Mechanical Response Of Consolidation State To Soil Between Underwater Compaction Piles Strength Recovery

During the analysis of soil strength between piles in composite foundation with gravel column, the consolidation state of the undisturbed soil should not be neglected. Underwater sand compaction piles are adopt to treat soft foundation in the Hong Hong-Zhuhai-Macao bridge engineering which provides an opportunity to study composite foundation's characteristics and the mechanical property of the soft soil. In order to declare the strength increase-process of soil between piles in composite foundation, the high pressure consolidation test, vane shear test and standard penetration test are achieved. What's more, the effective additional stress (p(0)) of the overlaying soils and over-consolidation ratio (OCR) are calculated with statistical data. On the basis of the least square method, the linear equation between undrained shear strength (C-u) and test depth (H) are obtained. The result shows that pile driving can change the consolidation state of soil between piles, that's to say, the under-consolidation soil can convert to over-consolidation soil, and the over-consolidation soil can convert to under-consolidation soil too. In addition, when the replacement rate is 25.6%, strength growth rate of under-consolidation soil between piles ranges from 16.4% to 80%. When the replacement rate is 55%, strength growth rate of over-consolidation soil between piles will become 19.4%. Considering the influence of test time, when the lasted time is 2 months, strength growth rate of under-consolidation soil between piles will become 13.2%similar to 27.3%. When the lasted time is 6 months, the strength growth rate keeps stable growth. When the time is 12 months later, the strength growth rate will increase to 164%. The obtained results can provide the foundation treatment experience for geotechnical engineers and the best time for the strength of pile testing.