The behavior of a buried pipeline is significantly influenced by its interaction with the surrounding ground as well as the backfill material. The thrust force generated by the action of internal water pressure tends to move the bend of underground pipeline to the back side. This thrust force is supported by the passive soil pressure that affects the back ground. The concrete block is also used at the bend to minimize the thrust. There is a lack of study on the magnitude of passive soil pressure and distribution of a pipe bend. Such information are required for design. In the current design standard for irrigation pipeline in Japan, back passive soil pressure is assumed to increase in depth with a trapezoid distribution. In other words, when the bend is buried without the thrust block, a trapezoidal passive earth pressure is assumed by projecting it laterally. However, the earth pressure distribution is not readily known when the pipe moves laterally in the ground. In addition, it is not clear about the relationship between pipe intrusion resistance and the interface of the pipe and ground. In this paper, pit tests were conducted using a model pipe having a diameter of 260 mm that was equipped with 20 bi-axial load cells. In addition, similar tests were conducted using a plate with bi-axial load cells. As the pipe moved horizontally in the ground, the distribution of the back earth pressure acting on the bend and plate, and development of slip surface in the backfill sand were measured and investigated.
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