WorldWide Drilling Resource

35 WorldWide Drilling Resource ® FEBRUARY 2017 San Francisco’s Leaning Tower Complied by the Editorial Staff of WorldWide Drilling Resource ® Most people have heard of the Leaning Tower of Pisa, but have you ever heard of the “Leaning Tower of San Francisco”? The skyscraper in question is the Millennium Tower, which has developed a worsening slant since its construction in 2009. The tower has sunk 16 inches and tilted at least 2 inches northwest at its base, which translates into an alarming 15-inch tilt at the top of the building. The Millennium has 58 floors and reaches an architectural height of 645 feet, making it the tallest residential building in the city. Though the glassy blue structure paints quite a splendid view in the downtown skyline, the focus has become its precarious lean and the possibility of sinking a total of 31 inches from its original foundation. Some settling is to be expected with very large structures like the Millennium. The problem engineers are trying to understand is why the tower is sinking more than the 4-6 inches it was expected to over the life of the building. Then, they can tackle the questions concerning what the building is going to do in the future, and how to stop further tilting and sinking. The project developer, Millennium Partners, has proposed the structural problems were caused by dewatering at the construction site of the Transbay Transit Center next door. Pump- ing out millions of gallons of groundwater from the area is thought to have softened and com- pressed the soil under the tower. However, Transbay believes the structural problems are caused by an improper foundation design by Millennium Partners. The building rests on more than 900 “friction piles” driven into dense, old bay mud at a depth of 60-91 feet. Transbay thinks the developers should have used “end bearing piles”, which would have reached down 200 feet into the bedrock. Prior to the Millennium project, no major building downtown had piles driven into bedrock, but since then, four projects by Transbay developers have used the method. Both techniques have worked in the area; however, Millennium Tower is five times heavier than other buildings with a similar foundation. Either dewatering or poor foundation de- sign could be correct, or perhaps a mixture of both, but it will remain speculation until results are in from an independent investigation. Soil experts have drilled a six-inch-wide hole using a rotary drill rig, which will eventually drill 260 feet into the ground. The hole will allow experts to drop three in- struments into the foundation, which will measure the buildings tilt, groundwater and soil conditions, and how much the soil under the building has settled. The plan is to use two holes along the front of the building, and a third around the cor- ner, with the intent of finding out where the soil is compressing and where it is settling. If it turns out the building does need to be fixed, the easiest solution would be to reinforce the foundation by injecting material and adding additional support; a more serious scenario could involve radical solutions like taking 20 floors off the top of the building to make the structure lighter. The Millennium Tower, courtesy of Michael Gimbel. March 9 - 10, 2017 Grand Traverse Resort and Spa Acme, MI For more information, call: (855) 225-6492 or visit us online: michigangroundwater.com Thursday Registration • McEllhiney Lecture • Legislative Update “State of Lansing” • DEQ Update • DOT Update • Tips from Toastmasters “How to be a better speaker and make your business stand out” • Auxiliary Function • Cocktails • Banquet and Awards • Entertainment • Casino Night and Microbrew/Winery Judging Friday Registration • MGWA Annual Meeting • MGWA Lunch and Trade Show 89 th Annual Convention and Trade Show Congratulati ons to : Toni Jean Unger Gouldsboro,, PA Winner for January! Time for a Little Fun! January Puzzle Solution: Infinity Tool Mfg. Wyo-Ben, Inc. Can you identify which ads in this issue these two photos came from? Win a prize! Send your completed puzzle to: WWDR PO Box 660 Bonifay, FL 32425 or fax to: 850-547-0329