粉煤灰增强回填碱渣工程特性的试验研究

An experimental study on the engineering properties of backfilled alkali wastes reinforced by fly ash

碱渣与饱和卤水混合制成浆体回填到盐矿废弃盐腔可同时解决碱渣处理问题和地下废弃盐腔存在的地质隐患。回填碱渣强度是影响充填效果的重要因素。因此,为了提高回填碱渣强度,采用掺入粉煤灰制成复合碱渣对其强度特性进行改良。针对不同粉煤灰掺合比的碱渣开展了组成、力学和细观试验。研究结果表明：（1）掺入粉煤灰能明显改善碱渣的强度,使其黏聚力、内摩擦角都大幅提高,抗剪强度大幅增加;（2）粉煤灰掺合比越大,增强效果越明显,但强度并非随掺合比呈线性变化,对黏聚力而言,在0~20%内的掺合比下增加速度最快,而对内摩擦角则在20%~30%的掺合比区间增加最快,对抗剪强度而言,0~20%的掺合比内增加最明显;（3）粉煤灰掺入还可显著改善碱渣的压缩固结特性,使其固结系数大幅提高,从而提高碱渣固结速度,缩短充填工期,其中在0~10%的掺合比内对压缩固结特性改善最显著;（4）矿物组成分析表明,粉煤灰掺入改变了矿物组成,使得亲水性矿物含量急剧锐减,进而改变了其沉积特性。而细观分析则表明,粉煤灰掺入使碱渣从絮凝团细观结构变成了粉煤灰充当骨架的充填结构,且粒间支撑和拉联效应明显。从增强效果提高、压缩固结特性增强、控制成本和工期综合分析表明,最优掺合比为20%左右,建议工程中以不高于20%的掺合比作为实用掺合比即可取得较为理想的充填增强效果。该研究为揭示碱渣增强机制及废弃盐腔碱渣充填工艺优化提供了有益参考。

The backfill of mixed slurry consisting of alkali wastes with saturated brine into abandoned salt cavern can simultaneously resolve the problems of alkali treatment and the potential geology disaster of abandoned salt caverns. The strength of the backfilled alkali wastes is a key parameter which affects the filling effect. In order to improve the strength of the backfilled alkali wastes, fly ash is used to make compound alkali. A series of mineral analysis, strength experiments and mesoscale testing have been conducted to determine the properties of the compound alkali wastes, showing that： （1） The mixing of fly ash can effectively reinforce the alkali wastes, resulting in the increases in the cohesion, the internal frictional angle and the shear strength; （2） The larger the mixing ratio of the fly ash, the stronger the reinforcing effect is; whereas, the strength increases nonlinearly with the increment of mixing ratio. For cohesion, its maximum increasing speed locates in the mixing ratio range of 0-20%; for internal frictional angle, it is in the mixing ratio range of 20-30%; and for shear strength, the maximum increasing speed locates in the mixing ratio range of 0-20%; （3） The mixing of fly ash can significantly improve the compression consolidation properties, inducing an increase in consolidation coefficient, thus the project time of backfill will greatly be reduced; the mixing ratio of 0-10% is most suited to the improvement of consolidation; （4） By mineralogical analysis, it is shown that the mixing of fly ash can change the components of the alkali wastes, significantly reducing the content of the hydrophilia minerals and changing the sedimentary properties. The meso-scale analysis shows that, owing to fly ash mixed into alkali wastes, the fiocculation structure of initial alkali wastes changes into the filling structure where the fly ash acts as main skeleton, in this structure the supporting and connecting effects between particles are also more obvious. Comprehensive analysis shows that the mixing ratio of 20% is ：the optimal ratio in terms of the improving strength, enhancing consolidation effect, shortening project period as well as saving cost. A value less than 20% is recommended for the practical mixing ratio in practice. The research results provide a good reference for revealing reinforcing mechanism of alkali wastes, as well as optimizing technologies for salt cavern backfill.