Effect of methods of adding urea in culture media on sand solidification tests
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摘要: 砂土固化技术可改善砂土力学特性,被广泛应用于工程中,而在菌种培养液中添加尿素可大大加快固化反应提高砂土固化效率。开展了在菌种培养液中添加尿素分析其对砂土固化影响的试验研究。首先将尿素添加方式分为灭菌前加尿素、灭菌后加尿素和不加尿素3种,研究不同方式对菌种生长和脲酶活性的影响;再控制不同尿素添加量对比分析得到适合的尿素添加量以便后续研究;然后在砂土固化试验中采用灭菌后加尿素的方式研究其对砂土固化的影响;最后通过控制砂柱长度、胶凝液灌注速度和砂土颗粒粒径等因素,得到各因素对砂柱固化效果的影响。结果表明培养液中添加尿素可提高脲酶活性,但稍微抑制菌种生长;适合的尿素添加量为5~20 g/L;灭菌后添加尿素能显著提高灌注部位的强度,但长砂柱却因强度不均而整体强度较低;灌注速度越快,整体强度越高;添加20 g/L尿素时,整体强度随颗粒粒径增大而增大,因此,该方法适用于粗砂。研究成果对后期砂土固化技术的应用具有重要指导意义。Abstract: The sand solidification technology can improve the mechanical properties of sands and is being widely applied in engineering. Adding urea to culture media can drastically accelerate the curing reaction. The influence of adding urea to culture media on sand solidification is studied. At first, three methods of adding urea are examined to investigate the effects of them on the growth characteristics and urease activity: that is, adding urea before sterilization, adding urea after sterilization and not adding urea. Different amounts of urea are then added to obtain the appropriate amounts of adding urea for subsequent experiments. Finally, the method of adding urea after sterilization, length of sand columns, injection speed of gelling solution and sizes of sand particles are investigated to observe the influences of different factors on the curing of sand. The results show that the method of adding urea to the culture media can increase urease activity, but it will slightly inhibit bacterial growth. The proper amounts of urea added are between 5 and 20 g/L. The method of adding urea after sterilization markedly increases the strength of the injecting path. However, a long injecting path leads to lower overall strength. The faster the injection speed, the higher overall strength the sand columns have. When 20 g/L of urea is added, the overall strengths of the solidified sand columns increase with larger sand particle size. Therefore, the method of adding urea to the culture media for sand solidification is suitable for coarse sand, which will act as a guide for the application of sand solidification technology.
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