Chapter 24.70 Clearing, Grading, And Retaining Walls

City Code Chapter

(Chapter amended by Ordinances 184522, 185448, 186053 and 188884, effective April 4, 2018.)

24.70.010 General.

(Amended by Ordinances 165678, 168340, 184522, 185448 and 186053, effective January 1, 2015.)  

  1. The provisions of this Chapter shall regulate clearing, grading and earthwork construction on private property.   Tree removal, whether associated with clearing, grading, earthwork construction or conducted separately shall be regulated pursuant to Title 11, Trees.  Erosion control is regulated by Title 10.

24.70.020 Permits.

(Amended by Ordinances 165678, 168340 172209, 173532, 173979, 184522, 185448, 186053 and 188884, effective April 4, 2018.)  

  1. Permits for clearing, grading, and retaining walls are required as specified in this Section.  Where a specific activity does not require a clearing or grading permit, a separate tree permit may still be required, as specified in Title 11 Trees.  Where a clearing or grading development permit shows trees to be removed and has been reviewed and approved by the City, a separate tree permit is not required in conjunction with the clearing or grading permit.  An erosion, sediment and pollutant control plan if required by Title 10 shall be submitted with clearing or grading permit applications.  Applicants for permits made in conjunction with land divisions shall be responsible for all clearing, grading, tree removal and erosion control within the land division, even where a specific activity is exempt from an individual permit.
  2. A.  Clearing Permits.  A permit is required and shall be issued in accordance with Section 24.10.070 for clearing activities in the following areas:
    1. 1.  The Tualatin River sub-basins, Johnson Creek Basin Plan District, environmental zones, greenway zones, or natural resource management plans; or
    2. 2.  Property larger than five acres.  Except that no permit shall be required for clearing an area less than 5,000 square feet.
  3. B.  Grading Permits.  A permit is required and shall be issued in accordance with Section 24.10.070 for all grading operations with the exception of the following:
    1. 1.  Grading in an area, where in the opinion of the Director, there is no apparent danger, adverse drainage, or erosion effect on private/public property, or inspection is not necessary;
    2. 2.  An excavation below finished grade for basements and footings of a building, retaining wall, or other structure authorized by a valid building permit.  This shall not exempt any fill made with the material from such excavation nor exempt any excavation having an unsupported height greater than 5 feet after the completion of such structure.
    3. 3.  Cemetery graves.
    4. 4.  Refuse disposal sites controlled by other regulations.
    5. 5.  Excavations for wells or tunnels.
    6. 6.  Mining, quarrying, excavating, processing, stockpiling of rock, sand, gravel, aggregate, or clay where established and provided for by law provided such operations do not affect the lateral support or increase the stresses in or pressure upon any adjacent or contiguous property.
    7. 7.  Exploratory excavations under the direction of soil (geotechnical) engineers or engineering geologists.
    8. 8.  An excavation which
      1. a.  Is less than 2 feet in depth, or
      2. b.  Which does not create a cut slope greater than 5 feet in height and steeper than 1‑1/2 horizontal to 1 vertical.
    9. 9.  A fill less than 1 foot in depth, and placed on natural terrain with a slope flatter than 5 horizontal to 1 vertical, or less than 3 feet in depth, not intended to support structures, which does not obstruct a drainage course and which does not exceed 10 cubic yards on any one lot.
  4. C.  Retaining Walls.  A permit is required and shall be issued in accordance with Section 24.10.070 for all retaining walls over 4 feet (1219 mm) in height measured from the bottom of the footing to the top of the wall, and for retaining walls supporting a surcharge.
  5. D.  Tree Removal.  Removal of trees six-inches and larger in diameter shall be reviewed with the clearing or grading permits as part of the Tree Plan review pursuant to Title 11.  When removing 5 or more trees on a site with an average slope of at least 20 percent, applicants shall provide a geotechnical engineering report that assesses the stability of the site after tree felling and root grubbing operations.
  6. E.  Permits required under this Chapter shall be obtained before the commencement of any tree removal, root grubbing or soil disturbance takes place.

24.70.030 Hazards.

(Amended by Ordinances 165678 and 188884, effective April 4, 2018.)  

