UPLIFTS IN STRUCTURAL FOUNDATIONS

Structures which have high lateral loads as compared to vertical loads tend to have uplift reactions in the foundation.

Signages, canopies, earth retaining boundary walls are some examples of these. Even uplifts can over locally in building foundations as well.

[1] Uplifts in the foundation must be avoided as it will create instability in structure by having loss of contact at the ground.

[2] There are various methods to avoid the uplift in the foundation, some of the those mentioned below & explained further.
           a) Changing the structural system or framing
           b) Increasing the dead load of structural member
           c) Additional soil fil
           d) Tying the foundation to adjacent areas
           e) Rock anchors

[3] Changing the structural framing: This can help when there is local uplift in the foundation of a building, tweaking the structural framing so that members with uplift get more dead load can solve the uplift.

[4] Increasing the self weight: This can help only in certain cases and might not be much cost effective. But this can work as good & only solution for cantilever retaining wall.

[5] Additional soil fill: At times when foundation is having high uplift forces additional soil fill over foundation slab can help to remove the tension. But it makes the foundation slab heavy.

[6] Tying foundation to adjacent areas: This is very effective solution when there is local uplifts in certain areas of raft foundation, tying these area together will control the uplift economically.

[7] Rock anchors: These are effective but costlier solution to control the uplift. Rock anchors are drilled into the ground hole which is filled grout (concrete without aggregate) and then these anchors are post tensioned.

This is post on ways to handle uplifts in the foundation, please share what other methods & strategies you follow to control the uplifts. Any comments or suggestions are welcomed.