Code of Massachusetts Regulations
780 CMR - STATE BOARD OF BUILDING REGULATIONS AND STANDARDS
Chapter 16 - Structural Design
Section 1610 - SOIL LATERAL LOADS
Subsection 1610.2 - Seismic Loads on Foundation Walls and Retaining Walls

Exterior foundation walls and retaining walls shall be designed to resist an earthquake force, Fw, for horizontal backfill surface, equal to:

Fw = 0.100(SS)(Fa)(Yt)(H)2

where SS is the maximum considered earthquake spectral response acceleration from Table 1604.11, Fa is the site coefficient from Table 1613.5.3(1), yt is the total unit weight of the soil, and H is the height of the wall measured as the difference in elevation of finished ground surface or floor in front of and behind the wall. The earthquake force from the backfill shall be distributed as an inverted triangle over the height of the wall.

Surcharges that are applied over extended periods of time shall be included in the total static lateral soil pressure and their earthquake lateral force shall be computed and added to the force determined above. The point of application of the earthquake force from extended duration surcharge shall be determined on an individual case basis.

If the backfill or the existing soil behind the backfill consists of loose saturated granular soil, the potential for liquefaction of the backfill or existing soil adjacent to the wall during seismic loading shall be evaluated in accordance with the requirements of section 1806.4. If the backfill or existing soil beyond the backfill is potentially subject to liquefaction, the increase in design lateral load on the foundation wall or retaining wall shall be determined by a registered design professional.

For wall strength design, a load factor of 1.43 shall be applied to the earthquake force calculated above.