Earthwork Section 31 23 33 – Trenching and Backfilling

DIVISION 31 – EARTHWORK SECTION 31 23 33 – TRENCHING AND BACKFILLING

DIVISION 31 – EARTHWORK SECTION 31 23 33 – TRENCHING AND BACKFILLING

PART 1 – GENERAL

1.01 SUMMARY

A. Section Includes 1. Excavating trenches for utilities. 2. Compacted fill from top of utility bedding to subgrade elevations. 3. Backfilling and compaction of utility trenches.

B. Related Sections: 1. Section 31 05 13 ‐ Soils for Earthwork 2. Section 31 05 16 ‐ Aggregates for Earthwork 3. Section 31 23 23 – Fill

1.02 REFERENCES

A. Pennsylvania Department of Transportation (PennDOT): 1. Publication 408 ‐ Specifications, latest edition, as amended. 2. PennDOT Chapter 459, Occupancy of Highways by Utilities, latest edition 3. PennDOT Chapter 203, Work Zone Traffic Control, latest edition

B. Department of Environmental Protection, Bureau of Waste Management: 1. “Clean Fill” Policy (Effective August 7, 2010).

C. American Society for Testing and Materials: 1. ASTM D698 ‐ Standard Test Method for Laboratory Compaction Characteristics of Soil Using Standard Effort. 2. ASTM D1557 ‐ Standard Test Methods for Laboratory Compaction Characteristics of Soil Using Modified Effort. 3. ASTM D2434 ‐ Standard Test Method for Permeability of Granular Soils (Constant Head). 4. ASTM D2922 ‐ Standard Test Method for Density of Soil and Soil‐Aggregate in Place by Nuclear Methods (Shallow Depth). 5. ASTM D3017 ‐ Standard Test Method for Water Content of Soil and Rock in Place by Nuclear Methods (Shallow Depth).

1.03 SUBMITTALS

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A. Submit under provisions of Section 01 33 00.

B. Informational Submittal: 1. Excavation Protection Plan: Describe sheeting, shoring, and bracing materials and installation required to protect excavations and adjacent structures and property; include structural calculations to support plan.

C. Samples: Submit aggregate samples when requested by Engineer and other required submissions to the Engineer's field office.

D. Material Test Reports: From a qualified testing agency indicating and interpreting test results for compliance of the following with requirements indicated: 1. Classification according to ASTM D 2487 of each on‐site or borrow soil material proposed for fill and backfill. 2. Laboratory compaction curve according to ASTM D 1557 for each on‐site or borrow soil material proposed for fill and backfill. 3. Laboratory compaction curve according to ASTM D 1557 for each aggregate material proposed for fill and backfill. 4. Density and moisture test reports for subgrades, fills and backfills.

1.04 QUALITY ASSURANCE

A. Qualifications 1. Prepare excavation protection plan under direct supervision of Professional Engineer experienced in design of this Work and licensed to practice at Project location. 2. Geotechnical Testing Agency Qualifications: An independent testing agency qualified according to ASTM E 329 to conduct materials, as documented according to ASTM D 3740.

B. Field Quality Control 1. All field quality control testing must be supervised by a Professional Engineer. 2. Reports of independent testing laboratory shall be considered as sufficient evidence of noncompliance with specifications.

1.05 PROJECT CONDITIONS

A. Removal of Obstructions: 1. Remove, realign or change the direction of above or below ground utilities and their appurtenant supports, if such is required in the opinion of the Engineer. Perform such work as additional work unless the Owner of the obstruction does such work without cost to the Contractor; however, Contractor shall uncover and sustain the obstruction at own expense prior to the final disposition of obstruction. The Contractor is not entitled to claims for damage or extra compensation due to the presence of such obstruction or delay in the removal or

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rearrangement of same. Additional precautions concerning obstructions as follows: a. Without relieving Contractors responsibilities, allow utility owners to take such measures necessary under the circumstances. Do not interfere with utility owner employing protective measures, removing, modifying or replacing their property or structures. b. Without extra compensation, break through and reconstruct if necessary, the invert or arch of a sewer, culvert or conduit that may be encountered if the said structure is in such a position, in the judgment of the Engineer, as not to require its removal, realignment or complete reconstruction.

B. Existing Utilities and Services 1. Known underground services and utilities are indicated on the Contract Drawings. No guarantee is given to completeness or accuracy. Contractor shall be responsible for verifying the location and/or depth of all utilities and services indicated within the areas of work. 2. Maintain existing utilities which must remain in service in the area of the excavation. 3. Record locations of underground utilities encountered. Location should include horizontal and vertical distance from grade and existing structures.

C. Unclassified Excavation: No consideration will be given to the nature of materials encountered in trenching operations. Therefore, as unclassified excavation, no additional payment will be made for difficulties occurring in excavating and handling of materials.

PART 2 – PRODUCTS 2.01 MATERIALS A. Pipe Bedding: Refer to Section 31 05 16 – Aggregates for Earthwork 1. Pipe diameter 24 inches and less: AASHTO No. 8 Coarse Aggregate. 2. Pipe diameter greater than 24‐inches: AASHTO No. 57 Coarse Aggregate.

