Hitoshi Nakase

Mechanical behavior of model pile with multiple stepped two diameters

A pile with multiple stepped two diameters showed higher bearing capacity than a conventional cylinder pile. In t his paper, model tests were conducted to examine for the bearing mechanism of this pile. The purpose of this study was as follows. (1) To measure the load bearing characteristics of model piles installed a small load cell at the end of pile. (2) To observe the behavior of soil particles around the model pile after loading by excavating the suction applied ground, and comparing with the behavior of soil particles of model piles of longitudinally half -cut shape (3) To measure load transfer characteristics by earth pressure transducers placed in the model ground in the loading tests. The same cases were analyzed by DEM (Distinct Element Method). As a result, it can be concluded that a multiple stepped pile shows higher bearing capacity because of the load transmitted from the convex parts to the outside diagonally.

Distribution of Traffic Loads for Shallowly Buried Pipe by D.E.M. Analyses

Shallowly buried pipelines may exhibit large deformation as a result of traffic loading, especially since the stress concentrates at the crown of the pipe. In this paper, numerical analysis was conducted using the discrete element method to investigate the behavior of shallowly buried flexible pipe due to traffic load. The pipe examined was a 2000 mm diameter pipe backfilled with gravel. As a new technique for dispersing traffic loads under shallow cover depth, an installation method utilizing sandbags in the backfill materials was explored. The results indicated that the stress acting on the top of the pipe was distributed by the sandbags.

LATERAL LOADING TESTS FOR BURIED PIPE WITH GEOSYNTHETICS

The thrust force generated due to internal water pressure in a pipe tends to move the bend of underground pipeline to the backside. This trust force is supported by the passive soil pressure at the back of the ground. The thrust force is commonly resisted by the concrete block at the bend. The earth pressure distribution at the back of the ground as the pipe moves laterally is not readily known. In addition, concrete block is not desired in the event of earthquakes because if its inertia force to move. In this paper, pit tests were conducted using a model pipe having a diameter of 90 mm in a dry sandy ground. Geosynthetic was used as anchor to resist the movement of the pipe. In addition, similar tests were conducted using a model pipe of square surface assuming it as a concrete block. The resisting force acting on the model pipe and the earth pressure in the sand ground were measured as the pipe moved horizontally in the ground. The development of slip surface in the backfill ground surface was also investigated. The test results showed that proposed lightweight method that used geosynthetic had significant effect in improving the resistance against thrust force.