水泥/粉煤灰碱改性对废弃粉质土砂配制盾构壁后注浆性能的影响

盾构废弃粉质土砂矿物组成复杂、泥质含量高，易引起水化反应不彻底及团聚现象，导致浆液性能的劣化，然而，使用废弃粉质土砂配制壁后注浆浆液，替换商品砂比例只能在30%～40%才能满足现场及通用指标要求。依托实际工程现场开展高掺量废弃粉质土砂部分替换商品砂(60%)配制壁后注浆实验，分析水泥及粉煤灰碱改性策略对高掺量废弃粉质土砂壁后注浆浆液性能影响规律。结果表明，当改性水泥替换比例不超过50%时，对粉质土砂壁后注浆具有积极的影响，可以在缩短凝结时间和降低泌水率的同时，使流动度与抗压强度依然符合通用指标；改性粉煤灰相较于改性水泥对浆液的影响比较小，但在小幅降低浆液抗压强度的同时，仍可以有效缩短浆液的凝结时间和泌水率。分析原因在于，水泥进行碱性改性，加速了水泥的水化反应，进而可以缩短浆液的凝结时间且对于用水量也会有所影响，进而也会影响浆液的流动度以及稠度；而粉煤灰减改性则破坏了粉煤灰中莫来石和石英原本有序的玻璃相结构，虽然后期产生的C-A-S-H(水化硅铝酸钙)对力学性能有一定的影响，但由于粉煤灰转化为沸石样物质的原因，仍然可以优化浆液的凝结过程及用水量。

Effect of Cement/Fly Ash Alkali Modification on Back-filled Grouting Performance of Shield Tunnel Prepared with Waste Silty Soil Sand

The complex mineral composition and high mud content of abandoned silty soil sand in shields can easily lead to incomplete hydration and agglomeration, resulting in deterioration of the grouting performance. However, the use of abandoned silty soil sand to prepare back-filled grouting, the proportion of replacement commercial sand can only be around 30%-40% to meet the site and general index requirements. This paper is based on the actual engineering site to carry out a wall grouting experiment by partially replacing commercial sand (60%) with high content of abandoned silty soil sand, and analysis of the effect of cement and fly ash alkali modification strategies on the performance of post-wall injection grouting with high-mix abandoned silty soil sand. The results show that when the replacement proportion of modified cement does not exceed 50%, it has a positive effect on the back-filled grouting of abandoned silty soil sand, which can shorten the setting time and reduce the water secretion rate while still making the flow and compressive strength conform to the general index; modified fly ash has a smaller effect on the grouting compared to modified cement, but it can still effectively shorten the setting time and water secretion rate. The reason for this is that the alkaline modification of the cement accelerates the hydration reaction of the cement, which in turn reduces the setting time of the grouting and has an effect on the water consumption, which in turn affects the flow and consistency of the grouting; whereas the fly ash modification destroys the originally ordered glass phase structure of mullite and quartz in the fly ash, although the later generation of C-A-S-H (calcium silicate aluminate hydrate) has an effect on the mechanical properties. Although the C-A-S-H (hydrated calcium silicate) produced at a later stage has a certain effect on the mechanical properties, it can still optimise the setting process and water consumption of the grouting due to the conversion of fly ash into zeolite-like material.