CHAPTER  900. Earthwork.

 

 901.  General. This section defines the requirements for excavation and backfill for structures, construction requirements for embankments and fills and subgrade preparation for pavements and other surface improvements.

 

 902.  Excavation for Structures. All structures shall be founded on undisturbed original subsoil or compacted fill material as required by the engineer.  All unauthorized excavation below the specified structure subgrade shall be replaced with concrete monolithic with that of the slab above or with coarse gravel thoroughly compacted into place.

 

                        Subgrade soil for all concrete structures, regardless of type of location, shall be compacted to 95% of AASHTO T‑180 Method "A" (Modified Proctor Density) and 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 sub‑soil reinforcement if satisfactory results can be obtained thereby.  Such material shall be applied in thin layers, 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 shall not be above the specified subgrade.  Six inches of granular material compacted to 95% of AASHTO T‑180 Method "A" (Modified Proctor Density) shall be placed on the sub base.

 

 903. Backfill Around Structures.  Backfill around structures shall be placed to the lines shown on the approved drawings, or as directed.  After completion of foundations 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 excavated material or borrow of sand, gravel or other suitable material and shall be placed in layers not exceeding eight inches in un-compacted thickness.  Each layer shall be compacted by hand or machine tampers or by other suitable equipment to a density equal to ninety‑five percent (95%) AASHTO T‑180, Method "A" (Modified Proctor Density).

 

 904.  Construction of Embankments and Fills. Unsuitable materials that occur in the foundations for embankments and fills shall be removed by clearing stripping and/or grubbing.  Where materials occur, after stripping, the foundation shall be scarified to a depth of not less than six inches, and the loosened material shall be moistened and compacted as hereinafter specified for each layer.  All materials in the embankments and fills shall be placed, moistened and compacted as provided in the following paragraph.

 

                        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 engineer 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 O.1 feet of the design grade.

 

 905.  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.

 

                        Prior to and during compaction operations, the material shall have near optimum moisture content required for the purpose of compaction and the moisture content shall be uniform throughout the layers insofar as practicable.  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 less 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 herein before specified, the backfill or embankment shall be compacted as follows:

 

 

(1)        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 ninety five percent (95) of maximum dry density as measured by AASHTO T‑180 Method "A" (Modified Proctor Density).

 

(2)        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 ninety‑five percent (95%) of maximum dry density as measured by AASHTO T‑180 Method "A" (Modified Proctor Density).

 

(3)        Other Fills and Embankments not listed above shall be compacted to a density equal to not less than ninety five percent (95%) of maximum dry density as measured by AASHTO T‑180 Method "A" (Modified Proctor Density).

 

 906.  Road Subgrade Preparation. In both cut and fill areas, paving subgrade shall be scarified to a depth of six inches and compacted to the equivalent of ninety five (95%) of maximum dry density as measured by AASHTO T‑180.  No rocks larger than three inches in diameter, organic material, soft clay, or any other deleterious material will be permitted in this scarified subgrade layer.  Rough sub-grades shall be shaped and graded to within a tolerance of +/‑ 0.15 feet of design grade and drainage shall be maintained at all times.

 

 907.  Grading and Erosion Control Design Standards and Regulations. All subdivision improvement work shall be accomplished in conformance to the following grading and erosion control design standards and regulations:

 

(1)        Hours of Operation. All grading operations in or contiguous to residential neighborhoods shall be carried on between the hours of 7:00 A.M. to 5:30 P.M.  The City Engineer may waive this requirement if it is shown that by restricting the hours of operation it would unduly interfere with the development of the property and it is shown that the neighboring properties would not be adversely affected.

 

(2)        Dust and Dirt Control. All graded surfaces of any nature shall be dampened or suitably contained to prevent dust or spillage on city streets or adjacent properties.  Equipment, materials and roadways on the site shall be used or treated so as to cause the least possible annoyance due to dirt, mud or dust conditions.

 

(3)        Un-developable Slopes. Any natural slopes identified on a Slope Classification Map of forty (40) percent or greater shall be designated un-developable area.  Said slope, if retained within the subdivision may be designated and maintained as common area.  In no event shall streets traverse such slopes.

 

(4)        Finished Cuts and Slopes. Limitations shall be applied to the extent of Cut and Fill slopes to minimize the amount of excavated surface or ground area exposed to potential erosion or settlement.