B. Initial Backfill: Refer to Section 31 05 16 – Aggregates for Earthwork 1. Pipe diameter 24 inches and less: AASHTO No. 8 Coarse Aggregate. 2. Pipe diameter greater than 24‐inches: AASHTO No. 57 Coarse Aggregate.

C. Backfill 1. Clean Fill Material: The evaluation of fill materials shall be in accordance with DEP’s “Clean Fill” regulations and procedures for determining whether material is clean or regulated. 2. Suitable Trench Backfill Material: On site excavated soil or soil rock mixed materials free of topsoil, vegetation, lumber, metal and refuse; and free of rock or similar hard objects larger than 6 inches in greatest dimension. Rock to soil ratio shall not exceed one part rock to three parts soil. 3. Clean Organic Material Backfill: One site excavated material free of vegetation, lumber, metal and refuse, and free of rocks or similar hard objects larger than

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one inch in greatest dimension. 4. Aggregate: PENNDOT 2A Coarse Aggregate as specified in Section 31 05 16 – Aggregates for Earthwork. 5. Flowable Backfill: Type A or B in accordance with PennDOT Publication 408, Section 220. 6. Clay Dikes: Compacted Clean Earth Material suitable for use as trench plug.

D. Misc. Concrete: For use with encasements, cradles, anchors, pipe abandonment and thrust blocking. Concrete shall have a 28‐day compressive strength of 3,000 psi.

E. Suitable Bearing Material: AASHTO No. 3 Coarse Aggregate as specified in Section 31 05 16 – Aggregates for Earthwork.

PART 3 – EXECUTION 3.01 PREPARATION

A. Verify site conditions: 1. Sedimentation and erosion control facilities in accordance with the requirements of Section 31 25 00. 2. Dewatering, as required, in accordance with the requirements of Section 31 23 19.

B. Other Utilities: 1. Notify PA One Call System at least 3 days prior to any excavation in order that all utility locations may be marked. 2. Notify utility owners to remove and/or relocate utilities. 3. Protect utilities indicated to remain from damage.

C. Identify required lines, levels, contours, and datum. 1. Verify and protect survey bench mark and intended elevations for the Work are as indicated on Drawings.

D. Protect plant life, lawns, and other features remaining as portion of final landscaping.

E. Protect existing structures, fences, sidewalks, paving, and curbs from excavating equipment and vehicular traffic.

F. Establish temporary traffic control and detours when trenching is performed in public right‐of‐way. Relocate controls and reroute traffic as required during progress of Work.

3.02 REQUIREMENTS AND RESTRICTIONS

A. Keep excavations free from water. Divert any runoff from trench. If required, lower water table below excavation bottom by deep wells. 1. Dispose of water removed from excavations in a manner that will not cause injury to the public health, to public or private property, to the work of other

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Contractors, to any portion of the Work completed or in progress, or to produce impediment to the use of highways, roads, lanes and streets by the public. No additional payment will be made for pumping or other difficulties encountered due to water.

B. Maintain storm sewers, drains and ditches free of debris to convey surface drainage. 1. Do not dam or pond runoff in gutters or other waterways. 2. Do not direct flow of water across pavements except through approved pipes or properly constructed troughs. Provide pipes or troughs of such sizes and lengths as may be required. 3. Control grading in the vicinity of excavations so the ground surface is properly pitched to prevent water from running into excavated areas.

C. Control groundwater and surface water during construction in order to maintain soil stability. Maintain the water table elevation sufficiently below the levels of excavations that slopes will remain stable and bottoms of excavations will not become loosened by flow of water. If the foundation material loses its strength due to improper dewatering techniques, over excavate the material and replace it with Structural Fill at no additional cost to Owner.

D. Do not perform excavating when weather conditions or the condition of materials are such that the Work cannot be completed in accordance with the Specifications.

E. Prevent spread of dust during performance of work by thoroughly moistening excavation areas by sprinkling or other methods approved by Engineer.

F. No right of ownership of excavated materials is granted to Contractor prior to backfilling. This provision does not relieve Contractor of his responsibility to remove and dispose of surplus excavated material.

G. Assume sole responsibility for the condition and results of excavations. Slides and cave‐ ins shall be removed without additional compensation at whatever time and under whatever circumstances they may occur.

3.03 TRENCHING

A. Existing Pavement Removal: Saw cut existing pavement using a mechanical saw to neat lines equidistant from the centerline of the trench. Initial Saw cut shall be made prior to staring trench excavation

B. Excavate subsoil required to depths indicated for utility installation.

C. Remove lumped subsoil, boulders, and rock.

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D. Perform excavation within 24 inches of existing utilities in accordance with utility’s requirements.

E. Do not advance open trench more than 200 feet ahead of installed pipe.

F. Cut trenches to width indicated on Drawings, sufficiently wide to enable installation and allow inspection. Remove water or materials that interfere with Work.