  1. The Director may determine that any clearing, grading, retaining wall, or geologic condition on private property has or may become a hazard to life and limb, or endanger property, or cause erosion, or adversely affect drainage or the safety, use or stability of a public way or drainage channel.  Upon receipt of notice in writing from the Director, the owner shall mitigate the hazard and be in conformity with the requirements of this Title.  The Director may require that plans and specifications and engineering reports be prepared in compliance with this Chapter.

24.70.040 Special Definitions.

(Amended by Ordinance 188884, effective April 4, 2018.)  

  1. The definitions contained in this Section relate to excavation and grading work only as outlined in this Chapter.
  2. A.  “Approval” shall mean a written engineering or geological opinion concerning the progress and completion of the work.
  3. B.  “As graded” is the surface conditions exposed on completion of grading.
  4. C.  “Bedrock” is in‑place solid rock.
  5. D.  “Bench” is a relatively level step excavated into earth material on which fill is to be placed.
  6. E.  “Borrow” is earth material acquired from an off‑site location for use in grading on a site.
  7. F.  “Civil engineer” shall mean a professional engineer registered in the State to practice in the field of civil works.
  8. G.  “Civil engineering” shall mean the application of the knowledge of the forces of nature, principles of mechanics, and the properties of materials to the evaluation, design, and construction of civil works for the beneficial uses of mankind.
  9. H.  “Clearing” is the cutting or removal of vegetation which results in exposing any bare soil.
  10. I.  “Compaction” is the densification of a fill by mechanical means.
  11. J.  “Earth material” is any rock, natural soil, or fill and/or any combination thereof.
  12. K.  “Engineering geologist” shall mean a geologist experienced and knowledgeable in engineering geology and registered as an engineering geologist in the State of Oregon.
  13. L.  “Engineering geology” shall mean the application of geologic knowledge and principles in the investigation and evaluation of naturally occurring rock and soil for use in the design of civil works.
  14. M.  “Erosion” is the wearing away of the ground surface as a result of the movement of wind, water, and/or ice.
  15. N.  “Excavation” is the mechanical removal of earth material.
  16. O.  “Fill” is a deposit of earth material placed by artificial means.
  17. P.  “Geological hazard” shall mean a potential or apparent risk to persons or property because of geological or soil instability either existing at the time of construction or which would result from construction.
  18. Q.  “Grade” shall mean the vertical location of the ground surface.
  19. R.  “Existing grade” is the grade prior to grading.
  20. S.  “Rough grade” is the stage at which the grade approximately conforms to the approved plan.
  21. T.  “Finish grade” is the final grade of the site which conforms to the approved plan.
  22. U.  “Grading” is any excavating or filling or combination thereof.
  23. V.  “Key” is a designed compacted fill placed in a trench excavated in earth material beneath the toe of a proposed fill slope.
  24. W.  “Retaining Wall” is a structure that provides lateral support for a mass of soil or fluid and other imposed loads.
  25. X.  “Site” is any lot or parcel of land or contiguous combination thereof, under the same ownership, where grading is performed or permitted.
  26. Y.  “Slope” is an inclined ground surface the inclination of which is expressed as a ratio of horizontal distance to vertical distance.
  27. Z.  “Soil” is naturally occurring surficial deposits overlying bedrock.
  28. AA.  “Soil (Geotechnical) engineer” shall mean a civil engineer competent by education, training, and experience in the practice of soil engineering.
  29. BB.  “Soil (Geotechnical) engineering” shall mean the application of the principles of soil mechanics in the investigation, evaluation, and design of civil works involving the use of earth materials and the inspection and testing of the construction thereof.
  30. CC.  “Terrace” is a relatively level step constructed in the face of a graded slope surface for drainage and maintenance purposes.

24.70.050 Information on Plans and in Specifications.

(Amended by Ordinances 173532, 184522, 185448, 186053 and 188884, effective April 4, 2018.)   

