While the provided documents don't explicitly state that a trench box must be level with the ground, it is implied that the trench box should be installed in a manner that provides adequate protection against cave-ins and structural collapses [1]. This would necessitate proper leveling to ensure the shield system functions as intended [2].

Here's why leveling is important for trench boxes:

• Stability: A level trench box is more stable and less likely to shift or move, especially under lateral loads [2].
• Even Load Distribution: Leveling ensures that the load from the surrounding soil is evenly distributed across the shield, maximizing its effectiveness [2].
• Proper Function: The design of a trench box assumes it will be installed in a way that allows it to resist cave-in forces effectively. Uneven placement could compromise its structural integrity [1].

Additionally, consider these points:

• Manufacturer's Recommendations: Always follow the manufacturer's instructions for installation and use of the trench box [1].
• Competent Person: A competent person should inspect the trench and protective systems daily to identify any potential hazards [3].

Therefore, while not explicitly stated, ensuring a trench box is level with the ground is a key aspect of safe installation and utilization.