G. Excavate bottom of trenches maximum 2 feet wider than outside diameter of pipe.

H. Excavate trenches to depth indicated on Drawings. Provide uniform and continuous bearing and support for bedding material and pipe.

I. Do not interfere with 45 degree bearing splay of foundations.

J. When Project conditions permit, slope side walls of excavation starting 2 feet above top of pipe. When side walls cannot be sloped, provide sheeting and shoring to protect excavation as specified in this section.

K. When subsurface materials at bottom of trench are loose or soft, excavate to greater depth as directed by Engineer until suitable material is encountered. Notify Engineer, and request instructions.

L. Cut out soft areas of subgrade not capable of compaction in place. Backfill with Structural Fill and compact to density equal to or greater than requirements for subsequent backfill material.

M. Trim excavation by hand for bell and spigot pipe joints. Remove loose matter.

N. Correct areas over excavated areas with compacted backfill as specified for authorized excavation or replace with fill concrete as directed by Engineer.

O. Remove excess subsoil not intended for reuse, from site.

P. Stockpile excavated material in area designated on site in accordance with Section 31 05 13.

3.04 SHEETING AND SHORING

A. Sheet, shore, and brace excavations to prevent danger to persons, structures and adjacent properties and to prevent caving, erosion, and loss of surrounding subsoil.

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B. Support trenches more than 5 feet deep excavated through unstable, loose, or soft material. Provide sheeting, shoring, bracing, or other protection to maintain stability of excavation.

C. Design sheeting and shoring to be removed at completion of excavation work.

D. Repair damage caused by failure of the sheeting, shoring, or bracing and for settlement of filled excavations or adjacent soil.

E. Repair damage to new and existing Work from settlement, water or earth pressure or other causes resulting from inadequate sheeting, shoring, or bracing.

3.05 BACKFILLING

A. Backfill trenches to contours and elevations with unfrozen fill materials.

B. Systematically backfill to allow maximum time for natural settlement. Do not backfill over porous, wet, frozen, or spongy subgrade surfaces.

C. Place material in continuous layers as follows:

1. Subsoil Fill: Maximum 8 inches compacted depth. 2. Structural Fill: Maximum 6 inches compacted depth. 3. Granular Fill: Maximum 6 inches compacted depth.

D. Employ placement method that does not disturb or damage foundation perimeter, utilities in trench, or other work.

E. Maintain optimum moisture content of fill materials to attain required compaction density.

F. Do not leave more than 50 feet of trench open at end of working day.

F. Protect open trench to prevent danger to Owner and the public.

3.06 TOLERANCES A. Section 01 40 00 ‐ Quality Requirements: Tolerances. B. Top Surface of Backfilling under paved areas: Plus or minus 1 inch from required elevations.

C. Top Surface of General Backfilling: Plus or minus 1 inch from required elevations.

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3.07 FIELD QUALITY CONTROL

A. Section 01 40 00 ‐ Quality Requirements and Section 01 70 00 ‐ Execution and Closeout Requirements: Field inspecting, testing, adjusting, and balancing.

B. Perform laboratory material tests in accordance with ASTM D1557.

C. Perform in place compaction tests in accordance with the following:

1. Density Tests: ASTM D2922 2. Moisture Tests: ASTM D3017

D. When tests indicate Work does not meet specified requirements, remove Work, replace, compact, and retest.

E. Frequency of Tests:

1. One compaction test shall be performed at every two vertical feet of backfill every 400 linear feet in roadways, paved areas, and driveways, etc unless PennDOT requires otherwise. 2. One compaction test shall be performed at every four vertical feet of backfill every 2,000 linear feet in all other areas.

3.08 PROTECTION OF FINISHED WORK

A. Section 01 70 00 ‐ Execution and Closeout Requirements: Protecting finished work.

B. Reshape and re‐compact fills subjected to vehicular traffic during construction.

C. Do not excavate wet subsoil or excavate and process wet material to obtain optimum moisture content.

D. When excavating through roots, perform Work by hand and cut roots with sharp axe.

E. Remove excess subsoil not intended for reuse, from site.

F. Storage of Approved Materials:

1. Store on site all unused approved materials. 2. Do not mix unused approved materials of differing types. 3. Do not mix unused approved materials with unapproved materials.

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G. Benching Slopes: Horizontally bench existing slopes greater than 1:4 to key placed fill material to slope to provide firm bearing.

H. Stability: Replace damaged or displaced subsoil as specified for fill.

I. Excavation Below Planned Subgrade:

1. Do not excavate below depths indicated on the Contract Drawings or such depths as required for the proper installation of the Work, unless otherwise directed by Engineer.

2. Excavation below depths indicated on the Contract Drawings or as required for the proper installation of the Work through the fault of the Contractor, shall be restored to the indicated or required depths with Structural Fill at the expense of Contractor.

3. If the foundation for any structure is required by Engineer to be carried lower than the planned subgrade elevation shown on the Contract Drawings, the voids caused by this excavation shall be backfilled with Structural Fill up to subgrade elevation. Payment for the additional work will be made in accordance with the applicable General Conditions.

END OF SECTION

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