ARCHITECTURAL ENGINEERING CONSTRUCTION MANAGEMENT THESIS
Jennifer Drilling 9/30/2002 Advisor: Riley
TOYOTA
Real Estate & Facilities Corporate Headquarters
Torrance , CA
SUBSURFACE & SOILS ANALYSIS
Scope of Soils Report:
Leighton and Associates, Inc were responsible for the Soils Engineering of the Toyota Project. The scope of work for the geotechnical investigation included review of available data, field exploration consisting of drilling 19 borings, laboratory testing, geotechnical analyses of collected data, and preparation of a Soils Report to be provided to Turner before excavation took place. Also included in the report were preliminary recommendations for grading and design of foundations, slabs, and pavements. Based on the investigation, Leighton and Associates, Inc concluded there appeared to be no significant geotechnical constraints onsite that could not be mitigated by proper planning, design, and sound construction practices.
Distribution:
The preliminary geotechnical report, created in January of 2001 was distributed to the contractors for bidding. The final report was completed August 27, 2002, just twenty days before excavation actually started. The Grading, Foundation, and Structural Permits were already being processed for the project at the time of the Final Report Submission.
Differing Site Conditions (DSC) Contract:
The DSC Clause is of typical use for Turner in LA. Declared in Form 26 of Turner’s Contract, the DSC Clause states that Turner is not responsible for any soils they encounter that are not specified in the Subsurface/Soils Report.
Soils Report Summary :
A. Geologic Settings
The site of the Toyota Real Estate & Facilities was a vacant parcel of land located southeasterly of the intersection of Western Ave and 195 Street in Torrance, California. The topography of the site is generally flat with no distinct drainage pattern. The southern portion of the site is covered with medium to heavy growth of native vegetation. Other areas are clear. There was a minor amount of scattered debris covering the surface. The site is approximately 55 feet above mean sea level.
B. Surface Soil and Groundwater Conditions.
Based on the field investigation, the subsurface soils at the site generally consist of silty clay and poorly graded silty and clayey sands. The soils up to a depth of approximately 5 feet below the existing ground surface are soft to moderately stiff. The subsurface soils, 5 to 30 feet in depth are of dark to reddish-brown sitly clay and generally stiff to very stiff. The granular soils underlying the silty clay layer are generally moderately dense to very dense. Groundwater was not encountered in any of our borings to a depth of 61.5 feet below the existing ground surface and is not expected to have any adverse effect on site grading.
C. Seismic Hazards
There are no know landslides or active faults at the site. The major/closest active faults that affect the site include the Compton Blind Thrust, Palos Verdes, and Newport-Inglewood (LA Basin) Faults. These are all minuscule in relations to the largest active fault in California, the San Andreas Fault which is roughly 54.8 miles northeast of the site.
The site is likely to be subject to strong ground shaking during the life of the project. To evaluate the ground motion and determine a peak level of ground acceleration, the following approaches were used and then averaged:
· Deterministic- assumed an earthquake of specific magnitude by the closest fault
· Probabilistic- forecasted future ground motion based on historical seismicity and the geological slip rate.
The official hazard map by California Department of Conservation Division of Mines and Geology of the area does not indicate the potential for liquefiable soil onsite. The investigation also concluded this since the groundwater was not observed in the borings until 61.5 feet below the ground surface.
D. Expansion Potential
The materials encountered in the borings possessed a high expansion potential. Grading of the site may expose materials with a different expansion potential, which may affect design and construction. As-graded conditions should be evaluated upon completion of grading. If unmitigated, damage to concrete and asphalt pavement due to heaving (expansion) and shrinkage of onsite soils is expected to be high.
E. Soil Corrosivity
Chemical contents within fine-grained, cohesive soils, such as clays and silts, can deteriorate concrete structures when present in high concentrations. Soils with chloride content over 500 parts per million (ppm) are considered corrosive to metal. The chloride content of the site soils range from 104 to 158 ppm. The site soils are considered mildly corrodible to buried metallic structures in contact with onsite soil. Underground metallic structures should be protected against corrosive attack.
S cope of Excavation:
Based upon the grading plans, the finish pad elevation of the proposed buildings will be at 60 feet and the finish floor will be at 60.75 feet. Isolated footing depths typically vary between approximately 4 and 4.5 feet below finish grade. Continuous perimeter footings are typically 3.6 and 5.6 feet below finish grad. Isolated grad beam footings are between 7 and 9.5 feet below grade.
The soil at the site should be readily excavated by conventional earthmoving equipment. Temporary shallow excavations with vertical slopes not exceeding 5 feet in height are suitable.
The field observations indicated that the surface soils are not adequate to support the structures. It is recommended by the Soils Report that all existing unsuitable materials be removed and replaced with properly compacted fill. Removals should be made to firm native ground and should extend a minimum of 2 feet below the bottom elevation of proposed footings.
Where fills are to be placed on ground with slopes steeper than 5:1 (horizontal to vertical units), the ground shall be stepped or benched. The lowest bench or key shall be a minimum of 15 feet wide and at least 2 feet deep, into competent material as evaluated by the Geotechnical Consultant.
For areas greater than 5 feet in depth, retaining walls will be used with level backfill and a drainage system, to prevent hydrostatic pressure build up behind the wall.
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