| Neritic deposit soft soil is widely distributed in Chinese coastal areas,disproportionately affect the project. Muddy clay is one of the most typical neriticdeposit soft soils. Its main feature is that the natural water content and the void ratioare big, the gravity density is small, and the plasticity index is high. Its macroscopicproperties show as low intensity, small-capacity, low permeability, highcompressibility, and significant secondary consolidation characteristics. Secondaryconsolidation characteristics and microstructure of soft soil have an importantinfluence on the macro mechanical properties, thus causing problems such asexcessive settlement of buildings, undesirable deformation and long-term deformationinstability.In view of that mentioned above, we chose the undisturbed muddy clay in7meters depth underground at Tianjin Binhai Nangang area as the object to test andresearch. Through staged loading one-dimensional consolidation tests andpreconsolidated individual loading one-dimensional consolidation tests, we studied onsecondary consolidation characteristics of muddy clay that under different loadingmodes. Through microscopic test, we analyzed the relationship between themicrostructure changes and the macro mechanical properties in the process ofsecondary consolidation. Combining with a preloading engineering case, we analyzedthe test results, and then present some conclusions and suggestions for soft soilfoundation engineering construction and foundation preload. The main researchharvests are as follows：(1) The preconsolidation pressure pcof the muddy clay used in this study is63kPa，and the OCR (over consolidation ratio) is about1. It belongs to the normallyconsolidated soils in traditional concept. One-dimensional consolidation test resultsshow that the primary consolidation lasted about150to200minutes and then enterthe secondary consolidation stage. Compared to the loading ratio η, the consolidationpressure p has more influence on the secondary consolidation characteristics. Whenthe consolidation pressure p increases gradually from a small value, the secondaryconsolidation coefficient increases gradually; when the p is close to2pc, the secondary consolidation coefficient reaches the maximum; with the further increase ofconsolidation pressure, the secondary consolidation coefficient decreases gradually;after p>400kPa, the secondary consolidation coefficient decays more and moreslowly.(2) Microstructure test reveals the initial microstructure of muddy clay, and themicrostructure changes in the process of secondary consolidation. The test also hasobtained the aging rules of some main micro morphological parameters.(3) On the variation of secondary consolidation coefficient and compressionmodulus in the process of secondary consolidation has been studied. The results showthat: under the same load stress, with the load time sustaining, the secondaryconsolidation coefficient has a decreasing trend and decays more and more slowly;the compression modulus has an increasing trend without significant numerical rules.Based on the secondary consolidation coefficient attenuating property, and on thebasis of previous research, we analyzed and improved the general secondaryconsolidation settlement calculation formula.(4) After analysis and study on the test results and soft soil preloadingengineering practice, we conclude that: within the range of ultimate bearing capacityof the foundation, appropriate surcharge preloading can make soft soil occurredearlier part of secondary consolidation deformation, and the secondary consolidationsettlement after construction will be decreased; to take effective drainage measures toquickly eliminate the excess pore water pressure in soil, to reduce soil porosity toreduce the particle connectivity rate, can make the secondary consolidation coefficientdecreases to some extent, also are conducive to reduce the secondary consolidationsettlement after construction. |
PDF Full Text Request