Earthquakes - Geotechnical Engineering Investigation - page 986

proximity, faulting evidence, etc. with regard to the necessity of a detailed investigation to
evaluate the capability of a particular fault. Fault characteristics and identification are
described in Sections 6.5 and 11.3.2. Study procedures are given in Section 11.4.6,
“Geologic Study.”
Detailed reconnaissance and remotely sensed imagery interpretation are performed for each
lineament of interest to identify faulting evidence, fault type, past displacements, and
apparent activity on the basis of observations.
Fault zone extent and control width: Fault traces near the plant site are mapped along the
fault for a distance of 10 mi in both directions from the point of its nearest approach to the
site, as shown in Figure 11.45. Because surface faulting may have occurred beyond the
limit of the mapped fault traces, detailed faulting investigation of a zone beyond the con-
trol width is required. The width of this zone depends upon the largest potential earth-
quake related to the fault as given in Table 11.18.
Explorations are made of candidate faults with geophysical surveys, vertical and angle
borings (including coring, sampling, and sensing with nuclear probes), and trenches to
determine fault existence, zone width, and geometric attitude.
Quaternary dating: Numerous methods have been developed to date geologic forma-
tions. Radiometric dating (Appendix A.4 and Table 11.8) , performed to evaluate fault activ-
ity as exposed in test trenches, is still the most popular.

Investigate Other Major Hazards

Flood potential (see Section 8.2.3)

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Slope stability (see Sections 9.5 and 11.3.4)

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Ground subsidence and collapse, faulting, and induced seismic activity from
fluid extraction (see Section 10.2)

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Ground subsidence and collapse from subsurface mining (see Section 10.3.5)

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Ground collapse from failure of cavities in soluble rock (see Section 10.4.3)

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Liquefaction and subsidence potential (see Section 11.3.3)

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Site Soil and Foundation Studies
Objectives
Soil formations : Determine stratigraphy and soil types, identify the potential for ground
compression and heave, and measure static and dynamic strength, deformation proper-
ties, and permeability.
Rock formations : Determine stratigraphy and rock types, and identify the degree and
extent of weathering and distribution and the nature of discontinuities. Measure pertinent
engineering properties.
Groundwater conditions : Locate the static, perched, and artesian conditions, and deter-
mine water chemistry. Evaluate susceptibility to changes with time and weather, or other
transient conditions.

Explorations
Terrain analysis and field reconnaissance are performed to provide data for a detailed geo-
logic map of surface conditions.
Stratigraphy is investigated with geophysics, test borings, trenches, pits, etc.
Samples for identification and laboratory testing are obtained from borings, trenches,
and pits.