Civil Engineering Reference
In-Depth Information
TABLE 15.1
Summary of Site Investigation (
Continued
)
Topic
Discussion
Slope
stability
Evaluate the three-dimensional geometry, stratification, folding, and strike and
dip of bedding and joints with relation to the slope. Investigate faults, breccia,
and shear zones with relation to the slope and slide. Consider the chemical,
mechanical, and solution weathering characteristics of the slope materials and the
depth and variability of weathering. Analyze tension cracks at the top of slopes
to determine their significance on the stability of the slope. Tension cracks are
usually an early and important warning sign of impending slope failure.
The rate of slope movement is important and thus evaluate from visual
accounts, evidence in vegetation, evidence in topography, and aerial photographs.
Install inclinometers and settlement monuments to determine the horizontal
movement, settlement at the top of slope, and time history of movement.
Correlate slope movement with groundwater, weather, prior earthquakes, and
human activity.
Landslides
Check for active and inactive landslides on or adjacent (uphill and downhill) to the
site. Evaluate off-site conditions, such as rockfall, avalanches, and flow slides that
could be triggered by an earthquake.
History of
site changes
Consider natural processes, such as long-term geologic changes, erosion, evidence
of past movement, submergence, or emergence. Evaluate human activities, such
as cutting, filling, clearing, excavation, cultivation, paving, flooding, and sudden
drawdown of reservoirs. In addition, consider changes in surface drainage,
groundwater, and vegetation cover.
Changes
due to
development
Evaluate the changes due to the proposed development, such as anticipated
changes to the surface and subsurface hydrology (due to watering of lawns, on-site
sewage disposal systems, concentrated runoff from pavements, etc.), that could
increase the potential for liquefaction, slope movement, landslides, etc. Other
changes include proposed grading operations, such as cut areas, fill placement,
steepening or undercutting of slopes, excavation of shear keys, construction of
buttresses, etc.
Engineering
and geologic
analyses
Perform engineering and geologic analyses to determine earthquake parameters
(peak ground acceleration, earthquake magnitude, etc.), liquefaction potential,
settlement, bearing capacity, slope stability, retaining wall parameters, and
provide recommendations to mitigate earthquake effects.
Report
preparation
Prepare reports that describe the investigation, summarize the results of the
engineering and geologic analyses, and provide mitigation recommendations.
Reports should include the following:
●
Results of the screening investigation and quantitative evaluation (Sec. 5.7)
●
Liquefaction analysis (Sec. 6.5)
●
Settlement and bearing capacity analyses (Sec. 8.5)
●
Slope stability investigation (Sec. 9.8)
●
If applicable,
International Building Code
requirements (Sec. 14.2.9)
See App. D for an example of a geotechnical earthquake engineering report.
