Division 4. Technical Construction Requirements

Chapter 5.65
EARTHWORK

Sections:

5.65.010    Description.

5.65.020    Encroachment permits.

5.65.030    Compaction.

5.65.040    Materials.

5.65.050    Trench excavation and backfill.

5.65.060    Structure excavation and backfill.

5.65.070    Embankment construction.

5.65.080    Temporary paving.

5.65.010 Description.

Earthwork shall consist of performing all operations necessary to excavate earth, rock and/or other materials from the trench or excavation; to excavate all material, of whatever nature, necessary for the construction of foundations for structures, sewers, and drainage facilities; to construct embankments; to place backfill around structures, sewers and drainage facilities, and over sewers, culverts and drainage pipes; to backfill ditches, holes, pits and other depressions within the work area; to construct temporary and permanent trench surfacing; to remove unsuitable material and replace with suitable material; and to construct earth protection dikes. [Ord. 2014-2 (Att. § 13-01).]

5.65.020 Encroachment permits.

For all work within public rights-of-way, the contractor shall secure all necessary encroachment permits from the agencies having jurisdiction and shall comply with all requirements of the encroachment permits. [Ord. 2014-2 (Att. § 13-02).]

5.65.030 Compaction.

Compaction of materials shall be defined as follows:

(1) “Relative compaction” refers to compaction of soil and aggregate base as defined by ASTM 1557-78.

(2) “Relative density” refers to the density of crushed rock as defined by ASTM D 2049-69. [Ord. 2014-2 (Att. § 13-03).]

5.65.040 Materials.

The contractor shall provide and install all materials as shown on the drawings and/or as specified herein and as defined hereinbelow.

(1) Crushed Rock. Crushed rock shall be hard, sound and durable and shall not slake or disintegrate in water. One-and-one-half-inch crushed rock shall be uniformly graded with 100 percent passing a one-and-one-half-inch sieve and not more than five percent passing a three-eighth-inch sieve. Three-quarter-inch crushed rock shall be uniformly graded with 100 percent passing a three-quarter-inch sieve and not more than five percent passing a one-quarter-inch sieve.

(2) Class 2 Aggregate Base. Class 2 aggregate base shall conform to Section 26, Aggregate Bases, of the State Standard Specifications, Paragraph 26-102 A. The grading shall be three-quarter-inch maximum.

(3) Lightweight Rock Fill. Lightweight rock fill shall weigh 60 pounds per cubic foot or less when compacted to 90 percent relative compaction. The rock sizes can be either three-quarter-inch or one-and-one-half-inch, except that within six inches of the slab, the rock size shall be three-quarter-inch. The rock shall be compacted in 12-inch lifts with a lightweight vibratory compactor.

(4) Slurry Cement Backfill. Slurry cement backfill composition and placement shall conform to Section 19 of the State Standard Specifications, Paragraph 19-3.06 B.

Slurry cement backfill shall be used to backfill any undermined areas and may be used as an alternate to Class 2 aggregate base for intermediate backfill to grade. Care shall be taken not to disturb the slurry cement backfill after placement.

(5) Structural Fill. Structural fill when specified for fill or structural backfill shall consist of excavated on-site soil and/or imported material (not bay mud). Excavated on-site soil or imported material to be used as structural fill shall be so prepared that it is free of unsuitable material as defined herein in subsection (6) of this section and shall have a plasticity index of 20 or less and a liquid limit of 40 or less. Structural fill shall be capable of being compacted to the required relative compaction. A sample of the material shall be submitted for approval by the District prior to placement.

(6) Unsuitable Material. Unsuitable material is material containing debris, roots, wood, vegetable matter, scrap metal, asphalt, plastic and rocks over six inches in greatest dimension.

(7) Topsoil. Topsoil shall be imported commercially manufactured, fertile, friable, natural, productive soil containing a normal amount of humus and capable of sustaining healthy plant life. Topsoil shall be free of subsoil, heavy or stiff clay, rocks, gravel, brush, roots, weeds, noxious seeds, sticks, trash, and other deleterious substances. Soil shall not be infested with nematodes or with other noxious animal life or toxic substances. Soil shall be obtained from well-drained, arable land and shall be of an even texture. Soil shall not be taken from areas on which are growing any noxious weeds, such as morning glory, sorrel, or Bermuda grass.

