Experimental study on compressibility and permeability characteristics of dewatered slurry cake backfill

WANG Zi-ang , ZHAN Liang-tong , GUO Xiao-gang , LIU Chao-yang , YAO Jun 脱水泥饼是工程泥浆经压滤脱水后形成的块状产物,经装卸、转运等处理环节破碎成尺寸不一的碎散体,其堆填体具有明显的双孔隙特征,由块体间的大孔隙和块体内的小孔隙组成。为了指导泥饼堆填作业,对泥饼堆填体的压缩性及渗透性开展研究。利用大尺寸固体废弃物压缩-渗透装置模拟了泥饼堆填过程中上覆荷载增加,泥饼堆积单元体逐渐被压密的过程,并利用CT扫描对压缩后泥饼块体间大孔隙的变化情况进行了分析；同时测试了泥饼堆积单元体在压缩过程中的渗透性变化规律。试验结果表明：泥饼堆积单元体试样随着上覆荷载增加逐渐被压密,泥饼间孔隙与泥饼内孔隙的尺度差异逐渐减小,双孔隙特征减弱。在上覆荷载为295 kPa时,试样空气孔隙率为5%,此时试样已成为均质块状泥饼,对应压实度为0.87,试样透水性已由初始阶段（0 kPa）的中等透水等级转变为弱透水等级。考虑可操作性和经济性,建议将0.85作为泥饼堆填作业过程中的压实度控制指标。 Abstract: After the slurry is dewatered by pressure filtration, the dewatered slurry cake is formed. After loading and unloading, transportation and other processing links, the dewatered slurry cake is broken into pieces of different sizes. Dewatered slurry cake backfill has obvious dual-porosity characteristics, including macro-pores between cakes and micro-pores inside cakes. In order to guide the filling operation of the dewatered slurry cake, the compressibility and permeability of the dewatered slurry cake backfill are studied in this research. The compaction of the dewatered slurry cake as the load increases during the backfilling is simulated by using the large-scale solid waste compression-permeation experimental system. The change of pore structure in the sample during compression is analyzed based on the CT scan. And the change of permeability of dewatered slurry cake backfill in the process of compression is studied at the same time. The results show that the sample of the dewatered slurry cake is compacted gradually with the increase of external load. The scale difference between the macro-pores and the micro-pores decreases gradually, and the dual-porosity characteristics weakens with the process of compression. When the overlying load is 295 kPa, the volume ratio of air of the sample is 5%. At this time, the sample becomes a homogeneous lump slurry cake, and the corresponding compaction degree is 0.87. In addition, the permeability of the sample also changes from a medium permeability grade at the initial stage (0 kPa) to a weak permeability grade. Considering the operability and economy, it is suggested that the compaction degree should be set as 0.85 during the backfilling of the dewatered slurry cake.