課程名稱︰環境土壤物理學
課程性質︰探討土壤的結構與質地如何跟空氣與水作用
課程教師︰李達源
開課學院：農學院
開課系所︰農化系第一類群組必修
考試日期（年月日）︰Apr. 18, 2008
考試時限（分鐘）：兩節課，100鐘
是否需發放獎勵金：是
（如未明確表示，則不予發放）
試題 :
1. Please define the following term in a few sentences: (15%)
(a) Pore size distribution of soils
(b) Aggregated soil structure
(c) Reference state of soil water potential
(d) Matric potential of soil water
(e) Osmotic pressure of soil water
2. Find the total potential head components at points A and B in the
following equilibrium system consisting of (16%)
(a) A salt solution of relative humidity of 0.65 in a closed chamber next
to a soil sample at T = 27C.
(given surface tension of water = 72 dynes/cm, R = 8.314 J/K mol)
┌──────────────────────────┐
│ │
│ │
│ │
│ │
│ │
│ │
│ │
│ A B │
│ │﹌﹌﹌﹌﹌﹌﹌│ │﹌﹌﹌﹌﹌﹌│ │
│ │ Solute │ │ Solute │ │
│ │ │ │ │ │
│ └───────┘ └──────┘ │
└──────────────────────────┘
(b) ↑ ┌───┐ ← Soil sample
│ │ │ A (no evaporation)
│ ┌─┴───┴─┐
50cm │ └──┬─┬──┘← Porous ceramic
│ │ │
│ │ │
↓ │ │
B │﹌﹌﹌│ │ │
│ │ ← free solution │ │
└┬─┬┘ S = -200cm │ │
│ │ │ │
│ │ │ │
│ │ │ │
│ │ │ │
│ │ │ │
│ ╰────┬──────╯ │
╰──────┴────────╯
↑ membrane impermeable to solutes,
permeable to water.
3. Describe what information related to soil water is measured or prepared by
the following instruments. (15%)
(a) Tensiometer
(b) Thermal couple psychrometer
(c) Gypsum block
(d) Neutron probe
(e) Time Domain Reflectometer (TDR)
5. The accompanying data were obtained with tension plate and pressure plate
extraction devices from two soils of unknown texture.
────────────────────────────────
Suction head (cm) Volumetric water content (%)
────────────────
Soil A Soil B
────────────────────────────────
0 52 44
10 52 44
20 52 43.9
50 51 38
100 48 22.5
300 32 12.5
1000 20 7
10000 13.5 5.2
20000 13 5.1
100000 12.4 4.9
────────────────────────────────
(a) Sketch the two soil moisture characteristic curves. (6%)
(b) Estimate the bulk density, assuming that the soils do not swell or
shrink. (5%)
(c) Estimate the field capacity and the volumetric water content at
wilting point. (5%)
(d) What are the likely soil textures of soil A and B and explain why? (4%)
5. A mercury manometer tensiometer is inserted 100cm below the soil surface
into a region of soil with matric potential head h = -50cm. The mercury
reservoir has a free surface 10cm above the soil surface. Calculate how
high above the free mercury surface column will rise at equilibrium?
(ρHg = 13.5g/cm^3) (10%)
6. A vertical saturated soil column of height 25cm has 10cm of water ponded on
it at t = 0. Four hours later the height of weater ponded has dropped to
5cm. What is the satureated hydraulic conductivity of this soil? (4%)
7. A long soil column (101cm) containing 100cm of sand of saturated hydraulic
conductivity 10cm/hr has a thin caly lens (1cm) of saturated hydraulic
conductivity 0.1cm/hr located somewhere inside of it. (10%)
(a) What is the effective saturated hydraulic conductivity of the entire
column?
(b) If the clay lens is on the bottom, what is the flux through the column
if 10cm of water are continously ponded on the top? What is the
pressure at the sand-caly interface?
│﹌﹌﹌﹌│
│ │10cm
├────┤
│ │↑
│ ││
│ sand ││
│ ││ 100cm
│ ││
│ │↓
├ －－－ ┤←─ P = ?
│ clay │1cm
└────┘
↓
J = ?
8. A capillary tube of r = 0.1cm radius and L = 10cm length has a hydraulic
head difference of 10cm across it. Calculate the discharge Q in cm^3/sec
and the flux in cm/sec through the tube. How many tubes of r = 0.01cm
radius and L = 10cm length with the same hydraulic head gradient are
required to produce the same discharge and what is the flux through such a
network? (viscosity coefficient of water ν= 0.01g/cm/sec) (10%)
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