(8) Water. Water used for dust control and moisture conditions for compaction shall be reasonably free of objectionable quantities of silt, oil organic matter, alkali, salts and other impurities as determined by the District. Bay water or water from drainage ditches on the project site shall not be used. If available, reclaimed wastewater conforming to Health Department requirements shall be used. [Ord. 2014-2 (Att. § 13-04).]

5.65.050 Trench excavation and backfill.

(1) Trench Excavation. Trench excavation shall include the removal of all materials or obstructions of any nature, the installation and removal of all sheeting and bracing, and the control of water necessary to construct the work as shown on the plans. Excavation for sewers shall be made only after pipe and other necessary materials are delivered on the site of the work. After such delivery, trench excavation shall proceed as rapidly as possible and the pipe installed and the trench backfilled without undue delay. The District shall have the authority to limit the amount of trench to be opened or left open at any one time. In public street areas, excavation and pipe laying shall be coordinated to the end that a minimum of interference with public traffic will result.

In public street areas, excavation and pipe laying shall be coordinated so that the trench at the end of each day shall not be excavated for more than 50 feet in advance of pipe laying, nor left unfilled for more than 50 feet where the pipe has been laid for a total of 100 feet of trench under construction at any one time. During nonworking hours, all trenches in public streets shall either be backfilled and temporarily paved or shall be shored and covered with steel plates suitable to carry H-20 traffic loads. The District may require the contractor to submit engineering calculations demonstrating that the steel plates meet this requirement.

All temporary steel trench traffic plates shall be secured and flat on the road surface. Trench plates shall overlap the existing pavement by a minimum of 18 inches on each side of the excavation and shall be properly beveled with compacted AC at all edges to make a smooth surface between street level to steel plates for all traffic, including pedestrian, bicycles, skateboards, etc. All trenches and excavations shall be properly braced and shored before steel plates are placed. Lighted barricades and signs warning of uneven pavement shall be placed on either side of traffic plates.

Unless otherwise permitted by the encroachment permit, where trenching occurs in paved areas, the pavement shall be blade cut or scored and broken ahead of the trenching operations, and shall be saw cut (using a concrete saw) to a neat edge after backfilling and prior to paving. The proper tools and equipment shall be used in marking and breaking so that the pavement will be cut accurately and on neat lines parallel to the trench. Any pavement damaged outside these lines shall be recut along lines as directed by the District or agency having jurisdiction and restored at the expense of the contractor.

Trenching may be accomplished by use of trenching machines, except where their use will result in damage to existing facilities. Trenching for all pipe shall, unless otherwise specified, be open cut to the lines and grades shown on the plans except those sections specifically indicated on the plans or designated by the District to be tunneled to protect existing trees or structures.

When the contractor is digging in the vicinity of a sewer or utility, he shall carefully pothole, i.e., expose, for the sewer or utility.

Trenches shall be excavated below the barrel of the pipe to be installed and the bottom refilled with approved bedding material (as shown in the Typical Trench Section (SD 4), SD5MCC 5.105.010).

(2) Trench Width. The allowable width of trench shall be as shown in the Typical Trench Section (SD 4), SD5MCC 5.105.010. Where shoring is required, the width of the trench shall be increased only by the thickness of the sheathing.

Trenches shall be excavated with full depth vertical sides where possible. Minimum vertical trench shall be from pipe flow line to a point two feet above the top of pipe. Whenever the maximum allowable trench width is exceeded for any reason, the contractor will be required, at his expense, to install special pipe, and/or concrete encasement, and/or special backfill as directed by the District.

(3) Trench Bracing. Excavations shall be adequately shored and braced as necessary to protect workmen, so that the earth will not slide, move or settle and so that all existing improvements of any kind will be fully protected from damage.