 

(a)        The exposed or finished cuts or slopes of any fill or excavation shall be smoothly graded.

(b)        All cut and fill slopes shall be re-contoured and re-vegetated by the subdivider in accordance with an approved plan.

(c)        Cut or fill slopes shall normally be limited to fifteen (15) feet in vertical height.  However, upon review and favorable recommendation of the City Engineer, the Planning Commission may recommend that the Mayor approve cut or fill slopes exceeding fifteen (15) feet provided that such variations be allowed on a limited basis after thorough review of each request, and only when balanced by offsetting improvements to the overall aesthetic, environmental and engineering quality of the development.

(d)        No excavation creating a cut face and no fill creating an exposed surface shall have a slope ratio exceeding one‑half horizontal to one vertical.

 

                        EXCEPTION:

(1)        No slopes shall cut steeper than the bedding plane, fracture, fault or joint in any formation where the cut slope will lie on the dip of the strike line of the fracture, bedding plane, fault or joint.

(2)        No slopes shall be cut in an existing landslide, mud flow or other form of naturally unstable slope except as recommended by a qualified geological engineer. 

(3)        Where the formation is exposed above the top of the cut which will permit the entry of water along bedding planes, this area shall be sealed with a compacted soil blanket having a minimum thickness of two feet.  The soil for this blanket shall be relatively impervious and shall be approved by the City Engineer. 

(4)        If the material of a slope is of such composition and character as to be unstable under the anticipated maximum moisture contents, the slope angle shall be reduced to a stable value or retained by a method approved by the City Engineer, and certified as to its stability by the soils engineer or geologist.  Said retaining method shall include design provisions which are conducive to vegetation for soil stability and visual impact; used for selected areas of the state and not as a general application; limited to tiers each of which is no higher than six (6) feet, separated by plantable terraces a minimum of two feet in width; and any retaining system shall remain and be maintained on the lots until plans for construction are approved and a building permit is issued.  The plans shall include provisions to integrate driveway access to the lot, while maintaining the structural integrity of the retaining system.

            (e)        The City Engineer may require the slope of a cut or fill be made more level if at any time it is found that the material being cut or the fill is unusually subject to erosion, static or dynamic instability or if other conditions make such requirements necessary for stability.

 

(5)        Abatement of Hazardous Conditions.

 

(a)        If, at any stage of grading, the planning director or city engineer determines by inspection that the nature of the formation is such that further work as authorized by an existing permit is likely to imperil any property, public way, watercourse or drainage structure, the Planning Director or City Engineer shall require, as a condition to allowing the work to proceed, that reasonable safety precautions be taken as are considered advisable to avoid likelihood of such peril.  Such precautions may include, but shall not be limited to any of the following: specification of a more level exposed slope; construction of additional drainage facilities, berms, or terraces; compaction or cribbing; installation of plant materials for erosion control; and reports of a registered soils engineer and/or of an engineering geologist whose recommendations may be made requirements for further work.  Such a requirement by the Planning Director or City Engineer shall constitute a required change order in the work to be performed under permit. Said changes may be required to be reflected in amended plans. 

 

(b)        Where it appears that damage from storm drainage may result from work performed hereunder, such work may be stopped and the permittee required to take such measures as may be necessary to protect adjoining property or the public safety.

 

(c)        The City Engineer may require additional tests or information, if, in his opinion, the conditions or materials are such that additional information is necessary, and may modify or delete any of the above listed requirements that, in his opinion are unnecessary to further the purpose of this title.

 

(6)        Erosion Control and Re-vegetation. All cut and fill surfaces created by grading shall be planted with a ground cover that is of a drought resistant variety. Topsoils are to be stockpiled during rough grading and used on cut and fill slopes.  Cuts and fills along public roads are required to be landscaped according to an approved plan.  All plant materials must be approved by the Parks Department and Planning Commission Planning Director prior to subdivision approval.

 

(7)        Drainage.

 

(a)        Adequate provisions shall be made to prevent any surface waters from damaging the cut face of an excavation or any portion of a fill.  All drainage ways and structures shall carry surface waters without producing erosion to the nearest practical street, storm drain or natural water course as approved by the City Engineer.  The City Engineer may also require drainage structures to be constructed, or installed as necessary to prevent erosion damage or to prevent saturation of the fill or material behind cut slopes.

