What are the best foundation design practices for high snow loads in seismic zones?

1 Snow loads and seismic zones

Snow loads are the forces exerted by accumulated snow and ice on a structure, which depend on factors such as snow density, depth, shape, wind, temperature, and roof slope. Seismic zones are areas where earthquakes are more likely to occur, and where the ground motion can vary in intensity, duration, and frequency. Both snow loads and seismic zones can affect the design of the foundation, which is the part of the structure that transfers the loads to the ground and provides stability and support.

3 Shallow foundations

Shallow foundations are foundations that are placed near the surface of the ground, and that have a depth less than or equal to the width of the foundation. Shallow foundations are suitable for structures with low to moderate snow and seismic loads, and for soils that have adequate bearing capacity and low compressibility. Some examples of shallow foundations are strip footings, isolated footings, combined footings, and raft footings. Shallow foundations should be designed to have enough width and depth to distribute the loads evenly to the soil, to have adequate reinforcement and anchorage to resist the bending and shear forces, and to have sufficient frost protection and drainage to prevent frost heave and water accumulation.

4 Deep foundations

Deep foundations are foundations that are placed below the surface of the ground, and that have a depth greater than the width of the foundation. Deep foundations are suitable for structures with high snow and seismic loads, and for soils that have low bearing capacity or high compressibility. Some examples of deep foundations are piles, caissons, and drilled shafts. Deep foundations should be designed to have enough length and diameter to transfer the loads to a deeper and more stable soil layer, to have adequate connection and lateral support to resist the axial and lateral forces, and to have sufficient corrosion resistance and quality control to ensure long-term performance.

6 Pile foundations

Pile foundations are foundations that consist of vertical or inclined members that are driven or drilled into the ground, and that are connected by a pile cap or a beam to support the loads. Pile foundations are suitable for structures with high or eccentric snow and seismic loads, and for soils that have low bearing capacity or high liquefaction potential. Some examples of pile foundations are end-bearing piles, friction piles, batter piles, and micropiles. Pile foundations should be designed to have enough capacity and spacing to resist the axial and lateral forces, to have adequate group effect and interaction to account for the pile-soil-pile behavior, and to have sufficient detailing and testing to ensure the pile integrity and performance.

7 Here’s what else to consider

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