Canopy addition adjacent to an existing building

[GalileoG]

I am designing a 1-bay canopy adjacent to an existing building, the new canopy columns will be approximately 1.5ft away from the face of the foundation wall. A test pit was conducted to determine the condition of the existing foundations and discovered that the existing foundation walls did not have a strip footing (very old construction). One bay over from the new columns adjacent to the existing foundation wall, I have new columns on spread footings cast integrally with a retaining wall.

Initially, I wanted to place spread footings adjacent to the existing foundation wall, but the pier would be very eccentric to the footing. I also had concerns with stressing the soil beneath the existing foundation wall which may induce new settlement of the existing building. I also had concerns with how the existing foundation wall can be braced during excavation.

I am now leaning towards placing helical piles with concrete piers for the line of columns adjacent to the existing foundation wall, but 1-bay over, the new columns will be on spread footings cast integrally with a retaining wall. Here I have concerns with mixing shallow with deep foundations, especially over such a short bay (17 feet).

I am stomped on this one. Any ideas? Thanks in advance.

 

[ishvaaag]

Then use your helical piles at both alignments... columns integral with a retaining wall, in what way? if the ground is sloping inwards or flat you may have a near deep foundation due to the wall, if sloping outwards, then the helical piles need not be detrimental to safety ... that's it, if well built ...whilst opposing differential settlement.

 

[Ron]

GalileoG...most canopies are very lightly loaded, usually with the foundation being the heavier part. Helical piers or small drilled piers usually work well in confined areas. Overturning and uplift usually control such in my area because of wind loads.