Page 168 - Geotechnical Engineering Soil and Foundation Principles and Practice

Particle Size and Gradation
Particle Size and Gradation 163

Answer:
(a) G ¼ 90/(690.0 þ 90.0 – 746.0) ¼ 2.65.
(b) Dividing by 0.998 to correct for water temperature does not affect the
answer.
0
(c) G ¼ 91/(690 þ 91 – 746) ¼ 2.53. A suggested assumed value would be
more accurate.

Problems

7.1. Plot a particle size accumulation curve for soil No. 4, Table 7.5, by enter-
ing the data on a computer spreadsheet and selecting the logarithmic
option for the particle sizes. (Optionally this can be done manually using
5-cycle semilogarithmic paper.) (a) Evaluate the effective size and unifor-
mity coefficient. (b) What is the median grain size? (c) Defining clay
as 50.002 mm, silt as 0.002–0.074 mm, sand as 0.074–2.0 mm, and gravel
as 42.0 mm, what are the percentages of clay, silt, sand, and gravel?
7.2. Classify soil No. 4 according to the chart in Fig. 7.7 after adjusting the
percentages for gravel content.
7.3. Plot a particle size accumulation curve for soil No. 1, Table 7.5. (a) Identify
the median and mode(s). (b) If there are two modes, what is the approxi-
mate percentage of each soil in the mixture? (c) Using the size grades
defined in Problem 7.1, find the percentages of clay, silt, sand, and gravel.
(d) Adjust the grade percentages for gravel and classify the soil by the chart
in Fig. 7.7.
7.4. Calculate the effective size and uniformity coefficient for soil No. l.
Answer: D 10 ¼ 0.0039 mm, C u ¼ 192.

7.5. By inspection indicate which of the soils in Table 7.5 should be designated
as gravelly.
7.6. For the first five soils in Table 7.5 compare measured 0.002 mm clay
contents with those interpolated from the 0.001 mm and 0.005 mm clay
contents by eq. (7.5).
7.7. What is meant by a ‘‘well-graded’’ soil? What is the reason for considering
such a soil to be well graded?
7.8. Which soils in Table 7.5 can be injection-grouted with a mixture of Portland
cement, fly ash, and water?
7.9. Soil No. 12 in Table 7.5 is to be separated from No. 14 by means of a filter.
From the two particle size accumulation curves, define (a) desirable
characteristics of a geotextile filter, (b) the gradation(s) required for soil
filter(s): if a single filter layer is not adequate, use two. (c) Select appropriate
soil(s) from the table to use as filter(s).

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