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Section 19 – Trench Excavation, Bedding and Backfill

left in the trench wall or embedment materials by support removal shall be carefully filled with

bedding material and compacted. Removal of bracing between sheeting shall only be done

where backfilling proceeds and bracing is removed in a manner that does not relax trench

19-1.07 Special Foundation Treatment

Whenever the bottom of the trench is soft or rocky, or, in the opinion of the Agency,

otherwise unsuitable as a foundation for pipe bedding, the unsuitable material shall be removed

to a minimum depth of six inches (6”) and replaced with crushed rock, gravel, or sand as

directed by the Agency. When the trench bottom is cobbled or of any other material which

might, in the opinion of the Agency, allow loss of sand backfill, the backfill material shall be

crushed rock or gravel graduated so that one hundred percent (100%) will pass the three-

quarter inch (3/4”) sieve and not more than fifteen percent (15%) will pass the number 8 sieve.

Crushed rock or gravel shall conform to Section 50-14, “Crushed Rock”, of these Specifications.

Sand backfill, when permitted by the Agency, shall conform to the requirements in Section 50-

13.01, “River Sand”, of these Specifications. Such backfill material shall be compacted to a

minimum relative compaction of ninety percent (90%).

As an alternate to the bedding materials specified above, the Agency may direct the

Contractor to furnish and place geotextile fabric below the bedding materials. The geotextile

material shall be a high modulus woven fabric, and shall be inert to commonly encountered

chemicals, rot-proof and resistant to ultraviolet light exposures, insects, and rodents. The

geotextile fabric shall have a minimum grab tensile strength of two hundred pounds (200 lbs.) in

any direction as measured in accordance with ASTM D 1682, a Mullen burst strength of at least

four hundred pounds (400 lbs.) per square inch per ASTM D 3786, and an Equivalent Opening

Size no larger than U.S. Standard Sieve Number 50 as determined by U.S. Corps of Engineers

Specification CW-02215. Geotextile fabric shall be Mirafi 600X, or equal. Each roll of fabric

used shall be labeled in accordance with ASTM D 4873. Geotextile fabric shall be handled and

placed in accordance with the manufacturer’s recommendations. Furnishing and placing of

geotextile fabric will be paid for as extra work as provided in Section 9, “Changes and Claims”,

of these Specifications.

If material more than twelve inches (12”) below the typical trench bottom is ordered removed

by the Agency, the excavation below that point and the imported material required to backfill the

trench to that elevation will be paid for as extra work as provided in Section 9, “Changes and

Claims”, of these Specifications unless otherwise specified in the Special Provisions. Before

excavation of the pipe trench in fill areas or roadway embankments, the fill area or embankment

shall be completed to a height above the pipe invert grade line of not less than twice the internal

pipe diameter or to final fill or embankment subgrade, whichever is lower, but in no case less

than twelve inches (12”) above the top of the pipe. Such embankment shall be compacted to a

minimum relative compaction of ninety percent (90%) for a distance on each side of the pipe

equal to at least two (2) pipe diameters. The remainder of the embankment shall be compacted

to the minimum relative compaction specified elsewhere in these Specifications for the type of

construction being done, or as specified in the Special Provisions or on the Plans. Special

foundation treatment for cast-in-place concrete pipe shall be as specified in Section 36-4, “Cast-

In-Place Concrete Pipe (CIPCP) - Special Foundation Treatment”, of these Specifications.

19-1.08 Excavation Method

Methods used in excavation shall not cause damage to surrounding property or damage

remaining pavement and other existing improvements that are to remain. Outriggers for

excavation equipment, and other heavy equipment, shall be fitted with street pads to prevent