How the AML920 Groundwater Flow Meter Helps Reduce Drilling Costs
In subway, high-speed railway, and other large-scale infrastructure projects, groundwater velocity and flow direction are important parameters in hydrogeological investigations. Measurement results not only influence groundwater flow field analysis but also provide a reference for foundation pit construction, groundwater control, and related engineering design.
Three months ago, Manager Wang, who was responsible for a subway infrastructure project in Guangdong, contacted us to learn about the AML920 groundwater flow meter. His core challenge was how to reduce the number of boreholes and control investigation costs while obtaining reliable groundwater velocity and flow direction data that met the project’s measurement requirements.
This was not our first experience with groundwater monitoring requirements in the rail transit sector. Over the past two years, the AML920 groundwater flow meter has been used for downhole measurements in multiple subway and high-speed railway-related projects.
Based on Manager Wang’s project requirements, we compared the traditional three-borehole method with the single-borehole particle-tracking measurement solution, focusing on measurement principles, drilling investment, applicable depth, and the limitations of data application.
1. Why Is Accurate Groundwater Velocity and Flow Direction Measurement Important in Subway Projects?
Compared with general shallow groundwater investigations, subway and railway infrastructure projects often face more complex site conditions.
1. Reliable measurement results are essential
Deviations in groundwater flow direction can affect subsequent hydrogeological analysis and engineering plans. For projects involving large construction areas and complex geological conditions, measurement data should have a clear technical basis rather than relying solely on experience.
2. Hydrogeological conditions vary along the route
Subway lines often cross different geological formations and hydrogeological units. Groundwater velocity, flow direction, and aquifer characteristics may change with location and depth. Therefore, the appropriate measurement method should be selected according to the actual investigation objectives.
3. Deep-well measurements place higher demands on equipment
Some projects require groundwater velocity and flow direction measurements in relatively deep monitoring wells. The equipment must not only meet measurement requirements but also accommodate probe dimensions, cable length, well structure, and on-site operating conditions.
For these projects, traditional multi-borehole measurement methods remain valuable. However, when a project requires the groundwater flow vector at a specific well location while controlling the cost of additional drilling, single-borehole measurement technology deserves further evaluation.
2. What Are the Limitations of the Traditional Three-Borehole Method?
During discussions with Manager Wang, one of the main topics was the implementation cost of the traditional three-borehole method.
This method generally uses groundwater level measurements from three boreholes or monitoring wells arranged in a triangular pattern. The data are then used to analyze groundwater flow direction through groundwater equipotential contour mapping. Its technical basis involves Clause 7.2.4 of GB 50021, Code for Investigation of Geotechnical Engineering, and the relevant explanatory notes. Actual applications should follow the official standard text and the conditions applicable to the project.
Although this method can support regional groundwater flow field analysis, it also has certain limitations in practical engineering applications.
1. More Boreholes Increase Investigation Costs
When using the three-borehole method, multiple measurement wells must be positioned appropriately according to hydrogeological conditions and relevant technical requirements.
If the project also requires groundwater velocity measurements using other testing methods, additional test and observation wells may be necessary. The actual number of boreholes depends on the investigation objectives, geological conditions, and design requirements. Not every project necessarily requires four or five wells.
The combined costs of drilling, well completion, well development, field testing, equipment mobilization, and site coordination can increase both the project timeline and financial investment.
2. Regional Flow Direction Estimation Differs from Local Velocity Measurement
The three-borehole method primarily analyzes groundwater hydraulic gradients and flow direction based on groundwater level relationships among multiple measurement points. This is not the same technical approach as directly measuring groundwater velocity and flow direction within a specific well interval.
If an engineering project needs to understand groundwater movement at a particular well location and depth, regional-scale flow direction estimates alone may not satisfy every measurement requirement.
Therefore, when selecting a measurement solution, it is important to determine whether the project requires regional hydrogeological analysis, a local groundwater flow vector, or both.
3. How Does the AML920 Groundwater Flow Meter Enable Single-Borehole Measurement?
To address Manager Wang’s concerns about drilling costs and downhole measurement requirements, we introduced the particle-tracking measurement solution provided by the AML920 groundwater flow meter.
Unlike methods that estimate groundwater flow direction solely from water level differences between multiple boreholes, this equipment observes the movement of tracer particles in a well to obtain groundwater flow information at the corresponding measurement location.
Core Measurement Principle
The AML920 groundwater flow meter combines the following technical processes:
- Microscopic magnification and CCD imaging: Captures tracer particle trajectories and provides image data for velocity calculations.
- Electronic compass orientation: Obtains the directional information required for measurement.
- Three-dimensional vector calculation: Combines relevant measurement data to calculate groundwater velocity and flow direction at the measurement location.
According to the equipment’s design principle, the measurement does not rely solely on water level relationships between multiple boreholes to estimate local flow direction, as the traditional geometric water-level method does.
