PERMFILE55017

• Permit No: C1996083
• IBM Index Class Name: Permit File
• Doc Date: 3/24/2004
• Doc Name: Section 11
• Section_Exhibit Name: Volume VII Geotechnical Studies
• Media Type: D
• Archive: No

•
Before mapping discontinuities, a site reconnaissance must be
conducted. This involves systematically walking the site (with
maps and plans if available) to become familiar with all aspects
of the project. Observations should be recorded in a field
notebook or on an audio cassette recorder for later transcription.
The general geologic nature of the site, rock types, types of
discontinuities and their general characteristics, obvicus
clustering of discontinuity orientations, sur_°ace drainage, ground
water characteristics, and major features such as faults should be
noted.
2. 2lappinq the site
A rock slope stability analysis requires a survey of the
orientations and characteristics of the discontinuities in the rock
mass. Examples of discontinuities are joints, faults, shear zones,
bedding surfaces, and foliations. The physical characteristics of
discontinuities greatly affect slope stability and include
geometry, spacing, surface roughness, physical properties of
adjacent rock, presence of infilling material, and ground-water
conditions. Discontinuities in a rock mass are sampled and mapped
using procedures such as the following.
Line mapping - involves placing a 100 foot measuring tape along
the slope face and recording data for every discontinuity that
crosses the tape. Figure 1 is an example of a data sheet for line .
mapping. Included are measurements of position so that spacing may
be statistically examined during computer analyses. The principal
advantage of line mapping is the control that it imposes upon the
collection of data for statistical purposes. A major disadvantage
of line mapping is that it becomes tedious when large areas are
mapped. It should be kept in mind that although much of the data
are subjective in nature, they may be quite useful when analyzing
potential failure surfaces.
Window maooina - all discontinuities falling within "windows" on
the slope are examined. The author utilizes windows that are
approximately 5' tall by 25' long with 20' to 25' between windows
as permitted by site conditions. It is important collect a
statistically significant number of discontinuities in the windows
and to use sound geological judgement when visually examining areas
outside the windows for ancmalous features. Windcw mapping has the
advantage of being slightly faster than line mapping but has less
statistical control.
Outcrop maooina - limited discontinuity data may be obtained from
rock outcroppings in the vicinity of proposed excavations. These
data usually compare favorably with data collected after excavation
except for having less detail and less resolution of the clusters.
Oriented core loaaina - cores are sometimes used to obtain
discontinuity data in areas where excavation has not yet begun.
Some means of orienting the core with respect to its insitu
stereonet Analyses 2 Appendix A
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