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Abstract Meso-structure characterization of sand was studied on pile-bucket foundation bearing uplift load. Based on a series of uplift loading model tests，analysis of the failure modes and the development of slide rupture body in soil of pile-bucket foundation and the deformation process of soil is performed. Then soil meso-structure on plane of rupture and pile side is recorded with photos. Uplift failure of the pile-bucket foundation can be analyzed as compressive deformation of soil on the top part of the bucket-developed plastic zones—complete shear fracture of progressive failure. The frictional force of the bucket and pile will cause an increase in the shear stress of the soil surrounding the bucket and pile，and it will also cause developed plastic zones—complete shear fracture and progressive failure in the soil. The cracks on the surface of the soil are based on the centre of the concentric circle ring cracks in the centre of the foundation. The radius of the outer flank of the circle ring cracks has a good correlative relationship with the width of the foundation，about approximate 5.6 times against that of the bucket radius. Change of soil meso-structure characterization was researched. Load increasing，quantities of large pores increasing，and pore volumes will play leading roles in the change of soil structure；and gradually the direction of sand grains plays a leading role. Therefore，soil structure is loose，and contact points of grains are decreased；interlocking contact of grains are decreased. The grains have been marked directionality on plane of rupture. The relation of meso-structure parameters and pull strength on plane of rupture，porosity，incremental porosity，total grains，grains area and eccentricity of grains of rupture of plane have sudden change on uplift load；and their rates of change all are maximum. When load increasing and porosity are increased，the total grains，grains area and eccentricity are decreased. The porosity of soil structure of pile side is influenced by the uplift load，it will be influenced by pile sliding，and be influenced by general-shear failure. The results have important values on meso-mechanics study of subgrade bearing uplift load.
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Received: 28 July 2006
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