2011-08-01_REVISION - M1978210 ‎(15)‎

• Permit No: M1978210
• IBM Index Class Name: REVISION
• Doc Date: 8/1/2011
• Doc Name: Submittal
• From: Weld County
• To: DRMS
• Type & Sequence: TR3
• Media Type: D
• Archive: No

Sieve Size
% Passing
2" (50.8mm)
>
80
3/8" (9.52mm)
>_
65
#20 (0.850mm)
40
— 85
#200 (0.075mm)
30
- 45
5.6 Slurry Wall Backfill Type and Placement
The slurry wall shall be backfilled with SB backfill mixture consisting of a composite of
excavated material from the trench (working platform, overburden, sand and gravel), clay
borrow, bedrock additional dry bentonite, and bentonite slurry. All oversized material greater
than 6- inches in diameter (cobbles, boulders) and bedrock shall be discarded and not used in the
backfill mixture. The clay borrow should have at least 60% passing the #200 sieve and a PI > 8.
The SB backfill shall have the following properties.
• Minimum 30 percent fines and maximum 45 percent fines (passing No. 200 sieve);
• Gradation as per the following table:
• 0.5 percent additional dry bentonite by dry weight of backfill;
• Slump of 3 to 6 inches;
• Roll 1/8" thread
• Wet Density 15 pounds per cubic foot greater than the in -trench slurry density; and
• Permeability of less than or equal to 1.0 x 10 -7 cm/sec.
These criteria were based on the mix design and other backfill mix designs used for other slurry
walls designed by Lyman Henn, Inc. Table IV of this report presents performance results for
backfill and slurry planned for use on this project.
SB backfill shall be mixed alongside the trench in a contained area and have the consistency of
wet concrete when placed. The specification requires that backfill be plastic enough to roll an
1/8" thread, but no Atterberg limits are required for the backfill material. The SB backfill shall
be placed from one end of the trench and advance across the trench at a self - seeking slope,
typically inclined at 5:1 to 10:1 (horizontal: vertical). The toe of the backfill slope shall extend
to the bottom of the excavated trench, such that no more than 5 ft of trench remains open
between the toe of the backfill and the active excavation.
A clean slurry trench bottom and backfill slope shall be maintained prior to the placement of
backfill. The profile of the slurry trench bottom and the backfill slope shall be measured at the
end of a backfill placement shift and prior to the next backfill placement shift at intervals of no
more than 20 ft. If profiling prior to the next backfill placement shift indicates sedimentation or
cave -in has occurred on the slurry trench bottom or the backfill slope, the material shall be
removed by backhoe, clamshell, airlift pump, or other suitable equipment. This equipment shall
be operated in a manner that prevents removal of material from the walls of the Slurry Trench.
G:\PROJECTS \111025 Geisert Gravel Pit Slurry Wall\O\O1 \Geisert Slurry Wall Design Report.doc 9