31 23 16.13 - Trenching.pdf

31 23 16.13 - TRENCHING

Herbert, Rowland & Grubic, Inc. 31 23 16.13 - 1 011361.0461

SECTION 31 23 16.13 - TRENCHING

PART 1 - GENERAL

1.1 SUMMARY

A. Section Includes:

1. Excavating trenches for utilities.

2. Compacted fill from top of utility bedding to subgrade elevations.

3. Backfilling and compaction.

B. Related Sections:

1. Section 31 05 16 - Aggregates for Earthwork: Aggregates for fill.

1.2 REFERENCES

A. American Association of State Highway and Transportation Officials:

1. AASHTO T180 - Standard Specification for Moisture-Density Relations of Soils

Using a 4.54-kg (10-lb) Rammer and a 457-mm (18-in.) Drop.

B. ASTM International:

1. ASTM D698 - Standard Test Method for Laboratory Compaction Characteristics of

Soil Using Standard Effort (12,400 ft-lbf/ft3 (600 kN-m/m3).

2. ASTM D1557 - Standard Test Methods for Laboratory Compaction Characteristics of Soil Using Modified Effort (56,000 ft-lbf/ft3 (2,700 kN-m/m3).

3. ASTM D2922 - Standard Test Method for Density of Soil and Soil-Aggregate in

Place by Nuclear Methods (Shallow Depth).

4. ASTM D3017 - Standard Test Method for Water Content of Soil and Rock in Place by Nuclear Methods (Shallow Depth).

1.3 DEFINITIONS

A. Utility: Any buried pipe, duct, conduit, or cable.

1.4 SUBMITTALS

A. Section 01 33 00 - Submittal Procedures: Requirements for submittals.

B. 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. Product Data: Submit data for geotextile fabric indicating fabric and construction.

D. Materials Source: Submit name of imported fill materials suppliers.

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1.5 QUALIFICATIONS

A. Prepare excavation protection plan under direct supervision of Professional Engineer experienced in design of this Work and licensed in State of Pennsylvania.

1.6 FIELD MEASUREMENTS

A. Verify field measurements prior to fabrication.

1.7 COORDINATION

A. Section 01 31 13 – Project Coordination: Coordination and project conditions.

B. Verify Work associated with lower elevation utilities is complete before placing higher elevation utilities.

1.8 JOB CONDITIONS

A. 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.

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

PART 2 - PRODUCTS

2.1 FILL MATERIALS

A. Structural Fill: Type PennDOT 2A as specified in Section 31 05 16.

B. Granular Fill: Type AASHTO No. 57 as specified in Section 31 05 16.

PART 3 - EXECUTION

3.1 LINES AND GRADES

A. Lay pipes to lines and grades indicated on Drawings:

1. Owner reserves right to make changes in lines, grades, and depths of utilities when changes are required for Project conditions.

2. Contractor shall not be entitled to extra compensation or to a claim for damages if change does not involve abandonment of an excavated trench.

Herbert, Rowland & Grubic, Inc. 31 23 16.13 - 3 011361.0461

B. Use laser-beam instrument with qualified operator to establish lines and grades.

3.2 PREPARATION

A. Call Pennsylvania One Call System, Inc. at 1-800-242-1776 not less than three working days before performing Work.

1. Request underground utilities to be located and marked within and surrounding construction areas.

B. Identify required lines, levels, contours, and datum locations.

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

D. Protect bench marks, existing structures, fences, sidewalks, paving, and curbs from excavating equipment and vehicular traffic.

E. Maintain and protect above and below grade utilities indicated to remain.

F. Establish temporary traffic control when trenching is performed in public right-of-way.

Relocate controls as required during progress of Work.

3.3 TRENCHING

A. Excavate subsoil required for utilities to locations shown on Drawings and necessary to complete work.

B. Remove lumped subsoil, boulders, and rock. Excavation for this project shall be considered unclassified. No additional payment shall be made for rock removal of any kind.

C. Perform excavation within 24 inches of existing utility service in accordance with utility's requirements.

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

E. Cut trenches sufficiently wide to enable installation and allow inspection. Remove water or materials that interfere with Work.

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

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

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

I. When Project conditions permit, side wall of excavation may be sloped 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.

Herbert, Rowland & Grubic, Inc. 31 23 16.13 - 4 011361.0461

J. When subsurface materials at bottom of trench are loose or soft, notify Engineer, and request instructions.

K. Cut out soft areas of subgrade not capable of compaction in place. Backfill with AASHTO No. 3 coarse aggregate to within 6 inches of subgrade followed by AASHTO No. 57 coarse aggregate wrapped in non-woven geotextile and compact to density equal to or greater than requirements for subsequent backfill material.

L. Trim excavation. Hand trim for bell and spigot pipe joints. Remove loose matter.

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

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

3.4 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.

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 and subsurface material.

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

3.5 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 8 inches compacted depth.

3. Granular Fill: Maximum 8 inches compacted depth.

D. Employ placement method that does not disturb or damage utilities in trench.

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.

Herbert, Rowland & Grubic, Inc. 31 23 16.13 - 5 011361.0461

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

3.6 TOLERANCES

A. Section 01 40 00 - Quality Requirements: Tolerances.

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

3.7 FIELD QUALITY CONTROL

A. Section 01 40 00 - Quality Requirements: Field inspecting, testing, adjusting, and balancing.

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

C. Perform in place compaction tests, by a certified testing agent, 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. Within PennDOT right-of-way:

a. Comply with PennDOT requirements and complete PennDOT CS-6 forms.

b. Contractor and Contractors certified testing agent shall complete and submit compaction test results and PennDOT CS-6 forms to Engineer daily.

2. Outside PennDOT right-of-way:

a. On the 1st day of backfilling to determine the level of effort required to achieve the contract required compaction requirements.

b. Provide a minimum of one (1) site visit per sewer pipe run installation between manhole structures.

c. Provide a minimum of one (1) site visit per each 400 foot section of force main pipe and low pressure sewer main installation.

d. Compaction tests shall be performed at varying depths and locations per site visit, as determined by the Engineer.

e. Contractor and Contractors certified testing agent shall complete and submit compaction test results to Engineer following each site visit.

3.8 PROTECTION OF FINISHED WORK

A. Section 01 73 00 - Execution Requirements: Protecting finished work.

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

3.9 SCHEDULE

A. Sanitary Sewer Pipe Bedding:

Herbert, Rowland & Grubic, Inc. 31 23 16.13 - 6 011361.0461

1. Provide pipe bedding depth and initial backfill as indicated on the plans. Bedding and initial backfill to be AASHTO No. 8 or No. 57.

B. Sanitary Sewer Pipe Backfill over initial bedding (under Asphalt pavement areas):

1. Cover pipe and bedding with Fill Type: PennDOT 2A aggregate, to subgrade elevation.

2. Compact uniformly to minimum 100 percent of maximum density.

C. Sanitary Sewer Pipe Backfill over initial backfill (under grass areas):

1. Cover pipe and bedding with Fill Type: Suitable Backfill and Embankment

Material, to subgrade elevation.

2. Compact uniformly to minimum 90 percent of maximum density.

D. Concrete Manholes initial bedding:

1. Bedding: Provide bedding as indicated on the plans. Bedding to be No. 57 coarse aggregate.

E. Concrete Manholes backfill over initial bedding:

1. Provide backfill as indicated on the plans. Backfill to be PennDOT 2A aggregate, to subgrade elevation.

END OF SECTION