Section 105.97. Stability of structures

(a) Dams must be structurally sound and be constructed of sound and durable materials. The structure must be stable during and at the completion of construction.

(b) As part of the permit application for the construction or modification of a dam, the design engineer shall submit to the Department, under professional seal and certification, a report entitled ‘‘Dam Stability Report’’ which clearly demonstrates to the Department that the requirements of subsection (a) have been satisfied. At a minimum, this report must address the following considerations:

(1) The physical properties of the materials available for construction.

(2) A stability analysis based on the properties of the structure’s materials and on the seismic forces and seepage conditions affecting the structure.

(3) The methods of construction.

(4) The conditions of operation of the dam and reservoir.

(c) Earthfill dams must be demonstrated to be stable for the following conditions:

(1) Normal pool with steady-state seepage conditions with a factor of safety of 1.5.

(2) Maximum pool with steady-state seepage conditions with a factor of safety of 1.4.

(3) Sudden drawdown from normal pool conditions with a factor of safety of 1.2.

(4) Normal pool with steady-state seepage conditions under seismic forces produced by the maximum credible earthquake with a factor of safety of 1.1.

(5) Completion of construction with no pool with a factor of safety of 1.3.

(d) Gravity dams must be demonstrated to be stable for the following conditions:

(1) Normal pool with appropriate uplift pressures, ice loads and silt loads with a factor of safety of 2.0.

(2) Maximum pool with appropriate uplift pressures and silt loads with a factor of safety of 1.7.

(3) Normal pool with appropriate uplift pressures and silt loads under seismic forces produced by the maximum credible earthquake with a factor of safety of 1.3.

(e) For gravity dams, the overturning stability is acceptable when the resultant of all forces acting on the dam is located as follows:

(1) Within the middle third of the structure for normal pool conditions.

(2) Within the middle half of the structure for maximum pool conditions.

(3) Within the structure for earthquake conditions.

(f) For gravity dams, the foundation bearing pressures must be less than or equal to the allowable for no pool, normal pool and maximum pool conditions and less than 133% of the allowable for earthquake conditions.

(g) The factors of safety for earthfill dams or gravity dams must be the higher of:

(1) The factors of safety in subsections (c) and (d).

(2) The factors of safety in the most recent Engineering Manuals developed by the United States Army Corps of Engineers relating to stability of dam structures.

(h) The Department may, in its discretion, consider a revised factor of safety for a class of dams or reservoirs when it can be demonstrated that the factor of safety provides for the integrity of the dams or reservoirs and adequately protects life and property.

The provisions of this § 105.97 adopted September 26, 1980, effective September 27, 1980, 10 Pa.B. 3843; amended January 7, 2011, effective January 8, 2011, 41 Pa.B. 219. Immediately preceding text appears at serial page (207722).

Notation

Authority

The provisions of this § 105.97 under section 5 of the Dam Safety and Encroachments Act (32 P. S. § 693.5).

Cross References

This section cited in 25 Pa. Code § 105.81 (relating to permit applications for construction and modification of dams and reservoirs); and 25 Pa. Code § 105.89 (relating to Letters of Amendment and Letters of Authorization for modification of dams and reservoirs).