Civil Engineering Reference
In-Depth Information
the undrained shear strength
s
u
or shear strength parameters from triaxial tests. Subsoil
profiles, such as shown in Figs. 8.13 and 11.21, should be developed that show the different
soil and rock layers at the site and list the various field and laboratory test results. The
location of the groundwater table should be shown on the subsoil profile and its location
may need to be adjusted based on historical evidence. A summary of the site investigation
is presented in Table 15.1.
TABLE 15.1
Summary of Site Investigation
Topic
Discussion
Screening
investigation
The purpose of the screening investigation is to screen out those sites that do
not have geologic hazards or to assess the severity of the geologic hazards at the
site (Sec. 5.2). Evaluate potential on-site and off-site geologic hazards, such as
fault zones, regional subsidence, underground caverns, abandoned mines, etc.,
that could affect the proposed development. Check references such as geologic
reports, aerial photographs, and special study hazard maps.
Earthquakes
Evaluate seismic events and determine the peak ground acceleration and earth-
quake magnitude (Sec. 5.6). If applicable, consider vibrations due to blasting,
heavy machinery, etc.
Topography
Review the site topography for anomalous patterns, such as jumbled features,
scarps, and slope bulges. Evaluate the surface drainage conditions along with the
geology and contour map. Check on topographic changes in the past and correlate
with groundwater, weather, and seismic history.
Geologic
formations
Perform subsurface investigation to identify geologic formations and other earth
materials located on or adjacent to the site that are susceptible to liquefaction,
slope movement, landslides, etc. Also, identify the formations at the site and
consider the sequence of formations, presence of colluvium, formations with bad
experience, rock minerals susceptible to alteration, and rock fracture conditions.
Susceptible
landforms
Investigate susceptible landforms, such as steep slopes, colluvium-filled
swales, cliffs or banks undercut by stream or water action, areas that have
recently experienced slope failures, and liquefaction-prone areas.
Soil and rock
layers
Perform subsurface exploration to classify the materials, obtain soil and rock
samples, and perform field tests such as the SPT and CPT to determine the
liquefaction potential, settlement potential, foundation bearing capacities, etc.
(Sec. 5.4). Perform laboratory tests to evaluate their moisture content, density,
uniformity, compressibility, shear strength, etc. (Sec. 5.5). Prepare subsurface logs
and develop subsoil profiles, such as shown in Figs. 8.13 and 11.21, that describe
the soil and rock layers at the site and list the various field and laboratory test results.
Groundwater
Investigate the presence of springs, seeps, vegetation differences, and any damp
areas that may indicate the presence of groundwater. Determine if there are
potential pathways or sources of concentrated water infiltration on the site and
upslope of the site. During subsurface exploration, install piezometers to evaluate
hydrostatic, perched groundwater, or artesian pressures and the relationship to
the geologic formations and structure. Check on the variations in groundwater
levels due to rainfall, seasonal fluctuations, year-to-year changes, and effect
of snowmelt. Determine the effect of human activity on groundwater, such as
groundwater pumping, impoundment, groundwater recharge, changes in ground
cover, infiltration changes, and changes to the surface drainage. If needed, check on
groundwater chemistry, such as the presence of dissolved salts and gases.
