# Field Treatment of Storage Sludge and Stability Analysis of Overlying Municipal Waste Landfilling
## 6 Conclusions  
In this study, the layered sedimentary patterns of the physical properties of the storage sludge at the Qizishan landfill was investigated using field and laboratory tests. A stratified treatment method was proposed for the field disposal of deep storage sludge, which comprises ex situ dehydration using a geotextile tube, in situ solidification of the shallow sludge by stirring, and in situ solidification of the deep sludge by high-pressure churning. Moreover, the stability of the waste slope above the sludge pond was analyzed. The conclusions were as follows:  
1. The raw storage sludge in the sludge pond at the Qizishan landfill is stratified into layers, which are mud-water mixing sludge, fluid sludge, and fluid-plastic sludge layers. As the buried depth increases, the water content of the sludge decreases and the undrained shear strength increases. The water content ranges from 172% to 7270%, with an average of about 1397%, and the strength remains at a low level overall, which ranges from 0.20 kPa to 14.90 kPa.
2. The ex situ dehydration of the mud-water mixing sludge uses the geotextile tubes, in which the flocculation is conducted, and is followed by the high-pressure dehydration. The fluid and fluid-plastic sludges are solidified through in situ stirring and high-pressure churning, respectively. The stratified treatment results in a significant decrease from 1398% to 88% in the average water content and an increase to 23.52 kPa, on average, in the cohesion.
3. The strength of the deep solidified sludge varies more dramatically with the water content than that of the shallow solidified sludge. The high content of clay particles,  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Material** & **Unit Weight** & **Cohesion** & **Internal Friction** \\  & **(kN/m3)** & **(kPa)** & **Angle (°)** \\ \hline Shallow waste & 11.7 & 20.8 & 21.4 \\ Old waste & 12 & 29.5 & 0 \\ Fresh waste & 10 & 21.6 & 9.6 \\ Waste dam & 20 & 200 & 50 \\ Mud-water mixing sludge & 10 & 0 & 0 \\ Fluid sludge & 10.02 & 4 & 0 \\ Fluid-plastic sludge & 10.08 & 10 & 0 \\ Composite liner & 18 & 0 & 20 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Shear strength parameters used for the stability analysis.  
low amount of solidification products, and high water content together result in the strength of the deep solidified sludge having a higher sensitivity to the water content than that of the shallow solidified sludge.
* The landfill body is prone to sliding along the inside of the sludge pond when the waste is piled directly above the raw sludge pond. The stability analysis of the waste body on the solidified sludge pond shows that the potential sliding surface occurs in the fresh waste body rather than in the solidified sludge pond, and the Fs is increased from 0.934 to 1.464, which verifies the validity of the presented sludge pond treatment.  
Conceptualization, K.A.; Funding acquisition, Y.C.; Project administration, Y.C.; Supervision, L.Z.; Writing--original draft, K.A.; Writing--review & editing, W.L., D.Z. and A.A. All authors have read and agreed to the published version of the manuscript.  
This work was supported by the Basic Science Center Program for Multiphase Media Evolution in Hypergravity of the National Natural Science Foundation of China (No. 51988101), the Fundamental Research Funds for the Central Universities (No. 2020 QNA4020), and the National Natural Science Foundation of China (Grant no. 51478426).  
The authors declare no conflict of interest.