Dam, Tailing Dam and Reservoir Monitoring
Oil Platform Monitoring
Pipeline and Undersground Structure Monitoring
Mining Operations Monitoring
The main purpose of monitoring civil structures is to support regular visual examinations or inspections based on non-destructive testing techniques. Sensor networks can be used to monitor a certain region of a structure providing data about different physical measures. Some properties to be measured in-situ are the Eigenvibrations of the structure, humidity and temperature outside and inside the structure, unusual stress and strain, and the detection of cracks and other deteriorations.
Continuous structural health monitoring provides data from the inside of a structure to better understand its structural performance and to predict its durability and remaining lifetime. There are a significant number of factors that influence structure life including loading, fatigue, corrosion and temperature cycling. One example of an application is bridges that currently endure higher static and dynamic loads than for which they were designed. Another example is structures that were built 50 or 60 years ago that today have exceeded the expected lifetime. There are many cases of structures designed with old seismic codes that do not match with the actual requirements, and have not yet been retrofitted.
The complex instrumentation on new and existing structures not only monitors the structure's response to seismic activity based on time-lapse observations and early warning systems, but also enables rapid deployment and prioritized inspections to address the need for safe and cost-effective operation of structures.
The system is designed to monitor the effects of reservoir and dam loads on the dams and their foundations, ensuring that any adverse conditions that develop during initial filling and operation are detected as soon as possible. When the facility is located in a seismically active area, the dam deformation monitoring program could be supplemented by an on-site GPS area monitoring network that is connected to the continuously operating (GPS) with known reference stations.
In addition to routine visual inspection, the system consists of:
- Geotechnical monitoring instrumentation consisting of strong motion accelerographs, piezometers, load cells, weirs, inclinometers, crack meters, and extensometers, supported by the Automated Dam Monitoring System (ADMS)
- Hydrometeorological sensors
- A real-time GPS monitoring system
- An automated terrestrial geodetic monitoring system consisting of eight permanently installed robotic total stations and an array of 228 prisms mounted on the faces of the monitored structures.
- If the facility is located in a seismic area, a local seismic network of at least five seismic stations is recommended.
The automation of data gathering and the use of the state-of-the-art technologies allow:
- Real time monitoring of the behavior of the dam.
- To optimize the measurements, with high degree of reliability and repetitiveness.
- To compare the measurements with the design values and to correlate between them.
- To define the safe levels of operation.
- To identify the occurrence of events that could affect the integrity of the dam.
Advantages of an automated monitoring system
- Data gathering, diagnosis, calibration and remote programming.
- 10 to 100 times higher precision, avoiding human errors.
- The readings are automatically taken and more frequently, reducing the instrumental error.
- Graphic display and on time processing.
- Digital data is more reliable, robust, and easy to process and plot.
- Minimize the cost of specialized labor.
- The information is always accessible when it is needed.
- It is possible to have an early warning and alarm system.
Relative disadvantages of an automated dam monitoring system
- Large data volumes.
- High initial installation costs, but the reduction of specialized labor cost will overcome this cost in a few months.
- The technical staff is less concerned with the field observation.
- The system requires a permanent power supply.
- Lightening could affect the system.
- It requires experienced IT personnel.
- Maintenance costs.
Typical dams' instrumentation
The vibration activity monitor is a relatively simple hardware and software system designed to provide updated predictions of the fatigue-loading activity in the jacket major-member welds of offshore oil platforms. Positioned on the platform cellar deck, the vibration recorder measures platform deck motion with two orthogonal accelerometers. These motions are processed in real-time to provide continuous records of the direction and frequency of platform motion. The recorded data is combined with transfer functions from a finite element structural model, which may be the platform design model or a refined version thereof, in order to predict and rank the fatigue activity in the joints. These predictions are used:
1. To verify and refine the platform design fatigue analysis;
2. To focus on areas where unanticipated fatigue activity has been observed;
3. To help select the welds for detailed underwater inspection.
This type of monitoring system could be installed on jackets, jack-ups, FPSOs, concrete platforms, offshore wind turbines / farms, offset risers, and pipelines.
In seismic areas that could be affected by hurricanes, a strong motion system is required. It should have three component sensors at the free field in the ocean bottom deployed about 100 meters away from the center of the platform.
The response of the structure to influences, such as the environmental loading or structural modification, can provide important information to assist in the verification of the design, assure long-term structural integrity and improve the operating parameters for the structure. The information gained will provide the opportunity for significant cost savings, maximized operating window (with substantial economic benefits), increased safety, minimized fatigue on critical elements, and improved understanding of the platform behavior.
