MgO固化–碳化盾构离心高液限粉土界限含水率试验研究

Experimental Study on the Limit Water Content of MgO Modified Carbonized Shield Tunnel Centrifugal High Liquid Limit Silt

摘要: 针对泥水盾构产生的工程废弃土可塑性无法满足工程规范要求的问题，开展活性氧化镁固化–碳化高液限粉土的界限含水率试验研究。分析液、塑限及塑性指数变化规律，探究可塑性变化原因。高液限粉土在掺入氧化镁后，增大掺量或延长碳化时间均可使固化–碳化土的塑限提高，液限和塑性指数降低，塑性指数最低为7。可塑性不断降低的原因可能有两种：一是由于氧化镁掺入后产生的水化产物与细粒颗粒胶凝团聚，使细粒含量降低，土体吸水能力减弱，导致土体液限降低；二是由于氧化镁颗粒的掺入及反应使级配更加合理，水分对土体结构的影响降低，导致塑限升高。wL和wp的变化共同导致塑性指数的降低。

Abstract: In response to the problem that the plasticity of engineering waste soil generated by slurry shield tunneling cannot meet the requirements of engineering specifications, an experimental study on the limit water content of activated magnesium oxide modified carbonized high liquid limit silt was conducted. Analyze the change rule of liquid and plastic limit and plasticity index, and investigate the reason of plasticity change. It is found that after the high liquid limit silt is mixed with magnesium oxide, increasing the amount of MgO or prolonging the carbonization time can make the plastic limit of the modified-carbonated soil increase, the liquid limit and plasticity index decrease, and the plasticity index is as low as 7. The reason for the plasticity decreasing may be two kinds: firstly, due to the hydration products produced after the magnesium oxide mixing with the fine particles gelling agglomeration, so that the fine particles content decreases, and the soil body’s ability of absorbing water is weakened, which results in the decrease of the liquid limit of the soil; and secondly, because the magnesium oxide particles are not mixed with the liquid limit of the soil, it is the reason for the decrease of the liquid limit. Due to the magnesium oxide particles and reaction to make the grading more reasonable, the influence of water on the soil structure is reduced, resulting in higher plastic limit. The changes in wL and wp together lead to a decrease in the plasticity index.