**Experiment 1** Students assembled a constant-head permeameter apparatus to measure the h… — ACT

Experiment 1
Students assembled a constant-head permeameter apparatus to measure the hydraulic conductivity ( $K$ ) of a compacted soil core. The apparatus consisted of a cylindrical soil container fitted with porous end plates to retain the soil while allowing water flow. Water was continuously supplied to an upper overflow reservoir to maintain a constant head difference ( $\Delta h$ ) between the inlet at the top and an overflow outlet at the bottom. Two manometer tubes were tapped directly into the side of the soil container at a fixed vertical distance ( $L$ ) apart to monitor pressure head within the soil core. Water discharging from the bottom outlet was collected in a graduated cylinder over a measured time interval ( $t$ ).

What was the primary function of tapping the two manometer tubes directly into the sides of the soil container rather than relying on the water levels in the external upper and lower supply reservoirs?

To measure the hydraulic head loss specifically within the soil specimen while isolating it from resistance caused by the porous end plates and tubing connections.Answer
B
To increase the total volumetric flow rate of water passing through the apparatus during each trial.
C
To serve as a negative control group to demonstrate that hydraulic conductivity is independent of soil compaction.
D
To regulate and hold constant the independent variable of water collection time across multiple test runs.

Answer

The primary function of tapping the two manometer tubes directly into the side of the soil container was to measure the head loss strictly across the soil specimen itself, excluding energy losses associated with the porous end plates and inlet/outlet fittings.

The correct answer correctly identifies that placing manometer taps directly along the soil column isolates the hydraulic head drop across the soil distance

L

. This eliminates measurement errors caused by head loss across the entrance/exit porous plates and connecting hoses, ensuring accurate determination of the soil's intrinsic hydraulic conductivity.

Step-by-Step Solution

Analyze the role of manometer tubes in fluid head measurement within a permeable medium.

Manometers register hydraulic pressure head at specific physical tap locations along the fluid flow path.

Direct pressure taps give local pressure readings within the sample column.

Evaluate why internal tap points differ from external reservoir levels.

External reservoir levels include additional head losses from fluid passing through boundary elements like porous plates, mesh filters, and connection tubes.

Isolating the measurement points to the interior of the soil core ensures Darcy's Law calculations reflect only the soil matrix properties.

Key Concept

Analyzing apparatus component functions to eliminate head loss measurement errors in flow experiments

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