# Numerical Simulation on Backfilling of Buried Pipes Using Controlled Low Strength Materials
## 4 Results
### Analysis of Soil Pressure Characteristics  
For the buried pipeline, numerical simulation is carried out under three conditions of loose backfill, dense backfill and CLSM backfill. The stress data of soil peri-pipe under different working conditions were extracted, and the change of soil pressure around pipe  
Figure 8: Deformation nephogram of dense backfill. Figure 7: Lateral earth pressure of the pipe. Figure 9: Deformation nephogram of CLSM backfill. was studied. The vertical earth pressure of the pipe is S1 and S2, and the interval between the two is 15 cm. The horizontal earth pressure on the right side of the pipe is S3 and S5, and the vertical earth pressure is S4 and S6. The interval between the two is 15 cm. The arrangement of earth pressure monitoring around the pipe is shown in Figure 10.  
Figure 11 shows the earth pressure at various locations in the soil at a surface pressure of 200 kPa. Comparing the loose backfill around the buried pipe with the dense backfill, the earth pressure change trend is basically similar at each location. Under the condition of loose backfill, the vertical earth pressure S2 at the top of the pipe and the horizontal earth pressure S3 on the pipe side increased compared with the dense backfill. Vertical earth pressure increased by 8% and horizontal earth pressure S3 increased by 30.6%. The vertical earth pressure of the pipe top and the horizontal earth pressure on the pipe side of the pipe are not conducive to the force of the pipeline. Compared with the use of CLSM for buried pipe backfilling, the vertical earth pressure S1 at 15 cm above the pipeline increased, compared with the dense backfill around the pipeline increased by 6%. The vertical earth pressure S2 and the horizontal earth pressure S3 of the pipe side are significantly reduced. Figure 12 shows the change of vertical earth pressure S2 at pipe top with the increase of surface pressure under different backfill conditions. As the surface pressure increases, the earth pressure above the pipe roof gradually increases. The loose backfill around the pipe and the dense backfill were compared with the use of CLSM backfill. When the surface static pressure is 200 kPa, the earth pressure S2 of the dense backfill and the pipe roof using  
Figure 11: The earth pressure at each position when the static load pressure is 200 kPa. Figure 10: Schematic diagram of the location of earth pressure monitoring. CLSM backfill is smaller than that of the loose backfill. The vertical earth pressure S2 of the loose backfilled pipe top was reduced by 5.1% and 66.9%, respectively, compared with the compact backfill and CLSM backfill. The above can be concluded that loose backfill is not conducive to the force of the pipeline. Dense backfill can improve the force characteristics of the pipe, which can reduce the earth pressure at the pipe top. For the backfilling of buried pipelines using CLSM, the pressure of the pipe top can be significantly reduced, and the pipeline can be well protected. Figure 13 shows the ratio Sh/Sv (S3/S4, S5/S6) of horizontal earth pressure (S3, S5) to vertical earth pressure (S4, S6) at each monitoring position on the right side of the pipeline Sh/Sv. It can be seen from the figure that for the comparison of dense backfill and CLSM backfill, the ratio of horizontal earth pressure to vertical earth pressure in each monitoring position on the right side of the pipe is constantly decreasing. When the surface pressure is 200 kPa, the S3/S4 of dense backfill and CLSM backfill are 0.64 and 0.25, respectively. Compared with dense backfill, the ratio of horizontal earth pressure to vertical earth pressure for backfilling or using CLSM is reduced by 60.9%. For the earth pressure on the pipe side, CLSM backfilling will reduce the horizontal earth pressure of the pipe and weaken the \"earth arch effect\" phenomenon of the pipe. The stress of the pipe changes from the pipe-soil interaction to the majority of the solidified CLSM. The stress of the pipeline decreases, which is beneficial to the safety of the pipeline.