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Consulting Engineers and Geologists <br />Due to the wide variety of soil types and compaction conditions the lab- <br />oratory permeability tests had a broad range of values. Permeabilities <br />for the samples tested ranged from 1.4 X 10-3 feet per second to 7.5 X <br />10-10 feet per second (4.3 X 10-2 cm/sec to 2.3 X 10-8cm/sec). The <br />nature of the embankment necessitated the use of an average permeability <br />for the entire embankment. The value used for our analysis was 1.4 X <br />10-5 feet per second (4.3 X 10-3 cm/sec). <br />Materials Shear Strength. Due to the erratic density and moisture <br />contents ,as well as the nature of construction, the embankment <br />exhibits a wide variety of material types and corresponding shear <br />strengths. The large rock fragments made retrieval of quality in- <br />situ samples for shear strength evaluation difficult, and the samples <br />obtained were highly disturbed. It is our opinion that the disturbed <br />state of field samples, if tested by conventional shear strength testing <br />(i.e., triaxial, direct shear, or unconfined compression test), would <br />not be indicative of the true shear strength of the embankment soils. <br />A probabilistic approach to the analysis of the standard penetration <br />test was, therefore, required in order to determine shear strengths <br />and confidence levels for the penetration values obtained in the field. <br />The statistical methods used for determining the level of confidence <br />for Standard Penetration Tests are explained in detail in Mechanics <br />of the Particulate 14edia by M. E. Harr (Bibligraphy Reference No. 4 ). <br />An outline of this statistical approach used in the analysis is <br />presented in the following paragraphs. <br />Refer to Histogram of Standard Penetration Tests, Figure 6. This <br />histogram plots the frequency of occurrence on a vertical axis versus <br />the Standard Penetration Test values in blows per foot. The distribu- <br />tion of the main portion of the curve approximates a normal distrib- <br />ution. The sample size analyzed used 68 entries. Values of the <br />Standard Penetration Tests greater than 45/12 containing large rock <br />-7- <br />