  1. Plans and specifications shall be submitted in accordance with Section 24.10.070 and in addition shall comply with the following:
  2. A.  Plans shall be drawn to scale upon substantial paper or cloth and shall be of sufficient clarity to indicate the nature and extent of the work proposed and show in detail that they will conform to the provisions of this Title and all relevant laws, ordinances, rules, and regulations.  The first sheet of each set of plans shall give the location of the work and the name and address of the owner and the person by whom they were prepared.
  3. The plans shall include the following information.
    1. 1.  General vicinity of the proposed site.
    2. 2.  Property limits and accurate contours of existing ground and details of terrain and area drainage for the site and surrounding area.
    3. 3.  Limiting dimensions, elevations, or finish contours to be achieved by the grading and the proposed drainage channels and related construction.
    4. 4.  Detailed schedule of when each portion of the site is to be graded;  how long the soil is to be exposed;  and when the area is to be covered with buildings, paving, new vegetation or temporary erosion control measures.
    5. 5.  Detailed plans of all surface and subsurface drainage devices, walls, retaining walls, cribbing, dams, and other protective devices to be constructed with, or as a part of, the proposed work together with a map showing the drainage area and the estimated runoff of the area served by any drains.
    6. 6.  Location of any buildings or structures on the property where the work is to be performed and the location of any buildings or structures on land of adjacent owners or trees in the adjacent rights-of-way that are within 15 feet of the property or which may be affected by the proposed grading operations.
    7. 7.  Specifications shall contain information covering construction and material requirements.
    8. 8.  Civil engineering report.  The civil engineering report, when required by the Director, shall include hydrological calculations of runoff and the existing or required safe storm drainage capacity outlet of channels both on site and off site, and 1 in 100 year flood elevations for any adjacent watercourse.  The report shall include recommendations for stormwater control and disposal.
    9. 9.  Soil (Geotechnical) engineering report.  The soil engineering report, when required by the Director, shall include data regarding the nature, distribution, and strength of existing soils, design criteria, and conclusions and recommendations applicable to the proposed development.  The report shall include recommendation for subdrainage, and for groundwater control and disposal.  Recommendations included in the report and approved by the Director shall be incorporated in the plans and specifications.  For single family residences, a surface reconnaissance and stability questionnaire may be substituted for a formal soils report at the discretion of the Director.
    10. 10.  Engineering geology report.  The engineering geology report, when required by the Director, shall include an adequate description of the geology of the site, and conclusions and recommendations regarding the effect of geologic conditions on the proposed development and site(s) to be developed.
    11. Recommendations included in the report and approved by the Director shall be incorporated in the grading plans and specifications.
  4. B.  Issuance.  Section 24.10.070 is applicable to grading permits.  The Director may require that:
    1. 1.  The amount of the site exposed during any one period of time be limited; and
    2. 2.  Grading work be scheduled to avoid weather periods or avoid critical habitat use periods for areas existing on, or adjacent to, the development site.
  5. Subsequent to the issuance of the grading permit, the Director may require that grading operations and project designs be modified if delays occur which can result in weather generated problems not considered at the time the permit was issued.

24.70.060 Bonds.

  1. The Director may require bonds in such form and amounts as may be deemed necessary to assure that the work, if not completed in accordance with the approved plans and specifications, will be corrected to eliminate hazardous conditions.
  2. In lieu of a surety bond the applicant may file a cash bond or instrument of credit with the Director in an amount equal to that which would be required in the surety bond.

24.70.070 Cuts.

  1. A. General. Unless otherwise recommended in the approved soil engineering and/or engineering geology reports, cuts shall conform to the provisions of this Section.
  2. B. Slope. The slope of cut surfaces shall be no steeper than is safe for the intended use. Cut slopes shall be no steeper than 2 horizontal to 1 vertical.
  3. C. Drainage and terracing. Drainage and terracing shall be provided as required by Section 24.70.100.

