AlaaElnahas
Geotechnical
Dear All,
I am designing Variable Message Signs (Gantries) on a motorway in NorthWest England. The worst Loading condition leads to vertical and lateral loads [Pz and Px]on each Gantry foundation of 145 kN and 101 kN, respectively. In addition, there are bending moments [Mx, My, and Mz (Torsion)] of 528, 589, and 442 kN.m. For some of the Gantrys, I can find a reliable foundation layer of Stiff clay or dense sand and gravel (N>28) at about 3-3.5m below the ground surface, underneath the embankment, so I think they are better to be founded on deep footings that are founded on these layers. For others, the reliable foundation layers are deeper (5-7 m below the ground surface) and subsequently will be founded on piles. In all of the gantry positions, the embankment will fill (with a height range between 0.5 and 4 m). My questions are:
1- How to assess the resistance of the deep footings and piled foundations to the torsion, caused by the Mz? If, for example, we use horizontal keys that work as fan blades to resist torsion, how to assess the earth pressure on them?
2- Is the piled foundation a good solution with these high bending moments? If not, how to found the gantries on about 5-6m of soft/unreliable ground?
3- Given the high eccentricity applied on the footing or pile cap, in this critical loading condition, and that there are other loading conditions with smaller bending moments, what should I do to reduce the high bending moments.
4- If you know of Books, Specs, or published case studies the cover the estimation of the bearing capacity of such foundations, I would be thankful, if you could send me any information about them.
Many Thanks
Ala'a
I am designing Variable Message Signs (Gantries) on a motorway in NorthWest England. The worst Loading condition leads to vertical and lateral loads [Pz and Px]on each Gantry foundation of 145 kN and 101 kN, respectively. In addition, there are bending moments [Mx, My, and Mz (Torsion)] of 528, 589, and 442 kN.m. For some of the Gantrys, I can find a reliable foundation layer of Stiff clay or dense sand and gravel (N>28) at about 3-3.5m below the ground surface, underneath the embankment, so I think they are better to be founded on deep footings that are founded on these layers. For others, the reliable foundation layers are deeper (5-7 m below the ground surface) and subsequently will be founded on piles. In all of the gantry positions, the embankment will fill (with a height range between 0.5 and 4 m). My questions are:
1- How to assess the resistance of the deep footings and piled foundations to the torsion, caused by the Mz? If, for example, we use horizontal keys that work as fan blades to resist torsion, how to assess the earth pressure on them?
2- Is the piled foundation a good solution with these high bending moments? If not, how to found the gantries on about 5-6m of soft/unreliable ground?
3- Given the high eccentricity applied on the footing or pile cap, in this critical loading condition, and that there are other loading conditions with smaller bending moments, what should I do to reduce the high bending moments.
4- If you know of Books, Specs, or published case studies the cover the estimation of the bearing capacity of such foundations, I would be thankful, if you could send me any information about them.
Many Thanks
Ala'a
