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How Controlled Blasting Methods Kept a Water Tower Safe

How do you execute a quarry blast just 30m from a water tower without causing structural damage?

At the Powhatan quarry in Virginia, high-stakes blasting near infrastructure was necessary to straighten a bench face 30m from a water tower and adjacent to a new crusher. But close-proximity blasting demands precise control over burden distribution and energy release – any miscalculation could have resulted in severe structural damage. As the shotfirer put it: “This was a hero or zero shot.”

Using 3GSM software, a high-resolution 3D photogrammetric model, adaptive borehole geometry, and electronic detonation sequencing, engineers successfully executed a controlled blast that prevented all damage to the water tower and conveyer belt from flyrock.

Figure 1. A photograph of the area to blast (circled) and the water tower 30m away. On the left, there is a newly erected crusher.

Surveying the Site With High-Resolution 3D Modelling 

To optimize quarry blast design, a drone-based photogrammetric survey was conducted, capturing 170 high-resolution images of the blast site. These images were processed into a 4-million-point 3D model in BlastMetriX with a ground sample distance of 1.2cm and a residual error of 1.7cm. This level of precision ensured the blast plan accounted for localized variations in geological conditions, which reduced uncertainty in execution. 

Specifically, this dataset provided: 

  • High-fidelity burden analysis, so adjustments to hole spacing and inclination could be made. 
  • Accurate georeferencing enables precise bench face profiling, interactive blast design, and the staking out and drilling of the optimized pattern.  
  • Burden heat mapping, which allowed for real-time modifications to the drill pattern. 
Figure 2. A 3D model of the area to blast, including the camera locations from the drone survey.

Designing the Blast for Maximum Control 

Given the proximity of infrastructure, standard blast parameters were adjusted to mitigate damage from flyrock: 

  • Boreholes adjacent to the water tower were inclined at 10°, following the standard pattern. However, using the burden heat map for optimization, inclinations were adjusted between 15° and 20°. 
  • Increased burden (6.7m vs. 4.9m in the main blast zone) as specified for the row facing the water tower to modify the blast’s geometry and loading conditions. 
  • Stemming depths of 9.1m, applied to boreholes near the water tower, in accordance with the blast plan. 

The borehole distribution was dynamically adjusted using burden heat maps, ensuring that each hole adhered to site-specific geometric constraints. 

Figure 3. The burden distribution visualization that dynamically updates when the drill pattern is adjusted. The left side, facing the water tower, was designed with intentional overburden for added control.

Executing a Precise Blast with Electronic Detonators 

To further refine control, electronic detonators were used, allowing millisecond-scale precision in the firing sequence. The timing was structured to: 

  • Initiate the free face centrally, as designated in the firing sequence to control the progression of the blast. 
  • Utilize a 25ms delay between adjacent holes to regulate detonation timing across the pattern. 
  • Introduce a 100ms delay in the row facing the water tower, following the design parameters for sequencing near critical infrastructure. 
  • Reduced powder factor in critical areas (89 g/t vs. 200 g/t in the main shot) following design specifications for the row closest to the water tower. 

The Results: A Successful, Damage-Free Blast 

Using high-resolution surveying, adaptive blast modeling, and precision electronic detonation, the team successfully executed a high-risk quarry blast with zero collateral impact and damage on the nearby infrastructure.  

Figure 4. A photograph of the blast, which went absolutely controlled with no damage detected to existing infrastructure.

Incorporate 3GSM Into Your Workflow 

With BlastMetriX, you can execute controlled blasts reliably and safely. Start your free trial of 3GSM software here and see how advanced 3D modelling and burden analysis can improve your next blast design.