Civil Engineering Reference
In-Depth Information
Site Description
The subject site is located at the southeast corner of the intersection of Wake Street and
Highway 1. The site and surrounding areas are level (i.e., level-ground site). It is our under-
standing that the proposed development is to consist of a medical library. It is also our
understanding that there will be three buildings, containing a library, administration
offices, and a conference center. In addition, there will be a plaza to be constructed adja-
cent to the building. The proposed site development will also include the construction of an
entrance roadway and parking facilities. The final size and the location of the building,
plaza, and parking facilities are in the planning stages. No details on the foundation loads
were available at the time of preparation of this report.
SITE GEOLOGY AND SEISMICITY
Geology
The site is located in the peninsular ranges geomorphic province of California near the
western limits of the southern California batholith. The topography at the edge of the
batholith changes from the typically rugged landforms developed over the granitic rocks to
the more subdued landforms characteristic of the sedimentary bedrock of the local embay-
ment.
The subject site contains a 10-ft-thick upper layer of cohesive soil that is underlain by a
25-ft-thick layer of soft clay and submerged loose sand. It is our understanding that the site
was used as a reservoir in the past and that the 25-ft-thick layer is an old lake deposit. The
top of the groundwater table is approximately at the top of the lake deposit layer.
Underlying the lake deposit (at 35-ft depth), there is Eocene aged stadium conglomer-
ate bedrock. The stadium conglomerate bedrock is a very dense sedimentary rock com-
posed of hard and rounded cobble-size particles embedded within an orange to yellow,
cemented sandstone matrix. The cobbles typically comprise approximately 30 to 50 percent
of the stadium conglomerate bedrock. The nature of the material (i.e., cemented stadium
conglomerate) makes it an adequate bearing material.
Seismicity
The site can be considered a seismically active area, as can all of southern California. There
are, however, no active faults on or adjacent to the site. Seismic risk is considered moder-
ate compared to other areas of southern California. Seismic hazards within the site can be
attributed to ground shaking resulting from events on distant active faults. There are sev-
eral active and potentially active faults which can significantly affect the site. The
EQSEARCH Version 2.01 (Thomas Blake) computer program was used to estimate the
peak ground acceleration at the site due to earthquake shaking on known active faults.
Based on an analysis of possible earthquake accelerations at the site, the most significant
event is a 6.5 magnitude event on the La Nacion fault, which lies approximately 4 mi to the
southwest of the site. The ground surface accelerations produced at the site by such an event
would exceed those events on any other known fault. The Rose Canyon fault zone is the
closest active fault, which lies approximately 10 mi to the west of the site.
Based on an analysis of the earthquake data, the peak ground acceleration used for the
geotechnical engineering analyses is 0.20
g.
As discussed in the next section, it is anticipated
