2011-01-06_REVISION - M1977300

• Permit No: M1977300
• IBM Index Class Name: REVISION
• Doc Date: 1/6/2011
• Doc Name: Corehole Grouting Plan
• From: Whetstone Associates
• To: Cotter Corporation and DRMS
• Type & Sequence: TR16
• Email Name: DB2
• Media Type: D
• Archive: No

TP- 16
l1-I L777 X300
Whetstor?re
ASsoCci 'teS Technical Memorandum
r
To: Randy Whicker, John Hamrick (Cotter Corporation (N.S.L.)) 4109C
From: Scott Effner, P.G.
Date: January 6, 2011
Subject: Corehole Grouting Plan
Cotter Corporation (N.S.L.) intends to grout a small-diameter angled corehole at the Schwartzwalder
Mine. The following grouting plan has been developed to meet the objectives of the corehole
grouting program. Specifically, the goal of the grouting program is to seal off all groundwater that
may be entering the pipe or flowing in the annular space outside of the pipe and in nearby fractures.
1. PROCEDURES FOR COREHOLE GROUTING AT THE SCHWARTZWALDER MINE
Water testing of the corehole will be performed before grouting. Results from the water tests will be
used to select the starting grout mixture for the corehole. It is anticipated that the test pressure will
be 15 to 20 psi over the natural hydraulic pressure at the corehole collar.
In the United States, a standing rule of thumb has been to limit grouting pressures to 1 psi per foot of
depth below the top of bedrock plus 0.5 psi per foot of overburden to avoid hydrofracturing. This
rule is based on the weight of the rock and the overburden above the grouted interval. While this
criteria is appropriate when grouting at shallow depths, 30 feet or less, it is probably too conservative
for most other rock grouting (Army Corps of Engineers, 1984). Factors which affect the maximum
safe grouting pressure include rock strength, fracture orientation and spacing, and the radius
influenced by grouting. Based on recommendations by the Army Corps of Engineers, safe grouting
pressures can range from 1 to 4 psi per foot of depth in bedrock (Army Corps of Engineers, 1984).
Because pressure is one of the most important criteria influencing the radius of penetration for grout,
the maximum safe pressure will be used but will not exceed 2 psi per foot of depth in bedrock.
Grouting pressures in unconsolidated deposits will not exceed 1 psi per foot of depth.
Refusal is the point at which grouting is discontinued on a corehole or a stage. The refusal criteria
for the project will be "no take" by the corehole or stage during a 15 minute period at the maximum
allowable safe pressure. No take will be verified by physical observation of the grout level in the
agitator. In the case of excessive or runaway grout takes, grouting may be paused for a period of
time and restarted.
Grout components will be mixed in the specified proportions to ensure consistency and quality of the
grout. Mixed grout will contain 3 percent bentonite by dry cement weight. Bentonite decreases
cement particle settling and bleed water formation. It also reduces the plugging of grouting lines. It
is anticipated that the range of watencement ratios (W:C) used during the program will be between
3:1 and 0.6:1. When possible, W:C ratios of less than 1:1 will be used to increase grout strength and
reduce .shrinkage. The grout will be mixed using a high shear "colloidal" type mixer. The mixture
will be prepared by adding water to the hopper first, followed by bentonite and then by cement. The
bentonite will be allowed to mix for sufficient time to ensure complete dispersion before adding
cement to the hopper.
Whetstone Associates, Inc.
243 N. Main St. ? Gunnison, Colorado 81230 ? Phone [phone] ? Fax [phone]