geot88
Geotechnical
- Apr 30, 2013
- 30
The company I'm currently working for has been called to do the Geotechnical design of many monopoles in the city. They gave us a sample study (they have worked like that in other countries) and wanted us to do something similiar here.
The requirements were:
-Do SPT continously up to 6 meters.
-correct N to N60 and get friction angle and Su values from correlations.
-calculate bearing capacity of a shallow foundation (from 5x5 m. to 7x7 m.), Df= 2 m.
They insisted that they have used a shallow foundation 90% of the times that they have contructed monopoles. (Monopole height = 36 m.)
We did our job, SPT 6 meters. Found clay (N= 1 to 7) from 0 to 4.5 meters, then found fine sand (N= 7 to 13) from 4.5 to 6.5 m.
water table was at 2.00 meters down the surface. We got friction angle for sand and Su for clay (correlations)
Then we analyzed it under undrained conditions. we gave friction angle = 0 to the clay (undrained condition) and used Hansen theory. q adm was around 30 kPa.
Later they told us that the Moment of the monopole was 2100 kN-m and the wind speed was 140 Km/h -which I think is really really high. Vertical force was 1400 kN.
Should I analyze eccentricity? I analyzed it and it was (M/V = 1.5 m). and B/6 is 7/6 = 1.16 m. So I suggested deep foundations.
However, they insist in using a shallow one.
My questions are: are those wind values real? Is eccentricity calculated well? I know I have to calculate it for strip and spread footings, does the same rule apply to concrete slabs, mats or rafts?
The requirements were:
-Do SPT continously up to 6 meters.
-correct N to N60 and get friction angle and Su values from correlations.
-calculate bearing capacity of a shallow foundation (from 5x5 m. to 7x7 m.), Df= 2 m.
They insisted that they have used a shallow foundation 90% of the times that they have contructed monopoles. (Monopole height = 36 m.)
We did our job, SPT 6 meters. Found clay (N= 1 to 7) from 0 to 4.5 meters, then found fine sand (N= 7 to 13) from 4.5 to 6.5 m.
water table was at 2.00 meters down the surface. We got friction angle for sand and Su for clay (correlations)
Then we analyzed it under undrained conditions. we gave friction angle = 0 to the clay (undrained condition) and used Hansen theory. q adm was around 30 kPa.
Later they told us that the Moment of the monopole was 2100 kN-m and the wind speed was 140 Km/h -which I think is really really high. Vertical force was 1400 kN.
Should I analyze eccentricity? I analyzed it and it was (M/V = 1.5 m). and B/6 is 7/6 = 1.16 m. So I suggested deep foundations.
However, they insist in using a shallow one.
My questions are: are those wind values real? Is eccentricity calculated well? I know I have to calculate it for strip and spread footings, does the same rule apply to concrete slabs, mats or rafts?