A bore log (also called a drilling report or borehole log) is a written and graphical record of the soil and rock layers encountered during a geotechnical drilling investigation. It provides engineers with essential subsurface data needed to design foundations, retaining walls, and other structures that interact with the ground.
In Dutch construction practice, this document is known as a “boorstaat.” It is produced by specialist geotechnical firms and forms a key part of the soil investigation report submitted during the building permit process.
Application
Bore logs are used throughout the design and construction process for critical decision-making:
- Foundation design: Engineers use bore log data to determine whether shallow foundations (strip or pad footings) are sufficient, or whether deep foundations (piles) are required.
- Soil classification: Each layer is described by type (clay, sand, peat, gravel), colour, consistency, and moisture content according to standardized classification systems.
- Groundwater level: The bore log records the depth at which groundwater is encountered, which affects excavation methods and waterproofing requirements.
- Bearing capacity calculation: Layer thickness and soil properties from the bore log feed directly into load-bearing capacity calculations.
- Contamination assessment: Samples taken during drilling can be tested for pollutants, and their depth is referenced on the bore log.
A typical bore log includes a header with project information, borehole coordinates, date, drilling method, and operator details. The main body presents a scaled column showing each soil layer with its depth, thickness, description, and any test results (such as Standard Penetration Test blow counts). Multiple bore logs across a site allow engineers to create a three-dimensional model of subsurface conditions.
Related terms
- Cone Penetration Test (CPT)
- Soil investigation
- Foundation pile
- Groundwater table
- Geotechnical report
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