# Field Treatment of Storage Sludge and Stability Analysis of Overlying Municipal Waste Landfilling
## 2 Raw Storage Sludge Characterization
### Physical Properties
Thirdly, below the fluid-like sludge layer, at depths of 10-10.7 m in C1, 19.4-19.7 m in C2, 10-12 m in C3, 15.3-22 m in C4, and 12.5-13.1 m in C5, the CPT readings showed a significant increase with the increasing depths. This means that the sludge was in a fluid-plastic layer. It is worth noting that the CPT tests at location C1 revealed that at 11.3 m, the probe rod began to bend, presumably because this depth was the location of the interface between the mountain and the bottom of the sludge pond. Additionally, it should be noted that the sampling point of C2 was the center of the raw sludge pond and the bottom surface shape of the pond influenced the sedimentation of the sludge, which contributed to the different stratification thickness in C2 from other points. The apparatus used for the vane shear test was the vane of 50 mm \(\times\) 100 mm \(\times\) 2 mm (diameter \(\times\) height \(\times\) thickness) and the test procedure was according to ASTM D2573 [25]. Figure 6 shows the change of the undrained shear strength of the raw storage sludge with the corresponding depth in the sludge pond. The undrained shear strength of the raw storage sludge within the buried depth of 8 m or 9 m was about 0.1-1.9 kPa at V1, V3, V4, and V5. Within the buried depth of 17 m at V2, the raw sludge presented the undrained shear strength of 0.2-1.1 kPa. The distribution of these strength values is consistent with  
Figure 4: Water content of raw sludge, varying with the depth. the mud-water mixing appearance of the aforementioned depth range. As the buried depth increased, the undrained shear strength increased slightly and the appearance of the sludge showed as a slurry. The raw storage sludge at V1, V3, V4, and V5, with the buried depths of 12 m or 13 m, had the maximum undrained shear strength of 4.1-14.9 kPa. The raw storage sludge at V2 with a buried depth of 18 m had a maximum undrained shear strength of 4.7 kPa. In addition, below the aforementioned buried depths, the tested undrained shear strengths presented an obvious increase with the depth. The undrained shear strength of the raw storage sludge with the specified buried depth is listed as follows: the buried depth of 14 m at V1 was 11.2 kPa, the buried depth of 19 m at V2 was 10.9 kPa, the buried depth of 12 m at V3 was 12.7 kPa, the buried depth of 11 m at V4 was 14.6 kPa, and the buried depth of 13 m at V5 was 14.9 kPa. These strength values correlated with self-weight consolidation and were consistent with the appearance of the fluid-plastic. The sampling and field tests indicated that the sludge within the depth of 0-9 m was a mud-water mixing layer. The raw sludge in the fluid-plastic layer had a thickness ranging from 2.0 m to 9.7 m, and the minimum buried depth of that was 4.5 m. Additionally, the other areas of the hole positions were in the fluid-like layer. That indicates that the sludge  
Figure 5: Cone penetration test results of the raw sludge, varying with depth: (**a**) cone tip resistance and (**b**) cone sleeve resistance. Figure 6: Undrained shear strength of the raw sludge varying with the depth. pond was irregular in depth, with a deep center and a shallow edge, rather than a pond of equal depth.