When a quadrangular pyramid is cut into a quadrangular pyramid (four hypotenuses extend at one point), the two formulas are completely equivalent, and the formula 1/3 is only applicable to standard pyramids, which can be proved by the fact that the arithmetic mean is greater than the geometric mean.

The frustum must be truncated without any problem (all bus extensions must intersect at one point).

The foundation pit with irregular bottom can only be analyzed in detail, and it can also be divided into certain grids. According to surveying and mapping data, approximate calculation. After all, the calculation of engineering quantity is not a mathematical operation, which allows certain errors and has limited impact on the cost.

Extended data:

Earthwork construction steps include: construction preparation; Site cleaning (measuring and setting out, controlling elevation); Earthwork excavation; Surface drilling; Lime soil backfill.

Earthwork includes: site leveling, subgrade excavation, civil air defense engineering excavation, ground filling, subgrade filling and foundation pit backfilling. To arrange the construction plan reasonably, try not to arrange it in the rainy season. At the same time, in order to reduce the construction cost of earthwork and implement the principle of not occupying or occupying less cultivated land and being beneficial to land reclamation, it is necessary to formulate a reasonable earthwork allocation plan and make overall arrangements.

In building engineering, the most common earthworks are: site leveling, foundation pit (ditch) excavation, floor filling, subgrade filling and foundation pit backfilling.

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