# Dynamic Simulation of Underground Cable Laying for Digital Three-Dimensional Transmission Lines
## 4 Engineering Examples and Analysis of Results
### Safety Survey and Hazard Analysis
#### 4.2.3 Pulley Load Capacity Analysis  
In order to investigate the variation of loads borne by the pulleys during cable laying, the values of loads suffered by the pulleys during the passage of cables are extracted. Through the simulation results, potential risks and problems are identified, thus reducing the incidence of problems in the actual construction. For the actual construction, the selection of the maximum load-bearing capacity of the pulley provides a theoretical basis. In the cable laying system, the load data of pulleys No. 1, 2, 3, and 4 are extracted from right to left in sequence.  
Figure 13 illustrates that when the cable passes through the end pulley, the first pulley, second pulley, third pulley, and fourth pulley experience sudden loads due to the collision and contact between the cable and pulleys. The first pulley experiences a momentary load fluctuation of approximately 2.8 kN; the peak load on this pulley is about 56% higher than the load during uniform motion. The second pulley is subjected to an instantaneous increase of 2 kN; the peak load on this pulley is about 40% higher than the load during uniform motion. The third pulley experiences a momentary increase of 1 kN; the peak load on this pulley is about 20% higher than the load during uniform motion. The fourth pulley is almost unaffected.  
Figure 11: Axial tension at the moment when the cable micro-section crosses the pulley.  
Figure 12: Ratio of maximum axial tension to theoretical calculation value.  
In this study, the selected pulleys have a rated load capacity of 160 kN. Through simulation, it was verified that the maximum load experienced by the pulleys during operation does not exceed their rated value, confirming that these pulleys can meet the demands of actual applications. However, in practical construction, factors such as improper operation by workers can lead to impact loads that may cause the load increment on the pulleys to exceed their rated load, potentially resulting in permanent deformation or displacement, causing the cable to slip off and lay on the pulleys.  
Considering these factors, in-field installations require that the selected pulleys have a load-bearing capacity exceeding 60% of the load experienced by the pulleys during uniform movement of the cable, providing a sufficient safety margin to prevent phenomena such as plastic deformation of the pulleys.  
In summary, the digital cable laying system model for the Huangjia Lake civil engineering cable tunnel construction site has been validated as correct and feasible. It demonstrates the dynamic variations in cable speed, axial tension, and traction force during the pulling process, leading to an overload safety factor for traction force, \(\alpha=1.5\). Furthermore, it allows for reasonable pulley selection based on the load-bearing capacity, providing a certain reference value for eliminating safety hazards such as collisions during actual construction and ensuring the safety of the cables.  
Figure 13: Data diagram of load borne by the pulley. (**a**) Load on pulley 1. (**b**) Load on pulley 2. (**c**) Load on pulley 3. (**d**) Load on pulley 4.