MICP胶结液中尿素过量的影响研究

Study on Influence of Excess Urea in MICP Cementation Solution

分析了研究人员对于胶结液中尿素对MICP影响的不同认识之间存在的分歧,利用水溶液试验及一维砂柱加固试验,对比研究了胶结液中尿素过量(双倍浓度)对MICP的影响。在水溶液和砂柱中,进行了三种氯化钙浓度(0.25 M,0.5 M,1.0 M)条件下尿素过量与否的对比试验。测试对比了水溶液试验过程中NH4+,Ca2+变化规律、砂柱试验中Ca2+消耗,CaCO3生成情况和砂柱无侧限强度等。研究结果表明:(1)水溶液试验中,过量的尿素在反应初期不利于尿素水解与碳酸钙沉积;(2)在砂柱试验中,过量的尿素也对MICP不利,加固后土体强度较低,加固效果较差;(3)砂柱试验中这一现象与注浆方式(间隔12 h直灌式注浆)和较短的胶结液停留时间有关;(4)在水溶液和砂柱两种环境下,低氯化钙浓度(0.25 M)情况下尿素过量对MICP的影响都最为明显。

The controversy of researchers on the effect of urea in cementation solution on MICP was analyzed. The effects of excess urea(double concentration) on MICP were compared and studied through a series of aqueous tests and cemented tests on one-dimensional sand column. Comparison tests were carried out on the aqueous solution and the sand column under the condition of three concen-trations of CaCl2(0.25 M,0.5 M,1.0 M). Changes of NH4+,Ca2+ in the water solution,Ca2+ consumption,CaCO3 formation and compression strength of the sand samples in the sand column tests were compared and analyzed. The results show that:(1)In aqueous test,excess urea has an ad-verse effect on urea hydrolysis and calcium carbonate deposition at the early stage of the reaction;(2)In sand column test,excess urea is also unfavorable to MICP and leads to lower strength of soil sam -ple;(3)The phenomenon in the sand column test is related to injection method and short retention time of the cement(direct grouting at intervals of 12 h);(4)The negative effect of excess urea on MICP under low calcium chloride concentration(0.25 M)is most pronounced in both aqueous and sand column environments.