Behavior of a buried flexible steel pipe under groundwater level

A steel pipe 2m in diameter and 20 mm in thickness surrounded by “panel type earth pressure gauges", which can simultaneously measure both normal and tangential components of earth pressure of a backfill soil against a pipe was embedded in soil. After measuring earth pressure of soil in the dry state, groundwater level was raised by pouring water into the bottom of the backfill. The tangential components of earth pressure changed remarkably, but the normal components of earth pressure did not change much, contrary to our prediction. The earth pressure from the side direction decreased with the rise of groundwater. The pipe was elongated horizontally, and the bending moments of the pipe increased accordingly. The apparent earth pressure distribution used for designing flexible pipes gives a triangular shape, but the measured one was similar to the trapezoidal shape just like the earth pressure on the back of retaining walls. The earth pressure was changed by a strong earthquake which happened while the test was being conducted.