Engineering Solutions for Erosion and Water Management in Mining Construction During the Rainy Season

Introduction:

The rainy season in Mexico can pose significant challenges for construction and mining projects, threatening the integrity of structures and causing costly delays. Effective erosion and water management are crucial to ensuring structural stability, protecting the environment, and maintaining operational efficiency. This article will explore key engineering strategies and materials used to mitigate the impact of torrential rains in general and practical terms, drawing on examples from one of our recent projects; ROM Pad at La Terronera.

Understanding the Challenge:

During intense rainfall, uncontrolled runoff can cause significant erosion, resulting in the movement of soil and sediment. This can compromise the integrity of slopes, clog drainage systems, and negatively impact water quality. In mining construction, where large earth works are common throughout all stages of a mine’s lifecycle, from exploration, construction, operation, and closure, these challenges are significant, both for the mine and for the nearby communities. It’s important to note that proper management of these works is mandatory to comply with federal and international regulations.

Solum’s Engineering Strategies and Solutions:

To manage erosion and water efficiently and effectively, engineers employ a combination of design strategies and the use of different types of materials:

• Water Diversion
  • Temporary ditches and water diversion crossings are used to divert and control stormwater from critical or heavily traveled areas. These structures are designed with appropriate slopes and dimensions to manage anticipated flows according to established project criteria and an acceptable risk level for each structure type.
  • Crossings (surface crossings) can also be implemented to facilitate water flow through access roads or platforms, preventing water accumulation in undesirable areas and maintaining necessary vehicular traffic.
• Sediment Control
  • Horizontal ditches are constructed along slopes to intercept runoff and reduce its velocity, thus minimizing erosion.
  • Sediment barriers, such as those constructed from sandbags filled with local material, can further impede sediment transport.
  • Rock barriers placed within ditches every 10 to 20 meters also help slow water flow and trap sediment.
  • Geomats and geogrids are placed to minimize water velocity, thus minimizing the transport of unwanted sediment.
  • Constructing sediment control basins is a very effective and rapid method without the need for special materials.
• Slope Stabilization
  • Geobags are often used to build temporary retaining walls and reinforce slopes, either mid-slope, placed on a curb, or at the foot of the slope. These bags are filled with granular material, which is then compacted, achieving the desired structural support based on the density generated in each geobag. The design of these structures must be reviewed to avoid creating an unstable structure that could cause failure and rapidly discharge the retained material, causing additional damage downstream.
  • Geotextiles can be used in conjunction with geobags to provide filtration and separation (using a woven geotextile), preventing sediment from seeping through the geobag structure.
• Drainage Management
  • Proper design of drainage systems, including culverts and channels, is essential for safely evacuating water from the site.
  • Modifying the slope of access roads and other surfaces can also help control water flow and prevent it from entering vulnerable areas.

It is important to have a contingency plan for work areas that may be impacted by rainfall and cause unexpected delays or damage. Solum prepared a Rainfall Contingency Plan for La Terronera Mine that describes specific actions for the different work areas:

Materials and Construction Techniques

The selection of appropriate materials and construction techniques is critical to the success of erosion and stormwater management strategies. Common materials may include:

• Locally sourced soil and rock.
• Geotextiles (woven or nonwoven depending on the application)
• Geomats and Geogrids (coconut fiber, geosynthetics)
• Geobags/Geotubes
• Gabion walls
• Steel reinforcement (for anchoring structures such as raffia sacks).

Construction techniques emphasize:

• Building structures in a specific sequence, often from the bottom up, to ensure their stability
• Properly compact materials to create stable structures.
• Place materials with attention to detail to maximize their effectiveness.

Conclusion

Proper erosion and water management are essential components of responsible mine construction. Understanding the area’s rainfall, hurricane impacts, available material types (soil and rock), and vegetation is essential to estimate the impacts and volume of stormwater and sediment to be managed. By applying sound engineering principles, using appropriate materials, and implementing rigorous construction techniques, it is possible to mitigate the challenges of the rainy season and ensure the long-term stability and sustainability of mining projects.