may not satisfy the excavator operator. Possibly if a blast is oriented to move in a specific direction it may result in higher than allowed vibrations and the safety for relative structures.

## Site Evaluation

A thorough site evaluation identifies specific site factors that restrict or "limit" a blast design. It also includes review of past blast performance so that good practices are repeated and poor ones avoided. At a minimum, the factors in table 6.3 should be investigated and reviewed in advance. As a result, a complete site evaluation ensures that as many design limiting factors as possible are identified and addressed. Limiting factors discovered too late may prevent achieving the desired results and may also compromise safety. A well-documented evaluation ensures issues do not go addressed and overlooked.

It is apparent that any one of the factors in table 6.3 can limit one or more design parameters. Three factors that typically limit designs are (1) geologic structures and rock quality variations, (2) ground water conditions, and (3) proximity to sensitive locations. For example undetailed design changes in geology can adversely affect delay patterns, affect final wall conditions, or create over drillers. When unforeseen ground water conditions occur, the explosive performance may be affected if the water is not removed or the explosive changed. As the project development progresses, the blast site may get too close to inhabited buildings or roadways limiting the blast design. When time limiting factors are recognized they can be addressed with effective design changes or other alternatives.

### Limitations of Blast Site Factors

| **Factor** | **Limitation** |
|---|---|
| Rock type | Explosive selection |
| Rock mass blastability | Fragmentation results |
| | Vibration results |
| Project specifications | Blast movement limitations |
| Proximity to sensitive locations | Vibration restrictions |
| | Rock movement limitations |
| Changing rock condition and quality | Flyrock potential |
| | Air blast |
| Free face condition and relief | Ore damage |
| | Noise potential |
| Size and topography of site | Rock movement |
| | Fragmentation |
| Geologic structures and rock quality variations | Potential ore dilution areas |
| | Optimum face orientation |
| | Air blast |
| Potential water conditions | Explosive choice |
| | Dewatering requirements |
| | Regulatory compliance |
| Topography of drilling surface | Requires varying borehole depths |
| Available explosives | Pattern |
| | Product water resistance |
| Available drill types | Borehole diameter |

*Table 6.3 – Blast site evaluation list.*

## Design The Blast

Initially the designer should be guided by only what is necessary to break the rock to achieve the objective. This focused approach results in an objective design solution. This section's discussion sets a systematic rigor for the design process. Final design parameters are interdependent and must be considered in total. Since one parameter affects another, the final effects should be reviewed and redesigned as suggested in table 6.4 to ensure their collective performance. Regardless of the factors driving the design, the final design should review parameters in this sequence to verify the design.

### Downstream Effect of Blast Design Parameters

| **Parameter** | **Downstream effect** |
|---|---|
| Rock Mass | Determines starting set of specific energy characteristics |
| Rock Structures | Deck placement and size |
| Explosive type | Match performance characteristics to rock |
| Explosive selection | Specific explosives must have desired properties and performance characteristics (verify with manufacturer) |
| Borehole diameter | Size must allow required energy level through loading density |
| Borehole length | Produces required bench depth or round advance |
| | Multiple pass operations should optimize drill pass capability |
| | Possible underburden at hole and may result in potential possible radial cracking ratios |
| Burden | Supports fragmentation at grade |
| | Forces radial cracks damage to bust heel or toad rock |
| Stemming type | Dry design assures height |
| | Pure also helps for air overpressure |
| | Prevents flyrock |
| Delay sequence | Determines crack burdens and spacing ratios to direct rock movement |
| Decks | Split charges by created energy losses at geologically weak areas |
| | Split charges for separate delay times |
| | Enhance performance in the column (air decks) |
| | Reduce explosive cost |

*Table 6.4 – Ideal Blast designing sequence.*

All other factors than those listed in table 6.4, including site conditions, equipment availability, explosives availability, budgets, and regulatory rules only serve to limit the design and cause it to be modified. If these other factors are moved too early in the decision process, the most objective solution may never be considered.

All limiting factors should be evaluated to determine, if not accommodated, they could cause financial or legal penalties or future operational problems. At this point all factors should be ranked in order of their importance to the project because it may not be possible to effectively address all of them in the design.

In this way, the blast will satisfy the most vital conditions for the project. When one parameter is changed, its effect on other parameters should be investigated. Refer to table 6.4 for guidance. This ensures the modifications are compatible with all other decisions already finalized.

To minimize the time required for this refining process, the designer should collect as much information about the blast site and performance of previous blasts as soon as possible. The final design must satisfy the five basic performance factors discussed in chapter 14 as illustrated in figure 6.2.

![Figure 6.2: The five principal blast performance factors](images/050.png)

*Figure 6.2 – The five principal blast performance factors.*

## Communicate The Requirements

Once the design is reviewed and agreed to by all "stakeholders", the designer should communicate the design in writing to the driller and explosives supplier to ensure that on the blast loading day the drills are drilled correctly and adequate quantities of products are available. The blast design is the vital element of the blast plan that specifies how the blast will work by (1) stating the objective and specific goals, (2) quantifying all design parameters, and (3) stipulating all explosive requirements.

## References

Rorke, Albie, Peter G. Gilmer. 2009. Improvements in blasting technology at Culls Natural Resources. International Society of Explosives Engineers (ISEE) Proceedings of the 35th Annual Conference on Explosives and Blasting Technique, February 8 – 11, Denver, CO. ISEE, Cleveland, OH.

## Additional Resources

Adbitkari, G.R. 2004. Blast design methodology for surface mines an integrated approach to optimization, Part I. The Journal of Explosives Engineering, Vol. 18, no. 44, pp. 1 – 3. International Society of Explosives Engineers, Cleveland, OH.

Adbitkari, G.R. 2004. Blast design methodology for surface mines an integrated approach to optimization, Part II. The Journal of Explosives Engineering, Vol. 18, no. 5, pp. 1 – 4. International Society of Explosives Engineers, ISEE, Cleveland, OH.

Higgins, Mike. 1997. JK Simblast-New software for the design, simulation, and analysis of blasting. JK Tech, JKMRC, Commercial division: Australia; International Society of Explosives Engineers Seventh High Tech Seminar, Orlando, FL.

Sames, Frank, Brad Terhune. 2004. Engineering control and information management of blasting programs in construction and quarrying operations. International Society of Explosives Engineers Proceedings of the 30th Annual Conference on Explosives and Blasting Technique, February 1 – 4, New Orleans, LA. ISEE, Cleveland, OH.

Wallace, Jerry. Handling Third-party Assigned Risk in construction Blasting. Wallace Technical Blasting, Inc.