About this tool Calculate the quantities of filter sand, bentonite seal, and cement-bentonite grout needed for a standpipe or piezometer installation. Enter borehole and standpipe dimensions, response zone depths, and seal thickness — the tool calculates annular volumes and material masses with a 20% wastage factor.
Essential for pre-ordering materials before drilling and for checking actual consumption against theoretical quantities during installation. Under- or over-consumption indicates potential issues such as cavities, incorrect borehole diameter, or seal bypass.
Designed for standard monitoring well installations per BS ISO 5667-22 and Environment Agency guidance on groundwater monitoring boreholes.
How to use this tool 1. Enter borehole and standpipe diameters — select from common sizes or enter custom dimensions.
2. Enter total depth and response zone — filter pack spans from response zone top to base.
3. Set bentonite seal thickness — minimum 1m per best practice. Sits directly above the filter pack.
Technical information Annular volume = π/4 × (D²_bh - D²_pipe) × length
Filter sand bulk density: ~1600 kg/m³ | Bentonite pellet bulk density: ~1050 kg/m³
All quantities include a 20% wastage factor to account for borehole irregularities and material loss.
Limitations Assumes a uniform circular borehole. Actual consumption may be higher in soft or fractured ground where the borehole is oversize or irregular.
Bulk densities are typical values. Actual density depends on the specific product used — check supplier data sheets.
Does not account for head of water in the borehole, which may affect bentonite pellet hydration rate and placement. In deep water-filled boreholes, consider coated pellets or granular bentonite.
Revision history 1 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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