The contractor shall furnish, install, and maintain such sheet piling, timbering, lagging, and bracing, as necessary to support the sides of the trench. The protection of adjacent structures from movement of the ground and the elimination of the element of danger to life, property, or to existing improvements is the intent of this requirement.

All such piling, timbering, lagging, and bracing shall, unless otherwise required by the District, be removed during backfilling in such a manner as to prevent any movement to the ground or damage to the piping or other structures. When sheet piling, lagging, and bracing is left in place, such materials shall be cut off where designated and the upper part withdrawn.

Undisturbed material outside the planned excavation slopes, which is unstable and constitutes a potential slide, and material which has already come into the excavation, shall be removed.

The contractor alone shall be responsible for the safety of his workmen and adjacent improvements and property. All shoring shall comply with Federal and State safety orders. Attention is directed to the “Trench Construction Safety Orders” of the California State Industrial Accident Commission which the contractor is required by law to obey, and which are adopted by reference as a part of these specifications.

(4) Control of Water. The contractor shall remove all water which may accumulate in the excavation during the progress of the work so that all work can be done in a dry trench. The contractor shall at all times have on hand sufficient pump equipment and machinery in good working condition for all ordinary emergencies and shall have available at all times competent mechanics for the operation of all pumping equipment. Trenches or other excavations shall be kept free from water while the pipe or structures are being installed, while concrete is setting, and until backfill has progressed to a sufficient height to anchor the work against possible flotation or leakage.

Water from excavations and trenches shall be disposed of in such a manner as to comply with all applicable Federal, State and local laws and regulations.

(5) Temporary Diversion of Sewage. The contractor shall maintain the flow of sewage past the work area at all times. Where the new sewer line is constructed in the alignment of the existing sewer, the contractor shall pump the sewage around the work area during working hours. During nonworking hours, a temporary connection shall be made from the existing sewer to the new sewer. Laterals and sewers crossing the trench shall be temporarily reconnected until they can be connected to the new sewer. Discharge or bypassing of sewage to waterways is not permitted.

(6) Disposal of Excess Excavated Material. All material excavated in streets, roadways, and rights-of-way, which is determined to be unsuitable for use as backfill or in excess of the amount required for backfilling, shall be removed immediately and disposed of at a legal disposal site. No stockpiling of excavated materials will be allowed at any time in public rights-of-way areas.

Where excavated material is specifically permitted to be used for backfill, it shall be laid away from the side of the trench to prevent caving or undue loading on the shoring and kept trimmed up so as to cause as little inconvenience as possible to the normal use of adjacent properties. Free access must be provided to all fire hydrants, water gates, meters, and private drives. Drainage ways shall be kept clear unless other provisions are made for handling drainage. In bay mud areas, excavated material must be kept well away from the edge of the trench to prevent heaving of the bottom of the trench.

(7) Unsuitable Material. In advance of placing sewer pipe or structures, existing material within the area where such pipe or structures are to be placed, which is unsuitable as a foundation for the pipe, including but not limited to bay mud, soft material, vegetable matter, garbage and junk piles, either on the surface or buried, shall be removed and disposed of at a legal disposal site.

In rock excavation or a mixture of rock and earth excavation, such material shall be loosened and broken up for the full width of the trench so that no ribs, rocks, or solid projections will be within six inches of the sewer pipe. The material thus broken up shall be removed and disposed of and the resulting space refilled with approved bedding material.

When unsuitable material is removed, the resulting space shall be refilled with three-quarter-inch crushed rock or other approved material. In bay mud, one-and-one-half-inch crushed rock shall be used to replace the unsuitable material.

(8) Pipe Bedding and Pipe Zone Backfill. All pipelines shall be bedded in an approved bedding material as shown on Standard Drawing SD 4, SD5MCC 5.105.010. The pipe bedding and pipe zone backfill material shall be placed uniformly on each side of the pipe to prevent displacement. In wet or unstable bedding conditions, three-quarter-inch or one-and-one-half-inch crushed rock shall be used.

All bedding materials shall be compacted to a minimum of 90 percent relative compaction, and materials shall be carefully handled to prevent intrusion of foreign materials.

