Geotextile Dewatering Bag: Dry Solids, Cake Volume, Water Released & Bags Needed

The formula

This is the expression the tool evaluates. Every term is named underneath, with the unit it must be supplied in.

How the result is derived

Step by step, from the values you type to the figure on screen.

1. The 7 inputs are read from the form on every keystroke: Slurry Volume to Pump, Dry Solids in the Slurry (by Mass), Density of the Solids, Cake Solids after Dewatering, Solids Captured by the Fabric, Volume of One Bag or Tube and Share of That Volume You Will Fill.
2. Each value is checked against the accepted range in the input table below. A value outside its range stops the calculation rather than producing a misleading figure — the results blank out and a message appears.
3. The validated values are substituted into the expression above, which resolves Bags or Tubes for the Final Cake together with every supporting figure in one pass — no value is carried over from a previous entry.
4. The supporting outputs — Slurry Density, Slurry Mass Pumped, Dry Solids Pumped, Dry Solids Kept in the Bags, Wet Cake Mass, Cake Density (Saturated), Cake Volume, Water Released through the Fabric and Volume Reduction, Slurry to Cake — come from the same pass, so they always describe the same case as the headline figure.
5. Results are rounded for display only. The full-precision value is used throughout the chain, so reading a rounded intermediate figure back into the tool by hand can shift the last digit.

What each input means

Where to read each value on the floor, the unit it must be in, and the range the tool accepts.

What the tool returns

The headline figure and every supporting value it is built from.

Worked example

Substituting

Five hundred cubic metres of slurry ends as seventy-two of cake. Sizing bags to the pumped volume would buy seven times too many.

How to use it

1. Work through the input groups in order — Slurry and Dewatering Test & Bag. The defaults are a realistic case, so you can change one value at a time and watch what moves.
2. There is no calculate button. Every figure recalculates as you type or drag, which is what makes this usable for a what-if sweep rather than a single answer.
3. Read Bags or Tubes for the Final Cake in the dark results panel — that is the headline figure, expressed in bags.
4. Check the supporting rows underneath (Slurry Density, Slurry Mass Pumped, Dry Solids Pumped, Dry Solids Kept in the Bags, Wet Cake Mass, Cake Density (Saturated), Cake Volume, Water Released through the Fabric and Volume Reduction, Slurry to Cake) before acting on the headline — they are where an implausible input usually shows itself first.
5. Reset to defaults returns every field to the reference case, which is the quickest way to check whether a surprising result came from the tool or from an input you had changed earlier.

Where this is used

• Process planning — establishing Bags or Tubes for the Final Cake before a trial is booked, so machine time and material in Geosynthetics & Civil Engineering are committed against a calculated figure rather than an estimate.
• Costing and quotation — Bags or Tubes for the Final Cake is an input to the cost sheet, and quoting from a worked number rather than a remembered one is what keeps a margin intact.
• Troubleshooting — when the floor result drifts from plan, entering the measured values (starting with Slurry Volume to Pump) shows how much of the gap in Bags or Tubes for the Final Cake each variable explains.
• Teaching and study — the accepted ranges bracket normal Geosynthetics & Civil Engineering practice, so moving one variable at a time shows the shape of the relationship rather than a single answer.

Reading the result

Typical bands and what each one is telling you.

Assumptions and limits

• The tool balances masses; every property is yours. Solids content and solids density come from the slurry sample, cake solids and capture from a bench dewatering test with the polymer you will use, and the bag volume and fill share from the supplier. Cake density assumes a saturated cake with no air, which is how a dewatered cake sits in a bag; a cake that dries and cracks later takes less room. Water released is the slurry mass less the cake mass, counted at one tonne per cubic metre, so it carries the escaped solids with it. The bag count is for the final cake: bags are filled, left to drain and refilled many times, so this is the number that are full at the end. **This is a quantity estimate, not a tube design: it does not check the fabric strength, the fill height or the site.**
• Every input is bounded to the range normal practice occupies (Slurry Volume to Pump 1 to 1000000 m³, Dry Solids in the Slurry (by Mass) 0.1 to 60 % and Density of the Solids 1 to 5 t/m³, and so on for the rest). Those bounds are guard rails against typing errors, not a claim that the formula fails one unit outside them.
• The calculation is deterministic: the same inputs always give the same result. It carries no allowance for machine condition, operator skill, ambient conditions or lot-to-lot material variation unless an input above explicitly represents one.
• Nothing is sent anywhere. The maths runs in your browser, so the numbers you type never leave the page.

Standards and further reading

• ASTM D7880/D7880M, Standard Test Method for Determining Flow Rate of Water and Suspended Solids Retention from a Closed Geosynthetic Bag.
• GRI-GT14, the hanging bag test, and GRI-GT15, the pillow test (Geosynthetic Institute): field tests of a fabric and a polymer on your own slurry.
• The discharge permit for the site, which sets what the filtrate may carry back to a watercourse or sewer.

Questions people ask