Application of Piezometers to Assess the Risk of Tailings Dams Instability During Staged Construction

Author: Mohsen Moogui
Date: November 2024
First Presented: GeoTails website

INTRODUCTION

The stability of tailings dams is a critical concern, particularly during staged construction. As these dams are raised in phases, the risk of instability increases due to changing loads and the potential development of excessive pore water pressure within the dam structure or its foundation. Effective monitoring of these pressures is essential to ensure the safety and integrity of the dam, especially during construction stages when risks are heightened.

Role of Piezometers in Tailings Dam Monitoring: Piezometers are widely used to monitor pore water pressure in tailings dams, providing essential data for stability assessments. Vibrating wire piezometers (VWPs) offer significant advantages over traditional standpipe piezometers, particularly in low-permeability materials such as clay and tailings. The ability of VWPs to provide real-time responses to changes in external pressure is crucial for managing the dynamic conditions of staged construction.

Advantages of Multilevel Vibrating Wire Piezometers:

  1. Targeted Monitoring of Geological Units: Multilevel VWP units can be installed at a single location to monitor different geological layers, offering a comprehensive view of the drainage regime within the earth fill embankments and foundation. This provides critical insight into how various layers respond to construction loads and environmental changes.
  2. In-Depth Analysis of Drainage Regime: The ability to monitor multiple depths enhances understanding of the internal drainage patterns, helping to identify areas of concern that may not be apparent with single-depth measurements.

 

Key Benefits of Piezometer Monitoring:

  1. Real-Time Data for Decision-Making: VWPs provide live data on pore pressure changes, allowing timely adjustments during construction to prevent instability.
  2. Direct Water Table Measurement: Standpipe piezometers, while not as responsive as VWPs, offer direct measurements of the water table, contributing to a holistic assessment of the dam’s stability.
  3. Comprehensive Risk Assessment: Combining VWP data with standpipe readings allows for a more accurate interpretation of the pore pressure distribution, especially in complex site conditions.

 

Crucial Factors in Data Interpretation: Interpreting piezometer data requires extensive expertise, particularly in complex sites where multiple factors can influence pore pressures, such as:

  • Excess Pore Pressure: Understanding how excess pressures develop during construction and how they dissipate over time.
  • Seasonal Rainfall Impact: Recognizing how precipitation affects pore pressures, particularly in regions with significant seasonal variations.
  • 3D Groundwater Regime: Accounting for the three-dimensional movement of groundwater that can influence pore pressures and dam stability.
  • Perched Water Tables: Identifying the presence of perched water tables that can create localized zones of high pore pressure.

 

Adopting a Risk-Based Approach: A risk-based approach to instrumentation ensures that the most effective combination of tools is used to address major risks during staged construction. This involves:

  • Strategic Integration of Multilevel VWPs and Standpipe Piezometers to capture a complete picture of the dam’s performance across different layers.
  • Continuous Monitoring and Data Analysis to adapt construction practices in real time, optimizing safety and efficiency.

 

Conclusion: The use of advanced piezometer systems, particularly multilevel VWPs, is crucial for assessing the risk of instability in tailings dams during staged construction. GeoTails Consulting leverages these technologies to deliver tailored monitoring solutions that ensure safe, efficient, and sustainable tailings management.

Contact GeoTails Consulting today to discuss how our expertise in piezometer data interpretation and tailings management can support your next project.

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