My WebLink
|
Help
|
About
|
Sign Out
Home
Browse
Search
2016-08-08_PERMIT FILE - C1981019 (49)
DRMS
>
Day Forward
>
Permit File
>
Coal
>
C1981019
>
2016-08-08_PERMIT FILE - C1981019 (49)
Metadata
Thumbnails
Annotations
Entry Properties
Last modified
9/28/2016 1:02:43 PM
Creation date
9/28/2016 1:00:52 PM
Metadata
Fields
Template:
DRMS Permit Index
Permit No
C1981019
IBM Index Class Name
Permit File
Doc Date
8/8/2016
Doc Name
Geotechnical Report - Collom Temporary Spoil Fill and Pond
Section_Exhibit Name
Volume 20 Exhibit 23 Item 2
Media Type
D
Archive
No
There are no annotations on this page.
Document management portal powered by Laserfiche WebLink 9 © 1998-2015
Laserfiche.
All rights reserved.
/
14
PDF
Print
Pages to print
Enter page numbers and/or page ranges separated by commas. For example, 1,3,5-12.
After downloading, print the document using a PDF reader (e.g. Adobe Reader).
View images
View plain text
Colowyo Coal Company, L.P. <br />Attn.: Mr. Juan Garcia <br />March 10, 2015 <br />Page 3 of 7 <br />SHANNON 8 WILSON. INC. <br />geometry used in our previous stability analyses remains valid for the revised fill <br />configuration. <br />Visual observations and the topography indicate the width of the valley at the revised <br />location is significantly narrower compared to the previous location. The longitudinal <br />slope of the valley floor is steeper. Based on our experience across the Colowyo site, this <br />indicates the clay soils in the valley floor will likely be shallower and, in our opinion, the <br />engineering properties of the clay foundation materials at the revised location will be <br />similar or better than the materials encountered in our borings further downstream. <br />■ Spoil material properties are not anticipated to vary and our previously estimated <br />engineering properties remain valid for the revised fill. <br />To confirm the effect of the steeper valley floor on stability is minor, we revised Trial 3 <br />from our previous study to include the steeper floor geometry (Figure 4). This trial <br />included a water height of 40 feet above the clay layer which is conservative considering <br />a drain will be installed in the valley. For the larger scale failure path the calculated FS is <br />2.03 for the revised condition compared to the previous FS of 2.06. This indicates only a <br />minor change in FS due to increasing the slope of the base clay layer. The calculated FS <br />for the smaller toe failure path is 1.68 compared to the previous FS of 1.70 also indicating <br />a minor change. <br />Based on the above factors, it is our opinion the results of the previous stability analyses remain <br />valid with a long term FS of 1.5 or greater indicated for the revised spoil fill. <br />As discussed in our previous report (Section 8.4), preliminary analysis indicates the short term <br />FS may be marginal near the toe of the fill when considering undrained clay shear strength <br />estimates. At the revised location, the valley narrows significantly, the maximum width of the <br />clay deposit is relatively small and we expect it to be shallower. A two dimensional stability <br />analysis does not include three dimensional effects in a narrow valley that will limit the size of a <br />potential failure. <br />The short term FS will depend on the rate of fill placement. After fill placement and <br />consolidation of the underlying clay, the long term FS will apply. In our opinion, this condition <br />is limited to a small area at the toe and is a construction issue that can be addressed <br />operationally. Options include staged construction to allow drainage of the clay. Because the <br />valley is significantly narrower, it may be possible to remove the clay layer if it is found to be <br />shallow. Additional evaluation with input from Colowyo operations should be performed as <br />recommended in our previous report. <br />23-1-01403-002 <br />
The URL can be used to link to this page
Your browser does not support the video tag.