What kind of shield systems can be used in trench excavations?

In trench excavations, the use of shield systems is crucial for ensuring the safety of workers and maintaining the structural integrity of the excavation. The correct answer, which allows for either permanent or portable structures, reflects the flexibility that construction projects may require.

Permanent shield systems are those that are intended to remain in place for the long term, often used in deep or extensive excavations where the risk of cave-ins is significant. These structures are designed to provide ongoing protection over the duration of the excavation and may be integrated into the final structure of a project.

On the other hand, portable shields are temporary systems that can be moved and reused at different excavation sites. They are particularly beneficial in projects where excavations may vary in size or location from one job to another. These portable options allow contractors to adapt to different job requirements without the need for investing in entirely new systems for each project.

This combination of both permanent and portable options provides the necessary adaptability for various excavation situations while ensuring compliance with safety regulations. The use of either type also emphasizes that a trench excavation can be executed in a manner that maximizes both functionality and safety, accommodating different construction scenarios.

Other options suggest a limitation that does not reflect industry practices; only using one type of shield system could restrict