## 2 Materials and Methods
### Data Collection and Data Set Construction  
#### 2.3.1 Soil Sampling and Data Measurement  
The cone penetration device designed in this study was used to randomly measure 83 soil sites in the test base at Huazhong Agricultural University (GPS: 30.4664\({}^{\circ}\) N, 114.3483\({}^{\circ}\) E), Wuhan of Hubei Province from the 16 to 30 March 2021. This test base was dominated by clayed soil, and the structural compositions of the soil samples are listed in Table 1.  
During penetration experiments, the cone vertically penetrated into soils at a penetrating speed of 20 mm/min with a penetration depth of 15 cm. The sensor data were collected by the automatic measuring and collection system in real time. In order to reduce the chance of operating errors, the measurements were repeated three times for each measuring point, and the average values were taken as the final result. Calculating the standard deviation of three repeated measurements, we found that the standard deviation of all 83 measuring sites was less than 5%, so the measurement results were considered reliable. Field measurements from the CPT device are shown in Figure 6a, and the typical output signals of the sensors are shown in Figure 6b. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Clay (g/g)**} & \multirow{2}{*}{**Silt (g/g)**} & \multirow{2}{*}{**Sand (g/g)**} & **Liquid Limit** & **Plastic Limit** & **Specific Gravity** \\  & & & **(\%)** & **(\%)** & **(g/cm\({}^{3}\))** \\ \hline
0.54–0.68 & 0.14–0.36 & 10.00–0.18 & 34.31–41.47 & 25.80–27.65 & 2.62–2.79 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: The basic physical properties of soil in study area. Figure 5: Sensor’s calibration test. (**a**) Load cell; (**b**) film sensor. In Figure 6b, the sensors' original data shows obvious ripples due to the vibration of the stepper motor and the difference in soil penetration resistance. The load cell signal ripple fluctuates more significantly than the film sensor ripple signal, which may be caused by the stepper motor transmitting the penetrating driving force in the vertical direction. To eliminate the ripple interference, we used the 20 th-order median filtering method to process the sensors' original data and obtain smooth curves; however, in this study, the calculation error may have come mainly from the filtering process. Because of the arithmetic rounding of the digital filter, some calculation error is inevitable [42]. By comparing the measured values with the filtered values, it was found that the average error between them is less than 3%, which is considered acceptable. After the penetration test, soil sampling and laboratory measurement were carried out to obtain soil water content, bulk density, soil cohesion, and internal friction angle at the CPT measuring points. Within 20 cm of each PCT measuring point, the original soils at a depth of 10 cm from the ground were collected by carefully hammering metal cylinders (inner diameter 61.8 mm, height 20 mm) vertically into the soil. The reason for taking soil samples at this depth is that the depth of mechanized rotary tillage of primary crops such as rapeseed in the research area was 10 cm. From each measuring site, 8 soil samples were collected, of which 4 samples were used for direct shear tests [43] to determine soil shear strength \(\tau\), and the remaining samples were used for measuring soil water content and bulk density. Laboratory direct shear tests were conducted as per China standard GBT50123-2019, using the ZJ-D strain control direct shear tester produced by Nanjing Nantu Instrument Equipment Co., Ltd. (Nanjing, China). The normal stress applied in each measurement was 100, 200, 300, and 400 kPa, respectively, and the shear rate was maintained at 1.2 mm/min [3]. The shear strength parameters were computed using the Mohr-Coulomb failure criterion. Based on the Mohr-Coulomb failure envelope of shear strength and positive stress, soil cohesion (\(c\)) and internal friction angle (\(\varphi\)) were determined.