APPCOR11629

• Permit No: C1981020
• IBM Index Class Name: Application Correspondence
• Doc Date: 2/4/1982
• Doc Name: REVIEW OF THE GEOTECHNICAL ASPECTS OF THE MUNGER CANYON COAL MINES SUPPLEMENTAL PERMIT SUBMITTALS
• From: MLRD
• To: JIM PENDELTON
• Media Type: D
• Archive: No

XX. Roads (2.05.3(31, 4.
The proposed haul road for the Munger Canyon mine is approximately 2 miles in
length. This road follows the alignment of an existing pioneer road excavated
in 2977. This road, as the applicant observes, can be divided into two
distinct design segments. The lower segment connects State Highway No. 139
(Sta. 0+00') and the confluence of the Munger Creek Canyon with the canyon
of the unnamed tributary to Munger Creek on which the portals are located
(Sta. 67+00'). This segment occupies the relatively broad canyon floor at a
fairly low gradient (2.6~). The majority of this segment consists of a low
constructed road berm.
The upper segment of the haul road connects the confluence of the two stream
valleys (Sta. 67+00') with the mine portal bench (Sta. 104+30'). This roughly
3700 foot long segment climbs at a steeper gradient (7.5,) along the southern
valley wall of the valley of the unnamed tributary to Munger Creek. The
southern wall of this canyon is steep, with cross-slopes in excess of 300,
obviously qualifying as a "steep slope mining area". In order to straighten
the alignment of the existing pioneer road in order to accommodate larger
coal hauling vehicles, the applicant proposes to enlarge existing road cuts
and construct berms across several drainage swales.
In response to comments made by the Division in its Preliminary Adequacy Review,
Sheridan Enterprises has submitted a geotechnical analysis and design recommendations
for the proposed haul road. This report, prepared by Geo-Hydro Consultants, Inc.,
contains geotechnical conclusions regarding the stability of the proposed haul
road corridor and recommendations for the construction of necessary road cuts and
road fill embankments. The consultant's methodology consists basically of
geological mapping of the affected area and observation of the performance of
cuts adjoining the existing pioneer road, which was constructed roughly 4 years
prior to this investigation.
The geotechnical investigation determined that four basic soil or rock types
are encountered along the road's alignment. While no major or deep-seated land-
slides have occurred along the pioneer road, some shallow sloughing has occurred.
ay observing the cut slope gradients in areas of sloughing and correlating these
observations with the four characteristic material types encountered, the
applicant's consultant has developed recommendations regarding the maximum stable
cut slope gradients for each characteristic material type. (See Table 2.2-2)
The consultant's methodology is sound in this analysis.
Geo-Hydro's report contains the statement; "If our recommendations are accepted,
the cuts will probably be stable for the lifetime of the mine; sloughing will
have to be expected and maintenance of the road will be required." The applicant's
consultant has determined those cut slope gradients which should be stable during
the operational life of the mine. In other words, the consultant has deduced what
cut slope gradients for each characteristic soil or bedrock type encountered will
assure a cut slope with a static slope safety factor which exceeds 2.0. The
applicant's consultant has not completed a mathematical stability analysis of the
cut slopes or fill embankments proposed to accommodate the enlarged haul road.