When well depth, borehole diameter, water quality, flow conditions, and equipment operating requirements are satisfied, a single well location can provide three-dimensional flow vector information for the measurement location. This helps reduce the need for additional boreholes installed specifically to obtain local groundwater velocity and flow direction data.
It is important to note that single-borehole measurement does not mean that all other investigation boreholes can be eliminated. Whether drilling can be reduced should be determined by considering the scope of the original investigation plan, regional flow field analysis requirements, and applicable standards.
Comparison of Three Groundwater Velocity and Flow Direction Measurement Methods
| Comparison Item | Three-Borehole Method | Thermal Pulse Method | AML920 Particle-Tracking Method |
|---|---|---|---|
| Basic principle | Analyzes flow direction using water level relationships between multiple points | Determines water movement from heat transport characteristics | Calculates flow information from tracer particle trajectories |
| Typical measurement approach | Multiple measurement wells work together | Downhole measurement under suitable conditions | Single-well measurement at a specified depth interval |
| Main characteristics | Supports regional hydraulic gradient and flow direction analysis | Affected by probe design, flow velocity, and site conditions | Provides local three-dimensional flow vector information |
| Main limitations | Requires appropriate well placement; local velocity measurement may require additional tests | Applicable depth and measurement range depend on the specific equipment and operating conditions | Results from one well cannot directly represent the groundwater flow field of an entire region |
| Engineering value | Suitable for regional hydrogeological investigations | Suitable for in-well testing when measurement conditions are met | Suitable for projects requiring local velocity and flow direction measurements while seeking to control additional drilling costs |
The actual performance and applicable conditions of different equipment vary. Equipment selection should be based on technical documentation for the specific model, actual site conditions, and verification results rather than assumptions based solely on measurement principles.
4. Why Do Water Transparency and Measurement Depth Matter?
In addition to the number of boreholes, Manager Wang was also concerned about two practical issues: whether measurements could be performed under different water quality conditions and whether the equipment could meet the requirements of deep-well projects.
1. Water Transparency and Particle Recognition
Some optical measurement devices need to identify features or particles in water through image recognition. When water is highly turbid, suspended matter may interfere with imaging. When the water lacks identifiable features, recognition may also become more difficult.
The AML920 uses particle tracking combined with CCD imaging. Its operating principle does not rely solely on water transparency to determine flow direction.
However, this does not mean that water quality has no effect on measurement. Actual testing still needs to account for particle detectability, interference from suspended matter, optical imaging conditions, and the in-well environment. For projects involving highly turbid water or unusual water quality, on-site suitability should be confirmed before formal implementation.
2. Deep-Well and Ultra-Deep-Well Measurement Capabilities
Deep-well projects require particular attention to the equipment’s effective measurement depth, cable configuration, pressure resistance, and downhole operating requirements.
According to the AML920 product configuration information, the standard measurement depth can reach 1,000 meters, while customized configurations can reach a maximum of 2,000 meters. Actual capability should be confirmed against the specific supplied model, configuration documentation, and project conditions. The maximum customized depth should not be interpreted as a guaranteed effective measurement depth under all field conditions.
For complex infrastructure projects such as subway and high-speed railway construction, confirming well depth and well conditions in advance helps reduce equipment selection and field implementation risks.
5. Project Results: Measurement Feedback and Drilling Cost Optimization
After comparing the traditional method with the single-borehole measurement solution, Manager Wang decided to use the AML920 groundwater flow meter for the relevant project measurements.
According to Manager Wang’s project feedback, the measurement data met the project’s requirements for accuracy and were accepted by the expert panel. At the same time, the project achieved reported savings of hundreds of thousands of yuan in drilling costs.
The value of this result was not limited to reducing the number of boreholes. It also involved avoiding unnecessary construction expenditure by matching the measurement method to the specific investigation task.
How Should Drilling Costs Be Calculated?
If the original plan genuinely required three measurement wells, while the revised solution needed only one well for the same local measurement task, reducing the number from three to one would theoretically eliminate the need for two additional boreholes.
However, the actual savings cannot be calculated from the number of boreholes alone. The following costs must also be considered:
- Direct costs: Drilling, well completion, well development, and related testing expenses.
- Indirect costs: Equipment mobilization, site coordination, construction organization, and time occupied by the work.
- Plan adjustment costs: Whether existing monitoring wells can continue to be used and whether regional flow field investigations or other necessary tests are still required.
Therefore, the savings of hundreds of thousands of yuan represent the feedback from this particular project. They should not be treated as a fixed amount that every subway project can achieve by adopting the AML920. Different regions, well depths, geological conditions, and construction requirements all affect the final cost.
For project managers, a more reasonable approach is to clarify the measurement objectives first and then compare the total costs of different solutions, rather than focusing solely on equipment purchase prices.
6. Application Limitations of the AML920 Groundwater Flow Meter
To ensure that measurement results are correctly applied, the following points should be considered during equipment selection and implementation.
First, single-borehole measurement cannot completely replace regional flow field investigations.
The AML920 provides local flow information for the corresponding well location and measurement depth interval. Regional groundwater flow field analysis may still require water level data from multiple wells, hydrogeological information, and other investigation results.
