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Geotechnical Monitoring Supported Devices:  

Piezometers

Piezometers are tools designed and used by geotechnical engineers for measuring the pressure of fluids, particularly water pressure within the ground. Here we discuss the role and types of piezometers commonly used in geotechnical monitoring, their importance in construction, dam/levee and mining & excavation monitoring, and how Inzwa's Cloud platform simplifies the acquisition, analysis and reporting of data from these mission-critical sensors.

How do we simplify your
piezometer monitoring?

Inzwa Cloud:

  • Centralizes all your data logger and piezometer sensor data on one platform.

  • Provides intuitive visualizations for instant insights.

  • Allows you to easily create custom formulas as needed.

  • Has prebuilt dashboards to get your analysis and reporting up and running quickly.

  • Provides alerts 24/7 on any screen via text or email.

  • Provides report templates for fast and easy report generation.

Piezometers: What are they?

Piezometers are essential geotechnical instruments designed to measure the pore water pressure within the ground, which is crucial for assessing the stability and health of soil and rock masses in various engineering projects. These devices play a pivotal role in geotechnical engineering by providing vital data on the water pressures that influence the mechanical behavior of soils and rocks. This information is instrumental in designing and maintaining safe structures, particularly in projects involving dams, embankments, tunnels, and slopes.

Typically, piezometers are used to monitor the potential for failures such as slope instability, liquefaction in earthquake-prone areas, and excessive settlement or heave in foundations. By measuring the pore water pressure, engineers can assess the effective stress acting within the soil or rock, which directly impacts its strength and stability. For instance, an increase in pore water pressure can reduce the effective stress, potentially leading to slope failures or the undermining of foundation support.

Piezometer Pore Water Pressure Monitoring

Installing Piezometers

Installation of piezometers varies depending on the type and the specific requirements of the project. The most common methods include drilling boreholes to the desired depth and installing the piezometer, which can be a vibrating wire, pneumatic, or standpipe type. The choice of installation method—such as fully grouted, sand-packed, or push-in—depends on the soil conditions, the required measurement accuracy, and the duration of monitoring.

When installing piezometers in boreholes, several important factors need to be considered to ensure accurate and reliable pore water pressure measurements, including:

 Borehole Preparation

  • Borehole diameter: The borehole diameter should be large enough to accommodate the piezometer and any other equipment required for installation, such as tremie pipes or grout pipes. Typical diameters range from 3 to 6 inches.

  • Borehole cleaning: The borehole should be thoroughly cleaned to remove any drill cuttings, mud, or debris that could interfere with the piezometer's performance or create preferential flow paths.

  • Borehole stability: Unstable borehole conditions may require the use of temporary casing or drilling mud to prevent collapse during installation.

 

Piezometer Selection

  • Piezometer type: The type of piezometer (e.g., vibrating wire, pneumatic, or open standpipe) should be selected based on factors such as the expected pore water pressure range, response time requirements, and site conditions.

  • Piezometer dimensions: The piezometer's dimensions, including its diameter and length, should be compatible with the borehole size and the depth at which it will be installed.

Installation Method

  • Fully grouted method: This method involves installing the vibrating wire piezometer directly into a borehole and completely backfilling the annular space around the piezometer with a cement-bentonite grout. The grout acts as a sealing material and hydraulic barrier between the piezometer and surrounding soil formation. This method is quick, easy to install, and provides excellent isolation between different measurement zones when multiple piezometers are installed in the same borehole. 

  • Sand-Packed Method:  The sand-packed method involves placing a sand filter or "sand pack" around the piezometer tip to create a permeable zone. This permeable zone is then sealed above and below by bentonite or cement-bentonite grout to isolate it from the rest of the borehole. This traditional method allows water to flow freely from the surrounding soil into the sand pack before being measured by the piezometer. It is more time-consuming than the fully grouted method but may be preferred in very permeable formations.

  • Push-In Method:  Push-in or drive-in piezometers are designed with a specialized housing that allows them to be directly pushed or driven into soft, cohesive soils like clays. This avoids the need for a borehole. The piezometer has a conical tip to minimize soil disturbance and excess pore pressure generation during installation. Push-in piezometers are quick to install but have a limited depth range compared to borehole installed piezometers. They are ideal for monitoring pore pressures in near-surface soils.

Types and Functions of Piezometers: Manual vs. Electronic

There are several types of piezometers, each suited for specific geotechnical monitoring needs. The primary differences between manual and electronic piezometers lie in their measurement methods, data accuracy, and ease of data collection.

Manual Piezometers

Manual piezometers require physical readings taken on-site, often using simple tools. They are generally less expensive but provide less frequent and potentially less accurate data. Types of manual piezometers include:

  • Casagrande Standpipe Piezometers: Designed for taking measurements in rock and soil where only non-time-sensitive readings are needed. They measure the water level inside a pipe using a dip meter.

  • Open Tube Piezometers: Used in simple hydrogeological conditions, consisting of a cracked or micro-slotted PVC pipe installed inside the probing hole.

