Understanding Tensiometer Pressure Calculation
This solution explains the calculation for the pressure at a tensiometer's porous cup within an unsaturated zone. It uses the provided gauge pressure, elevations, and the specific weight of water.
Given Data
- Elevation of Pressure Gauge ($h_g$): 145.8 m
- Elevation of Porous Cup ($h_p$): 144.2 m
- Pressure Measured at Gauge ($P_g$): $-19.62 \times 10^3$ $N m^{-2}$
- Specific Weight of Water ($\gamma_w$): 9810 $N m^{-3}$
Step-by-Step Solution
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Calculate Elevation Difference: Determine the vertical distance between the gauge and the porous cup.
Elevation difference ($\Delta h$) = $h_g - h_p$
$\Delta h = 145.8 \, m - 144.2 \, m = 1.6 \, m$
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Calculate Pressure Head: Compute the pressure exerted by the water column corresponding to the elevation difference.
Pressure due to water column = $\Delta h \times \gamma_w$
Pressure = $1.6 \, m \times 9810 \, N m^{-3} = 15696 \, N m^{-2}$
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Determine Porous Cup Pressure: Add the pressure due to the water column to the gauge pressure to find the pressure at the porous cup ($P_p$).
$P_p = P_g + (\Delta h \times \gamma_w)$
$P_p = (-19.62 \times 10^3 \, N m^{-2}) + 15696 \, N m^{-2}$
$P_p = -19620 \, N m^{-2} + 15696 \, N m^{-2}$
$P_p = -3924 \, N m^{-2}$
Estimated Pressure Result
The calculated pressure at the porous cup is $-3924$ $N m^{-2}$.
Important Questions from Soil Moisture Measurement
- An undisturbed soil sample is collected from a field with core cylinder having an internal diameter of $60\text{ mm}$ and length of $100\text{ mm}$. The weights of moist soil and oven dried soil are $0.48\text{ kg}$ and $0.44\text{ kg}$, respectively. Assuming density of water as $1000\text{ kg.m}^{-3}$, the water depth (in metres per metre depth of soil) is ________
(Rounded off to two decimal places) - In-situ volumetric soil moisture content measuring method(s) is/are:
- Tensiometer installed in the soil measures
Undisturbed soil sample is collected from a field when the soil moisture is at field capacity. The inside diameter of the core sampler is 7.5 cm with a height of 15 cm. Weight of the core sampling cylinder with moist soil is 2.81 kg and that with oven dry soil is 2.61 kg. The weight of the core sampling cylinder is 1.56 kg. Assuming $\pi = 3.14$, the water depth in centimeter per meter depth of soil (rounded off to two decimal places) is__________.
- Match the following items between Column-I and Column-II with the most appropriate combinations:
Column-I Column-II 1) Neutron Probe P) Open channel flow 2) Pressure Plate Apparatus Q) Deep percolation 3) Tipping Bucket R) Aquifer parameters 4) Current Meter S) Soil moisture 5) Pumping Test T) Rainfall intensity 6) Lysimeter U) Soil-moisture characteristic curve
