# Investigating the Physical Mechanisms of Quicksand Using a Custom-Designed Experimental Apparatus
## 2 Experimental Materials and Methods
### Experimental Steps  
1. Specim Preparation: Following the methodology of [PERSON] et al. [PERSON] et al. (2017) for permeability testing of calcareous sand in island reef reclamation projects, this experiment conducted hydrodynamic seepage tests on quartz sand specimens under identical relative density conditions (Dr = 66%) to simulate natural sandy soil site conditions. The permeameter specimen chamber accommodates cylindrical specimens with a diameter of 60.000 mm and a height of 120.000 mm. A multi-layer loading protocol was implemented, ensuring uniform mass and compaction duration across all layers. Post-loading pressure measurements were acquired synchronously from all sensor tiers.
2. Specim Saturation: The water reservoir of the supply unit was filled with distilled water, with pH effects on quartz sand permeability and quicksand behavior intentionally excluded. The water temperature was thermostatically maintained at 20.0 \(\pm\) 0.5 \({}^{\circ}\)C to simulate typical in-situ sandy soil thermal conditions. Priming Phase: The water injection unit outlet was opened until bubble-free water discharged uniformly, then connected to the permeameter's inlet. Controlled Saturation: Saturation permeation was conducted at a constant flow rate of 10 mL/min until uniform effluent was observed at the permeameter outlet. Process Monitoring: Multi-elevation pressure measurements (Bottom/Middle/Top) were recorded in real-time throughout saturation.
3. Flow Rate Regulation: This experimental series systematically investigates the permeability characteristics and quicksand evolution processes of quartz sand under varying particle gradation and hydrodynamic velocities. A controlled variable method was  
Figure 2: Installation of dynamic water infiltration test device and monitoring element.  
strictly implemented to gradually carry out the dynamic water permeability test under the various factor variable conditions, with a detailed experimental matrix provided in Table 2. To simulate the progressive dynamic evolution of hydraulic conditions in actual sandy soil foundation environments and systematically capture the full-process dynamics of quicksand from initiation to instability, each quartz sand specimen is subjected to five consecutive hydrodynamic seepage phases (10 min duration per phase): Low hydrodynamic pressure, initial seepage state \(\rightarrow\) Enhanced hydrodynamic pressure, minor particle migration \(\rightarrow\) Near-critical hydraulic gradient, quicksand precursor \(\rightarrow\) High hydrodynamic pressure, localized quicksand \(\rightarrow\) Extreme conditions, global quicksand initiation. Real-time pressure monitoring across vertical positions (Bottom/Middle/Top) was maintained throughout all permeation stages.
4. Seepage Monitoring: During hydrodynamic seepage testing, effluent discharged from the permeameter outlet was systematically collected and volumetrically quantified using graduated cylinders, with separate measurements recorded for each 10-min phase. This effluent volume dataset provides indirect characterization of porosity variation patterns during quicksand evolution in quartz sand specimens.