Electronic Piezometers

Electronic piezometers use advanced sensors and data logging systems to provide continuous, real-time data. They offer higher accuracy and can be monitored remotely, reducing the need for frequent site visits. Types of electronic piezometers include:

  • Vibrating Wire Piezometer: Measures pore-water pressure using a diaphragm, a tensioned steel wire, and an electromagnetic coil. Changes in water pressure alter the wire's tension and its resonant frequency, which is used to calculate pressure.

  • Pneumatic Piezometer: Utilizes gas pressure to measure pore water pressure in saturated soils. It features a simple, reliable transducer free from zero drift, with long-term performance enhanced by corrosion-resistant materials.

  • Titanium Piezometer: Especially useful in corrosive environments, these piezometers are known for their corrosion resistance.

  • Hydraulic (Flushable) Piezometers: Consist of a porous filter enclosing a reservoir of water, separated from a pressure gauge by flexible, water-filled tubes. They can measure both positive and negative pore water pressures.

  • Strain Gauge Piezometers: Feature a diaphragm sensor isolated from the surrounding environment by silicon oil, making them suitable for applications where the instrument is exposed to harmful liquids or gases.

GEOKON Piezometer for Pore Water Pressure Monitoring

Construction Site Monitoring with Piezometers:
Enhancing Safety and Stability

In the dynamic environment of construction sites, maintaining the safety and stability of the structures being built is paramount. Piezometers serve as essential tools in this endeavor by accurately measuring the pore water pressure within the soil and foundational materials. This critical data helps engineers and construction managers assess the condition of the soil, identify potential risks of soil liquefaction or instability, and make informed decisions regarding construction methods and safety measures. By deploying piezometers at strategic locations across a construction site, stakeholders gain valuable insights into the subsurface conditions, enabling proactive management of the site's geotechnical challenges and ensuring the long-term integrity of the structures being erected.

 

Click below to read how Inzwa’s Cloud Platform was used to continuously monitor several piezometers in a critical infrastructure rehabilitation project in Fraser, Michigan.
Piezometers for Construction Site Geotechnical Monitoring

Dam Monitoring with Piezometers: Ensuring Structural Integrity

Dams are massive structures that require constant monitoring to ensure their safety and integrity. Piezometers play a vital role in this process by measuring the water pressure beneath the surface, which is a key indicator of the dam's health. They are strategically placed at various depths and locations within the dam to provide a comprehensive understanding of the water pressure distribution and to detect any abnormal patterns that could signal potential issues.

Levees, like dams, are crucial for flood control and require meticulous monitoring. Piezometers are used to measure the water pressure within levees, providing a regular flow of data that can help predict and / or mitigate the risk of breaches or failures. This information is essential for taking proactive measures to reinforce levees and protect surrounding communities from flooding.  By monitoring the water pressure within levees, piezometers can alert engineers to potential weak spots or areas where water may be seeping through. This allows for timely interventions to strengthen the levee and prevent catastrophic failures.

Dam Monitoring with Piezometers
Dam Monitoring with Piezometers

Mining Applications with Piezometers: Safeguarding Operations

In the challenging and often hazardous field of mining and excavation, the use of piezometers is crucial for ensuring the safety of operations and the stability of excavation sites. By monitoring the pore water pressure in the surrounding geological formations, piezometers provide essential data that helps to predict and prevent water ingress and soil or rock failure, which are common risks in these environments. This information allows engineers to design and implement effective dewatering and stabilization strategies, thereby minimizing the risk of landslides, cave-ins, and other geotechnical failures. Strategically placed within the mine or excavation site, piezometers offer a continuous assessment of the hydrogeological conditions, enabling operators to make timely decisions and maintain the integrity of their operations under varying and often difficult conditions.

Piezometer Mining Applications

Inzwa Cloud Simplifies Piezometer Data Management

Inzwa Technologies’ Cloud sensor management platform supports a wide array of geotechnical monitoring devices, including piezometers. This platform provides centralized management of sensor data, intuitive data visualizations, customizable alerts, as well as pre-built dashboards and summary report templates for simplified data management and reporting. Inzwa's Cloud platform plug-and-play functionality and device-agnostic connectivity make it easy to integrate with a variety of sensor types, including those from third-party manufacturers. 

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Piezometer Case Studies

Remote Sensor Management on Lantau Island

Nicholas Cheng with Geotechnical & Concrete Engineering (GCE) knew this construction monitoring project would be a challenge. The project called for providing preliminary site data to inform the construction design of a major new highway... (more)

No More Sinkholes: 24/7 Remote Water Level Monitoring in Fraser, MI

What happens when a huge sewer line collapses on Christmas Eve, causing a sinkhole the size of a football field that destroys three homes, causes 22 more to be evacuated, and costs over $70MM to repair?  A huge infrastructure rehabilitation project, for starters.

Piezometer Case Study - Remote Sensor Management
Piezometer Case Study - 24/7 Water Level Monitoring
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