盾构淤泥质废弃黏土氧化镁固化-碳化试验及碳化机制研究

Solidification and carbonization experimental study on magnesium oxide in shield waste soil and its carbonization mechanism

盾构隧道施工产生的废弃土面临堆放、运输及处理等难题,将原材料丰富、生产耗能少、环境友好的MgO用于废弃土固化处理是一个值得探索的方法。通过改变MgO掺量a_(m)、养护龄期T、碳化时间H研究MgO固化-碳化淤泥质废弃黏土界限含水率w、无侧限抗压强度q_(u)、弹性模量E_(50),结合微观形貌及矿物成分变化规律探讨其固化-碳化机制。结果表明:MgO固化-碳化具有明显的加固土体效果,加固效果随a_(m)、T呈先上升后趋于稳定的趋势,随H呈先上升后下降的趋势;不同a_(m)、T下,碳化4h会使土体塑性指数I_(P)降低57%以上,土体可塑性显著下降;不同a_(m)和T的固化-碳化土q_(u)均在H为4h时取得峰值,最高可达1.4MPa,比碳化前强度提升了220%~350%;固化-碳化反应对土体的E_(50)提升受a_(m)影响较大,当a_(m)超过9%时,碳化4h试样的E_(50)增幅在500%左右;MgO固化-碳化过程中水化产物、碳化产物不断生成和发育,形成网状、花朵聚集状的形貌,填充土颗粒间的孔隙,增强了土颗粒间的胶结作用,土体结构更为密实。该研究为长三角地区土压盾构产生的淤泥质废弃黏土的固化-碳化处理与再利用提供了思路。

The waste soil generated during shield tunnel construction poses a challenge in terms of stacking,transportation,and treatment.One promising approach is the use of magnesium oxide (MgO) for the solidification treatment of waste soil,as it is abundant in raw materials,has low production energy consumption,and is eco-friendly.The limit moisture content w,unconfined compressive strength q_(u) and modulus of elasticity E_(50) of MgO solidified and carbonized mucky waste soil were studied by changing the MgO content a_m,curing age T,and carbonization time H.The solidification and carbonization mechanism of MgO-treated mucky waste soil was discussed in combination with the microstructure and the change rule of mineral composition.The results demonstrate that MgO solidification and carbonization have a significant reinforcing effect on the soil.The reinforcement effect initially increases and then stabilizes with increasing a_(m) and T,while it shows an initial increase followed by a decrease with H.Carbonization for 4hours reduces the soil plasticity index (I_P) by more than 57%under different a_(m) and T conditions,leading to a significant reduction in soil plasticity.The q_(u) of solidified and carbonized soils reaches a peak value at H of 4 hours,with values up to 1.4 MPa,which is220%–350%higher than the strength before carbonization.The effect of solidification and carbonization reaction on the increase in E_(50) of the soil mass is greatly influenced by a_m.When a_(m) exceeds 9%,the E_(50) increase of the sample carbonized for 4 hours exceeds 500%.During the process of MgO solidification and carbonization,hydration products and carbonization products are continuously generated and developed.They form a network and flower-like microstructure,filling the pores between soil particles,enhancing cementation between soil particles,and densifying the soil structure.The research provides insights into the efficient and eco-friendly treatment and reuse of mucky waste soil produced by earth pressure shield in the Yangtze River Delta.