Page 248 - Geotechnical Engineering Soil and Foundation Principles and Practice

Pore Water Pressure, Capillary Water, and Frost Action
Pore Water Pressure, Capillary Water, and Frost Action 243

What parallel can be drawn to compressive stress in the capillary zone
of a soil?
11.6. Two soils have the sorption characteristics shown in the accompanying
table. Draw the sorption curves with moisture content along the x-axis.

Moisture content (%)
Water, m Soil A Soil B

0.10 47 32
0.316 33 17
1.0 22 12
3.16 17 9
10.0 13 7
31.6 10 5

11.7. Assume that two masses of soils A and B in Problem 11.6 are at the same
elevation above a water table and are in intimate contact with each other.
If soil A contains 17% moisture and B contains 12%, will capillary water
flow from A to B or from B to A, or will it remain static?
11.8. A subgrade soil under an impervious pavement has the sorption
characteristics of soil A in Problem 11.6. What will be the accumulated
moisture content of the soil 0.3 m (1 ft) below the bottom of the pavement,
if the water table is constant at an elevation 1.5 m (5 ft) below the bottom
of the pavement?
11.9. Repeat Problem 11.8, using soil B in Problem 11.6.
11.10. What is meant by the zone of capillary saturation? Is the pressure in the
soil water within this zone greater than, less than, or equal to atmospheric
pressure?
11.11. In a certain locality the water table rises steadily from October to April and
then falls steadily from May through September. Will the zone of capillary
saturation extend a greater or lesser distance above the water table in July
than in March?
11.12. The water in a capillary tube extends 0.9 m (3 ft) above a free water surface.
Determine the pressure in the water in this capillary tube: (a) at the free
water surface; (b) 0.3 m (1 ft) above the free water surface; (c) 0.6 m (2 ft)
above it; (d) just below the meniscus; (e) just above the meniscus.
11.13. Explain to a 6-year-old why sand castles built at the water margin on a
beach crumble when the tide comes in. Do they also crumble when they dry
out?
11.14. What is the best time to drive a four-wheeler on a sandy beach, when the
tide is coming in or going out? Why?

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