A. This section provides the minimum requirements for the design and construction of rockery walls. Rock material shall meet the minimum requirements of the “Rock Wall Construction Guidelines”, as adopted by the Associated Rockery Contractors, dated August 15, 2000 edition, unless other materials are specifically pre-approved by the geotechnical engineer.
B. Definitions:
ROCK: | A natural solid mineral matter occurring in large masses or fragments. |
ROCKERY WALL: | A system of stacked rocks constructed to retain soil or rock and include rock faced slopes. |
C. Permit Requirement: Rockery walls three feet high and greater, as measured from the ground surface to the top of the uppermost rock layer shall be subject to the provisions of this section and shall require a permit issued by the Washington City Public Works Department prior to construction unless the wall was included and approved on the engineered construction drawings for the subdivision.
D. Documents Required: The following documentation shall be submitted at the time of application for a permit:
1. A dimensional drawing that identifies the location of each rockery wall with respect to the property lines, easements, streets, other rights of way, existing construction, required setbacks (as noted below), and drainage features shall be clearly identified on the drawings.
2. A cross section of the wall showing the minimum rock size for each lift, maximum wall height, reinforcing, backfill specifications, drainage, slope of adjacent ground, embedment, cuts and batter.
3. Engineering analysis and design is required for all rockery walls three feet (3') and greater in height, measure from the furthest point on the bottom to the furthest point on the top of the proposed rockery wall.
E. Site Conditions: The following specific site conditions shall be considered for each wall design and noted on the drawings submitted:
1. Future structures and landscaping.
2. Location of utilities and utility easements. The city reserves the right to deny a permit for a wall within, or over, a utility easement.
3. Location of existing or future utility installations within eight feet (8') of the base and top of the wall.
4. Data showing the subgrade soil conditions within eight feet (8') of the wall.
5. Type of fill material to be replaced or removed.
6. The drawings shall note the drainage for surface water within eight feet (8') of the wall and all walls shall be designed assuming wet conditions.
7. The drawings shall note the subsurface water conditions within eight feet (8') of the wall.
8. The drawings shall note the keyway/foundation depth and width,
9. The drawings shall note the slope conditions and surcharge loads.
10. Maintenance and service access shall be shown on the drawings.
F. Construction: All construction shall be done on private property and not from any public roads or right of ways. No walls will be permitted inside of, or upon any utility easement. The construction of all rockery walls shall adhere to the following:
1. Monitoring: All phases of the rockery wall construction shall be monitored by the geotechnical engineer employed by the owner/contractor to verify that the nature and quality of materials being used are appropriate and that the construction is in accordance with the approved engineered design. The geotechnical engineer shall verify to the city in writing that the materials and construction of the rockery wall as built is in accordance with the engineered design after construction is complete.
2. Fill Compaction: Where the rockery wall(s) is constructed in front of a fill, the fill shall be placed and compacted in a manner that will provide a competent fill mass as noted in the drawings. All fills shall consist of quality fill material meeting the geotechnical engineer’s recommendations as noted on the approved drawings and/or report.
3. Compaction Testing: Density tests to verify compaction shall be taken at random locations. At least two (2) tests per one hundred feet (100') of wall length and per two feet (2') of backfill shall be taken. In critical locations, the geotechnical engineer may request additional monitoring. The testing shall be conducted by a certified technician under the direction of the geotechnical engineer.
4. Fill Construction Reinforcement: All fill placed behind rockery walls shall be reinforced as recommended by the geotechnical engineer.
5. Rock Selection: The rocks used in the rockery wall should be of a generally cubical, tabular or rectangle shape. Rounded rocks should not be used and internal void spaces in the facing should be kept to a minimum. Prior to being placed, all rock shall be inspected and approved by the geotechnical engineer. The rock source shall be pre-approved by the geotechnical engineer. Rocks shall be placed to decrease in size with increasing wall height. Rocks shall be placed to bear on good flat to flat surfaces. The long dimension of the rocks shall extend back toward the cut/fill face. Rocks shall bear on at least two (2) or more other rocks. The contractor shall have sufficient space and stockpile material available to select from among a number of rocks for each space in the rockery wall to be filled.
