# Field Treatment of Storage Sludge and Stability Analysis of Overlying Municipal Waste Landfilling
## 4 Analysis of the Solidified Sludge  
### Field Sampling  
The water content of the sludge treated by the geotextile tube was designed to reduce to 400% for the subsequent solidification. Furthermore, the dehydration effect of the sludge treated by the geotextile tube was easily measured. However, the sludge treated by the in situ solidification was hard to measure in a unified way. Thus, the physical characteristics of the solidified sludge were analyzed emphatically. The field sampling was carried out at the solidified sludge pond after the curing time reached 28 days. To test the distribution of the physical properties along Profile 1-1 (Figure 1), the samples taken from the positions of ZK01, ZK02, ZK03, ZK05, ZK14, ZK10, ZK18, and ZK23 were analyzed emphatically. There were three types of solidified sludge appearances in the sludge pond (Figure 10). The solidified sludge that appeared to be solid was similar to clay, with low water content and high compactness. The solidified sludge that appeared to be plastic was similar to clay with low water content. The solidification effect of the sludge that had a soft-plastic state was worse than that of the plastic sludge, which was reflected in the water content and compressibility. The appearance of the samples along Profile 1-1 showed the solidified  
Figure 9: Photos of the sludge pond at the Qizishan landfill: (**a**) laying the composite liner after solidification, and (**b**) waste landfilling above the solidified sludge pond. sludge pond stratification (Figure 10). Different samples presented variable stratification along Profile 1-1, indicating a non-uniform solidification in the pond. The difference in the solidification results above and below a depth of 10 m showed the different effectiveness of the in situ techniques, i.e., stirring and high-pressure chemical churning. The high-pressure chemical churning improved the strength of the sludge pond by utilizing the combined action of the pile-forming and the sludge between the piles. So, the appearance of the solidified sludge in different locations of the sludge pond differed below a depth of 10 m. The lack of fine control and real time monitoring of the in situ equipment led to the poor uniformity of the solidification in the sludge pond. According to Figure 10, the solidified sludge at the positions ZK01, ZK02, ZK03, and ZK05 appeared generally solid-like, hence, presented an excellent solidification effect. These positions were located in the south of the sludge pond, and the water content of the raw storage sludge in these positions was lower than that of the raw storage sludge in the north of the sludge pond, such as the positions ZK10, ZK14, ZK18, and ZK23. The solidified sludge, with buried depth ranges of 6-10 m in borehole ZK01, 4-6.5 m in borehole ZK03, and 2-10 m in borehole ZK05, appeared to be in a plastic state due to the in situ stirring operation. At the position of ZK05, the solidified sludge appeared to be in a solid-like state at a depth of 2 m, benefited by sufficient operating capacity and proper operation of the in situ curing stirring equipment. In addition, 10-21-m deep solidified sludge was in a soft-plastic state, caused by the operation of the high-pressure chemical churning pile. The solidified sludge of the upper part, at ZK10, ZK14, ZK18, and ZK23, was in at least a plastic state, except the solidified sludge which appeared in a soft-plastic state in the ranges of 6-10 m at ZK05 and 4-10 m at ZK18. This may be due to the solidification of the upper area, whose buried depth was within 10 m, not being completed or the curing agent not reaching the specified depth. The solidified sludge at ZK10, ZK14, ZK18, and ZK23, whose buried depth was over 10 m, was in the plastic state or soft-plastic state. This is because the solidified sludge in these positions showed different distances from the jet grouting piles and the samples in different depths were in a different confining condition for the non-uniform piles.