24.70.080 Fills.

  1. A. General. Unless otherwise recommended in the approved soil engineering report fills shall conform to the provisions of this Section.
  2. In the absence of an approved soil engineering report these provisions may be waived for minor fills not intended to support structures. Such fills shall be subject to review at the discretion of the Director.
  3. B. Ground preparation. The ground surface shall be prepared to receive fill by removing vegetation, noncomplying fill, top-soil, and other unsuitable materials scarifying to provide a bond with the new fill, and where slopes are steeper than 5 to 1, and the height greater than 5 feet, by benching into competent material or sound bedrock as determined by the soils engineer. The bench under the toe of a fill on a slope steeper than 5 to 1 shall be at least 10 feet wide. The area beyond the toe of fill shall be sloped for sheet overflow or a paved drain shall be provided. Where fill is to be placed over a cut the bench under the toe of a fill shall be at least 10 feet wide but the cut must be made before placing fill and approved by the soils engineer and engineering geologist as a suitable foundation for fill. Unsuitable soil is soil which in the opinion of the Director or the civil engineer or the soils engineer or the engineering geologist, is not competent to support either soil or fill, to support structures or to satisfactorily perform the other functions for which the soil is intended.
  4. C. Fill material. Only permitted material free from tree stumps, detrimental amounts of organic matter, trash, garbage, sod, peat, and similar materials shall be used. Rocks larger than 6 inches in greatest dimension shall not be used unless the method of placement is properly devised, continuously inspected, and approved by the Director.
  5. The following shall also apply:
    1. 1. Rock sizes greater than 6 inches in maximum dimension shall be 10 feet or more below grade, measured vertically.
    2. 2. Rocks shall be placed so as to assure filling all voids with fines. Topsoil may be used in the top 12-inch surface layer to aid in planting and landscaping.
  6. D. Compaction of fill. All fills shall be compacted to a minimum relative dry density of 90 percent as determined in accordance with ASTM Standard D-1557-78. Field density verification shall be determined in accordance with ASTM Standard D-1556-82 or equivalent and must be submitted for any fill 12 inches or more in depth where such fill may support the foundation for a structure. A higher relative dry density, or additional compaction tests, or both, may be required at any time by the Director.
  7. E. Fill slope. The slope of fill surfaces shall be no steeper than is safe for the intended use. Fill slopes shall be no steeper than 2 horizontal to 1 vertical.
  8. F. Drainage and terracing. Drainage and terracing shall be provided and the area above fill slopes and the surfaces of terraces shall be graded and paved as required by Section 24.70.100.

24.70.085 Retaining Walls.

(Added by Ordinance 188884, effective April 4, 2018.)

  1. A.  Retaining walls not regulated by the Oregon Residential Specialty Code or the Oregon Structural Specialty Code shall be designed in accordance with ASCE 7-16 and this section.
  2. B.  Soil loads shall be determined in accordance with ASCE 7-16.  Retaining walls in which horizontal movement is restricted at the top shall be designed for at-rest pressure.  Retaining walls free to move and rotate at the top shall be permitted to be designed for active pressure.  Lateral pressure from surcharge loads shall be added to the lateral earth pressure load.  Lateral pressure shall be increased if soils at the site are expansive or the retaining wall will support an ascending slope.  Retaining walls shall be designed to support the weight of the full hydrostatic pressure of undrained backfill unless a drainage system is installed. 
  3. C.  Retaining walls supporting more than 6 feet of backfill height, measured from the base of the footing to the top of the wall, shall incorporate an additional dynamic seismic lateral earth pressure.  When the Monobe-okabe method is used to calculate the active dynamic seismic lateral earth pressure, a horizontal acceleration coefficient equal to or greater than one-half (0.5) the design peak horizontal ground acceleration shall be used.
  4. D.  Retaining walls shall be designed to ensure stability against overturning, sliding, excessive foundation pressure and water uplift.  Retaining walls shall be designed to resist the lateral action of soil to produce sliding and overturning with a minimum safety factor of 1.5 in each case.  The load combinations of ASCE 7-16 shall not apply to this requirement.  Instead, the design shall be based on 0.7 times nominal earth-quake loads, 1.0 times other nominal loads, and investigation with one or more of the variable loads set to zero.  The safety factor against lateral sliding shall be taken as the available soil resistance at the base of the retaining wall foundation divided by the net lateral force applied to the retaining wall.
  5. Exception: Where earthquake loads are included, the minimum safety factor for retaining wall sliding and overturning shall be 1.1.

24.70.090 Setbacks.

  1. A. General. The setbacks and other restrictions specified by this Section are minimal and may be increased by the Director, or by the recommendation of the civil engineer, soils engineer, or engineering geologist, if necessary for safety and stability or to prevent damage of adjacent properties from deposition or erosion or to provide access for slope maintenance and drainage. Retaining walls may be used to reduce the required setbacks when approved by the Director. 
  2. B. Setbacks from property lines. The tops of cuts and toes of fill slopes shall be set back from the outer boundaries of the permit area, including slope right areas and easements, in accordance with Figure No. 2 and Table No. 24.70-C at the end of this Chapter.
  3. C. Design standards for setbacks. Setbacks between graded slopes (cut or fill) and structures shall be provided in accordance with Figure No. 3 and Table No. 24-70-C at the end of this Chapter. 

