8 Ch06 Trenching
8 Ch06 Trenching
8 Ch06 Trenching
TABLE OF CONTENTS
6.1 GENERAL 6-1
6.1.1SCOPE 6-1
6.1.2LARIMER COUNTY URBAN AREA STREET STANDARDS 6-1
6.1.3QUALITY ASSURANCE 6-1
6.2 MATERIALS 6-4
6.2.1 STABILIZATION MATERIAL 6-4
6.2.2 PIPE ZONE BEDDING MATERIALS 6-4
6.2.3 GROUNDWATER BARRIERS 6-6
6.2.4 TRENCH BACKFILL MATERIAL 6-6
6.2.5 NATIVE SEED (IF USED) 6-7
6.3 CONSTRUCTION 6-8
6.3.1 PREPARATION 6-8
6.3.2 TRENCHING 6-8
6.3.3 PIPE ZONE AND SUBGRADE 6-9
6.3.4 STOCKPILING EXCAVATED MATERIALS 6-9
6.3.5 PIPE ZONE BEDDING 6-9
6.3.6 GROUNDWATER BARRIERS / CUT-OFF WALLS 6-10
6.3.7 BACKFILLING AND COMPACTION 6-10
6.3.8 MANHOLE FRAMES AND VALVE BOXES 6-10
6.3.9 FIELD QUALITY CONTROL 6-11
6.3.10 SEEDING (IF USED) 6-13
6.1 GENERAL
6.1.1 Scope
A. This chapter addresses trenching and backfilling including subsurface
drainage, dewatering, preparation of subgrades, pipe bedding, backfilling,
compacting, Construction Staking and finish grading for Public Water and
Wastewater Systems.
G. Services:
1. The water services should be bedded with the same material as the main
line.
2. The wastewater service should be bedded with the same material as the
main line.
Green 20
Stipa viridula Lodorm 28.9 10
needlegrass
6.3 CONSTRUCTION
6.3.1 Preparation
A. Topsoil shall be stripped from areas, which are to be disturbed by
construction, and stockpiled.
B. Topsoil shall be segregated from non-organic trench excavation material, and
debris. Sod shall be either ground up into the topsoil or segregated and
disposed of. No sod pieces greater than 3 inches shall remain in the topsoil.
C. Topsoil and other soil with organics or other unsuitable material shall not be
placed as trench backfill.
6.3.2 Trenching
A. Trenches shall be excavated by open cut methods, except where boring or
tunneling is shown on signed PICPs, or as otherwise approved by the
Department.
B. Trench width shall be maintained to within 3 inches of that specified on
Standard Drawings W-1 and W-22.
C. Care shall be used when operating mechanical equipment in locations where
it may cause damage to trees, buildings, culverts or other existing property,
utilities or structures above or below ground.
D. Mechanical equipment shall be operated in such a manner the bottom
elevation of the trench can be maintained with uniform trench widths and
vertical sidewalls of the bedding zone.
E. Trench alignment shall be sufficiently accurate to permit pipe to be aligned
properly with minimum clearances between the pipe and sidewalls of the
trench (or trench box) pursuant to Standard Drawing W-1 and W-22 of these
Standards.
F. The trench sidewall shall not be undercut in order to obtain clearance.
G. If the trench bottom is rock, the Contractor shall over-excavate the trench
bottom and backfill and compact with suitable bedding material. The
minimum over-excavation depth shall be 12 inches below the bottom of the
pipe. The trench width through the extents of the rock excavation shall
match the trench width above the top of rock elevation. The Department may
allow blasting within rock, with prior approval.
H. Over-excavation shall be backfilled and compacted with acceptable Bedding
Material or Stabilization Material at the Department’s discretion.
I. Contractor shall follow the most current regulations concerning excavations
set forth by OSHA. Trench safety is the sole responsibility of the contractor