| Cement-soil, with the characteristics of extensive sources, easy construction, low price and good performance, is widely used in foundation pit support, foundation treatment, slope reinforcement and other engineering projects. One of the important parts of the Hong Kong-Zhuhai-Macao Bridge is the connecting line project in Zhuhai, the basement of whose open excavation section is reinforced by combining the methods of high pressure jet grouting and deep mixing, thus the treated basement contains a lot of cement-soil. In the meantime, the groundwater under the basement is connected with erosive brine. The erosion of brine changes the mineral composition and microstructure of the cement-soil, thus deteriorates its mechanical properties and durability. Therefore, to explore the mechanical properties and durability of cement-soil under erosive environment are subjects that worthy pay great attention. In this paper, combined with the engineering practice of Hong Kong-Zhuhai-Macao Bridge, the change rule of strength of cement-soil under brine environment was studied. Then, an equivalent model of the strength characteristics of cement-soil under brine environment was established and used to forecast the durability of cement-soil under brine environment, which can serve as a guide to the engineering practice, and has great theoretical value and engineering significance.Firstly, in order to simulate the brine environment, a variety of chemical solutions were prepared and soaked the cement-soil samples of different characteristics in the chemical solutions at the scheduled times. Then, the uniaxial compression tests, electron microscope scanning and Ion chromatographic determination were performed. And unconfined compressive strength of the cement-soil samples, microstructure pictures of these samples and solution concentration after soaking were obtained respectively.Through analyzing the unconfined compressive strength datum of cement-soil under pure water, sodium chloride solution, magnesium chloride solution, magnesium sulfate solution, solutions of sodium chloride and magnesium chloride, the mixed solutions of sodium chloride and magnesium sulfate respectively, the relationship between the unconfined compressive strength of the cement-soil samples under these six kinds of solutions and the solution concentration as well as the erosion time was obtained. Then, the unconfined compressive strength of cement-soil under erosive environment was decomposed into two parts, the unconfined compressive strength under pure water and the unconfined compressive strength change under erosive environment. Based on the latter part, the relationship between the unconfined compressive strength and the solution concentration as well as the erosion time was studied. The microstructure picture of the cement-soil and the solution concentration were analyzed after the erosion. The relationship between the microstructure of cement-soil and the solution concentration as well as the soak time and the relationship between the ion concentration of erosive solution and erosion time were obtained respectively.Then, a cemented soil strength characteristic equivalent model was built. The strength of a cemented soil sample is mainly composed of.compaction rate of soil particle and cement filing between particles and cementing strength. Suppose that the erosive environment have no effect on compaction rate of soil particle,and only have effect on cementing agent between soil particle,based on damage mechanics and chemical kinetics, an erosion solution concentration-erosion time equivalence principle of cemented soil strength was deduced. Experimental data of strength change of cemented soil induced by erosive environment was used to test and verify erosion solution concentration-erosion time equivalence principle of cemented soil strength.Finally, rely on the basal treatment engineering of Gonbei tunnel, Zhuhai connecting line Hong Kong-Macau-Zhuhai Bridge, durability of cemented soil reinforcement body was analyzed. On the one hand, relationship between strength and age of cemented soil in fresh water environment was obtained from the experiment data, and then combined the experiment data of unconfined compression strength of cemented soil in NaCl erosive environment with combined with erosion solution concentration-erosion time equivalence principle of cemented soil strength to to get the relationship between age and unconfined compression strength change of cemented soil induced by0.34g/1(the concntration of the project site) chloride ion environment. Relationship further more, add unconfined compression strength of cemented soil in fresh water environment with that of unconfined compression strength change of cemented soil induced by erosive environment, relationship between age and unconfined compression strength of cemented soil in0.34g/1chloride ion environment was obtained. At last, according to relationship between age and strength of cenmented soil test block in fresh water environment, assume that unconfined compression strength of cemented soil remain unchanged after soaked in fresh water more then270d, applied the relational expression obtained above, long term strength of cemented soil reforcement boy only affected by chloride ion in seawater was forecasted. On the other hand, single pile design formulas of jet grouting pile and mixing pile were amended, recommended value range of correction factor was obtained. Durability analysis of cemented soil in brine environment, which guided from two aspects:design of cemented soil and long-term strength forecast, provide a significant reference frame for design, construction and running of cemented soil engineering in brine evironment. |
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