 

(b)        An excess storm water passage shall be provided for all storm water storage areas.  Such passage shall have capacity to convey through the proposed development the excess storm water. Passages shall be constructed in such a manner as to transport the peak rate of run‑off from a 100 year return frequency storm assuming all storm sewers are inoperative, all upstream areas are fully developed in accordance with the City's current land use plan, and that antecedent rain fall has saturated the tributary watershed.

 

(c)        No buildings or structures shall be constructed within such passage, however, streets, parking lots, playgrounds, park areas, pedestrian walkways, utility easements and other open space uses shall be considered compatible uses.  In the event such passageway is reshaped or its capacity to transport excess storm water is otherwise restricted during or after construction, the City Engineer shall notify the agency, party or parties causing said restriction to remove the same, and set a reasonable time for its removal.  If said parties refuse to or are unable to comply with said order, the City Engineer shall cause said restrictions to be removed at the expense of said parties. Where a proposed development contains existing natural drainage, appropriate planning measures shall be undertaken or required to preserve and maintain said natural drainage as part of the excess storm water passage.

 

(d)        Notwithstanding any other provisions of this title, whenever in the judgment of the City Engineer a condition occurs in a storm water storage area or passageway that creates a dangerous and imminent health and safety hazard, the City Engineer shall order such action as shall be effective immediately or in the time and manner prescribed in the order itself.

 

 

(8)        Additional Information. The following additional information may be required to be submitted, in sufficient numbers of copies as is determined by the planning staff, at the discretion of the Planning Director or City Engineer:

 

(a)        Slope Classification Map and analysis. 

(b)        Profiles or cross‑sections. 

(c)        Additional drainage calculations. 

(d)        Soils data including a report from a registered soils engineer, engineering geologist, or other qualified person. 

(e)        Statement of the estimated starting and completion dates for the grading work proposed and any re-vegetation work that may be required. 

(f)         Detailed re-vegetation plans for the site, and if appropriate, information relating to the landscaping on adjacent or surrounding areas affected by the proposed development.  Such re-vegetation plans shall be prepared by licensed engineer, architect, landscape architect, or other qualified person.  These plans shall show:

(1)        Distribution of plant material, existing trees and work involved as related to slope control and/or physical environment.

(2)        A plan describing the methods of planting the area to be landscaped with special emphasis on: (i) soil preparation, planting material and methods of planting; and (ii) initial maintenance of the plant material and slopes until a specified percentage of plant coverage is established uniformly on the cut and fill slopes.

(3)        Such other and further details as may be specified and required by the Planning Director to carry out the purposes of this title.  All such plans shall bear the name of the person responsible for the preparation of the plan.

(4)        The re-vegetation plan will be submitted by the developer to the city for review and approval.

(g)        The present contours of the site in dashed lines and the proposed contours in solid lines.  Contour intervals shall be not more than two (2) feet where slopes are predominantly five (5) percent or less, and five (5) feet where slopes are predominantly steeper than five (5) percent.

(h)        The location of all drainage to, from and across the site, the location of intermittent and permanent streams, springs and culverts and other drainage structures, and size and location of any precipitation catchment area in, above or within one hundred (100) feet of the site.

(i)         Detailed plans and locations of all surface and subsurface drainage devices, walls, dams, sediment basins, storage reservoirs and other protective devices to be constructed with or as a part of the proposed work together with a map showing drainage areas, and the complete drainage network including outfall lines and natural drainage ways which may be affected by the proposed project.  Include the estimated runoff of the areas served by the proposed drainage system. 

(j)         Whenever a proposed subdivision lies within 500 feet of an identified fault, a geological report and verification will be required.  These reports will be submitted for review to the Utah Geological and Mineral Survey by the Planning Director. 

(k)        Plan showing temporary erosion control measures to prevent erosion during the course of construction and a re-vegetation plan. 

(l)         A description of the method to be employed in disposing of soil and other material that is removed from the site, including the location of the disposal site.

(m)       A description of the method to be used in obtaining fill to be used on the site and the site of acquisition of such fill. 

(n)        Such other information as shall be required by the Planning Director.

 

(9)        Unusual Conditions. Where unusual site conditions exist the building official or City Engineer may specify the time at which grading may proceed and the time of completion or may require that the operation be conducted in specific stages so as to insure completion of protective measures or devices prior to the advent of seasonal rain.