17A.30.010 Excavation Standards | Pierce County Code

17A.30.010 Excavation Standards.

1. Slopes shall be no steeper than is safe for the intended use and shall not be steeper than 2 horizontal to 1 vertical, or as recommended by a soils Engineer.

2. The catch point of the top of the slope shall be set back from the site boundary line in accordance with the following table, unless a retaining wall is designed by the Engineer and constructed for the project.

Cut Depth	Setback Distance
Under 5 Feet	2 Feet
5 – 20 Feet	Height/2
Over 20 Feet	10 Feet

C. Cut slopes shall be constructed in a manner such that a factor of safety of at least 1.5 is achieved for static conditions and at least 1.2 for seismic dynamic conditions. Analysis of dynamic (seismic) conditions shall be based on a minimum horizontal acceleration as established by the most current version of the Building Code as adopted by Title 17C PCC.

D. The proposed cut slopes shall not create the need for landslide hazard buffers or setbacks on neighboring properties unless approved through a notarized written agreement with the property owner.

E. Interior cut slopes for surface mining projects which are part of an active mining operation are exempt from the 2:1 maximum cut slope angle requirement as long as access to the mine is controlled via fencing or other security measures to discourage entrance by unauthorized persons. Interior slopes are those slopes that do not impact the theoretical slope face that is created by applying a 2 horizontal to 1 vertical angle and the required setbacks to the property line. Cut slopes along the mine's property boundaries are allowed to be steeper than 2:1 if the applicant can show through the submittal of a stability study that there will not be a negative impact to neighboring properties in the form of stability impacts, increased setback requirements or increased buffer distances.

F. Refer to the Pierce County Stormwater Management and Site Development Manual, Volume 2, for additional excavation techniques.