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18 June, 14:07

The in situ moist unit weight of a soil is 17.3 kN/m3 and the moisture content is 16%. The specific gravity of soil solids is 2.72. This soil is to be excavated and transported to a construction site for use in a compacted fill. If the specification calls for the soil to be compacted to a minimum dry unit weight of 18.1 kN/m3 at the same moisture content of 16%, how many cubic meters of soil from the excavation site are needed to produce 2000 m3 of compacted fill?

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  1. 18 June, 17:55
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    Given that,

    Moist content w = 16%

    The in situ moist unit weight of the soil : γ (in situ) = 17.3 kN/m³

    Specific gravity of the soil

    G (s) = 2.72

    Minimum dry unit weight of the soil

    γd (compacted) = 18.1 kN/m³

    Moist content is same as above

    w = 16%

    Question

    how many cubic meters of soil from the excavation site are needed to produce 2000 m³ of compacted fill?

    Let determine the in situ dry unit weight γd (in-situ) using the relation

    γd (in-situ) = γ (in-situ) / [1 + (w/100) ]

    γd (in-situ) = 17.3 / [1 + (18/100) ]

    γd (in-situ) = 17.3 / (1 + 0.18)

    γd (in-situ) = 17.3 / 1.18

    γd (in-situ) = 14.66 kN/m³

    To determine the Volume of the soil to be excavated (Vex)

    Let the Volume to be excavated = V

    We can use the relation

    V=V (fill) * γd (compacted) / γd (in situ)

    Given that, V (fill) = 2000m³

    V (fill) is the volume of the compacted fill

    Therefore,

    V=V (fill) * γd (compacted) / γd (in situ)

    Vex = 2000 * 18.1 / 14.66

    Vex = 2469.13 m³

    So, the excavated volume of the soil is 2469.13 m³
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