muuddfun
Geotechnical
- Feb 4, 2008
- 107
I am looking for some ideas on what may be causing manholes and sewer mains to sink. I was recently called to check out the repair operation of a manhole and replacement of the sewer line where the line had been videoed and the pipe was so badly seperated near the manhole that the video camera could not pass the seperation. The sewer line is a 27 inch main. The depth of the sewer line is about 22 feet. The soils are clay (CH) and also some clayey silts / silty clays ML/CL that fall along the A line. The clays were fairly soft. Groundwater is about 6 to 10 feet below grade. There are occasional lenses of sand, though in the area of the sewer it appered to be mostly the clay that was present. The sediments are lake deposits. The clays are generally slightly overconsolidated. The sewer pipe is clay pipe encased in about 12 inches of unreinforced concrete. There was no other bedding material below the pipe. The sewer system is old probobly installed between 1900 and 1930. The area is subject to many earthquakes and strong ground shaking. This particular manhole was not in a high traffic area.
I am thinking about liquefaction, bearing failures of the clay, or infiltration of the fines into the line and errosion of soils surrounding and supporting the line. What else should i consider?
I am thinking about liquefaction, bearing failures of the clay, or infiltration of the fines into the line and errosion of soils surrounding and supporting the line. What else should i consider?