Vertical Earth Pressure on a Pipe in the Ground

Abstract

ABSTRACT Two main assumptions in Marston-Spangler theory on vertical earth pressure on a buried pipe, which are two vertical planes (a pair of vertical slide lines) and a plane of equal settlement are discussed by the use of X-ray film analysis. Sand surrounding a pipe fixed in a small sand bin is forced to settle by lowering a trap door, and just after lowering the trap door by a controlled amount, vertical earth pressure on the pipe is measured (see Fig. 4) and an X-ray film is taken (see Appendix). According to X-ray pictures which show slide lines, settlement of sand particles (small lead balls instead of sand particles) and location of the pipe, two vertical planes could not be signified and could not reach vertically the top of the embankment, but the plane of equal settlement could be suggested. Propagation of slide lines can be considered to depend upon H/D ratio (H: height of the sand layer above the pipe, D: pipe diameter). In the experiments, the ratio was 6.3 ~ 15.4. Only when the ratio is very small, a pair of slide lines will be supposed to reach vertically the top of the embankment. On the other hand, characteristic correlation between vertical pressure and settlement by lowering the trap door was obtained. Further analyses on the relation between the slide lines around a pipe and measured vertical earth pressure are necessitated to calculate vertical earth pressure on a pipe including the conditions which govern Marston-Spangler theory.