Field Test And Effect Evaluation Of Dredger Fill Foundation That Consolidated By Dynamic Compaction In Ganyu Port

The development of coastal regions of China leads to the problem of land shortage has become increasingly prominent, and reclamation silt, with its significant economic, environmental and social benefits, have been widely used in reclamation, ports and other projects. Dredger fill has become an important resource for coastal areas because it has solved the problems such as increasingly scarce and prices rising of traditional fillers. However, because the engineering properties of dredger fill is very complex, and the lack of systematic research so far, thus the technology of dredger fill foundation treatment still needs further exploration and improvement. As one of the most widely used technology of foundation treatment, there is less instance that dynamic compaction was used for dredger fill foundation treatment, the analysis of field test and effect evaluation of dredger fill foundation which strengthened by dynamic compaction are both need more comprehensive and in-depth study. This paper selects Ganyu port construction as the background, to participate in the design, construction and effect detection of the whole dynamic compaction construction, through theoretical research, laboratory tests, field tests and numerical simulation on consolidation of dredger fill foundation to conduct the system research. The main contents and results are as follows:(1) A profound understanding of reinforcement mechanism and engineering applications of dynamic compaction, combining with the complex engineering properties of dredger fill site, studying the mechanism of dredger fill foundation reinforced by dynamic compaction. According to the complexity and particularity of dredger fill foundation, this paper choosed the appropriate in situ test methods, and put forward a dynamic compaction effect evaluation system which combined of in situ test and mathematical analysis, this evaluation system includeds:1) the effect evaluation of the foundation’s strength improvement; 2) the foundation’s uniformity evaluation which combined with uneven foundation coefficient β and the coefficient of variation of soil strength index.(2) Making a detailed understanding of the dredger fill’s properties in Ganyu port by the site test and indoor test, clearing the engineering characteristics of the site before tamping. Analyzing the changes of pore water pressure, settlement and horizontal displacement in the process of single compaction test, results showed that the pore pressure dissipation time was about 17h, the effective reinforcement depth was about 6m, the plane influenced range was about 6.5m, the best tamping energy was 2000kN.m. Validating the inhomogeneity of dredger fill foundation quantitatively through the static cone penetration test. Determining the group rammed test program depended on the single compaction test results.(3) We found that tip resistance of soil and dynamic penetration were significantly improved in the effective reinforcement depth of 6m by in situ testing, the foundation did not appear obvious plastic deformation and failure in the load test, the allowable bearing capacity was 165kPa, met the design requirements. The evaluation results of reclaimed soil foundation effect after dynamic consolidation showed that, after the consolidation, the strength of dredger fill foundation was significantly improved, the differences among soil strength index were reduced, the uniformity of foundation had been significantly improved. Based on results of this study, it was suggested that in the similar projects, in situ test method should be preferred CPT, the testing data of the same soil strength index should be no less than 6 groups, the distance between two detection points should not exceed 25m, when chose the cone tip resistance’s variation coefficient of soil to evaluate the uniformity of foundation, the cone tip resistance’s variation coefficient of homogeneous foundation should be less than 25%.(4) Using the finite difference software FLAC3D to simulate the reinforcement of dredger fill foundation by dynamic compaction. Analyzing the dynamic stress’s distribution and development in the dredger fill foundation, the changes of settlement and horizontal displacement with tamping energy and the number of tamping, the results showed that the dynamic stress made the horizontal displacement and the bump of ground surface; the settlement showed a nonlinear increased with the tamping energy and the number of tamping, the effect of tamping on the ground surface was about 6m, the effect depth was about 8m, the suitable tamping number was determined as 9 when the tamping energy was 2000kN.m, which was same with the field test results.