Second, in-well velocity should not be directly equated with groundwater Darcy velocity.
The relationship between in-well measurement results and actual seepage parameters in an aquifer may be affected by well structure, in-well flow conditions, and hydrogeological factors. If Darcy velocity calculations or seepage analysis are required, conversion and verification should be carried out using appropriate calculation models and the necessary parameters.
Third, deep-well measurements require verification of site conditions.
For ultra-deep wells or special pressurized environments, cable specifications, probe design, pressure resistance, and equipment configuration should be confirmed in advance. A dedicated technical assessment may be necessary.
Fourth, velocity and flow direction measurements cannot replace water quality testing.
The equipment’s measurement results do not directly indicate groundwater chemical composition or pollutant concentrations. When investigating groundwater contamination, water samples must also be collected and analyzed through appropriate laboratory testing.
Fifth, equipment performance should be confirmed against the actual configuration and field verification results.
For key specifications such as measurement accuracy, applicable water quality, and maximum depth, the technical documentation for the specific model should be checked, and the equipment should be verified under actual well conditions.
7. Frequently Asked Questions About Groundwater Flow Meters (FAQ)
Q1: Can a groundwater flow meter replace three measurement wells with just one well?
For obtaining groundwater velocity and flow direction information at a specified well location and depth interval, the AML920 can use a single-borehole measurement approach when the measurement conditions are suitable. This can reduce the number of additional wells required specifically for that local measurement task.
However, if a project also requires regional groundwater flow field analysis, hydraulic gradient calculations, or compliance with other investigation requirements, multiple measurement wells and relevant hydrogeological data may still be necessary. Whether drilling can be reduced should be assessed against the complete investigation scope.
Q2: What measurement principle does the AML920 groundwater flow meter use?
The equipment uses particle tracking and CCD imaging to capture tracer particle trajectories. It combines this information with electronic compass orientation and three-dimensional vector calculations to obtain groundwater velocity and flow direction at the measurement location. Actual performance should be confirmed against the technical documentation for the specific model and field verification results.
Q3: Is the AML920 groundwater flow meter suitable for both clear and turbid water?
Suitability depends on the specific equipment’s operating principle and water conditions. The AML920 uses particle-tracking measurement and does not rely solely on water transparency to estimate flow direction. However, particle recognition, suspended matter interference, and imaging conditions may still affect measurements. For water with extremely high transparency or turbidity, on-site suitability should be confirmed in advance.
Q4: What is the maximum measurement depth of the AML920 groundwater flow meter?
According to the product configuration information, the standard measurement depth can reach 1,000 meters, while customized configurations can reach a maximum of 2,000 meters. The actual usable depth depends on the supplied configuration, well conditions, and field operating requirements. Technical confirmation is recommended before purchase.
Q5: Is the groundwater velocity measured by a groundwater flow meter the actual seepage velocity of groundwater?
Not necessarily. The velocity measured inside a well and the Darcy velocity in an aquifer are different concepts. Their relationship may be affected by effective porosity, well structure, and in-well flow conditions. Any conversion should be based on an appropriate hydrogeological model and field parameters.
Q6: How much drilling cost can a groundwater flow meter save?
The amount saved depends on the number of boreholes in the original plan, well depth, geological conditions, construction rates, and subsequent testing requirements. In this case, the customer reported savings of hundreds of thousands of yuan, but this result cannot be directly applied to other projects. It is advisable to calculate direct drilling costs and indirect costs, including time and coordination expenses, based on actual project quantities.
Q7: How can I determine whether my project is suitable for single-borehole groundwater flow measurement?
First, clarify whether the measurement objective is local groundwater velocity and flow direction or regional flow field investigation. Then confirm the well depth, borehole diameter, water quality, equipment configuration, and applicable standards. If the project primarily requires local three-dimensional flow information at a specific well location and aims to reduce unnecessary additional drilling, the suitability of the AML920 can be evaluated further.
Conclusion: Clarify the Measurement Objectives Before Optimizing Engineering Costs
Manager Wang’s project demonstrates that groundwater velocity and flow direction measurement in subway, high-speed railway, and other infrastructure projects requires more than attention to data quality. Drilling quantities, construction schedules, downhole environments, and technical suitability must also be considered.
Through particle tracking, CCD imaging, and three-dimensional vector calculations, the AML920 groundwater flow meter provides a single-borehole solution for measuring groundwater velocity and flow direction at specific well locations. Under suitable conditions, this approach can help reduce certain additional boreholes and their associated costs.
For engineering organizations with similar requirements, we recommend providing the well depth, borehole diameter, target measurement interval, groundwater conditions, and project measurement requirements before equipment selection. This information will help evaluate the appropriate equipment configuration and implementation plan.
If your project involves subway construction, high-speed railways, deep excavations, or other groundwater monitoring applications, please contact our technical team to discuss the applicability of the AML920 groundwater flow meter, measurement solutions, and potential opportunities for project cost optimization.