Bedding and pipe zone material for main sewers shall be an approved granular material, free from vegetable matter and other deleterious substances, graded so that it will compact readily to form a firm, stable base when compacted, as shown on Standard Drawing SD 4, SD5MCC 5.105.010. The use of sand for a pipe bedding or pipe zone backfill is not permitted.

Bedding material for building sewers shall be select granular material excavated from the trench, free of any organic matter, large clods or rocks. If the excavated material is determined to be unsuitable for bedding or pipe zone backfill, material similar to that specified above for main sewers shall be used.

The contractor shall construct four-foot-wide dams in pipe bedding and pipe zone backfill at 400-foot intervals using compacted clay or slurry cement backfill.

(9) Intermediate Backfill. Intermediate backfill material shall consist of imported material or material excavated from the trench. All intermediate backfill material shall be free from vegetable matter, concrete, stones or clods larger than four inches in diameter and other deleterious substances. The intermediate backfill material shall contain sufficient fines so that all voids will be filled when compacted, and shall be so constituted that the compaction requirements specified herein can be met. Sand is not permitted as intermediate backfill.

Intermediate backfill in public streets and highways shall be Class 2 aggregate base or shall otherwise conform to the requirements of the agency maintaining such streets and highways (i.e., the City, Town, County, Caltrans, etc.), but in no case will the requirements be less than those specified herein. Rounded or open graded aggregates, such as pea gravel, are not permitted for use as intermediate backfill. Use of native material for intermediate backfill within existing streets or paved areas is not permitted. All backfill materials shall be placed and consolidated in such a manner as to permanently prevent damage to the pipeline, structure, roadbed, road surfacing and private property, or inconvenience to the public.

In the case of sewer work done under permit within new subdivisions, the installation and compaction of intermediate backfill shall be in accordance with the recommendations and specifications of the developer’s soils engineer, as approved by the District. If, for some reason, a soils report is not prepared which makes such recommendations and specifications, the minimum trench backfill requirements shall be those specified herein.

All intermediate backfill shall be compacted in such a manner as to obtain 90 percent relative compaction. Backfill material shall be placed in layers not exceeding eight inches in loose depth and thoroughly compacted by tamping, rolling or otherwise to obtain the specified compaction.

Jetting of trenches to achieve compaction of backfill is not allowed.

The soils engineer hired by the developer or, in the case of District projects, the soils engineer hired by the District shall take compaction tests to verify compliance with the requirements of the agency exercising jurisdiction on the street or as required by the District. [Ord. 2014-2 (Att. § 13-05).]

5.65.060 Structure excavation and backfill.

(1) General. Structure excavation shall consist of the removal, to the lines designated on the plans or specified or ordered by the District, of all material of whatever nature necessary for the construction of foundations and other excavations specifically designated on the plans or in these specifications or in the special provisions.

Structure backfill shall consist of placing and compacting, to the lines designated on the plans or specified or ordered by the District, backfill material around structures, and other backfill specifically designated on the plans or in these specifications or in the special provisions.

Structure excavation and backfill shall include the furnishing of all equipment and the construction or installation of all cofferdams and other facilities which may be necessary to perform the excavations and place and compact the backfill, and the subsequent removal of such facilities except where they are required or permitted by the plans or specifications to remain in place.

(2) Excavation. All excavation for structures shall be done to the dimensions and levels indicated on the plans or specified herein. Excavation shall be made to such width outside the lines of the structure as may be required for proper working methods, the erection of forms, and the protection of the work. Care shall be taken to preserve the subgrade. If disturbed, the contractor shall replace the disturbed subgrade with compacted, crushed rock fill or other material approved by the District in a manner which will show by test an equal bearing quality with the undisturbed subgrade.

The contractor shall, where necessary, protect excavations from caving by shoring or similar protective measures shall be repaired by the contractor at his own expense. All shoring shall be removed prior to the placing of concrete and/or backfill material, unless otherwise specifically authorized by the District.

The excavation shall be kept free of water while construction work is in progress and any water encountered during the process of excavation shall be controlled to the satisfaction of the District.

