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367 g cmp3 = 1367 kg m - 3 pw = 90 cm3 b Pd = ~87= g0 . 7gcm-3 Zo*193 4min = 90 cm3 ~ (87 - 47) g p . 510 b. ps is the average density of the solid phase. The low value indicates that the soil is chiefly made up of organic matter, with a relatively small amount of mineral matter. This illustrates that one has to be careful with taking ps = 2650 kg m-3. This value is valid only for a mineral soil with a low organic matter content. 357 cm3 = 1 . 422 orOz 1000 PI W = b o r O ~ w - =P d0 . 357 cm3 4, = $min 4org = 0.
In that case, the stress can be measured as a pressure, p (Pa), and is, unlike force and acceleration, a scalar quantity. Question 2. I I Why is p scalar? 2), with horizontal upper and lower square planes with edges I and vertical planes with height Az. As usual, a coordinate system is chosen with x andy in horizontal directions and z , positive upwards, in the vertical direction. Suppose the average pressure on the vertical plane at the left-hand side is p l . Then the magnitude of the horizontal force on this plane is F , = I x Az x p , .
P. WARKENTIN, 1975. Soil properties and behaviour. , 449 p. Chapters I , 2 and 3. 6 ANSWERS CHAPTER 1 Answer I.! The only combinations of two phases that occur together in soil are: a. the solid and liquid phase; b. the solid and gas phase. The former occurs when the soil pores are completely filled with the liquid phase. The latter occurs when the soil is absolutely dry. 2 The only possibility for a soil to consist of one phase would be solid rock, and this is not considered to be a soil. 3 A good estimate for the density of a stone is 2700 kg m-3,, unless there are a great deal of clearly recognizable heavy minerals.