Along the proposed pipe lines as indicated on the plans, the contractor shall remove the surface materials only to such widths as will permit a trench to be excavated which will afford sufficient room for proper efficiency and proper construction. Where sidewalks, driveways, pavements and curb and gutter are encountered, care shall be taken to protect against fracture or disturbance beyond reasonable working limits. In areas specified on the plans, the top 12 inches shall be piled separately and preserved so that it may be restored after the remainder of the backfill is replaced.