Download Soil Moisture and Porosity Calculations using 3-phase Diagram and more Exams Chemistry in PDF only on Docsity!
Use of the 3-
phase
diagram
RobHarrison:whole soil structure texture
sand
sand
silt sand
silt silt silt
RobHarrison:whole soil structure texture
THE 3-phase
diagram
air water
solids
Wt Ws
Vt Ww
Va Vw Vs
Vp
Soil Relationshhips
• Vt=Va+Vw+Vs
• Wt=Ww+Ws
• Ww =VwDw (=Vw*1 g/cc)
• Ws=VsDp
air
water
solids
Wt
Ws
Vt Ww
Va
Vw
Vs
Vp
Definitions
Void ratio = e = Vp/Vs Porosity = n = Vp/Vt Water content = (^) m = Ww/Ws (moisture content) % moisture = Ww/Wt % solids = Ws/Wt Degree of saturation = S = Vw/Vp Particle density = Dp = Ws/Vs (specific gravity) Bulk density = Db = Ws /Vt
Note: all of these are normally expressed as a “%”, i.e., times 100%
Example 1
A soil has the following characteristics:
- wet weight = 2500 g
- dry weight = 2000 g
- void ratio = 100%
- particle density = 2.
wet weight = 2500 g dry weight = 2000 g void ratio = 100% particle density = 2.5 g/cc
air
water
solids
Wt
Ws
Ww Vt
Va
Vw
Vs
Vp
= 2500g
= 2000g
= 500g = 500cc
= 2000g/2.5 g/cc = 800 cc
e = Vp/Vs = 100%
= 800 cc
= 300 cc
= 1600 cc
Vp = 800 cc
Find
Water content = (^) m = Ww/Ws*100% (moisture content)
air
water
solids
Wt
Ws
Vt Ww
Va
Vw
Vs
Vp
2000g
500cc 500g
800 cc
800 cc
300 cc
1600 cc (^) 2500g
= 500 g/2000 g * 100% = 25%
Find
% moisture = Ww/Wt
air
water
solids
Wt
Ws
Vt Ww
Va
Vw
Vs
Vp
2000g
500cc 500g
800 cc
800 cc
300 cc
1600 cc (^) 2500g
= 500 g/2500 g * 100% = 20%
Find
% solids = Ww/Wt
air
water
solids
Wt
Ws
Vt Ww
Va
Vw
Vs
Vp
2000g
500cc 500g
800 cc
800 cc
300 cc
1600 cc (^) 2500g
= 2000 g/2500 g * 100% = 80%
MOISTURE RELATIONSHIPS
Water (moisture) content = 25% % moisture = 20% % solids = 80% Therefore: % moisture = 100% - % solids
Example 2
A soil has the following characteristics:
• Dry weight = 2000 g
• Moisture content= 50%
• Volume = 2000 cc
• Particle density = 2.65 g/cc
- Dry weight = 2000 g
- Moist. content = 50%
- Volume = 2000 cc
- Particle density = 2.65 g/cc
air
water
solids
Wt
Ws
Ww Vt
Va
Vw
Vs
Vp
= 3000g
= 2000g
= 1000g = 1000cc
= 2000g/2.65 g/cc = 755 cc
m = Ww/Ws 50% = Ww /2000g
= 1245 cc
= 245 cc
= 2000 cc
Ww = 1000 cc
Alternate for measuring pore space
Vp = Vt - Vs
Dp = Ws/(Vs)
Known volume
Oven dry sample determine dry weight
Vs
= Vt
