HPT & CPT Testing: Real-Time Subsurface Data
Understanding what is happening beneath the ground is critical for environmental and geotechnical investigations. Subsurface conditions can vary significantly across relatively small areas, making it important to obtain reliable information about soil layers, groundwater movement and hydraulic properties before designing remediation strategies or monitoring programs.
Hydraulic Profiling Tool (HPT) testing and Cone Penetration Testing (CPT) provide project teams with valuable, real-time subsurface data. When used individually or together, these investigation methods can help build a clearer understanding of site conditions while reducing the need for extensive conventional drilling.
What is HPT Testing?
Hydraulic Profiling Tool (HPT) testing is an in-situ investigation technique used to assess groundwater flow and estimate changes in hydraulic conductivity with depth.
During an HPT investigation, a probe is advanced continuously through the subsurface while water is injected into the formation. Measurements collected during the test can help identify changes in formation permeability and potential groundwater flow pathways.
HPT data can be particularly useful for environmental investigations where understanding how groundwater moves through a contaminated site is essential.
HPT testing can help identify:
Changes in hydraulic conductivity with depth
Potential groundwater flow pathways
More permeable and less permeable zones
Subsurface intervals that may influence contaminant migration
Areas that may warrant further investigation or monitoring
Because HPT provides data continuously as the probe advances, project teams can obtain a detailed vertical profile of subsurface hydraulic conditions without relying solely on discrete samples.
Why Use HPT for Groundwater Investigations?
Groundwater behaviour is often controlled by variations in the subsurface. Sand, gravel, silt and clay layers can have very different hydraulic properties, which can influence groundwater flow and the movement of dissolved contaminants.
Traditional investigation methods may provide valuable information from discrete locations, but HPT testing can provide a continuous profile that helps identify changes between sampling points.
This can support environmental consultants and engineers when developing conceptual site models, assessing potential contaminant pathways and determining where additional investigation or monitoring infrastructure may be appropriate.
What is CPT Testing?
Cone Penetration Testing (CPT) is a continuous in-situ investigation method used to characterise subsurface soils.
A CPT cone is hydraulically pushed into the ground at a controlled rate while sensors measure parameters such as cone tip resistance and sleeve friction. These measurements provide a continuous profile of soil behaviour with depth.
Unlike conventional borehole drilling, a CPT test does not require the collection of a continuous sequence of physical soil cores. Instead, the data is collected directly as the cone advances through the subsurface.
CPT testing can help identify:
Soil stratigraphy
Changes in soil behaviour
Relative soil strength and resistance
Potential interfaces between soil layers
Zones requiring further geotechnical or environmental investigation
This makes CPT a valuable tool for projects where a rapid and continuous understanding of subsurface conditions is required.
HPT vs CPT Testing: Understanding Subsurface Conditions
While Hydraulic Profiling Tool (HPT) testing focuses on groundwater flow and hydraulic conductivity, it is often used alongside Cone Penetration Testing (CPT) and Piezocone Testing (CPTU) to develop a more complete picture of subsurface conditions.
A CPT test measures soil resistance and stratigraphy, helping geotechnical and environmental professionals identify soil layers, strength characteristics and potential construction constraints.
A CPT cone penetration test provides continuous soil profiling without the need for conventional drilling, making it an efficient solution for many site investigations.
For projects requiring groundwater assessment, a CPTU cone penetration test combines traditional CPT measurements with pore pressure readings. This provides additional information about soil behaviour, groundwater conditions and subsurface response during penetration.
By combining HPT testing, CPT testing and CPTU investigations, project teams can improve site characterisation, support monitoring well placement and reduce uncertainty during environmental and geotechnical investigations.
HPT and CPT: Complementary Investigation Methods
HPT and CPT measure different characteristics of the subsurface, which is why using the techniques together can provide additional value.
For example, CPT data can help establish the geological and geotechnical framework of a site, while HPT data can help identify how groundwater may move through those materials.
When interpreted together, these datasets can help consultants develop a stronger understanding of:
Soil Structure
CPT can identify changes in soil behaviour and stratigraphy with depth.
Hydraulic Properties
HPT can provide information about relative hydraulic conductivity and potential groundwater flow zones.
Groundwater Conditions
CPTU can provide pore pressure data that adds another layer of information to the subsurface investigation.
Potential Contaminant Pathways
Understanding both soil conditions and groundwater movement can assist with identifying zones that may influence contaminant migration.
Applications for Environmental and Geotechnical Projects
HPT and CPT investigations can be used across a range of projects, including:
Environmental site investigations
Groundwater investigations
Contaminated land assessments
Remediation projects
Monitoring well planning
Hydrogeological investigations
Geotechnical site characterisation
Infrastructure projects
Industrial and commercial site investigations
The appropriate investigation method depends on the objectives of the project, existing site information and the conditions encountered during fieldwork.
Real-Time Data for Better Site Characterisation
One of the key advantages of HPT and CPT is the ability to collect continuous data while the probe advances through the subsurface.
Rather than relying entirely on information obtained from widely spaced discrete investigation points, continuous profiling can help reveal changes in subsurface conditions that may otherwise be missed.
Real-time data can also allow field teams and project consultants to make more informed decisions during an investigation, including identifying zones that require additional testing or targeted sampling.
Choosing the Right Investigation Method
There is no single investigation technique that is appropriate for every site.
HPT, CPT and CPTU each provide different types of subsurface information and can be selected according to the project's objectives.
For environmental projects, HPT may be particularly useful when groundwater flow and hydraulic conductivity are key considerations. CPT can provide continuous information about soil behaviour and stratigraphy, while CPTU adds pore pressure measurements for projects where groundwater and soil response need to be assessed together.
Combining complementary investigation techniques can provide a more comprehensive dataset and help project teams make better-informed decisions about subsequent investigation, monitoring and remediation activities.
Talk to Legion Drilling About Your Site Investigation
Selecting the right subsurface investigation method is an important part of developing an effective environmental or geotechnical investigation program.
Legion Drilling provides drilling and site investigation services for environmental, geotechnical and groundwater projects across Australia. Our experienced field teams can work with project consultants and engineers to determine an appropriate investigation approach based on site conditions and project requirements.
If your project requires HPT testing, CPT testing, CPT cone penetration testing, CPTU cone penetration testing, groundwater investigation services or complementary drilling services, contact Legion Drilling to discuss your site investigation requirements.