Variable Head Permeability Tests

Variable head permeability tests measure how quickly water flows through the ground around a borehole or standpipe. The result — the permeability coefficient (k) — tells engineers how easily water moves through the soil, which is critical for drainage design, dewatering, and contamination assessment.

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How the Test Works

Water is either added to (falling head) or removed from (rising head) a standpipe installed in the borehole. Timed readings of the water level are taken as it returns to its natural rest level. The rate of change gives the permeability.

The form writes to four AGS groups: FGHG (test setup), FGHI (instrumentation), FGHS (test stages), and FGHT (timed readings).

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Navigation

This form has a multi-level structure:

Item	Description
Test List	View all tests at this location, create new ones, or open existing ones.
Setup	Configure the test parameters.
Stages	Each test can have multiple stages (e.g. rising and falling head).
Readings	Timed water level readings within each stage.
Results	Auto-calculated permeability for each stage.

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Test Setup (FGHG)

Item	Description
Test Number	Auto-incremented.
Date	When the test was performed. Required.
Test Type	How water was displaced (e.g. falling head, rising head). Required.
Configuration	The hole setup type.
Depth Top / Base	The top and base of the slotted/response section in metres. Required.
Standpipe Diameter	Internal diameter in mm (default 50). Used in the permeability calculation.
Casing Depth	Bottom of casing in metres.
Rest Water Level	Depth to water before the test, in metres. Required — this is the baseline the water level returns to.

An optional Instrumentation section lets you record the dip meter or transducer details.

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Stages (FGHS)

Each test can have one or more stages. A stage represents a single displacement event (e.g. one bail-out or one pour). When you add a stage, you can record:

Item	Description
Applied Head	Height of water above rest level in metres.
Start / End Time	When the stage began and ended.
Remarks	Notes about this stage.

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Readings (FGHT)

Within each stage, take timed readings of the water level. Tap Stamp + New Row to add a reading with the current time pre-filled.

Each reading records:

Item	Description
Time	When the reading was taken (24-hour clock).
Depth	Depth to water in metres.
Elapsed	Auto-calculated from the first reading.

When you submit readings, the app auto-fills stage start/end times and calculates the permeability.

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Results

After submitting readings, the Results page shows:

Item	Description
Permeability (k)	Calculated using the Hvorslev method, displayed in m/s.
Applied Head	Derived from the rest water level and the initial reading.
Recovery	How much of the displaced water has returned to rest level.
Reading Summary	Start/end times, duration, and number of readings.

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Tips

• Always measure the rest water level accurately before starting — the entire calculation depends on it.

• Take readings frequently at the start (when the level changes fastest) and less frequently as it stabilises.

• The 'Stamp + New Row' button auto-fills the current time — just enter the depth reading.

• Multiple stages let you run rising and falling head tests at the same depth for comparison.

• The permeability result appears automatically once you have at least two readings in a stage.