Abstract: It is an innovation to use pebble cushion with furrow as the foundation of a large-scale immersed tunnel. In order to investigate the deformation characteristics of the pebble cushion subjected to engineering load under water, static load model tests are carried out in seven working conditions. The compression modulus of pebble cushion under various working conditions, the relationship between load and settlement are obtained. The effects of cushion thickness, ridge and furrow dimensions, preloading load and gradation on the mechanical properties of pebble cushion are analyzed. Unlike the gravel cushion, the settlement of pebble cushion initially changes nonlinearly with vertical load. With the increase of load, the settlement rate of the pebble cushion gradually decreases. The relationship between load and settlement tends to be linear after the cushion is compacted to a certain extent. The larger maximum size of the pebble results in a larger compression modulus of the cushion and a smaller settlement. The pre-compression leads to a significant reduction in the subsidence of the pebble cushion and an increase in compression modulus when compressed again. As the distance between the furrows increases and the compression modulus of pebble cushion decreases, the settlement increases. With increasing the thickness of the cushion, the settlement and compression modulus of the pebble cushion increase slightly. The research results can provide reference for the design of immersed tunnel cushion.

Key words: immersed tunnel, pebble cushion, deformation characteristics, experimental study