24.70.100 Drainage and Terracing.

(Amended by Ordinance 173270, effective May 21, 1999.)

  1. A. General. Unless otherwise indicated on the approved grading plan, drainage facilities and terracing shall conform to the provisions of this Section.
  2. B. Terrace. Terraces at least 6 feet in width shall be established at not more than 30-foot vertical intervals on all cut or fill slopes to control surface drainage and debris except that where only one terrace is required, it shall be at mid-height. For cut or fill slopes greater than 60 feet and up to 120 feet in vertical height one terrace at approximately mid-height shall be 12 feet in width. Terrace widths and spacing for cut and fill slopes greater than 120 feet in height shall be designed by the civil engineer and approved by the Director. Suitable access shall be provided to permit proper cleaning and maintenance.
  3. A single run of swale or ditch shall not collect runoff from a tributary area exceeding 13,500 square feet (projected) without discharging into a downdrain.
  4. C. Subsurface drainage. Cut and fill slopes shall be provided with subdrainage as necessary for stability. Adequate culverts shall be laid under all fills placed in natural watercourses and along the flow line of any tributary branches in such a manner that the hydraulic characteristics of the stream are not adversely altered. In addition, subdrainage shall be installed if active or potential springs or seeps are covered by the fill. All culverts/subdrainage shall be installed after the suitable subgrade preparation. Design details of culverts/subdrainage shall be shown on each plan and be subject to the approval of the Director and of other government/private agencies as may be required.
  5. A subdrain system shall be provided for embedded foundation/ retaining walls and floor slabs where ground water or seepage has a potential to affect the performance of the structure. The plans shall indicate
    1. 1. subdrainage details with appropriate specifications,
    2. 2. location of footing subdrain/discharge lines and,
    3. 3. method of disposal.
  6. In lieu of above, walls/floors may be waterproofed and designed to resist hydrostatic pressure.
  7. D. Disposal. All drainage facilities shall be designed to carry waters to the nearest practicable drainageway or approved stormwater management facility, as approved by the Director and/or other appropriate jurisdiction as a safe place to deposit such waters. Erosion of ground in the area of discharge shall be prevented by installation of non-erosive downdrains or other devices.
  8. Building pads shall have a drainage gradient of 2 percent toward approved drainage facilities, unless waived by the Director.
  9. Exception: The gradient from the building pad may be 1 percent if all of the following conditions exist throughout the permit area:
    1. 1. No proposed fills are greater than 10 feet in maximum depth.
    2. 2. No proposed finish cut or fill slope faces have a vertical line in excess of 10 feet.
    3. 3. No existing slope faces, which have a slope face steeper than 10 horizontal to 1 vertical, have a vertical height in excess of 10 feet.
  10. E. Interceptor drains. Paved interceptor drains shall be installed along the top of all cut slopes where the tributary drainage area above slopes towards the cut and has a drainage path greater than 40 feet measured horizontally. Interceptor drains shall be paved with a minimum of 3 inches of concrete or gunite and reinforced. They shall have a minimum depth of 12 inches and a minimum paved width of 30 inches measured horizontally across the drain. The slope of the drain shall be approved by the Director.

24.70.120 Grading Inspection.

(Amended by Ordinance 188647, effective November 17, 2017.)

