The pastoral lawns around the Kimbell Art Museum are surrounded by signs of construction. Postholes are being dug, trees have been tagged for removal, construction trailers are taking up residence on the Darnell Street parking lot, and the sidewalks are striped in orange and pink spray paint marking utility lines.Work is about to begin on the $125 million addition designed by Italian architect Renzo Piano.Construction was scheduled to begin in midsummer, but the late start will not affect the completion date or the budget, says Kimbell Director Eric M. Lee.Accommodations were made for unforeseen delays, and officials still expect the addition to open in spring 2013.The project involves construction of a separate building that will face the entrance to the Kimbell and will house touring exhibitions, an underground parking garage, offices and an auditorium. A model of the project has been placed in the front windows of the Kimbell overlooking the construction site.A few changes have been made since Piano unveiled his design. A berm that covers the back portion of the building now extends all the way from Camp Bowie Boulevard to Lancaster Avenue."There was a 9-foot incline that sloped up to Will Rogers, and that had to be taken into consideration," Lee said.Piano has also resolved his choice of exterior material. The outside of the structure will be concrete, as are the Kimbell's original building designed by Louis Kahn and the Modern Art Museum of Fort Worth designed by Tadao Ando.The new building will be known as the West Pavilion, with the original Kimbell structure called the East Pavilion.Details of the landscaping are still in flux but all trees that have to be removed will be replaced.Gaile Robinson is the Star-Telegram art and design critic. 817-390-7113.