Chapter 15.25
EARTHWORK

Sections:

15.25.010    General.

15.25.020    Subgrade soil under structures.

15.25.030    Backfill around structures.

15.25.040    Construction of embankments and fills.

15.25.050    Compacting earth materials.

15.25.060    Road subgrade preparation.

15.25.070    Slope safety.

15.25.080    Water settling.

15.25.090    Removal and replacement of defective fill.

15.25.010 General.

This chapter defines the requirements for excavation and backfill for structures, construction requirements for embankments and fills and subgrade preparation for pavements and other surface improvements. All earthwork shall conform to the APWA Standard Specifications unless noted otherwise in this chapter. [Ord. O-03-2010 § 1 (Exh. A § 5.010)].

15.25.020 Subgrade soil under structures.

Subgrade soil for all concrete structures, regardless of type or location, shall be firm, dense, thoroughly compacted and consolidated; shall be free from mud and muck; and shall be sufficiently stable to remain firm and intact under the feet of the workmen engaged in subgrade surfacing, laying reinforcing steel, and depositing concrete. Coarse gravel or crushed stone may be used for subsoil reinforcement if results are satisfactory to the city engineer or his/her designee. Such material shall be applied in layers, not exceeding eight inches in thickness, each layer being embedded in the subsoil by thorough tamping. All excess soil shall be removed to compensate for the displacement of the gravel or crushed stone and the finished elevation of any subsoil reinforced in this manner and shall not be above the specified subgrade. The city engineer may require a soil analysis and design for any area. [Ord. O-03-2010 § 1 (Exh. A § 5.020)].

15.25.030 Backfill around structures.

Backfill around structures shall be placed to the lines shown on the approved drawings, or as directed by the city engineer or his/her designee. After completion of foundation, footings and walls and other construction below the elevation of the final grades, and prior to backfilling, all forms shall be removed and the excavation shall be cleaned of all trash and debris. Material for backfilling shall consist of suitable materials as defined in EMMC 15.30.040 and shall be placed in layers not exceeding eight inches in uncompacted thickness. Each layer shall be compacted by hand or machine tampers or by other suitable equipment to a density equal to 95 percent of maximum dry density as measured by AASHTO T180 method C. No frozen material is allowed in the backfill. [Ord. O-03-2010 § 1 (Exh. A § 5.030)].

15.25.040 Construction of embankments and fills.

Unsuitable materials that occur in the foundation for embankments and fills shall be removed by clearing, stripping and/or grubbing. Where suitable materials occur, after stripping, the foundation shall be scarified to a depth of not less than eight inches, and the loosened material shall be moistened and compacted as hereinafter specified for each layer. All materials in embankments and fills shall be placed, moistened, and compacted as provided in this chapter.

When the embankment or fill exceeds the amount of excavation, sufficient additional material shall be obtained from borrow pits provided by the contractor. All material proposed to be imported shall be subject to the review and approval of the city engineer or his/her designee prior to starting of hauling operations.

The materials used for embankment and fill construction shall be free from sod, grass, trash, rocks larger than six inches in diameter and all other material unsuitable for construction of compacted fills. Grading of completed embankments and fills shall bring the surfaces to a smooth, uniform condition with final grades being within 0.1 foot of the design grade. [Ord. O-03-2010 § 1 (Exh. A § 5.040)].

15.25.050 Compacting earth materials.

The material shall be deposited in horizontal layers having a thickness of not more than eight inches after being compacted as hereinafter specified; provided, that when mechanical equipment is used for placing and compacting the material on a sloping foundation, the layers may be placed parallel to the foundations. The distribution of materials shall be such that the compacted material will be homogeneous and free from lenses, pockets, or other imperfections. No frozen material may be used. Prior to and during compaction operations the material shall have the optimum moisture content required for the purpose of compaction and the moisture content shall be uniform throughout the layers, insofar as practical. Moistening of the material shall be performed at the site of excavation, but such moistening shall be supplemented, as required, by sprinkling at the site of construction. If the moisture content is more than optimum for compaction, the compaction operations shall be delayed until such time as the material has dried to the optimum moisture content. When the material has been conditioned as hereinbefore specified, the backfill or embankment shall be compacted as follows:

A. Under roadways and extending one foot beyond the proposed curb line, the fill or embankment material shall be compacted to a density equal to not less than 95 percent of maximum dry density as measured by AASHTO T180 method C or the modified proctor test ASTM D1557.

B. Under sidewalks and driveways, the fill or embankment material (to at least one foot each side of the edge of the slab) shall be compacted to a density equal to not less than 95 percent of maximum dry density as measured by AASHTO T180 method C or the modified proctor test ASTM D1557.

C. Other fills and embankments not listed above shall be compacted to a density equal to not less than 90 percent of maximum dry density as measured by AASHTO T180 method C or the modified proctor test ASTM D1557. [Ord. O-03-2010 § 1 (Exh. A § 5.050)].

15.25.060 Road subgrade preparation.

In both cut and fill areas the paving subgrade shall be scarified to a depth of eight inches and compacted to the equivalent of 95 percent of maximum dry density as measured by AASHTO T180 method C or the modified proctor test ASTM D1557. No rocks larger than two inches in diameter, organic material, soft clay, spongy material or other deleterious material will be permitted in this scarified subgrade layer. Rough subgrades shall be shaped and graded to within a tolerance of 0.15 foot of design grade and drainage shall be maintained at all times. The developer shall provide to the city engineer or his/her designee the results of a subsurface investigation performed by the developer’s engineer and the recommendation as to whether existing material is adequate for road construction.

During the rolling operation, moisture content of the subgrade layer shall be maintained at no less than 97 or more than 105 percent of optimum moisture content. Rolling shall be continued until the entire road bed (to one foot back of curb) is compacted to the specified density to a minimum depth of eight inches. [Ord. O-03-2010 § 1 (Exh. A § 5.060)].

15.25.070 Slope safety.

All slope construction shall be in accordance with all city, state and federal regulations. Plans and specifications for structures must be approved by the city if the excavation is greater than five feet. No permanent slopes steeper than 3:1 shall be allowed without a retaining structure unless otherwise approved in writing by the city engineer or his/her designee. Cut slopes greater than 3:1 slope in bedrock may be allowed, provided the geotechnical report demonstrates that the bedrock is of sufficient depth and strength to support such cuts. The width of the excavation shall be increased if necessary to provide space for sheeting, bracing, shoring and/or other supporting installations. Unsafe slopes will be the cause for immediate shutdown of the project. [Ord. O-03-2010 § 1 (Exh. A § 5.070)].

15.25.080 Water settling.

Water settling may be permitted with pre-approval by the city engineer or his/her designee, depending upon the type of soil and location. When water settling is approved, a city representative shall be at the job site during the compaction. When the material has dried sufficient to allow compaction tests, the contractor shall dig test holes for compaction tests at locations and depths required by the city engineer or his/her designee. [Ord. O-03-2010 § 1 (Exh. A § 5.080)].

15.25.090 Removal and replacement of defective fill.

Fill not conforming to the requirements of this chapter shall be reworked to the requirements or removed and replaced with acceptable fill. [Ord. O-03-2010 § 1 (Exh. A § 5.090)].