(A) Fill slopes.
(1) Fill slopes shall not be constructed steeper than a two to one (2:1) horizontal to vertical slope 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, such as a geotechnical or soils report, 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/Public Works Director.
(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/Public Works Director, slopes may be constructed steeper than a two to one (2:1) horizontal to vertical slope ratio.
(3) In no case shall slopes exceed those specified in any conditions of approval for the development project for which the slope is associated.
(4) A slope stability analysis shall be included in all soil engineering reports for all slopes steeper than a two to one (2:1) horizontal to vertical 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) No fill shall be placed on existing ground until the ground has been cleared of weeds, debris, topsoil, undocumented fill, and other deleterious material, and such materials have been removed from the site.
(2) 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 fill. Where existing slopes exceed five feet in height and/or are steeper than a five to one (5:1) horizontal to vertical slope 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/Public Works Director. 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/Public Works Director.
(3) 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, that is highly fractured, or that has a high organic content; and in the opinion of the soil engineer or the engineering geologist, is not competent to support other soil or fill, support structures, or satisfactorily perform the other functions for which the soil is intended.
(C) Fill material. Fill material shall only be placed as determined by a geotechnical or soil engineer. Only soils material free from tree stumps, organic matter, trash, garbage, sod, peat, and other deleterious materials shall be permitted. Except as outlined below, no rock or similar irreducible material with a maximum dimension greater than six inches shall be buried or placed in fills. The City Engineer/Public Works Director may permit the placement of larger rock in fill when the geotechnical or soil engineer properly devises a method of placement, continuously inspects placement, and approves the fill stability and competency.
(D) Compaction. All fills shall be compacted to a minimum of 90% of the maximum density as determined by ASTM 01557, unless otherwise required by the City Engineer/Public Works Director. Sufficient maximum density determinations by test method ASTM 01557 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 01556, or equivalent, as approved by the City Engineer/Public Works Director. At least 25% of the total tests shall be by ASTM 01557 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 geotechnical or 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; 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 sub-drain 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 meet current applicable city standards for utility trenches. Backfill for on-site utility line trenches that affect the stability of foundations or other structures and 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 on-site 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/Public Works Director 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 prevent differential settlement. In no case shall this division 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. 2022-364, passed 11-16-2022)