What is a Borehole Log?
A borehole log is a document used to record information found in geotechnical sites called boreholes, well, or test holes. Boreholes are pits that were carefully dug with minimal environmental impact, allowing tools and probes to be lowered and collecting samples and information.
Different tools or probes are lowered into specific depths during the investigation to collect and record data such as groundwater level, permeability, pore pressures, and ground movement. The collected data can provide a lot of information regarding subsurface conditions that will be used in different geotechnical research and study fields.
What is Technical Information in a Borehole Log?
Although standard forms may vary from country to country, below are four technical information that is common among them. The information below is referenced according to the U.S. Geological Survey and Australia’s Geotechnical Borehole Logging Guideline.
Project and Location Information
Before starting the drilling and investigation process, inspectors would need to record the project and location information. The borehole log should include the details below:
- Project Name
- Project Location and Borehole Code
- Project Number/Code (Standard coding will vary from country to country)
- Height Datum
- Surface Relative Level
- Starting and Completion Date
- Drilling Company/Contractor
- Name of Geologist and Reviewers
Take note that the required project and location information will vary depending on the country. So, make sure to carefully cross-inspect the standard guidelines of the country where the site investigation will take place to prevent any issues upon submission of the documents.
General Drilling Data
This information refers to any information regarding the drilling process such as drilling methods, types of drill bits, sample types, and intervals, run lengths, core loss and recovery, and rock quality designation percentages. This information will be essential when studying the samples in the laboratory.
Another necessary information that should be included in the bore log is the depth at which groundwater is encountered during the drilling process. This will be used to compare with the previous records of the natural groundwater table of the location.
Soil Sample Logs
This information refers to the soil’s description, name, and classification. Some countries might also require the inspector to include inferences about the stratum or layer the soil is from.
Soil description is an assessment based on the visual and tactile condition of the soil samples. Usually, soil samples are taken through tube samplers attached to the drill. Some samples will be stored, and the other portion will be sent to laboratories for further analysis.
When writing soil descriptions in the bore log, it is essential to record the information below according to the Unified Soil Classification System (USCS):
- Color
- Consistency
- Grain Size
- Moisture Content
- Plasticity
- Organic Content
- Defects
- Particle Shape
Also, other soil descriptions might be required, so it is better to cross-reference the standards in the project location.
Rock Sample Logs
Similar to the soil sample logs, this information refers to the description, name, and classification of the taken rock samples in the borehole log.
Rock description is an assessment based on the visual and tactile aspects of the rock samples. To get the best analysis, it is recommended to assess as soon as the rock sample is taken.
When writing rock descriptions and names, it is recommended to follow the standards in the site investigation area or use the Unified Rock Classification System for reference. Below are some of the details that should be included:
- Degree of Weathering (includes color, grain size, texture, and rock strength)
- Secondary Minerals
- Alteration Zones
- Distinct Features
- Discontinuity Type
There might be other rock descriptions required, so it’s better to check the standards in the project location.
Two Important Applications of Borehole Logging
Borehole logs are a fundamental part of geotechnical research. Below are two important applications: investigation of groundwater quality and resource exploration. The information below is referenced from the publications of the U.S. Geological Survey.
Groundwater Quality Investigation
Groundwater is a good source of clean water since the soil and rock around it screens out the bacteria. It also has many dissolved minerals and organic substances that are beneficial to the human body.
But groundwater is very susceptible to contamination from natural and man-made sources. For example, mining of zinc and lead creates “footprints” or remnants of chemicals that can infiltrate the soil and contaminate the groundwater beneath.
Borehole logs can give insight into the groundwater contamination since it involves analysis of the soil and rock in the area of investigation. It is also recommended to combine the bore log with groundwater sampling to create a complete picture of the groundwater status in the investigation area.
Resource Exploration
Another important application of the borehole logs is resource exploration. This is accomplished by combining the collected from different probes that detect various physical properties like magnetic properties, electrical resistivity, density, porosity, radioactivity, and acoustic velocity.
For example, hydrocarbons can be detected by combining high resistivity, porosity, and separation of density. An algorithm will process these data and give information on hydrocarbons, which can then be extracted to be used as fuel and made into various materials.
Use The Advantages of a Digital Borehole Log App
The traditional filling out well logs with a pen and clip folder at the excavation site can be laborious and impractical. Time and again, papers get lost on the way to the office. That’s why switching to a digital alternative is all the more worthwhile.
Lumiform is a powerful mobile app and desktop software that makes it easy to perform audits and inspections on the spot. To do this, you use digital checklists or forms via your smartphone or tablet on site. All data is then stored centrally in the cloud. This gives you and your colleagues access to the data in real-time. With Lumiform apps, inspectors can also:
- Download ready-to-use drill log templates from the template library or convert your paper template to our digital format.
- Thanks to our flexible form builder, you can drag and drop to customize your logs, checklists, and forms or create your own from scratch.
- Record soil boring results on the go via the app using your smartphone or tablet, even when you’re offline
- Take photos and annotate them to make your report more descriptive.
- Automatically create a report that can still be sent on site – saving all the post-processing in the office.
- Quite easily assign tasks and corrective actions via the app, addressing issues immediately. Easily monitor via dashboard which tasks have been assigned and completed and which are overdue.
- All data is automatically uploaded via secure cloud storage to ensure no information is lost or accessible to unauthorized parties.