This is the 3480th most frequent Japanese word.
着工
Commencement of construction.
In this sentence, '着工' (chakko) is used as a noun to refer to the act of starting construction.
新しいビルの着工は来月の予定です。
The construction of the new building is scheduled to start next month.
Here, '着工' (chakko) is used as part of a passive construction to indicate that construction has been initiated.
そのプロジェクトが着工されて、進捗が順調です。
The project has begun construction, and the progress is smooth.
In this example, '着工' (chakko) is used as a verb (with 'する') to describe the action of commencing construction.