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Meeting Date: September 9, 2003

Subject/Title: Informational Report regarding revisions to the standard specifications for open cut trenches in existing streets.

Submitted by: Engineering: B. Grewal/B. Bornstein

Approved by: John Stevenson, City Manager

On April 27, 1997, The City Council approved Resolution No. 97-72 regarding updating the City of Brentwood Standard Plans and Specifications, establishing minimum standard for construction of public as well as privately owned improvements within the City, and authorizing the City Engineer to make appropriate revisions to the standard plans, specifications and minimum standards as necessary to maintain future quality construction.

Due to the immense amount of growth in the City of Brentwood, a significant amount of open cut trenching occurs when new development or City projects must extend or tie into existing utilities in the roadway. These utilities may vary from sewer, water, storm drain, and dry utilities (gas, electric, telephone, cable, and fiber optic). When this work is performed and the trench is restored, in many cases the new trench causes settlement in the roadway, and potentially roadway failure. This has been an ongoing issue for many municipalities over the years and was investigated by the Contra Costa City Engineering Advisory Committee (CCEAC) regarding the damage caused to our streets by utility trenches.

The results of this investigation show that there is a “zone of influence” that represents the extent of street damaged by the trench. Unfortunately, this “zone of influence” varies greatly by the size of the utility and the depth of the trench and soil type. Therefore, the CCEAC developed a standard trench section and investigated the possible establishment of a trench impact fee. This fee would be collected from all developers and utility companies when they apply for an encroachment permit. After further review of this proposal by the City/County Attorney’s Association, it was determined that it would be very difficult to prove a Nexus for the fees being collected and what damage would actually be caused by the trench cut operation. Further, numerous cities have tried to implement this “trench cut fee”, and lost legal battles with utility companies for not providing a clear Nexus. Therefore, City staff determined the best course of action would be to amend the standard specification regarding trench cuts to create a more stringent trench repair requirement to minimize or eliminate trench settlement throughout the City. The revised trench cut detail (City Standard Plan ST-25a and ST-25b) is included in this report. A summary of the following changes is as follows:

1. Utilize a slurry backfill rather than base rock to eliminate the issues regarding poor compaction and monitoring to ensure the 95% relative compaction required for the base rock. Many other cities have incorporated this specification for this reason, since many dry utility companies (PG&E, SBC, and Comcast) pull so many permits on a regular basis for route maintenance, it is difficult to oversee and enforce the compaction issue.

2. Where the edge of the trench is near the gutter or edge of pavement, the entire section must be replaced.

3. Permission to excavate/trench-cut in newly resurfaced streets will not be granted for three (3) years unless approved by the City Engineer.

4. Any street that is trenched for more than 100 feet in a traveled way or extends more than 8 feet from the curb face/edge of pavement or has more than three (3) cross trenches in 300 feet shall be overlaid as directed by the City Engineer.

5. An existing specification that has been added to this detail for more stringent enforcement is that all pavement shall be restored within fourteen (14) days from the time the trench is backfilled.

6. New trench section will require a 2 inch thick grind past the trench T-section and overlay with the final lift of pavement. This will help to reduce or eliminate the gradual settlement that occurs at the edge of the trench T-section.

7. For roadway widening projects, the City will require the existing pavement surface to be grinded a minimum of 1 ½ inches and an overlay is required over the entire roadway section.


City Standard Plan ST-25a and ST-25b


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