6. Rock Placement: Rocks shall be placed as recommended by the geotechnical engineer. A keyway (one foot (1') minimum) as recommended by the geotechnical engineer shall be constructed into unyielding soil.
7. Drainage: A rock drainage filter or geosynthetic filter fabric shall be installed between the rear face of the rockery wall and soil face being protected. The drainage design shall consider adjacent conditions and potential for water and erosion, and shall be constructed as directed by the engineer.
8. Surface Drainage: Surface drainage shall be directed away from the rockery wall face to a positive and permanent discharge well away from, and beyond the rockery wall. The surrounding site shall be graded such that water cannot flow over the top of the wall.
9. Steepness Of Walls: The steepness of the wall shall not exceed one (1) horizontal to six (6) vertical. Specific recommendations from the engineer are required and shall be noted on the drawings.
10. Slopes: Slopes above and below rockery walls shall not exceed two (2) horizontal to one (1) vertical.
11. Rock Stockpiles: Rock and other material shall not be stockpiled in or on public roads or right of ways.
G. Limitations:
1. Height: The height of any single rockery wall shall not exceed eight feet (8'), or as limited by the international building code, whichever is most restrictive.
2. Alignment: Walls shall be in continuous alignment without abrupt changes in direction.
3. Terminations, Intersections And Radii: Terminations, intersections, and radii of rockery walls shall be included in the engineering analysis.
4. Corner Lots: Corner lots require additional engineering and permits for setbacks, sight distance standards and public utility easements.
H. Setbacks:
1. Minimum Setbacks: The setback from a rockery wall to a building or structure shall meet all setback requirements as outlined in the international building code, foundation clearance from slopes, or the setback from a rockery wall shall be a minimum of the height of the rockery wall itself, whichever is most restrictive/greater.
2. Separate Rockery Walls Considered As One Wall: For height and setback restrictions, separate rockery walls shall be considered as one wall, unless separated by a horizontal distance greater than the vertical height of the lower wall. The distance shall be measured from the outside of the foundation of the structure to the exposed face of the rockery wall. This provision applies to buildings or structures at the low and high side of the wall.
3. Terraced Rockery Walls: Multiple rockery walls, designed as terraced retaining walls, shall be separated a minimum distance of one-half (½) the height of the lower rockery wall to another rockery wall. The height of an upper wall shall not exceed the height of a lower wall. The total combined height of all rockery walls shall not exceed eight feet (8').
4. Rockery Walls In Utility Easements: Rockery walls shall not be constructed within side or rear yard utility easements without prior written permission in a form acceptable to the city from each affected utility. Notwithstanding any written permission, the city reserves the right to deny a permit for a rockery wall within, or over, any utility easement.
I. Structural Analysis: All structural analysis shall be in accordance with adopted building codes of the city and in accordance with this section. The structural analysis shall also adhere to the following:
1. Factor Of Safety; Seismic Forces: The minimum factor of safety for sliding and over- turning of each rock in a rockery wall shall be two (2). This shall include load combinations with seismic forces.
2. Analysis Provisions: The following analysis provision shall apply:
a. The maximum unit weight of the rocks used in the design of a rockery wall shall be one hundred fifty five (155) pcf unless field verified by special inspection.
b. The maximum coefficient of friction between rocks in a rockery wall shall be 0.5.
c. Surcharge load shall be taken into consideration in the analysis.
d. Specifications shall be provided to clearly define acceptance criteria for rock materials.
J. Inspections: Construction of rockery walls shall be supervised and inspected by a qualified geotechnical engineer employed by the owner/contractor. Supervision and testing shall be at a frequency specified by the geotechnical engineer, and shall include all phases of construction.
1. Schedule Required: A schedule for the continuous or periodic supervision and inspection of construction shall be specified on the construction documents and all such supervision and inspections shall be verified in writing.
2. Final Compliance Report Required: Upon completion of the wall, the geotechnical engineer shall submit a final compliance report to the city. The report shall include a description of the rock wall, including type of rock, size of rock, rock placement, embedment, inclination, property line setbacks, separations, and height of the wall. The report shall provide a professional opinion as to the compliance with all of the design recommendations and acceptance of the construction. (Ord. 2019-20, 11-13-2019)