The structural monitoring provides the following range of services to the Offshore Industry:
- Design verification
- Installation control
- Structural integrity
- Riser Monitoring
- Noise and Vibration
- Collision detection
- Tow monitoring
- Vessel performance monitoring
- Platform Monitoring
- Instrumentation solutions for Wind Farms
The central data acquisition unit should have enough channels to record the accelerometers and several additional channels to record other sensors such as:
- Tilting and inclinometers to monitor the overall structure.
- Strain gauges located in the legs to monitor leg and overall structure loads and weight distribution.
- Relative motion monitoring system allows the motion of a jacket and cantilevered drilling jack up platform to be compared with allowable limits.
- Tides and ocean waves-height, measuring the air-gap measurements using a radar-based wave height sensor.
- Meteorological data (wind speed, wind direction, barometric pressure, temperature and humidity).
- Integrity monitoring for free standing risers.
Significant changes to the platform's structural integrity could be detected by monitoring its natural frequencies and comparing the response characteristics to agreed upon criteria. With this data it will be possible to:
- Reduce in frequency the periodic sub-sea inspection.
- Assess platforms following a hurricane.
- This allows the operator to prioritize remedial actions when resources are at a premium. A platform fitted with OLM can quickly be assessed and brought back into production.
- Reduce the time at risk of a failed member, minimizing the probability of catastrophic failure.
- Monitor systems installed on offshore facilities, especially those requiring extension of operating life.
Unlike for above-ground structures, earthquake-generated inertia forces are not the main cause of damage to underground structures such as tunnels, mines or pipelines. Rather, damage is closely related to ground motion. For this purpose, the seismic ground response can be roughly subdivided into two broad classes:
A) So-called induced deformation effects, such as ground failure due to fault ruptures, slope instability, liquefaction;
B) Ground shaking, associated to dynamic longitudinal or shear strains in the structure.
Given the spatial extension of the area covered by pipelines and underground structures, the objectives are to monitor both types of earthquake ground response.
The long length, high investments, sometimes high risk and environmental impact, and often difficult access conditions, make an automated monitoring system desirable.
Measurement of ground motion can be realized along pipelines, over oil and gas infrastructure in relation to landslip, river crossings, tectonic hazard zones, underground oil and gas storage facilities and mining areas using state-of-the-art techniques.
The main parameters to be measured are:
- Ground motion, mostly using strong motion instruments.
- Permanent ground displacement, using inclinometers, tiltmeters, extensometers, crack meters, and topographic or GPS measurements.
- Pipeline Temperature, there are several methods and sensors.
- Pipeline Strain, mostly with strain meters.
- Pipeline Strain and bending, mostly with strain meters and fiber optic.
- Leakage detection, with pressure meters located inside the pipeline.
- Third-party intrusion detection, using satellite images.
Other key elements are the pumping stations which, when damaged by an earthquake, render the whole system inoperable. In a seismic area, at least one strong motion instrument should be located at each pumping station.
Monitoring installations are essential for safe mining operations. For mining projects it is important to detect movement, the rate of movement and the rate of increase of the movement in order to identify potential failure modes. Monitoring provides the information needed to support a safe working environment and economic and efficient mining operations whilst mitigating the associated risk.
Highwalls, excavated faces and potentially unstable slopes which create hazardous work environments will be monitored by the system. Vibrations and movements of mine infrastructure and assets caused by mining activities such as blasting, drilling or excavating will be detected by the system. The early detection of potential failure of stockpiles and tailings dams which may dramatically impact short and long term mining operations is yet another monitoring objective.
Trimble 4D Control software is the key element of the Trimble Monitoring system. The modular design facilitates an industry specific solution capturing data from GNSS, optical, geotechnical, seismic and atmospheric sensors. The data is processed using advanced, state-of-the-art algorithms and presented in a powerful, yet user friendly, locally hosted Web Interface. It provides a variety of visualization and analysis tools to identify potential failure scenarios. Data from atmospheric or geotechnical sensors may be combined with displacement indicators like change in slope distance, settlement or lateral movements to detect common failure modes. A fully featured computation parser can be used to create customized observables presenting information of specific interest to the analyst. Significant events such as blasting, drilling, instrument maintenance, sensor replacement and related activities may be logged and displayed on the charts. Boolean comparators are used to integrate data from GNSS, optical, geotechnical, seismic and atmospheric sensors to create complex alarm conditions. Alarm notifications are issued by email and SMS to selected recipients and the system may also activate audible and visual alarms.
The Trimble Mine Monitoring Solution is designed specifically for the geotechnical, seismic and survey monitoring analyst. Intricate data from multiple sensor types is converted into meaningful information from which informed decisions can be made with confidence. The solution accommodates a smooth transition from periodic monitoring surveys using Trimble Access software and Trimble 4D Lite software into complex automated systems using Trimble 4D Control software.