The present study aims to clarify the role of geoenvironment in the benthic ecology and morphodynamics of intertidal flats and beaches on the basis of a new cross-disciplinary research field called Ecological Geotechnics. The principal findings and conclusions obtained through the combined use of field observations/surveys, laboratory experiments, conceptual and theoretical model and analysis are as follows.
　1) It has revealed two new burrowing criteria and burrowing mode adjustment in bivalves to varying geoenvironmental conditions in intertidal flats and beaches, highlighting their mechanics, as well as their role and implications, in the adult–juvenile spatial distributions and behavioral/morphological adaptations there.
　2) It is found that the burrowing benthos has a capability to detect suction gradient and actively selects the suitable geoenvironments for their burrowing, thereby generating patch formation.
　3) Suction governs various geophysical states of sandy beach sediments, and may uniquely determine the peak and critical area of densities for three dominant species inhabiting different coasts.
　4) There exist suitable and critical geoenvironmental conditions for the burrowing activities of diverse species, which are found to differ considerably between species, body sizes and weights. This has led to the development of an ecohabitat chart, which is found to be well consistent with the distributions and habitat selections of diverse benthos at various natural and artificial intertidal flats.
　5) The feedback between sediment transport and the suction dynamics effects has been found to play a crucial role in not only natural but also artificially reclaimed sandbars in intertidal zones, giving rise to an optimal design of such dynamically stable sandbars as habitats with diverse ecological activity.
　These findings are therefore expected to facilitate a new horizon of the performance-based geoenvironmental assessment and management for the diverse species. The developed design for achieving both biodiversity and morphodynamic stability may be used widely in future reclamation projects for intertidal flats and shallow sea.