(A) Fills - Maximum Slope, Construction.
(1) Fill slopes shall be no steeper than two horizontal to one vertical (2:1), exclusive of benches or terraces.
(2) All fill slopes shall be overfilled to a distance from finished slope face that will allow compaction equipment to operate freely within the zone of the finished slope, and then cut back to the finish grade to expose the compacted core. Alternate methods may be employed by the grading contractor subject to approval by the soil Engineer and Director of Public Works. In such instances, the grading contractor shall provide detailed specifications for the method of placement and compaction of the soil within a distance of an equipment width from the slope face.
(3) At least 20% of the field density test taken within the slope, during grading, shall be located within the outer three feet of the final slope surface, and at least one density foot shall be taken within the outer eleven inches of the finished slope face for every 5,000 square feet of slope area.
(4) Fill slopes shall not be constructed on natural slopes steeper than two horizontal to one vertical (2:1), or where the fill slope toes out within 12 feet horizontally of the top of existing cut slopes adjacent to the permit area boundary unless evidence is submitted by the soil engineer and/ or engineering geologist which indicates adequate stability and the proposed slope is approved by the Director of Public Works.
(5) Any grading plan which proposes fill slopes steeper than 5:1 and having a vertical height of six feet or greater shall be subject to the review and approval of the Planning Commission prior to permit issuance.
(B) Preparation of Ground.
(1) The ground surface shall be prepared to receive fill by removing vegetation; non-complying fill; topsoil and other unsuitable materials; and by scarifying to a minimum depth of 12 inches to provide a bond with the new fill. Where existing slopes exceed five feet in height and/or are steeper than five horizontal to one vertical (i.e., 5:1), the ground shall be prepared by benching into sound bedrock or other competent material as determined by the soil engineer and approved by the Director of Public Works. 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 a paved drain shall be provided.
(2) Where fill is to be placed over a cut slope, the bench under the toe of the fill shall be at least 15 feet wide and shall meet the approval of the soil engineer and/or engineering geologist as a suitable foundation for fill.
(C) Fill Material.
(1) Detrimental amounts of organic material shall not be permitted in fills. No rocks greater than six inches dimension shall be placed within five feet of the finished grade. 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.
(2) The Director of Public Works may permit placement of rock when the soils engineer properly devises a method of placement, continuously inspects placement, and approves the soil stability and competency. The following conditions shall also apply:
(a) Prior to issuance of the grading permit, potential rock disposal area(s) shall be delineated on the grading plan;
(b) Rock sizes greater than 12 inches in maximum dimension shall be ten feet or more below grade, measured vertically, and/or ten feet measured horizontally from slope faces whichever greater;
(c) When the design of the development or covenants and restrictions provide assurance that no structure or utilities will be placed on a precisely definable area, these dimensions may be reduced with the approval of the Director of Public Works.
(3) All rock shall be placed so as to be completely surrounded by soils; no nesting of rocks will be permitted.
(D) Compaction.
(1) All fills shall be compacted to a minimum of 90% of maximum density as determined by ASTM D1557-78 (five layer test). Field density tests shall be performed in accordance with ASTM D1556-78, or equivalent as approved by the Director of Public Works. At least 25% of the total test shall be by ASTM D1556-78 to verify the accuracy of the equivalent method. All such tests shall be reasonably uniformly distributed within the fill or fill slope surface (See division (A) of this section) so that representative results are obtained.
(2) Locations of field density tests shall be determined by the engineer or approved testing agency and as directed by the Director of Public Works, but shall be sufficient in both horizontal and vertical placement to provide 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.
(3) Sufficient maximum density determinations by test method ASTM 1557-78 shall be performed during the grading operations to verify that the maximum density curves used are representative of the material placed through the fill.
(E) Buttress/Stabilization Fills. Recommendations for buttress fills or stabilization fills by the soil engineer shall be accompanied by a report setting forth the soil or geologic factors necessitating the buttress/stabilization fill, stability calculations, the approved grading plan 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. Backfills for utility line trenches, such as stormdrain, water, sewer, gas, cable television and electrical services shall be compacted and tested in accordance with division (D) of this section. Alternate materials and methods may be used for utility line backfills, provided, that the material specification and method of placement are recommended by the soil engineer and approved by the Director of Public Works prior to backfilling. The final utility line 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.
(Ord. 1449, passed 10-19-05)