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GENERAL42342
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Last modified
8/24/2016 8:10:56 PM
Creation date
11/23/2007 11:43:56 AM
Metadata
Fields
Template:
DRMS Permit Index
Permit No
C1980007
IBM Index Class Name
General Documents
Doc Date
11/14/1997
Doc Name
GEOTECHNICAL REPORT SYLVESTER GULCH SITE DEVEOLPMENT 11/4/97 - 11/10/97
From
MOUNTAIN COAL CO
To
MLR
Permit Index Doc Type
EXPLORATION
Media Type
D
Archive
No
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~- <br />Reporting Period November 4, 1997 -November 10, 1997 <br />Field Observations, Data Collection, and Ongoing Evaluations <br />2 <br />A complete inspection .vas performed by MCC on November 7 and November 10 to visually observe and <br />evaluate the stability of slopes within the project area. Data collection efforts continue and evaluation or <br />re-evaluation of specific areas of concern is being performed as needed. Individual areas are discussed in <br />detail in the following sections. Supporting documentation is attached for your review. <br />Lower Sylvester Gulch Road: Final installation of culverts and road ditch french drains are in <br />progress. The top-of--slope french drains described in previous reports appear to working effectively in <br />that water is being captured at all locations where installed, and slopes below the drains are remaining <br />stable, with the exception of some minor sloughing. <br />Inclinometer 1-2 was read on November 5. The movement reported previously at 24' to 32' depth is <br />continuing, although velocities are less than the previous week. The benched slopes below I-2 were <br />inspected daily and no movement, cracking, or slumping was observed, although some minor seepage is <br />evident. The french drain in this area continues to flow at a moderate rate. Nevv stability analyses of <br />this slope were completed by Golder Associates using the current slope geometry and groundwater <br />data. These analyses, backed up by visual observations, indicate all probable failure surfaces will <br />daylight on intermediate benches above the design road elevation. In addition, any potential upslope <br />progression of [he slide mass is significantly limited by the close proximity of stable sandstone cliffs <br />behind the mass. MCC will continue to monitor this slope, however, no stabilization efforts are <br />planned at this time. <br />An unsuccessful attempt to read new inclinometer 1-4B was made on November 5. The probe would <br />not pass the previously identified shear zone at 24 feet below ground surface. A thorough inspection of <br />the slopes above and to the north and south of I-4B discovered small, discontinuous slope cracks <br />beginning in a stretch of the hillside approximately 200 feet north and south of I-4B. Slopes below I- <br />4B were inspected daily, were dry, and no movement, cracking, or slumping was observed, although <br />some minor seepage and bench sloughage is occurring approximately 200 feet north of I-4B. Using the <br />current slope geometry, water conditions, and inclinometer data, new stability analyses of this area <br />prepared by Golder Associates calculate that any probable failure surfaces will daylight above the <br />design road surface. Further calculations show that a rock buttress will be an effective stabilization <br />technique, and a change order was issued to the construction contractor for this work. Work was <br />begun on a 600 foot long rock buttress on November 6, extending 300 feet north and south of I~B. As <br />of today, the buttress is approximately 50%complete. <br />Observations of these slopes will continue. Another replacement inclinometer for I-4B is planned, and <br />horizontal drains in two locations north of I-4B are being evaluated. <br />Uooer Sylvester Gulch Road: No stability issues to report. <br />Main Embankment (F-Walls): Weekly measurement at I-9 and I-10 were taken on November 5. <br />Small increases in velocity were detected in both inclinometers. Pore pressures continue to remain <br />stable. MCC will continue to monitor the inclinometers and piezometers. <br />
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