Is the work of a civil engineer, which includes calculating "capital interest" in the estimation of construction project costs, considered permissible (halal) or forbidden (haram)?

It is permissible to work in the field of calculating "cost of capital" as an expense, because a company calculates the cost of capital as if it had deposited it in banks instead of investing it in the project, and this cost is included in the required price. This does not preclude working in the management of such projects.