Stormwater Manual - Pima County Flood Control District

When necessary, compact subgrade surfaces to density requirements for the backfill material
and prepare subgrade or previous layer of compacted fill prior to placement of additional fill
by scarifying or disking.
Cut out soft areas of subgrade not readily capable of in situ compaction. Backfill with
subsoil and compact to density equal to requirements for subsequent backfill material.
Backfill areas to contours and elevations. Use materials that are not frozen. The Contractor
shall keep the foundation and subgrade free from water or unacceptable materials after the
fill operations have started.
Backfill systematically, as early as possible, to allow minimum time for natural settlement.
Do not backfill over porous, wet, or spongy subgrade surfaces.
Place and compact soil fill materials in continuous layers not exceeding eight (8) inches loose
depth. Compact soil fill materials to 95 percent of maximum dry density. Field density tests
shall be performed on each lift. Areas that fail to meet the requirements will be reworked as
necessary to meet the requirements and then tested again. This process shall be repeated
until the compaction requirements are met.
Tests shall be performed on each 400 square feet of surface area and on each lift of the
surface area.
Maintain optimum moisture content of backfill material to attain required compaction density
as specified. Material deposited on the fill that is too wet shall be removed or spread and
permitted to dry, assisted by disking or blading, if necessary, until the moisture content is
reduced to the specified limits.
All crushed stone fill and crushed stone backfill under structures and pavements adjacent to
structures shall be DGA crushed stone per Kentucky Highway Department Standard
Specifications for Road and Bridge Construction, unless indicated otherwise. Stone fill and
backfill materials shall be placed in layers not exceeding six (6) inches in thickness and
compacted to 95 percent of maximum dry density.
Backfill shall not be placed against or on structures until they have attained sufficient
strength to support all loads to which subjected without distortion, cracking, or damage.
Deposit soil evenly around the structure.
Slope grade away from structures minimum two (2) inches in ten (10) feet, unless noted
otherwise.
Make changes in grade gradual. Blend slopes into level areas.
Remove surplus excavation materials to designated areas.
STORMWATER MANUAL 10-25 January 1, 2009
LEXINGTON-FAYETTE CO., KY.