(A) Fill slopes.
(1) Fill slopes shall not be constructed steeper than a two to one (2:1) horizontal to vertical ratio, or where the base (toe) of the fill slope would be within 12 feet horizontally of the top of a cut slope, unless evidence is submitted by the soil engineer or the engineering geologist which indicates the stability of the slope is adequate and the proposed slope is approved by the City Engineer.
(2) In special circumstances where no evidence of previous instability exists, and when recommended in the soil engineering report and approved by the City Engineer, slopes may be constructed steeper than a 2:1 slope ratio.
(3) In no case shall slopes steeper than a 2:1 slope ratio be approved if a 2:1 slope ratio or flatter is required as a condition of approval for the development project with which the slope is associated.
(4) A slope stability analysis shall be included in all soil engineering reports for all slopes steeper than a 2:1 slope ratio and for all slopes exceeding 20 feet in height regardless of the slope ratio. The soil engineer shall consider slope stability (both gross and surficial stability) and provide a written statement approving the slope stability. In addition, the soil engineer shall recommend alternate methods of construction or compaction requirements necessary for surficial slope stability.
(B) Preparation of ground.
(1) The ground surface shall be prepared to receive fill by removing vegetation, noncomplying fill, topsoil and other unsuitable materials and by scarifying to provide a bond with the new fall. Where existing slopes exceed five feet in height and/or are steeper than a five to one (5:1) horizontal to vertical ratio, the ground shall be prepared by benching into sound bedrock or other competent or formational material, as determined by the soil engineer and approved by the City Engineer. The lowermost bench beneath the toe of a fill slope shall be a minimum of ten feet in width. The ground surface below the toe of fill shall be prepared for sheet flow runoff or an appropriate drainage system shall be provided. French drains may also be required at the toe of fill slopes if determined necessary by the City Engineer.
(2) Where fill is to be placed over a cut slope, the bench under the toe of the fill shall meet the approval of the soil engineer or the engineering geologist as suitable foundation for the fill. Unsuitable soil is soil that is not dense, firm or unyielding; soil that is highly fractured; or soil that has a high organic content; and in the opinion of the soil engineer or the engineering geologist the soil is not competent to support other soil or fill, to support structures or to satisfactorily perform the other functions for which the soil is intended.
(C) Fall material. Detrimental amounts of organic material shall not be permitted in fills. Except as outlined below, no rock or similar irreducible material with a maximum dimension greater than 12 inches shall be buried or placed in fills. The City Engineer may permit the placement of larger rock in fill when the soil engineer properly devises a method of placement, continuously inspects placement and approves the fill stability and competency. The following conditions shall also apply to the placement of all fill material:
(1) Prior to issuance of a grading permit, potential rock disposal area(s) shall be identified on the grading plans;
(2) Rock sizes greater than 18 inches shall be placed a minimum of six feet below grade, measured vertically or ten feet measured horizontally, from any slope face except rocks placed in a proposed public right-of-way, which shall be placed a minimum of 20 feet below grade or as approved by the Public Works Inspector, but in no case shall be in conflict with future utility lines;
(3) Rocks sizes greater than 12 inches shall be placed so as to be completely surrounded by soil. No nesting of rocks will be permitted.
(D) Compaction. All fills shall be compacted to a minimum of 90% of the maximum density as determined by ASTM D1557. Sufficient maximum density determinations by test method ASTM D1557 shall be performed during the grading work to verify that the maximum density curves used are representative of the material placed throughout the fill. Field density tests shall be performed in accordance with ASTM D1556, or equivalent, as approved by the City Engineer. At least 25% of the total tests shall be by ASTM D1556 to verify the accuracy of the equivalent method. All such tests shall be uniformly distributed within the fill area and/or fill slope surface area in order to obtain representative results. The location of the field density tests shall be determined by the soil engineer or the testing agency, but shall be sufficient in both horizontal and vertical placement to provide a representative testing of all fill placed. Testing in areas of a critical nature or special emphasis shall be in addition to a network of representative sampling. At least 20% of the field density tests performed during grading shall be located within three feet of the final slope location, and at least one density test shall be taken in the outer 12 inches of the finished slope face for every 5,000 square feet of slope area.
(E) Buttress/stabilization fills. Recommendations for buttress/stabilization fills by the soil engineer shall be included in the soil engineering report and shall set forth the soil or geologic factors necessitating the buttress/stabilization fill, stability calculations based on both static and pseudo static conditions (analysis of pseudo static loads are not normally needed when the bedding planes are flatter than 12 degrees from horizontal), laboratory test data upon which the calculations are based, and a copy of the approved grading plans showing the location of the buttress/stabilization fill, a scaled section of the buttress/stabilization fill, and recommendations with details of subdrain requirements.
(F) Utility line backfill.
(1) Backfill for utility line trenches in the public right-of-way, including, but not limited to, water, sewer, gas, electrical, telephone and cable television utility line trenches shall be compacted to a 95% relative density. Backfill for on-site utility line trenches that effect the stability of foundations or other structures are located in parking lots or areas used by the general public or are in sloping surfaces steeper than a ten to one (10:1) horizontal to vertical ratio and which utilize onsite material as backfill shall be compacted and tested in accordance with this section. Alternate materials and methods for utility line trench backfill may be used provided that the material specification and method of placement are recommended by the soil engineer and approved by the City Engineer prior to backfilling.
(2) Utility line trench backfill for on-site areas other than those stated above do not need specific placement method or compaction criteria, but shall be sufficiently compacted to preclude differential settlement. In no case shall this subsection be construed to mean utility line trench backfill within any public rights-of-way.
(3) The final utility line trench backfill report from the project soil engineer shall include a statement of compliance by the soil engineer that the tested backfill is suitable for the intended use and that all tested areas meet the compaction requirements set forth in this section.
(Ord. 3378 § 5 (part), 2023; Ord. 2568 § 1, 2002.)