The contractor shall notify the District when excavation for a structure is complete and no forms, reinforcing steel, concrete, pipe or backfill material shall be placed until the excavation has been approved by the District.

(3) Cofferdams. Cofferdams for foundation construction shall be carried below the bottom of the footings and shall be braced and as water tight as practicable. The interior dimensions of cofferdams shall be such as to provide sufficient clearance for construction forms and, when no seal is placed, to permit pumping outside the forms.

In the judgment of the contractor, if the clearance provided on the plans between the outside of the footing and any pile or interior wall or surface is not sufficient to permit the expeditious driving of piles or building of forms, he may provide such necessary clearances by constructing the cofferdams sufficiently large to provide such clearance as he may deem necessary. It shall be considered and is agreed that any such enlargement in excess of the outside dimensions of the footing as designed is for the sole purpose of expediting the work of the contractor and quantities of such excavation and backfill will not be included in the quantities to be paid for.

Cofferdams which are tilted or moved out of position by any cause whatsoever during the process of sinking shall be righted or enlarged so as to provide the necessary clearance and proper location and such work shall be at the sole expense of the contractor.

In tidal waters or in streams at a time of probable flood, cofferdams’ walls shall be vented at low water elevation to insure full hydrostatic head both inside and outside of the cofferdam during the period of pouring and setting of seals.

No shoring will be permitted in cofferdams which will induce stress, shock, or vibration in the permanent structure.

When permitted by the District, cross struts or bracing may extend through foundation concrete. Such struts or bracing below low water will be permitted to remain in place. Struts or bracing above low water shall be removed and the volume displaced filled with concrete of the same mix as that specified for the surrounding concrete.

For substructure work, the contractor shall submit drawings showing its proposed method of shoring and cofferdam construction and other details left open to his choice or not fully shown on the plans. The type and clearance of cofferdams, insofar as such details affect the character of the finished work, will be subject to the approval of the District, but the other details of design will be left to the contractor, who will be responsible for the successful construction of the work.

After the completion of the substructure, the cofferdams with all sheeting and bracing shall be removed by the contractor, at his own expense, to the level of the stream bed, or ground water table, and such removal shall be performed in such a manner as not to disturb or mar the finished concrete or masonry.

(4) Foundation Treatment. When a concrete or masonry footing is to rest upon rock, the rock shall be fully uncovered and the surface thereof shall be removed to a depth sufficient to expose sound rock. The rock shall be roughly leveled off or cut to approximate horizontal and vertical steps, and shall be roughened. The overcut of the rock shall be filled with concrete as a part of the structure, or, upon specific approval of the District, may be filled with compacted Class 2 aggregate base or crushed rock.

When piles are to be used, the contractor, at his own expense, will be permitted to excavate a sufficient distance below the bottom of the footing as shown on the plans to take care of swell due to driving piles. After the piles are driven, if it is found that the ground has risen above the planned grade, the contractor shall remove such surplus material at his own expense. After the piles are driven, if it is found that the surface of the ground is below the planned grade, the contractor shall backfill, at his own expense, to the planned grade with material approved by the District.

(5) Disposal of Excess Excavated Material. All materials to be removed during the course of excavation in excess of that needed for backfill, or deemed by the District as being unsuitable for backfill, shall be hauled off the job site by the contractor and disposed of at his own expense at a legal disposal site.

(6) Inspections. In order to determine the character of the foundation material, the contractor shall, if ordered by the District, dig test pits, and make test borings and foundation bearing tests.

Whenever any structure excavation is completed to the grade of the bottom of the footing shown on the plans, or set forth in the special provisions, or ordered by the District, the contractor shall notify the District, who will make an inspection of the elevation and character of the foundation. No footing concrete or masonry shall be placed in a footing until the District has inspected and approved the elevation and character of the foundation for the footing.

(7) Backfill. Structure backfilling operations shall conform to the requirements of this section, and any requirements specified in the special provisions.

Structural fill material shall conform to the requirements of SD5MCC 5.65.040(5).