  1. A.  General.  All grading operations for which a permit is required shall be subject to inspection by the Director.  When required by the Director, special inspection of grading operations and special testing shall be performed in accordance with the provisions of Section 24.70.120 C.
  2. B.  Grading designation.  All grading in excess of 5,000 cubic yards shall be performed in accordance with the approved grading plan prepared by a civil engineer and shall be designated as “engineered grading.”  Grading involving less than 5,000 cubic yards may also be designated as “engineered grading” by the Director if the grading will
    1. 1.  support a building or structure of a permanent nature;
    2. 2.  support other engineering works such as, but not limited to, tanks, towers, machinery, retaining wall, and paving;
    3. 3.  be deemed a potential hazard under Section 24.70.030.  The permittee with the approval of the Director may also choose to have the grading performed as “engineered grading.”  Otherwise, the grading shall be designated as “regular grading.”
  3. C.  Engineered grading requirements.  For engineered grading, it shall be the responsibility of the civil engineer who prepares the approved grading plan to incorporate all recommendations from the soil engineering and engineering geology reports into the grading plan.  The civil engineer shall also be responsible for the professional inspection and approval of the grading within the civil engineer’s area of technical specialty.  This responsibility shall include, but need not be limited to, inspection and approval as to the establishment of line, grade, and drainage of the development area.  The civil engineer shall act as the coordinating agent in the event that need arises for liaison between the other professionals, the contractor, and the Director.  The civil engineer shall also be responsible for the preparation of revised plans and the submission of as‑graded grading plans upon completion of the work.  The grading contractor shall submit in a form prescribed by the Director a statement of compliance to said as‑graded plan.
  4. Soil engineering and engineering geology reports shall be required as specified in Section 24.70.050.  During grading all necessary reports, compaction data, and soil engineering and engineering geology recommendations shall be submitted to the civil engineer and the Director by the soil engineer and the engineering geologist.  The soil engineer’s area of responsibility shall include, but need not be limited to, the professional inspection and approval concerning the preparation of ground to receive fills, testing for required compaction, stability of all finish slopes, and the design of buttress fills, where required, incorporating data supplied by the engineering geologist.
  5. The engineering geologist’s area of responsibility shall include, but need not be limited to, professional inspection and approval of the adequacy of natural ground for receiving fills and the stability of cut slopes with respect to geological matters, and the need for subdrains or other ground water drainage devices.  The engineering geologist shall report the findings to the soil engineer and the civil engineer for engineering analysis.
  6. The Director shall inspect the project at the various stages of work requiring approval and at more frequent intervals necessary to determine that adequate control is being exercised by the professional consultants.
  7. D.  Regular grading requirements.  The Director may require inspection and testing by an approved testing agency.  The testing agency’s responsibility shall include, but need not be limited to, approval concerning the inspection of cleared areas and benches to receive fill, and the compaction of fills.  When the Director has cause to believe that geological factors may be involved the grading operation will be required to conform to “engineered grading” requirements.
  8. E.  Notification of noncompliance.  If, in the course of fulfilling their responsibility under this Chapter, the civil engineer, the soil engineer, the engineering geologist, or the testing agency finds that the work is not being done in conformity with this Chapter or the approved grading plans, the discrepancies shall be reported immediately in writing to the person in charge of the grading work and to the Director.  Recommendations for corrective measures, if necessary, shall be submitted.
  9. F.  Transfer of responsibility for approval.  If the civil engineer, the soil engineer, the engineering geologist, or the testing agency of record are changed during the course of the work, the work shall be stopped until the replacement has agreed to accept the responsibility within the area of their technical competence for approval upon completion of the work.

24.70.130 Completion of Work.

(Amended by Ordinance 188647, effective November 17, 2017.)

  1. A.  Final reports.  Upon completion of the rough grading work and that final completion of the work the Director may require the following reports and drawings and supplements thereto:
    1. 1.  An as‑graded grading plan prepared by the civil engineer including original ground surface elevations, as‑graded ground surface elevations, lot drainage patterns, and locations and elevations of all surface and sub‑surface drainage facilities.  The civil engineer shall provide approval that the work was done in accordance with the final approved grading plan.
    2. 2.  A Soil Grading Report prepared by the soil engineer including locations and elevations of field density tests, summaries of field and laboratory tests and other substantiating data and comments on any changes made during grading and their effect on the recommendations made in the soil engineering investigation report.  The soil engineer shall provide approval as to the adequacy of the site for the intended use.
    3. 3.  A Geological Grading Report prepared by the engineering geologist including a final description of the geology of the site including any new information disclosed during the grading and the effect of same on recommendations incorporated in the approved grading plan.  The engineering geologist shall provide approval as to the adequacy of the site for the intended use as affected by geological factors.
  2. B.  Notification of completion.  The permittee or his agent shall notify the Director when the grading operation is ready for final inspection.  Final approval shall not be given until all work including installation of all drainage facilities and their protective devices and all erosion control measures have been completed in accordance with the final approved grading plan and the required reports have been submitted.