CVEN 365

Sections 300, 301, and 303

Summer 2005

Assignment No. 6

(Textbook: Craig’s Soil Mechanics, 7th Edition, R. F. Craig)

Problem No. 1.

Work Prob. No. 7.2 in your textbook. Note that the laboratory data gives both the loading and unloading (or rebound) test results.

Problem No. 2.

Work Prob. No. 7.4 in your textbook.

Problem No. 3.

Work Prob. No. 7.6 in your textbook.

Problem 04. (Consolidation and Settlement)

Two nearby building sites are occupied by a building that was completed 10 years ago and a vacant lot where a new building is to be built. They are in a place known for its geological irregularity. The new building is to be 15 stories high and the building will apply pressure to the soil surface of 105 kPa. It will have 1.5 times the load of the old building at Site No.1, where the settlement up to the present time is 0.2 m.

The void ratio of the normally consolidated clay at Site No.1 is 0.8 and that at Site No.2 is 0.6 and their measured permeabilities are found to vary as the square of the void ratios. The unit weight of the sand is 17.3 kN/m3 and of the clay is 18.9 kN/m3 at both sites. The compression index of the clay at Site No.1 is 0.41 and at Site No.2 is 0.29. Answer the following questions:

  1. What is the initial effective stress at the middle of the clay layer at each site?
  2. What is the change of effective stress in the middle of the clay layer at each site due to the building load?
  3. What is the maximum settlement that will occur in Site No.1 and in Site No.2?
  4. What is the percent of the total settlement that has occurred to the present time at Site No.1?
  5. What is the current dimensionless time constant, T, for the building at Site No.1. (See Table 6.2, pg.179 in your text)
  6. What is the coefficient of consolidation, cv, of the clay at Site No.1?
  7. Assuming that the av of the clay is the same at both sites, how long will it take the building at Site No.2 to settle 60 percent of its total settlement?

Problem No. 5 (Expansive Clay)

A clay is made up of disk-shaped particles with an average specific surface area of 2 . What matric suction will this soil develop at a water content of 30% and temperature of 25C.? The surface tension is 73 .

1. ______kPa

2. ______psi

3. ______cm

4. ______pF

Problem No. 6

Given:

Soil borings on this site have produced the following information on the soils beneath the foundation:

Liquid Limit = 45%

Plastic Limit = 23%

% - #200 = 75%

% - 2 = 38%

Vertical Strain = 50% of total volume strain

Find.

Plasticity Index

Soil zone No. (I through VI) where the soil plots

Soil compression index for 100% fine clay

Soil compression index for the soil beneath the foundation

The change of pF at the edge of the foundation

The volume strain in the soil in the active zone (top 6 feet) (shrinkage)

The vertical shrinkage strain of the soil at the edge of the foundation

The vertical shrinkage at the edge of the foundation

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