# Study on Vertical Uplift Resistance Characteristics of Pre-Drilled Planted Piles in Boulder Strata
## 3 Design of the Planted Pile Model Tests Based on Transparent Soil  
### The Planted Pile Model Test Device and Transparent Soil Formulation  
The model test apparatus, as shown in Figure 3, mainly comprises a model box, loading system, and imaging and information collection and processing systems, among others. Referring to Ni [34], the width of the model box was determined to be 200 mm to achieve maximum transparency of the transparent soil. Considering the size effect from related literature [38], the internal dimensions of the box were set as 400 mm in length, 200 mm in width, and 450 mm in height, constructed using 5 mm thick transparent acrylic sheets. The experimental loading system consists of a reaction frame, pull rope, fixed pulleys, loading platform, and weights. The load application was achieved by increasing the number of weights. Two fixed pulleys were secured at designated locations on the reaction frame: one for positioning the model box (the center point of the model box, with distances of 200 mm and 100 mm from the edges) and the other for determining the load application position. A rope was passed through the pulleys, connecting the toggles at the top of the piles to the weight trays (where the experimental weights were placed). The imaging system includes a laser, a digital camera, a DH3816 static strain testing system, and a notebook.  
Figure 2: Schematic diagram of pre-drilled planted pile foundations in locations with boulders.  
The transparent soil used in this experiment is composed of a mixture of fused quartz sand, n-dodecane, and No. 15 white oil. The transparency of transparent soil is primarily determined by the degree of refractive index matching between the particles and the liquid. A closer match in refractive indices results in higher transparency, while ensuring uniform particle distribution, thorough mixing, and adequate degassing during preparation. The refractive indices of the three materials at a room temperature of 23 \({}^{\circ}\)C are shown in Table 1.  
The volume ratio of n-dodecane to No. 15 white oil is estimated using Equation (1):  
\[Ax+By=C(x+y) \tag{1}\]  
where \(A\) is the refractive index of n-dodecane, \(B\) is the refractive index of No. 15 white oil, \(C\) is the refractive index of fused quartz sand, and \(x/y\) is the volume ratio of dodecane to No. 15 white oil.  
N-dodecane and No. 15 white oil are mixed in a volume ratio of 1:24.67 to create a pore solution. After ensuring thorough mixing, the refractive index of the mixture was measured using an Abbe refracometer. The proportions of the two liquids were adjusted based on the observed refractive index until it reached 1.4585, which is equivalent to the refractive index of quartz sand. Once configured, the porous solution was poured into a model box lined with quartz sand, and after thorough mixing, approximately 30 min of vacuum treatment was conducted. After the vacuum treatment, the model box was placed in a thermostatic chamber at 23 \({}^{\circ}\)C for 24 h to ensure the soil particles within the box were adequately consolidated and any remaining air bubbles were expelled.