The contractor shall make his own arrangements for obtaining structure backfill material and all costs involved therewith shall be considered as included in the contract price paid for structure excavation, or for the structure being constructed.

Structure backfill shall not be placed until the structure footings or other portions of the structure or facilities to be below ground line have been inspected by the District and approved for backfilling. No backfill material shall be deposited against the outside walls of concrete structures until seven days have elapsed from the pour or until the concrete has developed the strength of 2,500 pounds per square inch in compression as determined by a break of a test cylinder cured under conditions similar to those prevailing at the site and tested in accordance with standard methods.

Backfill materials shall be placed in uniform horizontal layers not exceeding eight inches in loose thickness before compaction and shall be brought up uniformly on all sides of the structure or improvement in order to avoid bending or distortional stresses. Each layer of backfill shall be conditioned for optimum moisture as necessary and thoroughly tamped, rolled or otherwise compacted or necessary to achieve a relative compaction not less than 90 percent. [Ord. 2014-2 (Att. § 13-06).]

5.65.070 Embankment construction.

(1) General. Embankment construction shall consist of the construction of fills, including the preparation of the ground areas upon which they are to rest; the construction of earth dikes for site protection; and the placing and compacting of embankment material in holes, pits and other depressions within the work area.

(2) Subgrade Preparation. The relative compaction of the natural ground area upon which embankments are to be constructed, for a depth of not less than two feet below finished grade, shall not be less than 90 percent.

When necessary to conform to the above compaction requirements, the natural ground shall be excavated and the excavated material or other material designated by the District backfilled in the excavated area. The backfill material shall be placed in layers not to exceed eight inches in loose thickness before compaction and each layer shall be compacted as necessary to achieve a relative compaction not less than 90 percent.

When embankments are to be made and compacted on hillsides, or where new fill is to be compacted against existing embankments, the slopes of the original hillside, old or new fill, shall be cut into as the work is brought up in layers. Material thus cut out shall be recompacted along with the new fill at the contractor’s expense.

(3) Embankment Materials. Wherever selection is possible, embankment material having a sand equivalent value of less than 10 shall be deposited in the lower portions of embankments and no such material shall be placed within two feet of planned finished grade.

When the embankment material consists of large rocky material, or hard lumps such as hardpan or cemented gravel which cannot be broken readily, such material shall be well distributed throughout the embankment, and sufficient earth or other fine material shall be placed around the large material as it is deposited so as to fill the interstices and produce a dense compact embankment.

(4) Compacting. Embankments shall be constructed in compacted layers of uniform thickness and each layer shall be compacted by means of approved compacting equipment in strict accordance with the soils engineer’s recommendation. Jetting is not permitted.

At the time of compaction, the moisture content of embankment materials shall be such that the relative compaction specified may be obtained with the compacting equipment being used. Embankment material which contains less than the required moisture content shall be watered as necessary, and the water may be added to the material at the excavation site. Compaction of embankment material which contains excessive moisture shall not be commenced until material has been allowed to dry to such an extent that the relative compactions specified may be produced with the compacting equipment being used. At all times it shall be the responsibility of the contractor to employ such means as may be necessary to secure a uniform moisture content throughout the material being compacted. Full compensation for any additional work involved in drying embankment material to the required moisture content shall be considered as included in the contract price paid for excavating the material and/or constructing the embankment and no additional allowance will be made therefor.

Embankments shall be maintained to the grade and cross section shown on the plans until the acceptance of the contract and the contractor shall be responsible for the stability of all constructed embankments and shall replace any portions which have become displaced or damaged. [Ord. 2014-2 (Att. § 13-07).]

5.65.080 Temporary paving.

Temporary paving shall be a minimum of two inches thick and rolled with a roller after placement. The temporary paving shall be maintained by the contractor and shall be level with adjacent pavement in a safe and usable condition until permanent paving is installed. Temporary paving shall be placed at all locations where necessary to accommodate traffic. All temporary paving materials shall comply with the requirements of the Air Quality Management District. [Ord. 2014-2 (Att. § 13-08).]