# Study on the Optimization of Pile Length of Micropiles in Soil Landslides
## 2 Methods
### Optimization of Micropiles Length Based on Numerical Simulation
#### 2.4.2 Optimize Process Analysis  
The optimization problem in this study is to determine the safest pile length using our optimized mathematical model. The optimization process will include two main modules: theoretical calculations and numerical calculations. The specific implementation steps are as follows:  
Step 1: Analyze the landslide survey data, determine the calculation section of the landslide, and complete the related profile CAD drawings. Step 2: Determine the pile layout and calculate the landslide thrust. Step 3: Prepare the preliminary design parameters of the pile, such as pile diameter, spacing, length, material, foundation coefficient, stratum parameters, and calculation mode. Step 4: Calculate pile displacement, internal force, earth pressure, and pile length according to the calculation method described in Section 1. Step 5: Verify the foundation strength and micropile flexural bearing capacity. If satisfied, continue with Step 6. If not, return to Step 3. Step 6: Draw the internal force distribution and displacement maps of the pile and provide reinforcement suggestions. Step 7: Based on the CAD drawings obtained in Step 1, organize the stratum lines and save them as a CAD exchange file format \".dxf\". Step 8: Read and identify the stratum line exchange file, calculate the model's size parameters, and determine the modeling parameters and boundary parameters based on the calculation results. Step 9: Automatically create and mesh the numerical simulation grid and output the grid file. Step 10: Automatically create the numerical simulation command flow file for optimization calculations. Step 11: Call numerical simulation software for numerical optimization calculations and iterate for different pile lengths. Step 12: Read and analyze the optimization calculation results and provide optimization suggestions. The optimization flow chart is shown in Figure 4.  
In particular, the optimization command flow file created in Step 10 includes the core algorithm of the entire optimization process, including the following procedural steps:  
S1: Read the model grid file output by Step 9. S2: Perform initial stress equilibrium calculations: define the constitutive model as an elastic model; assign calculation parameters to all strata; create a contact surface between the sliding body and the sliding bed and assign parameters to the contact surface; further set boundary conditions and apply gravity, and calculate until convergence is reached. S3: \"Zeroing\" the model after initial stress calculations (eliminating displacement and plastic zones). S4: Change the soil constitutive model to the Mohr-Coulomb model and assign calculation parameters. S5: Structured modeling of micropiles and connecting beams (or plates) at the pile locations and assign structural calculation parameters. The pile length used in this modeling is the calculated pile length in Step 4, which is the upper limit of the design variable PLmax. S6: Set boundary conditions and calculate the slope safety factor after micropile reinforcement under self-weight working conditions. If the safety factor is not less than the allowable safety factor [Fs], proceed to the next step. Otherwise, it prompts an error message stating that the pile length design is deemed unreasonable or the simulation parameters are not set reasonably. Please review and attempt again. The flowchart of the optimization algorithm for micropile length is shown in Figure 5.  
Figure 4: Optimization Flowchart. (Note: the reason for triggering Error Prompt 1 is that when using the design calculated pile length PLmax for modeling and calculating, the safety factor is too low, indicating that the design pile length is too small to guarantee the landslide control effect, or there are problems with the numerical simulation of the strata parameters, resulting in unsafe numerical simulation calculation.) S7: Reset the pile length to the lower limit PLmin.