Study On The Technology Of Solidifying Coral Sand With Struvite Induced By Microorganisms In High Salt Environment

As an important node of the "The Belt and Road" strategy,the South China Sea is rich in resources and has high economic value.It is also the forefront of China's national defense.Coral sand is widely distributed in the islands of the South China Sea,and the biogenic coral sand has the characteristics of irregular shape,low strength,internal porosity,and fragility.The construction of the South Island Reef area is developing day by day,and the traditional foundation reinforcement methods will have shortcomings such as pollution of the marine environment and high transportation costs.The technology of using microorganism to induce struvite has the characteristics of simple mechanism,easy implementation,fast and high efficiency and cost saving,and can alleviate the problem of MICP ammonia pollution.Aiming at the high salinity of the South Island reef environment,this paper selected Bacillus Pasteurii with high urease production,and systematically analyzed the activity of microorganisms,urease production ability,and the solidification effect and influence factors of coral sand.Explore the effects of different salinity environments on bacterial culture,microbial mineralization,and sand pillar reinforcement.The ability of bacteria to precipitate crystals and its influencing factors are analyzed,the optimal reinforcement parameters are determined,and the effect and mechanism of microbial reinforcement on the mechanical properties of coral sand are studied.And came to the following conclusions:?1?The growth curve of bacteria in the medium is divided into three phases: retardation phase,logarithmic phase,and stable phase.The growth of microorganisms is inhibited by the salinity of the culture solution.As the salinity increases,it takes longer for the biomass to reach its peak state.In the culture solution with a NaCl concentration of 0.9 mol / L,a significantly lagging growth curve can be observed.When performing microbial culture,30 ° C is the optimal culture temperature.?2?The higher the bacterial concentration,the higher the urease activity.With the increase of urea concentration,urease activity first increased and then decreased.Taking the test results and economy into consideration,the bacterial concentration OD₆₀₀was 1.7 and the urea concentration was 1 mol / L.The optimal ratio of cement solution was determined through the struvite production test.In order to ensure the production of struvite,1mol/L urea,2mol/L K₂HPO₄,and 2.5mol/L MgCl₂ were used to carry out coral sand grouting reinforcement experiments.It is worth noting that the test results show that salinity is not conducive to the degradation of nitrogen-containing organic matter,high salinity inhibits the growth and metabolism of the strain,and the time to reach high pH is delayed,which eventually leads to the extension of the period of induction of bird droppings mineralization.?3?Grouting round is an important influencing factor in sand column grouting reinforcement.With the increase of grouting round,the uniaxial compressive strength of sand column also increases.In the same grouting round,as the salinity in the slurry increases,the strength gradually decreases.Corresponding to the lagging growth period caused by the high salt environment,the grouting rounds can be increased accordingly to achieve the corresponding strength.For different grouting rounds,the permeability of sand column still has the same trend.The grouting cycle is the same.The higher the salinity,the smaller the sand column permeability coefficient decreases;the more the grouting times,the larger the permeability coefficient decreases.For grouting-reinforced coral sand columns,the permeability is increased while increasing the strength.?4?Mineral analysis results show that the main components of sand column grouting reinforcement are calcium carbonate and struvite.The microscopic mechanism of cementation reinforcement is the struvite bonding and pore filling effect generated between coral sand particles,which is the fundamental reason for the decrease of sand column permeability coefficient and compressive strength.The mineralized struvite is a flat rectangular parallelepiped with a crystal grain size of about 100?m,which can effectively block the pores of coral sand.