Current through Register Vol. 24-06, March 15, 2024
Installation or replacement of pipelines along or crossing
highways shall ordinarily be controlled by end-product specifications. However,
to insure safety of traffic and preservation of the earth structure supporting
the pavement, any required construction shall be in accordance with the
following controls:
(1) Trenched
construction and backfill. The essential features for trench and backfill
construction are:
(a) Restoration of the
structural integrity of entrenched roadbed.
(b) Security of the pipe against deformation
likely to cause leakage.
(c)
Assurance against the trench becoming a drainage channel or against drainage
being blocked by the backfill.
(2) Trenched construction - bedding and
backfill.
(a) Trenches shall be cut to have
vertical faces, where soil and depth conditions permit, with a maximum width of
outside diameter of pipe plus two feet. Shoring shall comply with the
department of labor and industries safety code for construction and/or as
directed by the department.
(b)
Bedding shall be provided to a depth of six inches or half the diameter of the
pipe, whichever is least. Bedding should consist of granular material free of
lumps, clods, stones, and frozen material. Bedding shall be graded to a firm
but yielding surface without abrupt change in bearing value. Unstable soils and
rock ledges should be subexcavated from the bedding zone and replaced with
suitable material or as directed by the department. The bottom of the trench
should be prepared to provide the pipe with uniform bedding throughout the
length of the installation.
(c)
Backfill shall be placed in two stages:
(i)
Sidefill to the level of top of pipe.
(ii) Overfill to former grade surface.
Sidefill and overfill shall consist of granular material laid in six-inch
layers, each consolidated by mechanical tamping and controlled addition of
moisture, to a density of ninety-five percent in accordance with the current
Standard Specifications for Road, Bridge, and Municipal Construction.
Consolidation by saturation or ponding is not permitted. Backfilling and
methods of compaction should be adapted to achieve prompt restoration of
traffic. Additional cutback of base and surfacing and transitioning of trench
shoulders to minimize later development of sag in the grade of the pavement
over the trench shall be as directed by the department.
(3) Untrenched construction shall
be required on all pipeline crossings of limited access highways and:
(a) The width of untrenched construction
shall extend a minimum of six feet outside the roadway prism.
(b) Pipelines installed under a highway
without disturbing the surface shall be made using a technique approved by the
department.
(c) The size of the
opening shall not exceed five percent oversize in diameter. Backfill is
required for pipes over twelve inches in diameter.
(d) Overbreaks, unused holes, or abandoned
casings shall be backfilled as directed by the department.
Statutory Authority: Chapter 47.44 RCW. 89-05-022 (Order
119), § 468-34-250, filed 2/10/89. Statutory Authority: 1977 ex.s. c 151.
79-01-033 (DOT Order 10 and Comm. Order 1, Resolution No. 13), §
468-34-250, filed 12/20/78. Formerly WAC
252-04-215.