About this tool Calculate hydraulic conductivity (K) from constant head permeability tests. Three test types are supported: laboratory permeameter (BS 1377-5), borehole with casing open at the base, and borehole with an uncased test section.
The borehole methods use Hvorslev (1951) shape factors for the two most common borehole configurations. Results are classified from Very High (gravel) to Very Low (intact clay).
Essential for soakaway design, dewatering assessment, contaminant transport modelling, and foundation design in permeable ground.
How to use this tool 1. Select the test type — lab permeameter, cased borehole, or uncased borehole.
2. Enter the test parameters — flow rate, head, and geometry (sample dimensions or borehole details).
3. Read K in m/s and the permeability class — compare against design requirements.
Technical information Lab: K = Q·L / (A·h) — Darcy's law (BS 1377-5)
Borehole (cased): K = Q / (2.75·D·H) — Hvorslev (1951)
Borehole (uncased): K = Q / (2π·L·H) — Hvorslev (1951)
Limitations Hvorslev borehole methods assume isotropic, homogeneous soil around the test zone. In layered or anisotropic ground, the result is a composite value dominated by the most permeable layer.
Constant head tests measure the horizontal permeability component in boreholes. Vertical permeability may be significantly different, especially in layered soils.
Lab tests on disturbed or remoulded samples may not represent in-situ permeability. Undisturbed samples or field tests are preferred for design.
Revision history 15 September 2026: Initial release
Disclaimer This tool is provided for educational and general information purposes only. It is not a substitute for professional engineering advice, design or verification.
Diggy and its contributors are not licensed engineering consultants and no results generated by this tool should be used directly for construction, design or safety-critical decisions.
All values and outputs are based on published empirical correlations and should be independently checked and confirmed by a qualified geotechnical engineer before use.
By using this tool, you accept full responsibility for how you interpret and apply the information provided.
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