## 5 Analysis of Numerical-Simulation Results
### Indoor Test Verification  
In this paper, three sets of indoor muddy-water seepage tests were conducted under the same conditions used for the prior numerical simulation using a custom-designed muddy-water seepage apparatus. The test apparatus is illustrated in Figure 22.  
The preparation material for the muddy water consisted of tailings-sand particles sourced from the dry beach of the Lixigou tailings dam, while the filter layer was composed of spherical transparent glass beads. The particle sizes of the tailings sand were 0.5-1 mm for Test 1, 0.25-0.5 mm for Test 2, and 0.075-0.25 mm for Test 3. The test procedure was as follows:  
(1) Filling of the filter layer: Before the filter layer was loaded, a 10 cm buffer layer of coarse particles was laid, and water is added to a depth of 10 cm to saturate the buffer layer. Then, 20 cm of filter layer was laid on top of the buffer layer and filled in four layers. Each layer was saturated before the next was added. (2) Instrument assembly: The main body of the instrument was connected to the water tank and the pressure-measuring tube. Fresh water was added to the water tank, and the valve was opened. The test is formally started after the head of the pressure measuring tube was stabilized. (3) The test began: At the start of the muddy-water percolation test, the anti-filtration layer was saturated before the first vacuum, and this step was followed by 30 min of clear-water percolation. During this period, the stability of the head of the pressure-measuring tube was observed and the flow rate was recorded every 5 min. Once a stable seepage field was formed in the anti-filtration layer, tailings-sand particles were added to the water tank to start the muddy-water percolation test. Throughout the muddy-water percolation test, continuous stirring of the tailings water in the tank was required to maintain a constant concentration of the test water. (4) Data collection: After the start of the turbid-water seepage test, pressure-tube readings were taken every 5 min and the flow rate was measured. Subsequently, the time intervals were gradually increased to 30-60 min. (5) At the end of the test, the filter layers tested at different locations were sampled in layers and dried separately. The particles of the filter layer were then separated from the tailings-sand particles and weighed individually. The results of the indoor tests are presented in Figure 23.  
Figure 22: Muddy-water seepage test instrument. The results of the indoor tests aligned with those of the numerical simulations. In terms of their influence on the clogging of the filter layer, the variation in 0.075-0.25 mm tailings-sand particles was minimal, whereas that in 0.25-0.5 mm particles was maximal. This indicates that, within a certain particle-size range, smaller tailings-sand particles have a greater impact on the permeability of the filter layer, although this influence diminishes beyond a certain threshold. This range can be assessed using the effective pore size of the filter layer. As this factor was analyzed in the previous section, it will not be elaborated here; however, the variation in the permeability coefficient observed in laboratory tests was significantly greater than that derived from numerical simulations. For instance, in Tests 1 and 2, the permeability coefficient of the 15-20 cm filter layer was greater than that of the 10-15 cm layer at the beginning but was lower at the end of the tests. The change in the permeability coefficient in Test 3 was also significantly greater than that of the numerical-simulation results. This discrepancy arises from the differences in the number of tailings-sand particles. In the numerical simulation, to maintain calculation speed, the number of tailings-sand particles must be limited; a larger number would significantly hinder computational efficiency. The model for the 0.075-0.25 mm group, which contained the greatest number of tailings-sand particles, is limited to only 50,000 particles.