major cross-section of subsidence trough

例句：

1. 1.The major cross-section of the tunnel is where the road meets the river.
   隧道的主要截面是道路与河流交汇的地方。
2. 2. The engineer studied the major cross-section of the bridge to determine its load capacity.
   工程师研究了桥梁的主要截面以确定其承载能力。
3. 3.The structural engineer analyzed the major cross-section of the building to ensure its stability.
   结构工程师分析了建筑的主要截面以确保其稳定性。